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Phase Equilibria in the Alkali Fluoride‐Uranium Tetrafluoride Fused Salt Systems: II, The Systems KF‐UF 4 and RbF‐UF 4
Author(s) -
THOMA R. E.,
INSLEY HERBERT,
LANDAU B. S.,
FRIEDMAN H. A.,
GRIMES W. R.
Publication year - 1958
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1958.tb12912.x
Subject(s) - eutectic system , chemistry , molten salt , alkali metal , fluoride , analytical chemistry (journal) , salt (chemistry) , phase (matter) , uranium , inorganic chemistry , mineralogy , materials science , crystallography , metallurgy , chromatography , organic chemistry , microstructure
Mixtures of alkali fluorides with uranium tetra‐fluoride are of potential importance in molten‐salt reactors and in the reprocessing of nuclear fuels. In this paper detailed phase diagrams are presented for the binary systems KF‐UF 4 and RbF‐UF 4 . Data for the determination of phase boundaries were obtained in large part by quenching after equilibration. Thermal analysis and visual observation were used as supplementary methods. Phase identifications were made by X‐ray powder diffraction and by optical microscopy. In the system KF‐UF 4 four compounds have been identified. Two of these, 3KF.UF 4 and 7KF.6UF 4 , melt congruently at 957°C. and at 789°C., respectively. The compound 2KF UF 4 melts incongruently to 3KF.UF 4 and liquid at 755° C., and the compound KF.2UF 4 melts incongruently to UF 4 and liquid at 765° C. There are three eutectic points in the system: 15.0 mole % UF 4 , 735° C.; 38.5 mole % UF 4 , 740° C.; and 54.5 mole % UF 4 , 735° C. The compound 2KF.UF4 decomposes during cooling to 3KF.UF 4 and 7KF 6UF 4 at 608° C. Two other compounds, KF 3UF 4 and KF.6UF 4 , have been described by another investigator. One of these, KF 3UF 4 , was not obtained at all in the present investigation. The other, KF.6UF 4 , was not obtained under equilibrium conditions and was found only in KF‐UF 4 mixtures that had been exposed to the atmosphere while molten. Seven solid compounds are present in the system RbF‐UF 4 . All of these melt incongruently with the exception of 3RbF.UF 4 and RbF‐UF 4 , which melt at 995° C. and at 735° C., respectively. The incongruently melting compounds and their melting points, peritectic compositions, and melting products are: 2RbF UF 4 , 818°C., 38 mole % UF 4 , 3RbF ‐UF 4 + liquid; 7RbF.6UF 4 , 693° C., 44 mole % UF 4 , RbF.UF 4 + liquid; 2RbF.3UF 4 , 722° C., 56.5 mole % UF 4 , RbF.3UF 4 + liquid; RbF. ‐3UF 4 , 73O°C., 57 mole % UF 4 , RbF.6UF 4 + liquid; and RbF.6UF 4 , 832°C., 70.5 mole % UF 4 , UF 4 + liquid. The three eutectic temperatures and compositions in the system are: 10.0 mole % UF 4 , 710°C.; 43.5 mole % UF 4 , 675°C.; and 55.0 mole % UF 4 , 714°C.