Phase Equilibria in the Ternary Fused‐Salt System LiF‐BeF ₂ ,‐UF ₄

Abstract

The phase diagram for the ternary fused‐salt system LiF‐BeF 2 ‐UF 4 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·6UF 4 , LiF·4UF 4 , and UF 4 covered most of the liquidus surface. Small areas of the liquidus surface were covered by the compounds BeF 2 , 2LiF·BeF 2 , and 4LiF·UF 4 . The compound 4LiF·UF 4 , which was stable at the binary liquidus temperature, decomposed in the ternary system when the liquidus temperature decreased below 480°C. No ternary compounds or solid solutions were observed. Two ternary eutectics were found. The first, containing 48 mole % LiF, 51.5 mole % BeF 2 , and 0.5 mole % UF 4 , melted at 350°C. The second, containing 69.5 mole % LiF, 22.5 mole % BeF 2 , and 8 mole % UF 4 , melted at 427°C.