Soluble Silicates 9780841207301, 9780841209015, 0-8412-0730-5

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Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.fw001

Soluble Silicates

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.fw001

Soluble Silicates James S. Falcone, Jr., E D I T O R

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.fw001

The PQ Corporation

Based on a symposium jointly sponsored by the Divisions of Industrial and Engineering Chemistry and Inorganic Chemistry at the 182nd National Meeting of the American Chemical Society, New York, New York, August 26-27, 1981.

ACS SYMPOSIUM SERIES

AMERICAN CHEMICAL SOCIETY WASHINGTON, D. C. 1982

194

Library of Congress Cataloging in Publication Data

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.fw001

Soluble silicates. (ACS symposium series, ISSN 0097-6156; 194) "Based on a symposium jointly sponsored by the Divisions of Industrial and Engineering Chemistry and Inorganic Chemistry at the 182 nd National Meeting of the American Chemical Society, New York, New York, August 26-27, 1981." Includes bibliographies and index. 1. Silicates—Congresses. I. Falcone, James S., 1946- . II. American Chemical Society. Division of Industrial and Engineering Chemistry. III. American Chemistry Society. Division of Inorganic Chemistry. IV. Series. TP245.S5S64 1982 ISBN 0-8412-0730-5

66l .068324 82-11514 ACSMC8 194 1-374 1982 /

Copyright © 1982 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 spécifie 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 copying fee for each chapter is indicated in the code at the bottom of the first page of the chapter. 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

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.fw001

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Advisory Board David L. Allara

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James D . Idol, Jr.

Davis L. Temple, Jr.

Herbert D . Kaesz

Gunter Zweig

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.fw001

FOREWORD T h e A C S S Y M P O S I U M 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 A D V A N C E S IN C H E M I S T R Y 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.

As a further

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Papers published in the A C S S Y M P O S I U M

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are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.

PREFACE

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.pr001

Q P O D I U M S I L I C A T E S W E R E I N T R O D U C E D commercially in the United States over 100 years ago as a replacement for rosin in soaps. Today the use of soluble silicates in industry is widespread and effective. And for the past 30 years, users of soluble silicates have considered James Vail's two volume ACS Monograph No. 116, "Soluble Silicates: Their Properties and Uses," the definitive work on the subject. Since then significant advances have been made in understanding the chemistry of both the sodium silicates and their various derivative materials. Recently, however, the development of S i F T - N M R spectroscopy combined with X-ray structural information on solids and the refinement of chromatographic methods for silicate solutions and solids have begun to provide a clearer picture of the distribution of species in solution. The results of these efforts are only now beginning to shed further light on the complex chemistry of these materials. It is expected that the emerging knowledge of the structure and the influence of that structure on solution properties and reactivity will further enhance the value that these materials have in industrial processes. As we learn more about these "structured solutions," we can expect better understanding of silicate glass chemistry, the equilibria of species in soil and water, cement chemistry, the synthesis of synthetic silicates, and the role of silicates in industrial and biological systems. The 21 papers presented in this timely volume represent the recent work or summaries of studies of a significant cross section of researchers who have been studying soluble silicates and other relevant technologies. The topics may be viewed as four allied themes. The first group of papers deals with the history of these materials, modern instrumental methods for analysis and reviews their current environment, health, safety and regulatory status. Next, several papers cover aspects of the structural, colloid, and solution chemistry of soluble silicates, the solubility of amorphous silica, and a review of the chemistry of silanol groups. This last subject is included because evidence shows that the reaction chemistry of species in solutions of silicates with high S i 0 / N a 0 ratios may be analogous to the surface chemistry of a high surface area porous silica gel. 29

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The next group of papers discusses recent applications of the soluble silicates with particular emphasis on oil recovery. This is an application which arose by analogy to the use of soluble silicates in detergency; it is particularly interesting because here, as in detergency, many of the chemical properties of soluble silicates, acting in concert, play a role in the enhancement of oil production, i.e., basicity, the reactivity of silicate anions with metal ions and oxide surfaces, their hydrophilic nature and ability to form gels at higher concentration. The last section is made up of several papers on the preparation and properties of novel silicate materials of current interest. In closing, I would like to acknowledge The PQ Corporation for allowing me the time and support to bring together the many people interested in understanding and applying these useful materials and to acknowledge the contributions of the authors who share my enthusiasm for silicate chemistry. It is my feeling that this is simply the beginning of a new and exciting chapter in die growth of the understanding and use of these "inorganic polymers" for the future. J A M E S S. F A L C O N E , JR.

The PQ Corporation Research and Development Center Lafayette Hill, P A 19444 March 1, 1982.

χ

1 A Short History of the Manufacture of Soluble Silicates in the United States JOHN H. WILLS

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch001

K e n n e t Square, PA 19348

The manufacture o f s o l u b l e silicates o f soda and potash i n the USA began i n the 1850's and received a v i g r o r o u s push when it was found to be a s a t i s f a c t o r y replacement for r o s i n i n the manufacture o f strong soaps during the war between the s t a t e s . Continuous manufacture o f the g l a s s was introduced by the E l k i n t o n family, soap and candle makers i n P h i l a d e l p h i a , PA. The a l k a l i n e crystallized products now used widely in detergents were developed i n the e a r l y 1930's, based on the patents and phase s t u d i e s of Chester L. Baker. In that decade, Dr. W i l l i a m S t e r i c k e r took the lead i n the development o f coated r o o f i n g granules and the manufacture o f b l a c k and white t e l e v i s i o n tubes using potassium silicate to bind the pigment to the g l a s s face. The manufacture o f c a t a l y s t and other g e l s and replacement o f phosphates i n detergents by s o l u b l e silicates and other a d d i t i v e s i n the 1950's overshadowed the l o s s o f the corrugated box i n d u s t r y to s t a r c h adhesives. What I want to cover i s something o f the i n d u s t r i a l beginnings o f the s o l u b l e s i l i c a t e s , how t h e i r use has grown, perhaps a f e e l i n g o f the burgeoning o p t i m i s t i c aspect o f the world i n which i t took root and o f the people who i n f l u e n c e d and l e d i t s growth. Much reference i s made to the P h i l a d e l p h i a Quartz Co. (PQ Co.) - now the PQ Corporation because t h i s company has been a major f a c t o r throughout the whole period and because i t has been able to make much more e a r l y d a t a available.(Ο Most of you know that the s o l u b l e s i l i c a t e s are p r i m a r i l y the sodium s i l i c a t e s which are a v a i l a b l e over a range o f concentrations and r a t i o s o f Si(>2:Na20, i n c l u d i n g water s o l ­ u t i o n s , g l a s s e s , and c r y s t a l s according to the needs which i n d u s t r y has found f o r them. The s t o r y o f the i n d u s t r y began with a German p r o f e s s o r , Johann Nepomuk von Fuchs o f the German U n i v e r s i t y o f Landshut.

0097-6156/82/0194-0003$06.00/0 © 1982 A m e r i c a n C h e m i c a l Society

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He became i n t e r e s t e d i n t h i s chemical about 1818 and i n the next twelve years worked out the b a s i c technology f o r production and suggested most of the p o s s i b l e uses as i n d i c a t e d by h i s study of i t s p r o p e r t i e s . Under r o y a l e d i c t , i t was used for a time to protect the stages and c u r t a i n s of theatres from c a t a s t r o p h i c d i s a s t e r s by f i r e s current at the time. Kuhlman in France for a period took up the l e a d e r s h i p i n European development, but von Fuchs i n 1855, j u s t before he died i n 1856, wrote a f u l l report on h i s work and suggestions f o r use of s o l u b l e s i l i c a t e s and t h i s was widely read.(2) One major European a p p l i c a t i o n was the replacement of animal dung i n a t e x t i l e process c a l l e d "dunging , and Gossage developed a very good soap using s o l u b l e s i l i c a t e . His company, C r o s f i e l d s , prospered and e v e n t u a l l y became the leading soap and detergent producer under the s t y l e of Unilever. Also about t h i s time, there was a s e r i e s of patents i n the USA f o r the p r e p a r a t i o n and use of waterglass, p a r t i c u l a r l y i n soap. These give us some i n s i g h t i n t o the men who began the i n d u s t r y i n the USA.(3) The p r a c t i c e of shipping s o l u b l e g l a s s as b a l l a s t seems to have been a major problem f o r would be manufacturers i n New York and Boston. Philadelphia was the center of American chemical i n d u s t r y at the time and seems to have been b e t t e r s i t u a t e d . R e l a t i o n s between the North and South were s t r a i n e d , and the expectation of war threatened the supply of colophony or r o s i n on which the many small soapers r e l i e d for the p r e p a r a t i o n of stronger laundry products.(4) Most of these soapers a l s o made candles, and kerosene lamps were r a p i d l y reducing the demand for them.

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Industry

I n d u s t r i a l development of sodium s i l i c a t e i n America begins with Dr. Lewis Feuchtwanger. He had studied about 1830 with Professer Dobereiner at Jena. The professor had been f a s c i n a t e d by Fuchs reports and was working with s o l u b l e silicates. Feuchtwanger brought h i s enthusiasm home with him and w r i t e s that i n 1832, with the permission of Admiral Perry, he c a r r i e d out some s u c c e s s f u l t e s t s at the Brooklyn Navy Yard. The cannons were protected from rust for several years by a coating of mixed sodium s i l i c a t e and asphaltum. He a l s o extended the l i f e of the wooden docks s e v e r a l times by impregnating the wood p i l e s and substructures with d i l u t e sodium s i l i c a t e . The saturated wood prevented attack by teredo worms. He probably bought t h i s s i l i c a t e from Germany and d i s s o l v e d i t here but he does c l a i m that he was manufacturing i t i n 1869.15) I have found no other evidence that he had a p l a n t , but a Mr. Sawyer of P i t t s b u r g h , Pa. reported i n 1864 that he had been buying from Feuchtwanger(1_), and i n 1867 a t r e a t i s e on soap making states that Mr. D i e t e r i c h s , chemist for the " A t l a n t i c 1

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Quartz Co. of West P h i l a d e l p h i a " had also been buying from him.(6) I have found no other reference to t h i s company i n any d i r e c t o r i e s . Feuchtwanger's f i r s t p u b l i c a t i o n seems to have been w r i t t e n out longhand, although i t i s p o s s i b l e that the manuscript I saw had been copied from h i s book, a p r a c t i c e not uncommon at the time. J.M. Ordway deserves mention i n our record for besides the patents f o r making a l k a l i s i l i c a t e s by reducing sodium s u l f a t e and preparing an e a s i l y s o l u b l e powder by coacervating the l i q u i d noted e a r l i e r , he published an a r t i c l e on the h i s t o r y and use of s o l u b l e s i l i c a t e i n S i l l i m a n ' s Journal i n 1861 and a s e r i e s of a r t i c l e s i n the American Journal of Science i n 1861, 1862, 1865 and f i n a l l y i n 1907; an a c t i v e s c i e n t i f i c l i f e o f 45 years. In h i s a r t i c l e of 1861 ( 7 ) , he gives a complete de­ s c r i p t i o n of the state of the a r t from melting to d i s s o l v i n g . He was already aware that the raw m a t e r i a l s should be o f the highest p u r i t y and that soda ash was e a s i e r to use. Since sodium s u l f a t e was cheaper, the r e a c t i o n was f u l l y s t u d i e d . Glass furnaces from which i t was p o s s i b l e to draw a l i t t l e fused s i l i c a t e at a time and then add more charge were used. Consistent r e s u l t s were d i f f i c u l t to o b t a i n and he recommended melting the charge completely and drawing the melt at once. He mentions furnaces with beds of 24 and 40 square f e e t . Four charges of Na 0:2.5 S i 0 could be completed i n 24 hours. The charge was drawn i n t o i r o n pots, cooled, and ground to a d e s i r e d s i z e with cast i r o n , toothed, crushing r o l l e r s . If drawn i n t o water, i t would break i n t o small fragments which were d i f f i c u l t to dry. However they were r e a d i l y d i s s o l v e d by heating the water. The d i s i l i c a t e was e a s i e r to d i s s o l v e and was recommended for the c a l i c o p r i n t e r s . With soda ash as a l k a l i source he could draw s i x charges a day. 2

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In P h i l a d e l p h i a , a young Quaker named Thomas E l k i n t o n was coming o f age. His father had gone i n t o the manufacture of soap and candles i n 1831 a f t e r 15 years of missionary work with the Seneca and Iroquois Indians at Tunessassa, N.Y. Having served h i s time and needing to support h i s family, he followed a cousin i n t o t h i s new venture which required not only manual d e x t e r i t y but b a r t e r i n g s k i l l s and f a m i l i a r i t y with ship captains. The r e l a t i o n s h i p of the E l k i n t o n family of soap makers i n P h i l a d e l p h i a with a group s t y l e d v a r i o u s l y as the New York S i l i c a t e Co. or the New York Quartz Co. or the New York L i q u i d S i l i c a t e Co. as well as with J . M. Ordway and Hodges, S i l s b e e , and Richardson of Boston encompasses the r e a l foundation of the manufacture of s o l u b l e s i l i c a t e s i n t h i s country. Thomas E l k i n t o n was a young man of 22 when i n about 1857 he became i n t e r e s t e d i n applying s i l i c a t e s to the soap made by h i s f a t h e r . Q ) A f t e r he had read van Fuch's l a s t survey and had copied Gossage's E n g l i s h patent i n t o h i s j o u r n a l , Thomas E l k i n t o n bought i r o n pans for a furnace and i n 1858 spent $2.50

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for plans for a r e v e r b r a t o r y furnace. B r i c k s were ordered i n 1861, and the f i r s t four b a r r e l s of s i l i c a t e were sold i n e a r l y 1861. His US patent #39135 f o r a continuous furnace issued i n 1863. The design included a l l the b a s i c requirements f o r a s i l i c a t e furnace. This new furnace was b u i l t i n 1863 f o r $1,100. While the f i r s t attempt was a f a i l u r e because o f inadequate or inaccurate mixing of the sand and soda ash, h i s next attempt ( a f t e r a month given to d i g g i n g out and r e p a i r ) ran f o r a month and produced 122,000 pounds o f g l a s s . His patent and perhaps h i s other a c t i v i t i e s a l e r t e d the group i n New York. G. T. Vanderburg, Secretary o f the New York Quartz Co., obtained US patent #31648 i n 1863 and assigned i t to the L i q u i d Quartz Co. o f New York. T h i s improvement covered a soap i n which the added s i l i c a t e had a r a t i o o f Si02:Na20 above 1. Vanderburg had a l s o obtained US patent #28540 i n 1860 for a process f o r reducing a s i l i c e o u s substance to a f l u i d state using superheated steam. At about the same time, Thomas bought 10 pounds o f ground s i l i c a t e o f soda from the New York Quartz Co. and he a l s o met with Vanderburg to d i s c u s s the Gossage patent, perhaps at the time the ground g l a s s was ordered.(1) He had bought l i q u i d s i l i c a t e from them i n A p r i l , 1861. So, e a r l y i n 1864, the president of New York S i l i c a t e or Quartz Co. John Graecen, J r . and the Treasurer, Samuel Booth, approached Thomas and h i s brother Joseph at t h e i r soap f a c t o r y , 783 S. 2nd S t . , t h e i r father having passed the company t o them i n 1862. The New Yorkers mentioned that they owned the Vanderburg soap patent and suggested that i t was being i n ­ f r i n g e d . At the same time, they h i n t e d that they were a l a r g e and f i n a n c i a l l y sound company which could a f f o r d to manufacture s i l i c a t e at a p r i c e which would run the E l k i n t o n brothers out of the b u s i n e s s . They suggested a r o y a l t y of 1/4^ a pound f o r an a r t i c l e which sold f o r hi a pound, only 25% l e s s than today's bulk p r i c e o f 5.6^. The upshot was that a p a r t n e r s h i p was arranged, and the P h i l a d e l p h i a Quartz Co. came i n t o being as of February 25, 1864. The E l k i n t o n brothers were to be the a c t i v e partners and were to " c a r r y on the business i n accord with their religious principles." The New Yorkers arranged to l e a s e a property at 9th & M i f f l i n Streets from t h e i r e a r l i e r partner, a P h i l a d e l p h i a soap and candle maker with whom the brothers d e c l i n e d to be a s s o c i a t e d . This property was sold to Graecen and Booth i n 1867, and then on December 22, 1868 the E l k i n t o n brothers bought out t h e i r partners for about $23,000. In 1863-1864, Hodges, S i l s b e e , and Richardson o f I n d i a Wharf, Boston a d v e r t i s e d as agents for the New York Quartz Co. and the P h i l a d e l p h i a Quartz Co. Hodges was c u r i o u s and experimented with the production of s o l u b l e s i l i c a t e s using both ash and s a l t cake which r e q u i r e s C as a reducing agent and a l s o an o x i d i z i n g agent to get r i d of the d i s c o l o r a t i o n by the carbon. He described h i s work i n l e t t e r s to Thomas E l k i n t o n .

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In 1872, a f t e r the bankruptcy o f the New York Quartz Co., the Ordway patents were assigned f i r s t to Samuel Booth as r e c e i v e r and to Ordway and thence were assigned to Hodges and Co. Also i n 1872, the Vanderburgh patents were assigned to Booth by Ordway. F i n a l l y , i n the same year, a l l of these patents were assigned e q u a l l y to Coolidge and Hodges of Boston and the E l k i n t o n brothers o f P h i l a d e l p h i a . At about t h i s time Hodges advertised that h i s f i r m was the s o l e manufacturer i n New England at the Bayside A l k a l i Works i n South Boston. This i s r e a l l y the s t o r y of the beginning o f a l k a l i s i l i c a t e manufactured i n North America. The volume grew slowly. In 1893 Thomas wrote to C u r t i n , Hughes and Kellogg o f Boston that the commerical papers were u n l i k e l y to quote p r i c e s for a l k a l i s i l i c a t e s . He kept only small stocks f o r "outside users are so t r i v i a l that a chance order for a few g a l l o n s or b a r r e l s at a time w i l l cover the order."(1) The Centennial E x p o s i t i o n held i n P h i l a d e l p h i a i n 1876 seemed to dramatize the growth and excitement o f the times. Many companies had e x h i b i t s ; i n c l u d i n g Feuchtwanger and the Elkinton brothers. The P h i l a d e l p h i a Quartz Co. received the highest award of merit for "a most b e a u t i f u l e x h i b i t of s i l i c a t e of soda" according to one commentator. They had an a r r e s t i n g experiment i n which b l a c k , o i l y cotton rags used to wipe clean the many steam engines at the e x h i b i t i o n were washed with s i l i c a t e and turned out a l o v e l y s o f t white c o t t o n . The e a r l y development of furnaces and d i s s o l v e r s came at j u s t the r i g h t time, f o r the war between the s t a t e s i n 1861-1864 d i d cut o f f the r o s i n supply and created a demand f o r t h e i r product. The E l k i n t o n s had the advantage that they a l s o produced soap next door to the s i l i c a t e p l a n t . The s a l e o f s i l i c a t e was welcome, but e a r l y s a l e s records show only a few b a r r e l s . However, i n 1889 the P h i l a d e l p h i a Quartz Co. b u i l t a new plant at Anderson, Indiana r i g h t over a gas w e l l . It i s the oldest s i l i c a t e plant s t i l l producing and was next door to the l a r g e soap p l a n t of Peet Brothers. This e s t a b l i s h e d a custom s t i l l recognized i n the i n d u s t r y of s e l l i n g s i l i c a t e by p i p e l i n e . The F o r t v i l l e Chemical Co. was b u i l t near Anderson i n 1896 and was bought by G r a s s e l l i Chemical Co. i n 1902, as part of t h e i r expansion i n the a l k a l i business. Mechling Brothers b u i l t a plant i n Camden, NJ i n 1902 and the P h i l a d e l p h i a Quartz Co. expanded i n t o a l a r g e r plant on the Delaware River at Chester i n 1905. The Merrimac Chemical Co. at Lowell, Mass. produced s i l i c a t e i n 1890. This plant was acquired by Monsanto i n 1929. The Mechling p l a n t s , by then owned by A l l i e d Chemical Co, are now c l o s e d . One reason there i s very l i t t l e information on producers and s e l l e r s o f s i l i c a t e s i s that few people came seeking them. I assume that a drummer f o r s o l u b l e s i l i c a t e s came i n t o town, checked the l o c a l d i r e c t o r y (before phone books and yellow pages) and v i s i t e d a l l the l o c a l soap makers. In P h i l a d e l p h i a

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i n 1860 there were 45 and 22 i n New York. A s p e c i a l f a c t o r i n t h i s sales program was Charles Goudy, an Englishman with a broad background i n chemical manufacturing before c r o s s i n g the Atlantic. He s e t t l e d i n Marshalltown, Iowa for reasons having to do with h i s wife's h e a l t h and set up a very s u c c e s s f u l soap business. About 1876, he and Thomas E l k i n t o n , one or both, conceived the idea of a small machine c a r r i e d i n a s u i t c a s e which could demonstrate the use of s o l u b l e s i l i c a t e i n soap i n the would-be customer's o f f i c e . Goudy became a leading f i g u r e in PQ Co. and continued to t r a v e l u n t i l he was 80. He was t h e i r f i r s t development chemist and one of the f i r s t i n our chemical i n d u s t r y . In l a t e r years he was joined by h i s son George who had experience i n soap manufacture p r e v i o u s l y and became a leader i n PQ Co. as well as an i n d u s t r i a l statesman. The Growth of the Industry There i s a long l i s t o f companies and works b u i l t , bought, s o l d , merged, enlarged, or dismantled. The record i s not always c l e a r or exact and seems unnecessary to review. Figure 1 attempts to show the growth of production from 1850 to 1980 i n terms o f the l i q u i d s i l i c a t e which i s most common. This curve i s a composite from s e v e r a l sources, not a l l of which agree, and I have not t r i e d to show the y e a r l y ups and downs which appear when the annual census f i g u r e s are p l o t t e d . The curve follows i n a general way the growth of population as well as the gross n a t i o n a l product, but i t i s u s u a l l y hedged against depressions by the growth of the i n d u s t r i e s i t serves as well as i t s cost which makes i t a candidate for r e p l a c i n g more expensive items. The f i r s t f i f t y years are a record compiled by W.T. E l k i n t o n o f the production by the P h i l a d e l p h i a Quartz Co., p r i m a r i l y f o r the E l k i n t o n Soap Co., but f o r many other customers. I t does not include imported m a t e r i a l or the production by known competitors such as F o r t v i l l e i n 1896 or around Boston. I would suggest that the l i n e represents from 50 to 75% of the s i l i c a t e used up to 1900. This growth was p r i m a r i l y for use i n soap. James G. V a i l joined PQ Co. i n 1905 before f i n i s h i n g c o l l e g e . He then f i n i s h e d h i s formal chemical education at the I n s t i t u t e of Technology, Darmstadt, Germany, became president of the U.S. S o c i e t y of Chemical Engineers i n 1945-46 before r e t i r i n g f i n a l l y i n 1952 and wrote the major books on s o l u b l e s i l i c a t e s issued i n 1928 and i n 1952,(3) the year he d i e d . Soluble s i l i c a t e s as an adhesive had long been used i n small amounts when i n the 1890*s there began an i n t e n s i v e and continuing e f f o r t to produce paper boxes to compete with the wooden packaging then i n general use. Paperboard with a corrugated p l y between two sheets and complex machines were developed. The l a t e r development o f adhesive and cement uses

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5.0

4.0

3.0

2.0

1.0

0.0 2000

1850 1861 Figure

L

U.S. production

YEAR of soluble silicate 3.22 SiO :Na 0,1.39 g

2

in 10 pounds Sp. Gr. 9

of liquid,

equal

to

10

of s o l u b l e s i l i c a t e s has been reviewed on adhesives and cements.(8)

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i n a s e r i e s o f volumes

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Hydrous S i l i c a t e s During much o f the same period there was a l e s s important but more g e n e r a l l y known a p p l i c a t i o n that i s for the p r e s e r v a t i o n o f eggs. Many people had t h e i r own chickens or were canny enough to buy eggs when they were cheap i n the s p r i n g and summer. They kept ceramic crocks i n the c e l l a r f i l l e d with d i l u t e waterglass. The excess eggs were placed i n the crocks and the s i l i c a t e reacted with the s h e l l preventing e i t h e r l o s s or increase i n the water content o f the egg, entrance o f i n f e c t i v e agents, or l o s s o f the a i r c e l l and even when kept nine months of so they were s t i l l poachable. George Goudy conceived the need for a powdered s i l i c a t e which could be r e a d i l y d i s s o l v e d at home. Using L.B. Edgerton's patents issued i n 1916 ( 9 ) , f o r atomizing l i q u i d s i l i c a t e s , a d e s i c c a t e d s i l i c a t e was produced and sold as "Goudy s Egg P r e s e r v e r " i n 56oz. packages which would make 7 g a l l o n s o f d i l u t e d waterglass, a l l f o r one d o l l a r . Demand appeared to r i s e a f t e r the war, and i n 1930 arrangements were made to i n s t a l l a spray tower imported from Germany. With the i n c r e a s i n g use o f r e f r i g e r a t i o n and l a r g e s c a l e continuous production o f eggs, the market for egg preserver evaporated, but other developments such as muds for d r i l l i n g through heaving shale areas kept the new l a r g e r d e s i c c a t i o n tower i n operation. 9

The Development of the A l k a l i n e S i l i c a t e s f o r Detergents I suppose there are s t i l l soapers who consider s o l u b l e s i l i c a t e s an a d u l t e r a n t , a derogatory word. Following World War I, many researchers c a r r i e d out vigorous programs o f i n v e s t i g a t i o n and w r i t i n g to demonstrate the s e v e r a l ways i n which s o l u b l e s i l i c a t e s act as detergents themselves and a i d as b u i l d e r s i n c l e a n i n g i n combination with soaps and other detergents. J.D. C a r t e r ' s papers published about 1930 have been considered c l a s s i c s i n the f i e l d as they set out c r i t e r i a for s o i l i n g and measuring detergency.(10) Even before the f i r s t world war, the c l e a n i n g i n d u s t r y had begun to d e s i r e more a l k a l i n e detergents. The P u r i t a n Soap Co. suggested combinations of s i l i c a t e and soda ash, but a l l such combinations seemed l i a b l e to cake i n t h e i r c o n t a i n e r s . Chester L. Baker, a f t e r an e a r l y i n d o c t r i n a t i o n i n the c r y s t a l l i z a t i o n o f commercial borax and other s a l t s of S e a r l e s Lake, CA, i n 1927, became C h i e f Chemist of the P h i l a d e l p h i a Quartz Co. of C a l i f o r n i a , an a f f i l i a t e formed i n 1917 and owned 50% by the S t a u f f e r s . Baker arid l a t e r h i s a s s i s t a n t , Ralph Jue, worked long hours developing the phase r e l a t i o n s h i p s f o r the c r y s t a l l i z a t i o n of hydrated m e t a s i l i c a t e s o f sodium over

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the range o f 0 to 90°C. They e s t a b l i s h e d the e x i s t e n c e o f and c a r e f u l l y described the p h y s i c a l c h a r a c t e r i s t i c s o f the 5, 6, 8, and 9 hydrates and the c o n d i t i o n s f o r t h e i r appearance and disappearance.(11) They a l s o found and d e s c r i b e d the s e s q u i s i l i c a t e Na3HSi04.5H 0 (3Na 0:2Si0 :11H 0). They showed that a s o l u t i o n c a r e f u l l y prepared at the composition o f Na Si03.5H 0 ( N a 0 : S i 0 : 5 H 0 , pentahydrate) could be seeded and allowed to c r y s t a l l i z e i n a soap mold and then ground and s i z e d . Since there was no excess l i q u i d s i l i c a t e , the product was s t a b l e enough to ship from San F r a n c i s c o through the humid Panama Canal to P h i l a d e l p h i a without c a k i n g . T h i s was taken as the c r u c i a l t e s t f o r a commercial product, and h i s work became the b a s i s f o r the great development o f the a l k a l i n e s i l i c a t e powders. The f i r s t sales were made i n C a l i f o r n i a i n 1928. Later he brought out the s e s q u i s i l i c a t e and l a t e r s t i l l worked out the process f o r a granulated sodium m e t a s i l i c a t e . 2

2

2

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2

2

2

2

In 1980, the c a p a c i t y o f sodium m e t a s i l i c a t e as penta­ hydrate was about 580 m i l l i o n pounds. PQ Corporation i s s a i d to have the l a r g e s t c a p a c i t y with S t a u f f e r and Diamond-Shamrock f o l l o w i n g i n that o r d e r . By c r o s s l i c e n s e with PQ Co., Pennwalt developed a hydrated form o f o r t h o s i l i c a t e r a t i o about 1938. I t was an i n t e g r a l product made by mixing NaOH with the necessary amount o f another s i l i c a t e or s i l i c a . I f the c r y s t a l l i z e r was kept t u r n i n g , the mixture went through a higher temperature f l u i d s t a t e and g r a d u a l l y transformed i n t o p a r t i c l e s which were s t a b l e enough f o r commercial use. I know o f no phase diagrams showing the e x i s t e n c e of s t a b l e Na4Si04 ( 2 N a 0 . S i 0 ) or i t s hydrates, and the process i s no longer used. A l l s o - c a l l e d o r t h o s i l i c a t e i s now compounded and i s included i n the meta­ s i l i c a t e f i g u r e s . As shown i n Table I, the production o f these a l k a l i n e products not a v a i l a b l e before 1928 i s now v e r y l a r g e . 2

2

Table I USA Production i n M i l l i o n s o f Pounds o f Sodium M e t a s i l i c a t e ( C a l c u l a t e d as Pentahydrate) and o f Sodium Orthois i l i c a t e Na Si0 Year Na9Si0^:5H 0 9

1928 1929 1930 1940 1950 1955 1960 1965 1970 1976 1979 1980

0.3 e s t . 1.8 e s t . 4 est. 40 e s t . 198 314 386 502 450 378 433 336

4

4

0 1 est. 60 76 60 76 76 84 72 63 52 60 e s t .

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The Development of Other End Uses The chemist who bore the brunt of the i n t r o d u c t i o n o f these new detergents to the laundry and metal trades was W i l l i a m S t e r i c k e r . He always maintained that no l e a d i n g detergent or laundry soap ever held a l e a d i n g p o s i t i o n for a long period without i n c l u d i n g a good p r o p o r t i o n of sodium s i l i c a t e . From the time, 1922, when he earned h i s graduate degree at Mellon I n s t i t u t e studying the p r o p e r t i e s of sodium s i l i c a t e , he developed an uncanny sense of how to use i t i n commerical processes.(12) It was mainly h i s i n s i g h t which helped the developers of r o o f i n g granules, welding rod c o a t i n g s , o s c i l l o g r a p h c o a t i n g s , methods for preventing c o r r o s i o n i n s u s c e p t i b l e water systems, and c o a g u l a t i o n with a c t i v a t e d s i l i c a s o l s for the c l a r i f i c a t i o n of water and sewage. Just before the second World War the new detergents and non-soap compounds were appearing, and S t e r i c k e r was a leader i n working with soap and detergent a s s o c i a t i o n s to e s t a b l i s h the e f f i c a c y of s i l i c a t e s i n such systems where phosphates were g e n e r a l l y accepted. F i r s t , he demonstrated the n e c e s s i t y f o r the a n t i - c o r r o s i o n p r o p e r t i e s o f the s i l i c a t e s . This development was e s p e c i a l l y welcomed by our i n d u s t r y because the s t a r c h adhesives developed with a l k a l i and borax i n the 30*s l a r g e l y replaced the s i l i c a t e adhesives for box making i n the 50's, and t h i s l o s s caused much c o n s t e r n a t i o n among us. The g e l a t i o n of s o l u t i o n s of s o l u b l e s i l i c a t e s with a c i d s and a c i d i c s a l t s i s very o l d , but i n d u s t r i a l development began with the Wheaton patents i n England about 1922,(13) These were for base exchange g e l s f o r s o f t e n i n g water and were used through the 30's when they were g r a d u a l l y replaced with organic agents of higher c a p a c i t y . Newer v e r s i o n s are now being used i n detergents. Desiccant g e l s also began to appear i n the 30 s and Davison Chemical Co. was the c h i e f developer. The use of c a t a l y s t g e l s i n the petroleum i n d u s t r y boomed with World War II. The s i l i c a s i n f i n e l y d i v i d e d form and as s o l s came along during and a f t e r the war. Much of the s i l i c a t e production for use i n these areas i s c a p t i v e . The l i t h i u m s i l i c a t e s ( 1 4 , 15) which became a v a i l a b l e i n the 5 0 s are more expensive but are u s e f u l i n b i n d i n g c o r r o s i o n r e s i s t a n t coatings to i r o n , i n cements, and i n molds. f

The C o n t r i b u t i o n s of James V a i l James V a i l was a great p u b l i c i s t . Besides w r i t i n g many a r t i c l e s and r e p o r t s on a l l phases of s i l i c a t e technology, he put out a small monthly sheet - P's and Q*s - for over twenty years, and t h i s was known i n the chemical i n d u s t r y f a r beyond the s i l i c a t e f i e l d . In 1928, he published ACS Monograph #46 "Soluble S i l i c a t e s i n Industry" and t h i r t y years l a t e r he acceded to many requests and wrote ACS Monograph #116 "Soluble

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S i l i c a t e s " i n two volumes.(3) While much has happened s i n c e 1952, the book has not yet been replaced as the primary reference for s o l u b l e s i l i c a t e technology and should be reviewed f o r references and b a s i c information on processes and products I have so b r i e f l y mentioned. James V a i l was a man of great i n s i g h t , a poet, author, and above a l l a humanitarian. He c a r r i e d out s e n s i t i v e , s i g n i f i c a n t , supportive programs i n many parts of the world f o r the American Friends Service Committee of which he was Foreign Secretary f o r a long p e r i o d , about 1938 to 1948. He was i n India on such a mission when he d i e d . In h i s f i n a l paragraphs of Chapter 1 of h i s l a s t book, he notes the r i s i n g world population and the need to conserve resources not r e a d i l y r e p l a c e d . He notes there that phosphates are i r r e p l a c e a b l e and badly needed for f e r t i l i z e r i n a g r i c u l t u r e . Food resources continue to be scarce, and he p o i n t s out that a r a t i o n a l s o c i e t y would preserve phosphates both by conserving t h e i r use i n detergents and r e f u s i n g to spend energy and f e r t i l i z e r for the production of starches and p r o t e i n s for i n d u s t r i a l use which could j u s t as well be replaced by s o l u b l e s i l i c a t e s prepared from s a l t and sand, raw m a t e r i a l s abundant i n t o the foreseeable f u t u r e , " . . . s o l u b l e s i l i c a t e s now serve so wide a range o f i n d u s t r y that they are to be regarded as a fundamental part of any long range planning for the conservation of n a t u r a l resources.(3) F i n a l Comments Perhaps t h i s i s a good place to stop. Table I I shows an estimate of the c a p a c i t y f o r production o f most o f the p l a n t s i n the USA. Table I I Capacity of the Soluble S i l i c a t e Industry i n the USA i n 1981 i n B i l l i o n s of Pounds o f Sodium S i l i c a t e L i q u i d Equivalent to 3.22 Si02:Na 0 Ratio by Weight at 42° Baume 2

Producer Diamond Shamrock duPont de Nemours PQ Corp. Chemical Products Grace Chemical PG Corp. E t h y l Corp. Engelhard J.M. Huber Associated Minerals Total

Plants 7 5 12 1 1 2 1 1 2 1

Capacity, pound 1.3 0.7 2.2 0.1 0.4 1.1 0.4 0.04 0.5 0.02 6.8

(10

captive tt

u II If

SOLUBLE

14

SILICATES

Table I I I gives an idea of the amounts r e q u i r e d by major a p p l i c a t i o n s (75% of c a p a c i t y as o f 1 9 8 0 ) . 29

Table I I I Soluble S i l i c a t e Use i n 1980 i n B i l l i o n s o f Pounds of L i q u i d Product Equivalent to 3.22 S i 0 : N a 0 Weight Ratio at 1.39 S p e c i f i c G r a v i t y 2

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch001

Application C a t a l y s t s and Gels Soap and Detergents Roofing Granules, Ceramics, T e x t i l e s , Rods, Foundry, e t c . Pigments Boxboard, Adhesives Ore, Paper, Water Treatment Total

Volume, pounds

2

9

(10 )

1.3 1.2 0.7 0.6 0.3 0.3 4.4

(or

75% of c a p a c i t y

New a p p l i c a t i o n s keep cropping up and o l d ones appear i n new guise. Soluble s i l i c a t e s are u s u a l l y r e l a t i v e l y inexpensive, but t h e i r s e n s i t i v e p r o p e r t i e s have to be understood and handled competently. Many a p o t e n t i a l a p p l i c a t i o n has f a i l e d because necessary precautions were not taken e i t h e r i n the use or i n the s t o r i n g and h a n d l i n g . The manufacturers have r e p r e s e n t a t i v e s ready and able to h e l p . I have mentioned only a few o f the i n d i v i d u a l s o f the many who have helped expand the a p p l i c a t i o n o f t h i s product which has so much to recommend i t . The b a s i c raw m a t e r i a l s , water, s a l t , and pure sand are a v a i l a b l e i n e s s e n t i a l l y u n l i m i t e d q u a n t i t i e s at low c o s t . While they r e q u i r e c o n s i d e r a b l e energy in p r e p a r a t i o n , they seldom cause environmental problems and r e a d i l y r e t u r n to the s o i l . They are inorganic m a t e r i a l s which, i t seems t o me, are only at the beginning o f t h e i r development by man. Anyone who contemplates the place o f s i l i c a i n n a t u r a l organic and inorganic systems has to r e a l i z e that we have a long way to go before we r e a l i z e the f u l l p o t e n t i a l of t h i s product which e x c i t e d the imagination o f Fuchs and others 150 years ago. As we go into the l a s t twenty years o f t h i s century, I am f i l l e d with optimism, not only because o f the a p p l i c a t i o n s which now appear promising and the i n c r e a s i n g l y e f f i c i e n t operations which the computer age suggests, but because I f i r m l y b e l i e v e we have not yet discovered a l l of nature's s e c r e t s about the a b i l i t y of s i l i c a to bind or r e a c t with i t s e l f and other substances. The development of detergents, adhesives, g e l s , s o l a r heating or power systems, f i r e prevention, and the i n c r e a s i n g understanding of chemical and p h y s i c a l bonds a l l suggest to me that we can expect the production curve to continue to r i s e .

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Literature Cited 1. Historical File - T. Elkinton's Journals and W.T. Elkinton's Compilation (1931), etc., The PQ Corporation, Valley Forge, PA. 2. Von Fuchs, J.N., "Bereitung, Eigenschaften und Nutzanwendung des Wasserglasses mit Einschluss der Stereochromie"; Literarisch-artistische Anstalt: Munchen, 1857. 3. Vail, J.G. "Soluble Silicates" 1 and 2, ACS Monograph Series #116; Reinhold Publishing Corp.: New York, 1951 (Chap. 1, especially p. 4-7, gives a brief historical review). 4. Annual Record of Scientific Discovery, Wells, D.A., ed.; Gould and Lincoln: Boston, 1864. 5. Feuchtwanger, L. "Practical Treastise on Soluble of Waterglass" 3rd ed.: New York, 1875. 6 Ott, A. "The Art of Manufacturing Soap and Candles"; Lindsay and Blakiston: Philadelphia, 1867. 7. Ordway, J.M., American Journal of Science and Arts, 2nd Series, 1861 32 153-165, . 8. Wills, J.H. :"Adhesion and Adhesives", De Bruyne, N.A.; and Houwink, R., Ed.; Elsevier Publishing Co., Amsterdam, 1951. 9. Edgerton, L.B., U.S. Patent 1194827 and 1198203 (1916). 10. Carter, J.D., Ind. and Eng. Chem.18,248 1926; 23, 1289 1931. 11. Baker, C.L. and Jue, L.R. J. Physical Chem. 1938 42, 165; J. Physical and Colloid Chem. 1950 54, 208. 12. Stericker, W. in J. Alexander "Colloid Chemistry" Chemical Catalog Co., Inc.: New York, 1928p289. 13. Hilditch, F.P. and Wheaton, H.J., U.S. Patent 1717777 (1929); 1879239 (1929); 1848127 (1932). 14. Iler, R.K. U.S. Patent 2668149 (1945). 15. Cuneo, F.L. U.S. Patent 3392039 (1968). RECEIVED March 2, 1982.

2 Modern Instrumental Methods for Analysis of Soluble Silicates JONATHAN L. BASS

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

The PQ Corporation, Research and Development Center, Lafayette Hill, PA 19444

Modern a n a l y t i c a l instrumentation has been used i n the l a s t 25 years f o r determining commercially important c h a r a c t e r i s t i c s o f soluble silicates, and the nature o f silicate species i n silicate glasses and s o l u t i o n s . The c l a s s i c a l wet methods for assay o f silicate s o l u t i o n s are alkali titration and g r a v i m e t r i c determination of silica, which can a l s o be determined, with l e s s e r p r e c i s i o n , by the alkali fluosilicate method. The a l t e r n a t i v e instrumental assay methods, X-ray f l u o r e s c e n c e , atomic spectroscopy and t h e r m o t i t r i m e t r y , will be compared with the classical methods f o r p r e c i s i o n and ease o f measurement. Instrumental methods have g r e a t l y extended the ability o f the analyst to detect trace c a t i o n s and anions i n s o l u b l e silicates. The scope and l i m i t a t i o n s , i l l u s t r a t e d by some a p p l i c a t i o n s , of atomic and X-ray fluorescence spectroscopy, i o n s e l e c t i v e e l e c t r o d e s , and other l e s s common methods f o r impurity a n a l y s i s will be d i s c u s s e d . The techniques o f i n f r a r e d , Raman, X-ray p h o t o e l e c t r o n , and sputter induced photon spectroscopy, used f o r identification of silicate species will be briefly reviewed.

Sodium s i l i c a t e was the 45th l a r g e s t volume chemical produced i n the United States i n 1980, according to the 1981 Chemical and Engineering News Survey (I). Obviously, the a n a l y s i s o f t h i s m a t e r i a l as w e l l as the other major s o l u b l e a l k a l i s i l i c a t e , potassium s i l i c a t e , i s v e r y important commercially. This paper w i l l b r i e f l y review the modern a n a l y t i c a l instrumental methods that are used to determine the q u a l i t y o f commercial s o l u b l e s i l i c a t e s and instrumental

0097-6156/82/0194-0017$06.00/0 © 1982 American Chemical Society

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techniques that are used i n s t r u c t u r a l c h a r a c t e r i z a t i o n s i l i c a t e s as glasses and i n s o l u t i o n . Assay of Soluble

of

Silicates

C l a s s i c a l Wet

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SILICATES

Chemical Assay Methods

Before d e s c r i b i n g the instrumental methods, i t i s important to discuss the c l a s s i c a l wet chemical techniques that form the foundation of a n a l y s i s of soluble s i l i c a t e s . The most e s s e n t i a l chemical property of s i l i c a t e i s the content of a l k a l i and s i l i c a i n e i t h e r the glass or s o l u t i o n . The standard method f o r determining the a l k a l i assay involves t i t r a t i n g a d i l u t e d s i l i c a t e s o l u t i o n with h y d r o c h l o r i c acid to e i t h e r a methyl orange or methyl orange-xylene cyanole end point ( 2 ) . The mixed i n d i c a t o r gives a more d i s t i n c t end p o i n t . S i l i c a content may be determined by e i t h e r the p r e c i s e , tedious gravimetric s i l i c a procedure (2) or the more r a p i d but l e s s p r e c i s e f l u o s i l i c a t e method ( 3 ) . The gravimetric method involves p r e c i p i t a t i o n of the s i l i c a with a c i d , c o l l e c t i n g the p r e c i p i t a t e , ashing, v o l a t i l i z i n g the s i l i c a with h y d r o f l u o r i c acid and determining the weight l o s s a f t e r v o l a t i l i z a t i o n . The f l u o s i l i c a t e method involves r e a c t i n g s i l i c a i n a p r e v i o u s l y n e u t r a l i z e d s o l u t i o n with sodium f l u o r i d e to form sodium f l u o s i l i c a t e and sodium hydroxide by the following reaction: Si(OH)

4

+ 6NaF =

Na SiF 2

6

+ 4NaOH

and t i t r a t i n g the hydroxide with h y d r o c h l o r i c a c i d to the methyl orange end p o i n t . S i l i c a t e to soda r a t i o s can a l s o be determined r a p i d l y for q u a l i t y c o n t r o l purposes by an a l k a l i t i t r a t i o n and a measurement of e i t h e r s p e c i f i c g r a v i t y or r e f r a c t i v e index and v i s c o s i t y which are c o r r e l a t e d to S i 0 / N a 0 r a t i o s using control charts. The c o n t r o l charts are based on samples p r e v i o u s l y analyzed by the p r e c i s e gravimetric method. The s p e c i f i c g r a v i t y method i s more commonly used i n commercial practice. 2

2

Assay by Instrumental Methods The character of chemical a n a l y s i s has changed d r a s t i c a l l y since World War II with the advent of s o p h i s t i c a t e d o p t i c a l systems and e l e c t r o n i c d e t e c t i o n devices, which have been combined into instrumentation now commonplace i n many i n d u s t r i a l l a b o r a t o r i e s . The major advantages of instrumental

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

2.

BASS

Instrumental

Methods

for

Analysis

a n a l y s i s are speed, s e n s i t i v i t y , v e r s a t i l i t y and r e l a t i v e ease of automation. There are two venerable methods o f instrumental s i l i c a t e a n a l y s i s that predate World War I I , flame photometry f o r the a l k a l i metals (4) and s p e c t r o s c o p i c d e t e c t i o n o f the s i l i c o m o l y b d a t e acid complex i n the v i s i b l e spectrum ( 5 ) . The spectroscopic method has been adapted f o r automated determination o f s i l i c a t e i n detergents ( 6 ) . The s i l i c o m o l y b d a t e method i s a l s o u t i l i z e d to monitor the l e v e l of monomeric s i l i c a i n s i l i c a t e s o l u t i o n s ( 7 ) . More r e c e n t l y developed instruments are capable of determining both a l k a l i and s i l i c a (8-11). Atomic spectrometric instruments determine the t o t a l amount o f an a l k a l i i o n , i n c l u d i n g that due to n e u t r a l s p e c i e s . Therefore the a l k a l i assay by these methods may be g r e a t e r than a t i t r a t i o n method. Atomic absorption (AA) and plasma emission spectroscopy (PES) i n v o l v e decomposition o f the ions i n s o l u t i o n to the atomic s t a t e . In the case o f AA, atoms and ions o f the element being analyzed are v o l a t i l i z e d i n t o the path o f a l i g h t beam emitted from a lamp, and absorb t h i s l i g h t , whose wavelengths are c h a r a c t e r i s t i c o f valence e l e c t r o n i c t r a n s i t i o n s i n the atomic s t a t e . PES i n v o l v e s the e x c i t a t i o n o f valence e l e c t r o n i c t r a n s i t i o n s o f atoms and ions v o l a t i l i z e d i n a plasma a r c . X-ray f l u o r e s c e n c e (XRF) involves e x c i t a t i o n o f core e l e c t r o n s by i n c i d e n t X-rays, followed by X-ray emission at wavelengths that are c h a r a c t e r i s t i c o f the elements present i n e i t h e r s o l u t i o n or s o l i d . F i n a l l y , the thermal t i t r a t o r i s capable of d e t e c t i n g both a l k a l i and s i l i c a by sensing a temperature increase i n an a d i a b a t i c system. In the case o f a l k a l i , the increase i s caused by the heat o f r e a c t i o n due to n e u t r a l i z a t i o n with a c i d , and f o r s i l i c a , by the heat produced during the f l u o s i l i c a t e r e a c t i o n . Comparison o f Wet

Chemical and Instrumental Methods

When choosing whether to use a wet chemical or instrumental methods f o r assay o f a l k a l i s i l i c a t e , the analyst must weigh the compromise between the u s u a l l y higher p r e c i s i o n of wet chemistry and the speed and v e r s a t i l i t y o f an instrument. In a d d i t i o n , the purchase o f an instrument i n v o l v e s a s u b s t a n t i a l c a p i t a l expense with higher operating annual expenses due to the requirements f o r p e r i o d i c maintenance and more expensive s u p p l i e s . However, i f a l a r g e volume o f analyses are run, the cost per sample may be lower using an instrument. Table I summarizes the r e l a t i v e p r e c i s i o n o f the v a r i o u s assay methods. These tabulated values are c o n s e r v a t i v e estimates; experienced a n a l y s t s may achieve b e t t e r p r e c i s i o n between d u p l i c a t e analyses. The t a b l e i n d i c a t e s a 3 to 5 f o l d advantage i n p r e c i s i o n f o r wet chemistry i n most cases.

S O L U B L E SILICATES

20

TABLE I RELATIVE PRECISION OF WET CHEMICAL INSTRUMENTAL ASSAY METHODS Wet

Chemical

Gravimetric s i l i c a +0.05% Fluosilicate

r e a c t i o n +0 .3%

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

A l k a l i T i t r a t i o n ^0.1%

AND

Instrumental Atomic absorption and emission S i l i c a +2% A l k a l i +1% X-ray Fluorescence S i l i c a +0.5% A l k a l i +1%

Thermometric t i t r a t i o n

Silica Alkali

+0.3% +1%

Silicomolybdate

Silica

+0.5%

However, i n the commercial world the u l t i m a t e i n p r e c i s i o n i s o f t e n not needed to s a t i s f y the s i t u a t i o n a l a n a l y t i c a l requirements. Because the g r a v i m e t r i c procedure involves many time consuming steps, the f l u o s i l i c a t e r e a c t i o n i s g e n e r a l l y p r e f e r a b l e as the usual s i l i c a wet chemical assay method. I t i s not as p r e c i s e as a normal a l k a l i t i t r a t i o n because of the d i f f i c u l t y of observing the end p o i n t . Instrumental methods p l a y an important r o l e i n s i l i c a t e assay when the content of a s p e c i f i c a l k a l i ion i s required or when a large volume of samples j u s t i f i e s the cost of labor saved by using an instrument. For example, the t i t r a t i o n method cannot d i s t i n g u i s h between sodium and potassium i n a mixed a l k a l i s i l i c a t e . A drawback o f atomic, molecular and emission spectroscopy as assay methods i s the extensive d i l u t i o n required to lower analyte concentrations to the l i n e a r o p e r a t i n g range of the instrument 9). This c o n t r i b u t e s a d i l u t i o n e r r o r which reduces the p r e c i s i o n of the a n a l y s i s . An advantage of X-ray fluorescence i s that samples can be analyzed without d i l u t i o n . It i s necessary to use a l k a l i r e s i s t a n t hardware. U n f o r t u n a t e l y , X-ray fluorescence i s the most expensive instrumental assay method. Several papers have appeared w i t h i n the l a s t s e v e r a l years d e s c r i b i n g the a p p l i c a t i o n of thermometric t i t r a t i o n s for s i l i c a t e a n a l y s i s (11). The instrumentation i s l e s s expensive than spectrometers but has not yet r e c e i v e d widespread use i n the U.S. s i l i c a t e i n d u s t r y . However, somewhat analogous procedures are commonplace f o r a n a l y s i s of c a u s t i c and alumina in the Bayer process streams of the aluminum i n d u s t r y (12). The method r e q u i r e s comparison against standards whose assay has been determined by other methods.

2.

BASS

Instrumental

Methods

for

Analysis

The s i l i c o m o l y b d a t e a c i d complex method i s used f o r in-process monitors f o r s i l i c a content up to 50 ppm i n process water. In combination with an automatic sampling and d i l u t i o n system, such a monitor could assay f o r s i l i c a i n a process stream with a p r e c i s i o n o f 0.5 to 1%, r e l a t i v e .

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

Instrumental

Techniques f o r S i l i c a t e Impurity

Analysis

The use o f modern a n a l y t i c a l instruments has g r e a t l y expanded the a n a l y s t ' s a b i l i t y to determine i m p u r i t i e s i n s i l i c a t e s . Wet chemical methods u s u a l l y are f a r too tedious, s u f f e r from s u b s t a n t i a l i n t e r f e r e n c e or are not s e n s i t i v e enough f o r impurity a n a l y s i s . Even some instrumental techniques are subject to i n t e r f e r e n c e s , r e q u i r i n g separation to be used i n the a n a l y t i c a l procedure. The analyst must a l s o decide on the s e n s i t i v i t y required since lowering d e t e c t i o n l i m i t s u s u a l l y increases the cost o f a n a l y s i s and the s o p h i s t i c a t i o n o f the a n a l y t i c a l procedure. Impurities o f major s i g n i f i c a n c e i n a l k a l i s i l i c a t e s are i r o n , alumina, calcium and magnesium, c h l o r i d e , s u l f a t e , carbonate and t i t a n i a . They may o r i g i n a t e as i m p u r i t i e s i n raw m a t e r i a l s , be added from the manufacturing equipment, or be absorbed from the atmosphere. The degradation o f product q u a l i t y may be manifested as undesirable c o l o r , t u r b i d i t y i n s o l u t i o n , c o r r o s i v e n e s s , l o s s o f a l k a l i n i t y or a l t e r e d r e a c t i v i t y o f products made from the s i l i c a t e (e.g., i r o n o r s u l f a t e may poison a s i l i c a - b a s e d c a t a l y s t manufactured from a silicate solution). Several instrumental techniques are a v a i l a b l e f o r d e t e c t i o n o f both c a t i o n i c and anionic i m p u r i t i e s i n a l k a l i s i l i c a t e s , with d e t e c t i o n l i m i t s ranging down to the parts per b i l l i o n or i n some cases, parts per t r i l l i o n l e v e l . The i n v e s t i g a t o r must be aware that these s e n s i t i v i t i e s are achieved using the analyzed sample. I f s u b s t a n t i a l d i l u t i o n i s required to b r i n g the o r i g i n a l m a t e r i a l i n t o the instrumental operating range, then the d e t e c t i o n l i m i t i n t h i s as-received sample i s f a r h i g h e r . For example, i f one can determine the presence o f element A at the 1 ppb l e v e l i n s o l u t i o n but a s i l i c a t e r e q u i r e s 1000-fold d i l u t i o n before i t can be analyzed, then the d e t e c t i o n l i m i t i n the o r i g i n a l s i l i c a t e i s 1 ppm. S i m i l a r l y , i f a separation procedure i s r e q u i r e d , the d e t e c t i o n l i m i t i n the o r i g i n a l m a t e r i a l i s higher than i n the a l i q u o t being analyzed. Table I I summarizes the c a p a b i l i t y o f s e v e r a l instrumental methods f o r d e t e c t i o n o f i m p u r i t i e s . This t a b l e provides broad guidance; i n the case o f a p a r t i c u l a r s p e c i e s , the analyst must consult the l i t e r a t u r e or perform experiments to f i n d the a c t u a l d e t e c t i o n l i m i t f o r that s p e c i e s .

ppb-ppm i n s o l u t i o n ppt-ppb i n s o l u t i o n ppb-ppm i n s o l u t i o n ppm as r e c e i v e d ppb-ppm i n s o l u t i o n ppb-ppm as r e c e i v e d ppb a f t e r s e p a r a t i o n

Separation, d i l u t i o n Separation, d i l u t i o n Dilution Direct Separation d i l u t i o n D i r e c t , separation

Flame AA Furnace AA Argon Plasma X-Ray Fluorescence Ion S e l e c t i v e Electrodes Neutron A c t i v a t i o n

Detection Limits ppm i n s o l u t i o n ppb to ppm i n s o l u t i o n Β, Ρ ppm i n s o l u t i o n ppm as r e c e i v e d 0.5% carbonate i n g l a s s ppb-ppm as r e c e i v e d ppb a f t e r s e p a r a t i o n

Sample P r e p a r a t i o n Separation, d i l u t i o n Separation, d i l u t i o n Dilution Direct Direct D i r e c t , separation

Technique

Ion Chromatography Ion S e l e c t i v e E l e c t r o d e s Argon Plasma X-Ray Fluorescence Raman Spectroscopy Neutron A c t i v a t i o n

D e t e c t i o n o f Anions

Detection L i m i t s

Sample P r e p a r a t i o n

Technique

D e t e c t i o n o f Cations

INSTRUMENTAL TECHNIQUES FOR SILICATE IMPURITY ANALYSIS

TABLE I I

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

2.

BASS

Instrumental

Methods

for

Analysis

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

D e t e c t i o n o f C a t i o n i c Impurities Probably the most commonly used instruments f o r c a t i o n impurity a n a l y s i s o f s i l i c a t e s are flame atomic a b s o r p t i o n spectrophotometers and i o n s e l e c t i v e e l e c t r o d e s . In most cases, s e p a r a t i o n o f s i l i c a i s r e q u i r e d to reduce i n t e r f e r e n c e s . The sample may a l s o have to be d i l u t e d t o b r i n g the analyte c o n c e n t r a t i o n w i t h i n the l i n e a r o p e r a t i n g range. For c a t i o n s , the atomic absorption spectrophotometer i s more v e r s a t i l e than i o n s p e c i f i c e l e c t r o d e s . I f the analyst i s concerned with the presence o f heavy metals, then a c c e s s o r i e s such as a hydride system f o r the elements that form high vapor pressure compounds, e.g., Sb, and a mercury vapor c o l d trap are u s e f u l . I f a l a r g e number o f elements are to be determined, a s u b s t a n t i a l investment i n hollow cathode and e l e c t r o d e discharge lamps must be made. Several gas mixtures w i l l also be r e q u i r e d . The flame atomic absorption spectrophotometer has d e t e c t i o n l i m i t s ranging from the ppb to ppm l e v e l , depending on the element analyzed. Improved s e n s i t i v i t y can be achieved with the use o f the g r a p h i t e furnace which has lower background and atomizes more e f f i c i e n t l y than the flame. In most cases a three order o f magnitude improvement i n s e n s i t i v i t y i s achieved. However, t h i s improvement i n s e n s i t i v i t y r e q u i r e s more c a r e f u l sampling, handling and u l t r a h i g h p u r i t y reagents to be used i n sample p r e p a r a t i o n . The c a l i b r a t i o n procedure i s a l s o more t e d i o u s . In the l a s t 6 to 7 y e a r s , argon plasma emission (PES) instrumentation has been commercialized with d e t e c t i o n l i m i t s u s u a l l y intermediate between flame and furnace AA. The two most common types o f plasma instruments are the i n d u c t i v e l y coupled plasma (ICP) and d i r e c t c u r r e n t plasma (DCP). Although the ICP i s somewhat more s e n s i t i v e i n terms o f reported d e t e c t i o n l i m i t s than DCP, the former cannot t o l e r a t e as high a d i s s o l v e d s o l i d s content as the l a t t e r . Therefore, on the o r i g i n a l s i l i c a t e m a t e r i a l s , the d e t e c t i o n l i m i t s are s i m i l a r . Another advantage o f PES compared to AA i s that commercial PES spectrometers can be configured f o r simultaneous m u l t i - e l e m e n t a l a n a l y s i s , while the c u r r e n t commercial m u l t i - e l e m e n t a l AAs are s e q u e n t i a l . The base p r i c e of PES equipment i s higher than AA but i f the sample load i s h i g h , the increased p r o d u c t i v i t y o f multi-elemental PES may r e s u l t i n a lower cost per a n a l y s i s . Table I I I l i s t s s p e c t r a l l i n e s that are u s e f u l f o r the spectroscopic a n a l y s i s o f major components and i m p u r i t i e s i n soluble s i l i c a t e s .

24

SOLUBLE

SILICATES

TABLE I I I TYPICAL SPECTRAL LINES FOR ATOMIC SPECTROSCOPIC ANALYSIS OF MAJOR AND TRACE ELEMENTS IN SILICATES

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

ELEMENT

PES

AA

Iron

248

Silicon

252

252

Magnesium

285

280

Titanium

365

335

Sodium

295

590

Calcium

211

397

Aluminum

309

396

Potassium

383

770

nm

238

nm

Two l e s s commonly used techniques, X-ray fluorescence (XRF) and neutron a c t i v a t i o n a n a l y s i s (NAA) have the advantage that as-received samples can be analyzed, glasses as w e l l as s o l u t i o n s . Both are more expensive than the p r e v i o u s l y mentioned techniques. The NAA technique that produces the greatest s e n s i t i v i t y r e q u i r e s i r r a d i a t i o n i n a research nuclear r e a c t o r and hence i s r e a l l y p r a c t i c a l only when d e t e c t i o n of low l e v e l s o f unusual c a t i o n s i s r e q u i r e d . Sodium s i l i c a t e i s somewhat more d i f f i c u l t to analyze than many other m a t e r i a l s because of the formation of the r e l a t i v e l y long l i v e d r a d i o n u c l i d e N a ^ whose emissions i n t e r f e r e with the d e t e c t i o n of other elements. Nevertheless we were able to determine, i n a sample of sodium s i l i c a t e , that many heavy elements of t o x i c o l o g i c a l concern were undetectable down to the ppm to ppb l e v e l i n the u n d i l u t e d s i l i c a t e (13). An XRF spectrometer can be configured to perform s e q u e n t i a l multi-elemental analyses. It i s less s e n s i t i v e to the elements of lower atomic number. A l s o , since the X-rays penetrate only to a depth of about 10 um, the sample must be homogeneous. S o l i d samples must be presented to the X-ray beam with a f l a t s u r f a c e . However, the r e l a t i v e ease of sample p r e p a r a t i o n and the a b i l i t y to run glasses and s o l u t i o n s with only minor d i l u t i o n make X-ray fluorescence a u s e f u l technique where a n a l y s i s f o r a wide range of i m p u r i t i e s is required.

2.

BASS

Instrumental

Methods

for

Analysis

D e t e c t i o n o f Anionic Impurities D e t e c t i o n o f anionic i m p u r i t i e s i n a l k a l i s i l i c a t e s has not been as f u l l y developed as f o r c a t i o n s . The anion o f greatest concern i s carbonate which i s absorbed from the atmosphere. P o t e n t i a l l y , carbonate could o r i g i n a t e from the soda ash or potash raw m a t e r i a l used i n s i l i c a t e manufacture but under normal furnace o p e r a t i o n the ash should be thoroughly decomposed. The standard c l a s s i c a l method f o r carbonate a n a l y s i s i n v o l v e s a c i d i f i c a t i o n and b o i l i n g o f the s o l u t i o n to r e l e a s e C 0 which i s adsorbed on A s c a r i t e * The procedure i s time consuming and subject to e r r o r s r e s u l t i n g from d i f f i c u l t i e s i n maintaining uniform flow. Two instrumental methods that show promise are i o n chromatography (14) and l a s e r Raman spectroscopy (15). Using a s i z e e x c l u s i o n column, carbonate has been determined down to the ppm l e v e l . This technique has not yet been a p p l i e d to s o l u b l e s i l i c a t e s , which may r e q u i r e s e p a r a t i o n o f the s i l i c a . Laser Raman spectroscopy has been a p p l i e d to carbonate determination down to the 0.5% l e v e l i n potassium s i l i c a t e g l a s s , using bands at 1770, 1428 and 575 cnf"l.

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

2

Using the proper choice o f separation column, i o n chromatography appears to be a p p l i c a b l e f o r the s e q u e n t i a l multicomponent a n a l y s i s o f other anions such as s u l f a t e , c h l o r i d e , f l u o r i d e and n i t r a t e . The d e t e c t i o n l i m i t s w i l l be s u b s t a n t i a l l y lower than the c l a s s i c a l g r a v i m e t r i c and potentiometric methods c u r r e n t l y used. Ion s e l e c t i v e e l e c t r o d e s are a v a i l a b l e f o r c h l o r i d e and f l u o r i d e . A s i l i c a t e sample r e q u i r e s s e p a r a t i o n i n order to remove interferences. As i n the case o f c a t i o n s , NAA and XRF permit d i r e c t a n a l y s i s f o r impurity elements that may be present i n an anionic form. XRF i s capable o f d e t e c t i n g P, S, CI, Br and I. NAA can determine CI, Br and I at the ppm l e v e l i n the as-received s t a t e , depending on the m a t e r i a l and at lower l e v e l s using radiochemical s e p a r a t i o n . F i n a l l y , argon plasma emission spectroscopy can determine the presence o f two other elements, which can be present as anions, Β and P. The technique i s f a r more s e n s i t i v e f o r the former element which can be detected at the ppb l e v e l i n s o l u t i o n , while Ρ can be detected at the ppm l e v e l . Both elements can also be analyzed by atomic absorption spectroscopy, but with l e s s s e n s i t i v i t y . A p p l i c a t i o n s o f Advanced Instrumentation to S i l i c a t e Structural Analysis The l a s t 25 years, and e s p e c i a l l y the l a s t 10, have seen the a p p l i c a t i o n o f advanced, expensive instrumental techniques

SOLUBLE

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

26

SILICATES

to the s t r u c t u r a l c h a r a c t e r i z a t i o n of s i l i c a t e s both i n the glass and s o l u t i o n s t a t e s . Other c o n t r i b u t o r s to t h i s symposium have discussed e x t e n s i v e l y the use o f nuclear magnetic resonance (NMR) spectroscopy and t r i m e t h y l s i l y l a t i o n combined with g a s - l i q u i d chromatography (GLC), g e l permeation chromatography (GPC) and mass spectroscopy (MS) to analyze the nature of s i l o x y b r i d g i n g i n s i l i c a t e s o l u t i o n s . This paper w i l l b r i e f l y d e s c r i b e the r e s u l t s o f some other techniques that are l e s s f r e q u e n t l y used. V i b r a t i o n a l spectroscopy, both l a s e r Raman (16) and i n f r a r e d (16, 17), can be a p p l i e d as a u s e f u l supplement to the data developed by NMR and TMS f o r c h a r a c t e r i z i n g s i l i c a t e species i n s o l u t i o n . The number of bands observed i n v i b r a t i o n a l spectroscopy depends on the symmetry o f the s i l i c a t e species present. Protons attached to the Si-0 bonds lower the symmetry compared to the S i O ^ i o n . In t h i s way, M a r i n a n g e l i , et a l (15), assigned seven l a s e r Raman bands i n a sodium m e t a s i l i c a t e s o l u t i o n adjusted to pH 14 to the presence of S i 2 ( 0 H ) 2 . The s p e c t r a are shown as Figure 1. As the pH was lowered, s h i f t s of bands to higher frequencies (930-1000 cm"" ) were observed. In unadjusted sodium m e t a s i l i c a t e s o l u t i o n (pH 13.3), i n f r a r e d bands a t t r i b u t e d to the transformation of Si02(OH2)~ i n t o SiO(OH)" and the dimer Si2C>3(0H)4 appear. These bands were assigned by analogy to bands observed i n the i n f r a r e d s p e c t r a of c r y s t a l l i n e s i l i c a t e s . When the s o l u t i o n i s further a c i d i f i e d , bands at higher frequencies (1000-1120 cm~l) assigned to polymeric species were observed. These s h i f t s were also observed i n the i n f r a r e d by Beard (17) who studied s i l i c a t e s of d i f f e r e n t s i l i c a to a l k a l i r a t i o s . He also observed changes i n i n t e n s i t i e s , over a period of s e v e r a l days, f o r s i l i c a t e s o l u t i o n s produced by dissolving s i l i c a in a l k a l i . These changes were a t t r i b u t e d to depolymerization o f the high molecular weight s i l i c a t e species o r i g i n a l l y formed. The nature of the s i l i c o n - o x y g e n bond i n a l k a l i s i l i c a t e glasses as the sodium content increases has been i n v e s t i g a t e d by e l e c t r o n spectroscopy f o r chemical a n a l y s i s (ESCA) and h i g h r e s o l u t i o n X-ray fluorescence spectroscopy (18-21). ESCA has shown that the binding energy o f oxygen Is e l e c t r o n s of non-bridging oxygen i s about 2ev l e s s than that of b r i d g i n g oxygens. This r e s u l t i s i l l u s t r a t e d by the deconvoluted 0^ ESCA spectrum i n Figure 2 (18) . At low sodium c o n c e n t r a t i o n , sodium i s a s s o c i a t e d with non-bridging oxygens ( i . e . , the network terminating oxygens). However, at higher sodium c o n c e n t r a t i o n s , the number of oxygen atoms with t h i s lower binding energy as i n d i c a t e d by the peak i n t e n s i t y i s l e s s than the number of sodium ions i n d i c a t i n g that some of these ions are d i s p e r s e d i n the network (18). In a d d i t i o n , the chemical 2

1

2

3

2

s

2.

Instrumental

BASS

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

1100

Figure 14 (a); 2.5 M 2.5 M

Methods

1000

900

for

800

Analysis

700

600

500

400

cm

1

1. Raman spectra of aqueous solutions of 2.5 M Na SiO$, 4 M NaOH, pH 2.5 M Na SiO , 0.5 M NaOH, pH 13.4 (b); 2.5 M Na SiO , pH 13.3 (c); Na SiO , 1.25 M HCl, pH 13 (d); 2.5 M Na SiO , 2.5 M HCl, pH 12.5 (e); Na SiO , 3.75 M HCl, pH 11.5 (f). (Reproduced, with permission, from Ref. 16. Copyright 1978, Multiscience Publications Ltd.) 2

2

2

s

2

s

2

2

s

s

s

525

530

535

540

545

Binding Energy (E.V.) Figure 2. 30% Na 0 2

Binding energy (EV). ESCA O(ls) spectrum of a sodium silicate glass, + 70% Si0 . (Reproduced, with permission, from Ref. 18. Copyright 1979, North-Holland Publishing Co.) 2

SOLUBLE

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

28

SILICATES

s h i f t i s l e s s pronounced at higher sodium c o n c e n t r a t i o n , i n d i c a t i n g a trend toward energy equivalence of the non-bridging and b r i d g i n g oxygens (19). These ESCA data are complemented by high r e s o l u t i o n X-ray fluorescence spectroscopic r e s u l t s which show a decrease i n the average strength of s i l i c o n - o x y g e n bonds (20) and a r e l a t i v e decrease of p o s i t i v e change on s i l i c o n atoms (21) with i n c r e a s i n g sodium c o n c e n t r a t i o n . These trends were monitored by observing chemical s h i f t s i n s i l i c o n Κ X-ray l i n e s . The e f f e c t o f h y d r a t i o n on hydrogen and sodium d i s t r i b u t i o n i n a l k a l i s i l i c a t e g l a s s e s has been studied by sputter induced photon spectroscopy (SIPS) and by i n f r a r e d r e f l e c t i o n and t r a n s m i s s i o n spectroscopy (22, 23). SIPS i s a r e l a t i v e l y uncommon but powerful technique which i n v o l v e s measuring the i n t e n s i t y o f c h a r a c t e r i s t i c emission l i n e s o f molecular and atomic fragments sputtered from the surface of materials. I t s advantages as a surface technique l i e i n the a b i l i t y to detect hydrogen ( u n l i k e ESCA or Auger spectroscopy) and n e u t r a l species ( u n l i k e SIMS) . Using t h i s technique Houser, et a l . , were able to determine that i n s i l i c a t e g l a s s hydrated at 30° for one hour hydrogen had d i f f u s e d inward from the surface f o r a d i s t a n c e of 2 urn, with accompanying d e p l e t i o n of sodium i n t h i s l a y e r . Figure 3 shows the depth p r o f i l e o f hydrogen and sodium i n a Na20*3Si02 g l a s s under these c o n d i t i o n s (22). The presence o f a broad band i n a t h i n f i l m of hydrated " s i l i c a t e at 3360cm" was i n t e r p r e t e d by Doremus (23) as i n d i c a t i n g the presence o f hydronium i o n s . He a l s o observed i n r e f l e c t i o n s p e c t r a o f hydrated s i l i c a g l a s s a decrease o f the 950 cm" band i n t e n s i t y , assigned to the Si-0 M s t r e t c h i n g v i b r a t i o n and a major increase i n the Si-O-Si s t r e t c h at 1050-1100 cm" . He a t t r i b u t e d these changes to the formation o f a porous g e l l a y e r produced by h y d r o l y s i s of the surface l a y e r . It i s l i k e l y that f u r t h e r a p p l i c a t i o n s of s o p h i s t i c a t e d instrumentation to a n a l y s i s of s i l i c a t e s w i l l appear i n future literature. In a d d i t i o n to ESCA, SIPS, X-ray spectroscopy, l a s e r Raman and d i s p e r s i v e i n f r a r e d spectroscopy, newer techniques such as F o u r i e r transform i n f r a r e d and photoacoustic spectroscopy may be used as t o o l s to characterize s i l i c a t e structure. 1

1

+

1

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

2.

BASS

Instrumental

Methods

for

Analysis

2.00

4.00

6.00

Figure 3. Depth profiles of H and Na in a Na O · 3Si0 glass after hydration of 1 hat 30° C. The intensities of both H and Na are expressed in photon counts/s. (Reproduced, with permission, from Ref. 22. Copyright 1980, North-Holland Publishing Co.) t

9

S O L U B L E SILICATES

30

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch002

Literature Cited 1. Chemical and Engineering News, 54, May 4, 1981. 2. J . G. Vail, "Soluble S i l i c a t e s " , V o l s . 1 and 2, Reinhold, New York (1952). 3. N. A. Tananaeff and A. K. Babko, Ζ. a n a l . Chem. 82, 145 (1930). 4. I. A. V o i n o v i t c h , J . Debras-Guedon and J . L o u v r i e r ; "The A n a l y s i s of Silicates"; Herman; P a r i s (1965). 5. J . D. H. S t r i c k l a n d , JACS 74, 862 (1952). 6. S. W. Babulak and L. Gildenberg, JAOCS 50, 296 (1973). 7. R. K. Iler, "The Chemistry o f Silica", John Wiley; New York (1979). 8. C. Manoliu, B. Tomi, A. Daescu and T. Petrue, Rev. Chim, 24, 639 (1973). 9. K. Govindaraju, G. Mevelle and C. Chouard, A n a l . Chem. 48, 1325 (1976). 10. W. W. F l e t c h e r , Glass Technology, 17, 226 (1976). 11. H. Strauss and R. Rutkowski, S i l i k a t t e c h n i k , 29, 339 (1978). 12. E. Van Dalen and L. G. Ward, A n a l . Chem. 45, 2248 (1973). 13. L. Kovar, p r i v a t e communication (1979). 14. H. Small, T. S. Stevens and W. C. Bauman, A n a l . Chem. 47, 1801 (1975). 15. H. V e r w e i j , H. Van den Boom and R. E. Breemer, J . Am. Cer. Soc., 60, 529 (1977). 16. A. M a r i n a n g e l i , M. A. M o r e l l i , R. Simoni and A. B e r t o l u z z a , Can. J . Spectroscopy 23, 173 (1978). 17. W. C. Beard, 3rd I n t e r n a t i o n a l Sumposium on Molecular Sieves, 162 (1973). 18. J . S. Jen and M. R. K a l i n o w s k i , J. Non Cryst S o l i d s , 38, 21 (1979). 19. R. Bruckner, H. W. Chun, H. G o r e t z k i and M. Sammet, J . Non C r y s t . S o l i d s , 42, 49 (1980). 20. S. Sakka and A. Senga, J . Mat. S c i . , 13, 505 (1978). 21. T. Maekawa, N. K i k u c h i , S. Sumita and T. Yokokawa, B u l l . Chem. Soc. Japan, 51, 780 (1978). 22. C. A. Houser, J . S. Herman, I. S. T. Tsong and W. B. White, J . Non C r y s t . S o l i d s , 41, 89 (1980). 23. R. H. Doremus, J . Non C r y s t . S o l i d s , 41, 145 (1980). RECEIVED

March

2,

1982.

3 Current Regulatory Status of Soluble Silicates J. G. BLUMBERG and W. L. SCHLEYER

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

The PQ Corporation, Research and Development Center, Lafayette Hill, PA 19444

Federal agency promulgations authorizing or affect­ ing the soluble silicates are compiled. Their safety has been extensively reviewed. For caution­ ary labeling, i t is industry practice to group com­ mercial soluble silicate products into three hazard classes. Occupational exposure limits vary simil­ arly with alkalinity. The warning language for con­ sumer products, notably household detergents, may be affected by the type and quantity of their sol­ uble silicate content. Soluble silicates have both GRAS and additive regulation status for food uses. As inert ingredients, sodium silicate and metasili­ cate are exempt from the requirement of a pesticide residue tolerance. They are also classed as active pesticidal ingredients and thereby exposed to inap­ propriate generic regulation. Only highly alkaline forms of sodium silicate are regulated as hazardous materials for transportation purposes and, when dis­ carded, are classified as hazardous waste. Except to that extent, soluble silicates are not hazardous substances under spill regulations. The proposed Preliminary Assessment Information Rule under TOSCA included soluble silicates. For inventory reporting purposes, currently available sodium silicates are three "chemical substances." The environmental­ -regulatory profile of soluble silicates provides incentive for their preference over more hazardous and more highly regulated alternate materials. Safety Reviews High tonnage production combined with consumer r e l a t e d uses i n food and detergents have occasioned extensive reviews o f the long-range s a f e t y o f sodium s i l i c a t e . Both i n the environment and i n the body, i t degrades to s i l i c a which i s i n d i s t i n g u i s h 0097-6156/82/0194-0031$06.00/0 ©

1 9 8 2 A m e r i c a n C h e m i c a l Society

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

32

SOLUBLE

SILICATES

able from n a t u r a l l y o c c u r r i n g forms. Furthermore, i t has a long h i s t o r y o f p r o d u c t i o n and safe use. Therefore, i t i s not s u r p r i s i n g that l i t t l e need has been seen to confirm the absence of c h r o n i c h e a l t h e f f e c t s by thorough l a b o r a t o r y s t u d i e s . The recent commercialization o f laundry detergent c o n t a i n i n g z e o l i t e A has, i n e f f e c t , added to the a v a i l a b l e i n f o r m a t i o n , because sodium s i l i c a t e forms when z e o l i t e A breaks down (\). A comprehensive review o f sodium and potassium s i l i c a t e was conducted by the Select Committee on GRAS Substances o f the L i f e Sciences Research O f f i c e , F e d e r a t i o n o f American S o c i e t i e s f o r Experimental B i o l o g y (FASEB) f o r the Food and Drug Administration. I t was concluded that "there i s no evidence i n the a v a i l a b l e information on ... potassium [and] sodium s i l i c a t e that demonstrates or suggests reasonable grounds to suspect a hazard to the p u b l i c when they are used at l e v e l s that are current or that might reasonably be expected i n the future" ( 2 ) . The e v a l u a t i o n was based i n part on a s c i e n t i f i c l i t e r a t u r e review with 544 r e f e r e n c e s , sponsored by the Food and Drug A d m i n i s t r a t i o n (3) . The I n t e r n a t i o n a l J o i n t Commission (U.S.-Canada) under the Great Lakes Water Q u a l i t y Agreement undertook a s a f e t y review o f detergent b u i l d e r s which encompassed both human h e a l t h and environmental aspects. The Task Force on the Health E f f e c t s o f Non-NTA Detergent B u i l d e r s o f the IJC*s Great Lakes Science Advisory Board concluded that "the use o f sodium s i l i c a t e i n detergents poses no hazard to man" (4·). A separate Task Force on the E c o l o g i c a l E f f e c t s o f Phosphate Replacements has not yet issued a r e p o r t , but i t i s understood to have concluded that there i s no cause f o r concern ( 5 ) . Sodium and potassium s i l i c a t e are the s o l u b l e s i l i c a t e s o f commercial importance. For potassium s i l i c a t e , not n e a r l y as extensive data from the l a b o r a t o r y or from human experience are a v a i l a b l e . The assumption of i t s s i m i l a r i t y to sodium s i l i c a t e i n h e a l t h and environmental e f f e c t s appears to be v a l i d , f o r an equivalent mole r a t i o o f S 1 O 2 to a l k a l i metal oxide. Although s o l u b l e s i l i c a t e s are produced from quartz sand, they do not c o n t a i n d e t e c t a b l e amounts o f c r y s t a l l i n e s i l i c a . A l l evidence p o i n t s to the moderate to strong a l k a l i n i t y o f s o l u b l e s i l i c a t e s as the sole source o f a p o t e n t i a l hazard to human h e a l t h or environment. The r e g u l a t o r y c o n t r o l s c u r r e n t l y i n e f f e c t stem e i t h e r from t h i s acute hazard or from t h e i r use i n regulated a p p l i c a t i o n s . The e n t i r e r e g u l a t o r y spectrum i s d e s c r i b e d here, i n s o f a r as i t would concern processors or users o f s o l u b l e s i l i c a t e s i n the United S t a t e s . Workplace Although chemical hazard communication has been o f concern

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

3.

BLUMBERG

A N D SCHLEYER

Current

Regulatory

Status

33

to the Occupational Safety and Health A d m i n i s t r a t i o n o f the U.S. Department o f Labor (OSHA) since i t s i n c e p t i o n i n 1972, c a u t i o n a r y l a b e l i n g o f i n d u s t r i a l chemicals remains to t h i s day a v o l u n t a r y i n d u s t r i a l p r a c t i c e . The most widely used system i s set f o r t h i n ANSI Standard Z129.1-1976 ( 6 ) . The standard d e f i n e s hazard c l a s s e s and s p e c i f i e s the a p p l i c a b l e l a b e l language. By these c r i t e r i a , the s i l i c a t e s c o n s t i t u t e three d i f f e r e n t hazard c l a s s e s because r i s i n g a l k a l i n i t y increases the s e v e r i t y o f the hazard. Since s i l i c a t e s are good b u f f e r s , t h e i r Si02/Na20 r a t i o i s a f a r more important determinant o f the degree o f a l k a l i n i t y than i s t h e i r c o n c e n t r a t i o n l e v e l . Commercial sodium s i l i c a t e l i q u i d s o f 2.0 r a t i o or g r e a t e r and d r y sodium s i l i c a t e o f at l e a s t 2.4 r a t i o c o n s t i t u t e the l e a s t hazardous group: they cause eye and s k i n i r r i t a t i o n . Sodium m e t a s i l i c a t e , sodium o r t h o s i l i c a t e and 1.6 r a t i o sodium s i l i c a t e l i q u i d s f a l l i n t o the c l a s s o f highest hazard: they are c o r r o s i v e , i . e . , cause eye and s k i n burns. The intermediate hazard c l a s s c o n s i s t s o f d r y s i l i c a t e s and l i q u i d s between the other two c l a s s e s i n r a t i o , which are considered c o r r o s i v e t o the eye but not to the s k i n . T y p i c a l i n d u s t r i a l l a b e l s f o r a r e p r e s e n t a t i v e sodium s i l i c a t e product from each hazard c l a s s are shown i n F i g s . 1-3. Since commercial potassium s i l i c a t e products range i n S 1 O 2 / K 2 O mole r a t i o only from approximately 2.5 t o 3.9, a l l f a l l i n t o the lowest hazard c l a s s : they are eye and s k i n irritants. Although OSHA Form 20 or one approved as e s s e n t i a l l y s i m i l a r i s mandatory only i n the maritime trades ( 7 ) , i t has become customary throughout the chemical i n d u s t r y to o b t a i n or prepare a m a t e r i a l s a f e t y data sheet before a new chemical enters a workplace. For products i n the same i n d u s t r i a l hazard c l a s s the information provided on the m a t e r i a l s a f e t y data sheet i s the same, except as modified by d i f f e r e n c e s i n p h y s i c a l p r o p e r t i e s . For example, the s p i l l removal i n s t r u c t i o n s f o r l i q u i d s are d i f f e r e n t from those f o r s o l i d s . F i g s . 4a and 4b show a m a t e r i a l s a f e t y data sheet f o r a dry, powdered sodium s i l i c a t e i n the lowest hazard c l a s s . Word processing equipment i s v e r y u s e f u l f o r m a i n t a i n i n g and p r o v i d i n g t h i s i n f o r m a t i o n , as well as f o r r e c o r d i n g and r e t r i e v i n g those who r e c e i v e d i t . I t may be noted that the sheet c o n t a i n s more than o c c u p a t i o n a l s a f e t y data. I t i n c l u d e s s p i l l response and TOSCA data as w e l l . It i s evolving into a s a f e t y and r e g u l a t o r y data sheet. There are no s p e c i f i c OSHA exposure standards f o r sodium or potassium s i l i c a t e . Depending on r a t e o f s o l u t i o n and degree o f a l k a l i n i t y o f a i r b o r n e m a t e r i a l s , a prudent i n d u s t r i a l exposure standard could range from the p e r m i s s i b l e exposure l i m i t (PEL) for i n e r t or nuisance p a r t i c u l a t e s up t o n e a r l y the PEL f o r sodium hydroxide.

SOLUBLE

34

WARNING! CAUSES IRRITATION Avoid contact with eyes, skin, and clothing. Wash thoroughly after handling. Wash contaminated clothing before re-use. FIRST AID: In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. Call a physician. Flush skin with water.

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

SPILLAGE: Mop up and flush to sewer with plenty of water. FOR INDUSTRIAL USE ONLY COVER WHEN NOT IN USE PROTECT FROM FREEZING Figure 1.

Sodium silicate cautionary label, least hazardous class.

DANGER! CAUSES EYE AND SKIN BURNS Do not get in eyes, on skin, on clothing. Avoid breathing mist. Keep container closed. Use with adequate ventilation. Wash thoroughly after handling. Do not take internally. When handling, wear goggles or face shield. Wash contaminated clothing before re-use. FIRST AID: In case of contact, immediately flush eyes or skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Call a physician. ANTIDOTE: If swallowed, do NOT induce vomiting. Give large quantities of water. Give at least one ounce of vinegar in an equal amount of water. Never give anything by mouth to an unconscious person. Call a physician. SPILLAGE: Mop up and flush to sewer with plenty of water. Figure 2.

Sodium silicate cautionary label, most hazardous class.

SILICATES

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

BLUMBERG AND SCHLEYER

Current

Regulatory

Status

DANGER! CAUSES EYE BURNS, CAUSES SKIN IRRITATION Do not get in eyes, on skin, on clothing. Avoid breathing mist. Keep container closed. Use with adequate ventilation. Wash thoroughly after handling. Do not take internally. When handling, wear goggles or face shield. Wash contaminated clothing before re-use. FIRST AID: In case of contact, immediately flush eyes with plenty of water for at least 15 miniutes. Call a physician. Flush skin with water. ANTIDOTE: If swallowed, do NOT induce vomiting. Give large quantities of water. Give at least one ounce of vinegar in an equal amount of water. Never give anything by mouth to an unconscious person. Call a physician. SPILLAGE: Mop up and flush to sewer with plenty of water. Figure 3.

Sodium silicate cautionary

label, intermediate

hazardous

class.

SOLUBLE

36

SECTION

1.

IDENTIFICATION

MANUFACTURER: ADDRESS:

PQ

OF

SALES N A M E :

CORPORATION

BRITESIL C-24

CHEMICAL NAME:

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

No.:

HAZARD

DOT

SHIPPING N A M E : N . A . SECTION

APPEARANCE Odorless.

PHYSICAL

& ODOR:

SPECIFIC G R A V I T Y

DATA

(liquids o n l y ) : N . A . Complete.

P R E S S U R E ( m m H g at ° F , nonaqueous liquids o n l y ) : N . A . RATE

CONTENT

BOILING POINT VAPOR

1344-09-8

A q u a m a r i n e glassy l u m p s , white granules, o r white powder.

IN WATER:

EVAPORATION SOLIDS

293-7200

CLASS: N.A.

2.

SOLUBILITY

(215)

sodium silicate

R

Silicic a c i d , s o d i u m salt*

CAS REGISTRY

DOT

VAPOR

PRODUCT

11 E X E C U T I V E M A L L , P . O . B O X 8 4 0 , V A L L E Y F O R G E , P A 19482

EMERGENCY TELEPHONE NUMBER:

TOSCA

SILICATES

( B u t y l acetate = 100, nonaqueous liquids o n l y ) : N . A .

(solutions dispersions, o r pastes only) : N . A .

( ° F , nonaqueous l i q u i d s o n l y ) : N . A .

DENSITY

(nonaqueous liquids o n l y ) : N . A .

p H (aqueous liquids only) : N . A .

SECTION

3.

F L A S H POINT

FIRE A N D EXPLOSION HAZARD

DATA

(°F): N . A .

F L A M M A B L E L I M I T S (vapor i n a i r , V o l . % ) : N . A . FIRE EXTINGUISHING

MEDIA:

SPECIAL FIRE FIGHTING

N.A.

PROCEDURES:

N.A.

UNUSUAL FIRE A N D EXPLOSION HAZARDS:

S E C T I O N 4. STABILITY:

REACTIVITY

None

DATA

Stable

CONDITIONS

TO AVOID:

INCOMPATIBILITY HAZARDOUS

N.A.

(Materials to A v o i d ) : N . A .

DECOMPOSITION

PRODUCTS:

None

N . A . = N o t Applicable * Includes other h a z a r d classes, to w h i c h different safety data sheets apply. Figure 4a.

Material safety data sheet; high ratio powders, side 1.

3.

Current

BLUMBERG A N DSCHLEYER

S E C T I O N 5.

SPILL OR L E A K

Regulatory

37

Status

PROCEDURES

S P I L L A G E : Sweep, scoop, o r v a c u u m discharged material. Observe environmental protection regulations.

F l u s h residue w i t h water.

W A S T E D I S P O S A L M E T H O D : N e u t r a l i z e with dilute acid and landfill solids according to l o c a l , state, a n d federal regulations. F l u s h n e u t r a l l i q u i d to sewer with plenty of water.

S E C T I O N 6. EYE

HEALTH HAZARD

CONTACT

Causes irritation.

SKIN CONTACT:

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

DATA

INHALATION :

Causes irritation.

D u s t m a y irritate respiratory tract.

F I R S T A I D P R O C E D U R E S : I n case of contact, immediately flush eyes w i t h plenty of water for at least 15 minutes. C a l l a physician. F l u s h s k i n w i t h water. M E D I C A L EXAMINATIONS: N.A.

S E C T I O N 7. RESPIRATORY occurs. GLOVES: EYE

SPECIAL PROTECTION PROTECTION:

Use N I O S H

INFORMATION approved

dust respirator where

dust

R u b b e r where contact l i k e l y .

PROTECTION :

C h e m i c a l goggles a n d / o r face shield.

OTHER PROTECTIVE EQUIPMENT: w i t h i n direct access.

Safety shower a n d eyewash fountain should be

P E R S O N A L H Y G I E N E : A v o i d contact with eyes, s k i n , and clothing. W a s h thoroughly after h a n d l i n g . W a s h contaminated clothing before re-use. ENGINEERING CONTROL:

S E C T I O N 8.

N.A.

SUBSTANCES FOR WHICH STANDARDS

SINGLE CHEMICAL SUBSTANCE: Percent: N . A . O S H A Exposure L i m i t : EXPOSURE ANALYSIS

S E C T I O N 9.

N.A.

COMPONENTS: Percent: N . A .

N.A.

O S H A Exposure L i m i t :

METHODS:

SOURCE OF

W a l t e r L . Schleyer

N.A.

HAVE BEEN

N.A.

INFORMATION

G o v ' t & Industry R e l a t i o n s M a n a g e r

Date: 7 / 1 7 / 7 9

N . A . = N o t Applicable Figure 4b.

Material

N.A.

safety data sheet; high ratio powders, side 2.

SET

38

SOLUBLE

SILICATES

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

Consumer Products Years ago, sodium m e t a s i l i c a t e was the only r e a d i l y s o l u b l e sodium s i l i c a t e a v a i l a b l e i n dry form. I t was used i n dry blended home laundry detergents and i n automatic dishwasher detergents. When low-phosphate and phosphate-free detergents f i r s t came on the market, some of them c a r r i e d an increased m e t a s i l i c a t e content, and concern arose about t h e i r safety i n the home. Although sodium m e t a s i l i c a t e i s c o r r o s i v e to b i o l o g i c a l t i s s u e , t h i s i s not n e c e s s a r i l y true of detergents i n which i t i s an i n g r e d i e n t . Among determining f a c t o r s are the amount used, i t s p a r t i c l e s i z i n g , the processing method, and the modifying e f f e c t of other i n g r e d i e n t s . The Consumer Product Safety Commission has recognized t h i s . It has e s t a b l i s h e d l a b e l i n g c r i t e r i a based on the r e s u l t s of b i o l o g i c a l t e s t i n g , as s p e c i f i e d under the Federal Hazardous Substances Act. I f the product contains 15% sodium m e t a s i l i c a t e or more and i f no animal t e s t data to the c o n t r a r y are a v a i l a b l e , i n s p e c t o r s are i n s t r u c t e d to r e q u i r e "DANGER! MAY CAUSE BURNS" on the l a b e l . Less severe warning language i s s p e c i f i e d f o r lower m e t a s i l i c a t e content and l e s s strongly a l k a l i n e types of s i l i c a t e i n g r e d i e n t s ( 8 ) . Both the animal t e s t methods (9) and the c a u t i o n l a b e l language are c u r r e n t l y under review w i t h i n the agency and i t s T o x i c o l o g i c a l Advisory Board. Readily soluble but l e s s s t r o n g l y a l k a l i n e hydrous sodium p o l y s i l i c a t e m a t e r i a l s have long since been a v a i l a b l e as i n g r e d i e n t s of dry blended detergents. Unlike sodium m e t a s i l i c a t e , these f a l l i n t o the intermediate or lowest s i l i c a t e l a b e l hazard c l a s s , depending on t h e i r Si02/Na2Û ratio. The household hazard i s correspondingly reduced. The bulk of household detergents i s spray d r i e d from s l u r r i e s which comprise a sodium s i l i c a t e s o l u t i o n . The f i n i s h e d product then c o n s i s t s of homogeneous beads, and not of d i s c r e t e p a r t i c l e s of i t s components, u s u a l l y r e s u l t i n g i n l e s s e r hazard characteristics. Food Uses We begin with a g l o s s a r y o f the terms by which the r e g u l a t o r y status of food i n g r e d i e n t s i s d e f i n e d . To be used i n food, a chemical substance must be e i t h e r a "food a d d i t i v e " or "Generally Recognized As Safe (GRAS)" or " p r i o r sanctioned." Each food a d d i t i v e and i t s uses i s described by an FDA r e g u l a t i o n (10), issued i n response to a food a d d i t i v e p e t i t i o n which was supported by f u l l r e p o r t s of i n v e s t i g a t i o n s i n t o i t s safety. A GRAS substance i s " g e n e r a l l y recognized, among experts q u a l i f i e d by s c i e n t i f i c t r a i n i n g and experience to evaluate i t s safety, as having been adequately shown through s c i e n t i f i c

3.

BLUMBERG A N D SCHLEYER

Regulatory

Status

39

procedures to be safe under the c o n d i t i o n s o f i t s intended use"(ll). A~" prior sanctioned" substance i s one which i s used i n accordance with a s a n c t i o n or approval granted p r i o r t o enactment o f the 1958 Food A d d i t i v e Amendments to the F e d e r a l Food, Drug and Cosmetic Act (11). Today the s c i e n t i f i c evidence r e q u i r e d to show GRAS s t a t u s i s equal i n extent t o the documentation which must be submitted i n support o f a food a d d i t i v e p e t i t i o n (12). However, there i s a grandfather c l a u s e i n the case o f a substance used i n food p r i o r to January 1, 1958: s a f e t y may be shown e i t h e r through s c i e n t i f i c procedures or through experience based on common use i n food (11). In 1973 FDA embarked on i t s GRAS review process, under which chemicals " G e n e r a l l y Recognized As Safe" are being reexamined for s a f e t y . Those affirmed w i l l be c o d i f i e d , that i s , l i s t e d i n T i t l e 21 o f the Code o f F e d e r a l Regulations (13). Those not affirmed w i l l no longer be considered GRAS by FDA, so that an approved food a d d i t i v e p e t i t i o n w i l l be r e q u i r e d f o r t h e i r use i n food (lb). Examples o f substances which are regarded as GRAS already appear i n the Code (15), but many more are p r e s e n t l y unpublished. Unpublished GRAS s t a t u s can a r i s e from an FDA o p i n i o n l e t t e r i n response to an i n q u i r y or from a determination by i n d u s t r y that a substance i s GRAS. FDA bears the burden o f proof that such a substance i s not GRAS (16). S p e c i f i c a t i o n s f o r food chemicals are to be found i n the Food Chemicals Codex (17). T h i s compendium i s prepared by the Food and N u t r i t i o n Board o f the N a t i o n a l Research C o u n c i l . I t contains monographs o f many food chemicals and i s recognized by the Food and Drug A d m i n i s t r a t i o n as d e f i n i n g t h e i r "appropriate food grade" w i t h i n the meaning o f FDA r e g u l a t i o n s (12,18). The use o f sodium s i l i c a t e for p r e s e r v i n g eggs apparently escaped government s c r u t i n y by timely obsolescence. The use o f sodium s i l i c a t e as a c o r r o s i o n i n h i b i t o r i n d r i n k i n g water was passed on a f f i r m a t i v e l y by the Surgeon General o f the P u b l i c Health Service i n 1937 (19). In the e a r l y 1960s FDA issued a s e r i e s o f o p i n i o n l e t t e r s s t a t i n g that sodium s i l i c a t e up t o 100 ppm would be " g e n e r a l l y recognized as s a f e " i n canned d r i n k i n g water as w e l l as i n other potable water systems ( 2 ) . L a t e r i t s use was mandated by a f e d e r a l m i l i t a r y s p e c i f i c a t i o n f o r canned emergency d r i n k i n g water (20), since sodium s i l i c a t e remained the only a d d i t i v e acceptable t o the Food and Drug A d m i n i s t r a t i o n . Because o f t h i s unpublished GRAS s t a t u s , sodium and potassium s i l i c a t e s were included i n the GRAS Review process. In 1979 the S e l e c t Committee on GRAS Substances issued an a f f i r m a t i v e report (2) [see Safety Reviews above] and i n d u s t r y submitted proposed food grade s p e c i f i c a t i o n s , but the r e g u l a t o r y process has not yet reached F e d e r a l R e g i s t e r p u b l i c a t i o n . Sodium and potassium s i l i c a t e and sodium m e t a s i l i c a t e monographs n

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

Current

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

40

SOLUBLE

SILICATES

have a l s o been proposed f o r i n c l u s i o n i n the Food Chemicals Codex. Sodium s i l i c a t e has published GRAS s t a t u s as a substance m i g r a t i n g t o food from paper and paperboard products used i n food packaging (21), and from cotton and cotton f a b r i c s used i n dry food packaging (22). These are i n d i r e c t food uses. Sodium s i l i c a t e has r e g u l a t i o n status as a b o i l e r water a d d i t i v e i n the p r e p a r a t i o n o f steam that w i l l contact food (23); i n z i n c - s i l i c o n d i o x i d e matrix coatings (24); and as a c o n s t i t u e n t o f cellophane used f o r packaging food TÏ5). Sodium m e t a s i l i c a t e , although merely one species o f sodium s i l i c a t e , has a r e g u l a t o r y i d e n t i t y o f i t s own, perhaps because of i t s c r y s t a l l i n e form and s t o i c h i o m e t r i c nature. I t has unpublished GRAS status f o r f r u i t and vegetable washing (26,29), as a r e f i n i n g agent f o r e d i b l e rendered f a t s (26); as a p e e l i n g s o l u t i o n f o r peaches (27); and as a component o f s a n i t i z i n g s o l u t i o n s intended f o r use on food contact surfaces (29)· I t entered GRAS review as a separate e n t i t y . The S e l e c t Committee, i n a 1977 t e n t a t i v e r e p o r t (26), d i d not pass on i t s s a f e t y , f e e l i n g i t had i n s u f f i c i e n t information. FDA then commissioned a l i t e r a t u r e review (28), and, i n a 1981 f i n a l r e p o r t , the S e l e c t Committee recommended Class I s t a t u s f o r sodium m e t a s i l i c a t e t o the FDA. This was expressed i n analogy t o the statement on sodium and potassium s i l i c a t e s , quoted on page 2 (29). C o d i f i c a t i o n , the f i n a l step i n the GRAS a f f i r m a t i o n process, could be another two years away. Sodium m e t a s i l i c a t e has food a d d i t i v e r e g u l a t i o n status as b o i l e r water a d d i t i v e i n the p r e p a r a t i o n o f steam that w i l l contact food (23). In a d d i t i o n i t i s b e l i e v e d to be " p r i o r sanctioned" under the Meat I n s p e c t i o n A c t f o r hog s c a l d i n g and t r i p e denuding. The U.S. Department o f A g r i c u l t u r e * s Food Safety and Q u a l i t y Service has o r i g i n a l j u r i s d i c t i o n under the Federal Meat Inspection Act and the P o u l t r y Products Inspection A c t . I t has approved sodium m e t a s i l i c a t e as c o o l i n g and r e t o r t water treatment agent, as t r i p e denuding agent, and as hog s c a l d agent (30) . Sodium ortho and sesqui s i l i c a t e s are s i m i l a r l y approved. Based on USDA s and FDA s r e g u l a t o r y schemes, the Meat and P o u l t r y I n s p e c t i o n Program, Animal and Plant Health Inspection Service o f the U.S. Department o f A g r i c u l a t u r e has approved s p e c i f i c sodium s i l i c a t e and/or sodium m e t a s i l i c a t e products as general c l e a n i n g agents f o r food contact s u r f a c e s , f o r t r e a t i n g b o i l e r and c o o l i n g system water, as water c o n d i t i o n e r , as wetting agent f o r use i n p o u l t r y s c a l d v a t s , i n hog s c a l d i n g and t r i p e denuding, and t o wash f r u i t and vegetables that are t o become i n g r e d i e n t s o f p o u l t r y , meat, r a b b i t and egg products (31) . The d i f f e r e n c e i n r e g u l a t o r y s t r u c t u r e i s that FDA and USDA r u l e s set generic standards, whereas the Méat and P o u l t r y Inspection Program must authorize every s i n g l e commercial product o f each s u p p l i e r , i n c l u d i n g p r o p r i e t a r y mixtures, before i t s admission t o a f e d e r a l l y inspected food packing p l a n t . f

9

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

3.

BLUMBERG A N D SCHLEYER

Current

Regulatory

Status

41

Recently the Safe D r i n k i n g Water Act t r a n s f e r r e d j u r i s d i c t i o n f o r potable water, other than water used i n food and b o t t l e d water, from the FDA to the Environmental P r o t e c t i o n Agency. EPA i s planning a c o n t r o l program f o r water treatment chemicals and, i n a memorandum o f agreement with FDA, announced (32) that i t had contracted with the N a t i o n a l Academy of Sciences to develop a compendium of approved substances and s p e c i f i c a t i o n s , comparable to the Food Chemicals Codex. No chemicals have so f a r become known to have been s e l e c t e d f o r i n c l u s i o n . H i s t o r i c a l l y , the use of sodium s i l i c a t e , and of a c t i v a t e d s i l i c a s o l prepared from sodium s i l i c a t e , f o r t r e a t i n g p u b l i c water s u p p l i e s has been authorized by p u b l i c h e a l t h agencies on the s t a t e l e v e l . The amount of s o l u b l e s i l i c a t e s consumed i n regulated food uses i s small compared to the tonnage consumed i n the c l e a n i n g of food contact s u r f a c e s . Since i t i s considered that there i s no residue of c l e a n i n g agents when the surfaces have been r i n s e d with potable water, the detergent uses are unregulated. Recognition of the s a f e t y of the s o l u b l e s i l i c a t e s i n food i s considered important because of the e v e n t u a l i t y that u t e n s i l c l e a n i n g agents would some day be regulated as chemical food ingredients. Pesticide

Formulations

Sodium s i l i c a t e and sodium m e t a s i l i c a t e are exempt from the requirement of a residue t o l e r a n c e i n p e s t i c i d e formulations a p p l i e d to growing crops or to raw a g r i c u l t u r a l commodities a f t e r harvest (33). The detergency b u i l d e r and b u f f e r i n g c h a r a c t e r i s t i c s of sodium s i l i c a t e and m e t a s i l i c a t e have l e d to t h e i r i n c l u s i o n i n about 480 EPA-registered detergent s a n i t i z e r products. Relying apparently on an h i s t o r i c a l master l i s t of substances f o r which p e s t i c i d a l a c t i v i t y had ever been claimed by any a p p l i c a n t f o r a p e s t i c i d e r e g i s t r a t i o n , EPA regards the s i l i c a t e s as a c t i v e i n g r e d i e n t s whenever they are part of a p e s t i c i d e formulation. In most i f not a l l such formulations, s i l i c a t e performs as an adjuvant and has no a n t i m i c r o b i a l a c t i v i t y o f i t s own at use c o n c e n t r a t i o n . Therefore i t does not meet FIFRA (34) d e f i n i t i o n of a p e s t i c i d e . With p e s t i c i d e r e g u l a t i o n tightened i n recent years, the presence of s o l u b l e s i l i c a t e s on EPA*s p e s t i c i d e a c t i v e s master l i s t threatens i t s i n d i s c r i m i n a t e r e g u l a t i o n , along with many other common i n d u s t r i a l chemicals of low hazard p o t e n t i a l . A c o n t r o l program (35) d i r e c t e d at t e c h n i c a l a c t i v e s not h i t h e r t o subject to p e s t i c i d e r e g u l a t i o n , such as kepone, should not be purposely or i n a d v e r t e n t l y extended to multi-purpose commodity chemicals which are already regulated under the Toxic Substances C o n t r o l Act (TOSCA). Examples of i n a p p r o p r i a t e uses of the

42

SOLUBLE

SILICATES

e n t i r e l i s t f o r r e g u l a t o r y purposes are: a proposed scheme f o r recordkeeping, r e p o r t i n g and p e s t i c i d e manufacturing establishment r e g i s t r a t i o n (36); and a p o s s i b l e generic OSHA standard f o r occupational exposure t o p e s t i c i d e s during manufacture and formulation (37). I t has been reported i n newsletters that EPA plans t o remove at l e a s t 114 chemicals, i n c l u d i n g the s o l u b l e s i l i c a t e s , from a c t i v e p e s t i c i d a l i n g r e d i e n t s t a t u s , but no o f f i c i a l a c t i o n has as yet been taken. Transportation Sodium s i l i c a t e l i q u i d s o f 1.6 Si02/Na 0 r a t i o or l e s s and sodium o r t h o s i l i c a t e meet the c r i t e r i a (38) f o r r e g u l a t i o n as c o r r o s i v e m a t e r i a l s f o r purposes o f t r a n s p o r a t i o n . As n e i t h e r substance i s l i s t e d s p e c i f i c a l l y i n the DOT Hazardous M a t e r i a l s Table (39), the proper shipping names are, r e s p e c t i v e l y , a l k a l i n e ( c o r r o s i v e ) l i q u i d , n.o.s. and c o r r o s i v e s o l i d n.o.s. DOT r e g u l a t i o n s p r e s c r i b e the proper manner o f packaging (38), preparing shipping papers, marking, l a b e l i n g (with the diamond-shaped l a b e l bearing the " c o r r o s i v e " legend and symbols), and v e h i c l e p l a c a r d i n g (40). "Limited q u a n t i t i e s " i n surface t r a n s p o r t a t i o n are exempt from many o f these requirements (41). More s t r i n g e n t r u l e s apply to t r a n s p o r t a t i o n by a i r (427, where a f u r t h e r d i s t i n c t i o n as t o net quantity l i m i t i n a s i n g l e package i s made between passenger-carrying and cargo-only a i r c r a f t . Only the DOT r u l e s which are generic t o c o r r o s i v e m a t e r i a l s apply t o those s o l u b l e s i l i c a t e s o f very high degree o f a l k a l i n i t y . Hence, they are mentioned as being a p p l i c a b l e , but not explained f u r t h e r . As discussed i n the next s e c t i o n , c e r t a i n sodium s i l i c a t e l i q u i d s which do not meet DOT c r i t e r i a f o r a c o r r o s i v e l i q u i d are hazardous waste under RCRA when discarded. These are DOT-regulated as ORM-E (43). S i m i l a r l y , the d r y blends which are i d e n t i f i e d i n the next S e c t i o n as EPA hazardous substances because o f t h e i r sodium hydroxide content are DOT-regulated as ORM-E, i f they c o n t a i n the r e p o r t a b l e quantity o f 1,000 l b . NaOH i n a s i n g l e package or bulk c o n t a i n e r .

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

2

P o l l u t i o n and Waste C o n t r o l The e f f l u e n t l i m i t a t i o n g u i d e l i n e s governing users o f s o l u b l e s i l i c a t e s are determined by t h e i r standard i n d u s t r y c l a s s i f i c a t i o n (SIC Number). I t may be noted that the sodium s i l i c a t e subcategory o f the Inorganic Chemicals Manufacturing Industry has been excluded from f u r t h e r rulemaking under the National Resources Defense Council v . C o s t l e consent decree because o f the absence or v i r t u a l absence o f 65 t o x i c p o l l u t a n t s from the i n d u s t r y s e f f l u e n t s (44). Because o f high temperature manufacturing processes, aqueous media and high i n s o l u b i l i t y o f 1

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

3.

BLUMBERG A N D SCHLEYER

Current

Regulatory

Status

43

the s i l i c a t e s of most metals, the commercial s o l u b l e s i l i c a t e s are g e n e r a l l y low i n both organic and i n o r g a n i c i m p u r i t i e s . T y p i c a l values are shown i n Table 1.(45). T h e i r range represents eleven producing p o i n t s which are l o c a t e d throughout the United States and employ d i f f e r e n t manufacturing processes. The s o l u b l e s i l i c a t e s are not designated as hazardous substances under Section 311 o f the F e d e r a l Water P o l l u t i o n ' C o n t r o l Act, r e l a t i n g to discharges or s p i l l s i n t o navigable waters (46). However, some commercial sodium o r t h o s i l i c a t e products are a c t u a l l y p h y s i c a l blends of sodium hydroxide and sodium m e t a s i l i c a t e p a r t i c l e s . Such mixtures are EPA hazardous substances by v i r t u e of t h e i r sodium hydroxide content, and t h e i r r e p a r t a b l e q u a n t i t y i s the equivalent of 1,000 l b s o f sodium hydroxide (47). In terms of the Resource Conservation and Recovery Act of 1976 (RCRA) sodium s i l i c a t e i s not among c e r t a i n chemicals which have been designated as rendering a waste hazardous (48). However, a waste i s a l s o c l a s s i f i e d as hazardous i f i t e x h i b i t s c e r t a i n c h a r a c t e r i s t i c s (49). One of these i s c o r r o s i v i t y . On the a l k a l i n e s i d e , c o r r o s i v i t y i s defined by a pH equal to or greater than 12.5, provided the waste i s aqueous (50). We have measured the pH o f v a r i o u s sodium s i l i c a t e s o l u t i o n s by EPA*s reference method. According to our r e s u l t s , sodium s i l i c a t e s o l u t i o n s have a pH of 12.5 or g r e a t e r when a. r e g a r d l e s s of c o n c e n t r a t i o n , the Si02/Na20 weight r a t i o i s l e s s than 2.0; and b. the Si02/Na20 r a t i o i s equal to 2.0 and the s o l i d s c o n c e n t r a t i o n i s approximately 44% or greater. Below that c o n c e n t r a t i o n and at a l l concentrations above 2.0 r a t i o the pH remained below 12.5. On November 17, 1980, EPA proposed t o grant a permit-by-rule to operators o f "elementary n e u t r a l i z a t i o n u n i t s , " d e f i n e d as devices that are used f o r n e u t r a l i z i n g wastes which are hazardous wastes only because they e x h i b i t the c o r r o s i v i t y c h a r a c t e r i s t i c s . Pending completion o f t h i s rulemaking, EPA has suspended i t s permit requirements f o r e l i g i b l e operators. As a r e s u l t , operators of "elementary n e u t r a l i z a t i o n u n i t s " no longer need RCRA permits on a case-by-case b a s i s , only a r e g i s t r a t i o n number (51). When sodium s i l i c a t e s o l u t i o n s at or above pH 12.5 become wastes, they are "hazardous wastes only because they e x h i b i t the c o r r o s i v i t y c h a r a c t e r i s t i c . " Consequently, t h e i r d i l u t i o n or n e u t r a l i z a t i o n i n accordance with EPA s operating c o n d i t i o n s does not r e q u i r e an i n d i v i d u a l RCRA permit provided, o f course, they are not part of an i n d u s t r i a l waste stream which has been designated as hazardous (52). I t should be noted t h a t , as o f t h i s w r i t i n g , the permit requirement i s only suspended, and the permit by r u l e i s not yet i n e f f e c t . Current EPA r e g u l a t i o n s should be reviewed concerning f u r t h e r developments and concerning a l l other a p p l i c a b l e requirements. f

44

SOLUBLE

SILICATES

I f a h i g h l y a l k a l i n e sodium s i l i c a t e waste i s c l a s s i f i e d as a hazardous waste under RCRA, i t i s a l s o a hazardous substance under the Comprehensive Environmental Response, Compensation and L i a b i l i t y Act of 1980 (CERCLA or Superfund A c t ) . The law s r e p o r t i n g requirements would apply to any r e l e a s e i n t o the environment. This i s a l s o true for the p r e v i o u s l y mentioned sodium o r t h o s i l i c a t e products which are EPA hazardous substances, s i n c e they are p h y s i c a l mixtures c o n t a i n i n g sodium hydroxide. For sodium hydroxide the r e p o r t a b l e quantity remains I, 000 l b . U n t i l r u l e s to implement the act are published, the r e p o r t a b l e quantity o f a c o r r o s i v e waste i s 1 l b . f

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

Toxic Substances C o n t r o l Act Following Chemical Abstract Service terminology, the commercial s o l u b l e s i l i c a t e s were reported to the i n i t i a l inventory of e x i s t i n g chemical substances as i n d i c a t e d i n Table II. Under the r e p o r t i n g r u l e s (53), a hydrated chemical was to be regarded as a mixture, and the anhydrous substance was to be reported. The only subsequent r e g u l a t o r y development thus f a r under TOSCA, d i r e c t e d s p e c i f i c a l l y at s o l u b l e s i l i c a t e s , was a proposed r u l e (54) under Section 8(a) which would r e q u i r e manufacturers to keep c e r t a i n records and report production and exposure r e l a t e d data on approximately 2300 chemicals to EPA. This information was held to be necessary to rank chemicals f o r i n v e s t i g a t i o n and to make p r e l i m i n a r y r i s k assessments. Sodium s i l i c a t e , potassium s i l i c a t e , sodium m e t a s i l i c a t e and sodium o r t h o s i l i c a t e were included on the candidate l i s t , presumably because r e p o r t s to the i n i t i a l inventory showed them to be manufactured i n high tonnage volume. It i s now understood that the l i s t has been pared down to about 300 chemicals. In view of the p u b l i c a v a i l a b i l i t y of previous h e a l t h hazard assessments by FDA, IJC and others, which has been pointed out to EPA i n comments on i t s proposal, i t i s expected that the s o l u b l e s i l i c a t e s are among the chemicals which have been s l a t e d to be e l i m i n a t e d from the l i s t . Discussion I t has been seen that even r e l a t i v e l y simple and f a m i l i a r chemicals l i k e the s o l u b l e s i l i c a t e s have become quite e x t e n s i v e l y involved i n the v a r i o u s r e g u l a t o r y schemes designed to p r o t e c t our h e a l t h and environment. The reason i s t h e i r high tonnage production and t h e i r broad d i s t r i b u t i o n , ranging from i n d u s t r i a l plants to the home. The s o l u b l e s i l i c a t e s are t r u l y r e c y c l e d by man: they d e r i v e e n t i r e l y from mineral d e p o s i t s and are returned to the

Current

BLUMBERG A N D SCHLEYER

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

Table I.

Regulatory

Status

Typical Impurity Levels in Commercial Sodium Silicates (ppm, ppb where noted)

+

4 H (aq)

W o l l a s t , e t a l . (28) report, that the e q u i l i b r i u m constant f o r t h i s r e a c t i o n i s i n the range of 10"^^ to 10~19 t 25°C i n seawater. Ion a c t i v i t y products c a l c u l a t e d f o r the data i n W i l l e y (1) a l l i n d i c a t e s o l u t i o n s undersaturated by s e v e r a l orders of mag­ nitude w i t h respect to s e p i o l i t e , and s l i g h t l y a

(8)

WILLEY

Aging

of Amorphous

Silica

under s a t u r a ted f o r data i n Jones and Pytkowicz (3) assuming a small temperature and p r e s s u r e e f f e c t on t h i s e q u i l i b r i u m constant. In order to c a l c u l a t e these i o n a c t i v i t y products, 0.22 was used as the a c t i v i t y c o e f f i c i e n t f o r M g , 1.0 was used as the a c t i v i t y c o e f f i c i e n t f o r d i s s o l v e d s i l i c a , the pH o f the s o l u t i o n s used by Jones and Pytkowicz (3) was assumed to be between 7.5 and 8.0. The data produced by W i l l e y (2) and G r i f f i n , e t a l . (4) c o u l d n o t have been a f f e c t e d by s e p i o l i t e formation b e ­ cause no magnesium was present i n the e x p e r i ­ mental s o l u t i o n s . The s o l u b i l i t y o f s e p i o l i t e should i n ­ crease w i t h i n c r e a s i n g p r e s s u r e based on a simple c a l c u l a t i o n o f AV^ f o r the d i s s o l u t i o n of s e p i o l i t e . Using p a r t i a l molal volume data for M g and IT*" compiled by Berner (29), along w i t h the value f o r s i ( O H ) 4 ( a q ) c a l c u l a t e d i n t h i s study and a molal volume f o r s e p i o l i t e c a l c u l a t e d from d e n s i t y data (2.08 to 2.45 gcm""3) compiled i n Donnay and Ondik (30), AV^ should be between - 37 and - 59 cm per mole of s e p i o l i t e d i s s o l v e d . The s i g n o f t h i s num­ ber i n d i c a t e s t h a t the s o l u b i l i t y o f s e p i o l i t e should i n c r e a s e w i t h i n c r e a s i n g p r e s s u r e . Based on t h i s c a l c u l a t i o n , s e p i o l i t e should not l i m i t s i l i c a s o l u b i l i t y any more a t higher pressure than i t does a t lower p r e s s u r e ; t h i s cannot be s a i d w i t h c e r t a i n t y , however, u n t i l more i n f o r m a t i o n on the s o l u b i l i t y o f s e p i o ­ l i t e as a f u n c t i o n o f p r e s s u r e i s a v a i l a b l e . A s i m i l a r c a l c u l a t i o n has been done by Sayles (31). The pH decrease (Table I I ) observed i n the e a r l y experiment when seawater came i n t o contact w i t h the amorphous s i l i c a s u r f a c e suggested p o s s i b l e s e p i o l i t e formation. How­ ever, i n subsequent experiments, a s i m i l a r pH change was observed f o r unwashed s i l i c a s u r ­ faces i n contact w i t h 0.9% NaCl + 0 . 1 % NaHC03 s o l u t i o n . The amount o f base r e q u i r e d to t i t r a t e each s o l u t i o n back t o pH 8 a f t e r the s o l i d phase was removed was g r e a t e r i n the s a l t s o l u t i o n than i n seawater. T h i s e x p e r i ­ ment shows that the pH decrease occurs i n s o l u t i o n s with no Mg2+(aq), so s e p i o l i t e formation i s n o t n e c e s s a r i l y i n v o l v e d w i t h the pH change.

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch010

2+

2 +

v

3

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch010

162

SOLUBLE

SILICATES

The c o n c e n t r a t i o n of d i s s o l v e d s i l i c a i n s a l t water s o l u t i o n s i n contact w i t h s o l i d amorphous s i l i c a may decrease f o r a time p e r i o d of s e v e r a l weeks to s e v e r a l months a f t e r the i n i t i a l d i s s o l u t i o n , and then a f t e r t h i s i n i t i a l aging process i s com­ p l e t e d the c o n c e n t r a t i o n remains s t a b l e f o r months or years ( 2 ) . Several s t u d i e s have r e p o r t e d t h i s e q u i l i b r i u m s o l u b i l i t y . Jorgensen (16) found that three to f i v e months were r e q u i r e d to achieve e q u i l i b r i u m i n h i s experiments, and a f t e r that time the same s o l u b i l i t y was determined from undersaturated or overs a t u r a t e d s o l u t i o n s i n contact w i t h s i l i c a f o r time p e r i o d s up to two y e a r s . Jones and Pytkowicz (3) found the same s o l u b i l i t y f o r aged s i l i c a a f t e r 66 o r 123 days of e q u i l i b r a t i o n time. W i l l e y (2) found no change i n the s o l u b i l i t y of s i l i c a aged f o r two months i n s a l t water s o l u t i o n a f t e r time p e r i o d s of up to f i v e y e a r s . G r i f f i n , e t a l . (4) determined s o l u b i l i t i e s u s i n g the crossover method of S i e v e r and Woodford (32) which does not r e q u i r e attainment o f e q u i l i b r i u m . With t h i s method (32), s o l u t i o n s which have d i f f e r e n t d i s s o l v e d s i l i c a concentrations are p l a c e d i n contact with s o l i d amorphous s i l i c a . The change i n c o n c e n t r a t i o n which r e s u l t s when e i t h e r d i s s o l u t i o n or p r e c i p i ­ t a t i o n occurs i n the s e v e r a l s o l u t i o n s i s used to c a l c u l a t e the solubility. In the study by G r i f f i n , et a l . (4), c o n c e n t r a t i o n change measurements were made a f t e r three weeks. Kato and Kitano (20) used an e q u i l i b r a t i o n time o f 500 days i n t h e i r s o l u b i l i t y experiments. A l l of these l o n g term s t u d i e s obtained s i m i l a r values f o r the s o l u b i l i t y o f aged amorphous s i l i c a i n s a l t water s o l u t i o n s . S i e v e r (22) obtained a s l i g h t l y higher s o l u b i l i t y value a f t e r an e q u i l i b r a t i o n time o f two y e a r s . These s t u d i e s show t h a t the s o l u b i l i t y o f aged amorphous s i l i c a i n s a l t water s o l u t i o n s i s s t a b l e f o r many months or years a f t e r an i n i t i a l aging time of s e v e r a l months. The trends observed f o r the aging of b i o g e n i c s i l i c a (11, 12) and thermodynamic c a l c u l a t i o n s (_7) suggest that t h i s i s not the u l t i m a t e e q u i l i b r i u m ; e v e n t u a l l y the amorphous s i l i c a should change to quartz which has a much lower s o l u b i l i t y than amorphous s i l i c a (4, _7, 13, 15, 21). Conclusions 1. The s o l u b i l i t y of amorphous s i l i c a i n s a l t water s o l u ­ t i o n s (at 0-3°C or 19-26°C, and over the pressure range from 1 to 1000 atmospheres) decreases by approximately 20% with time due to aging o f the s o l i d s i l i c a . 2. T h i s s o l u b i l i t y change makes amorphous s i l i c a s o l u b i l i t y d i f f i c u l t to determine, and c o n t r i b u t e s to the s c a t t e r i n pub­ lished s o l u b i l i t y values. 3. Other trends a s s o c i a t e d with t h i s aging of s i l i c a i n ­ clude a decrease i n s p e c i f i c s u r f a c e area and pore volume, and an i n c r e a s e i n d e n s i t y . S i m i l a r trends have been i d e n t i f i e d f o r biogenic s i l i c a .

10. WILLEY

Aging of Amorphous Silica

163

4. The rate of silica aging depends on experimental conditions, including the ratio of solid surface area to solution volume. 5. The solubility of amorphous silica in seawater or in salt water solutions similar to seawater is not affected by the extent of hydration of the solid phase, and is not limited by sepiolite formation. Acknowledgments

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch010

Discussions of importance regarding this work were held with R. Dayal and R. K. lier, and an earlier version of the manuscript was reviewed by L. M. Mayer. E. Malik typed the manuscript. All of this assistance is appreciated. Literature Cited 1. Willey, J. D. Mar. Chem. 1974, 2, 239-250. 2. Willey, J. D. Geochim. Cosmochim. Acta 1980, 44, 573-578. 3. Jones, M. M.; Pytkowicz, R. M. Bull. Soc. R. Sci. Liege 1973, 42, 118-120. 4. Griffin, J. W. ; Hurd, D. C.; Commeau, J . ; Poppe, L. Am. J. Sci. (in preparation). 5. Duedall, I. W.; Dayal, R.; Willey, J. D. Geochim. Cosmochim. Acta 1976, 40, 1185-1189. 6. Owen, B. B.; Brinkley, S. R. Chem. Rev. 1941, 29, 461-473. 7. Walther, J. V.; Helgeson, H. C. Am. J. Sci. 1977, 277, 1315-1351. 8. Sheinfain, R. Y.; Neimark, I. E. Chapter 8, in "Adsorption and Adsorbents" (ed. D. N. Strazhesko), Wiley, 1973, pp. 87-95. 9. Okkerse, C.; de Boer, J. H. Chapter 25 in "Reactivity of Solids" (ed. J. H. de Boer), Elsevier, 1961, pp. 240248. 10. Okkerse, C.; de Boer, J. H. Silic. Ind. 1962, 27, 195-202. 11. Hurd, D. C.; Theyer, F. Adv. Chem. Ser. 1975, 147, 211-230. 12. Hurd, D. C.; Wenkam, C.; Pankratz, H. S.; Fugate, J. Science 1979, 203, 1340-1343. 13. Stöber, W. Adv. Chem. Ser. 1967, 67, 161-182. 14. Hurd, D. C. Earth Planet. Sci. Lett. 1972, 15, 411-417. 15. Iler, R. K. "The Chemistry of Silica". Wiley, 1979. 16. Jorgensen, S. S. Acta Chem. Scand. 1968, 22, 335-341. 17. Vysotskii, Z. Z.; Galinskaya, V. I.; Kolychev, V. I.; Strelko, V. V.; Strazhesko, D. N. Chapter 7 in "Adsorption and Adsorbents" (ed. D. N. Strazhesko). Wiley 1973, 72-86. 18. Krauskopf, Κ. B. Geochim. Cosmochim. Acta 1956, 10, 1-26. 19. Kato, K.; Kitano, Y. J. Oceanogr. Soc. Jpn. 1968, 24, 147-152. 20. Lewin, J. C. Geochim. Cosmochim. Acta 1961, 21, 182-198.

164

SOLUBLE SILICATES

Siever, R. J. Geol. 1962, 70, 127-150. Iler, R. J. Colloid Interface Sci. 1973, 43, 399-408. Kitahara, S. Rev. Phys. Chem. Jpn. 1960, 30, 131-137. Marshall, W. L. Geochim. Cosmochim. Acta 1980, 44, 907-914. Hurd, D. C. Geochim. Cosmochim. Acta 1973, 37, 2257-2282. 26. Willey, J. D. Geochim. Cosmochim. Acta (in press). 27. Willey, J. D. "The Physical Chemistry of Silica in Sea Water and Marine Sediments"; Ph.D. Thesis, Dalhousie University, 1975, 195 pp. 28. Wollast, R.; MacKenzie, F. T.; Bricker, O. P. Am. Mineral.

21. 22. 23. 24. 25.

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch010

1968, 53, 1645-1662.

29. Berner, R. A. "Principles of Chemical Sedimentology"; McGraw-Hill Book Company, 1971, p. 212. 30. Donnay, J. D. H.; Ondik, H. M. "Crystal Data Determinative Tables"; Volume 12, U. S. Department of Commerce, National Bureau of Standards, and Joint Committee on Powder Diffraction, 1973, p. 0-51. 31. Sayles, F. T. Geochim. Cosmochim. Acta 1981, 45, 1061-1086. 32. Siever, R.; Woodford, N. Geochim. Cosmochim. Acta 1973, 37, 1851-1880. RECEIVED March 2, 1982.

11 S i l a n o l Groups and Properties of S i l i c a Surfaces

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

J. J. FRIPIAT C.N.R.S. C.R.S.O.C.I., 45045 Orléans, France

This paper begins by reviewing briefly different techniques, namely precipitation of organic and inorganic compounds, oxidation of volatile silicic compounds and acid attack of magnesium silicates, for preparing porous and non porous silicagels with various surface coverages and distributions of silanol groups, and the effect of heating on these materials. Infrared spectroscopic investigations coupled with chemical specific reactions as well as with magnetic nuclear resonance (NMR) permit a characterization of these surfaces. The chemical properties of silanol groups and of silica surfaces are then studied from the point of view of adsorption processes, involving mainly water, methanol ammonia and amines. Proton interaction and exchange between silanol group and those reagents are studied using physical techniques and particularly pulse NMR. The proton exchange process is related to the acid properties of the silanol groups. Estherification reactions of silanol groups with chloro-alkyl silane, methanol and other reagents and the properties of the reaction products are examined. The reduction of silica surface at high temperature by the so-called spillover process leading to the formation of exposed silicon atoms and Si-H groups, is finally studied. The hydrolysis of soluble silicates or of silicon organic derivatives such as silicic ether in aqueous solution yields silicagels with variable but generally high, specific surface areas. 0097-6156/82/0194-0165$06.00/0 © 1982 American Chemical Society

166

SOLUBLE

SILICATES

For i n s t a n c e , as shown i n Table I, when 0.6 ml of Si(0C H^) i s mixed with 10 ml of water and t r e a t e d at 150°C under the c o r ­ responding water pressure the p r e c i p i t a t e d s o l i d s outgassed at 100°C have s p e c i f i c s u r f a c e areas between 52 and 578 m /g accor­ ding to the i n i t i a l pH c o n d i t i o n s * 2

2

Table I - Nitrogen B.E.T. s p e c i f i c surface areas obtained by h y d r o l y z i n g S i ( 0 0 2 ^ ) 4 a t 150° under 6 atm water pressure (J_)

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

Hydrothermal treatment, aging (days) 2 8 16

Precipitation F i n a l pH

pH

2 2.5

3.5 3.6

5.5 4.5

8 5.2

578 520 365

345 309 155

58 78 52

112 70 115

T h i s i s an i l l u s t r a t i o n among many others of the importance of the aging time, and of the pH of h y d r o l y s i s on the f i n a l p o l y ­ m e r i z a t i o n degree. S i l i c a g e l s are X-rays amorphous but the r a d i a l d i s t r i b u t i o n f u n c t i o n obtained according to the technique i n i t i a l l y proposed by Warren and c o l l a b o r a t o r s (2) r e v e a l s that i n the t e t r a h e d r a l u n i t SiO^ the Si-0 d i s t a n c e s are between 1.66 and 1.61 Â, e.g. i n the domain observed f o r c r y s t a l l i z e d s i l i c a t e s and that there i s some order i n the s t r u c t u r a l arrangement of the second c o o r d i ­ n a t i o n s h e l l (J_) . The Si-0 d i s t a n c e w i t h i n a tetrahedron i s s l i g h t l y s h o r t e r i n gels prepared from S i ( O C 2 H 5 ) , at pH between 3 and 6 and somewhat l a r g e r at lower or higher pH. The S i j - 0 - S i 2 angle v a r i e s between 145 and 180° according to the p r e p a r a t i o n procedure ( 1 ) . In 3 c r i s t o b a l i t e t h i s angle i s 180° whereas i n α and 3 quartz and α c r i s t o b a l i t e i t ranges between 143° and 150°. Thus a s i l i c a g e l may be considered as formed of small u n i t s , i n v o l v i n g the second c o o r d i n a t i o n s h e l l , which are c h a r a c t e r i z e d by s t r u c ­ t u r a l arrangements such as those found f o r these c r y s t a l l i n e solids. S i l i c a g e l s prepared from d i s t i l l e d SiiCK^H^)^ are of course q u i t e pure, the main impurity being N a ions from the NaOH s o l u ­ t i o n used to adjust the pH. With respect to a c r y s t a l l i n e s i l i c a t e c o n t a i n i n g a dense network of s i l i c o n t e t r a h e d r a sharing corners, the main s t r u c t u r e breaking element i s the proton forming inner or e x t e r n a l s i l a n o l groups. In a d d i t i o n , h y d r a t i o n water may be^ r e t a i n e d by these groups because of the formation of S i - O H — 0 ^ hydrogen bonds. The s i l a n o l group may be thus considered as a structural defect. Numerous workers have t r i e d to measure the r e l a t i v e c o n t r i b u ­ t i o n s of the inner and e x t e r n a l s i l a n o l group as w e l l as that of h y d r a t i o n water. I t i s not a simple problem because the amorphous nature of the g e l precludes the use of thermal methods such as +

11.

Silanol

FRIPIAT

Groups

and

167

Properties

DTA or TGA. The h y d r a t i o n and c o n s t i t u t i o n a l water are l o s t i n an almost monotonous manner. Figure 1 shows an e a r l y attempt to make that type of d i s t i n c ­ t i o n (3) u s i n g a combination of i n f r a r e d technique and chemical determinations. A l l r e s u l t s are expressed as OH i r r e s p e c t i v e of the simultaneous presence of h y d r a t i o n water and of s i l a n o l groups. The g e l i s the A e r o s i l Degussa obtained by flame p y r o l y s i s of S i C l ^ , I t s N 2 B.E.T. surface area amounts to 180 m /g. Curve 1 i s obtained from the weight l o s s . Curve 2 i s obtained using the r e a c ­ t i o n of 0H s ( s i l a n o l or water) with LiCH^ or CH^Mgl, producing methane, whereas curve 3 i s the h y d r a t i o n water content deduced from the IR absorption bands i n the OH s t r e t c h i n g and the H 0 de­ formation r e g i o n s . The g e l was outgassed during 45 hrs at 25°C under a dynamic vacuum between 10~5 and 10~6 t o r r before these determinations were c a r r i e d out. The t o t a l OH content was about 2.9 10~ mole/g at 25°C and the e v o l u t i o n of the r a t i o of the surface to the t o t a l hydroxyl content i s shown i n Figure 2. To o b t a i n these r e s u l t s i t was assumed that the surface s i l a n o l s only react with the organometallic reagents. This example i l l u s t r a t e s the f a c t that the q u a n t i t a t i v e de­ termination of surface s i l a n o l groups r e q u i r e s a combination of d i f f e r e n t techniques, and yet i t r e q u i r e s hypothesis open to c r i ­ t i c i s m s . According to F i g u r e 1, the surface d e n s i t y i n s i l a n o l s i s about 4 3 OH per nm . I t seems s t a b l e up to 300°C and i t s t a r t s decreasing above that temperature. A f t e r h e a t i n g between 600-700°C, the surface d e n s i t y reaches a value of about 1.5 (OH)/.nm . I t i s at t h i s dehydroxylation s t a t e that an i s o l a t e d OH s t r e t c h i n g v i ­ b r a t i o n appears as a narrow band at 3740 cm" . At lower dehydra­ t i o n temperature but above 250°C, when most of the h y d r a t i o n water i s removed (see Figure 1, curve 3), the s i l a n o l s t r e t c h i n g band i s more complex because of c o n t r i b u t i o n s of i n t e r hydrogen bonds. The value which i s now g e n e r a l l y accepted ( 4 ) f o r surface d e n s i t y i n s i l a n o l s i s about 4.5 OH/nm . I t i s to the p r o p e r t i e s of the surface s i l a n o l s that t h i s c o n t r i b u t i o n i s devoted. f

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

2

3

2

%

2

1

2

D i s t r i b u t i o n of s i l a n o l groups on s i l i c a

surfaces

On the surface of amorphous s i l i c a g e l s , the d i s t r i b u t i o n of the s i l a n o l groups i s most probably random. T h i s means that there i s some p r o b a b i l i t y that any s i l a n o l group may have a near neigh­ bour s i l a n o l which might be bound to the same s i l i c o n or most probably, which i s l i n k e d to an adjacent s i l i c o n i n a =Si(0H)-0Si(OH)=arrangement. For instance on a deuterated A e r o s i l surface outgassed at 27°C, the s t r e t c h i n g 0D r e g i o n shows bands at 2760 cm" , 2665 cm" and a shoulder at 2573 cm""l. These bands correspond to OH v i b r a t i o n a l bands at 3740, 3607 and 3480 cm" r e s p e c t i v e l y . The 2573 cm~l band r e i n f o r c e s When D 0 i s p h y s i c a l l y adsorbed whereas the 2760 cm~l i n d i v i d u a l i z e d as a s i n g l e band upon outgassing at i n c r e a s i n g temperature. T h i s band i s , as s a i d before, due to i s o l a t e d deuterated s i l a n o l whereas the 2665 cm" 1

1

1

2

1

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

168

SOLUBLE

0

100 200

300 400 500

600

700 000

SILICATES

T[°C]

Figure 1. In abscissa: sample outgassing temperature under vacuum. Key: upper curve ( ), OH (gravimetric) content (including H O); curve 2 ( ), evolved CH for the reactions with either CH Li (O) or CH MgI (^); curve 2b, curve 2 corrected for physically adsorbed water; curve 2a; surface silanols content; lower curve (A) H 0 content (in OH) determined by IR spectroscopy. t

k

s

s

2

f 2oL of 0 Figure 2.

I

I I I 200 400

I

I 600

I

I

I

T[C]

Relative surface hydroxyl content as a function of outgassing ture.

tempera-

11.

Silanol

FRIPIAT

Groups

and

169

Properties

1

band (e.g. the 3607 cm"" OH band) may be t e n t a t i v e l y assigned to hydrogen bonded s i l a n o l s . Of course these v i b r a t i o n a l bands are not n e c e s s a r i l y those of surface s i l a n o l s s i n c e d e u t e r a t i o n may a f f e c t i n t e r n a l s i l a n o l s as w e l l . I t has been shown (5) that the r a t e s of i s o t o p i c exchange are d i f f e r e n t f o r i s o l a t e d and bridged s i l a n o l s but these k i n e t i c s data could not be used to c a l c u l a t e t h e i r r e s p e c t i v e c o n t r i b u t i o n s to the s i l a n o l s u r f a c e d e n s i t y . The second moment of the proton NMR resonance l i n e of s i l i c a g e l s from d i f f e r e n t o r i g i n has a l s o been proposed to o b t a i n more s i g n i f i c a n t data ( 6 ) . The c l a s s i c a l equation f o r the second moment M i s 2

M

2

= 3.56 1

ΙΟ"

4 6

2

Σ Σ rT? (gauss ) i

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

(1)

1 J

j where r . . i s the d i s t a n c e between protons i and j i n a volume that c o n t a i n s N protons. Any motion o c c u r i n g i n the domain of the pro­ ton n u c l e a r resonance frequency (^ 10 Hz) would reduce the second moment even i f the average d i s t a n c e remains constant. I f the pro­ tons were homogeneously spread on the s u r f a c e i n r i g i d p o s i t i o n s M should be 0.12 gauss f o r a s u r f a c e d e n s i t y of 4.4 proton/nm ^). J

8

2

2

2

In Table I I , the experimental second moments observed f o r va­ r i o u s s i l i c a g e l s are given as w e l l as the references t o the paper where a p a r t i c u l a r g e l has been c h a r a c t e r i z e d . The outgassing con­ d i t i o n s and the temperature dependence of M« are a l s o i n d i c a t e d . Table I I - Second moment of the proton NMR f o r v a r i o u s gels (6) Gel

Outgassing temperature (°C)

M

2

2

(gauss )

resonance

line

observed

Temperature dependence observed f o r M 2

Fibrous gel(6)

100

Aerogel

(8)

100

2.33

Constant -160°C.

from 20°C to

Xerogel

(9)

100

3.00

Constant -160°C.

from 140°C to

Davison

(JO)

500

0.51

Constant -210°C.

from 280°C to

(JLL>

unknown

0.55

unknown.

K

4

V a r i a b l e see Table I I I

10.7

The f i b r o u s g e l , w i t h the highest M was obtained by h y d r o l y z i n g completely asbestos c h r y s o t i l e i n a 6 Ν (50% water, 50% i s o p r o panol) HCl s o l u t i o n at 5 0 ° C In a l l cases, the experimental M are c o n s i d e r a b l y l a r g e r than that c a l c u l a t e d f o r an homogeneous d i s t r i b u t i o n . Because of the 1/r.. dependence of M , t h i s means 2

2

?

170

S O L U B L E SILICATES

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

that there are patches with higher concentrations i n s i l a n o l s . For the f i b r o u s g e l t h i s can be q u a l i t a t i v e l y explained by sketching the s t r u c t u r e of the h y d r o l y s i s product of the c h r y s o t i l e by the f o l l o w i n g arrangement, each Si-O-Mg bond being r e p l a c e d by one s i ­ l a n o l group. OH OH

The approximate average d i s t a n c e between protons i n such an arrangement i s of the order of 2.3 A whereas f o r the Xerogel i t i s of the order of 3.2 A. I t may thus be expected that upon h e a t i n g the f i b r o u s g e l above 500°C, the number of i s o l a t e d OH w i l l be r a t h e r small since water molecules n u c l e a t e r e a d i l y from coupled OH's. A c t u a l ­ l y no band above 3700 cm" appears i n the f i b r o u s g e l i n opposite to what i s observed f o r the Xerogel under the same c o n d i t i o n s . A l s o the second moment i s a p p r e c i a b l y temperature dependent i n the f i b r o u s g e l (Table I I I ) whereas i t i s p r a c t i c a l l y constant f o r the other gels (Table I I ) . The proton m o b i l i t y i s thus enhan­ ced by a more r e g u l a r and c l o s e packed d i s t r i b u t i o n of s i l a n o l s . However the NMR technique of measuring second moment or the obser­ v a t i o n of the OH i n f r a r e d bands as such do not allow to d i s t i n ­ guish between i n t e r n a l and e x t e r n a l OH. 1

Table I I I - V a r i a t i o n of M with the measurement f o r the f i b r o u s s i l i c a g e l (6) 2

Τ

(°K)

temperature

2

S (Gauss ) 2

293

10.7

198

16.5

118

17.5

80

18.6

Measurements of the s u r f a c e d e n s i t y i n s i l a n o l s groups are founded on two types of technique i ) r e a c t i n g the weakly a c i d hydroxy1 group with an adequate reagent l i k e c h l o r o s i l a n e , aminos i l a n e , e t c ; or i i ) i n t e r a c t i n g the s u r f a c e OH with p h y s i c a l l y adsorbed molecule. In both cases u s i n g I.R. the m o d i f i c a t i o n i n the hydroxyl s t r e t c h i n g r e g i o n can by f o l l o w e d . The f i r s t type of method has been b r o a d l y used (12). The* second type has been l e s s popular s p e c i a l l y f o r non-polar molecules condensed at low temperature. The a d s o r p t i o n of rare gases 0 , N , CH^ on the s t r e t c h i n g band of i s o l a t e d s i l a n o l s produces frequency s h i f t s 2

2

11.

FRIPIAT

Silanol

Groups

and

Properties

171

1

between 8 and 43 cm" depending upon the p o l a r i z a b i l i t y o f the adsorbate (13). More r e c e n t l y , the s p e c t r o s c o p i c p r o p e r t i e s of these i s o l a t e d OH upon adsorption of weak hydrogen bond acceptor molecules, l i k e benzene, a c e t o n i t r i l e , e t c . were observed (14). The s h i f t s were o f course l a r g e r than those observed f o r non-polar adsorbates, ran­ ging from 87 t o 216 cm"" . From hydrogen bonding s t u d i e s i n s o l u ­ t i o n , the frequency s h i f t s f o r two H bond donors R - HX and R X H i n t e r a c t i n g with v a r i o u s acceptors are o f t e n compared by p l o t t i n g the r e l a t i v e s h i f t frequency(Δν/v ) of one donor w i t h respect t o ( Δ ν / ν ) f o r the other. Such BHW p l o t s (Bellamy, Hallam and Williams) (15), are l i n e a r and q u i t e d i f f e r e n t Η-bond accep­ t o r s f i t onto the same s t r a i g h t l i n e when the proton b e a r i n g atoms i n both bonds are the same. Therefore the frequency s h i f t s observed f o r a r e f e r e n c e proton donor provide a u s e f u l s c a l e f o r p r e d i c t i n g the s h i f t s o f donors c o n t a i n i n g the same f u n c t i o n a l group. The slope i s an estimate of the r e l a t i v e Η bonding s t r e n g t h . With ρ-fluorophenol, f o r example, l i n e a r r e l a t i o n s h i p s have been observed (14) and by comparing the BHW slope and the p K o f v a ­ r i o u s proton donors,the pK o f i s o l a t e d s i l a n o l groups i s determi­ ned t o be about 7. T h i s i s w e l l i n the range o f the values r e v i e ­ wed by l i e r (4) (p.660). The studies performed on i s o l a t e d s i l a ­ n o l s o f f e r the advantage of being r a t h e r simple t o interprète s i n c e most of these groups are on the e x t e r n a l surface a v a i l a b l e to the reagent (see F i g u r e 2 f o r instance) and the problem i s l e s s complicated than f o r surface bridged OH's. 1

f

f

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

0

&

It i s a matter f a c t that the problem of d i s t r i b u t i n g the surface hydroxyls i n t o two populations (bridged and i s o l a t e d surface s i l a n o l s ) has not y e t been s a t i s f a c t o r i l y s o l v e d . The techniques o f r e a c t i n g the surface with reagents forming r e a l chemical bonus may be expected t o change the o r i g i n a l surface s t r u c t u r e . Hence, even f o r a g e l heated at 800°C, thus bearing i s o l a t e d s i l a n o l s , over 40% S i C l ^ molecules r e a c t with two OH groups (16). The use o f diborane, f i r s t proposed by Shapiro and Weiss (17) i n 1953, f a i l e d t o lead t o unambiguous r e s u l t s s i n c e none o f the workers (18,20) who had followed by i n f r a r e d t h i s r e a c t i o n agree w i t h each other. A good example o f surface r e c o n s t r u c t i o n by r e a c t i n g the surface o f s i l i c a with a m i l d reagent (CH^OH) has been s t u d i e d i n d e t a i l (21). The methoxylation o f an A e r o g e l s u r f a c e p r e t r e a ted at 110°C i n vacuum was s t u d i e d between 150 and 190°C. I t was found that the r e a c t i o n proceeds not o n l y by es t e r i f i c a t i o n of the s i l a n o l group but a l s o through the opening o f the s i l o x a n e b r i d g e s , as f o l l o w s k

= SiOH + CH-OH

l

> Ξ Si-0-CH + H 0 r

(3)

?

k

2 Ξ Si-O-Si=+CH~0H — - — > Ξ Si-OH + = Si-0-CH

Q

(4)

The competition o f the two r e a c t i o n s i s evidenced by a maximum

172

S O L U B L E SILICATES

i n the number o f s u r f a c e s i l a n o l s ( t i t r a t e d by LiCHg) d u r i n g the course o f the r e a c t i o n . The a n a l y s i s o f the experimental r e s u l t s showed t h a t k j / k - 3.0 a t 150°C and 1.5 a t 190°C. Thus, a t h i g h temperature the opening o f s i l o x a n e b r i d g e s c o n t r i b u t e s more e f ­ f i c i e n t l y t o the methoxylation process. I t was a l s o shown i n t h i s work that the probable intermediate i n the r e a c t i o n process i s CHgOH . T h i s aspect w i l l be examined l a t e r . 2

2

Dynamics o f a d s o r p t i o n processes on s i l i c a g e l

surfaces

There have been many s t u d i e s concerned with t h e a d s o r p t i o n o f water on s i l i c a g e l s but i n order to study the dynamic aspects o f these processes, H 0 i s not the best s u i t e d molecule. Indeed pro­ ton exchange between the adsorbate and t h e s u r f a c e s i l a n o l s and s u r f a c e d i f f u s i o n occur simultaneously and these mechanisms cannot be separated e a s i l y . I t i s f o r t h i s reason that methanol was chosen, f o r the methyl group doesn't exchange w i t h s u r f a c e OH whereas the a l c o h o l i c OH does. By u s i n g CD^OH o r CH^OD and hyd r o x y l a t e d o r deuterated s u r f a c e s , i t i s p o s s i b l e by measuring the ^H o r ^H n u c l e a r resonance r e l a x a t i o n r a t e s , t o d i s t i n g u i s h b e t ­ ween both kinds o f processes. The s p i n - l a t t i c e r e l a x a t i o n r a t e T J obtained by p u l s e n u c l e a r magnetic resonance i s the F o u r i e r transform o f the a u t o - c o r r e l a t i o n f u n c t i o n G ( T ) which d e s c r i b e s the e v o l u t i o n o f the system.

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

2

1

1

τ" -

G(T)COS ω τ d τ

I J

(4)

o

where G(T)

= < f(t)

f * ( t + τ) >

(5)

f contains the i n f o r m a t i o n about the motions. Random r e o r i e n t a t i o n or t r a n s l a t i o n a l jumps obey g e n e r a l l y the c o r r e l a t i o n f u n c t i o n : G

= < f(0)

(6) c where τ , the c o r r e l a t i o n time, d e f i n e s the time s c a l e o f the microscopic events which causes r e l a x a t i o n , ω i s the resonance frequency. The data obtained i n r e f e r e n c e s (8),(9) and (22) have been reviewed by F r i p i a t (23) and they w i l l be summarized here a f t e r . In order t o understand t h e experimental r e s u l t s , the s u r ­ face h e t e r o g e n e i t y must be accounted f o r . T h i s i s u s u a l l y done by c o n s i d e r i n g a l o g normal d i s t r i b u t i o n o f c o r r e l a t i o n time P(T ) C

d î

f*(0) > exp

= 3" 7T 1

c

1 / 2

exp(-Z/3)

2

d Ζ

(7)

where Ζ = In τ /τ , 3 being the spreading c o e f f i c i e n t o f the d i s ­ t r i b u t i o n f u n c t i o n and τ the average c o r r e l a t i o n time m τ - τ exp(H/RT) (8) ° where Η i s the average a c t i v a t i o n enthalpy o f some k i n d o f motion. m

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

11.

FRIPIAT

Silanol Groups and Properties

173

Since the adsorbent i s made of a c o l l e c t i o n of surfaces ran­ domly o r i e n t e d and confined w i t h i n an i n t r i c a t e network of pores, the approximation f o r i s o t r o p i c m o t i o n s ( r e l a t i o n s h i p 6) i s accep­ table. The a d s o r p t i o n of methanol has been studied f o r two g e l s . The f i r s t , c a l l e d Xerogel, i s c h a r a c t e r i z e d by pores w i t h an average diameter of 17.5 Â and the second c a l l e d Aerogel, contains pores smaller than 10 Â . In order to a s s i g n the c o r r e l a t i o n times to some d e f i n e d motion, information must be obtained about the magnitude of the l o c a l magnetic f i e l d a c t i n g on the proton and a r i s i n g e i t h e r from other protons i n the same, or from other molecules. In t h i s case the measurement of the proton second moment (the average quadratic l o c a l magnetic f i e l d ) allows one to a s s i g n the measured c o r r e l a t i o n time (s) to some defined motion(s), these motion(s) modulating the l o c a l f i e l d and provoking r e l a x a t i o n . In the Xerogel (X) , independently of the degree of coverage (θ) , the second moment at a temperature of the order of -140°C c o r r e s ­ ponds to a molecule i n which the CH^ group i s already r e o r i e n t i n g r a p i d l y around the C« symmetry a x i s . By c o n t r a s t , at that tempe­ r a t u r e , there i s no f r e e r o t a t i o n of the CH^ group i n the A e r o g e l . When the l i n e a r r e l a t i o n s h i p s shown i n F i g u r e 3 are compared i t appears c l e a r l y that the average a c t i v a t i o n enthalpy (Equation 8) i s of a comparable magnitude i n the s i t u a t i o n s described by the Arrhenius p l o t s 2, 3 and 5 whereas f o r p l o t 4,(Aerogel), i t i s much l e s s . In s o l i d methanol the a c t i v a t i o n enthalpy f o r the r o t a t i o n i s 1.6 k c a l mole"l (29) whereas i n the l i q u i d s t a t e the a c t i v a t i o n enthalpy f o r d i f f u s i o n i s 3.2 k c a l m o l e ~ l . T h i s r e ­ mark and a l s o what has been s a i d about the low-temperature values of the second moment suggest that c o r r e l a t i o n times 2, 3 and 5 i n F i g u r e 3 are those of t r a n s l a t i o n a l jumps, whereas c o r r e l a t i o n time 4 i s that of the methyl group r o t a t i o n . In the l a r g e r pores of Xerogel and i n the temperature range - 140° to + 50°C, the methanol would thus d i f f u s e w h i l e the methyl group i s r o t a t i n g freely. In the narrower pores of Aerogel (A) , and i n the same temperature range d i f f u s i o n would not occur. The thermal a c t i v a t i o n r e s u l t s i n a p r o g r e s s i v e l y f r e e r r o t a t i o n of the methyl group. In Aerogel at decreasing Θ, the methyl group r o t a t i o n becomes p r o g r e s s i v e l y hindered while i n Xerogel,as shown i n Figure 4,the t r a n s l a t i o n a l c o r r e l a t i o n time decreases w i t h Θ. The a c t i v a t i o n enthalpy f o r d i f f u s i o n obtained at d i f f e r e n t degrees of coverage i s shown i n the enclosure. I t increases from about 4 to about 6 k c a l mole" i n p a s s i n g from h a l f to the com­ p l e t e monolayer content and then i t decreases p r o g r e s s i v e l y toward the value obtained f o r the f r e e l i q u i d at θ > 2. T h i s i n d i c a t e s that the d i f f u s i o n a l motions are s t i l l i n f l u e n c e d by the surface f o r molecules i n the t h i r d l a y e r . 1

174

SOLUBLE

Î




< 2

6 4

2 6

?

»*

ό

-f-

? .11 10

2

/

/

4

3

5

1

6 ΟΟΟΟ/Τ)!*· ]

Figure 3. Correlation times observed at the coverage θ= 1.3 for various systems. Key: 1, H resonance in the CD OH-XOH system, β = 3 and Η = 5.4 kcal/mol; 2, H resonance in the CH OD-XOD system, g_ = 3.25 and H = 5.5 kcal/mol; 3, *H resonance in the same system, β = 4 and Η = 5.2 kcal/mol; 4, H resonance in the CH OH-AOH system, β = 0.8 and Η = 2.32 kcal/mol. X, Xerogel (aver­ age pore diameter: 17.5 A); A, Aerogel (average pore diameter < 10 A); ω, proton resonance frequency in the 14-kgauss field of the NMR instrument. 2

s

%

s

1

s

FRIPIÀT

Silanol

Groups

and

Properties

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

11.

Figure 4. Variation of the surface diffusion coefficient measured at three different^ degrees of coverage for the CH OD-XOD system. In enclosure: variation of H with respect to the degree of coverage. s

175

176

S O L U B L E SILICATES

I t i s a l s o i n t e r e s t i n g t o p o i n t out that i n agreement w i t h de Boer (24), the a c t i v a t i o n enthalpy i s approximately h a l f the i s o s t e r i c heat o f a d s o r p t i o n obtained from q

2

s t

- - R T [(3£n p)/3T]

e

(9)

Indeed ( 8 ) , between θ = 0.7 and 6 = 1 , q • i n c r e a s e s from 10 t o 14 k c a l mole" and then i t decreases f o r 14 t o 12 k c a l mole" i n going from θ » 1 t o θ = 1.3. The molecular area o f methanol on the Xerogel and Aerogel surfaces i s about 25.5 A a t θ = 1. I f t h i s value i s considered as the q u a d r a t i c d i f f u s i o n a l jump, d i s t a n c e < t > and i f the surface d i f f u s i o n c o e f f i c i e n t i s approximated by 1

2

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

2

D - < l

2

>/6τ

m

(10)

then the s u r f a c e d i f f u s i o n c o e f f i c i e n t s shown by the s o l i d l i n e i n F i g u r e 5 are obtained f o r the Xerogel a t 25°C. Between the half-monolayer and the monolayer content a r a p i d i n c r e a s e i s observed. For Aerogel, the d i f f u s i o n c o e f f i c i e n t i s probably smaller than 10"10 cm s e c " s i n c e the t r a n s l a t i o n a l motion i s o u t s i d e the range o f o b s e r v a t i o n e.g., τ > 10"^ sec. By comparing the equations o f s t a t e f o r mobile and immobile f i l m s w i t h the i n f o r m a t i o n about the motions obtained by NMR, i t was shown (8) u s i n g the procedure proposed by Ross and O l i v i e r (25) that the equation f o r an immobile f i l m was f i t t e d by the adsorption data f o r Aerogel whereas the data obtained f o r Xerogel obeyed the equation f o r a mobile f i l m . Consider now the c o r r e l a t i o n time corresponding t o l i n e 1 i n F i g u r e 3. I t represents the c o r r e l a t i o n time obtained from the deuteron s p i n - l a t t i c e c o r r e l a t i o n time f o r the CD^OH - X OH sys-* terns a t three degrees of coverage : θ =* 0.8, 1.3, and 1.7, r e s ­ p e c t i v e l y . I n that case there i s no i n f l u e n c e by the degree o f coverage. T h i s i s not s u r p r i s i n g because the quadrupole-inner e l e c t r i c a l f i e l d gradient i p t e r a c t i o n (the s o - c a l l e d quadrupole c o u p l i n g constant,(QCC),represents the main c o n t r i b u t i o n t o the deuterium n u c l e a r r e l a x a t i o n . In that case the c o r r e l a t i o n time has been assigned t o molecules tumbling w i t h i n a s u r f a c e p o t e n t i a l w e l l . Indeed, t h i s motion should imply an average a c t i v a t i o n enthalpy s i m i l a r t o that o f d i f f u s i o n e.g., that of breaking hydrogen bonds, but i t should be coverage independent s i n c e oppo­ s i t e t o d i f f u s i o n , i t does not i n c l u d e any cooperative e f f e c t . F i n a l l y i t i s i n t e r e s t i n g t o p o i n t out the good agreement between c o r r e l a t i o n times 2 and 3 i n F i g u r e 3. C o r r e l a t i o n time 3 has been computed from the d i f f u s i o n a l c o n t r i b u t i o n t o t h e proton s p i n - l a t t i c e r e l a x a t i o n time measured f o r the CD^OH - X OH system, a f t e r t h e proton exchange c o n t r i b u t i o n has been removed, whereas c o r r e l a t i o n time 2 has been obtained, i n a s t r a i g h t f o r ­ ward manner, f o r the CH 0D-X-0D system. 1

q

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

11. FRIPIAT

Silanol Groups and Properties

177

178

SOLUBLE SILICATES

Proton exchange between s i l a n o l s and adsorbate

molecules

Although the s i l a n o l groups are weak a c i d , proton exchange may be observed by adsorbing NH^ f o r i n s t a n c e . T h i s process was studied simultaneously by IR spectroscopy and proton s p i n - l a t t i c e nuclear magnetic r e l a x a t i o n time measurements performed on Aerogel outgassed between 20°C and 200°C (26). Three deformation bands a t t r i b u t a b l e to the adsorbed species were detected at 1450 cm" (NH^), 1600 cm" (NH^) and at 1500 cm"" . The l a t t e r which becomes observable at degrees of coverage of the order or l a r g e r than the monolayer content f o r Aerogel outgassed at 120° or 200°C was t e n t a t i v e l y assigned tô a NH£ NH^ dimer. T h i s suggests that p r o ­ ton may be t r a n s f e r r e d e a s i l y by t u n n e l i n g along the N - H — Ν bond. At the monolayer coverage, the r a t i o (NH^/NHo) was of the order of 30%. At t h i s degree of coverage the jump frequency was about 0.5 10 s e c " at 2 5 ° C T h i s v a l u e compares w e l l w i t h that dedu­ ced from the r a t e constant determined by C l u t t e r and Swift (27) for proton t r a n s f e r i n l i q u i d a c i d i f i e d ammonia and e x t r a p o l a t e d to 25°C : t h e i r r e s u l t s was 2 10^ s e c " f o r the same r a t i o NH^/NHg. On the Aerogel s u r f a c e the r a t e of t r a n s f e r i s of course somewhat reduced but s t i l l of the same order of magnitude. 1

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch011

1

9

1

1

1

As compared t o NH^, CH^OH i s a weaker base and i t was t h e r e ­ fore i n t e r e s t i n g to i n v e s t i g a t e proton t r a n s f e r t between methanol and s i l i c a s u r f a c e . T h i s was performed (9) by combining the values obtained f o r the s p i n - l a t t i c e (Tj) and s p i n - s p i n ( T ) pro­ ton r e l a x a t i o n times f o r CD-OH adsorbed on Xerogel. In t h i s sys­ tem, two T were observed. The short one and the short T. c o n t r i ­ b u t i o n t o the experimental Tj averaging the d i f f u s i o n and the proton exchange processes permitted the c o r r e l a t i o n time (τ ) of the proton exchange to be measured. I t was found that τ i s always higher than τ^, but the a c t i v a t i o n energies f o r the two mechanisms are approximately the same. T h i s again may be a n t i c i p a t e d s i n c e both d i f f u s i o n and proton exchange processes imply breaking hydrogen bonds. At 22° and f o r 0.8 < θ < 1.7, τ = (2.1 ± 1) 10"8 sec. T h i s value i s one or two orders of magnitude longer than the pseudo f i r s t - o r d e r constants τ = 4.5 χ Ι Ο sec and ^ 4.2 1 0 " sec determined (28) f o r proton exchange i n a c i d i f i e d methanol according t o the f o l l o w i n g processes 2

2

β

β

- 9

10

2

CH 0H + H 0 3

+

3

3


CH OH 3

2

+ H0

(11)

>

CH OH

2

+ CH 0H

2

Τ CH 0H + CH OH 3

3

1 2


) summarizes several proposed mechanisms by which alkaline waterflooding w i l l enhance o i l recovery. These mechanisms include: emulsification and entrapment, emulsification and entrainment, and wettability reversal (oil-wet to water-wet or water-wet to oil-wet). Depending on the i n i t i a l reservoir and experimental conditions with respect to o i l , rock and injection water propert i e s , one or more of these proposed mechanisms may be controlling. 1

Current address: Cities Service Company, Energy Resources Group, Exploration and Production Research, Tulsa, OK 74102. 0097-6156/82/0194-0215$06.00/0 © 1982 American Chemical Society

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch013

216

S O L U B L E SILICATES

Many s t u d i e s to date, have r e l a t e d e m u l s i f i c a t i o n to o i l recovery. M c A u l i f f e ' s r e s u l t s (Jl*1) showed that the i n j e c t i o n of d i l u t e o i l - i n - w a t e r emulsions, prepared e x t e r n a l to the porous medium, enhanced o i l recovery. D ' E l l a ^ C8) a l s o showed that the i n j e c t i o n of prepared w a t e r - i n - o i l emulsions can be used e f f e c ­ t i v e l y i n secondary and t e r t i a r y recovery of v i s c o u s crude o i l s . Rather than the e x t e r n a l p r e p a r a t i o n of emulsions f o r enhanced recovery, Cash (£) proposes that r e s i d u a l o i l can be m o b i l i z e d by spontaneous e m u l s i f i c a t i o n w i t h i n the core. Each of these i n v e s t i g a t o r s has shown the c a p a b i l i t i e s of e i t h e r e x t e r n a l l y prepared emulsions or i n - s i t u generated emulsions f o r improving o i l r e c o v e r y . These emulsions can enhance recovery by improving the a r e a l sweep e f f i c i e n c y Q ) . In the case of the o i l e x t e r n a l emulsion, m i s c i b i l i t y w i t h r e s i d u a l o i l can occur, l e a d i n g to a d d i t i o n a l o i l recovery through m i s c i b l e displacement. R e s u l t s of our experimentation Q J suggests that the occur­ rence of p e r m e a b i l i t y r e d u c t i o n s during enhanced o i l recovery may be avoided and the formation of a continuous o i l bank may be i n i t i a t e d and maintained by u s i n g a s l u g of an e x t r a c t e d r e s i n ­ ous f r a c t i o n . These r e s u l t s support the work of L i c h a a and H e r r e r a (10,11), where they found that severe p e r m e a b i l i t y r e ­ ductions due to asphaltene d e p o s i t i o n , could be avoided by the i n j e c t i o n of a mixture of h i g h l y r e s i n o u s Boscon Crude (29% wt. r e s i n ) w i t h a Boscon r e f i n e d o i l . Cooke (2) recommended a s i m i l a r process where a bank of h i g h l y a c i d i c crude o i l would be i n j e c t e d p r i o r to the i n j e c t i o n of the a l k a l i n e water f o r cases where the crude o i l a c i d c o n c e n t r a t i o n i s low. The present study u t i l i z e s a microwave a t t e n u a t i o n t e c h ­ nique to study o i l bank formation and propagation d u r i n g l i n e a r core t e s t s . T h i s technique, f i r s t developed by Parsons (12). was employed to monitor the dynamic i n - s i t u water c o n c e n t r a t i o n during the a l k a l i n e core f l o o d i n g experiments. Experimental Two crude o i l s were used f o r t h i s study. Huntington Beach Crude from W e l l S-47, which has an API of 23.0 , an a c i d number of 0.65 mg KOH/gram of crude, and a b u l k shear v i s c o s i t y of 10 cp at the r e s e r v o i r temperature of 165°F. The other C a l i f o r n i a n crude o i l used was Wilmington F i e l d Crude from W e l l C-331. T h i s crude has an API of 21.3 , an a c i d number of 0.86, and a b u l k ο shear v i s c o s i t y of 35 cps at the r e s e r v o i r temperature of 125 F. The t e r t i a r y o i l recovery experiments were performed i n one i n c h by f o u r i n c h by twelve i n c h Berea sandstone c o r e s . The average p o r o s i t y was 0.20 and average b r i n e p e r m e a b i l i t y was 600 md. Each experiment was conducted i n the f o l l o w i n g sequence: (1) Purge core w i t h n i t r o g e n (2) Evacuate and b r i n e f l o o d at 45mm Hg Abs. to achieve f u l l i n i t i a l saturation.

13.

B R A U E R A N D WASAN

Emulsification

Phenomena

217

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch013

(3)

Heat core to r e s e r v o i r temperature w h i l e f l o w i n g two a d d i t i o n a l pore volumes of b r i n e f o r c l a y c o n d i t i o n i n g . Determine b r i n e saturated pore volume and b r i n e per­ m e a b i l i t y at r e s e r v o i r temperature. (4) O i l s a t u r a t i o n u n t i l produced oil/aqueous r a t i o exceeds 100/1. (5) B r i n e f l o o d (secondary recovery) u n t i l produced aqueous/ o i l r a t i o exceeds 100/1. (6) 1.0% B r i n e p r e f l u s h (0.05 pv. f o r Wilmington t e s t only) (7) Continous i n j e c t i o n of a l k a l i n e s o l u t i o n u n t i l f i n a l produced w a t e r / o i l r a t i o exceeds 100/1. F r o n t a l advance r a t e s were 1 f t / d a y a f t e r i n i t i a l b r i n e s a t u r a t i o n and 3 f t / d a y during b r i n e s a t u r a t i o n . The b r i n e used f o r the Huntington Beach core t e s t contains 0.75% NaCl, whereas the b r i n e used f o r the Wilmington F i e l d core t e s t s contained 1.0% NaCl and 1100 ppm Calcium Ion. S u f f i c i e n t back pressure was main­ t a i n e d on the system throughout the experiment to prevent the o i l from de-gasing w h i l e w i t h i n the core. Microwave scans were performed every two hours during t e r t i ­ ary recovery and more f r e q u e n t l y where r e q u i r e d . The data f o r each core f l o o d i s presented i n the form of microwave p r o f i l e s showing the v a r i a t i o n i n average o i l s a t u r a t i o n w i t h d i s t a n c e along the core. During t e r t i a r y recovery, the produced f l u i d s were analyzed m i c r o s c o p i c a l l y f o r the presence of o i l - i n - w a t e r and w a t e r - i n o i l emulsions. K a r l F i s c h e r a n a l y s i s was performed on the pro­ duced f l u i d samples i n order to determine the amount of o i l p r e ­ sent i n the aqueous phase and the amount of water present i n the o i l phase. A l s o pH readings were recorded f o r the produced aqueous phase throughout t e r t i a r y recovery. R e s u l t s and D i s c u s s i o n Several a l k a l i n e chemicals have been employed f o r v a r i o u s aspects of enhanced o i l recovery. Two of the most f a v o r a b l e a l k a l i n e chemicals t e s t e d and used i n t e r t i a r y o i l recovery are sodium o r t h o s i l i c a t e and sodium hydroxide. Comparing t h e i r char­ a c t e r i s t i c s , both chemicals r e a c t w i t h a c i d s i n crude o i l to form s u r f a c t a n t s , p r e c i p i t a t e hardness ions and change rock s u r f a c e w e t t a b i l i t y . One d i f f e r e n c e between the two chemicals i s that the i n t e r f a c i a l p r o p e r t i e s f o r sodium o r t h o s i l i c a t e systems are l e s s a f f e c t e d by hardness ions (13), hence s l i g h t l y lower i n t e r f a c i a l t e n s i o n s would occur. Lower i n t e r f a c i a l tensions can a i d i n i n - s i t u emulsion formation. T h i s study i s the s t a r t of a systematic study of v a r i o u s concentrations of sodium o r t h o s i l i c a t e and sodium hydroxide against Wilmington F i e l d Crude. I n i t i a l a l k a l i n e core t e s t s were performed u s i n g 0.6% sodium o r t h o s i l i c a t e or sodium hydroxide w i t h 1.0% NaCl. P r i o r to the continuous i n j e c t i o n of the a l k a ­ l i n e phase, a 0.05 pv s l u g of 1.0% NaCl was i n j e c t e d as a p r e -

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch013

218

SOLUBLE

SILICATES

f l u s h s o l u t i o n to separate the a l k a l i n e phase from the hardness ions i n the connate b r i n e . Core t e s t s r e s u l t s are presented i n Tables I and I I . R e s u l t s show that s l i g h t l y b e t t e r o i l r e ­ covery e f f i c i e n c y (27-28% v s . 21-22%) can occur when u s i n g the sodium o r t h o s i l i c a t e system. A t y p i c a l microwave p r o f i l e f o r secondary recovery of W i l ­ mington F i e l d crude i s presented i n F i g u r e 1. Examination of the microwave o i l s a t u r a t i o n p r o f i l e during t e r t i a r y o i l recovery f o r each of the f l o o d s , shows s i m i l a r o i l banking c h a r a c t e r i s t i c s f o r each a l k a l i n e chemical. In core t e s t s 1 and 2, using sodium o r t h o s i l i c a t e , e a r l y formation of an o i l bank was observed ( F i g ­ ure 2 ) . T h i s o i l bank flows down the l e n g t h of the core and o i l i s produced at hour 18 i n t o t e r t i a r y o i l recovery. Comparing the microwave s a t u r a t i o n p r o f i l e s f o r core t e s t s 3 and 4 u s i n g sodium hydroxide, e a r l y formation of an o i l bank was again ob­ served (Figure 3 ) . T h i s o i l bank a l s o i s continuous and i s pro­ duced at hour 18 i n t o t e r t i a r y recovery. Comparison of the o i l banking during t e r t i a r y o i l recovery f o r s i m i l a r c o n c e n t r a t i o n s of sodium o r t h o s i l i c a t e and sodium hydroxide w i t h i n a hardness i o n environment, d i d not i n d i c a t e why one chemical may be p r e ­ ferred . Comparison of the produced f l u i d a n a l y s i s f o r these f l o o d s w i l l g i v e us an i n d i c a t i o n of why one process may be p r e f e r r e d . Produced f l u i d a n a l y s i s f o r these f l o o d s show pH breakthrough o c c u r r i n g at s i m i l a r times f o r each process (Figure 4,5). So, the two processes cannot be separated by comparing c a u s t i c break­ through times. Each of these f l o o d s produced o i l - i n - w a t e r and w a t e r - i n - o i l emulsions c o i n c i d e n t w i t h pH breakthrough. These i n - s i t u gen­ erated emulsions d i d not cause s i g n i f i c a n t i n c r e a s e s i n the t o t a l pressure drop across the l e n g t h of the core. K a r l F i s c h e r a n a l y ­ s i s of produced o i l and aqueous phase showed that more emulsi­ f i c a t i o n occurred i n the sodium o r t h o s i l i c a t e f l o o d s . R e s u l t s i n d i c a t e over 2.3% i n c o r p o r a t i o n of water i n t o the o i l phase and over 4.0% i n c o r p o r a t i o n of o i l i n t o the water phase f o r the so­ dium o r t h o s i l i c a t e f l o o d s . For the sodium hydroxide f l o o d s , o n l y 1.4% water-in-oij. emulsion and 0.6% o i l - i n - w a t e r emulsion was produced. These p r e l i m i n a r y r e s u l t s suggest that t h i s sodium o r t h o s i l i c a t e system e m u l s i f i e s o i l b e t t e r than the sodium hydroxide system. These i n - s i t u generated emulsions may have i n c r e a s e d the displacement c a p a b i l i t i e s of the a l k a l i n e phase by improving the m o b i l i t y r a t i o and/or the a r e a l sweep e f f i c i e n c y w i t h i n the core, thus causing the s l i g h t i n c r e a s e i n t e r t i a r y o i l recovery f o r the sodium o r t h o s i l i c a t e f l o o d s . Previous work (1) i n core f l o o d s w i t h the system, Huntington Beach Crude v s . 0.5% Na^SiO^ p l u s 0.75% NaCl, showed channeling of the crude o i l during the i n j e c t i o n of the c a u s t i c s l u g ( F i g u r e 6). The channeling phenomena along w i t h the f a c t that emulsions were not observed u n t i l a f t e r 95% of the recovered o i l was p r o ­ duced, c o u l d have l e a d to lower o i l recovery e f f i c i e n c i e s . To

13.

TABLE I .

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch013

219

Emulsification Phenomena

BRAUER A N D WASAN

CORE TEST DATA

CORE TEST

POROSITY

CRUDE OIL

1

0.205

Wilmington F i e l d

0.6% Na,Si0, + 1.0% NaCl 4 4

2

0.225

Wilmington F i e l d

0.6% Na,Si0, + 1.0% NaCl 4 4

3

0.229

Wilmington F i e l d

0.6% NaOH + l.C)% NaCl

4

0.228

Wilmington F i e l d

0.6% NaOH + l.C)% NaCl

5

0.215

Huntington Beach

0.5% Na.SiO, + 0.75% NaCl 4 4

6

0.210

Huntington Beach

0.5% Na.SiO, + 0.75% NaCl 4 4

TABLE I I .

CORE TEST

s

o

i

S0

R

ALKALINE SLUG

CORE TEST DATA

% SECONDARY RECOVERY

S 0

F

% TERTIARY RECOVERY

1

0.72 pv

0.45 pv

38

0.33 pv

27

2

0.71 pv

0.41 pv

41.6

0.29 pv

28

3

0.73 pv

0.44 pv

39

0.35 pv

22

4

0.715 pv

0.42 pv

41.4

0.33 pv

21

5

0.64 pv

0.41 pv

37

0.31 pv

25

6

0.61 pv

0.37 pv

39

0.24 pv

31

SOLUBLE

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch013

220

1.5

2.5

3.5

4.5

INCHES Figure 1.

5.5

6.5

ALONG

7.5

8.5

9.5 10.5

CORE

Secondary recovery profiles for core test 1.

SILICATES

Emulsification

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch013

B R A U E R A N D WASAN

221

Phenomena

20 -15H ~L5

25

35

4.5 5.5 INCHES

Figure

3.

Microwave

Ί

20 pH

4.

δ\5 9.5 10.5

CORE

profiles for tertiary oil recovery, core test 3; 0.6% NaOH 1.0% NaCl vs. C-331 crude.

10 Figure

β'.5 75

ALONG

30

'—I

1

40

+

Γ

50

H O U R S INTO T.O.R.

The pH analysis of produced fluids, core tests 1 and 2; 0.6% Na SiO 1.0% NaCl vs. C-331 crude. k

k

+

222

S O L U B L E SILICATES

13-

Π

I

ι

0.5

1X

12H

L

1

^ P

V

i n j e c t e d . pH_

==5

11 PH

10-

3-W

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch013

9-

8 7

π

ι—ι—ι

0

Figure 5.

10

1

20

1

1

1

1—ι

1—ι r~

1

30 40 50 H O U R S INTO T.O.R.

60

70

The pH analysis of produced fluids, core tests 3 and 4; 0.6% NaOH 1 % NaCl vs. C-331 crude.

111

454035-

soy

'I / 1

β

/

/

20-^^^^v

/

6

/

/

\ > »

J*

32 —

· ^

< 30oc

+

/

8

D I-

/

^

·8 >·—#12 3 2

__e^^

y

^#54

< 252015-

54/

1

1

1

1.5 2.5 3.5 Figure

6.

4.5

5.5

6.5 7.5

INCHES A L O N G

CORE

I

8.5

1

1

9.5 10.5

Microwave profiles during tertiary recovery for core test 5; Beach crude vs. 5000 ppm orthosilicate + 7500 ppm NaCl.

Huntington

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch013

13.

Emulsification

B R A U E R A N D WASAN

223

Phenomena

examine the idea of u s i n g an e x t r a c t e d r e s i n o u s component to improve recovery e f f i c i e n c y , a deasphaltened s l u g of Huntington Beach Crude was prepared f o l l o w i n g standard ASTM procedures (13). Following completion o f secondary recovery and p r i o r to the con­ tinuous i n j e c t i o n of the a l k a l i n e phase, a 0.05 pv s l u g of t h i s deasphaltened Huntington Beach Crude was i n j e c t e d . R e s u l t s f o r t h i s core t e s t a r e a l s o summarized i n Tables I and I I . T e r t i a r y o i l recovery increased to 31% from the 25% recorded i n the core t e s t where a deasphaltened s l u g was not employed. Comparing the t e r t i a r y o i l s a t u r a t i o n p r o f i l e s f o r the two core t e s t s , the e a r l y formation of an o i l bank a t hour 2 f o r core t e s t 6 i s ob­ served (Figure 7). T h i s o i l bank i s formed because of the i n j e c ­ t i o n of the 0.05 pv s l u g of deasphaltened crude. The volume of o i l above r e s i d u a l s a t u r a t i o n (S0^) a t hour 2 represents the volume of o i l i n j e c t e d i n the deasphaltened crude s l u g . T h i s o i l bank flows down the l e n g t h o f the core and i s produced a t hour 9 (Figure 8 ) . Produced f l u i d a n a l y s i s showed pH breakthrough o c ­ c u r r i n g at hour 21 (Figure 8 ) . The i n i t i a l o i l that i s produced w i t h i n the bank does not c o n t a i n any emulsions, but the remainder of the produced o i l d i d c o n t a i n w a t e r - i n - o i l emulsions. Oil-inwater emulsions were produced c o i n c i d e n t with the o i l bank. These i n - s i t u generated emulsions may have aided i n improving the r e ­ covery e f f i c i e n c y f o r the deasphaltened crude core t e s t according to the reasons s t a t e d p r e v i o u s l y .

1.5

2.5

3.5

4.5

5.5

6.5

7.5

8.5

9.5

10.5

INCHES A L O N G C O R E Figure

7.

Microwave

profiles during tertiary recovery for core test 6.

S O L U B L E SILICATES

224

12 1110 PH

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch013

9 8 7 0

Figure 8.

8

16 24 32 40 48 HOURS INTO T.O.R.

56

The pH and fractional flow of produced fluids, core test 6.

Summary and Conclusion 1. I n - s i t u generated emulsions were produced c o i n c i d e n t with breakthrough. 2. More i n - s i t u e m u l s i f i c a t i o n was observed w i t h the sodium o r t h o s i l i c a t e system r a t h e r than the sodium hydroxide system. 3. I n - s i t u generated emulsions could enhance recovery t e c h ­ niques by improving the a r e a l sweep e f f i c i e n c y of the a l k a l i n e s l u g and by improving the dynamic m o b i l i t y r a t i o w i t h i n the c o r e . 4. Improvements i n enhanced recovery occurred when a de­ asphaltened crude o i l s l u g was i n j e c t e d p r i o r to the continuous a l k a l i n e phase. 5. The deasphaltened crude o i l s l u g , e x t r a c t e d r e s i n o u s com­ ponent, may have improved t e r t i a r y recovery by p r e v e n t i n g a s p h a l tene d e p o s i t i o n , thereby i n c r e a s i n g p e r m e a b i l i t y of o i l to rock, by forming an o i l bank, or again, i n - s i t u e m u l s i f i c a t i o n may have enhanced o i l recovery. pH

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch013

13. BRAUER AND WASAN

Emulsification Phenomena

225

Literature Cited 1. Pasquarelli, C. H.; Brauer, P. R.; Wasan, D. T.; Ciempil, M.; Perl, J. P., "The Role of Acidic, High Molecular Weight Crude Components in Enhanced Oil Recovery", SPE 8895. Paper pre­ sented at the 50th Annual California Regional Meeting of the Society of Petroleum Engineers of AIME. Los Angeles, California, April 9-11, 1980. 2. Cooke, C. E., Jr.; Williams, R. E.; Kolodize, P. Α., "Oil Recovery by Alkaline Waterflooding", JPT. December 1974, pp. 1365-1374. 3. Jennings, Η. Y.; Johnson, C. B.; McAuliffe, C. D., "A Caustic Waterflooding Process for Heavy Oils", JPT. December 1974, pp. 1344-1352. 4. Johnson, C. B., "Status of Caustic and Emulsion Method", JPT. January 1976, pp. 85-92. 5. Mayer, Ε. H.; Berg, R. L.; Carmichael, J. D.; Weinbrandt, R. Μ., "Alkaline Injection for Enhanced Oil Recovery--A Status Report", SPE 8848. Paper presented at the 50th An­ nual California Regional Meeting of the Society of Petroleum Engineers of AIME. Pasadena, California, April 9-11, 1980. 6. McAuliffe, C. D., "Crude Oil-in-Water Emulsions to Improve Fluid Flow in an Oil Reservoir", JPT. June 1973, pp. 721726. 7. McAuliffe, C. D., "Oil-in-Water Emulsions and Their Flow Properties in Porous Media", JPT. June 1973, pp. 727-733. 8. D"Elia-So, R.; Ferrer-G, J . , "Emulsion Flooding of Viscous Oil Reservoirs", SPE 4674. 48th Annual Fall Meeting. Las Vegas, Nevada, September 30 - October 3, 1973. 9. Cash, R. L., Jr.; Cayisas, J. L.; Haynes, M.; MacAllister, D. J.; Schares, T.; Schechter, R. S.; and Wade, W. Η., "Spontaneous Emulsification--A Possible Mechanism for En­ hanced Oil Recovery", SPE 5562. Paper presented at 50th Annual Fall Meeting of the Society of Petroleum Engineers of AIME. Dallas, Texas, September 28 - October 1, 1975. 10. Lichaa, P. Μ., "Asphaltene Deposition Problem in Venezuelan Crudes--Usage of Asphaltenes in Emulsion Stability". Paper presented at the Canada--Venezuela Oil Sands Symposium 77. Edmonton, Alberta, Canada, May 27 - June 4, 1977. 11. Lichaa, P. M.; Herrera, L., "Electrical and Other Effects Related to the Formation and Prevention of Asphaltene Deposi­ tion Problem in Venezuelan Crudes", SPE/AIME No. 5304. 1975. 12. Parsons, R. W., "Microwave Attenuation—A New Tool for Monitoring Saturations in Laboratory Flooding Experiments", SPE J. August 1975, pp. 302-310.

226

SOLUBLE SILICATES

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch013

13. Campbell, T. C., "The Role of Alkaline Chemicals in the Recovery of Low Gravity Crude Oils". SPE 8894. Paper presented at the 50th Annual California Regional Meeting of the Society of Petroleum Engineers of AIME. Pasadena, California, April 9-11, 1980. 14. Pasquarelli, C. Η., M.S. Thesis, Illinois Institute of Tech­ nology, Chicago, 1980. RECEIVED March 2, 1982.

14 Long-Term

Consumption

Solutions by

Petroleum

of

Caustic

and

Silicate

Reservoir Sands

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

VAN T. LIEU—California State University, Chemistry Department, Long Beach, CA 90840 SAMUEL G. MILLER—Department of Oil Properties, City ofLongBeach, LongBeach,CA 90802 STEPHEN J. STAPHANOS—California State University, Chemistry Department, Long Beach, CA 90840 A number of laboratory investigations were made into different aspects of consumption of sodium hydroxide and sodium orthosilicate in alkaline flooding of petroleum reservoirs for enhanced oil recovery. One investigation studied the role of reversible adsorption and of chemical reaction when petroleum reservoir sands are contacted with alkaline solutions. Another investigation studied the effect of flow rate on caustic consumption by means of a series of flow experiments through reservoir sand packs. A third series of high rate flow experiments studied changing alkaline consumption with time. The long term pulse study was devised to determine the time required for the alkalinity of a solution in the pores of a sand pack to reduce to zero. Ihis method provides a means for estimating the longevity of a given volume and concentration of alkaline chemical solution injected into an actual petroleum reservoir. In the past several years, renewed interest in enhanced o i l recovery by alkaline flooding has been evidenced. A l though the addition of alkaline chemicals to injection water has been proposed by many workers ever the past 50 years, in recent years, the subject has recently been seriously studied by several workers as prelude to actual field injection trials (1^4). At the present time, several field trials of alkaline flooding have been completed, are in progress or are being planned (5-10). One of the critical alkaline flood design parameters is the proper concentration of alkaline chemical to use. This concentration is dependent on the alkaline consumption by the reservoir sand during the time that i t takes for the solution to traverse the reservoir. 0097-6156/82/0194-0227$07.00/0 © 1982 American Chemical Society

228

SOLUBLE

SILICATES

The consumption of alkaline chemical i n the reservoir i s a function of the amount and type of rock minerals, surface area and of the sands compactness, alkaline chemical con­ centration used, reservoir temperature and the time the alkaline chemical i s exposed to the reservoir sand (1, 4, 11). These factors are interdependent and together determine the overall consumption.

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

Over the past several years ideas have changed about what constitutes the proper a l k a l i concentration f o r alkaline flood­ ing. Much higher concentrations are now being considered be­ cause i t i s new known that with sufficient time, the alkaline consumption can become very large. I n i t i a l l y , i t was thought that the " i n t e r f a c i a l tension window" should determine the proper concentration. This win­ dow i s a range of concentrations of a l k a l i i n formation brine which gives extremely low i n t e r f a c i a l tension values with o i l , thus producing the desired enhanced recovery effect. Concen­ trations below and above the window do not have the extremely low interfacial tension. Typically, t h i s concentration range i s i n the region of 0.2% sodium hydroxide. In the sands we have studied, concentrations of this level w i l l not survive where there i s a considerable duration of time i n the reservoir (measured i n several years, rather than i n several months). Basically, a higher i n i t i a l alkaline chemical concentration i s required to provide f o r the continued depletion of the alkaline chemical, which must survive the lapse of time between injection and producing well. Ihis paper describes our studies of various aspects of alkaline consumption i n reservoir sands and our efforts to de­ velop a test f o r determining the optimum concentration to use in an alkaline flood. Apparatus and Chemicals A l l sand packs were prepared i n l u c i t e columns approxi­ mately 6" or 12" i n length and 1-1/2" i n diameter. The two ends of a column were equipped with s o l i d l u c i t e plugs. Each column was also equipped with a stainless steel cage to hold the assem­ bly i n place. In sand pack preparation, wire gauze and a layer of reagent grade sand were packed at each end of the column to hold the reservoir sand sample i n place. The sand pack pore volumes f o r the 6" column were approximately 50 mis, and f o r the 12" column were approximately 110 mis. The pore volume was de­ termined gravimetrically by evacuation of the sand pack under vacuum and saturation with 1% NaCl.

14.

LIEU E T A L .

Long-Term

Consumption

229

A stock 10% sodium hydroxide and 1% sodium chloride solu­ tion was prepared from reagent grade solid sodium hydroxide and sodium chloride. A stock 10% sodium orthosilicate (i.e. a molar r a t i o of N a 0 / S i 0 o f 2/1) and 1% sodium hydroxide solution was prepared by mixing 112.5 parts by weight of "N sodium s i l i ­ cate" (PQ Corporation), 147.9 parts by weight of 50% sodium hy­ droxide and 739.6 parts by weight of 1% sodium chloride. A l l sodium hydroxide and sodium orthosilicate solutions used were prepared by d i l u t i o n of the stock solutions with 1% sodium chloride.

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

z

2

Sands from two different Pliocene-Miocene reservoirs i n Southern California were used i n our studies, from the THUMS Ranger Zone of East Wilmington and from the Lower Main Zone (IMZ) of Aminoil at Huntington Beach. A l l experimental work with THUMS Ranger sand was conducted at 125F and with Aminoil LMZ sand at 165F.

Static Equilibrium Study In order to gain some i n i t i a l understanding of the extent and rate of alkaline consumption of reservoir sands, s t a t i c equilibrium tests commonly known as "Jar" tests were performed individually by mixing Aminoil, THUMS and crushed Berea sand­ stone sands with a large excess of 0.2% or 0.4% sodium hydr­ oxide i n tightly capped p l a s t i c bottles. The sand samples were disaggregated and, i n the case of THUMS Ranger sand, the sample was extracted with toluene. Aliquots of the caustic solutions were collected at different times and analyzed f o r their alka1 i n i t i e s . The samples were agitated occasionally during soak­ ing. As can be seen from Figure 1, where sodium hydroxide con­ sumption i s plotted as a function of time, the consumption of caustic by a l l three sands was rapid; as much as 35 to 60 meq /100g sand were consumed after 62 days. The consumption reactions were s t i l l i n progress when the experiments were terminated. Fran this study, i t became obvious that caustic consumption by reservoir sand can be a long term phenomenon. One notes that the alkaline consumption values obtained after 62 days are much larger than the consumptions which cor­ responded to the range near the i n t e r f a c i a l tension window con­ centration of 0.2% NaOH o r 0.625 meq/100g sand. They are also f a r larger than those which were determined by the e a r l i e r short tests of some few hours or days duration and much larger than those which we determined f o r longer term flow study using sand packs. The reason f o r such high consumption i s the large

230

SOLUBLE

SILICATES

* Ο­ ίο

a UJ 30 Κ­ 2E => CO Ζ ο ο ω ο

g

20

oc

Ο >-

Ι

10

χ Lu

J. 0.2

0.4

0.6

0.8

1.0

FLOW RATE ( Ρ V / D A Y ) Figure 5. Effect of flow rate on caustic consumption. Plot of % NaOH as a function of flow rate at 5 pore vol. Conditions: 0.18% NaOH + solution through Aminoil LMZ sand packs at 165°F.

consumed 1 % NaCl

238

SOLUBLE SILICATES

The space velocity i s the volune (PV) of caustic solution pass­ ing through i n unit time (day) per unit pore volume. Spacetime-consumption i s the caustic consumption i n unit time (day) per unit pore volume and i s equal to the product of fractional caustic consumed and space velocity.

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

It i s seen franFigure 6 that space-time-consumption (or amount of caustic consumed per day) changes slowly with lower space velocities. Accordingly, a flow rate (or space velocity) of 1/3 PV/day was selected f o r a l l the subsequent flow tests. This rate i s an average o i l reservoir velocity and has the advantage determined here that the amount of caustic consumption per day would not be greatly affected by slight variation i n flew rates. Again, fran the same data from Figure 4, Figure 7 plots % NaOH i n the effluent at 5 pore volume versus time (days). I t i s significant to note that with higher flew rates the time re­ quired f o r a l k a l i n i t y "breakthrough" to occur i s reduced. Long Term Flew Study Seven flow study experiments were conducted to determine the long term effects of the consumption of alkaline chemicals on reservoir sands using 12" long sand packs. The treatment of Aminoil LMZ sand packs before alkaline injection was the same as that described i n the study of Flew Rate Effect On Caustic Con­ sumption. The treatment of THUMS Ranger sand was also the same except that after saturation with THUMS crude o i l , the sand packs were waterflooded with 1% NaCl to water "breakthrough". Water "breakthrough" i s defined as the point where water begins to appear i n the effluent i n significant quantity. Sodium hy­ droxide o r sodium orthosilicate solutions i n 1.0% sodium chlo­ ride were then injected a t the rate of 1/3 pore volume per day. The effluents collected were analyzed by t i t r a t i o n with standard hydrochloric acid to t h e i r phenolphthalein end points. Weight % alkaline chemical a l k a l i n i t y effluent vs. pore volume are plotted i n Figure 8(a) and 8(b). The following obser­ vations and interpretation can be made on the results obtained: The consumption of sodium hydroxide and sodium o r t h o s i l i cate i n reservoir sand i s a long term phenomenon. The number of pore volumes required f o r the concentration of effluent alkaline solution to reach the concentration of the injected solution ranges from 10 to 33 pore volume (or 30 to 99 days). On re­ ducing the flow rate from 1/3 pore volumes per day to 1/10 pore volume per day a f t e r the effluent appeared to have reached the concentration level of the injected solution, the concentration level of the effluent dropped t o a lower value, indicating the

14.

LIEU

Long-Term Consumption

ET AL.

239

a. 0.4 ι Ο û. LU

3

0.3|

_j ο > lu

GC

ο

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

? 0.21 Û.

o.l

co z ο ο ι LU

I LU

0.2

ο
-

2

g

0.10

co

X CD

15 T I M E (DAYS) Figure 7. Effect of flow rate on caustic consumption. Plot of % NaOH of effluent vs. time. Conditions: 0.18% NaCl solution through Aminoil LMZ sand packs at 165°F. Key: χ , 0.25; •, 0.33; Δ , 0.50; and 0 , 1 . 0 pore vol/d.

Figure 8(a). Long-term flow test with use of: X , 1.0% NaOH and 1.0% NaCl through THUMS Ranger sand pack; O, 0.182% NaOH and 1.0% NaCl through THUMS Ranger sand pack; and Δ , 0.182% NaOH and 1 % NaCl through Aminoil LMZ sand pack.

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

SODIUM ORTHOSILICATE + 1.0 % NaCl

Figure 8(b). Long-term through THUMS Ranger oil LMZ sand pack; Δ , pack; and •, 0.2%

flow test with the use of: X , 1.0% sodium orthosilicate and 1% NaCl sand pack; O , 1.0% sodium orthosilicate and 1% NaCl through Amin0.2% sodium orthosilicate and 1% NaCl through THUMS Ranger sand sodium orthosilicate and 1% NaCl through Aminoil LMZ sand pack.

PORE VOLUME (PV) SODIUM ORTHOSILICATE INJECTED

INJECTED SOLUTION CONCENTRATION» 1.0%

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

^ ^

242

S O L U B L E SILICATES

consumption of the alkaline chemical was s t i l l i n progress but at a lower rate.

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

The alkaline consumption f o r each of the flew experiments can be determined by measurement of the area between the "In­ jected solution concentrât ion" l i n e and the "% alkaline chemi­ cal a l k a l i n i t y i n effluent" curve less the area of the f i r s t pore volume. The f i r s t pore volume i s not included i n the c a l ­ culation to take into account that the sand pack was f i l l e d with 1% sodium chloride before alkaline injection. As shown i n Table III, which gives the alkaline consump­ tions f o r the seven flow experiments, the alkaline consumption, as expected, increased with increase i n concentration of the a l ­ kaline chemical solution used. For example, the alkaline con­ sumption f o r THUMS Ranger sand increased from 2.8 meq/100g sand using 0.2% sodiun orthosilicate to 9.2 mecyiOOg sand using 1.0% sodium orthosilicate. In comparing sodium hydroxide and sodium orthosilicate so­ lutions of the same concentration, the alkaline consumption f o r sodium orthosilicate was significantly lower than that f o r sod­ ium hydroxide. For example, the alkaline consumption of THUMS Ranger sand was 9.2 meq/lOOg sand f o r 1.0% sodium orthosilicate while the consumption was 25.1 meq/100g f o r 1.0% sodium hydr­ oxide. Thus sodium orthosilicate seems to be superior to sodium hydroxide f o r alkaline flooding. The same conclusion can be made by comparing the numbers of pore volumes of the two chemicals (of the same o r approxi­ mately the same concentration) required f o r the effluent alkarl i n i t y concentration to reach the concentration of the injected solution. For example, i n THUMS Ranger sand packs, about 30 pore volumes of 0.182% sodium hydroxide were required f o r the e f f ­ luent a l k a l i n i t y to reach the injected concentration, (Figure 8(a) 2), while only 15 pore volumes were required i n the case of 0.2% sodium orthosilicate (Figure 8(b) 6). Campbell (13) measured rock consumption by s t i r r i n g un­ consolidated reservoir sand with 0.5% sodium hydroxide o r 0.5% sodium orthosilicate and the alkaline consumptions were found to be about the same f o r the two solutions. The difference in the conclusions between our study and that of Campbell i s not understood and i s presently being studied. I t seems to be be related to the difference i n methods used ("Jar" test vs. Flew t e s t ) , the chemical compositions o f the sands, and the chemical ocnpositions of the alkaline solutions i n e q u i l i bruim with the sands.

14.

LIEU E T A L .

Long-Term

243

Consumption

TABLE III ALKALINE CONSUMPTIONS IN LONG TERM FLCW STUDY Alkaline Chemical

Alkaline Consumption (meq/100 g)

NaOH + 1% NaCl

THUMS Ranger

0.182% NaOH + 1% NaCl

THUMS Ranger

6.8

0.182% NaOH + 1% NaCl

Aminoil LMZ

6.0

1.0%

N a S i 0 + 1% NaCl

THUMS Ranger

9.2

1.0%

Na Si0 + 1% NaCl

Aninoil IMZ

6.9

0.2%

Na Si04 + 1% NaCl

THUMS Ranger

2.8

0.2%

N a S i 0 + 1% NaCl

M i n o i l IMZ

3.8

1.0%

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

Sand

4

4

4

4

4

4

4

25.1

As can be seen from table III the loss of a l k a l i n i t y (due to reversible adsorption and chemical consumption) i n a sand pack, by comparison, i s lower than that shown i n Figures 2 and 3 which involves reaction o f sand i n p l a s t i c bottles. This i s because the sand i n a sand pack i s more t i g h t l y packed, and thus lcwer surface area i s available f o r chemical consumption, reversible adsorption o r ion exchange. However, this loss of a l k a l i n i t y can be expected t o retard the advance rate of alka­ l i n e chemical. As shown i n the elution plots i n Figures 8(a) and 8(b), i n almost a l l cases, more than one pore volume of alkaline chemical solution was required f o r alkaline "break­ through". Similar retardation results were also observed by other workers (4,11,14). Furthermore, as the injection solu­ tion concentration i s lcwer, the alkaline chemical takes pro­ gressively longer to elute from the sand pack. For both so­ dium hydroxide and sodium orthosilicate, the alkaline "break­ through" o r 0.2% solution occured after about 2 to 3 pore volumes of injection. However, the alkaline "breakthrough" or 1.0% solution occurred after only about 1 t o 2 pore volumes of injection.

The delay i n alkaline "breakthrough" can be explained by the theory o f chromatography. According to the theory, the reversible adsorption isotherm slope controls the advance rate

244

S O L U B L E SILICATES

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

of alkaline chemical through the sand pack. The slope, under ideal conditions, i s a constant. Deviation from a straight l i n e to a lower slope indicates the saturation of the active adsoption or ion exchange s i t e s of the reservoir sand and thus there i s a reduction of the retardation effect on the advance of alkaline chemical. As can be seen from the reversible ad­ sorption curves f o r both sodium hydroxide and sodium orthos i l i c a t e , the slopes decrease with increase i n concentration of the alkaline chemicals i n the solutions. Higher concen­ trations have smaller slopes and hence y i e l d shorter delays in alkaline "breakthrough". Similar interpretation has been made by Bunge and Radke (14). As shown i n Figures 2 and 3, the loss of a l k a l i n i t y due to reversible adsorption o r ion exhange i s of the order of 1 meq/100g sand f o r both sodium hydroxide and sodium o r t h o s i l i cate. I t may be noted i n Figures 2 and 3 that i n addition to loss of a l k a l i n i t y due to reversible adsorption, loss of a l ­ k a l i n i t y due to non-reversible chemical consumption also occurs. In flow studies, the a l k a l i n i t y of effluents i n the i n i t i a l two o r three pore volumes i s very low (as shown i n Figures 8(a) and 8(b). For the i n i t i a l two o r three pore volumes, the portion of the sand near the i n l e t where the pH of the chemical solution i s s t i l l s u f f i c i e n t l y high, chemical consumption i s expected to occur and contribute to the delay in alkaline "breakthrough". As the solution advances through the sand pack, the pH of the solution becomes lower. In the portion of the sand pack near the outlet where the pH i s lew, l i t t l e o r no chemical consumption i s expected to occur. As the pH of the effluent from a sand pack increases, chemical consumption i s expected to become more important and becomes the main source of loss of a l k a l i n i t y . The long term flow study seems to reveal that at the i n ­ i t i a l one to three pore volumes there i s a chemical consump­ tion which i s limited to the front portion of the sand pack where the pH i s s u f f i c i e n t l y high and a rapid reversible ad­ sorption or ion exchange reaction which retard the advance rate of alkaline chemicals. After the i n i t i a l one to three pore volumes, this i s coupled with a slow non-reversible chemical consumption reaction which w i l l continue f o r a very long time. Long Term Pulse Study It was f e l t that none of the experiments that had been de­ vised thus f a r truly approached representing what i s happening in the reservoir. The s t a t i c equilibrium study experiments were

14.

LIEU E T A L .

Long-Term

Consumption

245

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

simply not long enough and the sands not appropriately com­ pacted. The long term flow study experiments likewise were of too short a durât ion, measured i n weeks, o r months rather than in years; they involved many pore volumes of solution and thus vastly overpowered the sand pack with fresh alkaline chemical. In an actual petroleum reservoir, the time may be a total of several years, the volume used i s usually even less than one pore volume, and the alkaline chemical concentration declines with time. To address t h i s , the long term pulse study was undertaken. Five sand packs were prepared with THUMS Ranger sand. The samples were made from the same disaggregated and extracted sand described above i n the Long Term Flew Study. Without any pre-treatment, the sand packs were each saturated with a com­ plete pore volume of an alkaline solution containing either so­ dium hydroxide o r sodium orthosilicate and 1% NaCl. The alka­ l i n e solutions were then displaced i n opposite direction to that of the i n i t i a l alkaline injection input with a 1% NaCl solution i n twelve small periodic increments over a long period of time. Each displaced increment was analyzed f o r i t s alka­ l i n i t y . The time period between increments was governed by the rate of alkaline consumption. Although this i s not exactly what happens i n a reservoir, i t may be imagined that the overall results approach being similar to what would be expected i f a "slug" of one complete pore volume of such a solution were placed i n the pores of a reservoir. Figure 9 i s a schematic depicting the long term pulse experiment compared with what i s occurring i n a reservoir. In the experiment, only one pore volume of alkaline solution i s used. I t i s expected to l a s t at least two months and possibly much longer. The i n i t i a l increments of effluent collected w i l l have been i n contact with the sand pack f o r relatively short periods of time and should resemble the alkaline solution near the injection well i n f i e l d conditions. The increments following the i n i t i a l increments w i l l have been i n the sand pack f o r longer periods of time and would contain much of the chemical reaction products. They might be expected to resemble the solution behind the alkaline slug front under f i e l d conditions. In general terms, the pulse study s t a t i c a l l y measures the time decay of the alkaline concentration i n a sand pack i n a way that resembles the dynamic time decay i n a similar 100% pore volume slug exposed to an actual petroleum reservoir. Ihe l a s t few increments were not used as some d i l u t i o n due to mixing of the alkaline solution and the 1% NaCl displacing f l u i d could have occurred. The extent of d i l u t i o n i s presently

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

246

SOLUBLE

A EFFLUENTS-

SILICATES

θ ««-pH

!%NaCI

LONG TERM PULSE STUDY PRODUCTION WELL

INJECTION WELL.—

r

fcr "]D 'FIELD CONDITIONS" Figure 9.

Schematic

comparison

long-term pulse study and the "field in a reservoir.

conditions"

14.

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AL.

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Consumption

247

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

being studied with the use of lithium chloride and sod ion thiocyanate. In the study, after the collection of 5 increments out of a total of 12 increments and after 240 days, l i t t l e or no mixing has been found by analysis of lithium and thiocyanate in each increment of the effluents. Comparing results obtained from Figure 10, using 1.0% sodium hydroxide and Figure 11, using 1.0% sodium o r t h o s i l i cate, the elapsed times required f o r the % NaOH and % sodium orthosilicate a l k a l i n i t y i n the backflow to drop to zero are 115 days and 145 days respectively. Since the l a s t increment of the effluent i n the backflow may resemble the solution at the alkaline slug front under f i e l d conditions, the 115 days and 145 days could represent the elapsed times required f o r the a l k a l i n i t y of the slug fronts to drop to zero. However, as the alkaline slug i s being carried forward, the solution behind the slug front retains a l k a l i n i t y which would be ex­ pected to persist beyond these elapsed times, since the l a t e r part of the slug w i l l contact sands which have already been p a r t i a l l y reacted. Figure 11 depicts plots of long term pulse study experi­ ments involving the use of different concentrations of sodium orthosilicate. I t can be seen that 0.4% sodium orthosilicate survived only about 50 days. However, as the concentration of orthosilicate increased, the elapsed time required for the a l k a l i n i t y i n the backflow to reduce to zero also increased. The experiment with 2.0% sodium orthosilicate i s s t i l l i n progress, and after 240 days i t seems the curve has leveled out, which would imply the a l k a l i n i t y w i l l survive f o r a much longer time. Although i t i s s t i l l quite uncertain, i t i s hoped that such a concentration would survive i n this kind of reservoir f o r several years. As a result, f o r f i e l d s i t u ­ ations which do take an average of several years between i n ­ jection well and producing well, enough a l k a l i n i t y should be present for the desired o i l enhancement effect to take place. For purpose of comparison, 2.0% sodium orthosilicate i s equivalent to 5.25 meq/100g sand i n a 25% porosity sand pack. Thus, f o r those operations which take several years to t r a ­ verse from injector to producer, i n this type of reservoir, the 1.5% - 2.0% sodium orthosilicate might be the lower l i m i t for the proper concentration f o r slug design. Field results from alkaline waterflooding have thus f a r been very limited. However, a survey (9) of f i e l d t r i a l s that reports positive enhanced o i l recovery results including Harrisburg Field, Nebraska, North Ward-Estes Field, Texas, and Singleton Field, Nebraska, a l l involved the use of caustic or sodium orthosilicate at concentrations of 2.0% or higher. The

American Chemical Society Library 1155 16th St. N. W. Washington, D. C. 20036

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

248 SOLUBLE

3QIX0UQAH INniQOS % SILICATES

LIEU E T A L .

Long-Term

Consumption

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch014

14.

Figure IL Long-term pulse study. Conditions for pore vol each: Δ , 0.4% sodium orthosilicate + 1% NaCl; Ο, 0.7% sodium orthosilicate + 1% NaCl; Χ , 1.0% sodium orthosilicate + 1% NaCl; and Π> 2.0% sodium orthosilicate + 1 % NaCl in THUMS Ranger sand packs being displaced in small increments with 1 % NaCl solution at 125°F.

249

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250

SOLUBLE SILICATES

notable exception is the Whittier trial in California (7) where, because of the short distance between injector and producer, caustic reached the producing wells within a few months or less, a situation compatible with survival of the 0.2% concentration which was used. The extent to which the long term pulse study is applicable to an actual petroleum reservoir is dependent on more field results, which will be forthcoming in the next several years. Acknowledgments ; Thanks are extended to the Department of Oil Properties of the City of Long Beach and THUMS Long Beach Company for the support of this study, to PQ Corporation for its support to participate in the Soluble Silicates Symposium and to Drs. R.M. Weinbrandt and T.C. Campbell of Aminoil, USA, Inc. for their help in providing material and technical assistanC.E. Literature Cited 1. Cooke, C.E. Jr.; Williams, R.E.,; Kolodzie, P.A. J. Pet. Tech. 1974, 26, 1365-1374. 2. Jennings, H.Y. Jr.; Johnson, C.E. Jr.; MacAnliffe, C.D. J. Pet. Tech. 1974, 26, 1344-1352. 3. Johnson, C.E. Jr. J. Pet. Tech. 1976, 28, 85-92. 4. Ehrlich, R.D.; Wygal, R.J., SPE J. 1977, 17, 263-270. 5. Leach, R.O.; Wagner, O.R.; Wood, H.W.; Harpke, C.F. J. Pet. Tech. 1962, 15, 206-212. 6. Emery, L.W.; Mungan, N.; Nicholson, R.W.; J. Pet. Tech. 1960, 12, 1569-1576. 7. Graue, D.J.; Johnson, C.E. Jr. J. Pet. Tech. 1974, 26, 1353-1358. 8. Carmichael, J.D.; Mayer, E.H.; Alpay, O.A.; Boyle, P.R. 5th DOE Symposium on Enhanced Oil and Gas Recovery and Improved Drilling Methods 1979. 9. Mayer, E.H.; Berg, R.L.; Carmichael, J.D.; Weinbrandt, R.M. SPE 8848, First Joint SPE/DOE Symposium on Enhanced Oil Recovery, 1980, 407-415. 10. Weinbrandt, R.M.; Buck, R.A.; Anderson, G.H. 31st Annual Technical Meeting of the Petroleum Society of CIM, 1980. 11. Somerton, W.H.; Radke, C.J. SPE 8845, First Joint SPE/DOE Symposium on Enhanced Oil Recovery, 1980, 363-378. 12. Holm, L.W.; Robertson, S.D. J. Pet. Tech. 1981, 33, 161-172. 13. Campbell, T.C. SPE 6514, 47th Annual California Regional Meeting of SPE of AIME, 1977. 14. Bunge, A.L.; Radke, C.J. SPE 10288, The 56th Annual Fall Technical Conference of SPE of AIME, 1981. RECEIVED March 2,1982.

15 Dehydrated S o d i u m Silicate B o u n d C o r e S a n d for Aluminum Casting

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch015

R. F. KIESEL and H. VAN OENE Ford Motor Company, Engineering and Research Staff, Dearborn, MI 48121

Presented are properties of sodium silicate and dehydrated silicate bound sand which delineate the utility of sodium silicate as a binder for foundry cores. These properties are: worklife of coated sand, variables affecting bound sand strength, storage stability of sand cores, and their high temperature properties. A new method of determining worklife of coated sand is presented. Data is given relating sand strength to processing variables. Moisture absorption rates, which affect storage life of bound sand are found to depend on relative humidity of the atmosphere and sodium content of the silicate. The strength, storage life and shake-out properties of cores produced by this process differ substantially from those of cores produced by the "CO -Silicate" process. ,

2

A process has been developed at Ford Motor Company that uses dehydrated sodium silicate as a core binder for aluminum casting. Silicate sand binders are attractive for their environmental qualities, such as the lack of organic emissions and odor, and for other properties beneficial to the casting process (1). A foundry core is a sacrificial aggregate that produces the interior configuration, or cavity, of a cast metal part. The main component of this core is usually silica sand but other particulate inert materials have been used. Sand is bonded by a core binder, which may be an organic resin composition such as a phenolic, furan, alkyd or isocyanate. Inorganic compositions of phosphates and silicates have also been used as core binders.

0097-6156/82/0194-0251$06.00/0 © 1982 American Chemical Society

252

S O L U B L E SILICATES

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch015

A core process encompasses the operations of a casting plant. In this paper some of the specific and unique material and process variables of the dehydrated s i l i c a t e process are reported. These are: Sand Coating and Coated Sand Worklife. Core Production from Coated Sand. Bound Sand Strength. Bound Sand Storage S t a b i l i t y . High Temperature Properties and C o l l a p s i b i l i t y of Sand from Aluminum Castings. Other process variables have been considered but w i l l not be reported i n this paper.

Sand CpaUre

Coated Sand WorfcUfe

Sand i s coated with aqueous sodium s i l i c a t e by conventional mulling. In practice, sand has been mixed i n batches from 1Kg, laboratory scale, to 600Kg, production scale. There i s no restriction as to type of sand muller used. However, i f solvent water evaporation i s significant the amount of water i n the formulation must be increased. This i s particularly the case when using "speed" mullers. Two factors define the worklife of coated sand and determine the usefullness of a coated sand mixture: the a b i l i t y to flow and be formed into a shape and the a b i l i t y to be cured into a r i g i d sand body. For the purposes of this paper, coated sand was judged unsuitable i f a cured sand body had a tensile strength lower than 0.7MPa, 100psi. Flow properties of coated sand are less readily defined. Since a suitable test has not been accepted by the foundry industry, the following test was devised to determine the flowability of a sand formulation: Coated sand, i n a glove box, i s riddled through a #4 Standard Screen sieve, 4.76mm mesh opening, into a 3cm deep pan. The relative humidity, carbon dioxide content and temperature of the box i s measured and controlled. The sand mass i s struck o f f but not tamped down. The bulk density of the resulting sand mass i s approximately 0.7 to 0.9 g/cc. At given time intervals steel b a l l bearings, 1/2 inch O.D. weighing 8.33g» are dropped on the sand from a height of 48 cm. The steel balls penetrate the sand and are not removed u n t i l the test i s terminated. As the sand gets s t i f f e r , due to environmental conditions or to the binder curing, the depth of penetration decreases. At the conclusion of the test the sand assembly i s transferred to a laboratory oven to set the remaining viable sand · The impact depths are determined and normalized to the i n i t i a l impact depth. This ratio i s called the Flow Index and i s an indication of the

15.

KiESEL AND

VAN OENE

Dehydrated

Silicate

Bound

Core

Sand

253

flow property of the coated sand when an imposed stress i s applied. The higher the Flow Index the e a s i e r i t i s to form a sand body by impact ramming , squeezing or blowing. Flow I n d i c e s f o r the same sand f o r m u l a t i o n , exposed t o f o u r test environments, are shown in Fig. 1. These test environments are c h a r a c t e r i z e d only by d i f f e r e n t relative humidity s i n c e the Flow Index f o r s i l i c a t e coated sand i s not significantly influenced by changes in temperature and anticipated C0 l e v e l s i n ambient a i r . When the Flow Jjaâgx. o f t h i s f o r m u l a t i o n drops to 0.55, cores blown with 85psi a i r pressure have the minimum acceptable s t r e n g t h . Sand with a higher Flow Index would produce more dense sand bodies and have higher s t r e n g t h . Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch015

2

The work l i f e of sand coated w i t h aqueous sodium silicate is dependent on the r e l a t i v e humidity of the environment . At 20? RH and 60$ RH, the work l i f e i s found to be 30 minutes and 90 minutes r e s p e c t f u l l y , F i g . 1. Coated sand t h a t i s sealed t o prevent water l o s s or COp a b s o r p t i o n , has a work l i f e i n excess of three weeks. Even a simple cover r e t a r d s moisture l o s s and extends the work l i f e ; f o r example , at 20? RH a cover i n c r e a s e s the work l i f e from 30 minutes to over 3 hours. Core Production frOP Çoatqd

$and

A comnon method o f producing foundry cores i s to f l u i d i z e the coated sand and blow i t i n t o a core box using a i r pressure. The s t r e n g t h o f bound sand i s determined i n p a r t by the bulk d e n s i t y of the sand body which i n t u r n i s determined by the a i r pressure used to blow the coated sand. Core blowing tends to dry coated sand prior to forming i n t o a sand body. Consequently, water based s i l i c a t e coated sand f o r m u l a t i o n s must c o n t a i n more moisture to allow f o r t h i s production c o n d i t i o n . The amount o f added water would depend on the r e l a t i v e humidity of the environment as w e l l as production v a r i a b l e s . In the l a b o r a t o r y bound sand bodies are a l s o prepared by ramming, squeezing and hand tucking. Ramming r e s u l t s i n extremely c o n s i s t e n t but high bulk d e n s i t i e s and consequently high s t r e n g t h s . Although core blowing more c l o s e l y represents production c o n d i t i o n s , most of the s t r e n g t h comparisons made will be with samples prepared by ramming because of the r e p r o d u c i b i l i t y o f the p r o p e r t i e s of the t e s t samples prepared by t h i s technique. Sand p r o p e r t i e s are determined u s i n g standard compression and t e n s i l e samples prepared according t o the "Foundry Sand Handbook, 7 t h . E d . ; American Foundrymens S o c i e t y Pub., pp8-4 n

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254

SOLUBLE

0

40

80

120

140 180

SILICATES

2 2 0 3 Weeks

TIME (min) AFTER C O M P L E T I O N O F M U L L CYCLE Figure 1. ppm CO ): t

Work life of silicate-coated sand. Key (% relative humidity and 340 • , 20%; Δ , 60%; O, 90%, loose cover over sand in 20% relative humidity environment; and |, 97% sealed container.

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255

and 1 3 - 1 . Blown tensile samples were prepared using a Mo·372 Hot Box Tensile Curing Machine from Harry W. Dietert Co. Silicates are already used as sand binders i n casting operations. The "CO^-Silicate Process" makes use of the acid base chemistry of soluole s i l i c a t e s (2). However, sand bodies produced using this gassing technique are weak. It i s not the purpose of this paper to discuss the "C0 -Silicate Process" as this has been presented i n the literature (3)· The process described here i s the physical dehydration of soluble s i l i c a t e coated sand. Fig. 2 shows the compressive strength of bound sand produced by the CO- process and the strengths produced by this dehydration process. Dehydration produces strengths an order of magnitude higher than those reported for the "C0 -Silicate Process" at the same binder level.

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch015

2

2

Hot-Box, Core Oven, and Microwave Radiation equipment have been used to dehydrate sand. The differences i n these processes are i n their rate of core production, the efficiency of energy u t i l i z a t i o n and the a v a i l a b i l i t y of process equipment i n the plant. No matter what process i s used to dehydrate the sand formulation so long as the entire sand body i s heated above 105°C, the bound sand properties, i e . strength, storage l i f e and post-casting sand shake-out remain the same. With Hot-Box dehydration, one inch thick test samples are dehydrated completely i n 50 seconds by contact with hot, >230 C, metal plattens. In this process the sand i s heated by conduction so the rate of dehydration varies with the thickness of the sand body · The Hot-Box process i s inefficient since there are significant energy losses by radiation from the hot metal patterns; however, Hot-Box equipment i s readily available in the casting industry (4). The advantage of using microwave power i s i t s efficiency. Only the sand and s i l i c a t e binder are heated (5). The dehydration rate depends on the microwave power used. The power requirement i s between 0.044 and 0.15 Kw hr/Kg sand (6K While microwave ovens are available commercially, only few casting plants have microwave f a c i l i t i e s (7).

BsmsA Sand Strength The strength of a bound sand system i s perhaps i t s most important property. The effect of process variables on strength i s shown i n Figures 2-5. The term " s i l i c a t e s o l i d " describes the s i l i c a t e content of the dehydrated sand specimen. This term applies to that portion of the s i l i c a t e binder that w i l l not evaporate when heated above 105°C. Thus, the solvent water and

SOLUBLE

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch015

256

S. Σ

SILICATES

DEHYDRATED

20. 15.

μ

ίο.

μ ONE DAY STORAGE

C0 -SIUCATE 2

IMMEDIATE T E S T

0.5 % Figure

2.

Compression

1.0

1.5

SILICATE

2.0

2.5

3.0

SOLID

strength of silicate-bound sand. Silicate mol ratio (COt-silicate data from Ref. 3.)

2.0:1.

15.

Dehydrated

KiESEL A N D V A N O E N E

Silicate

Bound

Core

Sand

257

loosely bound water are excluded from the s i l i c a t e concentration figures. The term " s i l i c a t e ratio" i s used to describe the mole ratio of s i l i c a , S i 0 , to soda, Na^O, used to manufacture the s i l i c a t e s . The "bound water r a t i o , " wa 0:HpO, depends on the s i l i c a t e ratio and the dehydration temperature (8). The network structure, hence, the cohehsive bond strength, of the cured polysilicate binder, i s defined by both the s i l i c a t e ratio and bound water ratio. 2

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch015

2

Mold Density and Sand Grain Shape. Each wetted grain to grain junction contributes to the strength of the dehydrated sand body. The greater the number of these junctions and the more binder solid at these junctions, the higher the strength of the bound sand part. As the bulk density of a sand body increases, the number of grain to grain contact points increase. For any sand used, the higher the a i r pressure, or ramming pressure, used to form the sand shape the greater w i l l be the bulk density of the resultant sand body. F i g . 3 shows the relationship between tensile strength and blown sand bulk density for two different sand systems. The lowest strength on each curve was obtained using 0.35 MPa, 50 psi, blow pressure. The highest strength was obtained using 0.65 MPa, 95 p s i , blow pressure. High bulk density sand bodies are produced from base sands that have a rounded grain shape and have broad grain size distribution, such as Wedron 5010 sand . The surface tension of the s i l i c a t e solution w i l l draw the s i l i c a t e solids into the region of the grain to grain contacts. When dehydrated, the s i l i c a t e solid e f f i c i e n t l y contributes to the strength of the sand body. Lake sand i s typical of that used by large casting plants. The sand grains have a more uniform size and are more angular i n shape. Lake sands are not pure s i l i c a but also contain other minerals i n minor amounts. The s i l i c a cleavage planes are sharp. When blown the bulk density of the resulting sand body i s not as high as with round grain sand. However, this by i t s e l f i s not sufficient to account for the lower strengths , since even at equivalent mold densities round grain sand yields stronger sand bodies than does angular sand. Silicate SoliA Content aj& Viscosity. As the s i l i c a t e solids content of a bound sand body increases, the strength of the sand body also increases as shown i n Fig. 4. The mold densities of a l l samples were held constant at 1.55-1.58 gm/cc

SOLUBLE

258

SILICATES

£ Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch015

lu

-J CL m

ζ

3 ω

Lu Ο

Ο Ζ LU

or

to ζ UJ

2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0

4-

_L

1.35

1.40

X

1.45

1.50

1.55

CURED S A N D B U L K DENSITY, g / c c Figure 3. Tensile strength vs. sand type and bulk density. Key: •, Wedron 5010 silica sand, round grain, AFS 65, four screen, 1.5% 3.0:1 silicate; and O, Lake Michigan silica sand, angular to subangular grain, AFS 45, two screen, 1.5% 3.32:1 silicate.

15.

Dehydrated

KiESEL A N D V A N O E N E

Silicate

Bound

Core

259

Sand

1 Έ

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LU

4.0

r

s! < if)

ο LU

3.0

Έ

2 2.0

S ce

1.0 ω z

Ul

_L 0.5

1.0

_L

_L

1.5

2.0

% SILICATE SOLID Figure 4. Tensile strength vs. silicate solid content; silicate ratio 3.0:1. Key: 39% solid, 61% solvent water; and 0,43% solid, 57% solvent water.

•,

SOLUBLE

260

SILICATES

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch015

and the same base sand type was used for both series* However, as i s also shown on Fig.4, for a given s i l i c a t e solid content the strength also depends on the water content of the s i l i c a t e solution. This effect may be due to differences i n wetting of the sand by the two solutions described on Fig. 4. The greater volume of dilute s i l i c a t e solution allows for more efficient wetting of the sand as well as buildup of solid s i l i c a t e at grain to grain junctions and a more efficient bond i s formed. The viscosity of the s i l i c a t e solution provides an alternate explanation for this phenomenon. The viscosity of soluble s i l i c a t e s increases sharply i n the concentration range used i n this investigation (j)). Solution viscosity would determine how much s i l i c a t e would be drawn into the grain to grain junction points. As the s i l i c a t e solid content i s increased i n the coated sand, the strength of each junction point attains i t s maximum value. In these higher s i l i c a t e solids cases, the viscosity of the s i l i c a t e solution i s not a determining factor and additional water has no effect on the strength of the bound sand samples. For each sand studied, and each s i l i c a t e ratio investigated, there i s a specific water content of the s i l i c a t e solution that gives optimum strength properties. S i l i c a t e Ratio. Tensile strength varies with the s i l i c a t e mole ratio as shown i n Fig. 5. The s i l i c a t e solid concentration, the bulk density and the base sand are kept constant i n these samples. The tensile strength i s shown at the optimum water level for each s i l i c a t e ratio. However, the 3.86:1 material was not investigated f u l l y . The strongest sand bodies were found with s i l i c a t e mole ratios approximately 3*0:1.

£suM Saytf storage stability Existing casting plant practice i s to prepare sand cores ahead of demand and then store them for later use. The question arises, how long w i l l dehydrated s i l i c a t e bound sand remain strong i n a casting plant environment? Test samples from different sand formulations were exposed to sets of environmental conditions and the resultant reduction i n strength was determined as a function of exposure (10)(11). Tensile strengths were determined using an Instron Mechanical Tester with a model "F" load c e l l . Because of the many variables involved i n strength properties, the strengths of the various bound sand systems are normalized to the pre-exposure strengths. The fraction of i n i t i a l strength that remains after exposure i s plotted as a function of the duration of exposure.

Dehydrated

KiESEL A N D V A NOENE

Silicate

Bound

Core

Sand

261

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch015

ο α. 2 LU -J û. S

2.5

h


2.0:1; ·, 2.38:1; •, 3.00:1; Δ , 3.32:1; and O, 3.86:1.

266

SOLUBLE

SILICATES

< Ζ Ο

CD OC

2.0 h

ι

M

SILICATE RATIO 2.0Ί

1.5 Ό

CO w — Φ

I .0

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch015

i i ο LU h-

2.4· I

0.5

I OC à$

_L


1200°C. H y d r o s i l i c a t e s w i t h Na 0 between 15 and 18 wt/o and de­ a l k a l i z e d a t 50° to 60°C i n 0.6 ΝΗι*Ν0 s o l u t i o n s were most l i k e l y to have the d e s i r e d pore s t r u c t u r e s . High s i l i c a , low expansion g l a s s up to 4mm t h i c k was obtained by t h i s approach. Shape and s i z e l i m i t a t i o n s may e x i s t . 2

2

2

3

286

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S O L U B L E SILICATES

Figure

4.

Porosity

as a junction of alkali content in hydrosilicate. Na O: a, 16%; b, 18%;and c,21%. z

Key for

%

BARTHOLOMEW ET AL.

Reconstituting

Sodium

Silicate

Glass

287

Ε

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch017

f

l a

§4?

So

Il si

1

SOLUBLE

SILICATES

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288

Figure

6.

Consolidated silica glass. Key: a, cross section with opaque core; magnified porous layer; and c, transparent glass body.

b,

17. BARTHOLOMEW ET AL.

Reconstituting Sodium Silicate Glass

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch017

Literature Cited 1.

Schloze, H.; Glass Ind. 1966, 47, 546, 622, 670.

2.

Boulos, Ε. N.; Kreidl, N. J., J. Can. Ceram. Soc. 1972, 41, 83.

3.

Ernsberger, F. M.; J. Am. Ceram. Soc. 1977, 60, 91.

4.

Bartholomew, R. F.; Butler, B. L.; Hoover, H. L.; Wu, C. Κ., J. Am. Ceram. Soc. 1980, 63, 481.

5.

Bartholomew, R. F.; Schreurs, J.W.H., J. Non-Crystall. Solids, 1980, 38/39, 679.

6.

Bartholomew, R. F.; Tick, P. Α.; Stookey, S. D., J. NonCrystall. Solids, 1980, 38/39, 637.

7.

Moriya, Y.; Nogami, M., J. Non-Crystall. Solids, 1980, 38/39, 667

8.

Takata, M.; Tomozawa, M., J. Am. Ceram. Soc. 1980, 63, 710.

9.

Wu, C. K., J. Non-Crystall. Solids, 1980, 41, 381.

10. 11.

Garfinkel, H. M. "Membranes, A Series of Advances:, Eisenman, G., Ed., Marcel Dekker, Ν. Y., 1972, Vol. 1, p. 199.

Doremus, R. Η., "Glass Science," John Wiley and Sons, N.Y., Ν. Y. 1973. RECEIVED March 2, 1982.

28

18 S i l i c o n A l k o x i d e s i n G l a s s Technology

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch018

L. C. KLEIN and G. J. GARVEY Rutgers University-The State University of New Jersey, Ceramics Department, Piscataway, NJ 08854

The sol-gel process for forming glasses from silicon alkoxides is described. The processing steps are forming the solution, gelling, drying and firing. The chemical reactions hydrolyzation and polymerization occur in solution depending on combinations of the variables pH, electrolyte, percent water, solvent and temperature. The advantages of the process are high purity, homogeneity and low temperature. Commercial applications of sol-gel glasses include coatings, microballoons, fibers, substrates and porous monolithic shapes. Though ethyl silicates and other silicon alkoxides have been commercially available for some time (1), their use in glass technology has only recently been well publicized (2). Perhaps the reason for so few investigations in the past into their use in glass technology is that the traditional ideas about glass formation have always involved high temperature. That is to form a glass, a material is heated above its liquidus temperature to disrupt its crystalline structure and, because of its viscous nature, the random liquid structure is trapped by a rapid quench. Once at room temperature, the glass is an unstable solid which is isotropic and in some cases transparent. Accepting this the formation of an isotropic, transparent amorphous material at low temperature is in conflict with this definition. Nevertheless, such a material can be made at room temperature through a sequence of chemical reactions including hydrolyzation and polymerization with silicon alkoxides. In the broader sense of glass formation, this paper will cover the raw materials for what is called the sol-gel process, the processing steps and variables, the applications of the technology and its advantages over traditional methods.

0097-6156/82/0194-0293$06.00/0 © 1982 American Chemical Society

294

SOLUBLE

SILICATES

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch018

Raw M a t e r i a l s Most s i l i c a t e glasses are made w i t h sand g r a i n s that range from a few to hundreds of microns i n s i z e . The process of melt­ i n g and homogenizing these glasses r e q u i r e s high temperatures and long times f o r s o l i d s t a t e r e a c t i o n s t o occur. Suppose the source of the s i l i c a i n the s i l i c a t e g l a s s was a f l u i d or a l i q u i d . This would e l i m i n a t e the long times needed f o r r e a c t i o n s . C o l l o i d a l s i l i c a s (3) and s o l u b l e s i l i c a t e s (4) can be used as f l u i d sources o f s i l i c a . S i l i c o n alkoxides can be used as w e l l , and i n p a r t i c u l a r the c l e a r l i q u i d t e t r a e t h y l o r t h o s i l i c a t e (TEOS from Dynamit-Nobel) was s e l e c t e d f o r t h i s study. Of the a v a i l a b l e s i l i c o n a l k o x i d e s , t e t r a e t h y l o r t h o s i l i c a t e (TEOS) appears to be the most popular. T h i s i s because i t r e a c t s more slowly with water than tetramethyl o r t h o s i l i c a t e , comes t o e q u i l i b r i u m as a complex s i l a n o l and i n a p a r t i a l l y hydrolyzed s t a t e i s s t a b l e over longer periods of time (5) . The c l e a r TEOS l i q u i d i s the product of the r e a c t i o n of S i C l 4 w i t h ethanol. The r e a c t i o n produces HCl along w i t h the e s t e r Si(0C2H5)4 (1). T h i s c o l o r l e s s l i q u i d of a density o f about 0.9 g/cm3 i s easy to han­ d l e and through m u l t i p l e d i s t i l l a t i o n extremely pure. T e t r a e t h y l s i l i c a t e i s i n s o l u b l e i n water ( 6 ) . In order to i n i t i a t e the h y d r o l y s i s r e a c t i o n , the TEOS and water must be introduced i n t o a mutual s o l v e n t . In t h i s study the mutual solvent i s ethanol. A t y p i c a l mixture i s 43 volume % TEOS, 43 volume % ethanol and 14 volume % water. For multicomponent g l a s s e s , the d e s i r e d a d d i t i o n s may be i n the form of a l k o x i d e s (7) or s o l u b l e s a l t s such as acetates and n i t r a t e s ( 8 ) . In t h i s way glasses c o n t a i n i n g B, A l , T i , Na, K, t r a n s i t i o n metals, r a r e earths and others are r e l a t i v e l y s t r a i g h t ­ forward i n p r a c t i c e to prepare. A longer chain a l c o h o l such as propanol may be used to slow the r a t e s of the chemical r e a c t i o n s and allow adequate time f o r complete mixing. In some cases where the high p u r i t y of TEOS i s not needed, a p a r t i a l l y condensed m a t e r i a l may be used. Such l i q u i d s have up to 40% by weight S 1 O 2 and d e n s i t i e s of about 1.05 g/cm . When i t i s p o s s i b l e t o s t a r t with t h i s p a r t i a l l y condensed TEOS, the advantage i s reduced weight l o s s i n the conversion t o an i n ­ organic g l a s s . These raw materials, are p r a c t i c a l i n small s c a l e operations as w e l l as l a r g e s c a l e . For s p e c i a l t y a p p l i c a t i o n s such as coat­ ings f o r s o l a r c e l l s , the m a t e r i a l s o f f e r high p u r i t y and ease of a p p l i c a t i o n ( 9 ) . For c o a t i n g window g l a s s e i t h e r t o improve chemical d u r a b i l i t y or to reduce r e f l e c t i o n l o s s e s , the s t a b i l i t y of the s o l u t i o n makes the c o a t i n g of many square meters of g l a s s a continuous process (10). In e i t h e r case, i t i s p r a c t i c a l t o r e c y c l e ethanol generated by the chemical r e a c t i o n s i n the s o l u ­ t i o n back i n t o the production of the raw m a t e r i a l , thus producing more TEOS. 3

18.

K L E I N AND GARVEY

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch018

Processing Steps and

Silicon

Alkoxides

in Glass

Technology

295

Nomenclature

The apparatus needed f o r l a b o r a t o r y s c a l e processing i s r e l a t i v e l y simple. As shown i n Figure 1, i t c o n s i s t s of a t h r e e necked f l a s k , a mechanical s t i r r e r , a r e f l u x condenser and a temperature probe c o n t r o l l i n g a constant temperature bath. The i n g r e d i e n t s are TEOS, ethanol and water. An e l e c t r o l y t e such as HCl or N H 4 O H may be used. The neck of the f l a s k f i l l e d by the temperature probe may a l s o be used f o r e l e c t r o l y t e a d d i t i o n s or sampling. The processing steps are, i n s h o r t , forming the s o l , g e l l i n g , d r y i n g , and f i r i n g . During the f i r s t step, a l l components must be mixed to form a c l e a r s o l . Cloudiness or p r e c i p i t a t i o n i n d i ­ cates a segregation of components which needs to be c l e a r e d up by an e l e c t r o l y t e a d d i t i o n or d i f f e r e n t s o l v e n t . Once a l l of the components are mixed, the water and alkoxides r e a c t to begin the g e l l i n g , the second step. While being continuously s t i r r e d the f l u i d s o l w i l l become i n c r e a s i n g l y more v i s c o u s . At a d e f i n i t e p o i n t the v i s c o u s s o l becomes an e l a s t i c g e l , and at t h i s p o i n t bubbles cease r i s i n g . One way to p i c t u r e the g e l i s as an e l a s ­ t i c sponge now f i l l i n g the volume once f i l l e d by the s o l . During the t h i r d step, the porous g e l w i l l exude l i q u i d and s h r i n k . While d r y i n g organics and water trapped i n pores w i l l escape. E v e n t u a l l y , the d r i e d g e l comes to an e q u i l i b r i u m w i t h ambient c o n d i t i o n s , and t h i s amorphous r i g i d s o l i d i s from then on f a i r l y i n s e n s i t i v e to moisture. I f the goal of t h i s process i s to make a m a t e r i a l with the same p h y s i c a l p r o p e r t i e s as g l a s s , the f i n a l step i s to heat the i n o r g a n i c sponge, d r i v e o f f absorbed water, react hydroxyls to form b r i d g i n g oxygens l i n k i n g the S 1 O 2 network, c o l l a p s e pores and s i n t e r to dense g l a s s . A l l of t h i s can be accomplished at 1/3 to 1/2 lower temperatures i n °K than used i n the c o n v e n t i o n a l method, w i t h (11) and without pressure ( 8 ) , i n vacuum and i n a i r (12). At the s o l - g e l t r a n s i t i o n , the molecular s t r u c t u r e of the g e l determines the p r o b a b i l i t y that a g e l w i l l dry i n one p i e c e or w i l l break i n t o fragments. I t i s convenient to t h i n k of t h i s t r a n s i t i o n as the formation of the l a s t bond needed to c r e a t e an i n f i n i t e molecule. However, t h i s t r a n s i t i o n has not been defined i n terms of thermodynamics, so i t may be m i s l e a d i n g to c a l l i t the s o l - g e l t r a n s i t i o n at a l l . Yet, i n p r a c t i c e the t r a n s i t i o n i s determined by q u a l i t a t i v e i n s p e c t i o n when an abrupt i n c r e a s e i n v i s c o s i t y occurs. The goal of t h i s work w i t h TEOS i s to f i n d the optimum combination of v a r i a b l e s which gives a s t r u c t u r e at the s o l - g e l t r a n s i t i o n which can be processed to form v a r i o u s l y f i b e r s , beads, f r i t s , m i c r o b a l l o o n s , shapes, s e a l s , coatings or i n o r g a n i c sponges.

S O L U B L E SILICATES

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch018

296

Figure

1.

Schematic

of apparatus for preparing

gels from silicon

alkoxides.

18.

K L E I N A N D GARVEY

Silicon

Alkoxides

in Glass

Technology

297

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch018

Chemical Reactions and Reaction Rates The chemical r e a c t i o n s that occur when water and TEOS are d i s s o l v e d i n ethanol are h y d r o l y z a t i o n and condensation polymer­ i z a t i o n . The s o l u t i o n i s a c t i v a t e d once the water r e a c t s w i t h alkoxy groups on the s i l i c o n t o form hydroxyl groups and a l c o h o l . T h i s h y d r o l y z a t i o n produces complex s i l a n o l s and ethanol w i t h TEOS, but t h i s never goes to completion. That i s the water i s not used up to form s i l i c i c a c i d . Instead condensation polymer­ i z a t i o n takes p a r t i a l l y hydrolyzed u n i t s and makes l a r g e r u n i t s with b r i d g i n g oxygens. T h i s condensation p o l y m e r i z a t i o n regen­ erates water. While h y d r o l y z a t i o n uses water as a r e a c t a n t , p o l y m e r i z a t i o n regenerates water as a product. The k i n e t i c s of t h i s process are very complex. In f a c t , the mechanism f o r r e a c t i o n s c a t a l y z e d by a c i d i s d i f f e r e n t from that c a t a l y z e d by base (5, 12). To moni­ tor the extent of these r e a c t i o n s , an experiment was devised t o simultaneously measure ethanol and water content i n the r e a c t i o n f l a s k (7). An i n c r e a s e i n ethanol content would i n d i c a t e prog­ r e s s i n h y d r o l y z a t i o n . A minimum i n water with a subsequent r i s e would i n d i c a t e progress i n p o l y m e r i z a t i o n . The experiment i n v o l v e s p e r i o d i c sampling of the s o l u t i o n i n the r e a c t i o n f l a s k . With a s y r i n g e , a sample i s e x t r a c t e d f o r ethanol a n a l y s i s i n a c a l i b r a t e d gas chromatograph (Bendix 2600 w i t h 6 foot Porapak S column). At the same time, the s o l u t i o n i s t i t r a t e d with K a r l F i s h e r reagent to give s e m i q u a n t i t a t i v e water a n a l y s i s . The data c o l l e c t e d are p l o t t e d i n F i g u r e 2. The open symbols are the volume percent e t h a n o l . N o t i c e that the ethanol l e v e l reaches a p l a t e a u . The time at which the ethanol l e v e l reaches t h i s p l a t e a u corresponds t o the minimum i n the water l e v e l . The f i l l e d symbols are the volume per cent water. The data were c o l l e c t e d a t 20°C, 60°C and 80°C, the r e f l u x i n g temperature f o r the s o l u t i o n . An i n t e r e s t i n g f e a t u r e i s that the p l a t e a u i n the ethanol l e v e l i s the same f o r a l l three temperatures. When the p l a t e a u i s reached, the p o l y m e r i z a t i o n process appears t o dominate the h y d r o l y z a t i o n process. Another i n t e r e s t i n g f e a t u r e i s that the water l e v e l does not go t o zero. There i s a minimum i n d i c a t i n g p o l y m e r i z a t i o n has begun before complete h y d r o l y s i s of a l l alkoxy groups. Beyond the minimum, the water l e v e l i n c r e a s e s l o g a r i t h m i c a l l y with time. The r a t e o f i n c r e a s e o f the water l e v e l i n c r e a s e s w i t h i n c r e a s e d temperature i n d i c a t i n g that p o l y m e r i z a t i o n speeds up with temperature. The data f o r water l e v e l extends t o the g e l p o i n t , so i n c r e a s e s i n temperature shorten the time t o g e l . The behavior f o r volume percent ethanol and volume percent water i n F i g u r e 2 i s t y p i c a l f o r s o l u t i o n s of TEOS i n ethanol with enough water f o r complete h y d r o l y s i s . The time to reach the ethanol p l a t e a u and the slope of the volume percent water

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch018

298 SOLUBLE SILICATES

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch018

18.

KLEIN AND

GARVEY

Silicon

Alkoxides

in Glass

Technology

299

vs time curve can be changed by changing the f o l l o w i n g v a r i a b l e s : pH, e l e c t r o l y t e , percent water, nature of solvent and temperature. F i r s t , the pH can be changed by adding more of an e l e c t r o ­ l y t e , f o r example IN HCl. In Figure 3, the e f f e c t of a d d i t i o n s of IN HCl on the v i s c o s i t y i s shown on a p l o t of v i s c o s i t y vs time. These measurements were made with a B r o o k f i e l d Viscometer at 50 RPM. The i n t e r e s t i n g f e a t u r e i s that the shape of the curve remains the same whereas the p o s i t i o n of the s o - c a l l e d knee s h i f t s to longer times with l a r g e r a c i d a d d i t i o n s . The knee s t a r t s at about 30 c e n t i p o i s e . For p r a c t i c a l purposes the s o l g e l t r a n s i t i o n i s at 2000 cp. The e f f e c t of these small a c i d a d d i t i o n s would appear to be a r e t a r d a t i o n of the bond formation needed to set to a g e l , though the eventual s t r u c t u r e i s p r e t t y much the same. Second, i t has already been mentioned that base c a t a l y z e d r e a c t i o n s are d i f f e r e n t from a c i d c a t a l y z e d r e a c t i o n s . Some p r e l i m i n a r y observations i n t h i s study were that an a c i d such as HCl drove the h y d r o l y s i s r e a c t i o n w h i l e impeding g e l l i n g . Then a base such as NH4OH l i m i t e d h y d r o l y s i s which made g e l l i n g im­ p o s s i b l e . However a s a l t such as NH4CI postponed h y d r o l y s i s , but t h i s was q u i c k l y followed by g e l l i n g . In a crude way, i t can be suggested that to speed up the o v e r a l l s o l - g e l process, i n i t i a l treatment should be with a c i d followed by a f i n a l t r e a t ­ ment w i t h base. T h i r d , the e f f e c t of water a d d i t i o n s to a s o l u t i o n w i t h 20 weight % Na20 i s l i s t e d i n Table I. With small a d d i t i o n s , the g e l l i n g time was s e v e r a l weeks and the product was p a r t i c u l a t e . With a d d i t i o n s greater than 1 mole water per mole of ethoxy groups, or 4 moles of water per mole of TEOS, the g e l l i n g time was l e s s than 40 seconds and the product was a f r i a b l e shape. Intermediate a d d i t i o n s gave a shape which stayed i n one p i e c e , but the i n t e r f e r e n c e of pores with l i g h t transmission made the piece opaque. In general an increase i n water increases the r a t e of g e l l i n g . Table I - E f f e c t of Water A d d i t i o n on G e l l a t i o n Time For 20 Weight % Na20-80 Weight % S1O2 S o l u t i o n Water A d d i t i o n moles H20/moles Ethoxy Group 0.18 0.36 0.53 0.71 0.89 1.07 1.25 >1.25

Time to Gel 3 weeks 3 weeks 36 sec 48 sec 43 sec 40 sec

Η

w

ο w

VO

Figure 2.

Intergrown

crystals of tetrabutylammonium faces.

hydrogen

silicate

hydrate

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch019

exhibiting

convex

19.

GERKE

ET AL.

Table I .

Tetrabutylammonium

Silicate

309

X-ray powder d i f f r a c t i o n data of tetrabutylammonium hy­

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch019

drogen s i l i c a t e hydrate ( C u K ^ , \ = 1.541 88).

m

I/I,

hkl

d[S]

I/I,

hkl

14.47

90

200

3.2079

50

840

10.22

85

220

3.0582

20

664

8.322

10

222

3.0079

15

931

7.190

35

400

2.8139

20

10.2.0,

5.859

8

422

2.5355

5

880

4.783

12

600, 442

2.5061

10

11.3.1,

971 882 866

862

4.328

50

622

2.4960

9

10.4.4,

4.137

10

444

2.4597

5

10.6.0,

3.985

7

640

2.4244

2

10.6.2

25

642

2.3890

7

12.0.0,

884

553, 731

2.3037

10

11.5.3,

975

2.2389

2

12.4.2,

886

3.8355

3.7385 100 3.5870

5

800

3.4810

95

820

3.3772

15

822, 660

3.3119

20

751,

3.2903

15

662

10.8.0 2.1925

5

13.1.1, 11.7.1 11.5.5,

555 2.0534

8

993

13.5.1, 11.7.5

S O L U B L E SILICATES

310

The c r y s t a l s are hydrophobic, i n s o l u b l e i n water, acetone, d i e t h y l e t h e r , toluene and trichloromethane, and s o l u b l e i n metha­ n o l , d i l u t e d a c i d s and bases. Chemical composition With chemical analyses the t o t a l amount of Si,C,N and H and the oxygen content i n excess of S i 0 ~ have been determined. The atomic r a t i o s observed are presented i n Table I I . They are i n good agreement w i t h atomic r a t i o s c a l c u l a t e d f o r the chemical composi­ tion [0.5 N ( C H ) " ] 0 · 7 . 1 4 S i 0

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch019

4

9

4

2

2

· 8.83 H 0.

(1)

2

Table I I . Comparison between observed atomic r a t i o s and those calculated for 0 . 5 [ N ( C H > j 0 · 7 . 1 4 S i 0 · 8 . 8 3 H 0 (calc. 1) 9

4

and f o r [ N ( C H ) ] 4

9

4

2 4

4

2

2

H ^ S i ^ O ^ ]

excess 0

Si

2

. 144 H 0 (calc. 2 ) 2

C

Ν

Η

observed

7.14

9.33

16

1.053

54.92

calc. 1

7.14

9.33

16

1.000

53.64

calc. 2

7.00

9.50

16

1.000

54.00

The s l i g h t excess observed f o r Ν and Η over those c a l c u l a t e d from chemical composition ( 1 ) i s perhaps due to some replacement of 2 ^ N ( C H ) ^ j by 2 N ( C H > + 2 H + H 0, the t r i b u t y l a m i n e being 4

9

4

+

+

4

9

3

2

formed by decomposition of tetrabutylammonium i o n s . T i t r a t i o n of an aqueous suspension of the m a t e r i a l a g a i n s t O.ln HCl and O.ln NaOH i n d i c a t e s four d i f f e r e n t r e a c t i o n s A, B, C and D (Figure 3 ) . The sharp step i n the t i t r a t i o n curve at = 6 i s due to the n e u t r a l i z a t i o n of the S i - 0 groups that are equiva­ l e n t to the number o f j^N(C^H^)^J c a t i o n s of the s i l i c a t e . At +

lower Pg values (region A of F i g u r e 3) the s o l i d c r y s t a l s are d i s ­ solved o b v i o u s l y by h y d r o l y s i s of S i - 0 - S i bonds. In the b a s i c r e ­ gion C a c i d hydrogen atoms of the s i l a n o l groups Si-OH r e a c t w i t h OH" i o n s . At s t i l l h i g h e r p^ v a l u e s (region D) S i - O - S i bonds are h y d r o l i z e d by hydroxyl groups. The amount of s i l a n o l groups determined from the amount of base used i n r e g i o n C i s i n agreement w i t h the chemical formula [ • « W j o . M O

H

1.72o[

S i

2° ] ' ' · 5

6

1

3

H

2°>

19.

GERKE ET

AL.

Tetrabutylammonium

Silicate

311

Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch019

PH

1

2

ml 0.1 n NaOH ml 0,1 n HCl Figure 3. Titration curve for tetrabutylammonium hydrogen silicate hydrate in aqueous suspension. Key: ®, SiOSi + H 0 ±^ SiOH + HOSi; (g) SiO~ + H* ±; SiOH; ©, SiOH + OH' ±^ SiO~ + H 0; and ®, SiOSi + OH' ±; SiO~ + HOSi. 2

2

SOLUBLE SILICATES

312

which i s r e c a l c u l a t e d from the chemical composition (1). Taking i n t o account the l a t t i c e c o n s t a n t s and the d e n s i t y of the c r y s t a l s a c e l l cantent of [N(C H ) ] 4

is

9

calculated.

4

2

4

This