Phase Equilibria in the Systems UF 4 ‐ThF 4 and Li F‐UF 4 ‐ThF 4

As part of a study of materials potentially useful as fluid fuels for high‐temperature reactors, equilibrium diagrams for the condensed systems UF 4 –ThF 4 and LiF‐UF 4 –ThF 4 have been determined. Both thermal analysis and quenching techniques were used with phase identification accomplished by microscopic and X‐ray dsraction analyses. A complete series of solid solutions without maximum or minimum is formed by UF 4 and ThF 4 . Within the system LiF‐UF 4 –ThF, there occur three invariant points and seven primary phases of which four are ternary solid solutions. Optical properties for all the solid solutions, fractionation paths for the ternary solid solutions, and compatibility triangles for the ternary invariant points have been determined.