Table Of ContentScience and Technology
of
Rare Earth Materials
Edited by
E. C. SUBBARAO
Department of Metallurgy
Indian Institute of Technology
Kanpur, India
W. E. WALLACE
Department of Chemistry
University of Pittsburgh
Pittsburgh, Pennsylvania
ACADEMIC PRESS 1980
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Library of Congress Cataloging in Publication Data
Indo-U.S. Conference on Science and Technology of
Rare Earth Materials, Cochin, India, 1980.
Science and technology of rare earth materials.
Proceedings of the conference held Mar. 3-8,
1980, in Cochin, India.
Includes index.
1. Earths, Rare—Congresses. I. Subbarao,
Eleswarapu Chinna, Date II. Wallace,
William Edward, Date III. Title.
QD172.R2I52 1980 546'.4 80-24273
ISBN 0-12-675640-6
PRINTED IN THE UNITED STATES OF AMERICA
80 81 82 83 9 8 7 6 5 4 3 2 1
Dedicated to our children
Veni, Ram, and Kanta
Richard, Donald, and Marcia
CONTRIBUTORS
Numbers in parentheses indicate the pages on which authors' contributions begin.
V. S. Arunachalam (415), Defense Metallurgical Research Laboratory, Hyder-
abad, India
R. S. Craig (329, 353), Department of Chemistry, University of Pittsburgh,
Pittsburgh, Pennsylvania
A. Elattar (329), Department of Chemistry, University of Pittsburgh, Pitts-
burgh, Pennsylvania
L. Eyring (99), Department of Chemistry, Arizona State University, Tempe,
Arizona
K. A. Gschneidner (25, 51), Ames Laboratory and Department of Materials
Science and Engineering, Iowa State University, Ames, Iowa
C. K. Gupta (3), Metallurgy Division, Bhabha Atomic Research Centre,
Bombay, India
K. P. Gupta (77), Department of Metallurgical Engineering, Indian Institute of
Technology, Kanpur, India
L. C. Gupta (155), Tata Institute of Fundamental Research, Bombay, India
H. Imamura (329), Department of Chemistry, University of Pittsburgh,
Pittsburgh, Pennsylvania
S. H. Liu (121), Department of Physics, Iowa State University, Ames, Iowa
S. K. Malik(143,197), Tata Institute of Fundamental Research, Bombay, India
M. B. Maple (167), Department of Physics, University of California at San
Diego, La Jolla, California
A. G. Moldovan (329), Department of Chemistry, University of Pittsburgh,
Pittsburgh, Pennsylvania
T. K. S. Murthy (3), Chemical Engineering Division, Bhabha Atomic Research
Centre, Bombay, India
xi
XI1 CONTRIBUTORS
K. S. V. L. Narasimhan (393), Crucible, Inc., Colt Industries, Pittsburgh,
Pennsylvania
S. Ramachandran (415), Steel Authority of India Ltd., New Delhi, India
S. Ramaseshan (247), Indian Institute of Science, Bangalore, India
T. G. Ramesh (247), National Aeronautical Laboratory, Bangalore, India
C. N. R. Rao(291), Solid State and Structural Chemistry Unit, Indian Institute
of Science, Bangalore, India
J. J. Rhyne (261), National Bureau of Standards, Washington, D.C.
D. D. Sarma (291), Solid State and Structural Chemistry Unit, Indian Institute
of Science, Bangalore, India
G. K. Shenoy (215), Argonne National Laboratory, Argonne, Illinois
V. Shubba (247), National Aeronautical Laboratory, Bangalore, India
H. K. Smith (353), Department of Chemistry, University of Pittsburgh,
Pittsburgh, Pennsylvania
E. C. Subbarao (375), Department of Metallurgical Engineering, Indian
Institute of Technology, Kanpur, India
R. Vijayaraghavan (143, 197), Tata Institute of Fundamental Research,
Bombay, India
W. E. Wallace (329, 353, 393), Department of Chemistry, University of
Pittsburgh, Pittsburgh, Pennsylvania
PREFACE
In recent years rare earths have been at the center of much scientific interest. A
variety of tools have been utilized to elucidate the electronic structure,
microscopic nature, and surface characteristics of rare earth metals, alloys, and
compounds. At the same time, theoretical models and calculations assist, and
are aided by, the experimental findings. Different extraction and purification
techniques, some of them unique, have made the so-called rare earths more
widely available and also of a higher purity than ever. The scientific investiga-
tions have led to a better understanding of the nature and properties of the rare
earths, which, in turn, is expanding their technological applications.
This volume is aimed at reviewing the important aspects of the science and
technology of rare earth materials, in depth and in contemporary terms. It
covers the entire spectrum from occurrence to applications of rare earths. The
concise, single volume is addressed to researchers and students by presenting an
up-to-date discussion of important topics involving the rare earths.
The occurrence, extraction, and production of rare earths are reviewed in the
first section, followed by purification methods employed for rare earths,
together with the role of impurities on their behavior.
The phase relations among the rare earth alloys, including a particular
reference to the technologically important rare earth-cobalt alloys, and phase
relations among the rare earth oxides are discussed in the second section. Defect
structures in oxides, as revealed by high-resolution electron microscopy, and the
theory of alloy formation have received special attention.
Studies of the electronic structure of rare earth materials are dealt with in the
succeeding two sections. The role of 4f electrons in the electronic structure of
these materials is crucial for understanding the systematics of their behavior.
Theoretical conceptions are set forth as well as the effect of crystal fields and
valence fluctuations on the properties of rare earth systems.
A wide variety of physical techniques such as NMR, Mössbauer, neutron
inelastic scattering, XPS, and TEP under high pressure are being employed to
elucidate the electronic structure and surface characteristics of the rare earth
xiii
XIV PREFACE
materials. A summary is provided of recent results obtained by these kinds of
studies.
In the final section discussion is presented of some of the extensive current
uses of rare earth materials such as in the steel industry and in permanent
magnets, as well as emerging applications in catalysis, hydrogen storage,
ferroelectrics, and fast ion conductors. The unique properties of rare earth
materials enable them to be cost-effective through miniaturization and energy
savings.
The various chapters in the book are substantially based on invited lectures
given at an Indo-U.S. Conference on Science and Technology of Rare Earth
Materials held at Cochin, India, March 3-8, 1980. The final versions of the
chapters benefited from the discussions at the conference attended by about 70
active workers in the field. The conference was sponsored by the Department of
Science and Technology, Government of India and supported by the U.S.
National Science Foundation. These and other who supported the conference
are separately acknowledged. Special thanks are due to Professor M. G. K.
Menor for constant encouragement and to Mr. M. A. Hadi, Mr. B. Para-
meswaran Nair, and their colleagues at the Indian Rare Earths Ltd. for the
excellent arrangements made for the Conference. We are grateful to the students
at the Indian Institute of Technology, Kanpur, in particular to E. M. T. Velu, N.
R. Bonda, and M. Mehra, as well as Nihal Ahmed, R. S. Misra, and Viswanath
Singh for assistance in bringing the volume together. Special thanks are also due
to Mrs. Laura Linck of the Department of Chemistry, University of Pittsburgh
for her fine assistance in typing many of the manuscripts. The cooperation of the
authors was, of course, essential and is greatly appreciated.
RARE EARTH RESOURCES, THEIR EXTRACTION AND APPLICATION
T. K. S. Murthy and C. K. Gupta
Bhabha Atomic Research Centre
Trombay, Bombay, India
1. INTRODUCTION
The "Rare Earths" consist of the sixteen elements - yttrium
(atomic number, Z=39) and lanthanum to lutetium (Z=57 to 71).
However, promethium (Z=61), a product of fission reaction, is
not found in nature. The remaining fifteen elements of this
group generally occur together in nature.
The account of rare earths can hardly begin without a
reference to some of their notable characteristics. Rare
Earths are well known for their chemical similarities. Table 1
summarizes some of the physical properties of the rare earths
(1,2). In general, density (with the exception of Eu and Yb),
atomic weight and hardness increase and ductility decreases as
the atomic number rises. The melting points with the excep
tion of Ce, Eu and Yb increase in a regular manner across the
series of Lu melting at almost twice the temperature needed
to melt La. All the metals with the exception of Eu, Sm, Ce
and Yb have close packed hexagonal structure at room tempera
ture. The metals become more oxidation resistant with decreas
ing atomic radius. Eu which has the largest radius is by far
the most reactive. The metal tarnishes almost immediately when
exposed to air at room temperature, particularly when the air
is moist, and turns to an oxide in a few days. Yb which has
the second largest radius is the lone exception and its reac
tivity with the atmosphere at room temperature falls between
that of Sm and Gd. The entire group listed in the lower part
of the Table can be classified as inert and can be stored in
air and will remain bright and shiny for years. All of the
rare earth metals, however, form very stable compounds with H2,
C, N2, 02/ S, P and the halides (Cl, F, Br and I). When hot,
the metals are among the best "getters" and will take the non-
metallic elements away from most other metals.
SCIENCE AND TECHNOLOGY OF 3 Copyright © 1980 by Academic Press, Inc.
RARE EARTH MATERIALS AH rights of reproduction in any form reserved.
ISBN 0-12-675640-6
Table 1. Some Physical Properties of Rare Earth Metals
Terres Absorption
trial Crystal cross-section
Chemical Atomic Atomic abund- Melting Boiling Density struc- for thermal
Name Symbol No. Weight ance Point Point ture neutrons Barns
(ppml C°C> (°C) Cg/cc) 10-2W
Yttrium Y 39 88,90 28 1522 3338 4.469 hep 1
Lanthanum La 57 138.91 18 918 3464 6,145 dhep 8
Cerium Ce 58 140,12 46 798 3433 6.770 fee 0
Praseodymium Pr 59 140.90 5.5 931 3520 6,773 dhep 11
Neodymium Nd 60 144.24 24 1021 3074 7,007 dhep 46
Promethium Pm 61 147.00 ~ 1042 3000* 7,260 dhep -
Samarium Sm 62 150.35 6.5 1074 1794 7.520 rhomb 5500
Europium Eu 63 151,96 1.0 822 1529 5.243 bee 4600
Gadolinium Gd 64 157.25 6,4 1313 3273 7.900 hep 4600
Terbium Tb 65 158.92 0.9 1356 3230 8.229 hep 44
Dysprosium Dy 66 162.50 4.5 1412 2567 8.550 hep 1100
Holmium Ho 67 164.93 1.2 1474 2700 8.795 hep 64
Erbium Er 68 167.26 2.5 1529 2868 9.066 hep 166
Thulium Tm 69 168.93 0.2 1545 1950 9.321 hep 118
Ytterbium Yb 70 173.04 2.7 819 1196 6.965 fee 36
Lutetium Lu 71 174.97 0.8 1663 3402 9,840 hep 108
hep - hexagonal close packed; dhep - double-C 1e xagonal close packed; rhomb - rhombohedral;
fee - face centered cubic; bee - body centered cubic.
*Estimated.
RARE EARTH RESOURCES 5
From the extraction point of view one finds many similari
ties between the rare earth metals and the refractory metals
like zirconium, titanium, niobium, tantalum, molybdenum and
tungsten. Rare earth metals, as will be seen from the summary
of their properties outlined above, are characterized by high
reactivity, similar to that of the refractory metals. Like
these, rare earth metals either react with or dissolve most
materials at sufficiently high temperature and this introduces
serious container problems. All these point out the unsuit-
ability of the conventional processes (as applied for the com
mon metals) to win the rare earth and the refractory metals.
As in the case of refractory metals the extraction of rare
earths involves application of specialized techniques and
processes. Today the rare earths are of great scientific and
technological interest and the rare earth industry is fairly
well established.
The extraction of rare earths covers four distinct areas -
(i) the mining and concentration of ore minerals, (ii) the
processing of the ores to obtain intermediate rare earth com
pounds of widely varying ranges of purity, (iii) the produc
tion of metals and alloys and (iv) the wide ranging applica
tion of rare earth products in traditional as well as sophis
ticated fields. This presentation attempts to review some of
these aspects briefly.
2. APPLICATIONS OF RARE EARTH METALS AND THEIR COMPOUNDS
Most of the traditional applications of rare earths in
industry are based on their similar chemical properties due
to essentially identical outer electronic configuration of
their atoms. For this purpose mixed rare earth compounds
obtained in anhydrous state by the first ore processing tech
niques are sufficient. Some of the major uses (3-7) in this
category are (i) rare earth chloride for misch metal produc
tion and incorporation in zeolite catalysts for petroleum
cracking, (ii) oxides for glass polishing, (iii) fluoride for
manufacture of arc carbons with well balanced light emission,
and (iv) rare earth metals and alloys for various metallurgical
applications.
The metallurgical applications of rare earth metals and
alloys form a sizeable industrial outlet (7-12). The main
application areas are summarized in Table 2.
More recent and sophisticated applications are based on
the specific properties of the individual rare earth products.
The difference in the 4f electrons of the rare earth atoms
play an important role here. One of the bulk uses of this
