The uranium-carbon system: The structure of dimethylberyllium and its bearing on chemical valence

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Title;

The Pranlua-Carbon System? the Structure of Dimethylberylllum and Its Bearing on Chemical Valence

A u t h o r ;_______ Adolph Isaac Snow

(Official certification of the classification shown is filed in the Ames Laboratory Document Library)

CLo-C

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»__________

W. E. Dreeszen Secretary to Declassification Committee

UNCLASSIFIED

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THE CRANIUM-CARBON SYSTEM; THE STRUCTURE CF BBffiTHYLBERYLLlUM AND ITS HARING ON CHEMICAL VALENCE

w Adolph Isaac Snoe

A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY

Maj or Subject.* .Physical. Chemistry

Approved *

In Charge of Major Fork

Head of Major Depart:

Dean of'Graduate "College

Ioca State College 1950

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UMI N um ber: D P 12965

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Q P 1 3 I - U T

SnG> i t - o

* 11 ■ TABLE OF COMEmS

X X K B W m X Q *............... THE

S30STH I. II. III. IV.

..................................

Introduction

3 3 3 4

8

Constitutional D i a g r a m .........

D. E. F.

Uranium Solid Transformations and Solidus from 0-4*8 wt.% Carbon ........... Identification of U C . Determination of Idquidus Lins from 0*4.8 wt*$ C a r b o n ............ Identification of U 0C3 and UC2 ...... 14 Melting Points of UC, U* ^ , and UC2 . . . . Equilibrium Relationships among UC, U^C3, aid UC2 . . . ....................

8 10 U 17 18

Hardness of U-C Alloys from 0-4*8 wt,$ Carbon • • • •

21

X-Ray Study of the Uranium-Carbon System

. . . . . .

21

Uranium lonocarbide, UC . . . . . . . . . . Hitrogen and Oxygen Contamination of UC • . Uranium Sesquicarbide,U 9C 3 ............ Uranium Bicarbide, UCa . .. . . . . . . . .

21 22 24 25

A. B. C. B. f II.

................

Materials and Apparatus . . . . . . . . . . . . . . .

B. C.

VI.

. . . . . . . . . . . . . . . . . . . .

Historical Background . .

A.

V.

1

Polishing and Etching

.................

27

THE STRUCTURE Cf DIKTffifLBERILLIUM AID ITS BEARIJG 01 CHEMICAL V A I E H C E ............................. I. II. III. M.

Introduction and Historical Background

40

. . . . . . .

40

Preparation of the Compound . . . . . . . . . . . . .

49

Identification of Dlmethylberyllium

..........

57

Determination of the Structure.. ..................

59

A. B. C.

X-Ray Equipment . . . . . . . . . . . . . . Measurement of Intensities • • • • • • • • • Laue Symmetry ...........

T/o 7^0

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59 59 61

- ill TABLE W CONTENTS (continued)

B. 1.

Determination of Lattice Constants....... Determination of the Density of DimethylberyIlium . . . . . . . . . . . . . f • Determination o£ the Possible Space Groups • G • Determination of Parameters . . . . . . . . H. Temperature Factor and Parameter Refinement I. Effect of the Hydrogen Atoms . . . . . . . . 3» Structure Factor Agreement . . . . . . . . . I. Discussion of the Structure . ..........

METALLIC VALENCES S U M ART

.............................. ...................

I. II, III.

TheDranium-Carbon System .

61 61 62 64 69 73 76 SI 91 100

....................... 100

The Structure of Diaeihylberyiliua

. . . . . . . . .

Metallic faiences

101 102

LITERATDBE C I T E D ................................

104

ACKNOWLEDGMENTS

109

.......................

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INTRODUCTION

The topics discussed in this thesis and the order in which they are arranged rather accurately reflect the trend of the authcar’s interests with time* Because of the work on the phase diagram described here and also experimental work on other alloy systems and some problems in the casting of metals and metal fabrication the author became interested in the bonding of solids.

This led to the use of X-ray diffraction

which is one of the most powerful tools for investigating the structure of solids. The determination of the structure of dimethylberylllum by means of X-ray diffraction is of theoretical value since it is another link in the chain of evidence concerning electron deficient compounds and, in fact, is a striking confirmation of the theory, first proposed by Dr. S. E. Bundle that metals with more low energy orbitals than valence electron® should form electron deficient compounds when combined with groups containing no unshared electron pairs.

The theory which explains

the bonding in dimethylberylllum may also be successfully applied to explain the bonding in various internetallic compounds and, in fact, has been so applied by Bundle and Pauling. Determination of crystal structures by means of X-ray diffraction led naturally to interest in the theory of internetallie bonding and, in particular, metallic valences which are discussed in the last section of this thesis.

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Thus, it may he seen that the apparently unrelated sections of this thesis are bound together by the author’s interests which hare progressed from the strictly experimental to the somewhat theoretical0

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the hmhibm-cabbqn s y s t e m

X*

Introduction

The need for a complete study of the uranium-carbon system arose fro®i

(l) experiments at Iowa State College (under contract with the

Manhattan District, U. S* Corps of Engineers) which showed that uranium could be cast in graphite without excessive carbon contamination and (2) requests for east forms of uranium carbide for experimental pile studies* Chemical, thermal, metallographic, and X-ray methods of analysis have been employed in this study which covers the entire binary system*

IX*

Historical Background

Perhaps the earliest attempt to make uranium carbides was that of Moissan (1) (1896) who reported the preparation of a metallic, crystal­ line material by reaction between D^Og and carbon in an electric furnace to give a compound which he supposed to be B^C . Although his analyses showed a carbon content slightly higher than the theoretical value, he thought that B2®3 *as a definite compound and also that it was the high­ est carbon compound possible in this system* In 1911 Lebeau (2) reported the preparation of IKJg which he assumed to be the same material as Moissan*s ^ Cj *

He explained the difference

in formula by supposed errors existing in the analysis method used by Moissan*

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Also in 1911* Ruff and Heinzelmann (3) reported the preparation of a compound analyzing closely to the theoretical composition of UC2 . They reported the melting point to be 2425°G. G.

Hagg (4) in 1931 determined the crystal structure of a UC,, sample,

prepared by Arnfelt, by means of X-ray diffraction studies. Polushkin (5) (1921) while investigating iron-uranium alloys, pro­ duced by reducing mixtures of U-0 and steel turnings with petroleum