Phase Equilibria in the Alkali Fluoride-Uranium Tetrafluoride Fused Salt Systems: III, The System NaF–LiF–UF4

The phase equilibrium diagram of the ternary system NaF–LiF–UF₄ described in this paper is based on evidence from thermal analysis and from microscopic and X-ray analyses of samples obtained from thermal gradient quenching experiments. Temperature-composition relations were established through the temperature interval between the liquidus and a lower limit of about 300°C. All the stable compounds in the binary systems LiF–UF₄ and NaF-UF₄, (including the subsolidus compound NaF·2UF₄) display primary phase fields in the ternary system. No ternary compounds of NaF–LiF–UF₄ occur. The following eutectics are to be found in the ternary system: 60 NaF, 21 LiF, 19 mole % UF₄, 480°C.; 35 NaF, 37 LiF, 28 mole % UF₄, 480°C.; 24.3 NaF, 43.5 LiF, 32.2 mole % UF₄, 445°C.; and 24.5 NaF, 29 LiF, 46.5 mole % UF₄, 602°C. The compounds 7NaF · 6UF₄ and 7LiF · 6UF₄ display limited solubility in each other. The exact limits of the miscibility gap in the 7NaF · 6UF₄-7LiF · 6UF₄ join have not been determined.