Industrial Applications of Rare Earth Elements 9780841206410, 9780841208377, 0-8412-0641-4

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Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.fw001

Industrial Applications of Rare Earth Elements

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.fw001

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Industrial Applications of Rare Earth Elements Karl A. Gschneidner, Jr., EDITOR,

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.fw001

Iowa

State

University

Based on a symposium sponsored by the Division of Industrial and Engineering Chemistry at the Second Chemical Congress of the North American Continent (180th ACS National Meeting), Las Vegas, Nevada, August 25-26, 1980.

164

ACS SYMPOSIUM SERIES

AMERICAN

CHEMICAL

W A S H I N G T O N , D. C.

SOCIETY 1981

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.fw001

Library of Congress CIP Data Industrial applications of rare earth elements. (ACS symposium series 164; ISSN 0097-6156) Includes bibliographies and index. 1. Rare earth metals—Congresses. I. Gschneidner, Karl A. II. American Chemical Society. Division of Industrial and Engineering Chemistry. III. Chemical Congress of the North American Continent (2nd: 1981: Las Vegas, Nevada). IV Series. TA480.R3I5 621.1'89291 81-10875 ISBN 0-8412-0641-4 AACR2 ACSMC8 164 1-297 1981

Copyright © 1981 American Chemical Society All Rights Reserved. The appearance of the code at the bottom of the first page of each article in this volume indicates the copyright owner's consent that reprographic copies of the article may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc. for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating new collective work, for resale, or for information storage and retrieval systems. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. PRINTED IN THE UNITED

STATES

OF

AMERICA

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.fw001

ACS Symposium Series M . Joan Comstock, Series Editor

Advisory Board David L. Allara

James P. Lodge

Kenneth B. Bischoff

Marvin Margoshes

Donald D . Dollberg

Leon Petrakis

Robert E. Feeney

Theodore Provder

Jack Halpern

F. Sherwood Rowland

Brian M . Harney

Dennis Schuetzle

W . Jeffrey Howe

Davis L. Temple, Jr.

James D . Idol, Jr.

Gunter Zweig

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.fw001

FOREWORD The ACS SYMPOSIUM SERIES was founded in 1974 to provide

a medium for publishing symposia quickly in book form. The format of the Series parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. Papers are reviewed under the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however, verbatim reproductions of previously published papers are not accepted. Both reviews and reports of research are acceptable since symposia may embrace both types of presentation.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

PREFACE

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.pr001

F

or the last twenty years conferences concerning rare earth materials have been held in the U.S.A. every 18 to 24 months. In general these conferences have dealt with the science of these materials, and only one or two sessions (~10% of the papers) were concerned with industrial and commercial aspects. This is also true for rare earth conferences held in other countries with one exception—the 1972 N A T O Conference on Analysis and Applications of Rare Earth Materials, in which about half of the papers dealt with their uses. The rapid and continued growth of rare earth markets in the last two decades—10 to 15% per year—suggested that an exclusive conference would be of considerable interest not only to the worldwide rare earth community but also to many scientists, engineers, and technical business managers in other industries and technologies that may have an interest in, or possible future applications involving the rare earths. The symposium that formed the basis of this volume was devoted exclusively to industrial applications and commercial aspects of the rare earths. The industrial applications of the rare earths can be divided into two categories—uses that involve the mixed rare earths in proportion to their occurrence in their ores or in concentrates (not exceeding 90% of any one rare earth element), and uses that involve the separated individual rare earth elements (> 90% pure). Of the total volume of rare earths consumed about 95% is in the form of mixed rare earths or concentrates, but in monetary terms the contribution by both categories is about equal. The mixed rare earths are used as additives to improve the properties of steel and ductile iron by removing the tramp elements and modifying the morphology of the metal product. The other major use is the addition of rare earths to zeolite cracking catalysts to improve the efficiency of gasoline refining processes. Other miscellaneous uses of the mixed elements are: lighter flints, alloy additives to nonferrous metals, carbon arc-cores for lighting, and glass polishing materials. Chemical concentrates, which contain up to approximately 90% of one rare earth element, are primarily used in the glass and ceramic markets, for example, C e 0 as polishing compounds and for decolorizing glass, L a 0 in glasses to increase the index of refraction (e.g., camera lenses), Ce0 , N d 0 , and P r O n for coloring glasses and ceramic tiles, and in temperature compensated capacitors. 2

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ix In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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The individual separated rare earth elements (chemical purities ranging from 95% to 99.999%) are used in advanced technological applications. These so-called exciting and glamorous uses include: phosphors for cathode ray tubes, color television, fluorescent lighting, and x-ray intensifying screens; magnetic bubble devices for computer data storage; microwave devices; the strongest known permanent magnets; hydrogen storage materials; oxygen and carbon sensors; electrooptical devices and lasers; control rods and burnable poisons for nuclear reactors; glass additives as decolorizing agents and also to impart color; simulated diamonds; and as alloying agents to improve the properties of high temperature oxidation/corrosion resistant alloys. The book is divided into three sections based on the nature of the rare earth application: metallurgical uses of the mixed rare earths; mixed rare earths in nonmetals; and individual rare earth element uses. The first section contains three chapters including an overview of the rare earth industry as developed from a historical perspective. The second section contains four chapters that deal with the use in the glass, glass polishing, and catalyst industries. The last section contains nine chapters covering a wide range of topics, including an overview of the industrial methods of separating the rare earth elements, three chapters on phosphors, and five chapters on a variety of applications. The authors of the chapters were asked to include the following information whenever possible: the description of the use or application; the scientific basis for the use; market size—current and future; competitive advantage of the rare earths; and competition from other markets. Naturally some chapters for various reasons did not discuss all of these points. The editor would like to acknowledge several friends in the rare earth industry for suggesting topics and potential authors. These are: G . A . Barlow (Union Molycorp), J. G . Cannon (Union Molycorp), I. S. Hirschhorn (Ronson Metals Corporation), W. A . Otis (Ronson Metals Corporation), and O. A . Wunderlich (Davison Specialty Chemical Company, W. R. Grace and Company). The efforts of the four Session Chairmen, I. S. Hirschhorn (Ronson Metals Corporation), J. R. Long (Aldrich Chemical Company, Incorporated), M . Tecotzky (United States Radium Corporation), and J. W. Cunningham (Research Chemicals, N U C O R Corporation), who kept the symposium running smoothly and on schedule were appreciated by the speakers and attendees. Particular thanks go to J. E . McEvoy (Councilor), W. N. Smith (Program Chairman), and R. A . Stowe (Program Secretary) of the Division of Industrial and Engineering Chemistry of the American Chemical Society who helped the editor in organizing this symposium. The editor appreciates the assistance of the sixteen unnamed persons who refereed the papers published in this volume. x In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

An acknowledgment is also due to the A C S Books Department for their guidance in getting this volume ready for publication—with special thanks to S. B. Roethel (Acquisitions Editor) and her secretary, A . Drexler. Finally the kind and wonderful assistance of the editor's staff and colleagues (C. J. Catus and B. L . Evans [Rare-Earth Information Center], and O. D. McMasters [Ames Laboratory]), and especially that of his secretary, L . M . McVicker, is deeply appreciated. K A R L A . GSCHNEIDNER, JR.

Iowa State University Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.pr001

Ames, Iowa 50011 March 5, 1981

xi In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

1 History of Rare Earth Applications, Rare Earth Market Today Overview

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E. GREINACHER Th. Goldschmidt A G , Goldschmidtstrasse 100,

4300 Essen 1, West Germany

About 25 000 tons of RE Metals - calculated as oxide - are currently consumed i n the world per year. This quantity i s divided among a dazzling variety of applications. In order to bring a certain systemization into this variety, these a p p l i cations and possible applications have been reviewed from 3 different aspects: from a h i s t o r i c development, from the special properties of the rare earths and from the degree of separation of the individual elements or group of elements of the rare earth metal series. The individual applications will be present i n more d e t a i l i n the following papers by experts i n the f i e l d s involved. History of the Applications of Rare Earth Elements The history of the rare earth elements begins i n 1788 i n Sweden. I would l i k e to divide the time between that year and the present day into 4 periods of application of the rare earths. F i r s t Period: 1788 - 1891 i s the preliminary period i n which the rare earth elements were s c i e n t i f i c a l l y examined but were not yet technic a l l y used. Second Period: 1891 - 1930 i s the period of first industrial usage of the mixed or simply separated rare earth elements. Third period: 1930 - 1960 i s the start of the wide usage of the properties of the rare earth elements, wherein the period from 1940 - 1960 i s distinguished by the systematic discovery of properties, of methods of separation and of usage of the rare earth elements as the by-product of the various atomic research programs i n the industrial countries, foremost among which were i n the USA and England.

0097-6156/81/0164-0003$05.00/0 © 1981 American Chemical Society In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Fourth period: From 1960 to the present i s the time of qualitatively and quantitatively rapidly r i s i n g applications of the rare earth elements which are now abundantly available i n every desired quality, although not always at a low price. Preliminary Period. In 1788 the mine foreman GEYER i n Ytterby, Sweden found a black mineral which was then called Ytterbite and later Gadolinite. In 1794 i t was studied by Professor Gadolin at the University i n Abo, later named Turku, Finland. He found for the f i r s t time a new kind of "earth" which he called the "rare earths". At that time the metallic oxides were generally called, "earth" for example: b i t t e r earths (magnesia), zirconium earths (zirconia) and beryllium earths (beryllia). In 1803 Klaproth and independently Berzelius found at an abandoned iron ore mine at Bastnas, likewise i n Sweden, a mine r a l which received the name Bastnasite. In this mineral the researchers found new earths which they named "ochroite earths" because upon heating of the mineral a yellow substance resulted. They gave the assumed metal the name cerium after the small planet Ceres. In 1839 Mosander began for the f i r s t time systematically to analyze the mixed rare earths. This work of separation of the rare earth elements was carried forward by a number of scientists and achieved particularly useful results through the work of Bunsen and Kirchhoff, who introduced spectroscopy as a useful control instrument for the separation of the rare earth elements. Up to the year 1891 a great many learned men with famous names busied themselves with the rare earth elements and reported interesting work. Nevertheless, no applications or industrial usage came out of these e f f o r t s . In t h i s early period of general industrial development and of the beginning growth of our large c i t i e s , there arose a primary technical problem, Whose scale we can hardly imagine today. This was the certain, r e l i a b l e , rapid and cheap production of l i g h t . There was a search for the p o s s i b i l i t y of u t i l i z i n g the night hours above a l l during the winter. This problem i s today so f u l l y solved that except for a couple of specialists we no longer give i t many thought. The three major (and up to the year 1930 only) uses for the rare earth elements were related either d i r e c t l y or indirectly to l i g h t . Two of these important inventions stem from the great Austrian scientist, inventor and entrepreneur, Carl Auer von Welsbach. His greatness can be gauged by h i s basic contributions to both of the major developments i n the production of l i g h t . He discovered a useful gas lamp and made a significant c o n t r i bution to the development of the e l e c t r i c incandescent lamp. A photograph of von Welsbach i s shown i n Figure 1 and a sketch of h i s laboratory i n figure 2 (1_).

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Overview

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GREINACHER

Technisches Museum

Figure 1. Carl A uer von Welsbach (1)

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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The problem of production of l i g h t had been investigated above a l l i n England for 60 years. This preliminary work provided a clear objective but no technically useful path thereto u n t i l the invention of Auer von Welsbach. I t was required to bring a hot gas flame to luminosity and to radiate as much v i s i b l e l i g h t as possible. The solution was already available: a s o l i d of suitable composition with maximum surface area had to be brought to radiation i n the hot zone of the flame. The large surface area was necessary i n order to radiate as much l i g h t as possible with good thermal efficiency. Auer von Welsbach had already reported i n 1885 a patent f o r a lanthanum-zirconium incandescent element and also produced them. This incandescent mantle had two properties: I t consisted of a s o l i d body (LaJD- + ZrOj vvhich thanks to i t s composition was stimulated by the neat of the flame (Bunsenf lame) to give of f a high radiation of light i n the v i s ble range. The method of production was simple: A cotton sock was saturated with a s a l t solution of such composition that upon ignition a mixture of oxides yielding optimum radiation with large surface area was formed i n the hottest zone of the flame, see figure 3. The incandescent mantle was however not accepted by consumers because i t was too b r i t t l e and produced a "cold" bluegreen l i g h t . Period of F i r s t Industrial Usage. By improvement of this f i r s t discovery there arose the f i r s t industrial consumption of rare earths and the hour of b i r t h of the rare earth industry i n the year 1891, when Auer von Welsbach reported h i s patents f o r the Auer incandescent mantle which i s composed of 99 % thorium oxide and 1 % cerium oxide. This light was superior for decades to e l e c t r i c l i g h t . I t was cheaper so that u n t i l the year 1935 approximately 5 b i l l i o n incandescent mantles had been produced and consumed i n the world. Even today this method of light production remains superior t o e l e c t r i c lighting systems i n remote areas or i n signal devices for railroads. For example, i n front of my house i n Essen, Germany, there are open street lanterns with gas-heated Auer-incandescent mantles which provide a pleasant l i g h t on our quiet street. The carbon filament lamp which was developed i n p a r a l l e l at the beginning of t h i s century was always several times as expensive i n use as an Auer incandescent mantle. As a result, this f i r s t use of the rare earth elements achieved great economic success and thanks to h i s capabilities Auer von Welsbach played a major role i n this worldwide achievement. He was i n the position to survive the extraordinarily complicated and o b s t i nately pursued patent battles.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

GREiNACHER

Overview

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1.

Figure 3.

The preparation

of an incandescent

gas mantle

(1)

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch001

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Gadolinite and bastnasite from Sweden served at f i r s t as raw material for the rare earth elements and thorium. Later i t was necessary to seek new raw materials and the so-called "Carolina sand" was found i n the USA, a monazite which cjcxrurred there i n certain gold-panning areas. F i n a l l y a nearly inexhaustible reserve of monazite was discovered i n B r a z i l which guaranteed raw material supplies far into the future. Again, we take a short look into the origin of this d i s covery. Auer von Welsbach had accumulated so much thorium i n the processing of rare earths for production of lanthanumzirconium incandescent mantles - the predecessor of Auer incandescent mantles - that he had to look for a use for them. He established that thorium oxide provided an interesting l i g h t radiation at elevated temperatures and that this l i g h t radiation became poorer as the thorium oxide became purer. He further established that cerium was the main impurity and i t was not d i f f i c u l t from t h i s to come to the optimum dosage of thorium oxide with cerium oxide. So i t was at the beginning of the industrial applications of the rare earth elements the need of the rare earth industry to u t i l i z e valuable residual fractions. Up to the present day, this remains a problem to be solved by research departments, applications technicians, inventors and developers of the rare earth industry. Two situations lead to the next use of rare earths by Auer von Welsbach: the large quantities of rare earth elements which were l e f t over from the production of Auer incandescent mantles had accumulated i n large waste p i l e s , and the necessity to find a simple ignition system for Auer lamps. In ignition, e l e c t r i c incandescent lamps were far superior to the Auer l i g h t s . But t h i s situation was ameliorated i n 1903 when von Welsbach was granted a patent for a pyrophoric metal a l l o y ("flintstone") composed of 70 % nuschmetal and 30 % iron. This patent was also strenuously l i t i g a t e d but victoriously defended. After the discovery of pyrophoric alloys, the so-called Auer-metals, the main problem was to produce nuschmetal from the large dumps resulting from the production of Auer incandescent mantles. To do this Auer von Welsbach founded i n 1907 the Treibacher Chemische Werke i n the rooms of an iron works. In 1908, for the f i r s t time, he succeeded i n producing pore-free nuschmetal by fused s a l t e l e c t r o l y s i s . 800 k i l o s of nuschmetaliron f l i n t s were brought on to the market i n 1908. The imagination of the inventor was tremendous. Among other things, he proposed to use f l i n t s for ignition i n gasoline engines, an idea which one perhaps should think through again today i n view of

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch001

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Overview

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the efforts to mate our engines and cars lighter. A fascinating idea, instead of the quite complicated e l e c t r i c a l ignition mechanisms, one inserts every 10 000 miles a set of f l i n t s into the engine for ignition. Unfortunately, an estimate shows that t h i s would be too expensive. At this point I would l i k e to present a brief biography of the founder of the rare earth industry: Auer von Welsbach was born i n Vienna i n 1858. His father was a creative inventor and expert i n the f i e l d of printing. Early i n h i s l i f e he l e f t his children such a large inheritance that h i s son Karl was able t o pursue h i s studies of chemistry i n 1878 i n Vienna with Professor Lieben and i n 1880 with Bunsen i n Heidelberg without material worries. In the laboratory of Bunsen he was f i r s t introduced into the chemistry of the rare earth elements. U n t i l h i s death i n 1929 he remained true to this f i e l d of work. The intensive involvement i n spectroscopy with Bunsen also made him familiar with the problems of radiant l i g h t which without doubt was important for h i s later invention of Auer-Light and with that the use of the rare earth elements. Further, he had an insight into the work of winning the rare earth metals from their salts through Bunsen, Hillebrand and Norton who succeeded for the f i r s t time i n 1875 to produce rare earth metals by electrolysis which later was further developed i n Munich by Muthmann. The concepts "pyrophor" and "pyrophoricity" originate from Auer von Welsbach. The third major invention for the use of the rare earth elements was the addition of rare earth fluoride as a wick i n arc light carbons which, a t that time, were used for a wide range of lighting purposes and later also for cinema production and for search lights. This use of rare earth compounds i s based on the intensive arc l i g h t developed by Beck i n Germany i n 1910. In the 22 years between 1908 and 1930 about 1 100 - 1 400 tons of f l i n t s were produced as the most important rare earth product. This required the consumption o f about 1 300 - 1 800 tons of rare earth oxides i n the form of rare earth chloride. If one adds to t h i s the other applications, the consumption was probably between 2 000 - 3 000 tons of oxides. On the other hand, at the same time, about 7 500 tons of thorium nitrate were needed for Auer incandescent mantles. I f one assumes that monazite contains 6 % thorium oxide and 60 % rare earth elements, then 30 000 tons of rare earth oxides were produced during t h i s period of which only about 10 % was consumed. Period of Wide Technical Application. In the time between 1930 and 1940 work was done on various applications for the rare earth elements. Particularly successful was the production of sunglasses ("Neophan"), polishing media from rare earth oxides to replace iron oxide, decolorization of glass using cerium oxide, pure cerium oxide as opacifier i n ceramic glazes, use of cerium

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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oxalate in per«mesin" to combat seasickness and nausea during pregnancy/ and neodymium i n "Thrcmbodym" to combat thromboses. A l l of these applications however had only relatively small use during this transition period as compared to the large quantities of rare earths which continually became available, as for example, from use of ThCL as a catalyst i n plants for production of gasoline by the Fischer-Tropsch Process. After a few years Th0 was replaced i n this application by MgO. This disequilibrium was greatly increased i n the f i f t i e s at f i r s t i n the USA and England, later i n other countries as major programs for use of atomic energy were carried out. The large stockpile purchases of thorium by the atomic states as feed material for atomic breeder reactors l e f t behind at the end of the f i f t i e s - beginning of the s i x t i e s , huge quantities of rare earth by-products. This disequilibrium was again eliminated by the middle of the sixties following termination of the stockpile programs. Since then, thorium i s accumulating i n large inventory stocks at a l l monazite processors u n t i l perhaps i n the near future a new use for this material w i l l be found. The large atomic programs provided a great advantage for the rare earth industry. The rare earth elements which occurred abundantly i n the f i s s i o n products of atomic reactors were intensively s c i e n t i f i c a l l y examined at great expense and their separation from each other was pursued so that by the end of the f i f t i e s a large volume s c i e n t i f i c research results and properties of the rare earth metals were known. In particular I mention Prof. Spedding and the rare earth center he established in Ames/Iowa. Building on this stable s c i e n t i f i c foundation, which i n the following years further widened, there developed between 1960 and the present day a wide usage of the rare earth elements with an exponentially increased consumption. However, u n t i l today, the coupled production remains the fate and the task of the rare earth industry: i f one rare earth element i s needed then automatically a l l the others become available. So at the beginning of the sixties there was a market for lanthanum i n the optical glass industry, for cerium i n polishing media and for praseodyrninium/neo^niium (so-called "didymium") in the glass industry for coloring and decolorization but no one wanted to have samarium and europium. At Goldschmidt, for example, there had at that time accumulated large stocks of these materials i n the form of concentrates and high purity with a book value of zero. Ihis changed suddenly when i n 1965 europium was used i n the USA as a red phosphor i n color IV; however even then the samarium oxide continued to remain behind. These stocks were f i r s t reduced by the development of magnet materials i n recent years. A balance between the various applications must be achieved i n order that the costs for each application should not

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Overview

r i s e excessively. This w i l l also apply to the future; however, i t i s indicated that with the great broadening of the use of the rare earths the balance has become easier to achieve. Most importantly, there are today enough uses for mixtures of the rare earth elements. So, for example, i t makes l i t t l e d i f f e r ence i n catalytic cracking that samarium and europium have been previously extracted. Ihis provides a certain e l a s t i c i t y i n the use of the rare earth elements as f o r example with samarium and europium.

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The Special Properties of the Rare Earth Elements with Reference to their Use In order to bring about a systemization among the variety of uses I have broken down the uses of the rare earth elements into f i v e groups of properties: chemical, metallurgical, optical, magnetic and nuclear. Chemical Properties. In the uses of chemical properties the high a f f i n i t y of the rare earth metals for oxygen i s p r i marily involved. This leads to their application as f l i n t s , wherein their highly exothermic reaction with oxygen i n a i r i s used. On the same properties rests their application as getter metals, wherein residual oxygen, as for example i n amplifier tubes, i s bound up. The chemical-ceramic properties of the rare earth elements result from their high a f f i n i t y for oxygen yielding highly stable oxides which can be used i n high temperature materials; likewise the high melting points of sulfides are of interest. The use of the rare earth elements i n this f i e l d i s however limited because of their sensitivity toward C0 and water vapor. Yttrium oxide has become increasingly important i n the stabilization of Zr0 i * the cubic phase. This ZrC^ i s used as a high temperature material. Because a t high temperatures i t becomes conductive, the Y 0~-stabilized Zr0 serves also as an electrode, for example i n tne high temperature electrolysis of water, where i n addition yttrium-lanthanum oxide serves as the s o l i d electrolyte. ZrO /Y 0~ has a similar function as an electrode i n the so-cailea Lambda-Sensors, which are used to determine the oxygen content i n exhaust gases of automobiles. Chemical properties are also used i n the largest f i e l d of application for the rare earth elements: as catalysts. Most important are the cracking catalysts for the petroleum industry. The rare earth elements are combined into molecular sieves (Y-Zeolite) and serve i n f l u i d bed or fixed bed reactors to i n crease the y i e l d of gasoline. In addition thereto, there are the combustion catalysts for automobiles and for a i r pollution control. 2

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The chemical properties are at least i n part responsible for the use of rare earths i n polishing media. According to various researches, this involves, i n the polishing process, extensive chemical reactions on the surfaces of the glass which work to remove the material with mechanical abrasion perhaps also playing a role. Therefore, one must use different polishing materials for each material (for example metal or glass) and even for individual kinds of glass. The rare earth oxides, especially cerium oxide, have outstandingly j u s t i f i e d their use for the polishing of glass surfaces. The rare earth elements are physiologically inert and therefore present no danger to the environment. The two pharmaceutical applications which go back to the t h i r t i e s are based primarily on the anions or corresponding salts rather than on the effect of the rare earth metals: ceriumoxalate as treatment for seasickness and Nd-isonikotinate as treatment for thromboses. Metallurgical Properties. Here the rare earth elements operate as scavengers for oxygen and sulfur and other d e l e t e r i ous elements as well as being boundary surface active substances. This i s especially true i n the two most economically important f i e l d s of applications: the production of nodular graphite castings through spheroidization of graphitic components, and the treatment of steel for sulfide inclusion shape control. In both cases great effects are achieved with small additions. On the other hand, the use of rare earth metals for the f i x i n g of oxygen and sulfur i n l i g h t metals for production of conductive copper and conductive aluminum has remained i n s i g n i f i c a n t . However, the use of rare earth elements as magnesium hardeners remains important. Here the rare earth metals serve by precipitation of intermetallic compounds of high thermal stability. Optical Properties. The optical properties of the rare earth elements are of great importance i n their application. Due to the atomic structure of the 4 f - s h e l l there are narrow and sharp absorption and/or emission lines i n the v i s i b l e range which may be used i n various ways. In addition the oxides and/or oxide systems i n glasses provide a high index of refraction with low dispersion. The f i r s t applications of the rare earth elements* as already mentioned, were i n the optical f i e l d , namely the Auer incandescent mantles and the arc light carbons. In 1964/65 as a result of the work of Levine and P a l i l l a the use of the truly rare and therefore expensive europium together with yttrium made a major leap forward for the rare earth industry as red phosphors i n color TV screens. Due to the strong and sharp emission line of europium at 610 A, without a yellow component, which i s

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

1.

GREINACHER

Overview

13

perceived by the eye as a wonderfully saturated red color tone, i t was possible t o achieve i n color TV an evenly colored picture. Gd CL plays an important role i n x-ray i n t e n s i f i e r s . A f o i l with rare earth oxides i s placed on the x-ray f i l m and i s excited by x-rays to emit i n the v i s i b l e range. In this way the f i l m i s exposed with a minimum of radiation dosage. The coloring of glass with rare earth elements, for example with neodymium or praseodymium, i s also based on their selective absorption i n the v i s i b l e range. In the decolorizing of glass, the oxidation effect of 4-valent cerium i s combined with the absorption of small quantities of neodymium/praseodymium. Accordingly, cerium concentrates which always contain some praseodymium and neodymium are added t o glass melts. One achieves a chemical decolorization of iron by oxidation t o the 3-valent stage with physical decolorization by the selective absorption of didymium through o p t i c a l compensation. Therefore, a combination of chemical and o p t i c a l properties i s u t i l i z e d . The most important application of praseodymium i s the production of very beautiful high temperature resistant lemonyellow pigments f o r the ceramic industry. The praseodymium i s b u i l t into the zirconium s i l i c a t e l a t t i c e and thereby yields f u l l optical splendor. In the application of lanthanum oxide i n glass use i s made of the high index of refraction and the lack of color of this oxide. So today o p t i c a l glasses with up to 40 % lanthanum oxide are made which are corrosion resistant. Rare earth elements serve as activators i n laser glasses. Well-known i s the neodymium laser.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch001

2

Magnetic Properties. The rare earth elements show as a result of their atomic structure interesting magnetic properties which have led to various applications. Important i s the use of l i g h t rare earth elements for production of hard magnetic materials. Most prominent are alloys of samarium with cobalt i n the atomic r a t i o 1 : 5 or 2 : 17. I t may also be assumed that i n further development of these mat e r i a l s on a larger scale that praseodymium, neodymium, lanthanum and also individual heavy rare earth elements w i l l be used to achieve particular effects. Interesting i s the development of magnetic bubble memories based on gadolinium-gallium-garnets. They serve for storage of information because of their large storage density. The use of gadolinium metal as a heat pump i s a further magnetic application i n which the Curie Point, which l i e s a t room temperature for this material, can be very well utilized. Nuclear Properties. In connection with the major research programs for use of nuclear energy around 1960 there resulted interesting aspects for the rare earth elements, particularly

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch001

14

RARE EARTH ELEMENTS

the high capture cross-sections for thermal neutrons of Eu, Sm, Gd and Dy. Gadolinium and dysprosium were used as so-called burnable poisons to achieve a uniform neutron-flux during the lifetime of a fuel element. Europium shows exceptional properties insofar as a high capture cross-section of the natural isotopes i s combined with an uninterrupted series of f i v e isotopes/ a l l of which arise upon capture of a neutron and a l l of which have a high capture cross-section. Therefore, the capacity of such a neutron absorber i s extraordinarily great and there was an attempt to equip American atomic submarines with europium-bearing control rods. At the time this was not feasible because of an insufficient supply of europium. On the other hand/ yttrium metal was brought into use as a tubing material for molten salt reactors because i t has a low capture cross-section for thermal neutrons. Cerium and yttrium hydrides were successfully t r i e d as neutron moderators because of their temperature s t a b i l i t y . Applications According to Degree of Separation For particular applications the rare earth elements are used i n various purities according to whether the general properties of the rare earth elements or specific properties of individual elements are needed. The rare earth industry d i s t i n guishes i n general three grades of purity: the group of unseparated rare earth elements i n the composition which occurs naturally i n ores; concentrates producible by simple chemical precipitation reactions which i n general contain 60 - 90 % of the individual element desired; and the pure rare earth elements which contain between 98 and 99.999 % of a rare earth oxide. The price for the products rises over several degrees of magnitude i n the corresponding series. In the large scale application of rare earth elements as i n the steel industry/ i n catalysts and i n the polishing of glass, i n general, the naturally occurring mixtures or concentrates are u t i l i z e d . While with phosphors and electronic applications pure products with much higher prices are used. Therefore, the a p p l i cation of the rare earth elements requires careful consideration and close cooperation between producers and users so that the optimum between desired effects, purity and production costs can be found for each specific application. Allow me to c i t e three examples: F i r s t example - In the production of red phosphors for color TV where each screen requires about 5 - 10 g yttrium oxide and 500 - 1 000 mg europium oxide, high requirements are placed on the purity and with reference to specific rare earth e l ements or non-rare earth elements. As a result, the prices are expressed i n $/g.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

1.

GREINACHER

Overview

15

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch001

Second example - In the production of samariumcobalt permanent magnets impurities have practically only a d i l u t i o n effect. One can therefore use instead of a 99.9 % pure samarium metal a significantly cheaper 90 %, perhaps even 80 % pure metal with the balance other rare earths. In any case, i t i s necessary i n this instance that the composition of the other rare earth elements be held constant, which i s not always quite so simple. Third example - Although eerie oxide r e a l l y represents the active element i n polishing media, most of the polishing plants are s a t i s f i e d with about 50 % pure eerie oxide, which i s available i n the natural mixture of the l i g h t rare earth e l ements as they are extracted either from bastnasite or monazite, i n order to keep the cost of the product low. Substitution of the Application In the development of the rare earth industry, substitution of the rare earth elements by other cheaper processes or other substances has - and also i n the future w i l l play - an important role. The rare earth elements were never a cheap material a l though they occur abundantly i n nature. As we have heard, the cost of the rare earth elements rises rapidly i f a specific rare earth element i s required i n high purity. Therefore, there arose always the tendency for users of rare earth elements to look around for a cheaper solution for an established f i e l d of application. A danger which the rare earth industry often has learned to fear and which has led to a characteristic r i s e and f a l l of economic success for rare earth enterprises. Examples of such r i s e s and f a l l s resulting from substitution are given below. Through Processes: - replacement of Auer-incandescent gas mantles by incandescent lamps. - Replacement of rare earth elements for sulfide inclusion shape control by extreme steel desulfurization with the a i d of calcium. - Replacment of rare earth bearing arc l i g h t carbons by high pressure - argon - arc lights, particularly i n cinema projectors and i n searchlights. Through Other Substances: - Use of magnesium instead of mischmetal for production of nodular graphite castings. - Use of hafnium instead of europium i n atomic submarines for neutron absorption. - Replacement of eerie oxide by t i n oxide or zirconium oxide as opacifiers for enamels. - Use of titanium-iron alloy for hydrogen storage instead of LaNi . 5

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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RARE EARTH ELEMENTS

In general, however, one can say that where the o p t i c a l properties, the chemical properties and the magnetic properties are used, substitution i s not to be feared, while i n the use of metallurgical and nuclear properties there i s always the danger that a more economic solution of the problem can squeeze out the rare earth elements. Therefore, i t appears to me that the following f i e l d s of work are not threatened by substitution: polishing media, f l i n t s , catalysts, phosphors, magnets, optical glass components, coloring and decolorization of glass, pigment formers and x-ray intensifiers.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch001

Market Survey World demand for the rare earth elements i s established i n the range of 25 000 tons per year - calculated as rare earth oxides. These materials are available through production of bastnasite at the Mountain Pass Mine i n California, of monazite from Australia, India and B r a z i l , and of monazite as a by-product from the production of t i n ores, r u t i l e and various heavy mineral sands. From new information about the huge reserves i n the People's Republic of China, a ten-fold increase i n this demand could be s a t i s f i e d over a period of several years. Of particular interest i s the fact that the large occurrence i n the autonomous region of Inner Mongolia as a by-product of an existing hematite and magnetite mine i s f u l l y accessible through an infrastructure and railroad lines. The problem i n the processing of the ores can be comprehended and solved. The future supply of ore presents i n terms of quantity no problem for the rare earth industry. Another question naturally i s the development of prices which, with respect to ore, i s s t i l l characterized by a single dominant supplier. The consumption of the rare earth elements i s divided into four groups of application (2). One can see from this information that 98 % of the rare earth elements, with respect to quantity, are consumed i n the following f i e l d s of application: metallurgy, chemicals/catalysts, glass and polishing media. I f one however looks at the value of the products then the picture i s drastically altered, then phosphors are the most important f i e l d of application of the rare earth elements.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

1.

GREINACHER

17

Overview

Table I. Major world markets for rare earths (2) (% by weight on REO basis estimated) 1975

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch001

Metallurgical Chemical/catalysis Glass/ceramics Phosphors/electronics

45 36 17 2

1976

1977

32 38 28 2

34 39 26 1

1978 1979 32 32 35 1

43 26 31 %

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Mischmetal or Low Cerium Rare E a r t h s High Cerium Rare E a r t h s Cerium

50

90

Lanthanum

33

5

Neodymium

12

2

Praseodymium

4

1

Other Rare E a r t h s

1

2

Transactions of the American Foundrymen's Society

Figure 7. Photographs of CRT output of electron microprobe depicting heterogeneous particle at the center of two graphite nodules (11). Particles were identified as calcium-magnesium sulfides: a, 1375X; b, 5000X; c, 1250X; d, 5000X-

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

2.

LINEBARGER AND McCLUHAN

Nodular

Iron

Production

29

The r a r e earths p l a y three r o l e s i n the production o f nodular i r o n . These r o l e s are as a n o d u l i z i n g element (or as the growth m o d i f i e r ) as a means o f enhancing the nodule count (or n u c l e a t i o n ) and, f i n a l l y as c o n t r o l l e r s o f d e l e t e r i o u s elements. The use o f the r a r e earths f o r each of these purposes w i l l be described i n d e t a i l i n the f o l l o w i n g s e c t i o n s .

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch002

The Rare Earths as N o d u l i z e r s i n the Production o f Nodular Iron The modern foundry process f o r producing nodular i r o n can be o v e r s i m p l i f i e d by d e s c r i b i n g i t as the treatment o f a base i r o n (3% t o 4% carbon, 1% t o 2% s i l i c o n ) having low (0.005% t o 0.05%) s u l f u r l e v e l s and c o n t a i n i n g l i t t l e (' Similar steel plate and sheet after REM treatment (bottom) (33)

s t e e

Figure 13. Impact energy at 100% ductile fracture temperature, which is "shelf energy," as a function of REM-to-sulfur ratio retained in the 80,000 psi steel. Note the progressive effect of increasing REM additions on the transverse impacts while the longitudinal values remain virtually unchanged. The X points represent untreated steel.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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at lightning speed to other steelmaking plants i n the U.S., Canada and Europe. However mischmetal quickly displaced RES i n market share as discussed e a r l i e r . After an early start i n HSLA steels for automotive applications as exemplified i n Figure 1U (33)* the ^ of the usage of mischmetal shifted to line pipe steel, a market that was very active from 1970 to 197K 3nd caught most steelmakers o f f guard without other alternatives to control MnS inclusions. A recent application involving the node of en offshore platform with complex welding of tubular shapes i s shown i n Figure 15 ( 3 3 ) . Other applications which developed during the past decade were a l l directl y related to sulfide shape control. Resistance to spelling during cold punching of high carbon plow wheels for agricultural machines i s one example. Resistance to lamellar tearing of welded structures (31±), in which the elimination of elongated MnS inclusions i s essential, i s an other example. Finally, since late 1976, a large tonnage application has developed i n the U.S. involving high strength welded tubes for deep o i l well casing and d r i l l i n g , competing head-on with the more conventional seamless tubes produced through the Mannesman process. About 1500 tons of mischmetal per year are consumed for this l a t ter application. This total consumption i s expected to increase at least u n t i l 1983, when complete predesulfurization of the steel w i l l reduce the REM consumption per ton of steel by more than 50%. Today's average consumption per ton of steel treated i s about 1 3/h lbs of mischmetal or equivalent i n rare earth s i l i c i d e . I t should drop to 3/h lbs / ton by 1990.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch003

t u l

Steelmaking Practices. There are four techniques for adding mischmetal to l i q u i d steel, two involving the ladle and two i n volving the ingot mold. Without entering the details that can be found i n the literature (18, V9, 32), the ladle techniques are: one, the plunging of a canister containing from 100 to 1,000 lbs of cast mischmetal alloyed with a l i t t l e magnesium to promote agitation and mixing ( 3 5 ) ; and two, an introduction through the alloy feeding system of a ladle degasser, after degassing has been completed and an aluminum "trimming addition has completed the deoxidation prior to REM feeding ( 3 6 ) . The two mold practices involve hand feeding of preweighed bags during the early part of mold f i l l i n g to promote maximum mixing (37), and the "DELAYED MOLD ADDITION PRACTICE" described while discussing the physical properties of mischmetal U 8 ) . Other practices used less extensively and mostly i n Europe and Japan i n clude the feeding of a wire containing the alloy into the tundish or the mold of slab casters, the hanging of a mischmetal bar in the ingot mold during bottom pouring and the injection of REM a l loy powders with or after calcium s i l i c o n injection to improve sulfide shape control after desulfurization with calcium. Recoveries of the REM units vary from as low as 25% with the second l a dle practice to as much as 80% with the delayed mold addition and 95% with wire feeding i n the slab casting mold. 11

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch003

LUYCKX

Steel

AIME-NOHC Steelmaking Proceedings

Figure 14.

Examples of some automotive parts produced commercially using the cold formability introduced by the REM addition (33)

Figure 15. Off-shore platform node construction showing the complex welding assembly job requiring outstanding resistance to lamellar tearing in the electricresistance-welded (ERW) steel pipe stock. Excellent through-thickness ductility is obtained by low sulfur plus REM treatment in the ladle, plunging a mischmetal canister.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

58

RARE EARTH

ELEMENTS

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch003

Problems With REM Treatment, Subsurface Defects in Ingots. The precipitation of RE-OpS and RE S as solid particles i n the l i q u i d steel immediately after the adSi?ion i s conducive to inclusion clustering, the forming of large — up to inches i n diameter — spatial networks of small ~ 1 to 10 micron ~ non-metallic particles adhering to each other by surface tension (38). In addition, slow melting and dissolution particularly of rare earth s i l i c i d e leads to oxidation of the a l loy during mold addition resulting in solid scums and subsurface entrapments, which ultimately result in surface defects on the finished rolled product, Figure 16. The delayed mold addition technique a l l but eliminates these problems and the use of rare earth s i l i c i d e i n the mold has a l l but disappeared largely because of these problems. Ladle and Tundish Nozzle Blockage. The same clustering mechanism i s responsible for this serious operating problem which i s not specific to the use of REM's, but to any additive conducive to solid inclusions i n the l i q u i d steel. Deoxidation with aluminum, zirconium, titanium, even high additions of calcium, a l l can lead to AlpO^, ZrOp, TiOp, CaS inclusions which tend to accumulate i n the nozzle throat afld ultimately stop the flow of l i q u i d steel completely. An obvious solution would appear to be the feeding of REM's after the nozzle, for example in the form of wire. However, there i s then maximum tendency for the problem described above to develop i n the slab casting mold. The best solution to this problem i s to minimize the volume of inclusions passing through the nozzle by upgrading the ladle refractory and performing a suitable s t i r r i n g after the REM treatment to give the inclusion clusters maximum chance to separate out of the melt by adherence to the laddie slag or to a refractory wall Q £ ) . Above a l l , this problem can only be solved when i n i t i a l sulfur levels are low, ideally less than 0.007%, but no more than 0.012%. Bottom Cone Segregations. Layered accumulations of RE s u l fides and oxysulfides near the bottom of the ingot (the maximum concentration i s at about 25% of the ingot height) i s observed practically i n a l l large ingots with sulfur content over 0.010% and treated with REM's in the mold. This condition degrades the through thickness properties of steel plates because of the large concentration of small inclusions acting as notches. Among others, a strong research team at Kawasaki Steel, Chiba Works, headed t>y Drs. Sanbongi, Etai, Habu and others has made an exhaustive and constructive study of the phenomenon Q 2 , U0, h±). They proposed the following complete solution: with the required RE/S ratio of 2.7/1 for t o t a l MnS substitution, the controlling factor i n the severity of segregation i s the RE x S product or, ultimately, the

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Steel

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch003

LUYCKX

Figure 16. Shallow surface crack at the outer radius of a sharp V2T bend on 80,000 psi steel sheet (top). Corresponding subsurface concentration of REM oxysulfides and sulfides in a slab cross section near the surface. The parent ingot was treated with 5 lbs of rare earth silicide per ton of ingot steel (bottom). The bottom picture is from a Baumann print or sulfur print, not sensitive to the oxides and thus eliminating the argument of reoxidation as main cause of surface defects in REM treated steels. Magnification, 2.5X-

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

RARE EARTH

60

ELEMENTS

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sulfur content. For a RE x S product which they c a l l below or equal to 13 x 10"° the "bottom sedimental zone" disappears, leaving f a i n t l y "enriched A and V segregations" and less top segregation. This, i n turn, corresponds to a sulfur content of 0.007% maximum. However, a S of 0.005% i s preferred with the corresponding product o i P f o x 10 , because then a l l segregations disappear and the resulting steel reaches i t s maximum attainable properties with total shape control without side effects, Figure 17. REM Alloy Costs. For a typical North American sulfur specification of 0.015% max., a minimum retained REM content of 0.0U5 i s required to insure f u l l MnS substitution, i . e . a REM/S ratio of minimum 3/1. Using the delayed mold addition practice with at least 75% recovery and mischmetal @ $5.30/lb the current cost of a typical treatment i s : $ 5 > 3

x

a-OOO^x 2,000

u

^

9

3

$

/

n

Q

t

t

o

n

o

f

ingot

s

t

e

e

l .

With ladle plunging or additions through a degassing unit, the costs per ton can go as high as $12.00 per ton for guaranteed sulfide shape control and maximum transverse properties which genera l l y require a RE/S equal to U instead of 3. The direct and simple solution to this cost i s ooviously to lower the sulfur content prior to mischmetal addition. For every 0.001% reduction i n sulfur, there i s a minimum Li2#/ton saving using the delayed mold addition technique and the saving potential increases with other, less e f f i c i e n t practices. However, desulfurization costs increase rather sharply when reaching down to the low contents below 0.005%. In Figure 18, the preceeding discussion i s summarized showing a minimum i n the area of about 0.007% S which i s also desirable from a product quality standpoint. This minimum i s the t o t a l cost of sulfide shape control + desulfurization. This was f i r s t presented i n 1973 (Jj?) but has been readjusted to the new cost structures. Solutions to the Problems with REM. To summarize the solutions to a l l of the problems associated with REM additions to l i q uid steel, f i r s t i t i s essential to try and operate at much lower sulfur contents than normally practiced i n North America, ideally about 0.005 to 0.007% prior to REM addition. For ingot casting, the delayed mold addition, particularly coupled with low sulfur concentrations i s sufficient and economical for most applications. For severe property requirements and for continuous casting, the REM's should be introduced i n the ladle, using improved refractories and slags, and a good s t i r r i n g practice after the treatment. These requirements are essentially the same ones imposed by the vendors of the competing calcium practice. Wire feeding i n the slab casting mold i s not recommended.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch003

3.

LUYCKX

61

Steel

Sulfur, Weight %

Figure 17. Representation of the analytical limits to be kept for defect-free REMor Ca-treated steel. The shaded areas (deep shade only for calcium) are considered safe by the Kawasaki team.

005

oio

oi5

.020 .025 SULFUR %

Figure 18. Economic optimization of desulfurization plus sulfide shape control, using mischmetal at 50% recovery, by ladle addition for critical applications

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch003

Competing Techniques for Manganese Sulfide Control. In large part because of the problems described above, part i c u l a r l y the nozzle blockage problem, intensive development efforts have centered on desulfurizing the steel to the point at which shape control would no longer be required. Among the severa l techniques existing today, those combining injection of calcium alloys, basic slag mixtures and improved ladle linings have, i n effect, substituted the need for REM additions i n 80 to 90% of the potential use in Europe and Japan. The original claims that when 0.005% S i s reached, no more shape control i s needed (Q), have been replaced by the new claims that calcium also provides t o t a l shape control as well or better than the REM's (ji2« U3). As the Kawasaki research team mentioned earlier nave concluded, there i s also, with calcium, a Ca/S requirement as with the REM's for total MnS substitution (32). They have proposed the most reliable estimate so far of retained calcium requirement for "homogeneous sulfide shape control" which i s summarized i n Table IV and Figure 17. Table IV:

Minimum Ca/S Ratio Requirement in"Weights for Shape Control.

C r i t i c a l i t y Level of Properties

Manganese Content 1% 13# 2%

partial total

0.65 1.3

1* 2.5

1.5*. 3.2*

Prevention of ifydrogen Cracking: partial total

1.3 1.7

2.5 3.1

3.2; Iw5

Improvement i n Toughness:

Extrapolations from the discussions i n the text (32). The three manganese levels are typical of, respectively, Electric Resistance Welded pipe (ERW) at 1%; 0 . 0 pipe at 1^% (a newly developed forming technique for the manufacture of very large pipe out of heavy plate s^eel); and the new Mn-Mo-Cb steels developed mainly i n the U.S. by Amax (hk). Because of the limited s o l u b i l i ty of calcium in steel, the only way these ratios can be achieved, particularly i n high Mn steels and for the most c r i t i c a l property levels, i s by extreme desulfurization down to 0.00U% max. i n the easiest case and 0.001% max. in the most unfavorable situation. This discussion indicates that most steels produced today using the low sulfur practices, typically at 0.005% S, are not showing complete substitution of MnS inclusions. Fortunately, the property improvement i s generally sufficient to satisfy almost a l l specifications. However, the p o s s i b i l i t y exists of a p a r t i a l return to a f i n a l REM addition at the low sulfur levels obtained by calcium injection to achieve much easier shape control at low cost and without side effects, when c r i t i c a l performances are essential.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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LUYCKX

Steel

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Hydrogen-induced Cracking, the New REM Application Since 1977* Mechanism of Failure. Catastrophic failures of large diameter gas and o i l line pipe i n seawater and in hydrogen sulfide contaminated waters over recent years have been traced to disintegration of the steel structure by hydrogen. At the surface of the pipe, hydrogen atoms are liberated by an electro-chemical reaction and penetrate quickly by diffusion inside the steel structure to recombine i n molecular hydrogen as soon as they meet with a discontinuity i n the steel such as non-metallic inclusions. This molecular hydrogen can reach local pressures of 10,000 atm and more, developing tremendous localized stresses. Elongated inclusions, particularly i n groups as frequently exhibited by MnS, w i l l tend to open up under the applied stress and i n i t i a t e cracking at their tips, ultimately joining other cracks i n a step fashion unt i l macrocracks develop i n i t i a t i n g the catastrophic f a i l u r e . VJhen the steel i s i t s e l f under constant stress, for example from natur a l gas pressure, the hydrogen induced cracking i s greatly accelerated. The same phenomenon occurs i n deep sour gas wells only at even greater speed on account of HgS concentrations. The Sulfide Shape Control Effect. Italian and Japanese (U6) steel researchers have shown that sulfide shape control i s clearly more important i n this case than sulfur reduction. Figure 19 shows the progressive improvement i n crack appearance after standard exposure time, using progressively improved steelmaking practices in which the REM treatment introduces the most s i g n i f i cant progress (1+5)» Figure 20 shows similar results, this time on commercial seamless steel as opposed to line pipe steel, and clearly demonstrates that, even at 0.003% S, a REM addition can bring very substantial improvements i n resistance to hydrogen-induced stress corrosion cracking (i±6). The interpretation of these results i s simple: the replacement of elongated manganese sulfide inclusions by numerous, small REM oxysulfide and sulfide inclusions multiplies precipitation points for the transformation of hydrogen from atomic to molecular form and eliminates the severe weakening effect at the tips of elongated inclusions. As long as the REM/S ratio i s of the order of 3 to 6, this i s a satisfactory theory and i n the above mentioned examples, i t i s probably correct. The REM Hydride Effect. In a research report entitled "Inhibition of Hydrogen Bnbrittlenient i n High Strength Steel" C.S. Kortovich broke new ground when he added very large excess lanthanum and cerium to a k3h0 steel melt at 0.00li% S His retained REK/S ratios in the five (5) laboratory heats which were treated with up to 0.2% La and Ce, varied from 8/1 to 1|6/1i large excess, predictably, resulted i n precipitation of the low melting La-Fe or Ce-Fe eutectic at the primary grain boundaries as described earlier in this paper and i n hot shortness and loss of impact properties. A l l this was confirmed by the report, except T

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

n

s

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Figure 19. Dramatic prevention effect introduced by REM additions against disintegration of line pipe steel by hydrogeninduced cracking (HIC)

RESISTANCE TO HYDROGEN-INDUCED CRACKING IN COMMERCIAL 7"0 SEAMLESS TUBE STEEL

Fracture Time

(Ohki & al.,1977) Nippon Kokan

Figure 20. Improvement in lower critical stress as well as delayed cracking initiation introduced by REM additions even when the steel is down to 0.003% sulfur

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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that Kortovich misidentified the eutectic as a grain boundary oxide, the same error made by many steel m i l l metallurgists. Dramat i c improvement in resistance to hydrogen embrittlement was achieved by moving from the low cerium and lanthanum levels practiced by the other researchers aiming only at sulfide shape cont r o l , to 3 to 5 times that level-, aiming at REM hydride formation. That i s the breakthrough. In addition, there are inconsistent i n dications that the properties of the highly "doped" steel improved after hydrogen charging, certainly a startling observation. In Figure 21, the grain boundary precipitates are sketched and i n Figure 22, a summary of the hydrogen cracking results i s given with similar coordinates and units as i n Figure 20, for comparison. It i s nearly certain that hydrides have formed i n this application, as suspected by Kortovich. I t i s also highly probable that these hydrides have simply formed at the site of the grain boundary eutectics which contain about 92.5% Ce i n the Ge-Fe system and 95% La in the La-Fe system. This area of development i s perceived by this writer as having the most promising potential for new volume usage of the REM's i n steelmaking during the eighties. Summary of the Metallurgical Effects of REM's i n Steel. In Figure 23, a qualitative plotting of the effects of growing additions of REM's to steel on the most affected properties i s proposed. In this plot, i t i s clear that cold formability, impact resistance and hot workability — also improved weld integrity — quickly reach a maximum with f a i r l y small, economical additions because a l l of these improvements are d i r e c t l y related to sulfide shape control, and tramp element control i n the case of stainless steels. For details on the latter mechanism, not discussed i n this paper because i t has now become a minor application, please refer to the literature of the f i f t i e s (US)• Two other propert i e s , high temperature oxidation resistance (U9, j>0) and hydrogen cracking resistance, follow a d i s t i n c t l y separate course because the mechanism of action has l i t t l e or nothing to do with manganese sulfide inclusions. I t can be seen also that the latter two effects severely conflict with basic requirements of hot workability and plain strength of most steel grades. Ingenious manipulation of the "as-cast structures" may be one way to minimize the deleterious effects of the grain boundary eutectic while capitalizing on higher additions to stretch the resistance of our future steels to high temperature oxidation or hydrogen embrittlement. History of the Industrial Use of Mischmetal i n Steels. Origins. Since the 1890's, monazite, the f i r s t commercial rare earth ore, was mined from black beach sands i n B r a z i l and shipped to Austria for i t s 5 to 10% thorium oxide content. Carl Freiherr Auer von Welsbach spent 20 years of research work developing a bright incandescent gas mantle he discovered i n 1866 with

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.170% Ce .160% La

.092% Ce

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.078% La

Figure 21. Sketches of the grain boundary eutectic, RE-Fe at various La and Ce concentrations

.033% Ce AISI 4340. 0 004%S. Unetched, 500 X

Figure 22. Summary of HIC results with increased REM additions showing significant improvement only over 0.1% Ce or La in lower critical stress, suggesting hydride formation in the RE-Fe eutectic.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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ZrOp doped by La^Oy He capitalized on the longevity of ThO^ and the white brightness given by a few percent of CeOp i n order to meet the growing competition with Edison's new electric lamp. Dissatisfied with having to discard over 90% of the ore value, a phosphate of cerium, lanthanum and "didymium" after extracting the thorium as a nitrate, Auer von Welsbach researched and found the f i r s t metallurgical use for the l i g h t lanthanides as a f l i n t for cigarette lighters. To produce the pyrophoric alloy, which he coined "mischmetall, " he used the then recently developed fused salt electrolysis processes of Hillebrand & Norton, 1875 and of Muthmann, Hofer & Weiss, 1902. In 1908 the f i r s t company involved in the commercial production of rare earth metals was founded by von Welsbach at Treibach i n Karinthia. Today the company i s known as Treibacher Chemische Werke. In the U.S., Ronson Metals quickly followed suite starting production of lighter f l i n t s around 1915. It did not take long for curious ferrous metallurgists to try out the newly available metal. As early as 1913 i n iron (U), and 1922 i n steel Q ) , the f i r s t reports showed promise or dismal f a i l u r e . With today's knowledge of the mechanisms involved ( 2 0 ) , i t i s not surprising that G i l l e t and Mack at the Bureau of Mines, although reporting a drop i n sulfur, showed d i r t y steel and poor mechanical properties as a result of the f i r s t mischmetal t r i a l . This and other experiments with similarly dismal results put a considerable damper on the use of REM's i n steelmaking. It took almost half a century to understand steel thermodynamics and inclusion separation mechanisms to overcome this "dirt problem and to harness the lanthanides for economical and c r i t i c a l use i n massive steel production. During World War II, however, renewed interest centered around the use of rare earth fluoride fluxes as cleansing agents for a i r c r a f t landing gear steels and the likes ( 2 2 ) . 11

Early Success. After fast progress i n magnesium alloys spurred cy a i r c r a f t materials needs during the t h i r t i e s and after a b r i l l i a n t but brief flash of success i n the f i r s t nodular irons in 19U8 (but unfortunately quickly substituted by Mg) mischmetal f i n a l l y struck i t r i c h i n steel around 1950. With almost "miraculous effect" on the hot workability of highly alloyed stainless steel ingots, mischmetal entered the h a l l of fame of steelmaking history with the then popular appellation of " p e n i c i l l i n of steel." U.S. patent #2,553,330 to Carpenter Steel Co., the paper by Post, Schoffstall and Beaver (U8), and other subsequent papers described the practice. They discussed the dramatic improvements achieved and tried to theorize on the mechanisms by which Lanceramp," the popular alloy of the times (j^Jj affected the propert i e s . One clear-cut effect depicted in Figure 2ii from the f i f t i e s , shows a refinement of the as-cast grain size in certain grades such as AISI 310. Amidst confusion, there was evidence a l ready of the beneficial neutralization of the tramp elements, Fb, Sn, As, 3 i etc., and of the extreme reactivity with sulfur and oxygen. n

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Figure 23. Qualitative summary of the evolution of steel properties discussed in this chapter as a function of the retained REM content showing an early maximum for all properties associated with sulfide shape control and tramp element control but quite a different story for hydrogen and oxidation resistance

0 / 0

stained REM

Electric Furnace Proceedings

Figure 24. The mechanism that created the first REM boom in steelmaking in 1950 (5%). Cross section of S.A.E. grade 310 stainless steel billets pickled to show the solidification structure. On the left, normally coarse structure causing hot shortness; on the right, effect of 2 lbs of mischmetal added to the ladle to improve hot workability.

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Partly because of high mischmetal prices, substitution by boron alloys took most of the g l i t t e r out of the market for a decade. The Carpenter application i s now a negligible fraction of the tot a l consumption of mischmetal i n steels. Almost ignored at the time but a harbinger of today's main REM role i n steels, were papers such as the one by Berry and Dorvel i n 1951 reporting the elimination of low d u c t i l i t y and low impact strength in aluminum deoxidized cast steels by adding mischmetal after a l l other additions, "changing the shape and distribution of non-metallic inclusions." Such papers reflected Clarence Sims' views already published in 1935 (25) but not i n vogue at the time. By the late f i f t i e s , i t became increasingly clear that the aff i n i t y of the REM's for sulfur to the point of occasionally causing some startling desulfurization, was one of the main features distinguishing them from other "deoxidizers," T i , A l , Zr, V, etc. being tested at the time to improve steel cleanliness. The determination of cerium-sulfur solubility products i n steels by Langenberg and Chipman i n 1958 (52), i s a manifestation of this early understanding. However, because of the pervasive fashion from 1950 to 1965 of concentrating a l l metallurgical efforts on deoxidation processes for steel cleanliness and property control, the main marketing efforts for the development of mischmetal usage in steelmaking centered on the low oxygen equilibrium obtained i n steel by REM additions. Limited industrial tests along these lines in c r i t i c a l bar steel grades, for example, f a i l e d to bring the desired improvements largely from totally neglecting the sulfur component. Instead of analyzing subsurface " d i r t " concentrations which would have revealed high sulfur contents, the problem was attributed to reoxidation of the teeming stream. As a result, "ductile iron and magnesium alloys shared with lighter f l i n t s and small stainless steel usage the main uses for mischmetal and rare earth s i l i c i d e in a l l metallurgical f i e l d s as late as 1968" (53)> Total world consumption was probably less than 100 tons per year in steel i n 1968. The Second and Major Success. As with the f i r s t breakthrough, at Carpenter Steel, a pressing problem had to be solved fast to salvage four years of arduous and successful development on a new steel grade at Jones & Laughlin Steel. A l l systems were "go" on the f i r s t 80,000 p s i vanadium-aluminum-nitrogen HSLA steel control-cooled on the new hot s t r i p m i l l of the Cleveland Works, except for an unforeseen, nagging problem when the f i r s t 200 tons h i t the market. When the steel was bent on a tight radius i n a press-brake, with the axis of the bend p a r a l l e l to the hot r o l l i n g direction, deep cracks developed on the outer diameter of the bend, prompting scrapping of the part or extensive welding repair. It was the manganese sulfide exacerbated by lower than normal r o l l i n g temperatures necessitated by the new structure technology

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by extras low oxygen contents of the aluminum deoxidation and by the vastly increased Mn/S ratio. Early substitution tests using zirconium resulted i n a loss of 15j000 p s i because of predictable precipitation of a l l the nitrogen as ZrN i n the l i q u i d , removing an essential building block from the VAN-80 construction. In laboratory tests in 1968 the REM's met with t o t a l and instant success at low and reproducible levels ( 2 0 ) . Unlike the Carpenter application, the HSLA class of steel responded to a massive tonnage need both i n o i l and gas transportation and i n automotive truck frame, car weight reduction programs of the early seventies (55)* Except for a few German and Japanese mills, the steel industry was not prepared to take the other route, the extra-low sulfur alternative at 0.005% maximum which i s now common practice i n many large steel plants around the world. The REM's became locked i n with most HSLA steels for c r i t i c a l formability or impact applications and the consumption of REM's i n steels peaked i n 197U with nearly 6,000 metric tons of mischmetal equivalent, at least a 60 times rise in six years. In Figure 25* this evolution of consumption i s estimated from approximate figures compiled by Molycorp, the major world producer of the bastnasite ore. It also differentiates between mischmetal, rare earth s i l i c i d e and foundry alloy consumption of REM units. This world consumption diagram clearly demonstrates the astronomical impact — at the rare earth scale — of the simple mold addition technique requiring zero investment to achieve vastly improved engineering properties in l i n e pipe and automotive steels from 1970 to 197ll. After the Boom, The 3ust i n Europe i n 1975. In the midst of euphoria and hasty production capacity enlargements i n 197li-75* the four European mischmetal producers were stunned by a sharp downturn in orders. This was f i r s t attributed to the combination of a deep world-wide steel recession with the invasion of the market by a flooding of cheap Brazilian imports. In a record time since 1972, the Brazilians had b u i l t not less than three mischmeta l production plants to take maximum value out of their ore but they came on stream just after the peak. However, mischmetal consumption kept dropping through 1976 and 1977 while the steel market was recovering, which clearly demonstrated substitution. What happened? The German and Japanese steel metallurgists had understood much earlier in the game, during the sixties, the paramount importance of eliminating the manganese sulfide inclusions. Their equipment and highly quality-oriented minds allowed them to tackle the d i f f i c u l t orders ahead of everybody else. They firmly selected the low sulfur route and embarked in heavy investments for hot metal desulfurization equipment and later i n steel desulfurization (J>6). Until 1973, however, the sulfur levels achieved by hot metal desulfurization did not help the f i n a l sulfur content because of the contaminating effect of cooling scrap in the Basic Oxygen Furnace (B0F), except i n Japan where

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Figure 25. Evolution of commercial consumption of contained REMs in iron and steel starting in 1967 and projecting tentatively through 1985. Other metallurgical uses of mischmetal and RES are not included but amount to no more than 15% of the totals of the graphs.

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only ore was used as coolant. This i s the basic reason why the mischmetal market in steel was never large in Japan. From the Niederrhein division of Thyssen Stahl i n Oberhausen, West Germany, came the f i r s t comprehensively engineered steel desulfurization process based on calcium compounds and alloys i n jected deep in the steel ladle (,21). P contrast of smooth slab casting operation by using this technique with the nozzle blockage and subsurface contamination characteristic of the REM practice i n the ladle was the major drive for the switch. A much advertized lower alloy cost per ingot ton, using calcium alloys helped swallow the royalty and equipment costs estimated at over $1 million per unit i n 197h. What prompted steelmakers to move so fast was the large looming orders, mostly from the J.S.S.R., for low price gas line pipes with increasingly c r i t i c a l low temperature properties. The only way they could compete was by using the much lower cost slab casting route i n which, precisely, the REM practice was causing so much trouble. In a matter of months 15 units were sold around the world and installation of the equipment was given top p r i o r i t y and urgency. The claims of metallurgical superiority of calcium treated steels as compared to high sulfur REM treated steels were overwhelming: better cleanliness, higher impacts, sulfur content easily maintained below 0.005% and total sulfide shape control of the remaining sulfur by CaS l e f t l i t t l e or no hope for the alternate route, once the investment had been committed. The problems associated with the so called CAB or TN (for Thyssen-Niederrhein) practice surfaced only much later. They i n clude much higher refractory costs i n the ladle, expensive fume collection systems over the ladle, the injection of unwanted s i l i con with the calcium s i l i c o n alloy, the need for a new slag cover on the ladle of steel, the pick-up of 1 to 3 ppm of hydrogen with the injection and of 10 to hO ppm of nitrogen. The worst observation, which i s hotly disputed by the proponents of the TN technique, i s the general absence of total sulfide shape control i n slab-cast steels, particularly with high manganese contents and lengthy ladle holds typical of continuous casting operations. None of these problems, however are l i k e l y to deter steel operators from pursuing the injection practices which give them l i t t l e or no trouble at the slab caster. There are now of course many competing steel desulfurization techniques and the recent trend has been away from injection and towards more sophisticated new slag compositions to reach the 0.005% max. S without the pick-up of nitrogen and hydrogen and without the expensive basic ladle refractories. Japanese metallurgists who are currently in the lead have recognized the shape control d i f f i c u l t i e s associated with calcium and are reconsidering the use of the REM's i n small, c r i t i c a l l y adjusted quantities (32, 1+6), as an alternative to the need for a second calcium feeding i n the tundish or the mold for total sh8pe control of the sulfide inclusions. T h e

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The Contrasting U.S. Boom of the Late Seventies. While convulsions racked the European mischmetal market, consumption i n the U.S. increased steadily from 1973 to 1976, even through the 1975 steel recession. From a modest 1 million lbs per year market i n 1973, mischmetal f i r s t started substituting for rare earth s i l i cide from 197ii to 1976 and then struck i t r i c h again i n late 1976 with a new application i n ERW high strength tubes for o i l well casing and d r i l l i n g , to stabilize around 6 million lbs per year today i n the U.S. and Canada. A small fraction of that figure s t i l l goes to ductile iron, lighter f l i n t s and magnesium alloys, samarium oxide reduction for magnets and other more sophisticated applications. In Figure 25, discussed earlier, the market transfer from Europe to the U.S. around the mid-seventies i s quite evident. There i s now a net import situation to satisfy the demand while the American producers have increased their capacity for the third time i n a decade. The Outlook for This Decade and Beyond. Strong signs of substitution by low sulfur practices have appeared on this side of the Atlantic. U.S. Steel at Baytown, Texas i n 1976, Lukens Steel in Coatesville, PA i n 1975, Stelco i n Hamilton, Ontario i n 1979 and IPSCO, i n Regina, Saskatchewan i n 1980 have purchased ana i n stalled a TN unit essentially for large diameter pipe production. Other steelmakers have preferred competing devices. Oregon Steel has installed a Scandinavian Lancers Unit i n 1978, Bethlehem Steel has installed i t s internally developed unit at Burns Harbor i n 1979 and Republic, Armco and Jones & Laughlin are developing their own injection systems as well. While the above mentioned installations have already substituted the entirety of the REM usage for arctic line pipe application, they are only starting to make a dent i n the HSLA automotive market, with Bethlehem Steel announcing the f i r s t extra-low sulfur HSLA sheet steel called IF, to replace their previous t i t a nium bearing grades (j>7). The substitution of REM's i n the high strength o i l country goods w i l l not l i k e l y happen before 1983 i n the major producing plant at Lone Star Steel, Texas while i t w i l l happen much sooner at National Steel, Granite City Division, who embarked on a slab casting investment due to start before the end of the year 1980. Unless a major breakthrough in REM application occurs before 1983, such as the demonstration of drastically reduced susceptib i l i t y of pipes and tubes to hydrogen embrittlement (IV7), the domestic mischmetal market i n steelmaking w i l l f a l l f a i r l y sharply by 198U-85, despite the metallurgical i n f e r i o r i t y of the substitutes. If mischmetal was showing signs of pick-up in steel i n Japan, there would be a high probability of similar trends i n Europe and the U.S. after a delay period of 6 to 12 months, an eventuality that has not showed up yet i n the Japanese steel industry.

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As the steel market for mischmetal has been marked by quick booms followed by substitutional busts, i t i s not wise to make predictions of market size much beyond 1985, pending an other pot e n t i a l l y massive application. The base l e v e l , however tends strongly upwards, indicating an encouraging underlying current of increased confidence of the steelmakers towards the lanthanides. The trauma caused by severe operational and quality problems using the REM s without precautions gave the metal the black eye and an underdog status which w i l l require time and enlightened marketing efforts to overcome on the long term. With ever increasing demands on the engineering properties of our steels, I am confident that i t s superiority over a l l substitutional systems w i l l eventually give mischmetal not only the market volume but also the status that i t deserves i n the steelmaking community. Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch003

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Literature Cited 1.

Trombe, Felix. Rev. de Met., 1956,

53,

31-33.

2.

Savitskii, E. M. "Rare Metals & Alloys", Technology House (Dom Tekhniki), Moscow, 1959.

3.

Spedding F. H.; Daane A. H. "The Rare Earths", American Society for Metals; R. E. Krieger Publishing Co. Inc. Huntington N.Y., 1961; p. 501.

4.

Kleber, E. V.; Love, B. "Technology of Sc., Y, and the Rare Earth Metals". Pergamon Press, 1963.

5.

LeRoy Eyring. "Progress i n the Science and Technology of the Rare Earths" Vol. I I , Pergamon Press, London, 1964, p. 193-197.

6.

Anderson E.; Spreadborough J. Rev. Met., 1967, 64, 177-183.

7.

Hirschhorn I. S. "Use of Mischmetal (Mixed Rare Earth Metals) in Steels". Private Publ. by Ronson Metals Corp. 8/1968.

8.

Kippehan N.; Gschneidner, K. A., J r . "Rare Earth Metals i n Steels", IS-RIC-4; Rare Earth Information Center, Iowa State Univ., Ames, IA, 1970.

9.

Reinhardt K., Goldschmidt Informiert, 4/1974, (31), p. 2 , 7 , 3 3 .

10. Raman A. Z. Metallk.; 1976, 67, 780-789. 11. Waudby, P. E. Intern. Met. Reviews, 1978, 23, ( 2 ) , 74-98. 12. American Metal Market, Summer 1980, Rare Earth Metals Price List. 13. Bohunovsky, O. Proceedings of Metal Bulletin's F i r s t International Ferro-alloys Conference, Oct. 9-11, 1977, Zurich; Metal Bulletin Ltd, London, 1978, p. 86-89. 14. Industrial Minerals, 3/1979, (138),

36-37.

15. Private Communication with Santoku Metal Corporation. 16. Hultgren, R.; Desai, P. D.; Hawkins, D. T.; Gleiser M.; Kelley, K. K.; Wagman, D. D. "Selected Values of the Thermodynamic Properties of the Elements", American Society for Metals, Metals Park, OH, 1973. 17. Hilty, D. C.; Farley, R. W.; Sims, C. E. "Electric Furnace Steelmaking Vol. I I , Theory and Fundamentals" Iron & Steel Div. of AIME, 1967, p. 45.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

RARE EARTH ELEMENTS

76

18. Luyckx, L. "Mechanisms of Rare Earth Action on Steel Structures". American Society for Metals, Materials Science Symposium, Cincinnati, Nov. 1975, Private Publ. by Reactive Metals & Alloys Corp., 9/1976, p. 1. 19. Luyckx, L.; Jackman, J . R. Electric Furnace Conference Proceedings. 1973, 31, 175-181. 20. Luyckx, L.; B e l l , J. R. Trans., 1970, 1, 3341.

McLean, A.; Korchynsky, M. Met.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch003

21. Private Communications with Steel Company of Canada and Molycorp, 1970. 22.

Phelps, H. E. U.S. Patent #2,360,717,

1944.

23.

Overview, Molycorp, No 23, 12/1970, p. 1.

24. McGannon, H. E. "The Making, Shaping and Treating of Steel", United States Steel Corp., Herbick & Held, Pittsburgh, 1970, 9th Ed., p. 24. 25.

Sims, C.E. Trans. Met. Soc. AMIE. 1959, 215, 382-88.

26.

Gschneidner, K. A., J r . ; Kippenhan, N. "Thermochemistry of the Rare Earth Carbides, Nitrides and Sulfides for Steelmaking", IS-RIC-5; Rare Earth Information Center, Iowa State Univ., Ames, IA, 1971.

27. Gschneidner, K. A., Jr.; Kippenhan, N.; McMasters, O. D. "Thermochemistry of the Rare Earths, I Oxides, II Oxysulfides III Compounds with B, Sn, Pb, P, As, Sb, Bi, Cu, and Ag", IS-RIC-6; Rare Earth Information Center, Iowa State Univ., Ames, IA, 1973. 28. Wilson, W. G.; Kay, D. A. R.; Vahed, A. J. Metals, 26, ( 5 ) , 14.

1974,

29. Lu, W. K.; McLean, A. Ironmaking Steelmaking, 1, 1974, 228. 30. Samsonov, G. V. "High-Temperature Compounds of Rare Earth Metals with Non-metals"; 1965, New York, Consultants Bureau, p. 211. 31. Spetzler, E.; Wendorff, J . AIME-NOHC Steelmaking Proceedings, 53, 1975, 358-377. 32.

Sanbongi, K. Transactions ISI Japan. 19, 1979, 1-10. lecture).

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

(Special

3.

LUYCKX

11

Steel

33. Selleck, L. J.; Thompson, G. W.; Croll, J . E.; MacDonald, J . K. AIME-NOHC Steelmaking Proceedings, 61, 1978, 143-153. 34. Farrar, J . C. M.; Dolby, R. E. "Sulfide Inclusions i n Steel", American Society for Metals, Metals Park, OH, 1975, p. 252268. 35. Jackman, J . R. U.S. Patents #4,022,444 and #4,060,407, 1977. 36. Bennett, H. W. 31, 1973, 167.

Sandell, L. P., J r . Electric Furnace Proc.,

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37. Bingel C. J.; Scott, L. V. Electric Furnace Proc., 31, 1973, 171-174. 38. Torsell, K.; Olette, M. Rev. Met., 6 6 , 1969. 39. Luyckx, L. "Ladle Treatment of Carbon Steel", McMaster Symposium, McMaster Univ., Hamilton, Ontario, 5/1979, p. 12-1 to 13. 40. Emi, T.; Haida, O.; Sakuraya, T.; Sanbongi, K. AIME-NOH-BOSC Proceedings, 6 1 , 1978, 574-584. 41. Nakai, Y.; Kurahashi, H.; Emi, T.; Haida, O. Transactions ISI Japan, 19, 1979, 401-410. 42. Scott, W. W., J r . ; Swift, R. A. AIME-NOH-BOSC Proc., 61, 1978, 128-132. 43. Tivelius, B.; Sohlgren, T. "Ladle Treatment of Carbon Steel", McMaster Symposium, McMaster Univ., Hamilton, Ont., 5/1979, p. 3-16. 44. Mihelich, J . L.; Cryderman, R. L. "Low-Carbon Mn-Mo-Cb Steel for Gas Transmission Pipe"; ASME publication, Petroleum Mech. Eng. & Pressure Vessels & Piping Conf., New Orleans, 9/1972, p. 1-11. 45. Parrini, C.; DeVito, A. "High Strength Microalloyed Pipe Steels Resistant to Hydrogen-Induced Failures", Presented at Micon '78 Conf., Houston, Texas, April 3 - 5 , 1978, Private Publ. by Italsider, Taranto, Italy, also, ASTM book STP 672, Baltimore, 7/1979, p. 6 2 . 46. Ohki, T.; Tanimura, M.; Kinoshita, K.; Tenmyo, G. "Effect of Inclusions on Sulfide Stress Cracking", 1/1977, Private Publ. by Nippon Kokan Kabushiki Kaisha Technical Research Center, Japan.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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ELEMENTS

47. Kortovich, C. S. "Inhibition of Hydrogen Embrittlement i n High Strength Steel"; Technical Report #ER-7814-2, Prepared by TRW, Equipment Mat. Tech. for the Office of Naval Research, Contract #N00014-74-0365, 2/1977. 48. Post, C. B.; Schoffstall, D. G.; Beaver, H. O. J . Metals, 3, 1951, 973.

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49. Hessenbruch, W. "Metalle und Legierungen fur Hohe Temperaturen"; Julius Springer, Berlin, 1940. The influence of minor elements on the heat resistance of standard alloys. 50. Bailey, R. E.; Shiring, R. R.; Anderson, R. J . "Superalloys: Metallurgy and Manufacture", 3rd Internet. Sympos., Seven Springs, PA, 9/1977, p. 109. 51. Berry, C. D.; Dorvel, A. A. American Foundryman, 20, 1951, 45.

(12),

52. Langenberg, F. C.; Chipman, J . Trans. Met. Soc. AIME, 212, 1958, 290-93. 5 3 . Hirschhorn, I. S. "The Industrial Status of Mischmetal" Proceedings, 11th Rare Earth Conf., Traverse City, MI, 10/1974, p. 754-763. 54. Leclerc, J.; Beernaert, C.; Bouchon, J. Can. Met. Quart., 12, ( 2 ) , 1973, 201. 55. DuMont, T. C. Iron Age. ( 3 ) ,

1974.

56. Luyckx, L. "Sulfide Inclusions i n Steel", American Society for Metals, Metals Park, OH, 1975, p. 4 4 - 6 9 . 57. "Bethlehem Develops New Sheet to Provide Better Formability", American Metal Market, Sept. 12, 1980. 58. Electric Furnace Proceedings, 1955, A75. RECEIVED February 18,

1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

4 The Use of Rare Earths in Glass Compositions L. W. RIKER

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Schott Optical Glass Incorporated, Duryea, PA 18642

The use of rare earth oxides by glassmakers is relatively new when we consider that glass has been produced for over 4,000 years. Modern glass technology started about 1880 when Otto Schott in Jena, Germany made systematic studies of the affects of various oxides on the mechanical and optical properties of glass. He studied cerium oxide as a constituent in glass but did not put it to any practical use. (1) Winkleman and Straubel studied rare earth fluorescence at this time. In 1896, Drossbach patented and manufactured a mixture of rare earth oxides for decolorizing glass. This was the f i r s t commercial use of cerium. It was in a crude form with other rare earth oxides including neodymium. In 1912, Crookes of England made systematic studies on eye protective glasses and found cerium excellent for ultra violet absorption without giving color. The f i r s t use of lanthanum in optical glasses was in 1935 by Morey. (2) The most rapid growth of the use of rare earth oxides has taken place since World War II. New technology glasses have been developed requiring the use of purer materials. These have been successfully obtained through more advanced separation techniques by the rare earth manufacturers with purities up to 99.999%. Cerium has increased in use as a s t a b i l i z e r against browning of glass by cathode ray and gamma rays. Most cathode ray tube faceplates use cerium stabilized glass. The nuclear industry has required large quantities of radiation shielding windows which provide very high light transmission without darkening due to formation of color centers. Much of the development work to understand the mechanism of browning by gamma radiations was done during the 1950's and early 1960's in conjunction with the work on use of nuclear energy. New developments have been made in the photographic and optical f i e l d with the design of more sophisticated lenses. The lanthanum optical glasses with a high index of refraction and low dispersion have been an outgrowth of the post war period. Another growth area is the glass container industry. Cerium is used here to decolorize glass and to stabilize against solarization caused by U. V. rays. 0097-6156/81/0164-0081 $05.00/0 © 1981 American Chemical Society In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Neodymium oxide, which i s used as a coloring oxide in hand crafted glass, i s also used in doping laser glasses which i s another growing f i e l d . There are approximately 350 tons of rare earth oxides used yearly for glass making. Cerium concentrate makes up the biggest share of the market. This is i n the form of a mixed rare earth material containing about 88% Ce02/Total REO and the balance i s made up of La203, Pr60"|-|, and Nd203- The ratios will vary with the supplier and raw material source. Lanthanum oxide has the next largest market followed by 95% to 99.9% purity cerium oxide, neodymium oxide and small amounts of praeseodymium and erbium oxides. Glass is a unique material, appearing as a solid although often referred to as a super cooled l i q u i d . There have been many definitions of glass by dictionaries, encyclopedias, scientists, and government agencies. From a technical standpoint, one can define i t as "an inorganic product of fusion which has been cooled to a r i g i d condition without c r y s t a l l i z a t i o n . " ^ ) The most common commercial glasses are called soda-lime glasses. They are made from s i l i c a which i s the glass or network former. The melting temperature of the s i l i c a i s reduced by the addition of soda and potash which are fluxing agents. To promote chemical durability and stabilize the viscosity, lime, magnesia, and alumina are added. The glass must be refined to remove gaseous inclusions. This i s done chemically by the addition of sodium nitrate and sulfate, arsenic oxide and antimony oxide. The soda-lime glasses are used for plate and window glass, containers, light bulbs and ophthalmic lenses. There are many other families of glasses including leada l k a l i - s i l i c a t e s , borosil icate, barium-borosilicates and aluminosilicate glasses. In addition, there is the broad range of various optical and other technical glasses using a variety of glassmaking raw materials. Of the important properties of glass, color is one of the most interesting. Color is usually achieved by the addition of various metal oxides. The strongest of these are titanium, vanadium, chromium, manganese, selenium, iron, cobalt, nickel and copper. Silver and uranium will give weak colors. Some of the rare earths are also used as colorants with sharp absorption bands in contrast to the broad bands given by most colorants. (4) Color can be a desired property when purposely making a colored glass or i t can be detrimental such as iron and chrome impurities when making a high transmission optical glass. Since iron is a common impurity in many glass making raw materials i t must be removed during the material processing. Otherwise, i t will contribute a yellow-green color to the glass. To offset this problem, several materials act as decolorizers which lighten the color of the iron or neutralize i t . This will be discussed later along with the function of rare earth oxides in achieving decolorization.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Having briefly reviewed glass as a material and some of i t s properties, we should look at specific properties where rare earth oxides are used.

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The Coloring Effects of Rare Earth Oxides When transparent glasses absorb portions of the visible spectrum from 400 to 700nm, they will appear colored. The color is determined by the transmitted portion of the visible spectrum after subtracting certain wavelengths by absorption from the illuminating source. The rare earth oxides have absorption spectra consisting of a large number of relatively narrow bands through both the visible and invisible parts of the spectrum. It is interesting that there is l i t t l e change in the characteristic absorption spectra of rare earth oxides in various compounds, solutions and glasses. The colors in rare earth glasses are caused by the ion being dissolved and they behave uniquely because the 4 f electrons are deeply buried. Their colors depend on transitions taking place in an inner electronic shell while in other elements such as the transition metals, the chemical forces are restricted to deformation and exchanges of electrons within the outer s h e l l . Since the rare earth's sharp absorption spectra are insensitive to glass composition and oxidation-reduction conditions, i t is easy to produce and maintain definite colors in the glass making process. (5J Rare earth oxides used for coloring glass are neodymium, praeseodymium, and erbium. Cerium is only used in conjunction with other coloring oxides. Neodymium is the most commonly used oxide for coloring glass and gives a delicate pink t i n t with violet reflections. The hue of the color varies with glass thickness and concentration of neodymium and also the source of illumination. It goes from a light pink in thin sections to a beautiful blue-violet in thicker pieces. This characteristic is called dichroism. It is primarily used in art glasses in concentrations of 1% to 5% and for special f i l t e r s . Neodymium welding glasses are used by lamp workers and welders to protect their eyes from the yellow flare emitted by sodium vaporized from hot glass or fluxes. This is due to the narrow absorption peak of neodymium between 589 and 590 nm where sodium atoms emit their characteristic yellow l i g h t . A typical transmittance curve of a neodymium containing glass is shown in Figure 1. Praeseodymium is the next strongest rare earth oxide, giving a green color very similar to the eye as chromium containing glasses. Since the cost of praeseodymium is high compared to chrome oxide i t is not used to any extent except in special f i l t e r glasses, and in combination with neodymium in didymium welding glasses. See Figures 2 and 3.

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Figure 1.

Transmittance curve of a glass containing NdgOs

300

Figure 2.

400

500

600

700 Wavelengthfnrn)

Transmittance curve of a glass containing

400

500

600

700

Pr O 6

n

Wavength (nm)

Figure 3. Transmittance curve of a glass containing a mixture of Pr O 6

n

and Nd O

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

2

s

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Originally due to the d i f f i c u l t y in separating the various oxides, so called didymium oxides were used for glasses such as these special welding glasses and Crookes absorptive sun glasses. They contained the natural ratios of neodymium and praeseodymium along with the high amounts of cerium which gave a good U. V. cut-off. Most of the other rare earth oxides were present along with some thorium oxide. This made an inexpensive rare earth coloring material but was not always reproducable. Today for example, a lanthanum rare earth oxide can be used and by knowing the ratios of the neodymium and praeseodymium to the cerium and lanthanum, corrections can be made with 95% purity oxides to get the desired absorption characteristics. Erbium oxide gives a pale pink to the glass which cannot be obtained by any other means. As seen in Figure 4, i t has only one absorption peak in the v i s i b l e range. It is expensive and is used on a limited basis in photochromic glasses and some crystal glasses. Erbium is stable compared to CdS, copper, selenium and gold which require controlled redox and/or striking conditions to produce a red or pink color. (5J Figure 5 shows the absorption band of cerium as being very weak in soda-lime glasses in the blue and violet regions. When used in large concentrations i t gives a weak yellow color, and in combination with titania i t produces an attractive yellow color. This is often used in table ware but requires up to 3% of each oxide to produce a satisfactory color. In order to intensify the color, the cerium concentration is kept constant and the titania increased. {6_) In ophthalmic glass production, the cerium-titania complex is combined with manganese to produce the pink U. V. absorptive tinted glasses. The manganese which normally gives a purple color is toned down with the yellow color giving a yellowish pink. In addition, the cerium absorption in the U. V. is an important property of the glass. Discoloration of Glass by Radiation Cerium plays an important part in stabilizing glass against solarization and browning due to irradiation. In the case of solarization, the glass discolors due to absorption of ultra violet rays from sun light. In the case of browning, the source is from higher energy radiations. Solarization is a photochemical reaction which leads to a change in color in glass. It is the result of long term exposure to the ultra violet radiation from sunlight. When certain multivalent ions or combinations of ions are present, their valence can be changed by the ionizing radiation. For example, i f manganese in a two valent form absorbs a photon from the U. V. portion of the spectrum, i t changes to a three valent form plus an electron which becomes trapped in the glass structure, usually by ferric iron in a commercial glass.

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350

Figure 4.

i

300

Figure 5.

400 450 500 550 600 650 700 Wavelength (nm)

Transmittance curve of a glass containing

i.

1

400

i

500

i

Er 0 2

3

i

600 700 Wavelength (nm)

Transmittance curve of a glass containing Ce0

2

and Ce0

2

and

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Ti0

2

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The f e r r i c iron i s then changed to ferrous iron and with the oxidized manganese forms a purple color. This i s characteristic of bottles which have been subjected to the sun's rays for a period of time. The manganese i s added i n i t i a l l y to the glass as a decolorizer to offset the yellow color of the iron. (7j Other ions, especially arsenic in combination with iron, enhance the color from solarization. This i s especially c r i t i c a l in window glass where the glass i s clear and solarizes to a yellow-brown. It has been found that more than 0.005% cerium oxide in combination with arsenic will cause this yellowing effect with the strongest color being at 2.5% cerium. Higher cerium contents tend to reduce solarization by f i l t e r i n g off the actinic radiation. (1_) By removing the arsenic completely, small amounts of cerium can be added as an oxidizing agent f o r decolorizing glass and will aid in stabilizing against solarization. (8) Browning is another type of discoloration caused by x-rays, gamma rays and cathode rays. Cerium oxide i s an important ingredient in specialty glasses to reduce this browning characteristic. Ceric ions act as electron traps in the glass and absorb electrons liberated by these high energy radiations which keep the color centers from forming. Cerous ions are formed which have l i t t l e visible color and protect the glass from discoloration by high energy and nuclear radiations. Some of the uses of these nonbrowning glasses are in radiation shielding windows, television and other cathode ray faceplates. (3^ 7\ 9J The radiation shielding windows are made from high density lead glasses. They are used as viewing windows placed in thick lead and concrete walls for nuclear and radiochemical laboratories. In addition, cerium stabilized borosilicate cover plates are used on the hot side. Since the unstabilized glasses will darken from a radiation source such as cobalt - 60, the transmission of the windows decreases making them d i f f i c u l t for viewing. The intensity of the darkening effect i s a function of the energy of ionizing radiation, the intensity of radiation and the radiation dose. The darkening effect i s not stable and will fade slightly after exposure. Since these windows can be in excess of a meter thick, maximum transmission i s a necessity. Figure 6 illustrates the results on transmission of a 3.23 density lead glass stabilized with 1.5% Ce02 subjected to various radiation doses compared to a similar glass that is not stabilized. To produce the required nonbrowning s t a b i l i t y , cerium oxide is used in various amounts up to 2.5%. In the high lead glasses containing over 60% PbO, cerium additions make the glass amber prior to irradiation and reduce the overall transmission. These glasses are naturally resistant to coloration by irradiation and any color that develops, fades quickly. Therefore, cerium stabilization is usually used only on the lower density glasses. The stabilized glasses are normally used toward the hot side with the denser glasses used on the cold

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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350 400

500

600

700

800

900 1000

w a v e l e n g t h in n m

Figure 6.

The effect of various irradiation levels on (solid curves) Ce-stabilized and (curve labeled RS-323) nonstabilized lead glass

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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side of the window. A typical window cross section i s shown in Figure 7 u t i l i z i n g cerium stabilized 2.53 density borosilicate glass on the hot side with 3.23 density stabilized, and 5.2 and 2.53 density unstabilized toward the cold side.

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Decolorizing of Glass Iron oxide i s always present as an impurity in glass. It is introduced through the natural raw materials such as sand and limestone. Another source i s from trap iron mixed in the cullet and abraded metal from the handling of batch. All of this adds up to several hundred parts per million which causes light absorption at the ends of the spectrum rather than the middle and causes a yellow-green color in the glass. This can be overcome by a process known as decolorization. There are two types: chemical and physical decolorizing. [6) To chemically decolorize a glass, oxidizing materials are added to change the iron from the ferrous to the f e r r i c state. This shifts the maximum light transmission towards the yellow by absorbing more in the blue. Several of the more popular materials have been arsenic and manganese. In recent years, cerium has been substituted for these materials. An advantage of cerium is solarization does not occur as long as arsenic i s not present. Also, when the cerium i s used in conjunction with selenium and cobalt, the addition of 2-3 ounces per ton of batch can give a reduction in the usage of these two materials. (8) Physical decolorizing is accomplished by making the color of f e r r i c iron in the glass with complimentary colors. This makes the transmittance across the spectrum f a i r l y constant giving a neutral color. Physical decolorizing reduces part of the transmittance of the glass in getting r i d of the green color. A true colorless glass such as an optical glass must be made with very low iron materials since decolorizing agents would reduce the transmission. The main physical decolorizers are manganese, selenium, cobalt and neodymium oxides. Manganese with a l i t t l e cobalt i s effective in complimenting the iron in the f e r r i c state. Selenium i s one of the better decolorizers in tank melting. The iron i s neutralized by the pink t i n t of the selenium. Since a yellow shade i s s t i l l present, the decolorizing i s completed with the addition of a small amount of cobalt. Arsenic helps to stabilize the decolorizing with selenium but as the arsenic content increases more selenium i s required. The third oxide used for physical decolorizing i s neodymium oxide. Its absorption curve closely compliments an average mixture of ferrous and f e r r i c oxides especially with the strong absorption band at 589 nm. Neodymium oxide i s also stable against any state of oxidation change in the furnace. Neodymium i s exceptionally good as a decolorizer for potassium s i l i c a t e and lead glasses. If the redox balance i s not quite correct for the

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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vertical section

horizontal section

Figure 7. Radiation shielding window showing Ce-stabilized borosilicate glass cover plates (RS 253 G 18) on the hot side, stabilized lead glass (RS 323 G 15), nonstabilized high density lead glass (RS 520) and borosilicate glass cover plate

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iron, corrections can be made using small amounts of manganese oxide, nickel oxide, selenium or erbium oxide. It must be remembered that the quantities of rare earth materials being used for decolorizing are quite small per batch. The use of 25 grams of neodymium per 100 kg of sand is a l l that is required. To reduce the cost of cerium, i t can be introduced as a cerium concentrate containing 60% Ce02 which is a relatively inexpensive form.

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Optical

Glass

Up to this time, we have been discussing the influence of rare earth elements on the color and transmission characteristics of glass. The use of rare earths in optical glass is different since they must not give any absorption in the v i s i b l e range and are often used as major ingredients up to 40% of the batch. This compares with fractions of a per cent added for use as a decdlorizer and coloring oxides up to 5%. The properties of optical glasses differ substantially from other glasses. These glasses are used for optical lenses and elements to function in a wide variety of systems. Optical glasses are c l a s s i f i e d by their index of refraction and Abbenumber or reciprocal of i t s dispersive power. They must also meet special quality requirements such as a high degree of transparency or light transmission and be reasonably free of bubbles and solid inclusions. The glass must be homogenous and free of striations and be annealed to reduce internal stresses to a minimum. Optical glasses are c l a s s i f i e d by various families determined by their chemical compositions. Originally, there were two types; crown glass which is a soda-lime-silicate and f l i n t glass which is a l e a d - a l k a l i - s i l i c a t e . The addition of other oxides such as boron, barium, zinc and lanthanum have created new families designated as borosilicate crowns, zinc crowns, barium crowns, barium f l i n t s , and lanthanum crowns and f l i n t s . Each one of these glasses has i t s own characteristic optical properties as can be seen by the map of optical glasses in Figure 8. The raw materials going into an optical glass differ greatly in purity levels compared to other commercial glasses. Due to the high degree of light transmission required, i t is necessary that the chemical purity of the materials used be extremely high. For example, a normal s i l i c a sand used in glass may have iron oxide in purity levels around 300 ppm or more while in optical glass i t is in the range of 10 to 50 ppm or lower. Impurities from any of the transition metal oxides such as chrome, cobalt and nickel which could add color to the glass, must be limited to under 1 ppm. The rare earth materials must go a step further and be introduced as a 99.9% to 99.995% rare earth oxide purity. It is absolutely essential that no color occurs from the absorption

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Figure

£

to

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Compositions

93

bands of neodymium and praeseodymium. Traces of cerium must be eliminated to minimize U. V. absorption. It is due to these stringent requirements on raw material purity along with the type of glass making oxides used that optical glasses in general are rather expensive compared to other commercial glasses. The primary rare earth material used is lanthanum oxide. Another material, thorium oxide, although not a rare earth oxide but an element extracted from monazite sand, has been used along with lanthanum as a major ingredient. Since thorium i s a radioactive material, i t is no longer being used and new glasses have been developed to replace the thorium based glasses. Other rare earth oxides used in very small amounts are gadolinium, ytterbium, and another related element, yttrium. Lanthanum oxide is added primarily to obtain a high index of refraction and high Abbe-number. The result is a low dispersion glass. Looking at the optical map, i t can be seen that the highest index of refraction glasses are usually extra dense f l i n t s due to the high lead oxide content. These glasses have a low Abbe-number. The borosilicates have a low index of refraction and high Abbe-number. Barium crowns result in a high Abbe-number but an intermediate index. The lanthanum glasses were not developed until after 1935 and much of the experimentation on improvement of chemical durability and crystallization characteristics was performed during the 1950 s. These glasses have played a big part in overall improvements in many optical systems such as the modern camera. Lanthanum glasses are usually low s i l i c a and consist substantially of boric acid, zirconia, barium oxide and lanthanum with various other additives to help stabilize the viscosity and liquidus or crystallization temperature. (2, 10) ,

Fluorescence Fluorescence in glass is the result of atoms being excited by the absorption of light resulting in light emission. This is a phenomenum normally associated with certain minerals and other crystalline materials when subjected to ultra violet l i g h t . Most rare earth ions when added to glass exhibit fluorescence. (1_, 5j Practical application of the fluorescence of glass i s limited. With the development of the optical laser in 1960, neodymium doped glasses became important in the operation of high powered lasers. Neodymium glass lasers emitting at 1060 nm have received the greatest attention because they can operate at room temperature with relatively high efficiencies. Of importance as glass hosts are alkali-alkaline-earth-silicates and recently the fluoro-phosphates which help contribute to high efficiency. The neodymium oxide used in these glasses is at least 99.9% purity and gives a purple colored glass. E. Snitzer's paper on "Lasers and Glass Technology" gives a comprehensive review of this subject, ( r y

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Summary A historical review of the uses of rare earths in glass indicates that as new technology develops, the use of rare earths increase in glassmaking. The use of cerium oxide in stabilizing high energy radiation effects on glass, lanthanum oxide for new optical glasses and neodymium doped laser glass are a l l products of technology developed in the past 30 years. The classical uses of rare earths for coloring and decolorizing glass continue to grow. Literature Cited

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1. Weyl, W. A. "Coloured Glasses"; Dawson's Pall Mall: London, England, 1959; pp. 218-234, 439-514. 2. Tooley, F. V. Ed. "Handbook of Glass Manufacturing"; Books for Industry: New York, 1974; Chapt. 18. 3. Shand, E. B. "Glass Engineering Handbook"; McGraw-Hill Book Company Inc.: New York, 1958; pp. 3-9, 81-88. 4. Morey, G. W. "The Properties of Glass"; Reinhold Publishing Corporation: New York, 1938; pp. 435-436. 5. Herring, A. P . ; Dean, R. W.; Drobnick, J. L. "The Use of Rare Earth Oxides to Give Color or Visible Fluorescence to SodaLime Glasses"; presented at Am. Ceramic Society 70th Annual Meeting, Chicago, Ill., April 28, 1968. Reprints available from Molybdenum Corporation of America. 6. Scholes, S. R. "Modern Lass Practice"; Seventh Revised Edition, Rev. by C. H. Greene; Cahners Publishing Company: Boston, 1975; pp. 307-315. 7. Harding, F. L. "Introduction to Glass Science"; L. D. Pye, H. J. Stevens and W. C. LaCourse, Eds.; Plenum Press: New York, 1972; pp. 417-423. 8. Schutt, T. C.; Barlow, G. "Practical Aspects of Cerium Decolorization of Glass"; Amer. Ceram. Soc. B u l l . , 1972, 51, (2), 155-157. 9. Kreidl, N. J.; Hensler, J. R. "Formation of Color Centers in Glasses Exposed to Gamma Radiation"; J. Amer. Ceram. Soc., 1955, 38, (12), 423-432. 10. Kutzchmann, R. "Influence of L a 0 and Th0 on the Crystalline Behavior of Optical Glasses"; Glass Tech., 1965, 6, (5), 156-160. 11. Snitzer, E. "Lasers and Glass Technology"; J. Amer. Ceram. S o c , 1973, 52, (6), 516-525. 2

RECEIVED March 3,

3

2

1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

5 Rare Earth Polishing Compounds ROBERT V. HORRIGAN

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch005

8416 West Country Club Drive, North, Sarasota, F L 33580

There is little i n f o r m a t i o n in t h e literature r e g a r d i n g t h e first a p p l i c a t i o n s of cerium oxide o r c e r i u m - r i c h r a r e e a r t h oxide mixtures in g l a s s polishing, Duncan (1) mentions t h a t the application began in the European g l a s s i n d u s t r y about 1933, spreading to the Canadian optical i n d u s t r y about 1940. During World War II, an employee o f German-American descent working f o r the W. F. & J . Barnes Co. o f Rockford, Illinois, i n t r o d u c e d on August 31, 1943 a r a r e - e a r t h oxide (45% Ce0 ) polish c a l l e d B a r n e s i t e which enjoyed immediate success in the p o l i s h i n g of precision o p t i c s such as bombsights, range f i n d e r s , p e r i s c o p e s , and other fire c o n t r o l instruments. The Lindsay Chemical Co. o f West Chicago, Ill., e a r l y in World War II, i n t r o d u c e d a h i g h cerium oxide (90+% Ce0 ) polish c a l l e d Cerox f o r ophthalmic use. Other more s p e c i a l i z e d cerium-based products were added, a few competitors entered t h e field, and by 1960 more than 340 m e t r i c tons per year were being used f o r p o l i s h i n g m i r r o r s , p l a t e g l a s s , television tubes, opht h a l m i c lenses and precision o p t i c s . The advent o f the P i l k i n g t o n process, 1972-1973, f o r l a r g e s c a l e p l a t e g l a s s manufacture sev e r e l y reduced the market f o r cerium o x i d e , but still today over 1000 m e t r i c tons per year are s o l d in the U.S. From 1940 t o 1965, the p r i n c i p a l source of these r a r e e a r t h products was the m i n e r a l monazite (Th, RE orthophosphate) which f o r t u n a t e l y o r u n f o r t u n a t e l y , depending on one's p o i n t o f view, c o n t a i n s 4-6% thorium. Today, there i s e s s e n t i a l l y no market f o r thorium i n the U.S. The expense o f s e p a r a t i n g out thorium-free r a r e - e a r t h products from monazite i s not only e x c e s s i v e , but bound t i g h t l y i n governmental red tape because of the m i l d r a d i o a c t i v i t y of the thorium. This s i t u a t i o n does not apply i n France, B r a z i l , or I n d i a , whose governments are w i s e l y s t o c k p i l i n g a l l e x t r a c t e d thorium f o r f u t u r e atomic energy needs. L u c k i l y , the U.S. has the l a r g e s t b a s t n a s i t e (R.E. f l u o c a r bonate) mine i n the world l o c a t e d a t Mountain Pass, C a l i f o r n i a , owned and operated by Molycorp, I n c . , a s u b s i d i a r y o f Union O i l 2

2

0097-6156/81/0164-0095$05.00/0 © 1981 American Chemical Society In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

96

RARE EARTH ELEMENTS

Co. of C a l i f o r n i a . Proven orebody reserves at the end of December 1978 were 365,000 m e t r i c tons, w i t h i n d i c a t e d r e s e r v e s of over 3 m i l l i o n m e t r i c tons of r a r e e a r t h oxide (REO). Current mine prod u c t i o n c a p a c i t y i s 27,000 m e t r i c tons per year of b a s t n a e s i t e concentrate produced i n 3 grades: a 60% REO unleached concentrate, a 70% REO leached concentrate (SrO and CaO removed), and a 90% REO c a l c i n e d concentrate (CO2 removed). I n 1977, shipments t o t a l e d 13,521 m e t r i c tons of contained REO. P o l i s h i n g compounds consumed approximately 10% of t h i s p r o d u c t i o n . With s u i t a b l e chemical, mechanical and heat treatment, g l a s s p o l i s h i n g compounds of h i g h q u a l i t y have been produced from b a s t n a e s i t e concentrates s i n c e 1965.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch005

The S c i e n t i f i c B a s i s f o r the Uses A b r i e f d e s c r i p t i o n of g l a s s s u r f a c i n g techniques w i l l be u s e f u l p r i o r to our d i s c u s s i o n of the three p r i n c i p a l t h e o r i e s of the p o l i s h i n g mechanism. I n the ophthalmic f a c t o r y or p r e s c r i p t i o n l a b o r a t o r y , an o p t i c a l glass blank i s f i r m l y fastened to a lens chuck, which i s then pressed down on a curved g r i n d i n g t o o l and r o t a t e d at h i g h speed. To achieve the d e s i r e d l e n s c u r v a t u r e , one or two stages of diamond g r i n d i n g (generation) s u f f i c e . A l t e r n a t e l y one diamond generating step f o l l o w e d by g r i n d i n g (or f i n i n g ) w i t h l o o s e powdered a b r a s i v e s (such as corundum, emery, garnet, or s i l i c o n carbide) suspended i n a water s l u r r y may be employed. This i s rough treatment, and we may w e l l expect to f i n d some subsurface damage which h o p e f u l l y can be r e p a i r e d during the p o l i s h i n g step. The " f i n e d " l e n s , s t i l l attached to the l e n s chuck, i s r i n s e d f r e e of any adhering a b r a s i v e , and placed i n a p o l i s h e r . Here the t o o l contacted by the l e n s i s c a l l e d the " l a p " and may c o n s i s t of a wide v a r i e t y of m a t e r i a l s depending on the g o a l to be achieved. In the ophthalmic f a c t o r y , f o r example, t h i c k , hard t h e r m o p l a s t i c pads have good s u r f a c e q u a l i t y , curve c o n t r o l , long l i f e , and the a b i l i t y to operate w e l l under h i g h speeds and p r e s s u r e s . On the other hand, the p r e s c r i p t i o n l a b o r a t o r y w i l l f a v o r a p a p e r - t h i n p l a s t i c or c l o t h pad which i s used o n l y once. The p o l i s h i n g compound, u s u a l l y e e r i e o x i d e , z i r c o n i u m o x i d e , f e r r i c oxide ( j e w e l er's rouge), or s i l i c a (white rouge) i s s l u r r i e d i n water i n a c o n c e n t r a t i o n of 5-25% by weight, and i s r e c i r c u l a t e d c o n s t a n t l y over the l a p and l e n s . I n the f a c t o r y , l a r g e c e n t r a l systems c o l l e c t the p o l i s h i n g s l u r r y and pumps f u r n i s h the s l u r r y to the p o l i s h i n g bowls c o n s t a n t l y . The lens weight l o s s , w h i l e not g r e a t , i s r e a d i l y measured, and g l a s s removal r a t e i s of prime importance i n measuring the e f f i c i e n c y of a p o l i s h i n g compound. In our view, the p o l i s h i n g s l u r r y would have an i n d e f i n i t e l i f e were i t not f o r the f a c t t h a t the g l a s s products g r a d u a l l y d i l u t e and contaminate the s l u r r y . The b u i l d - u p of a l k a l i ions i s so g r e a t , t h a t d a i l y pH adjustments are necessary i n l a r g e c e n t r a l system s l u r r y tanks.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

5.

HORRIGAN

Polishing

97

Compounds

Over three hundred years ago Isaac Newton concluded t h a t p o l i s h i n g was nothing more than f i n e - s c a l e a b r a s i o n , E a r l y i n the t w e n t i e t h century, Lord R a y l e i g h found t h a t a p o l i s h e d s u r f a c e was e n t i r e l y d i f f e r e n t from a ground, or abraded s u r f a c e , and suggests ed t h a t the p o l i s h e d s u r f a c e was smooth on a molecular s c a l e , l i k e the s u r f a c e of water. L a t e r the B r i t i s h chemist, S i r George B e i l b y , a p p l y i n g chemical etchants to a p o l i s h e d s u r f a c e , found o r i g i n a l g r i n d i n g scratches to reappear. He concluded t h a t a molecular f l o w of m a t e r i a l (the " B e i l b y Layer") from h i g h to low spots took p l a c e , thus covering the s c r a t c h e s , (2, 5) Bowden and Hughes (2) at the U n i v e r s i t y of Cambridge i n the 1930 s r e a soned t h a t i f a b r a s i o n were the fundamental mechanism, then the hardness of the p o l i s h i n g m a t e r i a l should c o r r e l a t e w i t h a b i l i t y to p o l i s h ; they found t h i s not to be the case, but d i d f i n d a remarkable c o r r e l a t i o n between the m e l t i n g p o i n t of the p o l i s h i n g m a t e r i a l and the r a t e of p o l i s h . They concluded t h a t p o l i s h i n g was a m e l t i n g phenomenon, not a b r a s i o n . Let us t e s t t h e i r hypotheses a g a i n s t the m e l t i n g p o i n t s of known good p o l i s h i n g o x i d e s : ZrOo, 3000°C; Ce0 , 1950°Cj S i 0 1700°C; F e 0 , 1565°C; S n 0 , 1127*C. Except f o r s t a n n i c o x i d e , these high m e l t i n g p o i n t v a l u e s support the m e l t i n g hypothesis of Bowden and Hughes. Here the matter r e s t e d f o r twenty years or so, a b r a s i o n or m e l t i n g , take your p i c k , and each s i d e had i t s adherents. But now a t h i r d hypothesis was proposed and g r a d u a l l y took precedence over the f i r s t two. I n 1931 Grebenschikov (3) noted t h a t the presence or absence of water i n f l u e n c e d the p o l i s h i n g of g l a s s , and suggested that a l a y e r of s i l i c i c a c i d would b u i l d up on the s u r f a c e of the g l a s s being p o l i s h e d . This l a y e r would p r o t e c t the g l a s s from f u r t h e r e r o s i o n were i t not f o r the f a c t t h a t the p o l i s h i n g agent was at work to sweep away t h i s l a y e r and expose a f r e s h surface. Further work by C o r n i s h and Watt (4) and S i l v e r n a i l and Goetz i n g e r (5) e s t a b l i s h e d the a c t i v e r o l e played by the presence of water, and these authors concluded t h a t a chemical-mechanical hypothesis would f i t the observed data. I n the case of e e r i e oxide p o l i s h i n g of g l a s s , Cornish and Watt suggest the formation of a "CeO-Si" a c t i v a t e d complex which permits the r u p t u r e of the O-Si-0 bonds by h y d r o l y s i s . The complex "CeO-Si" then breaks a p a r t , the hydrated s i l i c a i s swept away along w i t h a l k a l i s r e leased from the g l a s s s u r f a c e , and the process r e p e a t s . The above i s a good example of Ce0 a c t i n g l i k e a c a t a l y s t . The author would l i k e to suggest another p o s s i b i l i t y which may add to the chemical theory. The e f f i c i e n t p o l i s h i n g compounds p r e v i o u s l y mentioned have not only high m e l t i n g p o i n t s , but a l s o have l a r g e u n s a t i s f i e d c o o r d i n a t e v a l e n c i e s . T y p i c a l l y , f o r example, the z i r c o n i u m atom w i l l a t t r a c t a cloud of h y d r o x y l r a d i c a l s to s a t i s f y i t s c o o r d i n a t e v a l e n c e s . Thus, a h i g h concentrat i o n of h y d r o x y l r a d i c a l s are r e a d i l y a v a i l a b l e at the g l a s s s u r f a c e to speed the h y d r o l y s i s r e a c t i o n .

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch005

f

2

2

3

2

2

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

2 >

98

RARE EARTH ELEMENTS

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch005

The f r e e world market f o r cerium-oxide based p o l i s h i n g compounds i s not l a r g e — a p p r o x i m a t e l y 4400 m e t r i c tons per y e a r — , and we do not see a s u b s t a n t i a l growth p o t e n t i a l d e s p i t e the 11% annual growth i n s a l e s of s p e c t a c l e l e n s e s . The reason i s twof o l d : f i r s t , f a s t e r more e f f i c i e n t p o l i s h i n g compounds a r e a v a i l a b l e which can be used i n s l u r r y c o n c e n t r a t i o n s one-half t h a t of a few years ago; second, f u l l y h a l f the market f o r ophthalmic g l a s s lenses has been captured by p l a s t i c lenses of CR-39 polymer. Cerium oxide i s i n e f f e c t i v e i n p o l i s h i n g t h i s m a t e r i a l ; s p e c i a l l y t r e a t e d alumina or s t a n n i c o x i d e a r e used. Table I shows our estimate of 1979 cerium-oxide based p o l i s h ing product consumption. TABLE I . CONSUMPTION OF CERIUM-OXIDE BASED POLISHING COMPOUNDS (1979) a COUNTRY

CONSUMPTION (METRIC TONS/YR.)

United S t a t e s Canada South America Far East Western Europe

a.

Ce0

2

1,600 200 350 850 1,400 4,400

content v a r i e s from 45-90%.

The estimated end-use p a t t e r n f o r cerium oxide based p o l i s h ing compounds i n the U.S. (1979) i s i l l u s t r a t e d i n Table I I . TABLE I I . ESTIMATED END USE PATTERN IN THE UNITED STATES FOR CERIUM-OXIDE BASED POLISHING COMPOUNDS (1979) a END USE, U.S.

CONSUMPTION PERCENT METRIC TONS

Glass l e n s e s , ophthalmic Glass lenses, p r e c i s i o n Mirrors TV tube f a c e p l a t e s M i s c . - photomasks, gem stones

a.

Ce0

o

720 192 320 240 128 1,600

45 12 20 15 8 100

content v a r i e s from 45-90%.

Competitive Advantage o f the Rare Earths - Competition from Other M a t e r i a l s As our s a l e s f o r c e never t i r e s o f r e p e a t i n g , " I t i s n ' t the cost per pound of cerium o x i d e t h a t m a t t e r s ; what matters i s your

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

5.

HORRIGAN

Polishing

99

Compounds

TABLE I I I . REPRESENTATIVE SPHERE AND TORIC POLISHING MACHINE CHARACTERISTICS, 1930 - 1980

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch005

NORMAL SPINDLE SPEED

TYPICAL SPINDLE FORCE

TYPICAL SPINDLE TIME

MODEL

APPROX. ERA OF ORIGIN

Hand Pan

1930's

300 RPM V a r i a b l e

15 Min.

Robinson- Greyhound Houchin #113

1950's

450 RPM

30 Lbs.

8 Min.

CMV

1CM-10

1970's

Upper=l,200 RPM Lower=l,800 RPM

90 Lbs.

1 Min.

Coburn

608

1970's

2,400 RPM

MANUFACTURER SPHERES Bausch & Lomb

100 Lbs. 3/4 Min.

TORICS Bausch & Lomb (used t o "rock" a t o r r i c ) Hand Pan

1930*s

American O p t i c a l 427

1940 s

Optek

400

1960's

American Optical

Super Twin 1970 s

f

f

Upper= Lower =

300 RPM V a r i a b l e

30 Min.

400 RPM 30 RPM

20 Lbs.

15 Min.

400 CPM*

30 Lbs.

5 Min.

550 CPM*

40 Lbs.

k\ Min.

*Cycles Per Minute.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch005

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cost per thousand p o l i s h e d s u r f a c e s ! " A h i g h q u a l i t y cerium oxide p o l i s h may be p r i c e d at $3.50 per pound; a good q u a l i t y z i r c o n i a based p o l i s h may be $1.50 per pound; red rouge ( f e r r i c oxide) may be p r i c e d at $0.40 per pound; and w h i t e rouge ( p r e c i p i t a t e d s i l i ca) a t perhaps $0.20 per pound. Without g e t t i n g i n t o d e t a i l s , a recent example may c l a r i f y the c o m p e t i t i v e advantage of cerium oxide. One of the l a r g e s t l e n s manufacturers i n America was persuaded to s w i t c h from z i r c o n i a to a h i g h q u a l i t y cerium o x i d e . I n the f i r s t n i n e months a savings of $400,000 was r e a l i z e d by more than h a l v i n g the amount of powder used, s h o r t e n i n g the time r e q u i r e d f o r p o l i s h i n g each l e n s , and i n c r e a s i n g the y i e l d of f i n ished l e n s e s i n the b a r g a i n . Other f a c t o r s are important, too. Z i r c o n i a has a nasty t e n dency to s e t t l e out rock-hard i n tanks and p i p e s , and besides the m a t e r i a l l o s s , clean-up c o s t s are severe. C e r i a w i l l s e t t l e event u a l l y , but always i s s o f t and easy to re-suspend. F e r r i c oxide (red rouge) i s an e x c e l l e n t , but slow p o l i s h , and a bad p o l l u t a n t due to i t s i r r e v e r s i b l e s t a i n i n g q u a l i t y . White rouge i s a very slow p o l i s h , and i s r a r e l y seen i n use today. High p o l i s h i n g speeds are e s s e n t i a l i n todays economy, and the l a t e s t equipment employs much h i g h e r s p i n d l e speeds and p r e s sures than those used j u s t a few years ago. Cerium oxide i s i d e a l under these more modern c o n d i t i o n s . A s p h e r i c a l l e n s that r e q u i r e d 8 minutes to p o l i s h 15 years ago i s now p o l i s h e d i n l e s s than one minute. A t o r i c ( c y l i n d e r ) l e n s that p r e v i o u s l y took 15 minutes to p o l i s h , now r e q u i r e s 4-1/2 minutes. Table I I I i l l u s t r a t e s the progress which has been made i n p o l i s h i n g machines over the l a s t f i f t y y e a r s . BIBLIOGRAPHY 1.

Duncan, L. K. "Cerium Oxide f o r Glass (1970), 41 ( 7 ) , 387-393.

2.

C o r n i s h , D. C. "The Mechanism of Glass Polishing" B.S.I.R.A. Research Report R267, British Scientific Instrument Research A s s o c i a t i o n , South Hill, C h i s l e h u r s t , Kent (1961).

3.

Grebenschikov, I . V. Keram. i S t e k l o , (1931), 7,

4.

C o r n i s h , D. C.; Watt, J. M. "The Mechanism of Glass P o l i s h i n g " a r e p o r t presented at the Symposium on the Surface Chemistry of G l a s s , Am. Ceramic Soc. Meeting, Wash. D.C. (May 11, 1966).

try,

5. Polishing"

Silvernail,

Polishing"

Glass

Indus-

36.

W. L.; Goetzinger, N. J . "The Mechanism of Glass Glass I n d u s t r y , (1971), 52 ( 4 ) , 130-152, 52 ( 5 ) ,

172-175. RECEIVED February 18,

1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

6 The Use of Rare Earth Elements in Zeolite Cracking Catalysts DAVID N. W A L L A C E

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch006

W. R. Grace & Company, Davison Chemical Division, Columbia, MD 21044

There are many areas o f application o f the r a r e e a r t h metals and their oxides i n c l u d i n g those in m e t a l l u r g y , t h e i r well known use as polishing compounds, and their ability t o provide unique g l a s s compositions. One of the l a r g e s t s i n g l e uses f o r r a r e e a r t h mixtures is in fluid c r a c k i n g c a t a l y s t s made f o r the petroleum refining i n d u s t r y . It is w i t h fluid c r a c k i n g c a t a l y s t s that r e f i n e r s produce the bulk of g a s o l i n e and fuel oil r e q u i r e d by the general p u b l i c . (1) Fluid c r a c k i n g c a t a l y s t s manufactured prior t o 1960 were amorphous mixtures o f silica and alumina, combined in such a manner that the mixture could be spray d r i e d i n t o a roughly s p h e r i c a l shape about 70 microns in diameter. Today's c r a c k i n g c a t a l y s t in a d d i t i o n contains an i n e r t filler and zeolite: the principle a c t i v e i n g r e d i e n t Of today's c r a c k i n g catalysts. To give a p e r s p e c t i v e o f c r a c k i n g c a t a l y s t usage world wide, we note that world wide oil refining c a p a c i t y is about 50,000,000 b a r r e l s per day 15% o f which can be catalytically cracked. Cracking c a t a l y s t usage t o handle t h i s amount o f o i l runs t o about 550 tons per day, o f which 90 t o 95% c o n t a i n z e o l i t e s . The t o t a l y e a r l y value o f c r a c k i n g c a t a l y s t s i s i n excess o f $100,000,000. The geographic d i s t r i b u t i o n of c r a c k i n g c a t a l y s t usage, F i g u r e 1, shows that i n the United States today z e o l i t e c r a c k i n g c a t a l y s t s are p r i m a r i l y used due to t h e i r p r e f e r e n t i a l s e l e c t i v i t y f o r g a s o l i n e p r o d u c t i o n . Other areas o f the world which do not have such a dependency on g a s o l i n e use both z e o l i t e c a t a l y s t s and amorphous c a t a l y s t s to produce a mix of g a s o l i n e and f u e l o i l s . F o l l o w i n g t h e i r i n t r o d u c t i o n t o the r e f i n i n g i n d u s t r y i n 1962, z e o l i t e c r a c k i n g c a t a l y s t s , have v i r t u a l l y replaced the amorphous s i l i c a alumina c r a c k i n g c a t a l y s t s that had p r e v i o u s l y dominated the marketplace. To the r a r e e a r t h i n d u s t r y the development o f z e o l i t e c a t a l y s t s represented a new end use without precedent. Nearly a l l z e o l i t e c r a c k i n g

0097-6156/81/0164-0101$05.00/0 © 1981 American Chemical Society In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch006

102

RARE EARTH ELEMENTS

HOr

Figure 1.

Geographic distribution of fluid cracking catalyst (FCC) usage

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

6.

WALLACE

Zeolite

Cracking

Catalysts

c a t a l y s t s c u r r e n t l y manufactured c o n t a i n r a r e e a r t h oxides present as a mixture o f the r a r e e a r t h elements. Today about 250 thousand tons per year o f f l u i d c r a c k i n g c a t a l y s t s a r e s o l d throughput the world. Of t h i s amount about 220 thousand tons a r e z e o l i t e c r a c k i n g c a t a l y s t s . I n the e a r l y days o f z e o l i t e c a t a l y s t s , the c a t a l y s t s contained on the average between 5 and 10% z e o l i t e . Today, however, average z e o l i t e contents run i n the range o f 10 t o 14 percent w i t h s e l e c t e d grades c o n t a i n i n g as much as 35 percent z e o l i t e . Assuming f o r the moment that the average l e v e l o f r a r e e a r t h oxides on these c a t a l y s t s i s 2% by weight, the estimated 1980 r a r e e a r t h oxide usage would be about 4,400 tons. This estimate i s on the low s i d e and i s based on the 10% z e o l i t e l e v e l . A more accurate z e o l i t e content estimate would be 15% i n which case 6,600 tons would be consumed. Data obtained from a 1979 U.S. Bureau o f Mines r e p o r t by C. M. Moore, ( 2 ) , F i g u r e 2, i n d i c a t e s that a sharp r i s e i n United States r a r e e a r t h demand accompanied the development of r a r e e a r t h exchanged z e o l i t e c r a c k i n g c a t a l y s t s and t h e i r r a p i d acceptance by the United States petroleum r e f i n i n g i n d u s t r y . Although usage i n c r a c k i n g c a t a l y s t s seems t o have l e v e l l e d o f f , t o t a l U.S. demand continues to swing upward suggesting that other segments o f U.S. i n d u s t r y have increased t h e i r usage o f r a r e e a r t h . The growth o f z e o l i t e c o n t a i n i n g f l u i d c r a c k i n g c a t a l y s t s skyrocketed during the mid-1960 s, F i g u r e 3, and today i t i s safe t o say that without exception a l l f l u i d c r a c k i n g unts i n the United States employ some form o f z e o l i t e c a t a l y s t s . -

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Z e o l i t e C a t a l y t i c Cracking Why was there such a phenomenal growth o f z e o l i t e c a t a l y s t s i n the r e f i n i n g i n d u s t r y ? The answer l i e s i n two parts. Z e o l i t e c a t a t a l y s t s containing rare earth are s t r u c t u r a l l y more s t a b l e and maintain t h e i r hydrogen t r a n s f e r (cracking) p r o p e r t i e s b e t t e r d u r i n g use than the o l d e r amorphous s i l i c a alumina c r a c k i n g c a t a l y s t s . These c a t a l y s t s are c a p a c i t y expanders by which r e f i n e r s are able t o i n c r e a s e the amount o f o i l processed and s t i l l o b t a i n the d e s i r e d product d i s t r i b u t i o n . In g e n e r a l , r e f i n e r y c a t a l y t i c c r a c k i n g u n i t s a r e l i m i t e d i n t h e i r throughput by the amount o f coke produced that has to be burned o f f i n the regenerator. Coke i s a by-product o f the c r a c k i n g r e a c t i o n . Z e o l i t e c r a c k i n g c a t a l y s t s lowered the coke p r o d u c t i o n s i g n i f i c a n t l y , thus a l l o w i n g r e f i n e r s to i n c r e a s e t h e i r throughput s u b s t a n t i a l l y w h i l e s t a y i n g w i t h i n coke burning l i m i t a t i o n s .

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YEAR

Figure 2.

Rare earth usage in petroleum cracking catalysts as a function of total U.S. rare earth demand

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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The a b i l i t y o f c a t a l y s t s to convert o r crack l a r g e molecular weight, h i g h b o i l i n g p o i n t organic molecules i n t o smaller molecular weight, lower b o i l i n g molecules depends t o a l a r g e extent on t h e i r a c i d i c p r o p e r t i e s . I n z e o l i t e s the a c i d s i t e p o p u l a t i o n and s t r e n g t h are s e v e r a l orders o f magnitude higher than i n the o l d e r amorphous s i l i c a - a l u m i n a g e l c a t a l y s t s and are b e l i e v e d t o be p r i m a r i l y Br^nsted a c i d s i t e s . F u r t h e r , the a d d i t i o n o f r a r e e a r t h to the z e o l i t e enables i t t o r e t a i n i t s inherent a c i d i c p r o p e r t i e s b e t t e r i n the harsh high temperature r e a c t i o n system o f the r e f i n e r y cat cracker than i t can without r a r e e a r t h . This a b i l i t y i s measured throughout the petroleum i n d u s t r y by a t o o l r e f e r r e d to as the m i c r o a c t i v i t y t e s t . In t h i s t e s t an o i l feedstock, b o i l i n g i n the range o f roughly 400-950°F, i s passed under c o n t r o l l e d flow r a t e c o n d i t i o n s over a f i x e d bed o f the c a t a l y s t a t a temperature of about 900°F. Chromatographic a n a l y s i s o f the product stream from t h i s r e a c t i o n f o r m a t e r i a l b o i l i n g below about 420°F i s made. The amount o f t h i s product found determines the conversion l e v e l . Conversion i s u s u a l l y expressed i n volume percent and i n c l u d e s g a s o l i n e range compounds and lighter materials. While the number o f f l u i d c r a c k i n g u n i t s i n the United States s w i t c h i n g t o z e o l i t e c a t a l y s t s was i n c r e a s i n g , the m i c r o a c t i v i t y v a l u e o f an average e q u i l i b r i u m mixture o f c r a c k i n g c a t a l y s t s a l s o increased as seen i n Figure 4. This meant that more o f the o i l feed to the f l u i d c a t a l y t i c c r a c k i n g u n i t was being converted to the more u s e f u l lower b o i l i n g compounds on the f i r s t pass through the u n i t . With the o l d e r amorphous c a t a l y s t s a s i g n i f i c a n t f r a c t i o n o f the o i l fed t o the u n i t was found to be r e l a t i v e l y unconverted on the f i r s t pass and had to be recycled back to the u n i t i n c r e a s i n g the coke burning load o f the regenerator and r e s t r i c t i n g f r e s h feed throughput. A higher c a t a l y s t m i c r o a c t i v i t y i m p l i e s a reduced amount of unconverted m a t e r i a l r e c y c l e d t o the c a t a l y t i c c r a c k e r , thus i n c r e a s i n g not only f i r s t pass feed conversion t o d e s i r a b l e products but a l s o p e r m i t t i n g higher throughput o f f r e s h feedstocks due to the r e d u c t i o n i n r e c y c l e m a t e r i a l . Consequently, the development o f z e o l i t e c a t a l y s t s proved a major boon to the r e f i n i n g i n d u s t r y . The Z e o l i t e o f Cracking

Catalysts

As mentioned e a r l i e r , f l u i d c r a c k i n g c a t a l y s t a r e p r e s e n t l y comprised o f three p r i n c i p a l i n g r e d i e n t s , an amorphous s i l i c a - a l u m i n a r e f r a c t o r y binder, a generally i n e r t f i l l e r and the z e o l i t e .

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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64

66

68

70

72

74

76

78

80

Yecr

Figure 3.

Growth of zeolite catalyst use in U.S. fluid cracking units

u

1962 64

66

68

70

72

74

76

YEAR Figure 4.

Yearly increase in microactivity (MA) and decrease in recycle caused by zeolite catalyst usage

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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The z e o l i t e component belongs to a broad c l a s s o f m i n e r a l s composed o f c r y s t a l l i n e hydrous alumino s i l i c a t e s c o n t a i n i n g one o r more a l k a l i o r a l k a l i n e e a r t h metals. Some o f the n a t u r a l l y o c c u r i n g z e o l i t e s a r e a n a l c i t e , c h a b a s i t e , mordenite, n a t r o l i t e and f a u j a s i t e , a l l o f which a r e g e n e r a l l y found i n small deposits. The z e o l i t e s used i n c r a c k i n g c a t a l y s t compositions a r e s y n t h e t i c a l l y made members o f the f a u j a s i t e f a m i l y i n c l u d i n g X and Y types. These d e s i g n a t i o n s a r e based on s p e c i f i c X-ray d i f f r a c t i o n p a t t e r n s but a r e commonly d i s c u s s e d on the b a s i s of s i l i c a to alumina r a t i o s . Y z e o l i t e ( a t S i 0 / A l 0 3 > 3.0) i s the p r e f e r r e d type f o r c r a c k i n g c a t a l y s t use s i n c e i t tends to be more h y d r o t h e r m a l l y s t a b l e than the lower r a t i o X v a r i e t y , which has a S i 0 / A l 0 r a t i o o f w i t h some hydrocarbons s t i l l adsorbed passes d i r e c t l y i n t o an o x i d i z i n g temperature zone o f 1250°F or h i g h e r . I n t h i s environment coke i s burned o f f the c a t a l y s t p a r t i c l e , regenerating i t f o r f u r t h e r use. I t i s important to note that i n burning o f f the coke, c a t a l y s t p a r t i c l e temperatures g e n e r a l l y exceed the average bed temperature by s e v e r a l hundred degrees. I n l a b o r a t o r y work c a t a l y s t p a r t i c l e s have been observed t o s c i n t i l l a t e d u r i n g b u r n i n g , suggesting temperatures w e l l i n the excess of 1500°F. Recent l e g i s l a t i o n has r e q u i r e d i n d u s t r y t o reduce s t a c k emissions o f such things CO, S 0 , N 0 and p a r t i c u l a t e matter. Although some o f these problems a r e s t i l l being addressed, a c a t a l y t i c method has been found f o r s i g n i f i c a n t l y r e d u c i n g CO emissions from the r e g e n e r a t o r s o f c a t a l y t i c c r a c k i n g u n i t s . This i s achieved by burning CO w i t h i n the regenerator stage. Doing t h i s g e n e r a l l y e l i m i n a t e s the need f o r expensive f

X

X

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110

rare

earth

elements

HEXAGONAL RING LINKAGE

"P-JJl 1

HEXAGONAL PRISM CAGE

m

i

i

i

SODALITE CAGE 1

' SUPERCAGE

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Figure 7.

Diagram of synthetic faujasite cages showing cation positions (SI, SI', Sir, SII, SHI) and pore openings

20

30

40

50

V% C o n v e r s i o n o f Gas O i l

Figure 8.

Correlation between catalyst activity for gas-oil cracking and Br0nsted acidity of Ca, Mn, and REX zeolites

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3

Products

Flue Gas £

Stripper

Gas O i l

Figure 9.

Diagram of a fluid catalytic cracking unit

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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c a p i t a l investment i n CO b o i l e r s , yet provides the heat necessary f o r m a i n t a i n i n g e f f i c i e n t r e f i n e r y o p e r a t i o n s . This technique causes regenerator temperatures to r i s e r e q u i r i n g improved regenerator metallurgy and s t a b l e c r a c k i n g c a t a l y s t s .

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Z e o l i t e Rare E a r t h L e v e l E f f e c t s Z e o l i t e s t a b i l i t y can be p a r t i a l l y c o n t r o l l e d by the exchange l e v e l of r a r e e a r t h , as shown i n Figure 10. Z e o l i t e thermal s t a b i l i t y i s measured as a f u n c t i o n of the r e t a i n e d surface area f o l l o w i n g a 2 hour a i r c a l c i n a t i o n at 1650°F. In t h i s p a r t i c u l a r case maximum thermal s t a b i l i t y was obtained at about 20 Wt.% r a r e e a r t h oxide (RE2O3) on z e o l i t e . At t h i s l e v e l of r a r e e a r t h , which i s f a i r l y t y p i c a l , n e a r l y complete exchange of the supercage and s o d a l i t e cage sodium ions by r a r e e a r t h ions i s obtained. I f a h i g h l e v e l of sodium were to remain i n the z e o l i t e a f t e r r a r e e a r t h exchange, f o r example, due to poor pH c o n t r o l , the z e o l i t e s t r u c t u r e would c o l l a p s e . Consequently, i t i s d e s i r a b l e to exchange out as much sodium as p o s s i b l e , r e p l a c i n g i t w i t h r a r e e a r t h . Hydrothermal (steam) s t a b i l i t y i s a l s o important, i n as much as the c a t a l y s t must pass through a high temperature s t r i p p i n g zone i n which the usual f l u i d s t r i p p i n g medium i s steam. In our l a b o r a t o r y , z e o l i t e hydrothermal s t a b i l i t y i s measured by comparing the x-ray c r y s t a l l i n i t y of the unknown f a u j a s i t e sample w i t h that of a f u l l y r a r e e a r t h exchanged reference standard f o l l o w i n g a 3 hour, 100% steam, 1500°F treatment. Figure 11 shows that maximum hydrothermal s t a b i l i t y f o r t h i s f a u j a s i t e was obtained a r a r e e a r t h oxide l e v e l of only 7 Wt.%. However, s i n c e maximum thermal s t a b i l i t y was achieved a t abou the 20% r a r e e a r t h oxide l e v e l , the exchange should be c a r r i e d out to the 20% l e v e l i n order to maximize o v e r a l l stability characteristics. Thermal and hydrothermal s t a b i l i t y are necessary but not s u f f i c i e n t c r i t e r i a f o r an acceptable c r a c k i n g c a t a l y s t , s i n c e both the l i f e expectancy and the a c t i v i t y of the z e o l i t e c a t a l y s t i s of importance to the r e f i n e r . A c t i v i t y i s c o n t r o l l e d by the c a t a l y s t manufacturer i n one of two ways, by e i t h e r adding more z e o l i t e or i n c r e a s i n g the s t a b i l i t y and a c t i v i t y of the z e o l i t e . L i k e both thermal and hydrothermal s t a b i l i t y , a c t i v i t y i s a f u n c t i o n of the l e v e l of r a r e e a r t h exchange as shown i n Figure 12. This graph i n d i c a t e s that maximum a c t i v i t y f o l l o w i n g a simulated commercial d e a c t i v a t i o n i s obtained by exchanging i n t o the z e o l i t e 20% by weight r a r e e a r t h (as the oxide) r e p l a c i n g sodium and/or the preexchanged ammonium c a t i o n used i n t h i s study to provide a constant base z e o l i t e Na 0 l e v e l . (Ammonia was d r i v e n o f f d u r i n g d e a c t i v a t i o n ) 2

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

WALLACE

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Catalysts

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6.

Figure 10.

Zeolite thermal stability response to rare earth content

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Figure 12.

Microactivity response of zeloite cracking catalyst to rare earth content

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Catalysts

While f u r t h e r exchange w i t h r a r e e a r t h beyond the 20 Wt. percent l e v e l i s p o s s i b l e , i t i s economically i m p r a c t i c a l p r i n c i p a l l y due t o the energy r e q u i r e d t o d i s l o d g e the remaining Na 0 and the l i m i t e d a c t i v i t y b e n e f i t s which accure. 2

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch006

The Future Role o f Rare E a r t h Exchanged Z e o l i t e s i n C a t a l y t i c Cracking What about the f u t u r e ? L i k e many other i n d u s t r i e s , c a t a l y s t manufacturers a r e dependent on r e f i n e r y requirements and crude o i l a v a i l a b i l i t y . Although crude o i l s u p p l i e s may become l i m i t e d and c a t a l y s t usage reduced, r a r e e a r t h usage i n c r a c k i n g c a t a l y s t may be u n a f f e c t e d . This i s because crudes that are l i k e l y t o be processed are expected to be more d i f f i c u l t t o crack r e q u i r i n g higher s t a b i l i t y and a c t i v i t y and thus more r a r e e a r t h exchanged z e o l i t e pef unit of catalyst. I f g a s o l i n e demand continues t o s l a c k e n , more feedstock may be targeted f o r e i t h e r f u e l o i l , o r d i e s e l p r o d u c t i o n . In t h i s case l e s s o f the r a r e e a r t h exchanged z e o l i t e s would be r e q u i r e d . F i n a l l y , the product s l a t e (e.g. o l e f i n p r o d u c t i o n , petrochemical feedstock p r o d u c t i o n ) , o r the product q u a l i t y (e.g. g a s o l i n e octane improvement) may d i c t a t e a r e d u c t i o n i n r a r e e a r t h usage. Which o f these w i l l come t o pass i s u n c e r t a i n . However, we do know that i n the long term the feedstocks w i l l be g e n e r a l l y more d i f f i c u l t to crack r e q u i r i n g process as w e l l as c a t a l t y i c improvement, and r a r e earths w i l l continue to p l a y a major r o l e i n f l u i d c r a c k i n g c a t a l y s t s . The author g r a t e f u l l y acknowledges the c o n t r i b u t i o n s o f Drs. J . S. Magee and E. W. A l b e r s i n p r e p a r i n g t h i s work, and the support o f the Davison Chemical D i v i s i o n o f W. R. Grace and Co.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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"Literature Cited"

RECEIVED

1.

Venuto, P. B.; Habib, E. T., Jr. "Fluid Cracking w i t h Z e o l i t e C a t a l y s t s " . Marcel Dekker, I n c . : New York 1 9 7 9 .

2.

Moore, C. M.; Rare E a r t h M i n e r a l s and Metals. P r e p r i n t from 1977 Bureau of Mines, "Minerals Yearbook", U.S. Department of Interior, Bureau of Mines: Washington, D.C.

3.

Gates, B. C.; K a t z e r , J . R,; S c h u i t , G.C.A.; "Chemistry of Catalytic Processess:. McGraw-Hill Book Co.: New York 1 9 7 9 .

4.

W o l l a s t o n , E. G.; Haflin, W. J . ; Ford, W. D.; D'Souza G. J.; Hydrocarbon P r o c e s s i n g , V o l . 54, September 1 9 7 5 . p. 9 3 . March 30,

Catalytic

1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

7 Rare Earths in Noncracking Catalysts A L A N W. PETERS and GWAN KIM

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch007

W. R. Grace & Company, Davison Chemical Division, Columbia, M D 21044

Since 1962 r a r e earths have been used t o stabilize z e o l i t e c r a c k i n g c a t a l y s t s f o r the petroleum i n d u s t r y (1, 2 ) . Until recently t h i s a p p l i c a t i o n t o catalysis has been the only commercially significant one. C u r r e n t l y , however, a number o f new a p p l i c a t i o n s of potential commercial s i g n i f i c a n c e are appearing. One of the most important of these is the use o f cerium in c a t a l y s t s f o r automobile exhaust emission c o n t r o l . We will emphasize t h i s application in our review without n e g l e c t i n g other a p p l i c a t i o n s . The r a r e e a r t h oxides have a number of distinguishing properties important in catalytic a p p l i c a t i o n s . The oxides are b a s i c (3) compared t o alumina, lanthanum oxide (La 0 ) being the most b a s i c . The oxides a l s o have good thermal stability, a valuable characteristic in most industrial a p p l i c a t i o n s . Some r a r e earths i n c l u d i n g cerium, praseodymium, and terbium form non-stoichiometric oxides ( 4 ) , an important property shared by many good o x i d a tion c a t a l y s t s . These mixed valence s t a t e compounds are typically polymorphic. Cost and abundance are important p r o p e r t i e s t o be considered f o r any commercial a p p l i c a t i o n . Table I l i s t s recent cost and abundance data o f i n d i v i d u a l r a r e earths d e r i v e d from major ores. The expensive oxides are the l e a s t abundant. Of the c a t a l y t i c a l l y i n t e r e s t i n g r a r e earths forming n o n - s t o i c h i o m e t r i c o x i d e s , cerium i s by f a r the most abundant and l e a s t expensive. Important p o t e n t i a l c a t a l y t i c a p p l i c a t i o n s i n c l u d e : • Ammonia Synthesis • Hydrogenation/Dehydrogenation • Polymerization • Isomerization • Oxidation • Auto Exhaust Emission C o n t r o l • Applications of Perovskites Some o f these areas have been r e c e n t l y reviewed by Rosynek (5), p o l y m e r i z a t i o n of o l e f i n s has been reviewed by Mazzei ( 6 ) , and Minachev (7) i n a recent paper summarized some experimental r e s u l t s i n the areas of i s o m e r i z a t i o n , hydrogenation, and o x i d a t i o n . We w i l l t r y not t o overlap these recent reviews. 2

3

0097-6156/81/0164-0117$05.00/ 0 © 1981 American Chemical Society

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TABLE I

Rare Earth Oxides Abundance and Cost* 3

$/lb. Pure Oxide Ce0

Nd 0 Pr 0n 2

3

6

Sni2 03

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Gd 0 Eu 0 2

3

2

3

Dy 0 Ho 0 Er 0 Tm 0 Yb 0 Lu2 0 Y 0 2

2

3

2

3

2

3

2

3

2

3 3

3

Abundance i n Ores B a s t n a e s i t e Xenotime

Monazite

7.50 7.25 18.00 32.00 32.00 55.00 700.00 350.00 45.00 120.00 45.00 1000.00 85.00 2000.00 30.00

2

La2 03

5

45 20 18 5 5 2 0.1

49 32 13 4 0.5 0.3 0.1

2.1

0.1

5 0.5 2.2 0.7 2 4 0.2 1.0 8.7 2.1 5.4 0.9 6.2 0.4 61

U Residues 4 0.8 4.1 1.0 4.5 9 0.2 1.2 11.2 2.6 5.5 0.9 4.0 0.4 51

Concentrates Cerium Lanthanum REO

0.85 1.05 0.80

(a)

M i n e r a l F a c t s and Problems, 5 t h . Ed., U.S. Bureau of Mines, 1975.

(b)

M i n e r a l s Yearbook, Volume 1, 1977, U.S. Bureau of Mines, 1980.

Performance o f the Cerium Promoted Lummus C a t a l y s t

TABLE I I

Average Reactor Temperature, °F

% NH i n Product Equilibrium Conventional 3

Ce Promoted

710

39

10.4

13.5

840

22.4

12.8

17.8

910

16.8

12.7

15.6

^250°F

V330°F

AT (T Max. - T i n l e t ) Conditions: 150 atm pressure Gas h o u r l y space v e l o c i t y = 16,000 Mole R a t i o H /N 2

2

=

^2.8

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

PETERS AND KIM

7.

Noncracking

119

Catalysts

Ammonia Synthesis

Ertl ten:

C a t a l y t i c ammonia s y n t h e s i s has been r e c e n t l y reviewed by (8) and by Emmett (9). The c a t a l y t i c r e a c t i o n s can be w r i t -

N (g) 2

^±

N (ad) 2

N ( a d ) JZ± 2N(ad) 2

H (g)

^±

N(ad)

+

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch007

2

2H(ad) 3H(ad)

NH (ad) « ±

3

NH (g)

3

The

NH (ad)

3

step: N ( a d ) Z ± 2N(ad) 2

i s r a t e determining, although a t h i g h conversions the removal o f NH from the c a t a l y s t s u r f a c e may be important. A t y p i c a l NH s y n t h e s i s c a t a l y s t (10) contains i r o n oxide p l u s 1% K 0 , 1-2% A 1 0 , and may c o n t a i n VL% CaO on the s u r f a c e . A f t e r f u s i o n and r e d u c t i o n the s u r f a c e i s l a r g e l y m e t a l l i c i r o n p l u s reduced promoters concentrated on the s u r f a c e (8). Sze and Wang (11) have shown that a c a t a l y s t washed w i t h C e ( N 0 ) and subsequently reduced i s much more a c t i v e than the c o n v e n t i o n a l c a t a l y s t , Table I I . Mischmetal s a l t s may be s u b s t i t u t e d f o r the c e r i um s a l t . Since i n d u s t r i a l c a t a l y s t s can be very s e n s i t i v e t o p r e t r e a t ment, the source of the a c t i v i t y improvement i s u n c l e a r . F o r example, washing even i n the absence o f cerium may have some c a t a l y t i c effect. 3

3

2

2

3

3

3

Hydrogenation In an i n t e r e s t i n g s e r i e s of experiments Van Mai and co-workers (12, 13, 14) have found that i f r a r e earths a r e combined w i t h t r a n s i t i o n metals a t h i g h temperatures, the a l l o y w i l l absorb l a r g e amounts of hydrogen as hydrides under m i l d c o n d i t i o n s ; 1 atm. H and room temperature. Some examples o f these compounds and t h e i r hydrides are: 2

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

120

RARE EARTH ELEMENTS

Compound

Hydrides

Ce Ni

CesNiHa.^

LaNi

LaNiH .i

3

LaNi YFe

3

LaNi5He

5

YFe H^. 3

3

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch007

YFe

8

YFezfti* • 2

C a t a l y t i c a p p l i c a t i o n s of these m a t e r i a l s to hydrogenation (15), methanation (16) and ammonia s y n t h e s i s (17) have been des c r i b e d and some i n f o r m a t i o n concerning the s t r u c t u r e s of these m a t e r i a l s i s a v a i l a b l e (18). By themselves, r a r e e a r t h s are l e s s a c t i v e than the convent i o n a l nickel/molybdenum/cobalt, tungsten combinations, the Raney N i a l l o y s , or the noble metal c a t a l y s t s . Polymerization A r e c e n t l y developed c l a s s of compounds c a l l e d "Super S l u r p e r s " based on s t a r c h - p o l y a c r y l o n i t r i l e copolymers are a b l e t o absorb as much as 500 to 1000 times t h e i r weight of water, dependi n g on the p u r i t y of the water (19, 20, 21). The formation of these copolymers i s c a t a l y z e d by C e ^ ^ i o n . These polymers were developed by the U.S. Department of A g r i c u l t u r e and have p o t e n t i a l a g r i c u l t u r a l uses as water storage a d d i t i v e s as w e l l as obvious consumer and i n d u s t r i a l a p p l i c a t i o n s . Oxidation A redox mechanism i n v o l v i n g l a t t i c e oxygen o r i g i n a l l y p r o posed i n 1954 by Mars and Van K r e v e l e n (22) f o r hydrocarbon o x i d a t i o n over V2O5 can be a p p l i e d to a v a r i e t y of c a t a l y t i c o x i d a t i o n r e a c t i o n s (23). The f o l l o w i n g i l l u s t r a t e s a l a t t i c e redox mechanism f o r CO o x i d a t i o n : 1.

CO A d s o r p t i o n C0(g)

2.

CO(ad)

CO O x i d a t i o n by L a t t i c e Oxide, C a t a l y s t Reduction 2

[oj "

+

CO (ad)

1

' 0

0.025

6

1

0.05

1

1

1

1

0.075 J (A/cm )

0.1

0.125

0.15

ELEMENTS

1

2

3+

Figure 7. Efficiency of green-emitting (Zn,Cd)S:Cu,Al relative to La 0 S:Tb as a function of electron beam current density: (O) 30 kV, O 25 kV, (A) 20 kV. Electron beam dwell is 0.5 fis and pulse repetition rate is 60 pps. 2

2

I

I

I

I

I

I

I

300

400

500

600

700

800

900

WAVELENGTH (nm)

Figure 8.

Spectral energy distributions of several blue-emitting cathode ray phosphors

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10.

McCOLL AND

PALILLA

TV

and

Cathode

Ray

187

Phosphors

s

value of P ^ i i determined by the n e c e s s i t y to have an adequate value f o r Z^lue as r e q u i r e d by Eq. (9). A measure of the q u a l i t y of the spectrum of a blue phosphor f o r t h i s purpose may be def i n e d as z = Z/E. Spectra and numerical data to i l l u s t r a t e t h i s p o i n t are p r e sented i n F i g u r e 8 and Table I I I . The best r a r e e a r t h blue l i n e e m i t t e r i s Tm , but i t s emission, as t y p i f i e d by ZnS:Tm (18) emission, peaks a t ^ 475 nm, a^wavelength that p o o r l y matches the z curve; thus z i s low and Tm emission c o n t r i b u t e s i n e f f e c t i v e l y to a white f i e l d . The standard c o l o r TV b l u e , ZnS:Ag,Al, has a broad emission spectrum, but i£s peak a t 445 nm matches the z curve w e l l . The emission of E u i n Sr^Cl(P0 ) : E u (19) w h i l e broad, i s n a r rower than that of the s u l f i d e , so the match i s even b e t t e r and z i s l a r g e r . U n f o r t u n a t e l y , the CRT energy e f f i c i e n c y ( u n l i k e that f o r uv e x c i t a t i o n , which i s e x c e p t i o n a l l y good) i s so low that the s p e c t r a l v i r t u e s of t h i s phosphor cannot be used to advantage. 3+

3

2

2 +

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch010

3

Rare Earth Host L a t t i c e s Most of the s u c c e s s f u l r a r e e a r t h a c t i v a t e d phosphors comp r i s e host l a t t i c e s i n which the host c a t i o n i s a l s o a r a r e e a r t h . A p r i n c i p a l reason f o r t h i s r e l a t e s to the o p t i c a l i n e r t n e s s of La, Gd, Y, and Lu; t h i s i s e s s e n t i a l to a v o i d i n t e r f e r e n c e w i t h a c t i v a t o r emission s p e c t r a . Close chemical c o m p a t i b i l i t y i n c l u d i n g a m e n a b i l i t y to s u b s t i t u t i o n a l i n c o r p o r a t i o n of r a r e e a r t h a c t i v a t o r s are a l s o e s s e n t i a l f e a t u r e s . Rare e a r t h h o s t s such as o x i d e s , o x y s u l f i d e s , phosphates, vanadates and s i l i c a t e s a l s o tend to be rugged m a t e r i a l s compatible w i t h h i g h temperature tube processing o p e r a t i o n s and salvage. The exceptions to the r u l e that r a r e e a r t h h o s t s are b e s t f o r r a r e e a r t h a c t i v a t o r s are s p e c i a l cases. For example, some anions such as s u l f i d e y i e l d compounds i n combination w i t h nonr a r e e a r t h c a t i o n s (e.g. Zn) which show higher luminescent e f f i c i e n c y than w i t h r a r e e a r t h s . A d d i t i o n a l l y , d i v a l e n t r a r e earth a c t i v a t o r s l i k e E u s u b s t i t u t e r e a d i l y f o r non-rare e a r t h divalent cations. 2 +

F a c t o r s A f f e c t i n g Rare Earth Consumption i n TV Phosphors The consumption of r a r e earths i n c o l o r TV i s d i c t a t e d i n the f i r s t i n s t a n c e by the choice to use r a r e e a r t h phosphors and the number of p i c t u r e tubes produced. W i t h i n these c o n s t r a i n t s , s e v e r a l other f a c t o r s tend to exert a downward i n f l u e n c e on r a r e e a r t h consumption. Reclaim, that i s , reuse of phosphor coated on but not r e t a i n e d by the p i c t u r e tube screen, i s now u n i v e r s a l l y p r a c t i c e d i n the U.S. TV i n d u s t r y . Reclaim was not p r a c t i c e d at the time of the i n t r o d u c t i o n of Eu-based reds. The h i g h cost and u n c e r t a i n a v a i l a b i l i t y of r a r e e a r t h phosphors

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

188

RARE E A R T H

.

.

1

J

ELEMENTS

x = .636 y = .353

A- .

x = .647

A:V

Y O :Eu(4.0%)

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch010

2

349

3

DIFFERENCEIX10)

^ _ _ ^ J

h .

I 400

300

I 500

•

I 600

700

W A V E L E N G T H (nm) 3

Figure 9. Dependence of emission spectrum of Y O :Eu * on europium concentration. The difference spectrum is defined as the normalized Y O :Eu (2.8%) spectrum minus that for Y O :Su (4.0%). This enhances perceptibility of the increased Dt emission (yellow and green lines) in the low Eu concentration phosphor. 2

s

2

2

s

s

5

Table III. RELATIVE BRIGHTNESS

MATERIAL ZnS:Ag,AI

Sr CI(P0 ) :Eu 5

4

3

2+

Blue Emitting Phosphors

COLOR COORDINATES X

Y

_Y

RELATIVE ENERGY Z _ EFFICIENCY

RELATIVE RELATIVE WHITE FIELD COLOR EFFECTIVENESS GAMUT COMMENT

=100%

0.148 0.060 0.094 1.23

=100%

=100%

=100%

«STDTV PHOSPHOR •SATURATES

14.9

0.154 0.028 0.052 1.53

27

32

118%

• ENLARGED COLOR GAMUT

74%

0.115 0.107 0.092 0.67

76

82%

•REDUCED COLOR GAMUT

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10.

McCOLL A N D P A L I L L A

TV

and

Cathode

Ray

189

Phosphors

d i c t a t e d c o n s e r v a t i o n measures, w h i l e t h e i r ruggedness made r e c l a i m p o s s i b l e . The a b i l i t y to r e c l a i m , on the other hand, has the p o s i t i v e e f f e c t of p r o v i d i n g a strong case f o r the continued use of r a r e e a r t h s . The i n t r o d u c t i o n of pigmented phosphors by RCA (20), f o l l o w e d by some but not a l l other manufacturers, i n d i r e c t l y reduces Eu consumption. Pigmented phosphors a r e coated w i t h compatibly c o l o r e d i n o r g a n i c pigments, whose purpose i s to improve c o n t r a s t by reducing r e f l e c t e d ambient l i g h t (red pigment i s used w i t h r e d e m i t t i n g phosphor, e t c . ) . We s h a l l show how t h i s permits r e d u c t i o n of Eu c o n c e n t r a t i o n i n the r e d phosphor. The s p e c t r a o f Y^O : E u a t two Eu l e v e l s , i n F i g u r e 9, help to show why r e l a t i v e l y l a r g e Eu c o n c e n t r a t i o n s have to be used i n these phosphors. The d i f ference spectrum b r i n g s out the f a c t that a t lower E u concent r a t i o n , emission from ^D^ l e v e l s , l y i f i g i n the green-yellow regions of the spectrum, i s enhanced a t the expense of the red -*D emission. The h i g h Eu c o n c e n t r a t i o n (3-5 m/o) found i n TV reds i s needed not so much f o r e f f i c i e n c y (which t y p i c a l l y peaks f o r Eu a t about 2 m/o i n these m a t e r i a l s ) but r a t h e r to y i e l d the r e q u i r e d s a t u r a t e d r e d emission c o l o r . The r e d pigment used i n t i n t e d r e d - e m i t t i n g phosphor p r e f e r e n t i a l l y absorbs i n the greeny e l l o w ; t h i s r e s t o r e s the c o l o r of low Eu phosphor to the d e s i r e d redness. The impact on Eu consumption i s s m a l l but not n e g l i g i b l e . 3 +

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch010

3 +

Q

Data D i s p l a y Phosphors An a l r e a d y s u b s t a n t i a l and r a p i d l y growing market f o r CRT phosphors and tubes i s i n the area of data d i s p l a y s , both a l p h a numeric and g r a p h i c , e.g., computer t e r m i n a l s and word processors. In s p i t e of dramatic advances i n other t e c h n o l o g i e s , CRT's a r e s t i l l the most cost e f f e c t i v e way to present i n f o r m a t i o n , and very l i k e l y always w i l l be. Most data d i s p l a y tubes do not use r a r e e a r t h phosphors; because o f t h e i r h i g h c o s t , r a r e e a r t h phosphors f i n d use o n l y when there i s a compelling need f o r t h e i r s p e c i a l p r o p e r t i e s . A t the present time, t h i s i s l i m i t e d to the use of Eu3+ reds i n t r i c o l o r tubes that use the same shadow mask p r i n c i p l e as c o n v e n t i o n a l c o l o r TV. There a r e s e v e r a l demonstrated, but not as y e t commercialized, schemes f o r two c o l o r , non-shadow mask, h i g h r e s o l u t i o n d i s p l a y tubes which could use r a r e e a r t h phosphors. The v o l t a g e penet r a t i o n (21) scheme uses a two l a y e r phosphor and e x p l o i t s the p r i n c i p l e t h a t e l e c t r o n beam p e n e t r a t i o n i n t o a phosphor i n c r e a s e s as beam v o l t a g e i s i n c r e a s e d . At low v o l t a g e , o n l y the surface l a y e r e m i t t i n g one c o l o r i s e x c i t e d , w h i l e a t higher v o l t a g e , e x c i t a t i o n reaches a deeper phosphor l a y e r e m i t t i n g a d i f f e r e n t color. A second scheme (22) u t i l i z e s a blend of s u b l i n e a r and superl i n e a r phosphors. A t low c u r r e n t , the s u b l i n e a r phosphor dominates the emission. As the beam c u r r e n t i s i n c r e a s e d , the emission o f the s u p e r l i n e a r phosphor begins to surpass t h a t of the

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

190

RARE E A R T H

ELEMENTS

s u b l i n e a r , y i e l d i n g a c o l o r s h i f t . D i s p l a y s u s i n g e i t h e r of these p r i n c i p l e s would not be capable of the f u l l c o l o r gamut of t r i c o l o r tubes, yet would be simple and y i e l d both high r e s o l u t i o n and the c o n t r a s t enrichment provided by the added dimension of c o l o r . A f i n a l comment i n the data d i s p l a y area concerns an u n f u l f i l l e d need that might c o n c e i v a b l y be met by r a r e e a r t h m a t e r i a l s . Some data d i s p l a y s u t i l i z e low frame r a t e s that can l e a d to the p e r c e p t i o n of f l i c k e r when c o n v e n t i o n a l short or medium p e r s i s tence phosphors are used. Long p e r s i s t e n c e , i . e . , long decay time, can reduce f l i c k e r , but u n t i l very r e c e n t l y , o n l y one c o l o r has been commercially a v a i l a b l e - the green emission of Zn SiO^:Mn,As. The need f o r other c o l o r s and higher e f f i c i e n c y i s so great t h a t new long p e r s i s t e n c e phosphors could be put to use immediately. Rare e a r t h phosphors have a p o t e n t i a l f o r f u l f i l l i n g t h i s need, but u s e f u l long p e r s i s t e n c e r a r e e a r t h phosphors have not yet been discovered. In response to t h i s need, GTE S y l v a n i a has r e c e n t l y introduced n o n f l i c k e r i n g red, y e l l o w and white e m i t t i n g phosphors.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch010

2

Recent Research A c t i v i t y i n Rare Earth CRT

Phosphors

S e v e r a l areas of recent research a c t i v i t y that have an impact on r a r e e a r t h usage i n CRT phosphors have a l r e a d y been mentioned—pigmented phosphors f o r c o l o r TV, and v o l t a g e penet r a t i o n and c u r r e n t s a t u r a b l e phosphors f o r two-color d i s p l a y s . There has been a c o n t i n u i n g emphasis on development of r a r e e a r t h a c t i v a t e d s u l f i d e s ; examples of such m a t e r i a l s are ZnS:Tm (18), ZnS: Cu,Er ( 2 D , S r G a ^ i E u " (14) and SrGa^S^Ce ^ (14). The m o t i v a t i o n f o r choosing s u l f i d e s f o r development i s , i n p a r t , simply t h a t the most e f f i c i e n t f a m i l i e s of CRT phosphors are s u l f i d e s : ZnS, CdS, and the a l k a l i n e e a r t h s u l f i d e s . However, r a r e e a r t h based s u l f i d e s have not achieved the CR e f f i c i e n c y of the c o n v e n t i o n a l s u l f i d e s . The s t o r y i s somewhat d i f f e r e n t when one i s i n t e r e s t e d i n absolute l i g h t output r a t h e r than e f f i c i e n c y ; YAG:Ce (24) can be used when l i g h t outputs i n excess of 10,000 f t L are r e q u i r e d . Even though i t s e f f i c i e n c y i s low, YAG:Ce can withstand the enormous energy i n p u t necessary f o r the generation of t h i s amount of l i g h t . A r e l a t e d phosphor, the p e r o v s k i t e YA10~:Ce , has r e c e n t l y (25) been developed as an e f f e c t i v e u v - e m i t t i n g beam i n dex phosphor. Beam index tubes are an a l t e r n a t i v e form of t r i c o l o r p i c t u r e tube t h a t have o n l y one e l e c t r o n gun and no shadow mask. The gun i s modulated so t h a t an a p p r o p r i a t e c u r r e n t f l o w s as the beam s t r i k e s each c o l o r e d phosphor during scanning. The a d d i t i o n a l u v - e m i t t i n g phosphor, i n c o n j u n c t i o n w i t h a uv sensor w i t h i n the tube, i s r e q u i r e d to m a i n t a i n proper s y n c h r o n i z a t i o n . The "golden" p e r i o d of the 1960 s when s e v e r a l important new r a r e e a r t h phosphors were developed each year appears to be over. Nevertheless, u s e f u l new CRT phosphors are s t i l l being developed, 3+

2

1 -

32

3+

3+

f

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch010

10.

McCOLL A N D P A L I L L A

TV

and

Cathode

Ray

191

Phosphors

some examples of which have been d i s c u s s e d above. A d d i t i o n a l l y , we have pointed out areas where u n f u l f i l l e d needs have y e t to be met. F i n a l l y , the impact o f e f f i c i e n t r a r e e a r t h phosphors on s t i m u l a t i n g b a s i c r e s e a r c h should be noted. This aspect of r a r e e a r t h phosphors has not been w i d e l y recognized because i t has been overshadowed by the p r a c t i c a l m e r i t s of these m a t e r i a l s . E s s e n t i a l l y , the r a r e e a r t h phosphors have provided a t o o l i n the form o f unique o p t i c a l s p e c t r a which a r e c o n v e n i e n t l y amenable to t h e o r e t i c a l i n t e r p r e t a t i o n . Because of the d i s c r e t e n e s s of the o p t i c a l a d s o r p t i o n and emission f e a t u r e s of r a r e e a r t h i o n s , s u b t l e changes i n t h e i r environment can be a s s o c i a t e d w i t h d i s t i n c t and measurable changes i n t h e i r s p e c t r a . Analyses of these changes t h e r e f o r e g i v e i n s i g h t s i n t o h o s t - a c t i v a t o r i n t e r a c t i o n s . These analyses have not been a v a i l a b l e i n e a s i l y i n t e r p r e t a b l e form w i t h non-rare e a r t h phosphors. Consequently, c o n s i d e r a b l e e f f o r t has s i n c e gone i n t o improving our t h e o r e t i c a l understanding of energy t r a n s f e r mechanisms i n phosphors as w e l l as i n understanding the e f f i c i e n c y of r a d i a t i v e (and n o n r a d i a t i v e ) mechanisms i n phosohors (26^27^28). Such research u l t i m a t e l y should permit a more r a t i o n a l s e l e c t i o n o f host a c t i v a t o r combinations f o r f u r t h e r i n v e s t i g a t i o n thereby m i n i m i z i n g the h i s t o r i c a l , more e m p i r i c a l , approaches to the development of phosphors f o r s p e c i f i c applications. Economic Impact o f CRT Phosphors On The Rare E a r t h Industry Phosphor manufacture i s s t i l l a dominant f a c t o r f o r s u p p l i e r s of r a r e e a r t h chemicals. According to i n d u s t r y sources (29), approximately 1/3 of the monetary volume of r a r e e a r t h chemicals i s used by the e l e c t r o n i c s i n d u s t r y . Included i n t h i s f i g u r e i s Sm^O^ f o r samarium-cobalt magnets. The remainder i n c l u d e s Gd^O^, L a 0 and Tbo ^ x-ray and l i g h t i n g phosphors, and ° 3 Eu 0^ f o r CRT and l i g h t i n g phosphors. E s s e n t i a l l y a l l of the Ei^O consumed, t o t a l i n g 6-7 tons i n the U.S., i s used f o r phosphor m a n u f a c t u r e — 8 0 % to 90% of t h i s f o r CRT's, the remainder f o r l i g h t i n g . About 2/3 of the Y 0 consumed (^ 100 tons U.S.) i s used f o r phosphors. This f r a c t i o n might decrease i f some other e n v i s i o n e d uses f o r y t t r i a - b a s e d ceramics, e.g., automotive emission sensors, reach f r u i t i o n . O v e r a l l , the t o t a l monetary volume of r a r e earths used f o r U.S. CRT phosphor manufacture i s $20-25M. The volume by weight i s o n l y roughly 1% of t o t a l r a r e e a r t h p r o d u c t i o n , but the monet a r y volume i s l a r g e because of the h i g h value of E^Oo * 2 ^ 3 compared to other r a r e e a r t h o x i d e s , and the h i g h p u r i t y r e q u i r e d of phosphor grade chemicals. 0

2

f

o

r

Y

3

a

2

2

2

anc

Y

Summary We have reviewed

some of the f a c t o r s governing

s e l e c t i o n of

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phosphors f o r c o l o r TV and other CRT a p p l i c a t i o n s from the p o i n t of view of r a r e e a r t h usage. The dominant use f o r r a r e earths f o r CRT phosphors i s , and w i l l very l i k e l y continue to be, y t t r i a based europium-activated, r e d - e m i t t i n g phosphors f o r t r i c o l o r TV and data d i s p l a y . A b i g decrease i n use of these red phosphors would be d e s i r a b l e from the p i c t u r e tube makers' v i e w p o i n t , b e cause of c o s t , but i s h i g h l y u n l i k e l y . New use of r a r e e a r t h phosphors i n c o l o r TV would most l i k e l y r e s u l t from choice of T b or Eu2+ based green e m i t t e r s . While s e l e c t i o n of these phosphors c o u l d r e s u l t from changes i n p i c t u r e tube d e s i g n , prospects f o r t h i s are s l i m . As we w i l l no doubt l e a r n i n the f o l l o w i n g two companion papers, the new developments i n phosphors that w i l l have the g r e a t e s t changing impact on the r a r e e a r t h i n d u s t r y w i l l almost s u r e l y occur i n the areas of l i g h t i n g and radiography.

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3 +

Ac knowledgements The authors are honored by the i n v i t a t i o n of K a r l A . Gschneidner, J r . to present t h i s paper at the Second Chemical Congress of the North American C o n t i n e n t . They are a l s o indebted to Joseph G. Cannon of M o l y c o r p , I n c . and H . H o l t Apgar of RhonePoulenc, I n c . f o r d i s c u s s i o n s r e l a t i n g to the market f o r r a r e e a r t h s . We acknowledge w i t h thanks Wayne Person of GTE S y l v a n i a , Towanda, PA, who provided the b r i g h t n e s s and c o l o r coordinate data i n Table I .

Literature Cited 1. Palilla, F.C., Keynote Address - Electrochem. Soc. Spring Meeting, Dallas, 1967, Abstract No. 68; Electrochem. Tech. 1968, 6, 39. 2. Palilla, F.C., Award Address, Electrochem. Soc. Spring Meeting, Washington, DC, 1971. 3. Larach, S., Hardy, A.E., Proc. IEEE, 1973, 61, 915. 4. Stevels, A.L.N., J. Luminescence, 1976, 12/13, 97. 5. Levine, A.K., Palilla, F.C., Trans. N.Y. Acad. Sci. Ser. II, 1965, 27, 517. 6. Nimeroff, I., "Colorimetry", NBS Monograph 104, US Gov. Printing Office: Washington, 1968, 7. Kelly, K.L., Bull. Natl. Formulary Comm., 1940, 8, 459 8. Levine, A.K., Palilla, F.C., Electrochem. Tech., 1966, 4, 16. 9. Levine, A.K., Palilla, F.C.,Appl. Phys. Lett., 1964, 5, 118. 10. Wickersheim, K.A, Lefever, R.A., J. Electrochem. Soc., 1964, 111, 47. 11. Hardy, A.E., IEEE Trans. Electron Devices ED15, 1968, 868; Royce, M.R., Smith, A.L. Electrochem. Soc. Spring Meeting, Boston, Abstract No. 34, 1968. 12. Wang, S.P., Landi, O., Lucks, H., Wickersheim, K.A., Buchanan, R.A., IEEE Trans. Nucl. Sci. NS17, 1970, 49.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

10.

13. 14. 15. 16. 17. 18. 19.

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20. 21. 22. 23. 24. 25. 26. 27. 28.

29.

McCOLL A N D P A L I L L A

TV

and

Cathode

Ray

Phosphors

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Lehman, W., Ryan, F.M., J . Electrochem Soc., 1972, 119, 275; 1971, 118, 477. Peters, T.E. Baglio, J.A., J . Electrochem. Soc. 1972, 119,230. Avella, F.J., J . Electrochem. Soc., 1971, 118, 1862. McColl, J.R., Dodds, R.E., Electrochem. Soc. Spring Meeting, Seattle, Abstract No. 325, 1978. Meyer, V.D., Palilla, F.C., J. Electrochem. Soc., 1969, 116, 535. Shrader, R.E., Larach, S., Yocom, P.N., J. Appl. Phys., 1971, 42, 4529. Palilla, F.C., O'Reilly, B.E., J. Electrochem. Soc., 1968, 115, 1076. Trond, S.S., Electrochem Soc. Spring Meeting, Seattle, Abstract No. 329, 1978. Hallett, J., Rhodes, C., Proc. SID, 1969, 10, 9. Sisneros, T.E., Faeth, P.A., Danis, J.A., NASA Report Cr-1228, 1969; Avella, F . J . , IEEE Trans. Electron Devices, 1971, 18, 719. Schlam, E., Pucilowski, J . J . , Reingold, I . , J . Electrochem. Soc., 1975, 122, 655. Blasse, G, Bril, A., Appl. Physics Lett., 1967, 11, 53; J. Chem. Phys., 1967, 47, 5139; Bril, A., Blasse, G., DePoorter, J.A., J. Electrochm. Soc., 1970, 117, 346. Taked, T., Miyata, T., Tomiki, T., Electrochem. Soc. Spring Meeting, Boston, Abstract No. 222, 1979. Struck, C., Fonger, W.H., J.. Luminescence, 1975, 10, 1. Riseberg, L.A., Weber, M.J., "Progress in Optics", Wolf, E., Ed.,North Holland, Amsterdam, 1975, vol.14. Alig, R.C., Bloom, S., Struck, C.W., Electrochem. Soc., Spring Meeting, St. Louis, Abstract No. 206, 1980; Alig, R.C. Bloom, S., J.Appl. Phys., 1978, 49, 3476; Robbins, D.J., Electrochem. Soc. Spring Meeting, St. Louis, Abstract No.207, 1980. Cannon, J., Personal Communication; Apgar, H., Personal Communication.

RECEIVED

March

3, 1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

11 Lamp Phosphors W. A. THORNTON

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch011

Westinghouse Electric Corporation, Bloomfield, N.J. 07003

This Symposium gives a fine overview of the contributions of the rare earth elements to human need and a c t i v i t y . Their applicability to iron and s t e e l , to other a l l o y s , glasses, abrasives, refineries, electronic parts is most impressive in its scope. But I note, with wry s a t i s f a c t i o n , that the lampmaker's use of rare earths is v i s u a l l y the most spectacular of all -- that of generating brilliant colored l i g h t s to see by. The rare earth ion being a sheltered place, inside, safe from disrupting influences of its environment, it can take a bit of absorbed energy, shape it, and spit it out in one of the purest forms of v i s i b l e l i g h t we know. These pure, brilliant, colored l i g h t s (termed spectral colors or spectral lights)show enormous promise for general illumination. What I would l i k e to do is to extend the description of phosphors, of the previous paper, to modern l i g h t i n g . Not long after the turn of the century, one of the magnificent red-emitting luminescent materials, activated by the rare earth europium, was discovered(1). I t s b r i l l i a n t red-orange l i g h t has a s p e c t r a l power d i s t r i b u t i o n as i n F i g u r e 1A. From that day to t h i s , no more e f f i c i e n t r a r e e a r t h m a t e r i a l f o r generating commercial l a m p l i g h t has ever been produced, and europium has r e c e n t l y begun to p l a y a major r o l e i n l i g h t i n g human a c t i v i t i e s a l l over the world. Generating b r i l l i a n t c o l o r e d l i g h t s i s e s s e n t i a l t o the lampmaker, because the white l i g h t he s e l l s i s composed o f a mixture of b r i l l i a n t c o l o r e d l i g h t s , and because he i s beginning to understand which c o l o r e d l i g h t s are most important to human v i s i o n . Some hundred and f i f t y s p e c t r a l l i g h t s are d i s t i n g u i s h a b l e by the normal human observer. They a r e , o f course, f a r from e q u a l l y e f f e c t i v e i n a i d i n g the human v i s u a l system to f u n c t i o n w i t h maximum e f f i c i e n c y . The v i s u a l system has three independent i n p u t s , a l l o w i n g i t to s o r t incoming l i g h t s i n three dimensions. There must be three independent s p e c t r a l responses, a s s o c i a t e d w i t h these i n p u t s , each s p e c t r a l response sampling a d i f f e r e n t r e g i o n o f the v i s i b l e spectrum, although there may be a great d e a l o f overlap between p a i r s o f responses. Each s p e c t r a l response may be c h a r a c t e r i z e d by 0097-6156/81/0164-0195$05.00/0 © 1981 American Chemical Society In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Figure 1.

400

500

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ELEMENTS

X)0 NM

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The brilliant orange-red emission of Eu * (A), contrasted to the bluishwhite spectral power distribution of average daylight (B)

80

60

40 CRI

20

0

-20 400

500 600 WAVELENGTH - NM

Figure 2. The color-rendering index (CRI), of similarity to daylight-rendering, dependence upon choice of triad of spectral lights to form white light of daylightcolor. Wavelengths of two components are fixed at their peaks, and the wavelength of the third component is varied. Optimum combination appears in Figure 3.

Figure 3. The three pure spectral colors, the "prime-colors," uniquely related to normal human vision. Combined, as shown here, they form a white-light mixture the color of sunlight.

_j J I • LA 400 500

iL_l 600 NM

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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a s i n g l e wavelengthC2,3)marking i t s peak, o r mean, s e n s i t i v i t y ; t h e r e s u l t i n g three wavelengths expectably p l a y a unique r o l e i n human v i s i o n , and the s p e c t r a l l i g h t s corresponding t o them may do the same i n i l l u m i n a t i o n . We name these wavelengths the " p r i m e - c o l o r s " o f human v i s i o n (A), and ask where i n the v i s i b l e spectrum they l i e . I f a r t i f i c i a l white l i g h t o f d a y l i g h t c o l o r i s composed o f t r i a d s o f s p e c t r a l l i g h t s , one soon f i n d s that the c o l o r - r e n d e r i n g o f such mixtures v a r i e s from very poor t o very good. E v e n t u a l l y i t i s found how c r i t i c a l the choice i s , that three s p e c i f i c wavelengths are necessary f o r greatest s i m i l a r i t y t o r e a l - d a y l i g h t - r e n d e r i n g , that the c o l o r - r e n d e r i n g o f t h i s unique t r i a d i s very good indeed ( b e t t e r than that o f most commercial lamps marketed), and that d e v i a t i o n i n wavelength from any one o f the three optimum s p e c t r a l l i g h t s r e s u l t s i n r a p i d d e t e r i o r a t i o n o f c o l o r - r e n d e r i n g o f the w h i t e l i g h t mixture(2_ 5) . The f i n a l i t e r a t i o n i s shown i n F i g u r e 2,where two o f the wavelengths are s e t a t optimum v a l u e s and the t h i r d wavelength i s v a r i e d . For each t r i a d , the c o l o r - r e n d e r i n g index (CRI, an index o f s i m i l a r i t y t o d a y l i g h t - r e n d e r i n g ) i s computed(60. I see no e x p l a n a t i o n o f F i g u r e 2 other than that the unique wavelengths mark the mean s e n s i t i v i t i e s o f the three v i s u a l r e s ponses, and can be thought o f as the "sampling p o i n t s " o f the v i s u a l system. I n any case, the w h i t e - l i g h t mixture o f F i g u r e 3, which i s about the c o l o r o f s u n l i g h t , renders the c o l o r o f complexions, foods, c l o t h i n g , f u r n i s h i n g s , p l a n t s , animals, and m i n e r a l s a s t o n i s h i n g l y w e l l , i . e . p l e a s a n t l y and expectably. The widths o f the components can be narrowed without l i m i t , u n t i l almost a l l o f the v i s i b l e spectrum i s empty. Yet moving one o f the components f i f teen nanometers can be d i s a s t r o u s . The c o l o r o f such p r i m e - c o l o r l i g h t may be v a r i e d by a l t e r i n g the r a t i o o f power i n the three components, t a k i n g care not t o a l t e r the mean wavelength o f any component. In a d d i t i o n t o s i m i l a r i t y t o d a y l i g h t - r e n d e r i n g , p r i m e - c o l o r white l i g h t y i e l d s an i l l u m i n a t e d scene which i s p e c u l i a r l y a t t r a c t i v e (_7) shows p e c u l i a r " v i s u a l c l a r i t y " ( 8 ^ , 1 0 ) ,and h i g h p e r c e i v d b r i g h t n e s s per f o o t c a n d l e ( l l ) . Other p s y c h o p h y s i c a l evidence(2,J3, 12,13)suggests t h a t the s p e c t r a l response o f the human v i s u a l s y s tem i s approximated by the dashed envelope o f F i g u r e 4; the three peaked responses are independent although o v e r l a p p i n g . The s o l i d curve i s the t r a d i t i o n a l luminous e f f i c i e n c y f u n c t i o n , a l l o w i n g only one-dimensional v i s i o n , o p e r a t i v e only under uncommon v i s u a l c o n d i t i o n s , y e t wrongly p r e s i d i n g over lamp development f o r more than s i x t y y e a r s . A modern o b j e c t i v e i s t o feed l i g h t i n g power i n t o the v i s u a l system a t i t s peaks o f response, as does the white l i g h t o f F i g u r e 3, f o r example. T h i s a r e v o l u t i o n a r y turnabout from t r a d i t i o n a l views o f how commercial l a m p l i g h t should be designed; the d a y l i g h t i n which we presumably evolved i s a continuum(Figure IB) as are f i r e l i g h t and l i g h t from the o i l lamp and the incandescent lamp. The primary use o f l a m p l i g h t i s t o l i g h t human a c t i v i t i e s , and i t i s h i g h time the l a m p l i g h t i s designed f o r the human v i s u a l system. 9

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Generating b r i l l i a n t c o l o r e d l i g h t s l i k e the components of F i g u r e 3 i s something r a r e earths can o f t e n do as no other m a t e r i a l s can. I d e a l l y , the components of l a m p l i g h t should comprise very narrow bands centered near 450nm, 535nm, and 615 nm. V a r i a t i o n of mean wavelength of one of the components by +5nm has l i t t l e d e l e t e r i o u s e f f e c t , but more than t h a t r e s u l t s i n r a t h e r r a p i d degrada t i o n of the v i s u a l e f f i c i e n c y of the l a m p l i g h t . P a r t i c u l a r l y to be s c r u p u l o u s l y avoided, i n the i d e a l case, are the " a n t i p r i m e " c o l o r s , v i o l e t , blue-green, y e l l o w and deep-red. Europium 3+ i s made to order f o r the red-orange p r i m e - c o l o r . The c r y s t a l p l a y i n g host to the europium i m p u r i t y must, however, s t r o n g l y f a v o r the ^ D Q — F e l e c t r i c d i p o l e t r a n s i t i o n , which y i e l d s s t r o n g emission i n the wavelength range 612-618nm. Some c r y s t a l s h o s t i n g Eu 3+ a l l o w magnetic d i p o l e t r a n s i t i o n s and thus strong yellow-orange emission near 590nm, and are u n s u i t a b l e ( 1 4 , 1 5 ) . The u s e f u l e l e c t r i c d i p o l e t r a n s i t i o n s are favored by oxygen-domi n a t e d l a t t i c e s ( s m a l l i o n , l a r g e charge). Perhaps the best luminescent m a t e r i a l of t h i s type, at l e a s t f o r use i n f l u o r e s c e n t lamps, i s Y2O3:Eu^ (Figure I A ) . A c h i e v i n g a p r i m e - c o l o r s p e c t r a l power d i s t r i b u t i o n l i k e t h a t of F i g u r e 3 r e q u i r e s good c o n t r o l of the e m i t t i n g species i n the commercial lamp. At p r e s e n t , the f l u o r e s c e n t lamp o f f e r s the best c o n t r o l . The v i s i b l e c o n t r i b u t i o n of i t s arc i s so f a r i n t r a c t a b l e but amounts to only a few percent of v i s i b l e output. The r e s t d e r i v e s of course from luminescent m a t e r i a l s which convert 254nm r a d i a t i o n from the mercury a r c , to u s e f u l l i g h t . The problem i s t h e r e f o r e to provide e f f i c i e n t luminescent m a t e r i a l s which emit the p r i m e - c o l o r s , p r e f e r a b l y one phosphor per p r i m e - c o l o r f o r ease i n c o l o r adjustment of the r e s u l t i n g l a m p l i g h t . Quantum e f f i c i e n c y ( v i s i b l e photons emitted per 254nm photon absorbed)must be 0.8-0.9 i n order to stay i n the f i e r c e l y c o m p e t i t i v e f l u o r e s c e n t lamp market. So Y 2 0 3 i E u ^ i s , except f o r i t s h i g h c o s t , not f a r from i d e a l as a photoluminescent orange-red prime-color generator. What about the b l u e - v i o l e t , and the green, prime-colors? The w r i t e r knows of no r a r e e a r t h i o n , i n any host c r y s t a l , which i s s t r o n g l y photoluminescent and emits a narrow band i n the b l u e - v i o l e t centered at 45tH5nm. Thulium 3+, i n YVO^ f o r example, emits near 475nm, which i s too g r e e n i s h . Praseodymium, even given an a p p r o p r i a t e host c r y s t a l , would probably be too green i n i t s emission a l s o . However, d i v a l e n t r a r e e a r t h ions can emit s t r o n g bands of r a t h e r pure v i s i b l e l i g h t , although i n t e r a c t i o n w i t h the c r y s t a l environment broadens the emission band f a r more than i s c h a r a c t e r i s t i c of t r i v a l e n t r a r e e a r t h emission. There are a number of host c r y s t a l s , perhaps the best of which i s s t r o n t i u m c h l o r a p a t i t e ( 1 6 ) , f o r d i v a l e n t europium. I t s emission spectrum appears i n F i g u r e 5A. Quantum e f f i c i e n c y i s c l o s e to 0.9, and f o r t u n a t e l y the emission band, w h i l e not i d e a l , feeds i n t o the human system w i t h great v i s u a l e f f i c i e n c y . I t i s the best we have, at any r a t e . I f a r a r e 7

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Figure 4. The three-peaked spectral response of the human visual system, the peak responses being marked by the prime-colors: ( ) the luminous efficiecy curve upon which much of modern lighting is wrongly based.

Figure 5. The brilliant blue-violet emission of Eu * (A), and the green emission of zinc silicate activated by Mn * (B). 2

2

Figure 6. The spectral power distribution of a fluorescent lamp containing two rare earth phosphors, those of Figures 1 (Curve A) and 5 (Curve A), and greenemitting zinc silicate:Mn. A closer approximation to Figure 3 is desirable.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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RARE E A R T H

ELEMENTS

earth-host c r y s t a l combination could be found, which concentrates i t s emission more c l o s e l y around 450nm, i t would be welcome indeed. The s i t u a t i o n i n regard to the green prime-color i s not as s a t i s f a c t o r y . T r i v a l e n t terbium, holmium and erbium have t r a n s i t i o n s i n the d e s i r a b l e wavelength r e g i o n s , but the l a s t two have not y e t been developed i n e f f i c i e n t photoluminescent m a t e r i a l s , and terbium has s p e c i a l problems. We need a narrow emission near 530nm o r 540nm, uncontaminated with s a t e l l i t e emission i n unwanted regions, p a r t i c u l a r l y the yellow. Terbium ions i n c e r t a i n c r y s t a l s make very f i n e phosphors(17), p o s s i b l y unmatched i n e f f i c i e n c y and ruggedness. (The mercury a r c i s a small i n f e r n o , and these i n o r ganic m a t e r i a l s have to be robust.) But terbium always, or at l e a s t so f a r , b r i n g s with i t sidebands i n the yellow and b l u e green. These r a p i d l y degrade the c l a r i t y and c o l o r a t i o n o f a scene i f they are present i n the white l i g h t i l l u m i n a t i n g the scene. So we have had to s t i c k with an o l d and trustworthy phosphor, z i n c s i l i c a t e : M n ^ , to provide our green emission(Figure 5B). I t i s not, however, q u i t e narrow enough, nor rugged enough. I would l i k e to take t h i s opportunity to ask, very s e r i o u s l y , f o r any help readers can give toward i d e n t i f y i n g an e f f i c i e n t pure-greene m i t t i n g luminescent m a t e r i a l . A new phosphor of that s o r t could have a profound e f f e c t on the q u a l i t y o f l i g h t i n g around the world. Hopefully some one o f the r a r e earths could help to b r i n g t h i s about. +

The s p e c t r a l power d i s t r i b u t i o n o f Figure 6 i s as c l o s e as we can p r e s e n t l y get to the i d e a l prime-color mixture. In summary, lamplight i l l u m i n a t e s human a c t i v i t i e s , so lamp phosphors should feed t h e i r l i g h t i n t o the human v i s u a l system with h i g h v i s u a l e f f i c i e n c y . R a r e - e a r t h - a c t i v a t e d phosphors tend to produce narrow, s t r o n g l y s a t u r a t e d , b r i l l i a n t l y c o l o r e d l i g h t s . I t begins to appear that r a r e earth emission i s not only u s e f u l , but made-to-order, f o r the requirements o f the human v i s u a l s y s tem f o r optimum seeing. The v i s u a l system has three w e l l - d e f i n e d peaks o f response, placed at three wavelengths unique to human v i s i o n . When white lamplight i s composed as n e a r l y as p o s s i b l e o f these three pure s p e c t r a l c o l o r s , and the remainder of the v i s i b l e spectrum i s l e f t as n e a r l y empty as p o s s i b l e , at l e a s t four strong p o s i t i v e v i s u a l e f f e c t s r e s u l t : The perceived b r i g h t n e s s per watt of lamplight exceeds that o f normal i l l u m i n a n t s by tens of percent. The v i s i b i l i t y o f a scene per watt of lamplight increases by l a r ger f a c t o r s s t i l l . C l a r i t y , i n the sense o f sharpness of d e t a i l i n a scene, i s enhanced. A t t r a c t i v e n e s s o f c o l o r a t i o n , measured i n terms o f what Judd c a l l e d " p r e f e r r e d c o l o r a t i o n " , exceeds that of d a y l i g h t , which i t s e l f excels normal i l l u m i n a n t s . The three spectr a l c o l o r s so important to human v i s i o n are: b l u e - v i o l e t near 450nm, green near 535nm, and orange-red near 615nm. The f i r s t and l a s t o f these c o l o r e d l i g h t s are f a i r l y s a t i s f a c t o r i l y s u p p l i e d by lamp phosphors a c t i v a t e d by europium 2+ and europium 3+, r e s p e c t i v e l y . The need f o r a b e t t e r pure green emission i s acute.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch011

11.

THORNTON

Lamp

Phosphors

201

Literature Cited 1. Urbain,G.,Ann.Chim.Phys.,1909,18,294. 2. Thornton,W.A.,J.Opt.Soc.Amer.,1971,61,1155. 3. Thornton,W.A.,J.Opt.Soc.Amer.,1972,62,457. 4. Thornton,W.A.,Westinghouse Engineer,1972,32,170. 5. Thornton,W.A.,J.I11.Eng.Soc.,1979,8,78. 6. CIE Pub.#13,E-l.3.2,1965,1st Ed. 7. Thornton,W.A.,J.I11.Eng.Soc.,1974,4,48. 8. Aston,S.N.,Bellchambers,H.E.,Lighting Res.Tech.,1969,1,259. 9. Bellchambers,H.E.,Godby,A.C.,Lighting Res.Tech.,1972,4.,104. 10. Thornton,W.A.,Chen,E.,J.I11.Eng. Soc.,1978,7,85. 11. Thornton,W.A.,Chen,E.,Morton,E.W.,Rachko,D.,J.I11.Eng.Soc., (in press). 12. Thornton,W.A.,J.Color Appearance,1973,II,23. 13. Thornton,W.A.,Lighting Pes.Appl.,1975,5,35. 14. Palilla,F.C.,Electrochem.Tech.,1968,6,39. 15. Blasse,G.,Bril,A.,Philips Tech.Rev.,1970,31,304. 16. Wachtel,A.Netherlands Patent 6906724,1969. 17. McAllister,W.A.,J.Electrochem.Soc.,1966,113,226. RECEIVED

January 8,

1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

12 Rare Earth X-Ray Phosphors for Medical Radiography JACOB G. RABATIN

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

Quartz and Chemical Products Department, General Electric Company, 1099 Ivanhoe Road, Cleveland, O H 44110

When a uniform flux of x-ray photons passes through an object, a radiologic image is formed of the object parts. In order to be viewed, this radiologic image must be converted into an optical image by means of inorganic crystalline phosphors which are disperesed in polymeric screens. The optical image can be viewed directly by means of fluoroscopic screens. However, in general radiological practices, the optical images are recorded on films which are subsequently viewed by radiologist. Without these x-ray intensifying screens, modern radiology would be impossible. The general physical aspects of diagnostic radiology have been thoroughly covered by M. Ter-Pogossian (I). For many years, most intensifying screens contained CaWO phosphors. After numerous improvements in CaWO efficiencies and particle shapes, a plateau was reached for the speed of these screens in recording satisfactory radiologic images. In recent years, several new phosphors were discovered which contain rare earth elements and are considerably more efficient under x-ray excitations. T h e s e n e w r a r e e a r t h p h o s p h o r s 4

include: L a 0 S : T b (2), G d 0 S : T b (2,3), BaFCIiEu (4,5), LaOBr:Tm (7). Several physical properties of these x - r a y p h o s p h o r s h a v e i m p o r t a n t effects o n t h e final image q u a l i t y as viewed b y the radiologist. These physical properties include x - r a y a b s o r p t i o n , c o n v e r s i o n efficiency, emission c h a r a c t e r i s t i c s , absolute d e n s i t y , particle size a n d shape a n d r e f r a c t i v e i n d e x . T h e p u r p o s e o f this p a p e r is to d e s c r i b e a n d c o m p a r e t h e s e p r o p e r t i e s f o r s e v e r a l p h o s p h o r s a n d to indicate d e s i r e a b l e p r o p e r t i e s n e e d e d i n f u t u r e more ideal x - r a y p h o s p h o r s . 2

2

2

2

Experimental Materials. A l l phosphors used in this study were p r e p a r e d b y solid state methods p r e v i o u s l y r e p o r t e d . LaOBr:Tb a n d L a O B r : T m p h o s p h o r s were p r e p a r e d b y a molten K B r flux r e c r y s t a l l i z a t i o n m e t h o d (8) w h i c h g i v e s c l e a r , s i n g l e c r y s t a l

0097-6156/81/0164-0203$05.00/0 © 1981 American Chemical Society

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

204

RARE E A R T H

particles

that have

activated

BaFCI

pheres can

(4).

The

resulting

be p r e p a r e d

La 0 S:Tb 2

and

2

method

as plates

crystal

particles when

Gd 0 S:Tb 2

involving

stallization

plate-like

habits.

phosphors were prepared

media.

polysulfides,

europium

reducing

irregular

an alkali

in

atmosshape

chloride flux

were prepared

2

alkali

are

Divalent

in

by

Na C0 2

a high and

3

These phosphor crystals

is

but

used.

temperature

sulfer

have

ELEMENTS

as

recry-

polyhedral

shapes. Screen fying

Preparations.

screens were prepared

techniques.

The

final

ings were d r i e d .

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

were prepared

In

100 m i c r o n t h i c k using standard

phosphor volume

most

instances,

using polyvinyl

butyral

to

care

t a k e n to a v o i d c o n v e c t i o n cell

section of the completed thick,

a

the

screen construction

50 m i c r o n t h i c k

micron

thick

acetate

butyrate

(Ti0

phosphor layer, top

is s h o w n

coat-

viscosities

(9).

and

A

in F i g u r e

(Mylar)

cross

I.

The

base about

reflector

a 10 m i c r o n t h i c k

protective

with

blade operation

formation

(rutile)

2

coating

the

phosphor suspensions

doctor

screens consist of polyester

intensi-

blade

50% w h e n

binders

adjusted was

2000 c e n t i p o i s e f o r

was

the

x-ray

doctor

layer, clear

a

10

mil.

100

cellulose

layer.

Measurements. Emission S p e c t r a . were obtained phosphor The tus

using cathode

powders

were uniformly

samples were excited w i t h 10 k i l o v o l t s

demountable meter

for

and

apparatus

shown

based on found

in

the

in t h e

fundamental

emission

absorption i/io

on conductive cathode

energetic

Data.

= e -

y

The

p

Israel for

x

ray

glass. appara-

electrons.

The

spectrophoto-

x-ray

absorption

using a computer

coefficients,

equation

14

spectra

purpose,

spectra.

2 were obtained

of Storm a n d

emission

For this

was c o u p l e d to a C a r y

mass a b s o r p t i o n paper

settled

7 microampere

Absorption

Figure

resolution

excitation.

in a demountable

r e c o r d i n g of the X-Ray

data

High

ray

(I0J)

x-rays

y,

program

total e n e r g y ,

and

using

as

the

(II).

(D

where l is the i n c i d e n t x - r a y b e a n , I is the t r a n s m i t t e d beam, p is the p h o s p h o r d e n s i t y a n d x is its t h i c k n e s s . T h e computer p r o g r a m i n c l u d e s a p p r o p r i a t e c h a n g e s in the e n e r g i e s o f t h e x r a y s p e c t r a a f t e r p a s s a g e o f 80 K V p e a k x - r a y s t h r o u g h a 10 inch human body equivalent absorption before impinging on the x-ray screens. T h e t h i c k n e s s x w a s s e t e q u a l t o 100 m i c r o n s (typical of x - r a y s c r e e n s ) . Not included are c o r r e c t i o n s for the e s c a p e o f some s e c o n d a r y r a d i a t i o n . T h e s e corrections are d i f f i c u l t to make a c c u r a t e l y (12). 0

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

RABATIN

X-Ray

Phosphors

for Medical

Radiology

205

SCREEN BASE-

PHOSPHOR

LAYER-

CLEAR LAYERFILM EMULSIONFILM BASE -

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

FILM EMULSIONCLEAR LAYERPHOSPHOR LAYERREFLECTOR SCREEN BASE-

Figure 1.

Cross section of x-ray screens and film assembly

Figure 2. Relative x-ray absorptions of 100-micron thick x-ray screens using a filtered 80 KV peak x-ray beam

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

206

RARE E A R T H

Relative surements a Faxitron

x-ray

DuPont

one u s i n g green Co.

Par

CaWOi*

green

3.

It

other

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

about

blue

hand,

480

for

noted

inch

body

using

aluminum

equivalent

speeds were

to set

commerequal

For phosphors Ortho

typical

G green

medical

films

blue emitting

or

blue

in medical

no effect

on

3M

film. are

shown

phosphors

sensitive blue

to

with

were used including

Co.

that

green

mea-

films.

emitting p h o s p h o r s with emissions

practically

used

One

film.

Kodak

curves

speed

settings

were compared

medical

either

green

nm h a v e

most commonly

exposures.

s e n s i t i v e films

should be

screen beam

a 10 i n c h h u m a n

film a n d

will e x p o s e e f f i c i e n t l y the

All

x-ray

screens whose

BB-54

log sensitivity

Figure

peak

for

simulate

emissions, green XM

KV

speed measurements

Kodak

brand

Relative in

All

80

apparatus

f i l t e r s w e r e u s e d to absorption. cial

Screen Speeds.

w e r e m a d e at

ELEMENTS

On above

sensitive

films

radiography.

Image Q u a l i t y . Resolution of screens were meas u r e d a t 50 K V p e a k x - r a y e x p o s u r e s a t f i l m d e n s i t i e s o f 1.0 u s i n g s t a n d a r d lead resolution g r i d s with sets of etched lines a b o u t I l i n e p a i r p e r mm u p t o 15 l i n e p a i r s p e r m m . The results are p e r mm.

reported

Other were measured measurements

by

as the

maximum

Measurements.

the

Coulter

w e r e made

set o f line

Particle

Counter

u s i n g the

pairs

size

method.

well k n o w n

resolved

distributions Absolute

density

pycnometer

method. Results and

form

Discussions

A t f i r s t g l a n c e , x - r a y i n t e n s i f y i n g s c r e e n s a p p e a r to p e r a simple f u n c t i o n o f c o n v e r t i n g x - r a y p h o t o n s to l i g h t

p h o t o n s w h i c h e x p o s e t h e film s a n d w i c h e d between two s c r e e n s ( S e e F i g u r e I). H o w e v e r , x - r a y s c r e e n s s e r v e a m u c h more important f u n c t i o n of faithfully c o n v e r t i n g radiologic images into optical images w h i c h a r e s u b s e q u e n t l y r e c o r d e d as p h o t o g r a p h i c images. T h e s e several complex processes are graphically illus t r a t e d in F i g u r e I a n d c a n be d e s c r i b e d as follows. After p a s s i n g t h r o u g h a b o d y p a r t , a beam o f x - r a y p h o t o n s c o n t a i n s useful information. A small f r a c t i o n , n , o f t h i s beam is a b s o r b e d b y t h e p h o s p h o r p a r t i c l e s in t h e x - r a y s c r e e n s p r o d u c i n g a radiologic image. A fraction of this absorbed energy a

is c o n v e r t e d i n t o a n o p t i c a l i m a g e o f u l t r a v i o l e t - v i s i b l e l i g h t with an e n e r g y efficiency given b y r i c - A f t e r multiple scatteri n g a n d a b s o r p t i o n e v e n t s , a f r a c t i o n , nt# of this light reaches t h e f i r s t e m u l s i o n o f t h e d o u b l e e m u l s i o n film u s e d in medical radiography. A m a j o r f r a c t i o n , r\f\, o f t h i s l i g h t is a b s o r b e d b y the first silver halide emulsion which on development p r o d u c e s a p h o t o g r a p h i c image. A s i g n i f i c a n t f r a c t i o n , nf , ° f t h i s l i g h t c r o s s e s o v e r to t h e s e c o n d e m u l s i o n a n d is a b s o r b e d . 2

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

RABATIN

Figure 3.

X-Ray

Phosphors

for Medical

Radiology

207

Blue and green x-ray film sensitivities to ultraviolet and visible light

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

208

RARE E A R T H

This

c r o s s - o v e r p h e n o m e n o n d e g r a d e s t h e image d u e to s p r e a d -

ing

of the light.

the

radiologic image

Other

processes which

include:

Several attempts phosphor noise

efficiencies

(12,J6,17,18).,

quality

(20 2TJ.

phosphors

(I3_, I4_,I5_), x - r a y

absorption a n d quantum

screen performance

(I4,I6,I7,J8,I9_) a n d i m a g e

studies adequately

In t h i s

to final

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

image q u a l i t y

study,

primary

emphasis is g i v e n to

X-Ray Absorption.

(I). 7

noise *

1

T h e s e fluctuations a n d as "quantum

films s i n c e t h e films h a v e a g r a i n y fluctuations

= ^pr

energies must

a r e often

mottle"

about

400 x - r a y

20.

in F i g u r e

photons.

2

area.

T h u s t h e signal to

T o increase t h e signal to noise

filtered

the relative

ratio

x-ray ab-

s c r e e n s u s i n g a n 80 K V p e a k In t h e i n c i d e n t b e a m

photon energies a r e between

Since these photons a r e more readily more desireable c o n t r a s t s r e s u l t .

Also

regard,

about

with

K-edge

35 a n d 50 K e V ( Z f r o m

a

ab-

greater

be only achieved with cations h a v i n g

small ionic r a d i i

most o f t h e s e

region,

absorption The

6.0 which c a n

O n l y a small n u m b e r o f u s e f u l x - r a y

h a v e b e e n d i s c o v e r e d w h i c h meet

in this

55 t o 6 5 ) .

s h o u l d h a v e a h i g h d e n s i t y o f at least

and G d .

parts,

the K

since a

p h o s p h o r with high y

p h o s p h o r should contain elements

phosphor

profile,

p h o t o n s a r e a b s o r b e d a s c o m p a r e d to

for a good x - r a y

energies between

beam

40 a n d 50 K e V .

absorbed by body

In t h i s

sorption edges o f L a a n d B a a r e more useful fraction of these x - r a y

x-ray

b y o n e i n c h a l u m i n u m t o s i m u l a t e a 10

inch human body absorption.

La

According

2 are the calculated absorption curves for

100 m i c r o n t h i c k

most o f t h e x - r a y

the

These

photons of -70 K e V

screen thickness a n d speed,

which h a s been

Gd.

(I7_).

must be i n c r e a s e d .

Shown several

to

viewed o n

b e a b s o r b e d b y a C a W O i * s c r e e n to p r o d u c e a

is a b o u t

for a given sorption

referred

when

appearance

by

form the

(2)

d e n s i t y o f 0 . 6 f o r a 0.1 m m

noise ratio

amount o f

in part,

photons that

N is the number of absorbed x - r a y

t o C l e a r e e t a l (I8_) film

contribute speed a n d

c a n b e e x p r e s s e d a s a signal to noise ratios (12).

o where

is limited,

fluctuations of the x - r a y

image

"quantum

which

regarding

T h e maximum

c o d e d in a r a d i o l o g i c image

statistical

radiologic

screen performance

characteristics.

Intrinsic

as

quanti-

simple comparative analyses c a n be made o f t h e

used.

information

covers the

screens o r is sufficiently

evaluation o f measurable phosphor properties significantly

account

screen performances including;

complete performance o f x - r a y tative so that

degrade

a n d rjfj.

h a v e been made to q u a n t i t a t i v e l y

None o f these

#

significantly

Hfl*

r i o ^t'

for various aspects of x - r a y

the

ELEMENTS

such as

phosphors

criteria.

Listed in Table I a r e the absolute densities,

relative

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

x-ray

RABATIN

12.

X-Ray

Phosphors

a b s o r p t i o n s o f 80 K V p e a k nal

to noise ratios

phosphors. data

these

x-rays

thickness,

images

to noise ratios

e t al (18)

ratios

a n d equation

209

Radiology

at equal

for the radiologic

T h e signal

of Cleare

later,

for Medical

and sig-

for several

x-ray

were calculated 2.

using the

A s will b e d i s c u s s e d

will d e c r e a s e a s s c r e e n s p e e d s , e t c . a r e i n -

cluded. TABLE Absolute

Densities,

Relative

Radiologic

Image S i g n a l

Ratios o f Several

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

I X-Ray

X-Ray

Absorptions and

to Noise Phosphors

Signal

Relative Phosphor

Density

Noise

X-Ray Abs.

CaWOjj

6.1

1.0

20

BaFCI :Eu

4.7

I.I

21

7.3

1.7

26

L a O B r . 002Tb

6.3

1.9

28

LaOBr.003Tm

6.3

1.9

28

La 0 S:Tb

5.9

1.7

26

G

d

2 ° 2

2

S

:

T

b

2

The

results

in T a b l e

will b e s i g n i f i c a n t l y as

compared

must

to C a W O i * .

be used

absorption.

I indicate

improved

in t h i c k e r In g e n e r a l ,

B e c a u s e o f its lower thicker

Emission S p e c t r a . spectra of several examine x-ray

briefly

films.

F o r many

screens have

x-ray

years,

to be most

to by

absorption

improve

light

blue

such parameters

properties. phors,

as grain

In o r d e r

green

coupled system. of blue a n d green

quire that

blue

special safe

it is u s e f u l

sensitive x - r a y

2

Figure x-ray

a n d other

2

2

has high were

3 shows typical films.

Green

in the d a r k

rooms.

emulsion

emission spectra

shown

in Figures

phos-

using a d y e -

relative

sensiti-

films h a v e It

needed

primarily

2

films were d e v e l o p e d

film in s p e e d o r r e s o l u t i o n . lights

have

speeds were adjusted

Green

no a d films

should be

b l u e e m i t t i n g p h o s p h o r s will also e x p o s e g r e e n The

films

Since A g B r

size o f A g B r

to

with

ultraviolet-blue

no special efforts

Film

sensitive x - r a y

vities

over

the emission

to u s e G d 0 S : T b a n d L a 0 S : T b

AgBr

vantages

region,

absorption.

resolution.

of the p h o s p h o r emission

s e n s i t i v e to t h e

in this

BaFCI :Eu x-ray

poorer

phosphors,

emissions o f phosphors s u c h as C a W O i * . intrinsic

image phosphors

density,

to increase

Before comparing

important

the interaction

been developed

that the radiologic

b y the use of rare earth

screens in o r d e r

to Ratio

re-

noted

film.

4 through

7 were

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

210

RARE E A R T H

ELEMENTS

UJ

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

cr

WAVELENGTH (nm)

Figure 4.

Emission spectrum of LaOBr.003Tm

under CR excitation

600

WAVELENGTH (nm)

Figure 5.

Emission spectrum of LaOBr.002Tb

under CR excitation

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

RABATIN

X-Ray

500

400

Figure 6.

Phosphors

for Medical

Radiology

WAVELENGTH (nm)

600

Emission spectrum of GD O S.005Tb 2

350

2

400 WAVELENGTH (nm)

700

under CR excitation

450

Figure 7. Emission spectrum of BaFCI.05Eu under CR excitation

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

212

RARE E A R T H

obtained spectra used

using cathode practically

(I5_).

Figure

L a O B r . 003Tm where the

(22).

The

2

to

with green

screens and Shown

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

At

in

occur

at

380,

sitive

films.

This in

'

500

Picker

nm w h i c h

Spectra

comparable

Co.

Quanta

At

higher

20% c o m p a r a b l e

to

emitting phosphors are

for

III

L a O B r . 002Tb

principal

emissions

be used with blue

screens and

Co.

green

sig-

LaOBr.003Tm

sen-

u s e d in A g f a - G e v a e r t

e m i s s i o n s p e c t r a emit p r e d o m i n a n t l y of about

the

can

the

These

screens.

Since

phosphor

Lanex.

emission spectrum

concentrations,

440

nm

unsharp-

I).

this

with speeds DuPont

tric

efficiencies

Figure nm,

400

less

are

for

screens.

p h o s p h o r is b e i n g

B l u e Max

n

(nf2 and

u s e d in

Rapide

5 is the

terbium

415 a n d

screens,

being

below

greatest,

s e n s i t i v e films

Ltd.

Figure

these

460

emission excitations

emission spectrum

s c r e e n s s u c h as K o d a k

currently

11 f o r d

give

x-ray

emissions are

less c r o s s over

2

phosphors are

MR

principal

e m i s s i o n s a l s o o c c u r at

is a l s o u s e f u l

which

to t h o s e w h e n

film a b s o r p t i o n s a r e

to G d 0 S : T b g r e e n

(23).

excitations

4 shows a typical

intrinsic

ness occurs due nificant

ray

identical

ELEMENTS

in t h e

terbium

Co.

General

Elec-

concentrations,

green

at

542

nm

with

Z n C d S : A g phosphors

suitable

for

green

(24).

sensitive

films. Figure The

6 shows the

principal

trations,

the

with green

Lanex

green

in

divalent nm.

This

To

be

phosphors 1)

suitable

is u s e f u l

must

listed

in T a b l e

La 0 S:Tb 2

the

film

to a b o u t

6% f o r

application

efficiency

to u s e f u l

n

=

%

\

n

t

is

used

in

Co.

green

Co.

Kodak

screens.

for

BaFCI.05Eu.

peaking Quanta

The

screens,

rare

about blue

earth (n

in

c

absorptions of x - r a y s several

rare earth

conversion efficiencies 20% f o r

at II

only.

intrinsic

I have

LaOBr :Tb

from

and

phosabout

(5,26,24)

as com-

CaWOi*. Systems.

of x - r a y

energy

nm.

h i g h c o n v e r s i o n efficiencies

to h i g h

with which

light

concen-

440

phosphor

band

in D u P o n t

intensifying

to a b o u t

2

Screen-Film to t h e

with blue

also have

in addition

Trimax

2

This

emission spectrum

is u s e d

in x - r a y

2

Tb

415 a n d

is b e i n g

3 M Co.

Gd 0 S.005Tb.

lower

380,

e m i s s i o n is a b r o a d

phosphor

used

in

7 is the

for

At

decreases.

emission characteristics.

10% f o r pared

Figure

europium

screens and

phors

nm.

sensitive films a n d

screens and

Shown

Figure

542

phosphor efficiency

useful

380

at

some e m i s s i o n s will o c c u r at

However,

The

emission spectrum

emissions are

A c c o r d i n g to L u d w i g

phosphors for the

incident

as g i v e n

(

3

by

the

(5),

intensifying

x-ray

energy

is

crucial

screens

is

converted

expression:

)

w h e r e nt the e f f i c i e n c y with which the light e n e r g y is t r a n s mitted t h r o u g h t h e s c r e e n to t h e f i l m . T h e processes n a n d ric have been d i s c u s s e d . T h e transmission, scattering and absorpt i o n p r o c e s s e s , r]^, a r e e x t r e m e l y c o m p l e x i n v o l v i n g s u c h p a r a i

s

a

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

RABATIN

12.

meters

X-Ray

as particle

Phosphors

size,

particle

dispersion and structure

for

Presently

(I8_,

these processes individually.

transfer

function

measurements

refractive

25).

the quality

no measurements

213

Radiology

shape,

mottle

these processes degrade image.

for Medical

index,

particle

A s indicated

of the original c a n be made

radiographic

which

Comparisons using i n v o l v e all image

earlier, account

modulation

degrading

p r o c e s s e s (l_, 21). Table phors

II

lists several

fractive

index

should be fairly

(polymer

Rl "1.5)

creased.

In t h i s

the number respect,

t u r e mottle a n d i m p r o v e hedral

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

physical properties

a s c o m p a r e d to those f o r a n ideal

shaped particles

phosphor Finally,

packing,

average

quality.

In a d d i t i o n

low s o t h a t

phenomena

B a F C I : E u is b e s t .

particle

T o reduce Further,

distributions

sizes between

system

are d e struc-

spherical or poly-

a r e most d e s i r e a b l e .

narrow

phos-

The re-

in a polymeric

of scattering

phosphor packing,

particle

Clearly

of various

phosphor.

to

improve

are best.

5 a n d lOy g i v e

best

n o n e o f t h e p h o s p h o r s meet all o f t h e s e

to t h e a b o v e ,

other

including coating operations

factors also affect

quality

(25).

TABLE Physical

image

image

criteria.

II

Properties of Various X - R a y

Phosphors

Avg Refractive Phosphor

Index

Ideal

BaFCI :Eu

Particle

Particle

Diameter

Shape

1.6

Polyhedral,

1.7

Spheres

1.7

Irregular-

Particle Distribution

5-1 Oy

Narrow

I0-I5y

Broad

Plates Gd 0 S:Tb

1.8

Polyhedral

8-15y

Broad

LaOBr :Tb

2.0

Plates

3-1 Oy

Narrow

L a O B r :Tm

2.0

Plates

3-1 Oy

Narrow

CaWO

1.9

Polyhedral

5-1 Oy

Broad

efficiency

of given

2

2

T h e overall equation

3.

interaction

x-ray

Screen speed, however, steps

rit|

is b e s t

to determine

system

(26)

a

n

c

*

nt2 shown

the overall

screen is g i v e n

by

a l s o d e p e n d s o n t h e film

in Fiqure

speed,

I.

In p r a c t i c e

S . of the screen-film

using the expression:

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

it

214

RARE E A R T H

where S R

is

s

relative screen s p e e d , S f

is a c o r r e c t i o n In

Table

speeds was

set equal

experimental average nal

1.

particle

takes

in

-

s

t

where

ria >

screen

Par

Table

h

III

n

e

purposes,

Kodak

thick

screen pairs

(APD)

DuPont

Blue Brand

also lists the

when

and

screen film

radiologic

sig-

expression

absorption

thickness

various

indicated

following

x-ray

equal

the

The

u s i n g the

reduced

speed for

Par

BB-54

resolution of

were u s e d .

were calculated

screen

^

of

1 and

diameter

^400

=

to

to a c c o u n t t h e

because of the

0

comparative

100 m i c r o n

to n o i s e r a t i o s

which

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

for equal

to

is r e l a t i v e film s p e e d ,

factor.

III,

were set

ELEMENTS

required

screens.

T

£

"a

S,

(5)

relative x - r a y

set equal

absorption

to o n e ,

Sj

(Table

is s p e e d of

I),

S is

speed

experimental

screen. The

results

thickness, LaOBr particle all

in T a b l e

screens have size of the indicated,

noise ratios the

indicate

the

best

all

the

It

was

x-ray

Size APD CaWO^Par)

BaFCI :Eu

5

12

size.

Par

to

obtain

III Radiologic

Experimental

Screens

Speeds

Resolution,

Blue Film

Green Film

Line Pairs P e r mm

1.0

-

7.2

20

3.4

2.5

5.4

II

S i g n a l to Noise Ratio

7

4.2

5.6

13

La 0 S:Tb

9

3.0

5.8

15

2

the to

screens.

2

2

at

signal

Gd 0 S:Tb 2

smaller

prepare

Clearly, lower

equal

The

to t h e

required

t o CaWOi+

Resolution and

Noise of Various

due

p o s s i b l e to

photons are

TABLE

Particle Relative

partly not

speed.

phosphors have

same film e x p o s u r e s a s c o m p a r e d

Speed,

screens of

highest

same p a r t i c l e

rare earth

since fewer

that for

the

resolution

phosphors.

p h o s p h o r s with about

speeds

III

L a O B r : T b screens have

L a O B r :Tm

4

4.0

4.2

7.0

14

LaOBr :Tb

4

5.0

4.0

7.0

12

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

RABATIN

12.

X-Ray

Phosphors

for Medical

215

Radiology

No easy c o m p a r i s o n s c a n be made o f commercial s c r e e n s r e garding

quantum

mottle,

resolution and speed since

screen constructions are used and particle factors cannot be easily compared. discussions earth

was to c o m p a r e s e v e r a l

x-ray

phosphors which

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

image q u a l i t y .

The kilo

Other

physical properties of

have an important

benefits of rare

R e d u c e d patient

R e d u c e d motion u n s h a r p n e s s ( 2 7 ) .

3.

R e d u c e d focal spot size o f x - r a y

4.

L o n g e r life o f x - r a y

tubes

5.

Better

use of

lower

powered

6.

Fewer

retakes

(28).

for rare

Earth

earth

derlying

to d i f f e r e n c e s

center on development

associated development x-ray

such

black a n d white

for greater

image

the use of color

of suitable

fast

appropriate

study

b y the author

(31)

with

c h o i c e o f two o r more x - r a y

of

emission colors.

indicates that

studies. b y the

phosphors mixed

r a t i o s will g i v e a d e s i r e d c o l o r w h e n

excited

in

by x-rays.

If o n e o f t h e s e p h o s p h o r s h a d G d a n d t h e o t h e r s c o n t a i n or

lower

Z elements

different the

2),

then,

are differentially

energy

profile

emit a g r e a t e r

absorbed b y body parts.

is h a r d e n e d

proportion of light Z elements.

compared to the p h o s p h o r s c o n -

lower

further

T h i s unbalancing of color can be

enhanced b y use of body contrast

potassium iodide solutions.

appropriate

x-ray

color films,

When

Color

rare

earth

x-ray

and brightness.

p h o s p h o r s suitable

points a n d emission colors u n d e r

are also listed.

It

media

s u c h as BaSO**

suitably coupled with

t h e s e c o l o r u n b a l a n c i n g s will

changes in h u e , color saturation several

A s the

t h e G d c o n t a i n i n g p h o s p h o r will

taining and

La, Ba

d u e to t h e p r e s e n c e o f

a b s o r p t i o n e d g e s , u n b a l a n c i n g o f t h e c o l o r will o c c u r a s

x-rays

x-ray

(See Figure

con-

radio-

color films

have different

On

in h u e ,

techniques a n d on the availability

phosphors which

infor-

The un-

d e v e l o p m e n t s to take place r e q u i r e s additional

recent

suitable

allowing

problems regarding

films

( 3 £ ) have

in s h a d e s o f g r e y .

colored images c a n h a v e variations

T h e main

efficient

Radiography.

black a n d white r a d i o g r a p h s .

brightness a n d color saturation trasts.

A

Contrast

100,000

that colored r a d i o g r a p h s contain more

conventional

hand,

(29).

u s e black a n d white

reasons for these advantages a r e that

other

For

generators

Studies b y Prins and coworkers

image c o n t r a s t s a r e limited

graphy

generators.

Phosphors for Color

record the images. than

screens include:

p h o s p h o r is at least

to

mation

rare

o n final

(28).

p r e s e n t all radiological examinations

clearly demonstrated

effect

exposure.

At

the

earth

2.

Rare

Other

T h e intent of the previous

1.

potential market annually.

different

sizes differ.

should be noted

Table

for this

90 K V p x - r a y

that

IV

show lists

purpose. excitation

for blue colors

ultra-

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

RARE E A R T H

216 violet

emitting

phosphors are

emulsion of color

suitable

will e x p o s e t h e

blue

film. TABLE Colors and Rare

Under

Earth

90 K V

Phosphor

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

and

ELEMENTS

IV

Color Points X-Ray

Peak

of

Phosphors

X-Ray

Excitations

Colors

Color

Prints

n Y 0 :Eu

Red

.655

.355

Y 0 S:Tb

Green

.336

.536

L a O B r . 05Tb

Green

.350

.533

L a O B r . 005Dy

Yellow

.430

.466

L a O B r . 005Sm

Orange

.546

.384

Cd 0 :Eu

Red

.655

.355

Gd 0 S:Tb

Green

.336

.536

BaFCI :Eu

for

Blue

Near

UV

Near

UV

L a O B r . 003Tm

for

Blue

Near

UV

Near

UV

2

3

2

2

2

2

3

2

Summary

and Conclusions

The

desireable

nificantly (Using

to f i n a l

Figure

phosphor properties

speed and

1 as

The

desireable

atomic

which

quality

contribute

include the

sig-

following

reference).

Intrinsic X - R a y

sities and

image

Absorption,

rja«

characteristics

numbers

from

about

are

high

55-65 to

absolute

reduce

den-

quantum

noise.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

12.

RABATIN

Emission

X-Ray

conversion

p r e f e r r e d emission

match the

spectral

to

cross

reduce

Scattering

and

I11

Radiology

of

are

ru,

should

in the

silver

near

color contrast

should

only

at

least

halide emulsions,

possess

Polyhedral shapes

structure

present

be

ultraviolet

15%.

to

rif|,

and

rjf2*

phosphors

these characteristics.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

efficiencies, spectra

sensitivity

over,

scattering.

reduced At

Medical

and Transmission Characteristics,

The reduce

for

Characteristics. The

The

Phosphors

low

rit*

refractive

promote

better

indices

to

packing

mottle.

rare earth

x-ray

Rare earth

phosphors

phosphors

meet most

are also useful

of for

radiography.

Acknowledgments The a u t h o r is e s p e c i a l l y g r a t e f u l to R o b e r t E v a n s f o r making numerous preparations, measurements and related studies.

References 1.

Ter-Pogossian, M.M. "The Physical Aspects of Diagnostic Radiology". Harper and Row Publishers: New York, 1967.

2.

Alves, R.V.; Buchanan, R.A. IEEE Trans. Nuc. Sci., 1972, 19, 415.

3.

Buchanan, R.A., Finkelstein, S.I., Wickersheim, K.A., Radiology, 1972, 105, 185-190.

4. 5.

Chenot, D.F. Canadian Pat. 896453, 1972. Stevels, A.L.N., Pingault, F., Phillips Res. Repts., 1975, 30, 277.

6.

Rabatin, J.G., U.S. Pat. 3,617,743, 1971.

7.

Rabatin, J.G., U.S. Pat. 3,795,814, 1974.

8.

Rabatin, J.G., U.S. Pat. 3,591,516, 1971.

9.

Rabatin, J.G., Extended Abstract, #220, Electrochemical Meeting, May 1979.

10.

Storm, E., Irael, H.I., Report LA3753 Los Alamos Scientific Lab., Univ. of Calif., 1967.

11.

Clark, G. "The Encyclopedia of X-Rays and Gamma Rays", Reinhold Publishing Corp., New York, 1963, 9.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

218

RARE E A R T H

ELEMENTS

12.

Swank, R.B., J. Appl. Phys. 1973, 44, 4199.

13.

Coltman., J.W., Ebbighausen, E.G., Altar, W.J., J. Appl. Phys., 1947,18,530.

14.

Grum, F., Costa, L.F., Donavan, J.L. J. Opt. Soc. Am.,

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch012

1969, 59, 848. 15.

Ludwig, G.W., J. Electrochem. So., 1971,118,1152.

16.

Venema, H.W., Radiology, 1979,130,765.

17. 18.

Lubberts, G., J. Opt. Soc. Am., 1968, 58, 1475. Cleare, H.M., Splettstosser, H.R., Seemann, H.E., Am. J. Roent. And Radium, 1962, 88, 168.

19.

Herz, R.H., Bri. J. Appl. Phys., 1956, 7, 182.

20.

Klasens, H.A., Philips Res. Rep., 1947, 2, 68.

21.

Morlotti, R., J. Photo. Sci., 1975, 23, 181.

22.

Rabatin, J.G., Extended Abstract #198, The Electrochemical Society Meeting, May 1975.

23.

Rabatin, J.G., Extended Abstract #102, The Electrochemical Society Meeting, May 1974.

24.

Ludwig, G.W., Kingsley, J.D., J. Electrochem. Soc., 1970,117,348. 25. Rabatin, J.G., Extended Abstract #220, The Electrochemical Society Meeting, May 1979.

26.

Moser, E.S., Holland, R.S., SPIE, 1975, 56, 26.

27.

Prasad, S., Marc Edwards, F., Hendel, W.R., Radiology, 1977, 123, 763.

28.

Thompson, T.T , Radford, E.L., Kirby, C.C., Applied Radiology, 1977 6, 71.

29.

Rucker, J.L., Applied Radiology, 1980, 9, 57.

30.

Prins, H.R., Katz, J.L., Billmeyer, F.W., Am. J. of Roent., 1966, 98, 966.

31.

Rabatin, J.G., Extended Abstract #332, The Electrochemical Society Meeting, May 1978.

RECEIVED

December 29, 1980.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

13 Bubble Domain Memory Materials J. W. NIELSEN

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch013

Bell Laboratories, Murray Hill, NJ 07974

The use of c y l i n d r i c a l domains to store information i n a sheet of magnetized material was first reported by Bobeck i n 1967 (1). He observed that c y l i n d r i c a l domains i n a magnetized plate of material were stable over a convenient range of bias field and could be readily moved about i n the plate under the influence of a field gradient. Bobeck called the domains "bubble" domains because their motion i n a perturbing f i e l d looked much like the motion of bubbles on the surface of a liquid. Since Bobeck's discovery, development of bubble domain memories has been carried on i n many laboratories all over the world, and production of bubble domain memories is underway at a few companies. As a result of all the work on bubble domain memories, and materials for them, a voluminous l i t e r a t u r e has been generated (2-10). Here we have space only to outline b r i e f l y the present state of bubble domain memory materials development. The reader may use the references to obtain a more detailed account of memory design and materials selection. M a t e r i a l Requirements A bubble domain i s most s t a b l e under b i a s when i t s diameter i s approximately equal t o , or s l i g h t l y more than, the t h i c k n e s s of the magnetic sheet i n which i t i s s i t u a t e d . Since economical packing d e n s i t i e s r e q u i r e domain diameters of three micrometers or l e s s , i t i s c l e a r that the magnetic medium i n a bubble domain memory must be a t h i n f i l m supported by a s u b s t r a t e . A major breakthrough i n memory development was the d i s c o v e r y by Bobeck et a l (11) that many r a r e e a r t h garnet c r y s t a l s grown from f l u x e s possess s u f f i c i e n t u n i a x i a l a n i s o t r o p y to m a i n t a i n bubble domain s t a b i l i t y . T h i s was s u r p r i s i n g s i n c e r a r e e a r t h magnetic garnets, l i k e the parent compound y t t r i u m - i r o n - g a r n e t , 3Fe50i2> are c u b i c , and i t was soon e s t a b l i s h e d t h a t the a n i s o t r o p y was induced during growth of the c r y s t a l s . v

0097-6156/81/0164-0219$05.00/0 © 1981 American Chemical Society In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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F o l l o w i n g the important d i s c o v e r y of a n i s o t r o p y , Shick et a l (12), and L e v i n s t e i n et a l (13), showed t h a t f i l m s of magnetic garnets could be r e a d i l y deposited by l i q u i d phase e p i t a x y from molten PbO-B203 s o l u t i o n s onto gadolinium g a l l i u m garnet, Gd3Ga 0 » (GGG) s u b s t r a t e s . There f o l l o w e d many s t u d i e s on a l a r g e number of garnet compositions i n the search f o r the optimum bubble domain m a t e r i a l (14). I t soon became apparent that p r o p e r t i e s d e s i r e d i n the garnet f o r best d e v i c e performance, i . e . , h i g h domain m o b i l i t y , low c o e r c i v i t y , h i g h a n i s o t r o p y and h i g h bubble s t a b i l i t y r e q u i r e d a c a r e f u l l y designed compromise i n the s e l e c t i o n of garnet s u b s t i t u e n t s . For example, s p h e r i c a l ions i n the garnet lead to h i g h domain m o b i l i t y and low c o e r c i v i t y , but low a n i s o t r o p y and s t a b i l i t y . Non-spherical i o n s , on the other hand, l e a d to h i g h a n i s o t r o p y and s t a b i l i t y but a t the same time y i e l d low m o b i l i t y and h i g h c o e r c i v i t y . I t i s testimony to the great v e r s a t i l i t y of the garnet system t h a t s u b s t i t u t e d garnets could be designed t h a t not only met the magnetic requirements f o r bubble domain memories but matched the l a t t i c e parameter of the most u s e f u l s u b s t r a t e , GGG, as w e l l (15). A t y p i c a l f i l m composition f o r 3um diameter bubble i s : 5

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch013

ELEMENTS

12

Y

1.25

L u

0.45

Sm

0.4

C a

0.9

F e

4.1

G e

0.9

°12"

Substrate P r e p a r a t i o n I t i s f o r t u n a t e t h a t the non magnetic garnet, GGG, w i t h a l a t t i c e parameter (12.383A) most n e a r l y matching those of u s e f u l magnetic garnets, i s a l s o one of the e a s i e s t garnet c r y s t a l s to grow. GGG melts congruently a t 1740°C and i s grown by the w e l l known C z o c h r a l s k i , or p u l l i n g technique. The c r y s t a l s are grown from melts contained i n i r i d i u m c r u c i b l e s under an atmosphere of N£ c o n t a i n i n g 2% 0 (16,17). C r y s t a l s weighing up to 10 kg. w i t h diameters of 75 mm are grown r o u t i n e l y (18). Substrates are prepared f o r f i l m d e p o s i t i o n from the c r y s t a l s by sawing, l a p p i n g and p o l i s h i n g u s i n g techniques s i m i l a r t o those used i n the semiconductor i n d u s t r y . 2

L i q u i d Phase E p i t a x y (LPE)

Garnets

Magnetic garnet f i l m s are deposited on GGG s u b s t r a t e s from s o l u t i o n s of the garnet oxides d i s s o l v e d i n Pb0~B203 m e l t s . The d i p p i n g technique i s used (13), and because of the great s t a b i l i t y of the s o l u t i o n s i n the supersaturated s t a t e , l a r g e numbers of s u b s t r a t e s , up to 30 at a time (19), can be dipped simultaneously under n e a r l y i s o t h e r m a l c o n d i t i o n s . Although the molten s a l t s o l u t i o n s are extremely complex i n that they may c o n t a i n up to n i n e components, they behave i n a s t r a i g h t f o r w a r d manner almost e x a c t l y l i k e the pseudo-ternary Y2O3 - Fe20 - PbO (20). T h i s s i m p l i f i c a t i o n permits great 3

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

13.

NIELSEN

Bubble Domain Memory

Materials

221

f l e x i b i l i t y i n a d j u s t i n g melt compositions to y i e l d garnet f i l m s meeting v a r i e d device s p e c i f i c a t i o n s . Temperatures f o r garnet LPE may range from 750° to 1100°C, but most experiments, and production runs, are c a r r i e d out near 950°C a t supercoolings of 10° - 40°C.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch013

Rare E a r t h Use i n Bubble Domain Memories Although the garnet compositions used i n memories c o n t a i n r a r e earths, the t o t a l r a r e e a r t h use i n magnetic f i l m s i s not s u f f i c i e n t to make much impact on the r a r e e a r t h market. The use of gadolinium oxide i n s u b s t r a t e c r y s t a l s i s another matter. I t has been estimated that by 1990 the annual use o f Gd203 f o r GGG substrates w i l l reach 40 metric tons, about twice the present r a t e (21). Conclusion The development of the bubble domain memory has been remarkable i n that s i n c e the d i s c o v e r y o f the growth induced anisotropy i n garnets, problems connected w i t h m a t e r i a l s have been r e l a t i v e l y few and not too d i f f i c u l t t o s o l v e . A major reason i s that the d i f f e r e n t s i z e s and magnetic p r o p e r t i e s of the r a r e earths o f f e r a wide range of choices f o r the m a t e r i a l s designer. The major problem s t i l l t o be solved i s development of a high speed m a t e r i a l w i t h bubble diameters of the order one micrometer. In view of the success i n developing garnet m a t e r i a l s so f a r , we can be o p t i m i s t i c about the s o l u t i o n of the small bubble problem (22, 23, 24, 25).

Literature Cited 1. Bobeck, A. H. Bell Syst. Tech. J., 1967, 46, 1901-25. 2. Smith, A. B. "Bubble Domain Memory Devices"; Artech House: Denham, Mass., 1973; p. 258. 3. O'Dell, T. H. "Magnetic Bubbles"; Macmillan: London, 1974; p. 159. 4. Bobeck, A. H.; Della Torre, E. "Magnetic Bubbles"; NorthHolland: Amsterdam, 1975; p. 222. 5. Chang, H. "Magnetic Bubble Technology"; IEEE Press: New York, 1975; p. 699. 6. Bobeck, A. H.; Scovil, H. E. D. Sci. Am., 1971, 224(6), 78-90. 7. Bobeck, A. H.; Bonyhard, P. I.; Geusic, J. E. Proc. IEEE, 1975, 63, 1176. 8. Van Uitert, L. G.; Bonner, W. A.; Grodkiewicz, W. H.; Pictroski, L.; Zydzik, G. J. Mater. Res. Bull., 1970, 5, 825-35. 9. Nielsen, J. W. IEEE Trans. Magnetics, 1976, MAG-12, 327-45.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch013

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RARE E A R T H

ELEMENTS

10. Nielsen, J. W. Am. Rev. Mater. Sci., 1979, 9, 87-121. 11. Bobeck, A. H.; Spencer, E. G.; Van Uitert, L. G.; Abrahams, S. C.; Barns, R. L . ; Grodkiewicz, W. H.; Sherwood, R. C.; Schmidt, P. H.; Smith, D. H.; Walters, E. M. Appl. Phys. Lett., 1970, 17, 131-34. 12. Shick, L. K.; Nielsen, J. W.; Bobeck, A. H.; Kurtzig, A. J.; Michaelis, P. C.; Reekstin, J. P. Appl. Phys. Lett., 1971, 18, 89-91. 13. Levinstein, H. J.; Licht, S. J.; Landorf, R. W.; Blank, S. L. Appl. Phys. Lett., 1972, 19, 486-88. 14. See in particular references 9 and 10. 15. Nielsen, J. W.; Blank, S. L . ; Smith, D. H.; Vella-Colerio, G. P.; Hagedorn, F. B.; Barns, R. L . ; Biolsi, W. A. J.. Electron Mater., 1974, 3, 693-707. 16. Brandle, C. D.; Valentino, A. J. J. Cryst. Growth, 1972, 12, 3-8. 17. Brandle, C. D.; Miller, D. C.; Nielsen, J. W. See Ref. 16, 1972, 195-200. 18. Brandle, C. D. "Crystal Growth, a Tutorial Approach"; Bardsley, W.; Hurle, D. T. J.; Mullin, J. B., Eds. North Holland: Amsterdam, 1979; p. 189-214. 19. Blank, S. L.; Licht, S. J. presented at INTERMAG, Boston, MA, March, 1980. 20. Blank, S. L . ; Nielsen, J. W. J. Cryst. Growth, 1972, 17, 302-11. 21. Arai, Shigeru presented at the First International Conference on Magnetic Bubble Materials, Santa Barbara, CA, January, 1980. 22. Hu, H. L . ; Hatzakis, M.; Geiss, E. A.; Plaskett, T. S. Shift Registers with Submicron Magnetic Bubbles on Epitaxial Garnet Films. Presented at Intermag, Washington, D.C. See also Abstr. 26.5 in Abstr. Dig. for the same conference, 1973. 23. Giess, E. A.; Davies, J . W.; Guerci, C. F.; Hu, H. L. Mater. Res. Bull., 1975, 10, 355-62. 24. Carlo, J. T.; Bullock, D. C.; Johnson, R. E.; Parker, S. G. AIP Conf. Proc., 1976, 29, 105-7. 25. Yamaguchi, K.; Inoue, H.; Asama, K. AIP Conf. Proc., 1976, 34, 160-62. RECEIVED May 7,

1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

14 Applications for Rechargeable Metal Hydrides E. L . HUSTON Ergenics Division MPD Technology, 681 Lawlins Road, Wyckoff, NJ 07481

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

J. J. SHERIDAN III Air Products and Chemicals, Incorporated, Corporate Research and Development Department, Allentown, PA 18105

Traditionally, hydrogen has been stored, transported and used in the form of compressed gas or cryogenic liquid. Rechargeable metal hydrides have been proposed as an alternative solid state storage method. A dynamic research community has assembled to explore the scientific basis and evaluate the technology of this hydrogen-metal reaction (1-4). Metal hydride topics have been discussed at each of the World Hydrogen Energy Conferences (1976 Miami, 1978 Zurich, 1980 Tokyo) and last year's ACS meeting in Hawaii. The International Symposium on Hydrides for Energy Storage - Geilo, Norway, August 1977 was attended by over 70 researchers. It's successor, the International Symposium on the Properties and Applications of Metal Hydrides - Colorado Springs, April 1980, had over 225 attendees. Approximately 35% of these participants represented industrial organizations. A third meeting of the metal hydride community is scheduled for Japan in 1982. Although the fundamental properties of metal hydride systems are still under intensive study, increased emphasis is being placed on developing the known applications for reversible metal hydrides, while the search for new applications continues. In t h i s paper, we w i l l summarize the current development a few s e l e c t e d a p p l i c a t i o n s .

status of

Chemical and Thermodynamic Fundamentals Many m e t a l s , a l l o y s and i n t e r m e t a l l i c compounds (Me) r e a c t r e v e r s i b l y with gaseous H2 to form a metal h y d r i d e , M e H , at p r a c t i c a l temperatures and p r e s s u r e s . T h i s simple r e a c t i o n , n e g l e c t i n g the s o l i d s o l u t i o n phase, may be w r i t t e n as: x

Me + I

H t 2

MeH . x

(Eq. l )

Absorption ( •+ ) and d e s o r p t i o n ( «- ) p r o p e r t i e s o f these r e v e r s i b l e metal hydrides are determined from pressure composit i o n isotherms ( P - C - T ) — a schematic o f which i s shown i n F i g u r e 1.

0097-6156/81/0164-0223$07.25/0 © 1981 American Chemical Society In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

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Figure 1. Ideal absorption and desorption isotherm for a metal-hydrogen system (1)

HYDROGEN/METAL American Chemical Society

HYDROGEN/METAL RATIO

Journal of Less-Common Metals

Figure 2.

Static hydrogen absorption/desorption isotherms for HY-STOR 207 (LaNi^AU.z) (2)

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Alloy

14.

HUSTON A N D SHERIDAN

Rechargeable

Metal

225

Hydrides

S t a r t i n g from p o i n t 1, a small amount o f hydrogen goes i n t o s o l u t i o n i n the metal phase as t h e H2 pressure i n c r e a s e s . At p o i n t 2, t h e h y d r i d i n g r e a c t i o n begins (Eq. l ) and H2 i s absorbed at n e a r l y constant pressure. This pressure Pp i s termed t h e "plateau p r e s s u r e " and corresponds t o a two-phase mixture o f metal, Me, and metal h y d r i d e , MeH . At p o i n t 3 , the metal has been completely converted t o t h e hydride phase. F u r t h e r i n c r e a s es i n H2 pressure (point k) r e s u l t i n only a small a d d i t i o n o f hydrogen i n s o l u t i o n i n t h e hydride phase. In p r i n c i p l e t h i s curve i s r e v e r s i b l e . E x t r a c t i o n o f H2 from the gas phase r e s u l t s i n the d i s s o c i a t i o n o f t h e hydride phase i n an attempt t o maint a i n the e q u i l i b r i u m p l a t e a u pressure. Isotherms f o r an a c t u a l system are shown i n F i g u r e 2. The a l l o y has t h e chemical composition L a N i i j . 7 A I 0 . 3 and i s manufact u r e d and marketed by Ergenics as HY-STOR A l l o y 207. Compared to the i d e a l curve (Figure l ) , the p l a t e a u i s s l i g h t l y sloped, the p l a t e a u l i m i t s a r e not as c l e a r l y d e f i n e d and t h e r e i s a measurable pressure h y s t e r e s i s between a b s o r p t i o n and d e s o r p t i o n . F i g u r e 2 a l s o shows a strong temperature dependence f o r t h e p l a t e a u pressure. This i s an important consequence o f the heat of r e a c t i o n , AH, a s s o c i a t e d with Eq. 1. Hydrogen a b s o r p t i o n (->) i s exothermic and d e s o r p t i o n («-) endothermic. The p l a t e a u p r e s sure i s r e l a t e d t o t h e absolute temperature, T, by t h e f a m i l i a r Van't Hoff equation:

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

x

(Eq. 2) where x i s d e f i n e d i n Eq. 1, AH i s t h e enthalpy change o f t h e r e a c t i o n , R i s t h e gas constant, and B i s a constant r e l a t e d t o the entropy change o f t h e r e a c t i o n . Thus, from a s e r i e s o f experimental isotherms (Figure 2) a p l o t o f InPp vs l / T can be constructed and t h e value o f AH i s determined from t h e slope. Van't Hoff p l o t s f o r a number o f r e v e r s i b l e metal hydrides are given i n F i g u r e 3. The chemical symbol M denotes mischmetal which i s a mixture o f r a r e e a r t h metals. The u s u a l mischmetal contains hQ-50% Ce, 32-3W La, 13-1W Nd, k-5% Pr, and 1.5% other r a r e e a r t h metals. The chemical formula l a b e l i n g each curve s p e c i f i e s t h e hydrogen/metal atom r a t i o f o r each Pp v a l u e . The heat o f r e a c t i o n f o r the LaNilj. 7AI0.3 a l l o y shown i n F i g u r e 2 i s -8.lkcal/mole H2. T h i s i s t h e heat generated during t h e h y d r i d i n g r e a c t i o n (absorption) and must be s u p p l i e d during d e s o r p t i o n . The magnitude o f t h i s heat i s only 15% o f the lower heating value o f t h e contained hydrogen and can be s u p p l i e d from "low grade" sources. Waste heat a t 70 °C would d i s s o c i a t e LaNi^^yAlQ.3Hg and provide H2 at approximately 2 atm a b s o l u t e . There a r e a number o f engineering p r o p e r t i e s r e l a t i n g t o p r a c t i c a l a p p l i c a t i o n s o f h y d r i d e s ; h y s t e r e s i s , r e v e r s i b l e capac i t y , d e c r e p i t a t i o n , a c t i v a t i o n , r e a c t i o n k i n e t i c s , impurity t o l e r a n c e s , chemical s t a b i l i t y , heat t r a n s f e r , s a f e t y , cost and m

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

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RARE E A R T H

ELEMENTS

Journal of Less-Common Metals

Figure 3.

Van't Hoff plots (desorption) for various hydrides (2)

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

14.

HUSTON A N D SHERIDAN

Rechargeable

Metal

Hydrides

227

availability. These p r o p e r t i e s have been d i s c u s s e d e x t e n s i v e l y by others ( l ^ 2 5_ 6, 7) and w i l l not be mentioned f u r t h e r unless c r i t i c a l to the understanding o f a p a r t i c u l a r a p p l i c a t i o n . 9

9

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

Hydrogen Storage V i r t u a l l y a l l a p p l i c a t i o n s f o r r e v e r s i b l e metal hydrides i n v o l v e the storage, at l e a s t t e m p o r a r i l y , o f hydrogen as a metal h y d r i d e . As i t turns out, s o l i d - s t a t e storage o f hydrogen o f f e r s advantages i n volume, weight, p r e s s u r e , energy savings and s a f e t y over cryogenic and compressed gas storage. Small hyd r i d e storage u n i t s are commercially a v a i l a b l e and t h e i r widespread use depends upon i d e n t i f i c a t i o n of a p p l i c a t i o n s where these advantages can be t r a n s l a t e d i n t o cost/performance b e n e f i t s . A comparison of hydrogen storage parameters f o r c r y o g e n i c , compressed gas (200 atm) and s e v e r a l hydrides i s made i n Table I. Storage pressure i s much lower f o r metal hydrides and l i q u i d hydrogen. Thus these storage v e s s e l s can be o f l i g h t e r c o n s t r u c tion. In p r a c t i c e , hydride storage systems should be designed f o r gas pressures s e v e r a l times (perhaps 2-5) the p l a t e a u p r e s sure to allow f o r r a p i d charging and ambient temperature changes. The high volumetric packing d e n s i t y f o r the hydrides i s evident i n Table I. Over three times as much hydrogen can be stored per u n i t volume with hydrides than f o r compressed gas at 200 atm. The volumetric d e n s i t y o f the hydrides shown approaches that of l i q u i d hydrogen. T h i s i s p a r t i c u l a r l y s t r i k i n g s i n c e the d e n s i t y c a l c u l a t i o n i n c l u d e s a 50$ v o i d volume f o r the hydride storage container and, t h e r e f o r e , represents the volumetric d e n s i t y f o r p r a c t i c a l hydride storage d e v i c e s . V o i d spaces are r e q u i r e d because of the p a r t i c u l a t e nature o f the metal hydride and a l s o to accommodate the volume expansion accompanying hydride formation. R e v e r s i b l e metal hydrides are comparable with conventional storage methods on a weight b a s i s . Cryogenic c o n t a i n e r s f o r l i q u i d hydrogen reduce the hydrogen c a p a c i t y t o about 5$ o f the system weight. A standard IA Mathieson hydrogen c y l i n d e r , weighs 135 l b s and contains o n l y 0.83$ hydrogen by weight. For tubet r a i l e r c y l i n d e r s , hydrogen c a p a c i t y i s i n c r e a s e d to about 1.3$ by weight. The values quoted i n Table I f o r hydride storage i n clude an allowance (25$ o f the hydride weight) f o r the c o n t a i n e r . Thus the F e T i and LaNijp type storage systems are comparable t o 200 atm compressed gas storage while the Mg systems compare with l i q u i d H but must be heated t o about 300 °C t o i n c r e a s e the hydrogen pressure t o one atmosphere f o r convenient d e s o r p t i o n . The f a c t t h a t the hydride storage can be done at modest pressure i s an obvious s a f e t y advantage. In the event of' cont a i n e r rupture, only a modest amount o f gaseous hydrogen i s r e l e a s e d . The bulk of the hydrogen i s contained as an endothermi c r e a c t a n t . Rupture t e s t s of hydride c y l i n d e r s (8_, _g) have shown an i n i t i a l f l a s h followed by a low flame as f r o s t forms on the container w a l l s . 2

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981. 2.5

0.01 0.01

V

Mg

Mg2.1+Ni

* Assumes 5 0 $ v o i d space i n h y d r i d e

containers

* Assumes c o n t a i n e r i s 2 5 $ o f hydride weight

1.7

LaNi5

(200 )

h.l

2

K l )

P l a t e a u Pressure (atm § 25°C)

FeTi

Compressed H

Liquid H2

Hp Storage Mode

3.1

5.6

0.9

600

670

620

T55

550

l.k 1.1

205

850

1.3

5.3

Storage Parameters Volumetric** Reversible* SCF Hp (vt $) f t 3 container

TABLE I - COMPARISON OF STORAGE PARAMETERS FOR SEVERAL MODES OF HYDROGEN STORAGE

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

14.

HUSTON A N D SHERIDAN

Rechargeable

Metal

Hydrides

A hydride storage u n i t manufactured by Laboratory Data C o n t r o l under the t r a d e name H2YCELL i s shown i n F i g u r e h. This u n i t contains 8 f t o f hydrogen as LaNi^Hg. I t i s e l e c t r i c a l l y heated and r e g u l a t e d t o d e l i v e r hydrogen at 215 p s i a at a r a t e o f 1 SCFH. The H2YCELL can be recharged from a low pressure e l e c trolyzer. I t i s being marketed f o r use with gas chromatography equipment i n a n a l y t i c l a b o r a t o r i e s and h o s p i t a l s . A l a r g e r u n i t manufactured by Ergenies i s shown i n F i g u r e 5. T h i s u n i t contains 90 SCF o f hydrogen and i s a v a i l a b l e with a v a r i e t y o f r e v e r s i b l e metal hydrides depending upon t h e p r e s sure requirements o f t h e a p p l i c a t i o n . The hydride i s contained i n 1" diameter capsules t o reduce t h e tendancy f o r h y d r i d e packing. Hydrogen charging curves f o r a u n i t c o n t a i n i n g HY-STOR 209 U . 1 5 0 . 8 5 are shown i n F i g u r e 6. The heat t r a n s f e r media has a pronounced i n f l u e n c e on t h e charging r a t e . With f o r c e d a i r c o o l i n g , t h e u n i t can be f u l l y recharged i n about 100 minutes. Discharge curves are shown f o r a flow r a t e o f 2 8 l i t e r per minute (lSCFM) i n F i g u r e 7 - Heat t r a n s f e r by s t i l l a i r l i m i t s desorpt i o n a f t e r about 20$ o f t h e hydrogen i s discharged. However, with f o r c e d a i r across t h e c o n t a i n e r tubes, a constant d e s o r p t i o n r a t e i s maintained u n t i l t h e hydride i s exhausted. The pressure i n s i d e t h e c o n t a i n e r d u r i n g d e s o r p t i o n i s shown i n F i g u r e 8. The poor heat t r a n s f e r p r o p e r t i e s o f s t i l l a i r allows the heat o f d e s o r p t i o n t o c o o l t h e metal hydrides and hence reduce t h e hyd r i d e p l a t e a u pressure so t h a t o n l y very low hydrogen flow r a t e s can be maintained. In f a c t , an i c e f i l m formed on t h e c o n t a i n e r during t h i s t e s t t o f u r t h e r aggrevate the heat t r a n s f e r . The E r g e n i c s u n i t i s modular i n c o n s t r u c t i o n and p o r t a b l e . A p p l i c a t i o n s i n c l u d e storage f o r f u e l c e l l s and e l e c t r o l y z e r s as w e l l as hydride modules f o r compressors and heat pumps. Two f a c t o r s c u r r e n t l y l i m i t r e v e r s i b l e metal h y d r i d e storage a p p l i c a t i o n s : cost and weight. The r e l a t i v e l y h i g h cost o f the elemental c o n s t i t u e n t s f o r t h e h y d r i d i n g a l l o y s ( N i , $3.^5/lb; T i , $8-10/lb; mischmetal, $5/lb) s e t a cost which cannot be reduced by e x i s t i n g m e t a l l u r g i c a l p r a c t i c e s . Magnesium-based h y d r i d i n g a l l o y s are l e s s expensive but are p r e s e n t l y l i m i t e d t o high temperature (*~300 °C) o p e r a t i o n . Because o f t h e m a t e r i a l s c o s t s , small storage u n i t s o r systems t h a t are c y c l e d r a p i d l y t o i n c r e a s e u t i l i z a t i o n are favored. Weight i s a l s o a f a c t o r f o r most mobile storage a p p l i c a t i o n s . Although many demonstration v e h i c l e s have been f i e l d e d w i t h hydrogen i n t e r n a l combustion engines f u e l e d by h y d r i d e storage systems, t h e f u e l system weight r e l a t i v e t o l i q u i d f u e l s i s not impressive. Comparisons w i t h e l e c t r i c s are much more f a v o r a b l e . Development work today i s focused on f l e e t v e h i c l e s with s p e c i a l i z e d a p p l i c a t i o n s (e.g. f o r k l i f t s , mine v e h i c l e s , downtown buses, e t c . ) . 3

M N i

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F e

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Figure 4.

H YCELL 2

Figure 5.

ELEMENTS

hydride storage unit manufactured by Laboratory Data Control

Hydride storage unit (90 SCF) manufactured by Ergenics

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Figure 6.

Hydrogen charging curve for Er génies storage unit (90 SCF)

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

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In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Figure 7.

Hydrogen discharge curves (1 SCFM) for Ergénies storage unit (90 SCF)

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

09

H

w

X m r w

H

>

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W

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In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Figure 8.

Hydrogen discharge pressure for Ergénies storage unit (90 SCF)

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

to

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Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

Hydrogen Separations During the past two y e a r s , the Ergenics D i v i s i o n of MPD Technology and A i r Products have been engaged i n a j o i n t venture R&D program t o develop hydrogen recovery processes f o r t r e a t i n g i n d u s t r i a l o f f - g a s streams based on the unique hydrogen absorpt i o n p r o p e r t i e s o f metal h y d r i d e s . C u r r e n t l y , l a r g e volumes o f o f f - g a s hydrogen are e i t h e r f l a r e d , burned as f u e l , or routed t o secondary operations w i t h i n the chemical and petroleum r e f i n i n g i n d u s t r i e s . Such o f f - g a s streams represent a p o t e n t i a l l y s i g n i f i c a n t source o f hydrogen t h a t , i f economically r e c o v e r a b l e , c o u l d p a r t i a l l y s a t i s f y the near term ( 1 9 8 8 - 1 9 9 0 ) hydrogen supply problems i n the U.S. Metal Hydride Absorption Process. B a s i c a l l y , the metal hydride process c o n s i s t s o f two steps: ( l ) hydrogen a b s o r p t i o n , and ( 2 ) hydrogen desorption. The process i s c a r r i e d out i n a packed-bed c o n t a i n i n g the hydride former (absorbent). During a b s o r p t i o n , the hydrogen p a r t i a l pressure o f the feed stream must be higher than the hydrogen p l a t e a u pressure f o r the hydride former t o enable a b s o r p t i o n o f the hydrogen by the bed. The absorbed hydrogen i s then recovered by desorbing the hydrogen from the bed v i a e i t h e r i n c r e a s i n g the bed temperature or loweri n g the system pressure. Hydrogen recovery depends on the r a t i o of the hydrogen p a r t i a l pressure of the feed stream and the p l a teau pressure o f the s e l e c t e d hydride former. Hydrogen d e l i v e r y pressure depends upon the bed temperature during d e s o r p t i o n . S u c c e s s f u l o p e r a t i o n of t h i s process depends upon the proper des i g n o f the hydride bed (absorber column). Our approach t o the design o f the absorber column i s t o develop H2 breakthrough data f o r a v a r i e t y o f system c o n f i g u r a t i o n s and stream c o n d i t i o n s . F i g u r e 9A shows a t y p i c a l hydrogen breakthrough curve f o r a hydride former i n a packed-bed. A feed stream c o n t a i n i n g hydrogen o f c o n c e n t r a t i o n C F i s fed i n t o the absorber. The breakthrough data are obtained by monitoring the hydrogen c o n c e n t r a t i o n i n the o u t l e t stream o f the absorber column. The e x i t hydrogen c o n c e n t r a t i o n i s reduced t o a value Co which i s dependent upon the hydride P-C-T p r o p e r t i e s . The i d e a l breakthrough curve i s a l s o shown on F i g u r e 9A and r e p r e sents the case o f instantaneous H a b s o r p t i o n . The breakthrough data can be employed t o c o n s t r u c t a waveor r e a c t i o n - f r o n t p l o t as shown i n F i g u r e 9B. T h i s curve r e p r e sents a s t a b l e r e a c t i o n f r o n t o f l e n g t h , L f , moving through the absorber column at v e l o c i t y , Vf. Along the r e a c t i o n f r o n t , the hydrogen l o a d i n g o f the absorbent v a r i e s . Upstream o f the f r o n t , the hydrogen c a p a c i t y o f the absorbent i s at s a t u r a t i o n ( f u l l c a p a c i t y ) . To the r i g h t o f the f r o n t (downstream) the hydrogen p a r t i a l pressure o f the stream i s l e s s than the p l a t e a u pressure and a b s o r p t i o n does not occur. In o p e r a t i o n , the flow t o an absorber column i s stopped and sent t o another column once the breakthrough p o i n t (Figure 9A) i s 2

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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B

LENGTH OF COLUMN

Figure 9.

Schematic (A) hydrogen breakthrough and (B) absorption wavefront curves for a hydride absorber column

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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encountered. Therefore, the shape o f the r e a c t i o n f r o n t (or breakthrough curve) d i c t a t e s the hydrogen recovery and bed u t i l i z a t i o n ( i . e . , l b s H2/lb absorbent) f o r the process. A shallow r e a c t i o n f r o n t leads t o poor bed u t i l i z a t i o n and hydrogen recovery; whereas, a steep r e a c t i o n f r o n t y i e l d s a h i g h e r bed u t i l i z a t i o n and recovery. For hydride absorbents, t h e shape o f the r e a c t i o n f r o n t depends on many f a c t o r s , f o r i n s t a n c e : pressure drop through the packed-bed, hydrogen absorption k i n e t i c s o f the a l l o y , gas b l a n k e t i n g ,

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

e q u i l i b r i u m P-C-T p r o p e r t i e s o f the a l l o y , hydrogen p a r t i a l pressure o f t h e stream, presence o f i n t e r f e r r i n g or i n h i b i t i n g gaseous components. Hydrogen separations with metal hydrides can be viewed as complementary technology t o cryogenic and adsorption (PSA) processes. A t t r i b u t e s o f t h i s new process are l i s t e d i n Table II. TABLE I I .

ADVANTAGEOUS FEATURES OF HYDRIDEHYDROGEN SEPARATION PROCESSES

REACTION SPECIFICITY

• Only H r e a c t s , u s e f u l f o r d i l u t e streams

HIGH RECOVERY

• Determined by H p a r t i a l pressure and hydride former

PRODUCT PURITY

•> 99.9%

ENERGY EFFICIENT

• Heat o f r e a c t i o n t y p i c a l l y 10-15$ of the lower h e a t i n g value o f H and can be p a r t i a l l y recovered

2

2

i f required

2

Metal Hydride Process f o r Ammonia Purge Gas. The metal hydride process w i l l be i l l u s t r a t e d u s i n g t h e case o f hydrogen recovery from an ammonia purge gas stream generated during ammonia manufacture. F i g u r e 10 i s a b l o c k diagram f o r ammonia s y n t h e s i s from steam reforming gas. As shown i n t h e f i g u r e , i n e r t gases such as argon and methane from the secondary reformer accumulate i n the s y n t h e s i s loop and decrease the p a r t i a l pressures o f hydrogen and n i t r o g e n which r e a c t t o form ammonia. Therefore, i t becomes necessary t o continuously remove (purge) these i n e r t s from the

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Product -4

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Figure 10.

Primary Reforming

Gas

Ammonia Synthesis

Recirculation

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Secondary Reforming

Air

I

Compression

Metal Hydride Hydrogen Absorbers

A

j _ - , • j

1

1

CO S h i f t

H2

Block diagram for ammonia synthesis by steam reformation

Ammonia Separation

Ammonia Purge G a s -

Desulfurization

Steam

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CO Removal

C02 Removal

c

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r e c y c l e gas i n order t o maintain a steady r a t e o f ammonia synthesis. The t y p i c a l composition o f the ammonia purge gas stream i s shown i n Table I I I . TABLE I I I TYPICAL COMPOSITION OF AMMONIA PURGE GAS STREAM Component

Mole Percent

H

2

63

N

2

21 12

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Ar NH3

2 2

Pressure

50-60

Temperature

i+0 °C

atm

C h a r a c t e r i s t i c breakthrough curves f o r s y n t h e t i c ammonia purge gas streams have been measured as a f u n c t i o n o f system parameters i n a bench s c a l e r e a c t o r . A N i - c o n t a i n i n g AB5 hydride former was used. Data f o r a stream c o n t a i n i n g 0 . 9 2 $ N H 3 i s given i n F i g u r e 1 1 . A steep breakthrough curve i s observed at a superf i c i a l gas v e l o c i t y o f approximately 3 f e e t per minute. F o r a constant ammonia c o n c e n t r a t i o n , the l e n g t h o f the r e a c t i o n f r o n t , L f , v a r i e s approximately as t h e square root o f t h e gas v e l o c i t y , F i g u r e 1 2 . The l e n g t h o f the r e a c t i o n f r o n t a l s o shows a weak dependence on ammonia c o n c e n t r a t i o n . F i g u r e 1 3 shows L f a ( N H 3 ) over the range 0 - 5 $ N H 3 . F o r t y p i c a l purge gas streams c o n t a i n ing 1 . 5 t o 2 . 5 $ NH3 (see band i n F i g u r e 1 3 ) the f r o n t v a r i e s from 1 . 5 t o 3 . 5 f e e t at s u p e r f i c i a l gas v e l o c i t i e s o f 3 . 5 t o 1 0 . 5 feet per minute. These r e s u l t s are not u n l i k e those reported by others, f o r separation o f gases with molecular s i e v e s . For example, when H S i s s t r i p p e d from n a t u r a l gas with a Davison 5 A molecular s i e v e , t h e r e a c t i o n f r o n t i s t y p i c a l l y 1 t o 5 f e e t at s u p e r f i c i a l gas v e l o c i t i e s o f 1 5 t o 3 0 f e e t per minute (_10). From t h i s p e r s p e c t i v e , the o p e r a t i o n o f a hydride-hydrogen s e p a r a t i o n s y s tem i s s i m i l a r t o conventional u n i t s . Our data i n d i c a t e t h a t ammonia acts as a m i l d i n h i b i t o r f o r hydrogen a b s o r p t i o n i n N i - c o n t a i n i n g AB5 a l l o y s . The measured heat o f a d s o r p t i o n o f NH3 on Ni i s about - 1 1 kcal/mol N H 3 , sugg e s t i n g weak, p h y s i c a l a d s o r p t i o n . Since Ni i s viewed t o be a c a t a l y s t f o r the h y d r i d i n g r e a c t i o n , weak j h y s i c a l adsorption o f NH3 at these Ni s i t e s would r e t a r d t h e r e a c t i o n and promote a broadening o f the r e a c t i o n f r o n t as shown i n Figures 1 2 and 1 3 . We have shown t h a t the adsorbed NH3 i s e a s i l y desorbed from t h e Ni s i t e s during hydrogen desorption and, t h e r e f o r e , acts only as a m i l d i n h i b i t o r f o r t h e absorption step. u

2

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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14.

Figure 11.

Hydrogen breakthrough curve for a 0.93% NH stream S

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Figure 12.

Figure 13.

Effect of gas velocity on reaction front length

Effect of ammonia on length of breakthrough front

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

ELEMENTS

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

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241

Process Economics. P r e l i m i n a r y process economics f o r r e c o v e r i n g hydrogen from the ammonia purge gas stream have been prepared. The H2 recovery c o s t s depend on many f a c t o r s and are i n t h e range 0.30-0.80 $/MSCF H 2 . These costs compare f a v o r a b l y with those f i g u r e s r e p o r t e d f o r cryogenic and molecular s i e v e (absorption) processes. The process can be s c a l e d t o produce u n i t s capable o f t r e a t i n g 10 MMSCFD o f H 2 . C u r r e n t l y , t h e developed process i s being r e a d i e d f o r p i l o t p l a n t t e s t i n g at an ammonia manufacturer's i n s t a l l a t i o n . A t y p i c a l hydride hydrogen s e p a r a t i o n u n i t s i z e d t o process 10 MMSCFD o f H2 would r e q u i r e 50 t o 100,000 l b s o f hydride formi n g a l l o y . Approximately 1/3 o f t h e a l l o y weight would be a r a r e e a r t h ( s ) i f AB5 a l l o y s are u t i l i z e d . A range o f a l l o y composit i o n s i s l i k e l y t o be r e q u i r e d t o optimize s e p a r a t i o n costs f o r d i f f e r e n t streams. Other A p p l i c a t i o n s . Metal hydrides are unique i n t h a t they are one o f the few compounds that s e l e c t i v e l y and r e v e r s i b l y absorb l a r g e q u a n t i t i e s o f hydrogen a t p r a c t i c a l temperatures and pressures. This property enables one t o t r e a t d i l u t e hydrogen streams t h a t cannot be otherwise economically t r e a t e d . Figure Ik shows t h e q u a l i t a t i v e e f f e c t o f hydrogen concent r a t i o n o f the stream on the p r o c e s s i n g costs t o recover hydrogen by the metal hydride, cryogenic and molecular s i e v e processes. C l e a r l y , the metal hydride process i s p r e f e r r e d f o r t r e a t i n g d i l u t e streams and i s a d i r e c t consequence o f the h i g h degree o f r e a c t i o n s p e c i f i c i t y o f hydride formers f o r hydrogen. Coupled with t h i s i s t h e property t h a t hydride formers can absorb hydrogen at r e l a t i v e l y low p a r t i a l pressures while r e t a i n i n g good k i n e t i c s and recovery. These two p r o p e r t i e s can be employed t o develop an a p p l i c a t i o n s map f o r the metal hydride process as shown i n F i g u r e 15. The regions o f the f i g u r e i n d i c a t e p r e f e r r e d operating parameters f o r the v a r i o u s processes. I t i s evident t h a t the metal hydride o p t i o n i s s u p e r i o r i n terms o f i t s a b i l i t y t o economically t r e a t t y p i c a l o f f - g a s streams. We are c u r r e n t l y i n v o l v e d i n a three phase developmental program t o extend the process t o other hydrogen c o n t a i n i n g streams. The program i n v o l v e s : screening candidate streams t o i d e n t i f y poisonous species f o r t h e metal h y d r i d e s , developing poison r e s i s t a n t processes f o r each stream, and demonstrating the process(es) on a p i l o t s c a l e t o e s t a b l i s h process economics. Hydrogen P u r i f i c a t i o n The s p e c i f i c i t y o f the h y d r i d i n g r e a c t i o n (Eq. l ) a l s o provides a method f o r the p u r i f i c a t i o n o f high p u r i t y hydrogen. The technology i s s i m i l a r t o t h a t p r e v i o u s l y d e s c r i b e d f o r hydrogen separations and i s capable o f producing p u r i t y l e v e l s exceeding 99.999$. I f the impure hydrogen i s already 99 % H 2 , s i n g l e ended r e a c t o r s can be employed. R e s i d u a l gases ( i m p u r i t i e s ) are +

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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0

20

40

60

H2 FEED CONCENTRATION

Figure 14.

80

ELEMENTS

100

(WT 7>)

Qualitative effect of hydrogen concentration on processing costs for various recovery methods

Figure 15. Applications map for hydrogen recovery process: A, ammonia purge gas; B, refinery stream; C, coal conversion recycle gas; D, ethylene plant cracked gas; E, FCC C minus gas h

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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SHERIDAN

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e x p e l l e d immediately a f t e r charging by simply desorbing a p o r t i o n of the hydride. The p r i n c i p a l a p p l i c a t i o n f o r u l t r a high p u r i t y hydrogen i s f o r heat t r e a t i n g atmospheres i n the semiconductor i n d u s t r y . Palladium p u r i f i e r s are the current i n d u s t r y standard. Experiments a t KFA J u l i c h have shown t h a t hydrogen can be p u r i f i e d t o g r e a t e r than 99.9999$ u s i n g s p e c i a l F e T i hydride tanks ( l l _ ) . The Laboratory Data C o n t r o l H2YCELL u n i t shown i n F i g u r e h claims even h i g h e r p u r i t y l e v e l s based on atomic absorpt i o n a n a l y s i s (12). Additional surface poisoning studies s i m i l a r t o the work sponsored by Brookhaven N a t i o n a l Laboratory will be r e q u i r e d t o d e l i n e a t e the types o f hydrogen streams t h a t can be processed by t h i s technology.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

Thermal Compression Hydrogen compression i s a v i t a l step f o r most i n d u s t r i a l uses o f hydrogen. Conventional markets f o r hydrogen are growing r a p i d l y and the s y n t h e t i c f u e l s programs w i l l m u l t i p l y the q u a n t i t i e s of hydrogen processed each year. T h i s assures i n creased demand f o r compression equipment. E x i s t i n g mechanical compressors, although w e l l engineered, are high maintenance, h i g h o p e r a t i n g cost items. Is t h e r e a b e t t e r way? The a b i l i t y o f r e v e r s i b l e metal hydrides t o absorb hydrogen at low pressures and temperatures, then when heated t o a higher temperature, desorbs the hydrogen a t a higher p r e s s u r e , i s the b a s i s f o r the hydride chemical compressor. The pressure-temperat u r e c h a r a c t e r i s t i c s are governed by the Van't Hoff equation (Eq. 2 ) . Compression r a t i o s f o r s e v e r a l hydrides o p e r a t i n g between 2 5 and 8 5 °C are given i n Table IV. These data are taken d i r e c t l y from F i g u r e 3 and range from 6 t o 9- The compression r a t i o v a r i e s d i r e c t l y w i t h the heat o f formation, AH, as r e q u i r e d by Eq. 2 . Hydride chemical compressors have two a t t r a c t i v e f e a t u r e s . Only low grade (low temperature) energy sources are r e q u i r e d . The example c i t e d r e q u i r e d 8 5 °C—typically a waste heat temperat u r e f o r most i n d u s t r i a l environments or a temperature r e a d i l y d e l i v e r e d by s o l a r h e a t i n g i n s t a l l a t i o n s . There are no r o t a t i n g p a r t s r e q u i r i n g maintenance. Check v a l v e s r e g u l a t e the hydrogen flow. Continuous o p e r a t i o n i s achieved by u s i n g m u l t i p l e hydride beds operated i n a staggered sequence. A preprototype ("proof o f concept") u n i t has been assembled and t e s t e d by Ergenics and Denver Research I n s t i t u t e with DOE funding through Brookhaven N a t i o n a l Laboratory. One h a l f o f the u n i t i s shown i n F i g u r e l 6 . A LaNil±. 5 A I 0 . 5 a l l o y was s e l e c t e d to permit a b s o r p t i o n o f hydrogen a t ambient temperature and a pressure o f 1 atmosphere absolute. Thus, the u n i t could be operated i n c o n j u n c t i o n with a low pressure e l e c t r o l y z e r . The hydride was contained i n capsules i n s t a i n l e s s s t e e l tubes which were e l e c t r i c a l l y heated and cooled by fans. A peak pressure o f 7 5 atm ( 1 1 0 0 p s i g ) was a t t a i n e d at 300 °C. In continuous operat i o n , the u n i t d e l i v e r e d h3 SCFH o f hydrogen a t h2 atm ( 6 5 O p s i g ) .

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

i

5

B 7

Thermal

LaNi^

CaNi

LaNitj

0

l

Al .3

O. 9 ^ 0 .

1.0

0.1+5

0.50

1.7

1.20

k.O

k.k

13

19

T

2.8

F e

2k

0 > 5

3.9

5

MNiU. Al

28

0

(atm,§5 C)

U.8

p

P (atm,25°C)

FeTi

Alloy

1.20

8.9

8.8

7.6

6.8

6.2

5.8

Ratio

H

-8.1

-7.6

-7.U

-7.0

-6.7

-6.7

(k cal/mole H 2 )

TABLE IV - COMPARISON OF THERMAL COMPRESSION RATIOS FOR SEVERAL REVERSIBLE METAL HYDRIDES BETWEEN 2 5 AND 85°C

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

HUSTON AND SHERIDAN

Rechargeable

Metal

Hydrides

245

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14.

Figure 16. Prototype hydride chemical compressor constructed by Ergenics and Denver Research Institute: (top) front view; (bottom) topview showing metal hydride tube bundle

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

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During c o o l i n g , t h e fans r a p i d l y c o o l t h e tubes t o ambient c o n d i t i o n s at which time a second check v a l v e opens a l l o w i n g reabsorpt i o n o f t h e compressed hydrogen. Some degradation o f performance was noted during c y c l i n g . As t h e c y c l e number i n c r e a s e d , time r e q u i r e d t o compress t h e same q u a n t i t y o f hydrogen i n c r e a s e d . This degradation i s b e l i e v e d t o r e f l e c t an i n s t a b i l i t y i n t h e hydride aggrevated by the 300 °C temperature e x c u r s i o n . The e f f i c i e n c y o f t h i s preprototype device was low due p r i n c i p a l l y t o t h e thermal mass o f t h e copper buss b a r s , convect i o n l o s s e s a s s o c i a t e d with t h e a i r cooled design and r a d i a t i o n l o s s e s at the h i g h o p e r a t i n g temperatures. Current work i s d i r e c t e d a t staged compressors (more than one a l l o y ) o p e r a t i n g over smaller temperature ranges s u p p l i e d by a l i q u i d heat t r a n s f e r media. Sandia L a b o r a t o r i e s (Albuquerque) has r e c e n t l y completed a study on c l o s e d - c y c l e h y d r i d e engines based on t h e hydride chemical compression c y c l e {13). A p r a c t i c a l demonstration u n i t was c o n s t r u c t e d t o operate a water pump (ih). The down-hole bladder pump i s capable o f pumping against l a r g e h y d r o s t a t i c heads. Coupled w i t h a s o l a r c o l l e c t i o n , t h i s concept should f i n d a p p l i c a t i o n s i n a r i d t h i r d world c o u n t r i e s . Heat Pumps and R e f r i g e r a t i o n The r e v e r s i b i l i t y o f t h e metal-hydrogen r e a c t i o n (Eq. l ) and the heat o f chemical r e a c t i o n (Eq. 2) p r o v i d e s t h e b a s i s f o r hydride heat pumps. These devices are c l o s e d u n i t s i n which hydrogen serves as an energy c a r r i e r between two o r more h y d r i d e beds. By s e l e c t i n g a p p r o p r i a t e h y d r i d i n g a l l o y s , heat sources and heat s i n k s , heat can be pumped over wide temperature d i f f e r e n t i a l s with no moving p a r t s except p o s s i b l y check v a l v e s . There are two b a s i c c y c l e s f o r heat pump o p e r a t i o n : convent i o n a l (l£) and temperature upgrading (_l6, JLl). I t i s convenient to v i s u a l i z e t h e operation o f these c y c l e s by f o l l o w i n g t h e changes i n pressure and temperature o f each a l l o y on a Van't Hoff p l o t . F o r ease o f n a r r a t i o n , these curves are i d e a l i z e d . Many engineering p r o p e r t i e s o f metal h y d r i d e s must be considered i n a d e t a i l e d explanation (e.g., h y s t e r e s i s , p l a t e a u s l o p e , c y c l i c s t a b i l i t y , e t c . ) . The two c y c l e s are shown i n F i g u r e 17. In t h e c o n v e n t i o n a l c y c l e , hydride B a t , say ho °C, i s heated t o about 90 °C. Heat i s absorbed (Qg) from the h i g h temperature bed t o d i s s o c i a t e hydrogen. This hydrogen i n t u r n r e a c t s w i t h h y d r i d e former A, r e l e a s i n g heat ( Q A ) a t t h e i n t e r mediate temperature. When the r e a c t i o n i s complete, a l l o y B i s cooled t o t h e i n t e r m e d i a t e temperature. Hydride A desorbs hydrogen and c o o l s , thereby absorbing heat ( Q A r e f r i g e r a t i o n ) a t a low temperature. The hydrogen r e a c t s w i t h a l l o y B r e l e a s i n g a d d i t i o n a l heat ( Q B ) at t h e intermediate temperature and completi n g t h e c y c l e . The net r e s u l t i s heat Q A + Q B d e l i v e r e d t o t h e intermediate temperature with Q B taken from a h i g h temperature

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

14.

HUSTON AND SHERIDAN

Figure 17.

Rechargeable

Metal

Hydrides

247

Schematic hydride heat pump cycles

Figure 18. Prototype 3.5 Kw heat pump constructed by Ergenics for New York State Energy Research and Development Administration

American Chemical Society Library 1155 16th St. N. w. Washington, 0. C. 20038

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

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ELEMENTS

source and Q A a low temperature source ( r e f r i g e r a t i o n ) . The c y c l e operates c o n t i n u o u s l y r e q u i r i n g o n l y s w i t c h i n g o f heat t r a n s f e r f l u i d s from the heat s i n k s and sources. A demonstration of t h i s c y c l e has been i n o p e r a t i o n f o r s e v e r a l years a t Argonne National Laboratories. The temperature upgrading c y c l e has t h e hydrogen f l o w i n t h e opposite d i r e c t i o n . This r e s u l t s i n the removal o f heat from t h e i n t e r m e d i a t e temperature bed and d e l i v e r y t o h i g h e r ( Q B ) and lower ( Q A ) temperature s i n k s . The temperature range ( 0 - 1 0 0 °C) i n F i g u r e 17 i l l u s t r a t e s t h a t t h e h y d r i d e heat pumps can operate w i t h low grade heat. Much l a r g e r temperature ranges can be achieved by s e l e c t i n g d i f f e r e n t a l l o y p a i r s (e.g., MggNi-LaNi^). A 3.5kw demonstration u n i t has been c o n s t r u c t e d by E r g e n i c s f o r New York S t a t e ERDA. The u n i t i s shown i n F i g u r e 18. LaNi5 and LaNili. 7 A I 0 . 3 were s e l e c t e d t o generate 9 5 - 1 0 0 °C water from 60 °C waste water and 20 °C c o o l i n g water. These v a l u e s were s e l e c t e d as r e p r e s e n t a t i v e o f a p p l i c a t i o n s i n t h e food p r o c e s s i n g i n d u s t r y . I n i t i a l t e s t s show t h a t t h e d e s i r e d thermal upgrading has been achieved and d e t a i l e d t e s t i n g and e v a l u a t i o n are now i n progress. DOE, through Brookhaven N a t i o n a l L a b o r a t o r i e s , has r e c e n t l y i s s u e d a c o n t r a c t f o r an i n d u s t r i a l team t o d e s i g n , b u i l d , and t e s t a p r o t o t y p e metal h y d r i d e heat pump f o r r e s i d e n t i a l , commerc i a l o r i n d u s t r i a l a p p l i c a t i o n s . T h i s t h r e e - y e a r program i s i n tended t o assess t h e commercial v i a b i l i t y o f t h i s technology. Concluding Remarks We have p r o v i d e d an i n t r o d u c t i o n t o the technology o f r e v e r s i b l e metal h y d r i d e s and reviewed the a p p l i c a t i o n s which are c u r r e n t l y b e i n g commercially developed. These i n c l u d e mobile and s t a t i o n a r y hydrogen s t o r a g e , hydrogen s e p a r a t i o n and p u r i f i c a t i o n , thermal hydrogen compression and heat pumping. Other a p p l i c a t i o n s i n e a r l i e r stages o f development i n c l u d e c a t a l y s i s (hydrogenation, F i s c h e r - T r o p s c h s y n t h e s i s ) and hydrogen b a t t e r y e l e c t r o d e s . To c a p i t a l i z e on the technology d e v e l oped so f a r , f u r t h e r advances a r e needed i n t h e f o l l o w i n g areas: l ) h y d r i d e s w i t h g r e a t e r hydrogen storage c a p a c i t y , 2 ) h y d r i d e s w i t h improved p o i s o n r e s i s t a n c e and thermal s t a b i l i t y , and 3) methods f o r enhancing the heat t r a n s f e r c h a r a c t e r i s t i c s o f h y d r i d e systems. Acknowledgment The authors are indebted to G.D. Sandrock (Inco Research and Development Center, Inc), F.E. Lynch (Hydrogen Consultants Inc), F. G. Eisenberg (Air Products and Chemicals Inc) and P.P. Turillon (Ergenics) for many helpful discussions and original research materials used in the preparation of this manuscript.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

14.

Rechargeable

HUSTON A N D SHERIDAN

Metal

Hydrides

249

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch014

L i s t o f Symbols B

constant, see Eq. 2

dimensionless

C

hydrogen

volume (or mole) percent

CF

gas volume

CFM

volumetric

concentration

cubic gas flow

feet

cubic f e e t per minute

ZiH

heat o f r e a c t i o n

k cal/mole H2

Lf

reaction front

feet

M

misch metal (U8-50* Ce, 32-3W La, 13-1W Nd, h-5% P r , 1.5* other rare earths)

psia

pressure absolute

l b . force/square i n c h

psig

pressure gauge

l b . force/square i n c h

SCF

gas volume a t standard c o n d i t i o n s , 1 atm pressure and 0°C

cubic

SCFM

volumetric

cubic f e e t p e r minute (M)

SCFH

a t standard

length

gas flow conditions

SCFD

feet

cubic f e e t per hour (H) cubic f e e t p e r day (D)

MSCF

gas volume a t standard conditions

103 cubic

MMSCFD

volumetric

1()6 cubic f e e t p e r day (D)

gas flow

at standard

feet

conditions

R

u n i v e r s a l gas constant

T

temperature

Vf X

reaction front v e l o c i t y s t o i c h i o m e t r i c coe f f i c i e n t f o r Eq. 1

Subscripts T and 0

feed and o u t l e t conditions, respectively

appropriate

units

°K (or °C) f e e t per minute dimensionless dimensionless

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

250

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4.

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EARTH

ELEMENTS

References 1. Sandrock, G.D.; Snape, E. "Rechargeable Metal Hydrides. A New Concept in Hydrogen Storage, Processing and Handling". ACS Symposium Series No. 116, Hydrogen Production and Marketing 1980, 293. 2. Huston, E.L.; Sandrock, G.D. "Engineering Properties of Metal Hydrides" to be published in J. Less-Common Metals, 1980. 3. Reilly, J.J.; Hydrogen It's Technology and Implications Vol. II, Chapter 2, Cox, K.E. and Williamson, K.D., editors, CRC Press, Boca Raton, Fl. 1977. Reilly, J.J. and Sandrock, G.D. "Hydrogen Storage in Metal Hydrides", Scientific American, 242 No. 2, 1980, 118. 5. Goodell, P.D. "Thermal Conductivity of Hydriding Alloy Powders and Comparisons of Reactor Systems", to be published in J. Less Common Metals, 1980. 6. Sandrock, G.D. and Goodell, P.D. "Surface Poisoning of LaNi , FeTi and (Fe,Mn) Ti byO2,COand H2O," ibid. 7. Goodell, P.D.; Sandrock, G.D. and Huston, E.L. "Kinetic and Dynamic Aspects of Rechargeable Metal Hydrides", ibid. 8. Howe, L.M. "Fire in the Water" ABC-TV Channel 7, Denver, Co. 1979. 9. Lynch, F.E. Hydrogen Consultants, Inc. Denver Co., Private Communication. 10. Chi, C.W. and Lee, H. "Natural Gas Purification by 5A Molecular Sieves and It's Design Method", AIChE, Symposium Series, Gas Purification by Absorption, Zwiebel, I.; Broughton, D.B. and Camp, D.T. editors. Vol. 69, 1973, 95. 11. Klatt, K.H.; Wenzl, H.; Carl, A. and Pick, M. "Hydrogen in Metals, Hydrogen Storage, Hydrogen Purification". Technische Information No. 6, Kernforschungsanlage Julich GMBH, 1976. 12. McCue, J.C. "The Commercial Development of H2YCELL; Rare Earth Metal Hydride Storage Device", to be published in J. Less Common Metals, 1980. 13. Hinkebein, T.E.; Northrup, C.J. and Heckes, A.A. "Closed Cycle Hydride Engines" Sandia Laboratories Report, SAND782228, Dec. 1978. 14. Heckes, A.A.; Hinkebein, T.E. and Northrup, C.J. "Hydride Engines" Hydrogen, Proc. 14th Intersociety Energy Conversion Engineering Conference, Boston, MA. American Chemical Soc. 1 743 (1979). 15. Sheft, I.; Gruen, D.M. and Lamich, G. "HYCS0S:A Chemical Heat Pump and Energy Conversion System Based on Metal Hydrides" 1979 Status Report, Angonne National Laboratory Report ANL-79-8. 16. Terry, L.E. "Hydrogen-Hydride Absorption Systems and Methods for Refrigeration and Heat Pump Cycles" US Patent 4,055,962 Nov. 1, 1972. 17. Sirovich, B.E. "Hydride Heat Pump" US Patent 4,200,144 April 29, 1980. 5

RECEIVED

February 18, 1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

15 Oxygen Sensors FREDERICK L. KENNARD III

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch015

A C Spark Plug Division of General Motors Corporation, 1300 North Dort Highway, Flint, MI 48556

Recent emission control system development in the automotive industry has been directed mainly towards the use of three-way or dual bed catalytic converters. This type of converter system not only oxidizes the hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas but will also reduce the nitrous oxides (NOx). An integral part of this type of system is the exhaust oxygen sensor which is used to provide feedback for closed loop control of the air-fuel ratio. This is necessary since this type of catalytic converter system operates efficiently only when the composition of the exhaust gas is very near the stoichiometric point. This type of emission control system has been in use in limited volumes in California since the 1977 model year, on nearly all California cars in the 1980 model year, and will apparently be on a majority of cars in this country in the 1981 model year. No other method has been nearly as effective in meeting the federally mandated emission requirements without severe penalties in performance and/or fuel economy. While this paper w i l l concentrate on oxygen sensors as used in automotive applications, there is increasing interest in their use i n the measurement and control of industrial and other furnaces in order to reduce fuel costs by maximizing the combustion efficiency. They have also been used for many years to measure the oxygen content of molten glass, of molten steel and other metals and for numerous other applications where a measurement of the oxygen partial pressure is desired. While several types of oxygen sensors have been investigated for automotive use, the most common type in commercial use consists of a galvanic c e l l with a f u l l y or p a r t i a l l y stabilized zirconium oxide electrolyte. Stabilized zirconia refers to a solid solution of zirconium oxide with one or more of a number of stabilizing oxides (CaO, MgO, Y 0^, or others) to form a cubic fluorite structure. This 9

0097-6156/81/0164-0251 $05.00/0 © 1981 American Chemical Society In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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ELEMENTS

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch015

reduces or transition and a l s o zirconium

e l i m i n a t e s the d e s t r u c t i v e m o n o c l i n i c - t e t r a g o n a l phase encountered w i t h pure z i r c o n i a d u r i n g thermal c y c l i n g g r e a t l y i n c r e a s e s the oxygen i o n c o n d u c t i v i t y . The and s t a b i l i z e r c a t i o n s f i l l the c a t i o n s i t e s and the 2 + d i f f e r e n c e i n valence between the s t a b i l i z i n g c a t i o n s (Mg , 2^" 3"^" i Ca , Y , Yb ) and the z i r c o n i u m c a t i o n s (Zr ) i s compensated f o r by oxygen v a c a n c i e s . This d e f e c t s t r u c t u r e leads to a h i g h e l e c t r i c a l c o n d u c t i v i t y which i s e s s e n t i a l l y completely due t o oxygen i o n t r a n s p o r t ( f ) . When a z i r c o n i a e l e c t r o l y t e i s exposed on d i f f e r e n t s i d e s t o gases w i t h d i f f e r e n t oxygen p a r t i a l pressures a r e l a t i o n s h i p such as shown i n F i g u r e 1 i s obtained. The v o l t a g e , E, developed w i t h t h i s type of g a l v a n i c c e l l i s g i v e n by the Nernst equation as shown below: E

In

=

4F where R i s the gas constant, T i s ^ t h e absolute temperature, F i s the Faraday constant and ^o^ and ^o^ are the p a r t i a l pressures of oxygen i n the two gases. While a number of designs have been used, most oxygen sensors f o r automotive a p p l i c a t i o n s c o n s i s t of a hollow, c l o s e d end tube, a schematic of which i s shown i n F i g u r e 2. As shown, the i n t e r i o r of the c l o s e d end tube i s open t o the atmosphere which serves as a constant or reference oxygen p a r t i a l pressure w h i l e the e x t e r i o r i s exposed to the exhaust gas. The v o l t a g e s i g n a l produced by the e l e c t r o l y t e i s sensed by e l e c t r o d e s on the i n n e r and outer surface of the sensor. These, i n t u r n , are connected to the e l e c t r o n i c s package of the c l o s e d loop system. The e q u i l i b r i u m oxygen content of an exhaust gas as a funct i o n of the a i r - f u e l r a t i o i s shown i n F i g u r e 3. I t must be emphasized t h a t , w h i l e the t r a n s i e n t oxygen content can be a f f e c t e d by many f a c t o r s , the e q u i l i b r i u m oxygen content depends s o l e l y on the gas composition, a i r - f u e l r a t i o , and temperature. I t should a l s o be noted t h a t at the s t o i c h i o m e t r i c p o i n t , a change i n oxygen p a r t i a l pressure of many orders of magnitude occurs. In order t h a t the e q u i l i b r i u m and not the t r a n s i e n t oxygen content i s sensed, the exhaust s i d e of the sensor gene r a l l y has c a t a l y t i c e l e c t r o d e s although other means are p o s s i b l e to achieve t h i s end. F i g u r e 4 shows the t h e o r e t i c a l output of a sensor c a l c u l a t e d u s i n g the Nernst equation and the oxygen p a r t i a l pressures of F i g u r e 3. Again note the step change a t the s t o i c h i o m e t r i c a i r - f u e l r a t i o . Many commercially a v a i l a b l e sensors have outputs t h a t c l o s e l y approach t h i s t h e o r e t i c a l r e l a t i o n s h i p .

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch015

15.

KENNARD

Oxygen

Figure 1.

253

Sensors

Schematic of oxygen sensor solid electrolyte galvanic cell

PLATINUM ELECTRODES

TO CLOSED LOOP

\\

CONTROL SYSTEM

J

"

-AIR

ZIRCONIA T U B E -

EXHAUST

EXHAUST PIPE

Figure 2.

Schematic of exhaust oxygen sensor

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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-10-

-20O

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch015

-30~ 400°C

RICH

LEAN

1 12

Figure 3.

1

13

1

1

14 15 AIR-FUEL RATIO

16

17

Exhaust gas equilibrium oxygen partial pressure as a junction of the air-fuel ratio

1200~ 1000-

400°C

=£> ~

800°C

y

~

600°C

^

Q.

O > LEAN

RICH 2

400-

~

800°C

200~

~ 12

13

400°C 14

600°C

R

15

16

17

AIR-FUEL RATIO

Figure 4.

Theoretical sensor output as a function of the air-fuel ratio

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch015

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Because o f t h i s type o f behavior, a sharp t r a n s i t i o n a t s t o i c h i o m e t r y but low s e n s i t i v i t y and temperature e f f e c t s e i t h e r r i c h o r l e a n o f t h i s p o i n t , the oxygen sensor i s most u s e f u l i n c o n t r o l l i n g a t the s t o i c h i o m e t r i c p o i n t . I t i s o f l i m i t e d usef u l n e s s a t other exhaust compositions. However, as shown i n F i g u r e 5, t h i s i s e x a c t l y the p o i n t a t which a three-way o r dual bed c a t a l y t i c converter i s most e f f i c i e n t . Only when the exhaust composition i s near the s t o i c h i o m e t r i c p o i n t w i l l both the o x i d a t i o n o f the HC and CO and the r e d u c t i o n o f the NO occur satisfactorily. F i g u r e 6 i s a schematic o f a c l o s e d loop ^system. I t c o n s i s t s b a s i c a l l y o f an oxygen sensor t o monitor the exhaust a i r - f u e l r a t i o , a "black box" e l e c t r o n i c c o n t r o l system, a c a r b u r e t o r o r f u e l i n j e c t o r which i s c o n t r o l l e d and adjusted by the "black box" and, f i n a l l y , a three-way o r dual bed converter. The s i g n a l from the oxygen sensor i s monitored c o n t i n u o u s l y by t h e e l e c t r o n i c s package which then a d j u s t s the c a r b u r e t o r o r f u e l i n j e c t o r t o c o n t r o l the a i r - f u e l r a t i o a t s t o i c h i o m e t r i c . E l e c t r o d e s and E l e c t r o d e P r o t e c t i v e Coating The e l e c t r o d e s and e l e c t r o d e p r o t e c t i v e c o a t i n g o f the oxygen sensor p l a y a c r u c i a l r o l e i n determining the performance c h a r a c t e r i s t i c s and d u r a b i l i t y (2). The e l e c t r o d e s used are the inner o r a i r - r e f e r e n c e e l e c t r o d e and the outer o r exhaust gas e l e c t r o d e . The p r o t e c t i v e c o a t i n g goes over the outer o r exhaust e l e c t r o d e . While a complete d i s c u s s i o n o f the requirements and p r o p e r t i e s o f the e l e c t r o d e s and e l e c t r o d e p r o t e c t i v e c o a t i n g i s beyond the scope o f t h i s paper, a b r i e f d e s c r i p t i o n w i l l be given. The i n n e r e l e c t r o d e must be o x i d a t i o n r e s i s t a n t a t temperatures up t o 1000 C, porous, and e x h i b i t good adhesion t o the electrolyte. The i n n e r e l e c t r o d e used f o r automotive a p p l i c a t i o n s has t y p i c a l l y been a t h i c k f i l m platinum m a t e r i a l . F i g u r e 7 i s a SEM micrograph o f a t y p i c a l i n n e r e l e c t r o d e . The outer o r exhaust e l e c t r o d e must s u r v i v e under both o x i d i z i n g and reducing c o n d i t i o n s a t temperatures up t o 1000 C, must a l s o be porous and have good adhesion t o t h e e l e c t r o l y t e and, i n a d d i t i o n , must be able t o c a t a l y z e r e a c t i o n s i n the exhaust gas i n order t h a t the e q u i l i b r i u m oxygen content i s measured. Again, platinum i s a good choice f o r t h i s e l e c t r o d e because o f i t s s t a b i l i t y under both o x i d i z i n g and reducing cond i t i o n s and because o f i t s e x c e l l e n t c a t a l y t i c p r o p e r t i e s . F i g u r e 8 shows a t y p i c a l t h i n f i l m outer e l e c t r o d e . F i n a l l y , t h e p r o t e c t i v e c o a t i n g over the outer e l e c t r o d e must r e s i s t a b r a s i o n by p a r t i c u l a t e s i n the exhaust gas, must be porous t o a l l o w access o f the exhaust t o t h e outer e l e c t r o d e , must adhere t o the outer e l e c t r o d e , must have expansion charact e r i s t i c s compatible w i t h the e l e c t r o l y t e , and must be s t a b l e under o x i d i z i n g and reducing c o n d i t i o n s a t temperatures up t o 1000 C. A flame sprayed s p i n e l (MgAl^O^) c o a t i n g as shown i n F i g u r e 9 meets these requirements.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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100

12

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14

15

16

17

AIR-FUEL RATIO

Figure 5.

Converter efficiency as a function of air-fuel ratio

Figure 6.

Schematic of closed loop system

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

ELEMENTS

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch015

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Figure 7.

Figure 8.

Oxygen Sensors

257

SEM micrograph of platinum thick film air electrode (bar = 75 microns)

SEM micrograph of platinum thin film exhaust electrode (bar = 7.5 microns)

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch015

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Figure 9.

ELEMENTS

SEM micrograph of flame sprayed spinel protective coating (bar = 75 microns)

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

KENNARD

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Electrolytes Many oxygen i o n conducting e l e c t r o l y t e s are a v a i l a b l e f o r sensor a p p l i c a t i o n s . These i n c l u d e mainly s o l i d s o l u t i o n s o f Z r 0 , HF0 , T h 0 , o r CeO . Of these, s t a b i l i z e d z i r c o n i a has been founa t o have the Best combination o f c o s t , mechanical, chemical, and e l e c t r i c a l p r o p e r t i e s f o r t h i s type o f a p p l i c a t i o n and has been the most w i d e l y used. Various s t a b i l i z e r s are a v a i l a b l e and have a s t r o n g e f f e c t on the p r o p e r t i e s obtained, p a r t i c u l a r l y the e l e c t r i c a l c o n d u c t i v i t y . The c o n d i t i o n s under which the sensor must perform s a t i s f a c t o r i l y are q u i t e severe. This i n c l u d e s a temperature range o f -40 t o 1000 C, o x i d i z i n g and reducing atmospheres, severe thermal shock c o n d i t i o n s and h i g h thermal and mechanical s t r e s s imposed due t o temperature g r a d i e n t s , v i b r a t i o n , e t c . The sensor must f u n c t i o n e l e c t r i c a l l y a t temperatures as low as 316 C and p r e f e r a b l y lower. This r e q u i r e s t h a t the e l e c t r o l y t e have good mechanical p r o p e r t i e s , h i g h r e s i s t a n c e t o thermal shock, good i o n i c c o n d u c t i v i t y a t low temperatures, and good chemical s t a b i l i t y over the temperature range o f use. I t must a l s o be a v a i l a b l e a t a reasonable cost. While t h i s r e q u i r e s some t r a d e - o f f i n p r o p e r t i e s , one e l e c t r o l y t e t h a t has had the most success i n meeting the above requirements i s a p a r t i a l l y s t a b i l i z e d z i r c o n i a body w i t h Y^O^ as a s t a b i l i z e r . A p a r t i a l l y s t a b i l i z e d body i s a body c o n t a i n i n g some percentage o f the u n s t a b i l i z e d m o n o c l i n i c z i r c o n i a phase w i t h the remainder the s t a b i l i z e d cubic phase. A t y p i c a l body f o r t h i s a p p l i c a t i o n contains 20% o f the m o n o c l i n i c phase. The p a r t i a l l y s t a b i l i z e d body gives g r e a t l y improved mechanical p r o p e r t i e s and thermal shock r e s i s t a n c e although a t a s a c r i f i c e i n e l e c t r i c a l conduct i v i t y w h i l e the use o f Y^O^ as a s t a b i l i z e r achieves a balance between c o s t , i o n i c c o n d u c t i v i t y , and chemical s t a b i l i t y . The f o l l o w i n g t a b l e c o n t r a s t s the p r o p e r t i e s o f a t y p i c a l partially stabilized zirconia (PSZ) body as used i n t h i s a p p l i c a t i o n w i t h a t y p i c a l f u l l y s t a b i l i z e d (Y 0~) body.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch015

2

2

2

9

FULLY STABILIZED

PARTIALLY STABILIZED

Transverse Bend S t r e n g t h (psi)

20-30,000

45-55,000

L i n e a r Thermal Expansion

11

7-8

(XIO"

6

in./in./°C)

Thermal Shock R e s i s t a n c e Ionic Conductivity

Poor -2 1 x 10

Good -3 4 x 10

(at 700°C) (ohm * cm

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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10-4-H—i—i—i 1200

1

1000 900 800

1

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600

ELEMENTS

1—i— 500

TEMPERATURE °C

Figure 10.

Figure 11.

Ionic conductivity of fully and partially stabilized zirconia bodies

Optical micrograph of high silica content (> 1%) yttria fully stabilized zirconia body (bar = 37 microns)

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch015

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As can be seen, the mechanical s t r e n g t h o f the p a r t i a l l y s t a b i l i z e d body i s approximately twice t h a t o f the f u l l y s t a b i l i z e d and the thermal expansion i s approximately 30% lower. Because o f t h i s , the thermal shock r e s i s t a n c e o f the PSZ body i s g r e a t l y improved. The i o n i c c o n d u c t i v i t y o f the PSZ body i s lower but i s s t i l l adequate f o r automotive a p p l i c a t i o n s . F i g u r e 10 compares t h e c o n d u c t i v i t y o f a y t t r i a p a r t i a l l y s t a b i l i z e d z i r c o n i a body w i t h s e v e r a l f u l l y s t a b i l i z e d bodies. F i g u r e 11 shows the m i c r o s t r u c t u r e o f a t y p i c a l fully s t a b i l i z e d body w i t h a high s i l i c a content (approximately 1% o r g r e a t e r ) w h i l e F i g u r e 12 i s f o r a low s i l i c a ( l e s s than 0.25%) f u l l y s t a b i l i z e d body. A l l o f the f u l l y s t a b i l i z e d p r o p e r t y data l i s t e d has been f o r a low s i l i c a compositions. The higher s i l i c a composition e x h i b i t s a much lower i o n i c c o n d u c t i v i t y without any s i g n i f i c a n t improvements i n other p r o p e r t i e s . F i g u r e 13 shows the m i c r o s t r u c t u r e o f a p a r t i a l l y s t a b i l i z e d body. Note the two phase s t r u c t u r e and very f i n e g r a i n s i z e o f t h i s body when compared w i t h the f u l l y s t a b i l i z e d bodies. The improved mechani c a l p r o p e r t i e s o f t h i s type o f p a r t i a l l y s t a b i l i z e d body are due mainly t o the f i n e g r a i n s i z e obtained w h i l e the r e d u c t i o n i n the i o n i c c o n d u c t i v i t y i s caused by the presence o f the lower c o n d u c t i v i t y monoclinic phase. I t should be noted t h a t i t i s p o s s i b l e t o produce f u l l y s t a b i l i z e d bodies w i t h much higher f r a c t u r e strengths than l i s t e d here b u t t h i s r e q u i r e s the use o f f i n e p a r t i c l e s i z e , c h e m i c a l l y prepared powders ( 3 ) . The use o f t h i s type o f m a t e r i a l i n v o l v e s a number o f p e n a l t i e s both i n cost and p r o c e s s a b i l i t y t h a t may be p r o h i b i t i v e f o r a high volume automotive a p p l i c a t i o n . I n a d d i t i o n t o the type o f p a r t i a l l y s t a b i l i z e d body described here, two other b a s i c types o f p a r t i a l l y s t a b i l i z e d bodies have been reported (4, 5). Both are c l a s s i f i e d as t r a n s f o r m a t i o n toughened p a r t i a l l y s t a b i l i z e d z i r c o n i a s and i n v o l v e d i f f e r e n t p r o c e s s i n g techniques t o o b t a i n a body w i t h v a r i o u s amounts o f a metastable t e t r a g o n a l phase. While the mechanical p r o p e r t i e s o f these mater i a l s have been s t u d i e d e x t e n s i v e l y , l i t t l e has been reported about t h e i r e l e c t r i c a l p r o p e r t i e s o r t h e i r s t a b i l i t y under the thermal, mechanical and chemical c o n d i t i o n s o f an automotive exhaust system. CaO has been used t o some degree as a s t a b i l i z e r and i s a t t r a c t i v e due t o i t s low c o s t . I t s i o n i c c o n d u c t i v i t y , however, i s approximately an order o f magnitude l e s s than an e q u i v a l e n t y t t r i a s t a b i l i z e d body. There has a l s o been some q u e s t i o n about the chemical s t a b i l i t y o f a CaO s t a b i l i z e d body, although t h i s may be more o f a f a c t o r w i t h a p a r t i a l l y s t a b i l i z e d body than a f u l l y s t a b i l i z e d body. C a l c i a f u l l y s t a b i l i z e d ZrO^ has been and may s t i l l be used i n commercial p r o d u c t i o n o f oxygen sensors. Yb^O^ s t a b i l i z e d e l e c t r o l y t e s have somewhat b e t t e r i o n i c c o n d u c t i v i t y than Y^Og s t a b i l i z e d m a t e r i a l s but are u n a t t r a c t i v e due t o the h i g h cosfT o f Yb 0^. 9

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Figure 12.

ELEMENTS

Optical micrograph of low silica content (< 0.25%) yttria fully stabilized zirconia body (bar = 75 microns)

Figure 13. SEM micrograph of yttria partially stabilized zirconia body (bar = 0.75 micron)

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Other f a i r l y common s t a b i l i z e r s f o r z i r c o n i a i n c l u d e MgO (low cost but poor i o n i c c o n d u c t i v i t y and s t a b i l i t y ) and Sc^O^ (good i o n i c c o n d u c t i v i t y but high c o s t ) . Other oxygen i o n conducting e l e c t r o l y t e s , CeO^, HfO^, and ThO^ doped with v a r i o u s oxides, g e n e r a l l y are found to have poorer ionic conductivity, may be unstable under certain c o n d i t i o n s and have other u n s u i t a b l e p r o p e r t i e s .

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch015

A l t e r n a t i v e Types of Oxygen Sensors One other type of oxygen sensor has r e c e i v e d considerable a t t e n t i o n as an a l t e r n a t i v e to the g a l v a n i c type of sensor. This i s the r e s i s t i v e type of sensor which uses a metal oxide whose resistance i s dependent on the oxygen p a r t i a l pressure (6). While a number of d i f f e r e n t oxides have been used, t i t a n i u m oxide appears to have the best combination of p r o p e r t i e s f o r automotive a p p l i c a t i o n s (7). Summary Oxygen sensors, i n low volume use as p a r t of a closed loop emission c o n t r o l system f o r automotive a p p l i c a t i o n s since 1977, have seen wide-spread use s t a r t i n g with the 1981 model y e a r . At the present time, a p a r t i a l l y s t a b i l i z e d z i r c o n i a e l e c t r o l y t e using y t t r i u m oxide as the s t a b i l i z e r appears to be the most common choice f o r t h i s a p p l i c a t i o n .

References 1.

Kingery, W. D.; Pappis, J . ; Doty, M. E.; Hill, D. C. J. Amer. Ceramic Society, 1959, 42 (8), 393398.

2.

Fleming, W. J. SAE Congress, 1977, Paper 770400.

3.

Scott, C. E.; Reed, J. S. Amer. Ceram. Soc. Bull., 1979, 58 (6) 587-90.

4.

Porter, D. L.; Heuer, A. H.; J. Amer. Ceram. Soc., 1977, 60 (34), 18384.

5.

Gupta, T. K.; Lange, F. F.; Bechtold, J. H. J. Mat. Sc., 1978, 13, 14641470.

6.

Logothetis, E. M., Ceram. Eng. & Sci. Proc. 1980, 1, 281301.

7.

Tien, T. Y.; Stadler, H. L.; Gibbons, E. F.; Zacmanidis, P. J . ; Amer. Ceram. Soc. Bull., 1975, 54 (3), 280-282.

RECEIVED

March 30, 1981.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

16 PLZT Electrooptic Ceramics and Devices GENE H . HAERTLING

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch016

Ceramic Products, Motorola Incorporated, 3434 Vassar N E , Albuquerque, N M 87107

Approximately ten years ago, i t was first reported by Haertling and Land (1) that optical transparency was achieved in a ferroelectric ceramic material. This material was, in reality, not just one composition but consisted of a series of compositions in the lanthanum modified lead zirconate-lead titanate (PLZT) solid solution region. The multiplicity of compositions, each with different mechanical, electrical and electrooptic properties; has led to a decade of study in defining the chemical and structural nature of these materials; in understanding the phenomena underlying their optical and electrooptic properties and in evaluating the practicality of the large number of possible applications (2-12). The purpose of this paper is to review the status of the PLZT materials, dealing particularly with specific compositions, processing and fabrication; and to demonstrate the application of these materials to practical devices. To date, these devices are largely confined to applications involving shutters and modulators, but PLZT ceramics also offer a promising solid state answer to display applications of the future. S p e c i f i c examples of m i l i t a r y and i n d u s t r i a l devices c i t e d i n t h i s paper i n c l u d e (1) the A i r Force sponsored Thermal/Flash P r o t e c t i v e Device, (2) B e l l and Howell's Data Recorder, (3) a stereo-viewing system manufactured by Megatek Corporation and (4) eye s a f e t y viewing d e v i c e s (welding helmet, i n s p e c t i o n goggles) by M o t o r o l a . Materials PLZT Compositional System. The s o l i d s o l u t i o n r e g i o n which forms the b a s i s o f the PLZT m a t e r i a l s i s a s e r i e s of compositions r e s u l t i n g from the complete m i s c i b i l i t y of l e a d z i r c o n a t e and lead t i t a n a t e (commonly designated a t PZT) i n each o t h e r . Modif i c a t i o n s to the PZT system by the a d d i t i o n o f lanthanum oxide has a marked b e n e f i c i a l e f f e c t upon s e v e r a l o f the b a s i c p r o p e r t i e s o f the m a t e r i a l such as decreased c o e r c i v e f i e l d and i n creased d i e l e c t r i c constant, electromechanical c o u p l i n g c o e f 0097-6156/81/0164-0265$05.00/0 © 1981 American Chemical Society In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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f i c i e n t , mechanical compliance and o p t i c a l transparency. The l a t t e r of these p r o p e r t i e s , o p t i c a l transparency, was only d i s covered i n r e c e n t years but came about as the r e s u l t o f an i n depth study of v a r i o u s a d d i t i v e s to the PLZT system. Results from t h i s work i n d i c a t e t h a t L a ^ , as a chemical m o d i f i e r , i s unique among the o f f - v a l e n t (chemical valency of the m o d i f i e r i s d i f f e r e n t or " o f f - v a l e n t " from t h a t of the i o n i t r e p l a c e s i n the +3 +2 l a t t i c e ; e.g., La r e p l a c i n g Pb ) a d d i t i v e s i n producing t r a n s parency. The reason f o r t h i s behavior i s s t i l l not f u l l y understood; however, i t i s known t h a t lanthanum i s , to a l a r g e extent, e f f e c t i v e because o f i t s h i g h s o l u b i l i t y i n the PZT oxygen o c t a h e d r a l s t r u c t u r e , thus producing an extensive s e r i e s of s i n g l e phase s o l i d s o l u t i o n compositions. The mechanism i s b e l i e v e d t o be one o f lowering the d i s t o r t i o n o f the u n i t c e l l , thereby r e ducing the o p t i c a l a n i s o t r o p y of the c r y s t a l l i n e l a t t i c e and a t the same time promoting uniform g r a i n growth and d e n s i f i c a t i o n of a s i n g l e phase, p o r e - f r e e s t r u c t u r e . A g e n e r a l i z e d formula f o r a l l compositions i n the PLZT system i s : l - x x < y l-y>l-x°3 4 where lanthanum ions r e p l a c e lead ions i n the A s i t e o f the p e r o v s k i t e ABO3 i o n i c s t r u c t u r e shown i n F i g u r e 1. Since L a ^ (added as La203) s u b s t i t u t e s f o r Pb , electrical neutrality i s maintained by the c r e a t i o n o f l a t t i c e s i t e v a c a n c i e s . The l o c a t i o n o f these vacancies i n e i t h e r the A(+2) s i t e s or B(+4) s i t e s o f the u n i t c e l l has not y e t been completely r e s o l v e d d e s p i t e numerous s t u d i e s on the subject; however, i t i s most probable t h a t both A and B s i t e vacancies e x i s t as p o i n t e d out by H a r d t l and Hennings (13). I f both A and B s i t e vacancies are present i n the l a t t i c e , i t i s £ expected t h a t the above f o r mulation would p r o v i d e excess Pb ions which are e x p e l l e d from the l a t t i c e (as PbO vapor) d u r i n g the d e n s i f i c a t i o n process a t elevated temperatures. T h i s behavior does, indeed, occur; and i n f a c t , i t has been r e p o r t e d by Snow (14) t h a t t h i s excess PbO cont r i b u t e s to a c h i e v i n g f u l l d e n s i t y by forming a l i q u i d phase a t the g r a i n boundaries and by i n h i b i t i n g g r a i n growth during the i n i t i a l stages of d e n s i f i c a t i o n . Both o f these e f f e c t s are benef i c i a l to the attainment of t h e o r e t i c a l l y dense m a t e r i a l by e l i minating r e s i d u a l p o r o s i t y before i t becomes entrapped w i t h i n the grains. The PLZT phase diagram i s given i n F i g u r e 2. As can be seen, the o v e r a l l e f f e c t o f adding lanthanum to the PZT system i s one o f decreasing the s t a b i l i t y of the f e r r o e l e c t r i c (FE) phases (a f e r r o e l e c t r i c m a t e r i a l possesses spontaneous i n t e r n a l p o l a r i z a t i o n , P, which can be switched by an e l e c t r i c f i e l d , E, as i l l u s t r a t e d i n the P vs. E h y s t e r e s i s loops i n F i g u r e 2) i n favor of the nonf e r r o e l e c t r i c c u b i c and a n t i f e r r o e l e c t r i c (AFE) phases. At a 65/35 r a t i o of PbZr03 to PbTi03, a c o n c e n t r a t i o n o f 9.5% l a n t h a num i s s u f f i c i e n t to reduce the rhombohedral-cubic phase t r a n s i -

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch016

+

P b

L a

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Ti

+

t

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+

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Figure 1. Configuration of the ABO unit cell shown with sites occupied by Pb, La, Zr, Ti and O atoms as in the paraelectric cubic phase of PLZT s

Figure 2. Room temperature phase diagram of the PLZT system illustrating phases present and typical hysteresis loops associated with each phase: compositions 1, 2 and 3 are 9565, 7065 and 12040, respectively

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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t i o n (Curie temperature) to below room temperature. Thus, a m a t e r i a l o f t h i s composition (designated as 9.5/65/35 or simply, 9565) i s n o n - f e r r o e l e c t r i c and cubic i n i t s v i r g i n c o n d i t i o n . I t i s i d e n t i f i e d as composition 1 on the phase diagram and w i l l be d i s c u s s e d l a t e r i n r e l a t i o n t o i t s o p t i c a l and e l e c t r o o p t i c properties. I t should be noted t h a t t h i s composition i s a l s o l o cated i n the c r o s s hatched p o r t i o n o f the diagram which i n d i c a t e s a r e g i o n o f metastable f e r r o e l e c t r i c phases t h a t can be e l e c t r i c a l l y induced with a s u f f i c i e n t l y high f i e l d . The phase diagram i s o n l y given to 15 atom percent La s i n c e a l l o f the compositions o f i n t e r e s t l i e w i t h i n t h i s range. A l though not shown, compositions with La c o n c e n t r a t i o n s higher than approximately 30% possess mixed phases and are o p t i c a l l y opaque. Processing and F a b r i c a t i o n . Ceramics are t r a d i t i o n a l l y prepared from powders formulated from the i n d i v i d u a l oxides; however, e a r l y attempts to produce the PLZT powders by t h i s method proved to be inadequate from the standpoint o f chemical and o p t i c a l u n i f o r m i t y . As a r e s u l t , a chemical c o - p r e c i p i t a t i o n method designed s p e c i f i c a l l y f o r the PLZT m a t e r i a l s which u t i l i z e d l i q u i d p r e c u r s o r m a t e r i a l s was developed and s u c c e s s f u l l y implemented as a p r o d u c t i o n process (15). F i g u r e 3 shows i n p i c t o r i a l form the v a r i o u s steps i n v o l v e d i n the powder p r o c e s s i n g and f a b r i c a t i o n o f the PLZT m a t e r i a l s . The high p u r i t y , l i q u i d organometallies, t e t r a b u t y l z i r c o n a t e and t e t r a b u t y l t i t a n a t e , are f i r s t i n t i m a t e l y mixed together i n a high speed blender along with the a p p r o p r i a t e amount of l e a d oxide powder and then p r e c i p i t a t e d by adding the lanthanum a c e t a t e s o l u t i o n while b l e n d i n g . As the lanthanum acetate i s introduced, the zirconium and t i t a n i u m butoxides are hydrolyzed by the water from the lanthanum a c e t a t e s o l u t i o n producing a p r e c i p i t a t e of mixed hydroxides. At the same time, lead oxide and lanthanum acetate r e a c t with the f r e s h l y hydrolyzed p r e c i p i t a t e to produce a f i n a l product c o n s i s t i n g of mixed oxides and hydroxides i n a t h i n s l u r r y form. The s l u r r y i s d r i e d , r e s u l t i n g i n the white p r e c i p i t a t e d powder shown i n F i g u r e 3. T h i s powder i s then c a l c i n e d or c h e m i c a l l y r e a c t e d a t an e l e v a t e d temperature (500°C f o r 16 hours) i n order to produce the d e s i r e d PLZT c r y s t a l l i n e phase. A f t e r c a l c i n i n g , the powder i s wet m i l l e d f o r s e v e r a l hours i n order to promote a d d i t i o n a l chemical homogeneity, d r i e d and prepressed i n t o a s l u g of proper s i z e and shape f o r hot pressing. A t y p i c a l hot p r e s s i n g setup i s given i n F i g u r e 4. Exp e r i e n c e has shown t h a t a simple u n i a x i a l , single-ended hot p r e s s i n g arrangement i s both r e l i a b l e and economical i n producing c o n s i s t e n t , o p t i c a l q u a l i t y m a t e r i a l . The prepressed s l u g i s p l a c e d i n t o a s i l i c o n c a r b i d e mold r e s t i n g on an alumina p l a t e and surrounded completely with a r e f r a c t o r y g r a i n such as magn e s i a or z i r c o n i a i n order to prevent r e a c t i o n with the mold a t high temperature. An alumina p l a t e and push rod are l o c a t e d

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch016

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Figure 3.

Electrooptic

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Various stages in the processing of PLZT ceramics

FORCE

Figure 4.

A typical setup for hot pressing PLZT ceramics

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on top of the s l u g and a modest amount of pressure i s a p p l i e d to the s l u g f o r alignment purposes. Heat-up of the furnace i s s t a r t e d , while a t the same time a vacuum i s drawn on the s l u g v i a a water-cooled vacuum chamber surrounding the furnace. Oxygen i s b a c k - f i l l e d i n t o the chamber a t 700°C, f u l l pressure i s a p p l i e d and the furnace temperature i s r a i s e d to i t s f i n a l value. Typic a l hot p r e s s i n g c o n d i t i o n s are 1250°C f o r 18 hours a t 2000 p s i . A f t e r hot p r e s s i n g , the s l u g i s extracted from the mold, i t s surfaces are cleaned, and i t i s then p o l i s h e d f o r o p t i c a l e v a l u a t i o n . T h i s method of vacuum/oxygen hot p r e s s i n g was s u c c e s s f u l l y used by Dungan and Snow (16) f o r f a b r i c a t i n g o p t i c a l q u a l i t y PLZT slugs up to f i v e inches i n diameter. An a l t e r n a t e method of hot p r e s s i n g i n flowing oxygen r a t h e r than vacuum/oxygen i s a l s o known to produce o p t i c a l q u a l i t y m a t e r i a l , but i t i s g e n e r a l l y l i m i t e d to s l u g s i z e s l e s s than two inches i n diameter. T y p i c a l examples of hot pressed ceramics are given i n F i g u r e 5. M i c r o s t r u c t u r e . Ceramic compositions i n the PLZT system c h a r a c t e r i s t i c a l l y e x h i b i t a h i g h l y uniform m i c r o s t r u c t u r e cons i s t i n g o f randomly o r i e n t e d , equiaxed g r a i n s ( c r y s t a l l i t e s ) i n t i m a t e l y bonded together. An example of such a m i c r o s t r u c t u r e i s shown i n F i g u r e 6 f o r PLZT 9565 thermally etched a t 1100°C. The average g r a i n s i z e of a given m a t e r i a l may vary from about two microns to 15 microns depending on the temperature and time of hot p r e s s i n g , with a t y p i c a l s i z e being approximately e i g h t microns average diameter. A uniform g r a i n s i z e i s a h i g h l y des i r a b l e f e a t u r e from the standpoint of performance. Another d i s t i n c t i v e c h a r a c t e r i s t i c of the PLZT m a t e r i a l s i s t h e i r f u l l y dense, p o r e - f r e e m i c r o s t r u c t u r e which i s devoid of any second phases. T h i s i s r e f l e c t e d i n measured bulk d e n s i t i e s which r o u t i n e l y exceed 99.9% of t h e o r e t i c a l d e n s i t y . The e x i s t ence o f pores or second phases i n the volume of the g r a i n s or i n the g r a i n boundaries i s undesirable s i n c e both a c t to i n c r e a s e l i g h t s c a t t e r i n g and reduce o p t i c a l transparency. O p t i c a l P r o p e r t i e s . The a d d i t i o n o f lanthanum oxide to PZT has a r a t h e r remarkable e f f e c t on the o p t i c a l transparency, e s p e c i a l l y when the amount of lanthanum exceeds seven atom p e r cent. Thin p o l i s h e d p l a t e s c h a r a c t e r i s t i c a l l y transmit about 67% o f the i n c i d e n t l i g h t . When broadband a n t i r e f l e c t i o n c o a t ings are a p p l i e d to the major s u r f a c e s , t h i s transmission i s i n creased to greater than 98%. Surface r e f l e c t i o n l o s s e s are a f u n c t i o n o f the index of r e f r a c t i o n (n = 2.5) of the PLZT. O p t i c a l absorption i n these m a t e r i a l s i s wavelength dependent, becoming extremely high i n the v i o l e t (short wavelength) end of the spectrum near 0.37 microns. In the i n f r a r e d p o r t i o n of the spectrum, transmittance remains high out to approximately 6.5 microns and then g r a d u a l l y decreases i n a r e g u l a r manner unt i l 12 microns, where the m a t e r i a l i s f u l l absorbing. The o p t i c a l t r a n s m i s s i o n c h a r a c t e r i s t i c s of three PLZT comp-

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch016

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Figure 5.

Figure 6.

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Examples of the optical transparency of quadratic PLZT ceramics

A typical microstructure of PLZT, composition 9565, illustrating the fully dense structure and uniform grain size

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch016

o s i t i o n s are given i n F i g u r e 7. These compositions (see F i g u r e 2) were s e l e c t e d because they represent m a t e r i a l s of d i s t i n c t l y d i f f e r e n t e l e c t r o o p t i c behavior. Composition 9565 i s s u b s t a n t i a l l y more transparent than e i t h e r of compositions 7065 or 12040. This i s most n o t i c e a b l e i n the blue end of the spectrum where absorpt i o n and l i g h t s c a t t e r i n g predominate. Both compositions 7065 and 12040 are f e r r o e l e c t r i c and hence possess domain w a l l s which produce index of r e f r a c t i o n d i s c o n t i n u i t i e s and l i g h t s c a t t e r i n g from w i t h i n the m a t e r i a l . The t e t r a g o n a l phase composition 12040 i s more transparent than the rhombohedral 7065 composition. A l l samples were measured i n the v i r g i n s t a t e . Electrooptic Properties, The e l e c t r o o p t i c p r o p e r t i e s of the PLZT m a t e r i a l s are i n t i m a t e l y r e l a t e d to t h e i r f e r r o e l e c t r i c properties. Consequently, v a r y i n g the f e r r o e l e c t r i c p o l a r i z a t i o n with an e l e c t r i c f i e l d such as i n a h y s t e r e s i s loop, produces a change i n the o p t i c a l p r o p e r t i e s of the ceramic. In a d d i t i o n , the magnitude of the observed e l e c t r o o p t i c e f f e c t i s dependent on both the strength and d i r e c t i o n of the e l e c t r i c f i e l d . PLZT ceramics d i s p l a y o p t i c a l l y u n i a x i a l p r o p e r t i e s on a microscopic s c a l e , and a l s o on a macroscopic s c a l e when p o l a r i z e d with an e l e c t r i c f i e l d . In u n i a x i a l c r y s t a l s there i s one unique symmetry a x i s , the o p t i c a x i s ( c o - l i n e a r with the f e r r o e l e c t r i c p o l a r i z a t i o n v e c t o r i n ceramic PLZT), which possesses d i f f e r e n t o p t i c a l p r o p e r t i e s than the other two orthogonal axes. That i s , l i g h t t r a v e l i n g i n a d i r e c t i o n along the o p t i c a x i s and v i b r a t i n g i n a d i r e c t i o n p e r p e n d i c u l a r to i t encounters a d i f f e r e n t index of r e f r a c t i o n (r^) than l i g h t t r a v e l i n g i n a d i r e c t i o n 90° to the o p t i c a x i s and v i b r a t i n g p a r a l l e l to i t ( n ) . The absolute d i f ference between the two i n d i c e s i s defined as the b i r e f r i n g e n c e ; i . e . , n - n = An. In ceramic m a t e r i a l s where a s t a t i s t i c a l array of randomly o r i e n t e d c r y s t a l l i t e s e x i s t , the macroscopic or e f f e c t i v e b i r e f r i n g e n c e i s designated by Ah. On a macroscopic s c a l e , "AH i s equal to zero before e l e c t r i c a l p o l i n g and has some f i n i t e value a f t e r p o l i n g , depending on the composition and the degree of p o l a r i z a t i o n . The An value i s a meaningful q u a n t i t y i n t h a t i t i s r e l a t e d to the o p t i c a l phase r e t a r d a t i o n i n the material. L i n e a r l y p o l a r i z e d l i g h t , on entering the e l e c t r i c a l l y energ i z e d ceramic, i s r e s o l v e d i n t o two p e r p e n d i c u l a r components whose v i b r a t i o n d i r e c t i o n s are defined by the c r y s t a l l o g r a p h i c axes o f the c r y s t a l l i t e s a c t i n g as one o p t i c a l e n t i t y . Because of the d i f f e r e n t r e f r a c t i v e i n d i c e s , n and nQ, the propagation v e l o c i t y of the two components w i l l be d i f f e r e n t w i t h i n the m a t e r i a l and w i l l r e s u l t i n a phase s h i f t c a l l e d r e t a r d a t i o n . The t o t a l r e t a r d a t i o n r i s a f u n c t i o n of both An and the o p t i c a l path length t (generally, t i s the p l a t e thickness) according to the r e l a t i o n ship of T = STTE". When s u f f i c i e n t v o l t a g e i s a p p l i e d to the c e r amic, a halfwave r e t a r d a t i o n i s achieved f o r one component r e l a t i v e to the other. The net r e s u l t i s one of r o t a t i n g the v i b r a e

e

Q

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In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch016

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t i o n d i r e c t i o n of the l i n e a r l y p o l a r i z e d l i g h t by 90°, thus allowi n g i t to be transmitted by the second (crossed) p o l a r i z e r i n the ON c o n d i t i o n . Switching o f the e l e c t r o o p t i c ceramic from a s t a t e o f zero r e t a r d a t i o n to halfwave r e t a r d a t i o n w i l l create an ON/OFF l i g h t shutter. S e l e c t i v e c o l o r f i l t e r i n g of white l i g h t may be achieved by extending the r e t a r d a t i o n beyond h a l f wavelength. Three common types of e l e c t r o o p t i c e f f e c t s are i l l u s t r a t e d i n F i g u r e 8; i . e . , q u a d r a t i c and l i n e a r b i r e f r i n g e n c e and memory s c a t t e r i n g . A l s o i n c l u d e d i n the f i g u r e i s a t y p i c a l setup r e q u i r e d f o r generating each e f f e c t along with the observed behavi o r shown i n terms of l i g h t i n t e n s i t y output (I) as a f u n c t i o n of e l e c t r i c f i e l d (E). The f i r s t and most widely a p p l i e d o f a l l of the e l e c t r o o p t i c responses i s the quadratic (Kerr) e f f e c t . I t i s generally d i s played by those m a t e r i a l s which are e s s e n t i a l l y cubic phase (comp o s i t i o n 1) but are l o c a t e d c l o s e to the f e r r o e l e c t r i c rhombohed r a l or t e t r a g o n a l phases. The d e s i g n a t i o n f o r t h i s e f f e c t i s d e r i v e d from the quadratic dependence o f An on e l e c t r i c f i e l d ; i . e . , An = k E . These m a t e r i a l s , by v i r t u e o f t h e i r n a t u r a l cubic symmetry, do not possess permanent p o l a r i z a t i o n and are not o p t i c a l l y b i r e f r i n g e n t i n t h e i r quiescent s t a t e . As such, they c o n t r i b u t e no o p t i c a l r e t a r d a t i o n to an incoming p o l a r i z e d l i g h t beam; however, when an e l e c t r i c f i e l d i s a p p l i e d t o the m a t e r i a l , an e l e c t r i c p o l a r i z a t i o n (and consequently, b i r e f r i n g e n c e ) i s i n duced i n the m a t e r i a l and r e t a r d a t i o n i s observed between crossed p o l a r i z e r s ( c a l l e d an ON s t a t e ) . On removing the e l e c t r i c f i e l d , the m a t e r i a l r e l a x e s again to i t s cubic s t a t e and i s i n the OFF c o n d i t i o n . Relaxation times to the OFF c o n d i t i o n vary w i t h comp o s i t i o n but g e n e r a l l y range from one to 100 microseconds. Turn ON times are o f the same magnitude and ON-OFF r a t i o s as h i g h as 5000 to one have been measured. A p p l i c a t i o n s f o r the q u a d r a t i c e f f e c t i n c l u d e s h u t t e r s , o p t i c a l gates, d i s p l a y s , s p e c t r a l f i l t e r s , l i g h t modulators and v a r i a b l e d e n s i t y windows. A second type of behavior e x i s t i n g i n the PLZT's i s the l i n ear (Pockels) e f f e c t which i s g e n e r a l l y found i n high c o e r c i v e f i e l d , t e t r a g o n a l m a t e r i a l s (composition 3). This e f f e c t i s so named because o f the l i n e a r r e l a t i o n s h i p between An and e l e c t r i c field. The t r u l y l i n e a r , n o n h y s t e r e t i c character of t h i s e f f e c t has been found to be i n t r i n s i c to the m a t e r i a l and not due to domain r e o r i e n t a t i o n processes which occur i n the q u a d r a t i c and memory m a t e r i a l s . The l i n e a r m a t e r i a l s possess permanent remanent p o l a r i z a t i o n ; however, i n t h i s case the m a t e r i a l i s switched to i t s s a t u r a t i o n remanence, and i t remains i n t h a t s t a t e . O p t i c a l information i s e x t r a c t e d from the ceramic by the a c t i o n of an e l e c t r i c f i e l d which causes l i n e a r changes i n the b i r e f r i n g e n c e , but i n no case i s there p o l a r i z a t i o n r e v e r s a l i n the m a t e r i a l . The experimental setup f o r observing t h i s e f f e c t , as seen i n F i g u r e 8, i s i d e n t i c a l to t h a t f o r the q u a d r a t i c response, except t h a t the PLZT p l a t e i s prepoled t o s a t u r a t i o n remanence before u s i n g . A p p l i c a t i o n s i n c l u d e modulators and s p e c t r a l f i l t e r s ; however, no devices have y e t emerged u t i l i z i n g t h i s e f f e c t . 2

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Figure 8. Operational configurations and typical light output responses of (A) quadratic (B) linear, and (C) memory PLZT materials; the heavy accented portions of the response curves indicate the usable range.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch016

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A t h i r d type o f e l e c t r o o p t i c behavior which i s employed a l most e x c l u s i v e l y f o r d i s p l a y s i s t h a t of e l e c t r i c a l l y c o n t r o l l e d l i g h t s c a t t e r i n g i n a memory m a t e r i a l . T h i s e f f e c t , as observed i n the Cerampic (ceramic p i c t u r e ) device, was f i r s t reported i n 1972 by Smith and Land (17). The experimental arrangement i n v o l v e d i n observing t h i s e f f e c t i s given i n F i g u r e 8. No p o l a r i z e r s are employed s i n c e i t i s predominantly due to l i g h t s c a t t e r i n g from domains (areas o f l i k e p o l a r i z a t i o n ) w i t h i n the material. The o r i e n t a t i o n o f these domains are e l e c t r i c a l l y a l t e r able; and because l i g h t i s p r e f e r e n t i a l l y s c a t t e r e d along the p o l a r d i r e c t i o n o f the domains, the l i g h t transmitted by the PLZT p l a t e i s a l s o e l e c t r i c a l l y c o n t r o l l a b l e . In a d d i t i o n , l o c a l areas can be p o l a r i z e d to d i f f e r e n t l e v e l s l e a d i n g to an a b i l i t y f o r s t o r i n g images with a gray s c a l e c a p a b i l i t y and a r e s o l u t i o n o f a t l e a s t 30 l i n e p a i r s per m i l l i m e t e r . Once a given l o c a l area i s switched to a s p e c i f i c p o l a r i z a t i o n s t a t e , i t i s permanently locked i n u n t i l i t i s e l e c t r i c a l l y switched to a new s t a t e or the m a t e r i a l i s heated above i t s Curie p o i n t (thermally depoled) which erases a l l o f the p o l a r i z a t i o n s t a t e s . The means by which l o c a l areas are switched independently of each other i s provided by the photoconductor l a y e r sandwiched between one of the transparent ITO (indium-tin oxide) e l e c t r o d e s and the PLZT. When l i g h t impinges on the photoconductor l a y e r , i t reduces i t s r e s i s t i v i t y by s e v e r a l orders o f magnitude, e l e c t r o n s from the voltage source are t r a n s f e r r e d from the ITO e l e c t r o d e to the PLZT and the l o c a l p o l a r i z a t i o n i s switched to a new s t a t e . Erasure o f the t o t a l image i s performed by f l o o d i n g the p l a t e with l i g h t while the voltage i s a p p l i e d i n the p o s i t i v e s a t u r a t i o n d i r e c t i o n . The maximum cont r a s t r a t i o may be as h i g h as 100 to 1. In a d d i t i o n to the above three e f f e c t s , there are two others; i . e . , memory b i r e f r i n g e n c e and d e p o l a r i z a t i o n s c a t t e r i n g , which e x i s t i n the PLZT m a t e r i a l s and have been proposed f o r device a p p l i c a t i o n s . These are described i n reference 5. Applications Modes o f Operation. F i g u r e 8 a l s o i l l u s t r a t e s the two b a s i c modes o f o p e r a t i o n used i n e l e c t r b o p t i c devices; i . e . , the t r a n s verse and l o n g i t u d i n a l modes. In the transverse mode, the e l e c t r i c f i e l d i s a p p l i e d i n a d i r e c t i o n normal to the l i g h t propagat i o n d i r e c t i o n while i n the l o n g i t u d i n a l mode, the f i e l d i s ap p l i e d along the l i g h t propagation d i r e c t i o n . In general, the transverse mode of operation i s most e f f e c t i v e f o r v a r i a b l e b i r e f r i n g e n c e devices, and the l o n g i t u d i n a l mode i s b e t t e r s u i t e d f o r variable l i g h t scattering devices. A l s o , c o l o r e f f e c t s can be produced with v a r i a b l e b i r e f r i n g e n c e whereas they cannot with s c a t t e r i n g . V a r i a b l e b i r e f r i n g e n t devices always r e q u i r e the use o f p o l a r i z e d l i g h t ; however, s c a t t e r i n g devices may or may not necessitate polarized l i g h t . I t should be recognized t h a t i n

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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order t o produce p o l a r i z e d l i g h t from an incandescent white l i g h t source there i s a s u b s t a n t i a l l o s s i n l i g h t i n t e n s i t y . In the case o f an i d e a l , l i n e a r p o l a r i z e r , t h i s l o s s amounts t o 50% o f the i n c i d e n t l i g h t ; but t h i s l o s s i n c r e a s e s t o approximately 70% with the use o f p l a s t i c sheet p o l a r i z e r s such as P o l a r o i d ' s HN32 material. In t r a n s v e r s e mode devices such as s h u t t e r s o r v a r i a b l e dens i t y f i l t e r s , the e l e c t r i c f i e l d i s g e n e r a l l y a p p l i e d by means o f s u i t a b l e e l e c t r o d e p a t t e r n on one o r both major s u r f a c e s o f a p o l i s h e d p l a t e o f m a t e r i a l . Since viewing i s accomplished through the gap between the p o s i t i v e and negative e l e c t r o d e s , i t f o l l o w s t h a t the a c t i v a t i n g v o l t a g e can be reduced, f o r a given o v e r a l l viewing area, by reducing the gap width and i n c r e a s i n g the t o t a l number o f gaps. T h i s r e s u l t s i n a number o f narrow, i n t e r d i g i t a l e l e c t r o d e s on a given p l a t e . By p l a c i n g the d e v i c e out o f the f o c a l plane o f the o p t i c a l system,the f i n e e l e c t r o d e s ( ~ 0.04mm wide) a r e v i r t u a l l y i n v i s i b l e , and image q u a l i t y through the dev i c e i s e x c e l l e n t . In c o n t r a s t to the l o n g i t u d i n a l mode, the t r a n s v e r s e mode produces l a r g e r e l e c t r o o p t i c e f f e c t s ; and i n the a c t i v a t e d or ON s t a t e , the m a t e r i a l i s o p t i c a l l y c l e a r with essent i a l l y no s c a t t e r i n g . Devices u t i l i z i n g t h i s mode may o r may not e x h i b i t memory, depending on the composition. In the l o n g i t u d i n a l mode, v o l t a g e i s a p p l i e d through the t h i c k n e s s o f the p l a t e n e c e s s i t a t i n g the use o f t r a n s p a r e n t e l e c trodes such as t i n oxide o r ITO. Since t h i s mode g e n e r a l l y a l i g n s the macroscopic o p t i c a x i s o f the m a t e r i a l p a r a l l e l t o the d i r e c t i o n o f viewing, o p t i c a l b i r e f r i n g e n t e f f e c t s are minimal. In t h i s mode, the s t r e n g t h o f the e l e c t r i c a l s w i t c h i n g f i e l d i s dependent on the t h i c k n e s s o f the p l a t e and the s p e c i f i c composition s e l e c t e d , but i s independent o f the area. Thermal/Flash P r o t e c t i v e Device, In 1975 Sandia L a b o r a t o r i e s of Albuquerque, New Mexico, began the design and development o f PLZT goggles f o r the U.S. A i r Force t o p r o v i d e p r o t e c t i o n f o r a i r c r a f t personnel from f l a s h b l i n d n e s s caused by a n u c l e a r e x p l o s i o n (18). A t t h a t time, the technology f o r producing such a d e v i c e was i n i t s i n f a n c y and many o f the techniques r e q u i r e d f o r i t s development and manufacture were non-existent. In the next three years, s e v e r a l new t e c h n o l o g i e s such as PLZT p o l i s h i n g and e l e c t r o d i n g , high performance p o l a r i z e r s , l e n s bonding and the f a b r i c a t i o n o f s p e c i a l i z e d e l e c t r o n i c s were a l l developed and p u t i n t o p r a c t i c e . The f i n a l product, o f f i c i a l l y designated as the EEU-2/P F l a s h b l i n d n e s s F l y e r s Goggles, i s shown i n F i g u r e 9. I t possesses s e v e r a l advantages over i t s predecessor, a l i q u i d photochromic system, among which are i n c l u d e d (1) s m a l l e r s i z e , (2) l e s s weight, (3) s o l i d s t a t e , (4) f a s t e r response and (5) higher p o r t a bility. I t has been i n p r o d u c t i o n f o r the l a s t two years and i s the f i r s t PLZT d e v i c e to reach t h i s stage. The f l a s h b l i n d n e s s goggle i s b a s i c a l l y a transverse-mode shut t e r o f the c o n f i g u r a t i o n shown i n F i g u r e 3(A). The s h u t t e r i s

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Sandia Laboratories

Figure 9.

PLZT Thermal/Flash Protective Goggle developed by Sandia Laboratories for the U.S. Air Force

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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operated i n the f u l l y open or energized s t a t e u n t i l a l i g h t hazard i s detected by means of sensors mounted behind the viewing l e n s . When t h i s occurs, the PLZT e n e r g i z i n g voltage i s r a p i d l y discharged causing the goggles to r e v e r t to the c l o s e d s t a t e . When the t h r e a t i s removed, the PLZT i s re-energized and the open s t a t e i s r e s t o r e d . The open and c l o s e d s t a t e s of the device have t y p i c a l l y 20% and 0.006% transmission r e s p e c t i v e l y . Closure time i s l e s s than 150 microseconds. Data Recorder. The second PLZT device to reach the product i o n s t a t e (1979) i s a data d i s p l a y recorder manufactured by B e l l and Howell of Pasadena, C a l i f o r n i a . T h i s device i s shown i n F i g ure 10. The CEC HR-2000 Datagraph works on a p r i n c i p l e not p r e v i o u s l y used i n analog data r e c o r d i n g ; i . e . , a d i g i t a l l y cont r o l l e d e l e c t r o o p t i c s h u t t e r using p o l a r i z e d l i g h t and a PLZT c e r amic p l a t e as the e l e c t r o o p t i c m a t e r i a l (19). By s e l e c t i v e l y passing or b l o c k i n g l i g h t through a l i n e a r array o f hundreds o f t i n y l i g h t gates or s h u t t e r s , each of which i s c o n t r o l l e d by d r i ver e l e c t r o n i c s , the input data s i g n a l s are a c c u r a t e l y reproduced. L i g h t which passes through the l i g h t gates impinges upon d i r e c t p r i n t r e c o r d i n g paper to r e c o r d data waveforms w i t h high f i d e l i t y and accuracy. The o p e r a t i o n a l setup o f t h i s transverse-mode dev i c e i s the same as t h a t d e s c r i b e d i n F i g u r e 8(A). At the h e a r t o f the r e c o r d e r i s the a r r a y o f l i g h t gates composed of a number of PLZT p l a t e s c o n t a i n i n g vacuum deposited e l e c trodes spaced 0.0125 inches apart, thus p r o v i d i n g h i g h r e s o l u t i o n . By using t h i s type o f f i x e d , d i g i t a l l y c o n t r o l l e d s o l i d s t a t e array, the data recorder has e l i m i n a t e d such problems as l i n e a r i t y , beam d e f l e c t i o n , t a n g e n t i a l e r r o r , overshoot and i n e r t i a which l i m i t present galvanometer and CRT r e c o r d i n g d e v i c e s . The instrument has a frequency response from dc to 5 kHz s i n e wave or 10 kHz square wave and a r e c o r d i n g speed of 0.01 to 129 inches of paper per second. Stereo-Viewing Device. T h i s d e v i c e , now being s o l d under the name o f Megavision, has r e c e n t l y been developed by Megatek Corpora t i o n o f San Diego, C a l i f o r n i a . I t makes p o s s i b l e t r u e s t e r e o s c o p i c three-dimensional viewing of images on both v e c t o r r e f r e s h and r a s t e r scan computer graphic d i s p l a y s . The device i s shown i n F i g u r e 11. I t c o n s i s t s of a p a i r of l i g h t w e i g h t (1.5 oz.) viewing g l a s s e s , each l e n s of which i s s e p a r a t e l y e l e c t r o n i c a l l y cont r o l l e d through a small c a b l e to a belt-mounted backup u n i t . Each l e n s i s e s s e n t i a l l y an independently c o n t r o l l e d transverse-mode s h u t t e r of the type d e s c r i b e d i n F i g u r e 8(A). The s h u t t e r s are synchronized to an a l t e r n a t i n g p a i r of d i s p l a y e d images so t h a t only the l e f t eye sees the l e f t - e y e view and the r i g h t eye the r i g h t - e y e view. The views are a l t e r n a t e d a t a r a t e more than 30 Hz f o r each l e n s , a l l o w i n g the observer to p e r c e i v e a s i n g l e , s t e r e o s c o p i c image wrth a l i f e - l i k e sensation of o b j e c t depth. Some a p p l i c a t i o n s of t h i s device are f l i g h t simulators and t r a i n -

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch016

HAERTLING

Figure 10.

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Datagraph display recorder developed by Bell and Howell

Megatek Corporation

Figure 11.

Stereo-viewing system developed by Megatek Corporation

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ers, a i r t r a f f i c c o n t r o l , medical imaging, s c i e n t i f i c radar and sonar d i s p l a y s and contour mapping.

ELEMENTS

modeling,

Eye Safety Devices. Personnel eye s a f e t y devices such as the e l e c t r o n i c welding helmet, i n s p e c t i o n goggles and s a f e t y flip-down g l a s s e s mounted on a hard hat are some devices t h a t are i n the l a t t e r stages o f development a t the Ceramic Products department of Motorola, Inc. i n Albuquerque, New Mexico. A l l o f these d e v i c e s operate i n a manner very s i m i l a r to t h a t o f the f l a s h b l i n d n e s s goggles developed by Sandia L a b o r a t o r i e s . They are transverse-mode s h u t t e r d e v i c e s assembled i n a c o n f i g u r a t i o n as d e s c r i b e d i n F i g ure 8(A). An example o f the e l e c t r o n i c welding helmet i s shown i n F i g u r e 12. The l i g h t sensors and power supply are mounted e x t e r n a l l y to the PLZT s h u t t e r s which a c t as the v a r i a b l e d e n s i t y f i l t e r p l a t e . When an arc i s s t r u c k or some other s i m i l a r l y i n t e n s e l i g h t source i s a c t i v a t e d , the sensors d e t e c t t h i s change i n l i g h t l e v e l and remove the v o l t a g e from the s h u t t e r s , causing them to i n s t a n taneously darken to a shade p r e v i o u s l y s e t by the o p e r a t o r . When the a r c i s i n t e r r u p t e d , the s h u t t e r s q u i c k l y and a u t o m a t i c a l l y r e a c t i v a t e to t h e i r f u l l ON c o n d i t i o n . Since t h i s automatic a c t i o n e l i m i n a t e s the n e c e s s i t y o f r a i s i n g and lowering the helmet, the mask can be worn i n the down p o s i t i o n a t a l l times, thus i n c r e a s ing p r o d u c t i v i t y and p r e v e n t i n g a c c i d e n t a l eye burns from neighb o r i n g welding o p e r a t i o n s . A wide range o f f i l t e r p l a t e s from shade 4 (5.2% transmittance) to shade 14 (0.0004%) are a v a i l a b l e . Image Storage Devices. Research and development a c t i v i t i e s are c o n t i n u i n g a t Sandia L a b o r a t o r i e s i n Albuquerque, New Mexico, on image storage devices u t i l i z i n g PLZT ceramics. The Cerampic d e v i c e has r e c e i v e d extensive study f o r the p a s t s e v e r a l years and shows promise f o r image storage a p p l i c a t i o n s o f the f u t u r e . I t i s a l o n g i t u d i n a l s c a t t e r i n g mode d e v i c e as d e s c r i b e d i n F i g ure 8(C). E a r l y designs u t i l i z e d a photoconductor l a y e r which provided the s p a t i a l v a r i a t i o n s o f s w i t c h i n g v o l t a g e when exposed to s p a t i a l v a r i a t i o n s o f l i g h t i n t e n s i t y ( u s u a l l y through a cont a c t negative) needed to produce the image i n the ceramic. This photoconductor was subsequently e l i m i n a t e d by exposing the image with near UV l i g h t c o n t a i n i n g band gap (3.35 eV) or higher energy photons which produce a space charge f i e l d , thus a i d i n g the domain switching process. S i g n i f i c a n t improvements i n the s e n s i t i v i t y o f the exposure and r e c o r d i n g process were r e p o r t e d by Land and Peercy (20) through the use o f i o n i m p l a n t a t i o n (hydrogen and helium) i n the s u r f a c e o f the PLZT. Reductions i n exposure energy by as much as 10,000 times have more r e c e n t l y been achieved through the c o - i m p l a n t a t i o n o f argon and neon. Present exposure energy values o f about 10 /xJ/cm compare f a v o r a b l y with 100 /xJ/cm r e q u i r e d f o r f i n e - g r a i n e d holographic f i l m . An example o f t y p i c a l image q u a l i t y i s shown i n F i g u r e 13. The image i n the ceramic (A) was obtained by c o n t a c t exposure o f a negative produced from the o r i g i n a l photograph (B). 2

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch016

HAERTLING

Electrooptic

Ceramics and

281

Devices

Motorola Incorporated

Figure 12.

Electronic welding helmet developed by Motorola Incorporated

Sandia Laboratories

Figure 13. Example of image storage quality in memory PLZT 7065: (left) stored image and (right) original positive; ceramic device under development at Sandia Laboratories

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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RARE E A R T H

ELEMENTS

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch016

Summary The development o f o p t i c a l transparency i n f e r r o e l e c t r i c PLZT (lanthanum modified l e a d z i r c o n a t e t i t a n a t e ) ceramics a decade ago has s t i m u l a t e d a c o n s i d e r a b l e amount o f i n t e r e s t i n the nature o f these m a t e r i a l s / t h e i r e l e c t r o o p t i c behavior and t h e i r a p p l i c a t i o n to e l e c t r o o p t i c d e v i c e s . Although some measure o f o p t i c a l t r a n s parency has now been achieved i n other s i m i l a r f e r r o e l e c t r i c mat e r i a l s , r a r e - e a r t h lanthanum oxide i s unique i n i t s a b i l i t y t o produce the h i g h e s t q u a l i t y m a t e r i a l ; and thus, i t remains the standard o f the i n d u s t r y . The ceramics a r e c h a r a c t e r i z e d by good e l e c t r i c a l and o p t i c a l p r o p e r t i e s , uniform g r a i n s i z e and micros t r u c t u r e , h i g h e l e c t r o o p t i c c o e f f i c i e n t s and e x c e l l e n t moisture r e s i s t a n c e . T h e i r unusual combination o f p r o p e r t i e s have made them u s e f u l m a t e r i a l s f o r such s p e c i f i c a p p l i c a t i o n s as nuclear f l a s h b l i n d n e s s goggles, a data d i s p l a y r e c o r d e r , a stereoviewing system, an e l e c t r o n i c welding helmet and an image storage d i s p l a y device. An estimate o f the annual amount o f lanthanum oxide p r e s e n t l y being used i n a l l PLZT a p p l i c a t i o n s i s approximately 300Kg. T h i s f i g u r e i s c o n s e r v a t i v e l y p r o j e c t e d t o i n c r e a s e twenty-fold i n the next f i v e years as p r o d u c t i o n volumes i n c r e a s e and new a p p l i c a t i o n s f o r these m a t e r i a l s are r e a l i z e d .

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Haertling, G.H.; Land, C.E. J. Am. Ceram. Soc., 1971, 54, 1-11. Okazaki, K.; Nagata, K. J. Am. Ceram. Soc., 1973, 56, 82-86. Meitzler, A.H.; O'Bryan, H.M. Jr. Proc. IEEE, 1973, 61, 959-966. Keve, E.T.; Annis, A.D. Ferroelectrics, 1973, 5, 77-89 Land, C.E.; Thacher, P.D.; Haertling, G.H., "Applied Solid State Science"; Academic Press, New York, 1974; p. 137-233. Micheron, F.; Rouchon, J.M.; Vergnolle, M. Appl. Phys. Lett., 1974, 24, 605-607. Drake, M.D. Applied Optics, 1974, 13, 347-352. Maldonado, J.R.; Fraser, D.B.; Meitzler, A.H., "Advances in Image Pickup and Displays"; Academic Press, New York, 1975, p. 65-168. Cutchen, J.T.; Harris, J.; Laguna, G. Applied Optics, 1975, 14, 1866-1873. Roese, J.; Khalafalla, A. Ferroelectrics, 1976, 10, 47-51. Land, C.E. Optical Engineering, 1978, 17, 317-326. Samek, N.; Raymond, W. Proc. of the 25th Intl. Instr. Symp., 1979, 16, 485-500. Hardtl, K.H.; Hennings, D. J. Am. Ceram. Soc., 1972, 55, 230231. Snow, G.S. J. Am. Ceram. Soc., 1973, 56, 91-96. Haertling, G.H.; Land, C.E. Ferroelectrics, 1972, 3, 269-280. Dungan, R.; Snow, G. Bull. Am. Ceram. Soc., 1977, 56, 781-782. Smith, W.D.; Land, C.E. Appl. Phys. Lett., 1972, 20, 169-171.

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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18. Cutchen, J.T. Ferroelectrics, 1980, 27, 173-178. 19. Howes, P.A. Proc. of the 25th Intl. Instr. Symp., 1979, 16, 199-210. 20. Land, C.; Peercy, P. Appl. Phys. Lett., 1980, 37, 39-41. December 19, 1980.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ch016

RECEIVED

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ix001

INDEX Amplifier tubes 11 A Analcite 107 Abrasion, mechanical 12 Antimony 34 Absorption Applications, history of rare earth .... 3-17 /desorption isotherm for metalArc light carbons, wick in 9 hydrogen system 224/ Arrhenium, C. A 136 /desorption isotherms, hydrogen .... 224/ Arsenic 89 of didymium, selective 13 alloyed with nodular iron 35 process, metal hydride 234-236 Atomic submarine control rods 14 properties of metal hydrides 223-225 Auer wavefront curve 235/ incandescent mantle 6 Abundance and cost, rare earth lamps, ignition system for 8 oxides 118* -metals 8 Abundance of elements in igneous von Welsbach, Carl Freiherr 4-6, 9, rocks of earth crust 140* 65-67 Acid site population and strength Automobile exhaust catalysts 126/ zeolites 105 emission control 117,121-129 Activators in laser glasses 13 Automotive applications, oxygen Activity of zeolite catalysts 112 sensors in 251-263 Air pollution control 11 Air reference electrode 255 B platinum 257/ BaFCl:Eu phosphors 203 Alloys boron 69 BaFC1.05Eu, emission spectrum of 211/, 212 cerium in treatment 32/ 95 costs, R E M 60 Barnesite 4, 8, 95-96, 137, 141 flotation 30 Bastnasite composition 143* of gray iron 23 decomposition of 145 hydriding 229 ore 27, 33, 47 hydrogen storage 170 decomposition with sulfuric iron-carbon-silicon 19 acid 147/ lanthanum in iron-base 170 production of 16 magnesium-ferrosilicon 27 treatment 147/ nickel-magnesium 25 Beam index tubes 190 pure rare earth metals and 97 related 167-175 Beilby layer 135 pyrophoric 67 Berzelium, J. J 204 used in steelmaking, rare earth 43-49 Binders, polyvinyl butyral 272 titanium 169 Birefringence devices, variable 275 Alloying elements quadratic and linear 273, 274/ in liquid steel, densities 46* 34 melting points of 46* Bismuth 246 in steel, vapor pressures of 44* Bladder pump, down-hole 69 Aluminum-deoxidized steels 51 Boron alloys Aminecarboxylic acids 156/ Bottom cone segregations in steelmaking 58-60 Ammonia 234-236 and breakthrough front 240/ Breakthrough, hydrogen curve 235/, 239/ purge gas, metal hydride process for 236-241 Breakthrough front, ammonia and .... 240/ 10 synthesis 236, 238 Breeder reactors catalytic 119 Br0nsted acidity, catalyst activity for gas-oil cracking and 110/ by steam reformation 237/ 287

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

RARE

288 Browning, stabilizing glass against ...85-89 Bubble domain memory materials .219-221 Bubble memories, magnetic 13 C Ca/S ratio for shape control in steel .. 62t CaO stabilized body 261 CaW0 phosphors 203 Ce-Fe eutectic 63 Ce on Pt/Rh catalysts, effect of 128/ CeO-Si activated complex 97 Ce0 effect on CO activity delay time .... 127/ catalyst 125 transmittance curve of glass containing 86/ and TiO 86/ CO activity delay time 126/ effect of Ce0 on 127/ conversion delay time 125 Pt catalysts for 128/ /Ce 128/ via water-gas shift reaction 127/ emissions from regenerators 109, 112 Calcination furnace 165/ Calcium 29,51 alloyability of 53 -carbide desulfurization 30 compounds, steel desulfurization based on 72 -magnesium sulfides 25 Capture cross-section 14 Carbide stabilizers 31, 34 Carbides, free energy of formation of 54/ Carbonfilamentlamp 6 Carbonatite(s) 141 deposits 141, 142/ Carrier solvent 159 Catalyst(s) activity for gas-oil cracking and Br0nsted acidity 110/ for automobile exhaust emission control 117, 121-129 cracking 11 rare earths in zeolite 101-116 performance in cycling test, three-way 126/ rare earths in noncracking 117-131 thorium oxide 10 Catalytic converter(s) 168 dual bed 121,251 efficiency 256/ three-way 251 Catalytic electrodes 252 Catastrophic failures of large diameter line pipe 63 4

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ix001

2

a

2

EARTH

ELEMENTS

Cathode ray excitation 204 faceplates 87 tube 81 phosphors, rare earths in 177-192 Cation exchange, zeolite 107-109 Ceramic(s) compositions, microstructure 270 device 275 industry, yellow pigments for 13 PLZT electrooptic 265-282 hot pressing 269/ processing of 269/ substrates 168-169 Ceria 100, 135-137 components of 137 Ceric oxide 15, 96 Cerite 135 Cerium 4,10,25,43,89,117 hydrides 14 -iron phase diagram 45/ oxalate 12 -oxide 8 in glass 81 polishing 95 polishing compounds, world market for 98 -promoted lummus catalyst 118f stabilization of glass 81, 87 -sulfur solubility products in steels 69 in treatment alloy 32/ Cerox 95 Chabasite 107 Chelating agents 155 Chemical compressor, hydride 243, 245/ decolorization of iron 13 glass decolorizing 89 modifiers 159,266 properties of rare earth 11-12 -ceramic 11 Chromaticity coordinates 179 diagram, CIE 178/ system, CIE 179 Chromium as glass colorants 82 CIE (Commission Internationale de l'Eclairage) 179 Cobalt 13,89,125 as glass colorant 82 oxide 89 Cold formability of steel 65 Cold punching, resistance to spalling during 56 Color-rendering index (CRI) 196/, 197 Colorant, neodymium oxide as glass . 82 Colorants, rare earth oxides as 83-85 Combustion efficiency 251

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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INDEX

Commission Internationale de l'Eclairage (CIE) 179 Compacted graphite iron 37 microstructure of 38/ Complexing agent 153 Compression ratios for hydrides ...243, 244/ Computer terminal phosphors 189 Consumption of cerium-oxide polishing compounds 98* Control analysis in liquid-liquid extraction 163/ Control rods, atomic submarines 14 Controlling deleterious elements in cast iron, rare earths in 34—38 Cooling rates of cast irons 21 Copper as glass colorant 82 Co-precipitation of PLZT powders, chemical 268 Cost, rare earth oxides abundance and 118* Countercurrent contacting, multistage 157,158/ Cracking catalysts 11 rare earths in zeolite 101-116 Cracking, catalytic 11 Cryogenic processes 241 Cryogenic storage systems 170 Crown glass 91 Crystal glasses 85 Crystallization, fractional 152 Cubic flourite structure 251-252 Cupolas, acid-lined 29 Cycling test, three-way catalyst performance in 126/

Desulfurization of base irons 29-30 steel 70 based on calcium compounds .... 72 plus sulfide shape control, optimization of 61/ Dichroism 83 Didymia, physical properties of 136/ Didymium, selective absorption of .... 13 Didymium welding glasses 83, 85 Diluent(s) 159 commercial 158* Discoloration by radiation, glass 85-89 Discovery and commercial separations, rare earths 135-166 Distribution coefficient 157 Divalent rare earth ions 198 Dysprosium metal 173-174 Dysprosium oxide 152

E

E r 0 , transmittance curve of glass containing 86/ Eu -activated phosphors 180, 183 E u emission (of) 177 blue-violet 199/ orange-red 196/ Earth crust, abundance of elements in igneous rocks of 140* Ekeberg, A. G 135 Electric dipole transition, ^ o - T a .... 198 Electric resistance welded pipe (ERW) 62 Electrode(s) air-reference 255 catalytic 252 D exhaust gas 255 276 5^-4/ electronic transitions 183, 185 Electroding, PLZT D - F electric dipole transition 198 Electrolysis, fused salt 8 Data display phosphors 189-190 Electrolyte(s) Data display recorder, PLZT 278, 279/ oxygen-ion-conducting 259-263 Decolorizing of glass 89-91 solid 11 Defects in steel ingots, subsurface 58 YboOs stabilized 261 Delay time, CO activity 126/ zirconium oxide 251-252 effect of Ce0 on 127/ Electronic shell transitions, inner 83 Delay time, CO conversion 125 structure of the lanthanides 150* Delayed mold addition practice in transitions, 5d-4f 183,185 steelmaking 48/ Electrooptic, PLZT Density(ies) ceramics 265-282 of alloying elements in liquid devices 265—282 steel 46* properties of 272-275 filters, variable 276 of x-ray phosphors, absolute 209* Element(s) in cast iron, rare earths in Deoxidation of liquid steel 58 controlling deleterious 34-38 Desorption isotherm for metalin igneous rocks of earth crust, hydrogen systems, absorption/ .. 224/ abundance of 140* Desorption properties of metal names, origins of rare earth 139/ hydrides 223-225 5

2

3

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3+

7

0

2

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In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ix001

290

RARE E A R T H

Eluting agent 153 Emission spectra of x-ray phosphors 209-212 Emission spectrum and europium concentration 188/ End use pattern in U.S. for ceriumoxide polishing compounds 98* Energy distributions of phosphors, spectral blue 186/ green 184/ red 182/ Energy efficiency, CRT 187 Epitaxy garnets, liquid phase 220-221 Erbium 83,174 oxide 85,91 trivalent 200 Ethylenediaminetetracetic acid 155 Europium 10, 12, 14, 152, 195 concentration, emission spectrum and 188/ -gadolinium separation factor 155 Eutectic, grain boundary 66/ Eutectic, MnS-Fe 51 Exhaust catalyst, three-way 121, 125 catalysts, automobile 126/ electrode, platinum 257/ emission standards for passenger cars, federal 124/ gas composition 124/ electrode 255 equilibrium oxygen partial pressure 254/ reactions 121, 125 oxygen sensor 253/ Extractant(s) 159 ionic 160/ Extracting agent(s) 157, 160/ Extraction, selective 145, 149, 153 Eye response principle 180 Eye safety devices, PLZT 280

FeS by MnS in steel making, replacement of 49 Faceplates, cathode ray 87 tube 81 Faceplates, television 87 Faujasite 107,108/ cages, synthetic 110/ Fecralloy 168 Federal exhaust emission standards for passenger cars 124/ Ferric oxide 96, 100 Ferroalloys, containing rare earths .... 33 Ferrocerium 49

ELEMENTS

Ferroelectric polarization 272 Ferrous metallurgy of R E M 49-58 Fission products of atomic reactors .... 10 Flashblindness goggle, PLZT 276-278 Flint(s) 11 glass 91 Flintstone 8 Fluid catalytic cracking unit 111/ cracking catalysts 101-116 usage, geographic distribution of 102/ cracking units, zeolite catalyst use inU.S 106/ Fluorescence in glass 93-94 Fluoride, rare earth 9 Fluxing agent(s) 49, 82 Fractional crystallization 152 Fused salt electrolysis 8 Future for rare earth elements 39-40 Future in steelmaking, R E M 73-74 G Gd 0 S:Tb phosphor(s) 203, 209 GdoO S.005Tb, emission spectrum " of 211/, 212 Gd 0 13 NNq Gadolin, Johan 135 Gadolinite 4,8,135 Gadolinium 43, 137, 153, 155 -gallium-garnets 13 metal 173-174 oxide 93 Galvanic cell, oxygen sensor solid electrolyte 253/ Gamma cross-section 174 Garnets, films of magnetic 219-220 Garnets, liquid phase epitaxy 220-221 Gas-oil cracking and Br0nsted acidity, catalyst activity for 110/ Gas velocity and reaction front 240/ Gasoline, production of 10 Glass(es) cerium-stabilized 81 coloring of 13 compositions, rare earths in 81-94 groups and glass types, optical map designating 92/ optical 91-93 polishing, cerium oxide in 95 surfacing techniques 96 soda-lime 82 Grain boundary eutectic 66/ Grain boundary(ies) in steel 47 precipitate 65 Granitic and syenitic rocks, hydrothermal fractions of 137 2

2

2

2

3

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Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ix001

INDEX

Granitic and syenitic rocks, pegmatitic fractions of 137 Graphite casting, nodular 12 in gray iron 22/ growth pattern 25 hexagonal structure of 22/ micrographs of flake 20/ morphology 31 in cast irons 23-25 of flake 21 in a nodular iron, flake 36/ nodule, x-ray scan of 26/ nucleation 25-27 sphericity of 34-35 spheroidal 23 in iron 36/ spheroids of 24/ Widmanstatten 34 Graphitization, primary 34 Gray iron 19-23 H Hafnium 169 Heat pump 13 cycles, hydride 247/ metal hydride 246-248 Hisinger, Wilheim 135 History of rare earth applications 3-17 Holmium, trivalent 200 Host lattices, rare earth 187 Hot -rolled steel, rare earth inclusion in 54/ -shortness in steel 47-49 workability of steel 65 Human visual system, spectral response of 199/ Hydride in steel, R E M 63-65 Hydride storage unit 230/ Hydrocarbon oxidation over V 0 .... 120 Hydrogen charging curve(s) 229, 231/ concentration and processing costs 242/ cracking resistance of steel 65 discharge curves 232/ discharge pressure 233/ -induced cracking, prevention of .... 64/ -induced cracking in steel 63-65 purification with metal hydrides .241-243 separations with metal hydrides .234-241 storage alloys 170 in metal hydrides 227-234 parameters 228* Hydrogenation, catalytic 119-120 Hydrothermal fractions of granitic and syenitic rocks 137 Hydrothermal stability, zeolite 112, 114/ 2

Igneous rocks of earth crust, abundance of elements in 140* Ignition system for Auer lamps 8 Image quality, x-ray 206 Image storage device(s), PLZT ...280,281/ Impact resistance 31 of steel 65 Inclusion clustering in steel 58 Intermetallics in cast irons, formation of 35-37 Ion exchange column, laboratory scale elution .... 154/ equilibrium 154/ separation 153 Ionic conductivity of stabilized zirconia bodies 260/ Iron(s) -base alloys, lanthanum in 170 carbides, eliminating 33 -carbon silicon alloys , 19 chemical decolorization of 13 foundries, malleable 34 as glass colorant 82 graphite in gray 22/ microstructures in cast 21 nodular 67 oxide in glass 89 rare earth elements in the production of 19-42 Isotopic exchange of oxygen of oxides with molecular oxygen 122/ K

Kerr effect Klaproth, M . H

273 135 L

5

La-Fe eutectic 63 LaCo0 125 LaNi H 229 LaOBr.002Tb, emission spectrum for 212 LaOBrrTm phosphors 203 LaOBr.002Tm, emission spectrum of 210/ LaOBr.003Tm, emission spectrum for 210/, 212 La 0 S:Tb phosphors 203, 209 Ladle blockage in steelmaking 58 Lambda-sensors 11 Lamellar tearing, resistance to 56 Lamp(s) carbon filament 6 metal halide 175 phosphors 195-201 Lanceramp 67 Lanthana, physical properties of 136/ 3

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RARE E A R T H

Lanthanide(s) contraction 149, 151/ electronic structure of 150/ and yttrium, separation of 149-155 Lanthanum 10,43,125 acetate 268 metal 169-170 optical glasses 81 oxide 13,93, 117 -zirconium incandescent mantle "... 6 Laser glasses, activators in 13 Lasers, neodymium glass 93 Lead 34 titanate 265 zirconate 265 Lens bonding 276 Light gates PLZT plates 278 production of 6-8 scattering devices, variable 275 Line pipe steel 56 Linear effect 273-275 Liquid-liquid extraction 155-159 control analysis in 163/ Liquid phase epitaxy garnets 220-221 Longitudinal mode 276 Lumen equivalent values of spectra distribution 181/ Luminescent efficiency 187 Luminosity response function 180 Luminous efficiency function 197 Lummus catalyst, cerium-promoted .. 118/ Lutetium and ytterbium separation .... 152 M M g A l 0 coating 255 Mg Si 30 Mn-Mo-Cb steels 62 Mn -activated phosphate 180 MnS by RES, replacing 53 in steelmaking, replacement of FeS by 49 in steelmaking, substitution of 51-53 Machinability of nodular iron castings 27 Magnesium 19,25,29 alloyability of 53 in cast iron, residual 30 -ferrosilicon alloys 27 addition of rare earths to 37 Magnetic bubble memories 13 Magnetic properties of rare earths .... 13 Magnets comparative properties for 171/ rare earth-cobalt permanent 171 samarium-cobalt permanent 15 2

2

2+

4

ELEMENTS

Manganese as glass colorant 82 oxide 89 sulfide(s) control 62 inclusion(s) 50/, 70 plasticity of 51 Mantle, incandescent Auer 6 gas 65 preparation of 7/ lanthanum-zirconium 6 Market for cerium-oxide polishing compounds, world 98 Market, rare earth 16-17 Mathieson hydrogen cylinder 227 Melting points of alloying elements ... 46/ Memory materials, bubble domain 219-221 Memory scattering 273, 274/ Metal(s) halide lamps 175 hydrides, rechargeable 223-249 -hydrogen system, absorption/ desorption isotherm for 224/ in steel, rare earth (REM) 43-78 Metallothermic reduction 168 Metallurgical effects of R E M in steel 65 Metallurgical properties of rare earths 12 Metallurgy of R E M , ferrous 49-58 Microactivity caused by zeolite catalyst usage, increase in 106/ response of zeolite cracking catalyst 114/ test 105 Microstructure of PLZT 271/ Microstructures in cast irons 21 Minerals, rare earth 137-142/, 149 Mischmetal 8, 25, 27, 43-47, 169, 172, 225 in liquid steel, solubility of 45/ producers of the western world 44 production capacity 44 in steels, use of 65-74 Mixer-settler 162/ Molecular sieve processes 241 Molecular sieves, separation of gases with 238 Monazite 8, 9, 65, 95, 137, 141 composition 144/ decomposition of 145, 149 deposits 146/ production of 16 sand 93 Mordenite 107 Morphology in cast irons, graphite ...23-25 Morphology of flake graphite 21

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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INDEX

Optical (continued) properties of PLZT 270-272 properties of rare earths 12-13 157, 158/ transmission characteristics of PLZT 274/ N transparency 266 Nd-isonikotinate 12 of PLZT ceramics 271/ Nd 0 , transmittance curve of glass Ore producers, rare earths ....141,145,146* containing 84/ Ores, rare earth 137-149 Pr Ou and 84/ Origins of rare earth element names .. 139/ NiMg 30 Oxidation Natrolite 107 catalytic 120-121 Neodymium 13, 43, 83 resistance of steel, high temperature 65 laser 13 selective 152-153 glass 93 Oxides as colorants, rare earth 83-85 oxide 89 Oxides, free energy of formation of .... 52/ as glass colorant 82 Oxygen Nernst equation 252 -ion-conducting electrolytes 259-263 Neutron lattice 120-121,125,198 absorber 14 mobility 121 capture cross-section 173 of oxides with molecular oxygen, generators, target materials in 174 isotopic exchange of 122/ radiography 174 partial pressure, exhaust gas Nickel equilibrium 254/ as glass colorant 82 sensors in automotive -magnesium alloy 25 applications 251-263 oxide 91 storage effect 125, 126/ Nitrides, free energy of formation of .. 54/ Oxysulfides, free energy of formation Nodular graphite castings 12 of R E M 52/ Nodular iron 67 flake graphite in 36/ P microsample 25/ rare earth elements in the Pr On and N d 0 , transmittance production of 19-42 curve of glass containing 84/ Nodule count and area of carbides .... 32/ Pr On, transmittance curve of glass Nodulizers in nodular iron containing 84f production 29-31 Pt Nodulizing elements 25, 29 catalysts for CO conversion 128/ Nuclear properties of rare earths 13-14 /Ce catalysts for CO conversion .... 128/ Nucleating agents 21 / R h catalysts, effect of Ce on 128/ rare earths 31-34 Packing density for hydrides, Nucleation, degree of 21 volumetric 227 Nucleation, graphite 25-27 Passenger cars, federal exhaust emission standards for 124* O Pegmatitic fractions of granitic and syenitic rocks 137 Off-gas hydrogen 234 35 Ophthalmic factory 96 Peralitic matrix 27 Ophthalmic glass 85 Percentages elongation, nodular irons Permanent magnets, rare earth-cobalt 171 Optical 15 anisotropy 266 Permanent magnets, samarium-cobalt 125, 129,190, compensation 13 Perovskite(s) 266, 267/ glass(es) 91-93, 96 industry 10 Petroleum cracking catalysts, rare earth usage in 104/ lanthanum 81 Pharmaceutical applications 12 images, conversion of radiologic 266, 267/ images to 206-208 Phase diagram, PLZT Phase transition, rhombohedralmap designating glass groups and cubic 266—268 glass types 92/

Mosander, C. G Multistage countercurrent contacting

2

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3

6

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

294

RARE E A R T H

Phosphates 141 Phosphor(s) blue 188/, 209 color television 185-187 CaW0 203 computer terminal 189 data display 189-190 green 184/ color television 183-185 lamp 195-201 manufacture 191 pigmented 189 rare earth(s) in cathode ray 177-192 for color contrast radiography 215-216 in color television 177-192 red 182/ color television ...10, 12-14, 180-183 sublinear and superlinear 189-190 word processor 189 x-ray for medical radiography 203-217 physical properties of 213/ rare earth 203-217 Photochromic glasses 85 Photon energies, x-ray 208 Photons, statistical fluctuations of x-ray 208 Physical glass decolorizers 89 Physical properties of x-ray phosphors 213/ Physico-chemistry of R E M 49-58 Picture tube, color 178/ television 177-179 Pigmented phosphors 189 Pigments for ceramic industry, yellow 13 Pilkington process 95 Platinum air reference electrode 257/ Platinum exhaust electrode 257/ Plasticity of manganese sulfides 51 Plasticity of sulfide inclusions in steel, hot 50/ PLZT compositional system 265-268 electrooptic ceramics 265-282 electrooptic devices 265-282 phase diagram 266 powders, chemical co-precipitation of 268/ Pockels effect 273-275 Polarization electric 273 ferroelectric 272 permanent remanent 273 spontaneous internal 266 Polarizers, high performance 276 Polishing compounds, rare earth 95-100 machine characteristics, sphere 100/

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ix001

4

ELEMENTS

Polishing (continued) machine characteristics, toric 100/ media 10,12,15 PLZT 276 slurry 96 Polymerization, catalytic 120-121 Polyvinyl butyral binders 204 Post inoculation of cast iron 33 Praseodymium 13, 43, 83, 172, 198 /neodymium 10 Prime-colors of human vision 197 Production capacity, mischmetal 44 Protective coating, electrode 255 Protective coating, spinel 258/ Pure rare earth metals and related alloys 167-175 Pure spectral colors 196/ Purity-based applications of rare earths 14-15 Pyrophoric alloy(s) 8, 67 Q

Quadratic effect Quantum efficiency of luminescent materials mottle noise

273 198 208 208

R Radiant energy of light 179 Radiation filtering actinic 87 glass discoloration by 85-89 shielding window(s) 87, 90/ Radiography neutron 174 rare earth phosphors for color contrast 215-216 x-ray phosphors for medical 203-217 Radiologic image signal to noise ratios of x-ray phosphors 209/ images to optical images, conversion of 206-208 signal to noise ratio 214 Rare earth inclusion in hot-rolled steel 54/ metals (REM) 43-78 in steel 43-78 silicide (RES) 47-49 replacing MnS by 53 Reactors, breeder 10 Reactors, fission products of atomic .. 10 Recycle caused by zeolite catalyst usage, decrease in 106/ Reduction, selective 152-153 Refinery catalytic cracking units 103

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

295

INDEX

Refrigeration, metal hydride 246-248 Regenerator of catalytic cracker 109 Rhombohedral-cubic phase transition 266-268 Rhone Poulenc ion exchange columns 156/ rare earths separation process ...159-161 separation facility 164/

S Sm Coi magnets 173* So poisoning, resistance to 129 Sr .3Llo.8Co0 129 Samarium 13,43,152 -cobalt magnets 171 permanent 15 -europium separation factor 155 metal 170-173 world production of 172* oxide 10 Saturation remanence 273 Scandium 174-175 Screen(s), x-ray -film systems 212-215 speed measurements 206 speed, resolution, radiologic noise of experimental 214* Scrubbing the extract 157 Seasickness, treatment for 12 Selenium 89 as glass colorant 82 2

7

2

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ix001

0

3

oxide

89

Separation(s) factor 152, 155 process, Rhone Poulenc rare earths 159-161 of rare earth elements 4 rare earths discovery and commercial 135-166 Shape control in steel, Ca/S ratio for 62* Shutter, electrooptic 278 Shutters, PLZT 276 Sieves, molecular 11 Signal to noise ratio(s), radiologic 214 of x-ray phosphors 209* Silica 96 Silicic acid 97 Silicide, rare earth (RES) 47-49 mixed 169 Silver as glass colorant 82 Sintered magnets 171-172 Slab-cast steels, sulfide shape control in 72 Soda-lime glasses 82 Sodalite cage 107, 108/ Sodium hydroxide treatment of monazite 145 Solarization, stabilizing glass against .85-89

Solubility of mischmetal in liquid steel 45/ Solubility products in steels, ceriumsulfur 69 Solute-solvent interaction 157 Solvating agents 159 Sources, analyses of rare earth 28* Spalling during cold punching, resistance to 56 Specific activities of rare earth oxides 123/ Spectral colors, pure 196/ distributions, lumen equivalent values of 181/ energy distributions of red phosphors 182/ power distribution of fluorescent lamp 199/ response of human visual system 199/ tristimulus values 181/ Sphere polishing machine characteristics 100* Spheroidal graphite 23 Spinel coating 255 protective 258/ Stabilization of glass, cerium 87 Standards for passenger cars, federal exhaust emission 124* Starch-polyacrylonitrile copolymers .. 120 Steam reformation, ammonia synthesis by 237/ Steel, rare earth metals (REM) in 43-78 Steelmaking practices 56-58 Steelmaking, R E M future in 73-74 Stereo-viewing device, PLZT 278-280 Stereo-viewing system, PLZT 279/ Strontium 125 chlorapatite 198 Sulfide(s) calcium-magnesium 25 free energy of formation of 52/ inclusions in steel, hot plasticity of .. 50/ shape control 56, 63, 65 optimization of desulfurization plus 61/ in slab-cast steels 72 Sulfur R E M affinity for 49-53 Sulfuric acid, bastnasite ore decomposition with 147/ Surface active elements 37 Surfacing techniques, glass 96 Superalloys 43, 169 Syenitic rocks, hydrothermal fractions of granitic and 137 Syenitic rocks, pegmatitic fractions of granitic and 137

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

RARE E A R T H

296

V

T

T-compound 49 T i 0 , transmittance curve of glass containing Ce0 and 86/ Target materials in neutron generators 174 Television faceplates 87 phosphors, rare earth consumption in 187-189 phosphors, rare earths in color .177-192 red phosphor in color 10, 12-13, 14 Tensile strengths, nodular irons 27 Terbium, trivalent , 200 Tetrabutyl titanate 268 Tetrabutyl zirconate 268 Thermal compression with metal hydrides .... 243 depolarization 275 /flash protective device, PLZT .276-278 /flash protective goggle, PLZT 277/ stability, zeolite 112, 113/ Thorium 8,95 nitrate 9 oxide 8,93 catalyst 10 removal processes 148 Thromboses, treatment for 12 Thulium 174 Thulium 3+ 198 Titanium 34,35-37,51 alloyability of 53 alloys 169 butoxide 268 as glass colorant 82 Toric polishing machine characteristics 100/ Transformation toughened partially stabilized zirconias 261 Transitions, inner electronic shell 83 Transmittance curve of glass containing Ce0 86/ and T i 0 86/ Er 0 86/ Nd 0 84/ Pr O 84/ and N d 0 84/ Transverse mode 276 Tri-H-butyl phosphate 145, 155 Trivalent species, separation of 155 Tundish nozzle blockage in steelmaking 58 2

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ix001

2

2

2

2

3

2

6

ELEMENTS

3

V 0 , hydrocarbon oxidation over .... 120 Vanadium-aluminum-nitrogen steel .. 69 Vanadium as glass colorant 82 Van't Hoff equation 225 Van't Hoff plots for hydrides 226/ Vapor pressures of alloying elements in steel 44/ Vision, prime-colors of human 197 Voltage penetration scheme 189 2

5

W Water-gas shift reactions, CO conversion via White field brightness Wick in arc light carbons Widmanstatten graphite Weld integrity of steel Welding glasses, neodymium helmet electronic helmet, PLZT electronic Word processor phosphors World market for cerium-oxide polishing compounds markets for rare earths production of rare earths production of samarium oxide

127/ 185 9 34 65 83 280 281/ 189 98 17/ 167 172/

X X-ray absorption, intrinsic 208-209 film sensitivities, blue and green .... 207/ intensifies 13 phosphors for medical radiography 203-217 phosphors for rare earth 203-217 screens absorptions of 205/ and film assembly 205/ intensifying 204 Xenotime 141 composition 144/ decomposition of 145, 149

n

2

Y

3

U U.O. pipe Uranium as glass colorant

62 82

Y faujasite Y zeolite Y b 0 stabilized electrolytes Y 0 stabilizer Ytterbite Ytterbium oxide separation, lutetium and 2

2

3

3

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

107 107 261 259 4 152 93 152

297

INDEX

Yttria 135-137 components of 137 oxides 138/ stabilized body 261 stabilized zirconia body 260/, 262/ Yttrium 12,29,43,153 hydrides 14 -lanthanum oxide 11 metal 168-169 oxide 11,93 separation of the lanthanides and 149-155

Z Zr0 , stabilization of 11 Zeolite(s) acid site population and strength .... 105

2+

Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0164.ix001

2

Zeolite(s) (continued) cracking catalysts, rare earths in 101-116 rare earth level effects 112-115 Zinc silicate :Mn 200 Zirconia(s) 100 body(ies) ionic conductivity of stabilized 260/ partially stabilized 259-261 transformation toughened 261 yttria stabilized 260/, 262/ Zirconium 51 alloy ability of 53 butoxide 268 oxide 96 electrolyte 251-252

In Industrial Applications of Rare Earth Elements; Gschneidner, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.