Phase equilibria in the systems BeF2-ThF4 and LiF-BeF2-ThF4

Abstract

As a part of a study of materials potentially useful as fluid fuels of high temperature nuclear reactors, equilibrium diagrams for the condensed systems BeF2-ThF4 and LiF-BeF2-ThF4 have been determined. Both thermal analysis and quenching techniques wire used with phase indentification accomplished by petrographic and X-ray diffraction analysis. The system BeF2-ThF4 contains a single eutectic at 2.0 ThF4 (mole %), melting point 527 ± 3°. In association with primary phase fields of the three components and five binary compounds there occur six ternary invariant points within the system LiF-BeF2-ThF4. Of these, only one invariant point is a eutectic. Unusual solid miscibility occurs in the compound 3LiF·ThF4 which appears as a single phase solid solution within the area bounded by 75 LiF, 25 ThF4-58 LiF, 16 BeF2, 26 ThF4-59 LiF, 20 BeF2, 21 ThF4 (mole %).