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ANP PROJECT PROGRESS REPORT
LiF
845
EUTECTIC
649
ternary eutectics shown in each of the three
compatibility triangles. There is a limited solid
solution region in the ternary system for a high-
temperature modification of 2NaF*BeF2, which is
not indicated on the diagram. It is not likely that
the limits of this region can be accurately de-
termined with the experimental methods now being
used.
The phase which was previously9 believed to
be a ternary compound and which was tentatively
assigned the formula LiF-7NaF*4BeF3 was
identified by G. D. White through the use of high-
temperature x-ray diffraction as a polymorph of
2NaF-BeF2. This phase, which is stable above
320°C, had not been reported in previous investi-
gations of the NaF-BeF, system10,l1 and had not
been found in quenched samples of NaF-BeF,
mixtures examined in this laboratory because its
inversion is too rapid for it to be quenched in the
EUTECTIC
'L. M. Brotcher, R. E. Meadows, and R. J. Sheil,
ANP Quar. Prog. Rep. March 10, 1956.ORNL-2061, P 75.
'E. Thilo and F. Liebau, Z. physik Chem. 199,
125-141 (1 952).
"De M. Roy, R. Roy, ond E. F. Osborn, I. Am.
Ceram SOC. 3605) 185 (1953).
88
Fig. 2.1.6. The System NaF-LiF-NaF*BeF,.
No F . BeF,
380
TERNARY EUTECTIC
-
ORNL-LR-DWG 14634
NoF
995
binary system. It is, however, stabilized by the
addition of LiF, with which it undoubtedly forms
a limited solid solution.
Quenching experiments with compositions on the
LiF-2NaF-LiF*2BeF2 join on both sides of the
mixture NaF-LiF-BeF, (37-26-37 mole %) show
this mixture to have approximately the compo-
sition of the eutectic which melts at about 340%
Petrographic and x-ray diffraction examinations
of quenched samples and slowly cooled prepa-
rations show that the 2NaF*LiF.2BeF2-2NaF*BeF,
join is a quasi-binary system with a eutectic
that contains 45 mole % NaF, 16.5 mole % LiF,
and 38.5 mole 95 BeF, and melts at about 343OC.
A phase that appeared at a tempe
about 32OoC in quenched samples was assigned
the formula 5NaF-LiFSBeF, because the x-ray
diffraction pattern of a quenched sample of this
composition was not found to contain lines that
could be assigned to any other known phase in the
system. The conclusion that this compound
exists only below the solidus temperature is
based on the following evidence. First, slowly
cooled preparations within the 2NaF*LiF-2BeF2-