ORNL-1771 - Oak Ridge National Laboratory

or nearly pure, UF,. Recent studies of LiF-UF,
mixtures have confirmed the belief" that no com-
pounds form and that these materials comprise a
simple eutectic system. A partial phase diagram
for this simple system is shown as Fig. 5.3.
The NaF-UF, system has been studied more
thoroughly than any other binary alkali-metal
fluoride-UF3 system. The best thermal analysis
data obtained for this system (data obtained with
those mixtures which showed the least evidence of
contamination of the melt by tetravalent uranium)
are shown in Fig, 5.4. The earlier data, ob-
tained by mixing NaF with previously synthesized
UF, in sealed capsules, are shown by open circles.
The more recent data, shown by solid circles, were
I2L. M. Bratcher et ul., ANP Quur. Prog. Rep. June 10,
1954, ORNL-1729, p 43.
l3V. s. Coleman and w. c. Whitley, ANP Qum. frog.
Rep. Sept. 10, 1952, ORNL-1375, p 79.
14W. C. Whitley, V. S. Coleman, and C. J. Barton, ANP
Qum. Prog. Rep. Dec. 10, 19S2, ORNL-1439, p 109.
Ir.
OANL-LA-OWG 29;
0 10 20 30 40 50 60 7C
UF, (mole Z)
Fig. 5.3. Tentative Partial Phase Diagram of
the LiF-UF, System.
PERIOD ENDING SEPTEMBER 70, 7954
obtained by reducing NaF-UF, mixtures with ex-
cess uranium in open crucibles protected by an
atmosphere of helium. Some data, also obtained
during the past quarter, were obtained by a method
which represents a compromise between the two
previously mentioned methods. Mixtures were pre-
pared in open stirrer-equipped crucibles by combin-
ing dry NaF with freshly prepared" UF,: These
data are indicuted in Fig.5.4 by the solid triangles.
The agreement between the data obtained by the
various methods is considered to be gratifying, in
view of the difficulties associated with the ease of
oxidation of U3+ to U4'. The identification of the
compound is based chiefly upon the results of
petrographic examination of slowly cooled melts.
The possibility that the compound might be Na,UF,
rather than Na,U,F, and the possibility that
appreciable quantities of UF, may be "hidden" in
these materials have not been completely ruled out
by these studies. Very few compositions contain-
ing more than 50 mole % UF, have been prepared,
and the data in this part of the system are probably
of little value.
*
ORhL-LR-DWG 2924
PREPARED :N Opt3
0 5 IO $5 20 25 30 35 40 45 50
UF3 (mole %I
Fig. 5.4. Tentative Partial Phase Diagramof
the NaF-UF, System.
Phase equilibrium studies of the KF-UF, and
RbF-UF, systems are not so far advanced. It
appears that the most probable compositions for
the compounds observed are K3UF,, K,U,F, and
Rb,UF, md that the KF-K,UF, eutectic melts at
about 720°C at approximately 15 mole % UF,. It
"Prepared by W. C. Whitley, July 1954.
59