ORNL-1816 - the Molten Salt Energy Technologies Web Site

ANP QUARTERLY PROGRESS REPORT
58
4emtr
ORNL-LR-DWG 3398
' I035'C
Fig. 5.1. Phase Diagram of the NaF-ZrF,-UF,
System.
rests, on a nickel wire support, which, in turn,
rests on a movable nickel platform at the bottom
of the hole. Temperatures are determined at 11
points along the sample length by means of thermo-
couples and can be varied by adjustment of the
various furnace windings. By moving the platform
to one side with a handle above the furnace, the
capsule and wire support are allowed to fall into
an oil quenching bath.
Phase Relationships in UF3-Bearing Systems
R. E. Moore R. E. Thoma
Mater io Is Chemistry Division
H. Insley, Consultant
Study of UF,-bearing systems has been con-
tinued on NaF-ZrF,-UF,, NaF-UF,, KF-UF,, and
ZrF,-UF4-UF, mixtures. In addition, work was
begun on NaF-LaF, and KF-LaF, systems, since
LaF, is known to be a stable "stand-in" for the
more difficultly handled UF,. Work on the KF-UF,
mixtures has revealed that a red phase, formerly
designated as K,UF, may have as much as 75%
of the uranium in the tetravalent state; its apparent
homogeneity over a wide range of U3'/U4' is
possibly due to a solid solution of K,UF, and
K,UF,. The existence of the latter has yet to be
demonstrated. It is now thought that NaUF,, rather
than Na,U,F9, as previously postulated, is the
empirical formula of an incongruently melting
compound in the NaF-UF, system.
UF, in ZrF4-Bearing Systems. Studies of ZrF4-
UF,-UF, mixtures were reported earlier.,', The
more recent of the reports4 indicated a probable
composition of 50 mole % ZrF4-25 mole % UF,-25
mole % UF, for a brownish, slightly birefringent
phase noted in this system. Recent studies of
mixtures in this system that were prepared by
adding uranium metal to ZrF,-UF, mixtures and
stirring the partially reduced melts until they
solidified indicated that the mixture with the above
composition consists of two phases, while a
mixture containing 33.3 mole % ZrF,-33.3 mole %
UF,-33.3 mole % UF, is essentially a single-
phase brownish crystalline material that is be-
lieved to be a compound. Another phase observed
at higher ZrF, concentrations, usually described
as olive-drab, appeared to be the only phase
present in a mixture containing 75 mole % ZrF,-
. - - -
12.5 mole % UF,-12.5 mole % UF,. All these I
compositions are theoretical compos it ions based
upon complete reaction between UF, and uranium J .
metal in the molten material. The meager analyti-
cal data available for such mixtures indicate that
the reactions probably did not go to completion in
all cases, and so the percentage of UF, is likely
to be higher and the percentage of UF, lower than
are shown by the formula.
In the NaF-ZrF,-UF, system, four compositions
were prepared along a join connecting the minimum
melting compositions in the NaF-ZrF, binary (42
mole % ZrF,; mp, 500°C) and the NaF-UF, binary
(29 mole % UF,; mp, 715OC). Liquidus tempera-
tures determined by thermal analysis for the
mixtures containing 5, 12, 20, and 25 mole % UF,
were 650, 775, 865, and 775OC, respectively. The
25 mole % UF, mixture contained free UF, in
addition to the NaF-UF, complex and Na,ZrF7.
KF-UF, System. Earlier studies of KF-UF,
mixtures5 indicated the existence of two com- -
plexes. A red crystalline phase observed as the
3V. S. Coleman, C. J. Barton, and T. N. McVay, ANP 5 -
Quar. Prog. Rep. June 10, 1953, ORNL-1556, p 41.
4C. J. Barton et aL. ANP Quar. Prog. Rep. Sept. 10,
1953, ORNL-1609, p 57.
5C. J. Barton et al., ANP Quar. Prog. Rep. Sept. 10,
1954, ORNL-1771, p 59.
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