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13. FB u orate
13.1 PHASE RELATIONS
IN FLUORQBORATE SYSTEMS
C. J. Barton J. A. Bornrriann'
L. 0. Gilpatrick H. Insley'
T. N. McVay2
H. H. Stone
Interest in low-melting, low-cost molten salts
for use as the coolant in molten-salt breeder
reactors has prompted reexamination of phase relations
in fluoroborate systeins. The system NaBF4-
KSF, was studied earlier at this Laboratory,
while Selivanov and Stender, reported low-melting
eutectics in the systems NaF-NaBF, and KF-
KHF,. More recentiy, Pawlenko' investigated the
ternary system KUF,-KF-KBF,OH and its associated
binary systems. Varying melting points
reported in the literature for the compounds NaBF,
and KWF, indicated the need for pure compounds
and care in heating them to prevent hydrolysis or
loss of BF3.
We found that recrystallization of commercial
preparations of NaBF, and KBF, from dilute
hydrofluoric acid solutions, usually 0.5 hi', gave
compounds with higher melting points than any
previoiusly reported. We find 569'C for KEF,
(previous high, 552O)' and 406°C for NaBF,
(previous high, 368"). The differential thermal
analysis (DTA)6 melting curve for KBF, was much
'Research participant from Lindenwood College, St.
Charles, hlo.
2Consul tan t.
,R. E. Moore, J. G. Surak, and U'. I