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W 2.1. PHASE EQUILIBRIUM STUDIES'
C. J. Barton R. E. Moore R. E. Thoma
H. Insley, Consultant
The several methods described in previous
reports of this series were used for further phase
equilibrium studies of a variety of binary, ternary,
and quaternary sysrems. Although the phase
diagrams are not considered to be final in every
respect, a compilation of the diagrams of binary
systems consisting of UF, or ZrF with each of
the alkali fluorides is presented here. The
striking differences observed in the diagrams for
these systems indicate a need for detailed study
of some of the complex crystal structures that
characterize certain of these materials.
The RbF-ZrF, and RbF-UF, systems now
appear to be moderately well described. A thermal
effect in the RbF-ZrF, system at 375OC that was
previously reported to be a eutectic temperature
has been shown to be a lowered inversion temper-
ature of the 2RbF-ZrF4 compound; the eutectic
contains 42 mole 75 ZrF, and melts at 41OOC.
Solvents with compositions near 35 mole % NaF,
25 mole % RbF, and 40 mole % ZrF, apparently
dissolve up to 4 mole X UF, at liquidus temper-
atures below 480OC and up to 7 mole % UF,
below 510OC. Such mixtures are of interest as
reactor fuels.
Detailed examinations of some ternary systems
containing BeF, are being made, While extremely
low melting points can be obtained (the lowest
eutectic observed to date in the NaF-LiF-BeFp
system melts at 31PC), it is not yet apparent
that these materials offer fuel mixtures that are
substantially better than those available in the
ZrF4-conta ining systems.
Studies of the phase behavior o
systems with alkali fluorides hav
These systems are of interest because of concern
over the behavior of fission-product fluorides in
hia
GENERAL COMPARISONS OF THE BINARY
SYSTEMS MF-ZrF, AND MF-UF,
R. E. Thoma
The two parallel families consisting of binary
systems of UF, and of ZrF, with each of the
alkali metal fluorides have been under investi-
gation here for several years, and the characteristics
of these systems are relatively well known.
In the course of this research many people have
contributed to an understanding of these phase
relationships, and the information on phase
behavior is scattered throughout a large number of
reports in this series. Accordingly it has seemed
worth while to prepare a brief summary of the
differences and similarities in these several
phase systems, No attempt has been made in this
concise compilation to give credit to those who
did the work.
Both these families of binary systems are much
more complex than a cursory examination would
indicate., It is obvious that fundamental studies
of the structures of the complex compounds
involved would be of general value. The large
number and wide variety of complex compounds
observed in these systems are indicated in
Table 2.1.1. (The ratios shown are the ratios
of the alkali fluoride component to the ZrF, or
the UF, component.) Comparisons of the phase
diagrams presented in Figs. 2.1.1, 2.1.2, and
2.1.3 display several of the striking characteristics
of these materials.
A stable, congruent, high-melting-point compound
(Fig.2.1.1) with the formula 3MF*ZrF, or 3MF.UF4
characterizes all the diagrams, except those for
LiF-UF, and NaF-UF,. For the LiF-UF s stem,
4 Y
which represents the lowest ratio of radius of
M+ ion to radius of M4+ ion, the 3:1 compound
does not exist; for this system, and this system
alone, an incongruent compound 4LiF*UF4 is
observed. In the NaF-UF, system the compound
3NaF*UF, is congruent but relatively low melting,
and it is unstable at temperatures below about
530OC.
'The petrographic examinations reported here were
performed by G. D. White, Metallurgy Division, and
T. N. McVay and H. Insley, consultants. The x-ray
examinations were performed by R. E. Thoma and
Be A. Soderberg, Materials Chemistry Division.
'The case of the related system KF-ThF4 Is similar.
The early concept of the system repated by E. P.
Dergunw, Dokhdy Akad Nauk S.S.S.R. 60, 1185-1188
(1948), was o simple one, but a more recent report by
W. J. Asker, E. R. Segnit, and A. W. Wylie, J. Cbem.
SOC. 1952, 4470, shows the system to be relatively
complex.
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