Metal Hydrides

795 Pages·1968·21.637 MB·English

by  William M. Mueller, James P. Blackledge and George G. Libowitz (Eds.)

METAL HYDRIDES
EDITORS AND MAJOR CONTRIBUTORS
William M. Mueller
AMERICAN SOCIETY FOR METALS
METALS PARK, OHIO
James P. Bfackledge
DENVER RESEARCH INSTITUTE
UNIVERSITY OF DENVER
DENVER, COLORADO
George G. Libowitz
LEDGEMONT LABORATORY
KENNECOTT COPPER CORPORATION
LEXINGTON, MASSACHUSETTS
Prepared under the direction of the Division of Technical Information, United States
Atomic Energy Commission
®
ACADEMIC PRESS New York and London 1968
COPYRIGHT © 1968 BY ACADEMIC PRESS, INC.
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List of Contributors
Numbers in parentheses indicate the pages on which the authors' contributions begin.
Richard L. Beck, Collins Radio Co., Newport Beach, California (241)
James P. Blackledge, Denver Research Institute, University of
Denver, Denver, Colorado (1, 119, 441)
Coy L. Huffine, Systems Development Division, IBM Corporation,
Rochester, Minnesota (675)
George G. Libowitz, Ledgemont Laboratory, Kennecott Copper
Corporation, Lexington, Massachusetts (490, 545)
Charles B. Magee, Denver Research Institute, University of Denver,
Denver, Colorado (165)
William M. Mueller, American Society for Metals, Metals Park,
Ohio (21, 241, 336, 384)
Bernard Siegel, Aerospace Corporation, El Segundo, California (545)
Rudolph Spieser, The Ohio State University, Columbus, Ohio (51, 90)
Refer requests to:
U.S. Dept. of Energy
Office of Scientific and Technical Information
P.O. Box 62
Oak Ridge, TN 37831
Preface
Combinations of hydrogen with metals provide a widely divergent
group of materials that run the gamut from extremely unstable com-
pounds to quite stable alloy-like materials. In this book considerable
emphasis is placed on the theories of hydride formation as well as on
experimental procedures involved in the formation of hydrides, the
reactions that occur between hydrides and other media, and the
physical and mechanical properties of the several classes of hydrides.
The use of metal hydrides in the control of neutron energies is dis-
cussed, as are many other immediate or potential uses, e.g., in the
production of high-purity hydrogen and in powder metallurgy.
It is hoped that this book will serve as a valuable reference to stu-
dents, research professors, and industrial researchers in metal hy-
drides and in allied fields. Selected chapters may serve specialists
in other fields as an introduction to metal hydrides.
We have attempted to cover completely the field of metal hydrides.
D. T. Hurd, in An Introduction to the Chemistry of Hydrides, John
Wiley & Sons, Inc., New York, 1952, and D. P. Smith, in Hydrogen in
Metals, The University of Chicago Press, Chicago, 1948, did this
adequately many years ago, but these two books are now outdated.
Recent books by G. G. Libowitz (Solid State Chemistry of Binary
Metal Hydrides, W. A. Benjamin, Inc., New York, 1965) and K. M.
Mackay (Hydrogen Compounds of the Metallic Elements, Barnes &
Noble, Inc., New York, 1966) introduce the field of metal hydrides
to graduate students and nonexperts but make no attempt to be
comprehensive. In addition to the published literature, we have
reviewed all appropriate unclassified information from classified
documents.
Many people were involved, either directly or indirectly, in the
completion of this book, and it is impossible to recognize each of them
individually. We want to take this opportunity to thank our friends and
colleagues for their understanding, their suggestions, and their criti-
vii
Vlll PREFACE
cism, which have done much to sustain us during completion of the
manuscript.
This book was sponsored jointly by the Division of Technical In-
formation, U. S. Atomic Energy Commission, and the University of
Denver. We are grateful to James D. Cape, U. S. Atomic Energy Com-
mission, for his encouragement and guidance and to Dr. Shirley A.
Johnson, Jr., Director, Denver Research Institute, University of
Denver, for his patience and understanding of the monumental effort
involved. We are most appreciative of the efforts of Marie Fay, Mildred
Cain, Linda Hahn, and Frances Haverley, who contributed much to
the editing and reproduction of the manuscript. We also express our
gratitude to Dr. Charles Magee, Richard L. Beck, Dr. Rudolph
Speiser, Dr. Bernard Siegel, and Dr. Coy Hufflne, who contributed
significant chapters or sections thereof. Finally, we must acknowledge
and thank our families who also contributed, by their understanding,
to the completion of this book.
It is our hope that the information contained herein will be of
lasting and practical value to the metallurgist, inorganic chemist,
solid-state physicist, nuclear engineer, and others working with
chemical or physical processes involving metal-hydrogen systems.
WILLIAM M. MUELLER
JAMES P. BLACKLEDGE
GEORGE G. LIBOWITZ
September, 1968
CHAPTER 1
An Introduction
to the Nature and
Technology of Hydrides
JAMES P. BLACKLEDGE*
Recent interest in hydrides stems from their potential application
as moderator, reflector, or shield components for high-temperature
mobile nuclear reactors. Certain of the hydrided metals and alloys
have useful elevated temperature strength and stability and good
hydrogen retention and can be fabricated with relative ease. Thus,
in part, the limitations of most organic and inorganic hydrogenous
materials have been overcome. These important potential applica-
tions have tended to overshadow other equally significant uses for
metal hydrides, e.g., metathetical reactions, preparation of pure-
metal powders, surface coatings, and metal-ceramic seals.
The term"hydride" is used in this volume in the generic sense to
describe the binary combination of hydrogen and a metal or metalloid.
Gibb1 has defined a hydride as a compound in which there is a metal-
to-hydrogen bond. The importance of this definition lies in the nature
of the bond; some limitation is imposed by use of the term "com-
pound." Often, particularly for metallic hydrides, the reaction between
hydrogen and a metal results in a homogeneous phase of somewhat
variable composition and with properties (e.g., structure) that are dif-
ferent from those of the metal. Although there has been some con-
troversy as to whether such phases are compounds or solid solutions,
the definition will be broadly interpreted to include both definite
compounds and definable phases of variable composition where an
exact stoichiometric ratio does not exist.
* Denver Research Institute, University of Denver.
1
2 1 THE NATURE AND TECHNOLOGY OF HYDRIDES
There may be several reasons for nonstoichiometry in metal hy-
drides. Apparent deficiencies in hydrogen may be due to impurities
in the metal, to trace impurities in the hydrogen which inhibit the
uptake of hydrogen by the metal, or to incomplete hydriding during
formation of the hydride. The presence of dislocations also may have
an effect on stoichiometry. Variability in composition can be ex-
plained2 on the basis of such lattice imperfections as hydrogen vacan-
cies or interstitials. The electronic structure of the metal and the elec-
tron-to-atom ratio also are major factors in many cases. 3
1-1 CLASSIFICATION OF THE HYDRIDES
Generally, hydrides are classified by the nature of the hydrogen
bond into three principal categories, covalent or volatile, saline or
ionic, and metallic, each of which has distinct properties. Such clas-
sification is not always completely descriptive, however. For example,
lithium hydride, classified as a saline hydride, actually exhibits some
covalent characteristics. The rare-earth hydrides are usually classified
with the metallic hydrides; however, they do exhibit some character-
istics similar to those of saline hydrides (e.g., high heats of formation
and high resistivities at higher hydrogen contents). It is interesting
also to observe that europium and ytterbium (as might be expected
from comparison of their other properties) form ioniclike dihydrides
that are isostructural with the saline-alkaline-earth metal hydrides.
The binary hydrides formed by metals (and some of the semi-
metals) are shown in Fig. 1.1 in terms of the periodic table. In every
instance the theoretical stoichiometric formula is given although in
many cases this composition cannot be attained. Many of the tran-
sition metals, such as Re, Os, Fe, and Co, form complex hydrides con-
taining carbonyl and chelating groups. These are discussed in Chap.
12.
1-1.1 COVALENT HYDRIDES
Covalent hydrides may be solid (usually polymeric), liquid, or
gaseous. They exhibit considerable similarity in their properties. The
bond between hydrogen and the element is of the nonpolar electron-
sharing type where valence electrons are shared on a fairly equal
basis between the elements held by the bond. Large differences in
electric charge do not exist. In general, molecules of covalent hydrides
1-1 CLASSIFICATION OF THE HYDRIDES 3
Saline—
—Covalent —
1
IA II A IIIB IV B |
Series
of Boron
Li H (BeH2)n Hydrides
Covalent (See
Chap. 12)
Complex
Covalent Series
ΝαΗ MgH2 SCehea p. 12 (AlH3)n oHfy dSrii des
(See
Chap. 12)
III A IV A VA VI A v 11 J\/ V 111 Ά \ 1 ±3 11 r>
Series
TiH2 of Ge
KH CaH2 ScH2 (acnudb ic VVHH 2 CCrrHH 2 Mn Fe Co NiH CuH (ZnH2)n (GaH3)n (HSyeder ides
tetrag.)
Chap. 12)
ZrH2
RbH SrH2 YYHH23 (acnudb ic NNbbHH 2 Mo Tc Ru Rh PdH Ag (CdH2)n (ClnnHH)3n) n SSnnH2H4 6
tetrag.)
See HfH2
CsH BaH2 REaarreth (acnudb ic Ta H W Re Os Ir Pt Au (HgH2)n ((TTIIHH)3n) n PbH4
Series tetrag.)
LaH2_3 CeH2_3 PrH2_3 NdH2_3 P?m SSmmHH32 EuH2 GGddHH32 TTbbHH32 DDyyHH32 HHooHH32 EErrHH32 TTmmHH32 YYbbHH32 (?) LLuuHH32
ThH2 NpH2 PuH2 AmH2
AcH2 Th4H15 PaH3 UH3 NpH3 PuH3 A1T1H3 (?)
FiG. 1.1 Binary hydrides formed by metals in the periodic table.
are not strongly attracted to each other, and this absence of strong
intermolecular forces results in the high degree of volatility and low
melting points of the covalent hydrides. The covalent hydrides are
generally thermally unstable, such instability increasing with in-
creasing atomic weight of the parent element. These hydrides for the
most part are extremely toxic and burn readily in the air or in oxygen
with liberation of considerable quantities of heat. Typical covalent
hydrides are aluminum hydride, tin hydride, the boron hydrides, and
the germanium hydrides. The covalent hydrides are discussed in
detail in Chap. 12.
4 1 THE NATURE AND TECHNOLOGY OF HYDRIDES
1-1.2 SALINE HYDRIDES
Saline hydrides are formed by the reaction of the strongly electro-
positive alkali metals and alkaline-earth metals with hydrogen, which,
because of electron transfer, becomes strongly electronegative. In
contrast to the covalent hydrides, the bond of the saline hydrides
results from the strong electrostatic forces existing between the dis-
similar electric charges of the two ions. Therefore, saline hydrides are
highly polar. These saltlike hydrides are crystalline, exhibit high heats
of formation and high melting points, and are electrical conductors in
the molten state. The saline hydrides are more dense than the alkali
metals (45 to 75%) and the alkaline-earth metals (20 to 25%). This is
due to the strong attraction between the metal and the hydride ions
and, for the alkali-metal hydrides, to the more efficient packing of
atoms in going from the body-centered cubic structure of the metal to
the face-centered cubic structure of the hydride. Hydrides of the alkali
metals are isostructural with sodium chloride; hydrides of the alka-
line-earth metals have an orthorhombic structure that bears some
resemblance to the barium halides. The saline hydrides are discussed
in detail in Chap. 6.
1-1.3 METALLIC HYDRIDES
Figure 1.1 shows that metallic hydrides are formed by the transition
metals. They generally exhibit metallic properties in the accepted
sense; these include high thermal conductivity and electrical resis-
tivity, hardness, luster, and in some instances useful mechanical
properties. Unlike metals, however, they are usually quite brittle.
For example, when massive uranium is hydrided, the reaction pro-
ceeds rapidly and efficiently at reasonably low temperatures to the
formation of finely powdered UH . Yttrium, on the other hand, may
3
be hydrided to form the massive dihydride YH , which possesses
2
useful mechanical properties, or it may be hydrided completely to
the trihydride YH , which forms as a finely divided friable material.
3
Because of the wide homogeneity ranges of most of the metallic
hydrides, they have sometimes been considered as solid solutions of
hydrogen in the metal. That this is not so can be seen in Table 1.1,
which shows that the structures of the hydrides are distinctly different
from those of the parent metal. Cerium, nickel, actinium, and palla-
dium do not change structure on hydriding, but they do undergo dis-
continuous increases in lattice parameter. Compound formation in
TABLE 1.1
STRUCTURES OF METALS AND CORRESPONDING HYDRIDES 0
Metal Metal sublattice
Metal structure' Hydride in hydride0
Ti, Zr, Hf H.c.p. TiH2, ZrH2, HfH2 F.c.c, f.c.t.
V B.c.c. VH B.c.t.
VH2 F.c.c
Nb B.c.c. NbH B.c.c, b.c. ortho-
rhombic
NbH2 F.c.c.
Ta B.c.c. TaH B.c.t., b.c. ortho-
rhombic
Cr B.c.c. CrH Hexagonal
CrH2 F.c.c
Ni F.c.c. NiH F.c.c
(flo = 3.52 Â) («o = 3.72 A)
Pd F.c.c. PdH F.c.c
(tfo = 3.89 Â) (a0 = 4.03Â)
La, Pr, Nd, Sc H.c.p. LaH2, PrH2, NdH2, F.c.c
ScH
2
Ce F.c.c. CeH2 F.c.c.
(cio = 3.52 Â) (a0 = 5.58A)
Sm Rhombohedral SmH2 F.c.c
SmH3 Hexagonal
Gd through Tm, H.c.p. Dihydrides F.c.c.
Lu, T Y
Trihydrides Hexagonal
Eu B.c.c. EuH2 Orthorhombic
Yb F.c.c. YbH2 Orthorhombic
(«0 = 5.49 Â) YbH2+8 F.c.c
(a = 5.19Â)
0
Ac F.c.c. AcH2 F.c.c.
(«0 = 5.31 Â) (fl0 = 5.67Â)
Th F.c.c. ThH2 F.c.t.
Th H B.c.c. (complex)
4 15
Pa B.c.t. PaH ß-W (cubic)
3
U Orthorhombic jS-UH j8-W (cubic)
3
a-UH B.c.c.
3
Pu Monoc linic PuH3 F.c.c.
PuH Hexagonal
3
Li, Na , K, B.c.c. LiH, NaH, KH, F.c.c
Rb, «C s RbH, CsH
Ca, Sr F.c.c. CaH2, SrH2 Orthorhombic
Ba B.c.c. BaH2 Orthorhombic
a From G. G. Libowitz, The Solid State Chemistry of Binary Metal Hydrides, p. 45,
W. A. Benjamin, Inc., New York, 1965.
b H.c.p., hexagonal close-packed; b.c.c, body-centered cubic; f.c.c, face-centered
cubic; f.c.t., face-centered tetragonal; j8-W, ß-tungsten structure; b.c.t., body-centered
tetragonal.
5