The phase diagram for the ternary fused-salt system LiF-BeF2-UF4 was determined from 300°C to the liquidus by differential thermal analysis, thermal-gradient quenching studies, and high-temperature filtration techniques. The samples prepared by quenching were examined by polarized-light microscopy and X-ray diffraction techniques. The experimental methods are described. The primary-phase fields for the compounds LiF, 7LiF.6UF4, LiF.4UF4, and UF4 covered most of the liquidus surface.Small areas of the liquidus surface were covered by the compounds BeF,, 2LiF.BeFz, and 4LiF.UF4. The compound 4LiF-UF4, which was stable at the binary liquidus temperature, decomposed in the ternary system when the liquidus temperature decreased below 48OOC. No ternary compounds or solid solutions were observed. Two ternary eutectics were found. The first, containing 48 mole yo LiF, 51.5 mole yo BeFz, and 0.5 mole yo UF4, melted at 350°C. The second, containing 69.5 mole yo LiF, 22.5 mole yo BeF,, and 8 mole % UF,, melted at 427°C.
The phase equilibrium diagram for the ternary fused‐salt system NaF–BeF2–UF4 was based on evidence from differential thermal analysis, polarized light microscopy, and X‐ray examination of samples obtained from thermal‐gradient quenching studies and from high‐temperature filtration experiments. All the stable compounds in the binary systems NaF–BeF2 and NaF–UF4 displayed primary‐phase fields in the ternary system, including a new subsolidus compound which was observed and tentatively assigned the formula NaF · 4UF4. No ternary compounds or solid solutions were observed. The following three eutectics were found in the ternary system: (1) 72.5 NaF, 17.0 BeF2, and 0.5 mole % UF4 at 486°C, (2) 56.0 NaF, 43.5 BeF2, and 10.5 mole % UF4 at 339°C, and (3) 43.5 NaF, 56.0 BeF2, and 0.5 mole % UF4 at 345°C.
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