Modelling and calculation of the phase diagrams of the LiF–NaF–RbF–LaF 3 system

Abstract

Four ternary phase diagrams of the quaternary system LiF–NaF–RbF–LaF 3 were calculated from the data of LiF–NaF, LiF–RbF, LiF–LaF 3, NaF–RbF, NaF–LaF 3 and RbF–LaF 3 binary phase diagrams using the Kohler symmetric and Kohler–Toop asymmetric approximation. Excess Gibbs parameters of all six mentioned binaries were optimized using the experimental results taken from the literature. For the LiF–RbF system our own data were used. In all cases very good agreement between the experimental data and our optimized values was achieved. Excess Gibbs functions for the liquid phases were obtained using the modified quasi-chemical method based on quadruplet interactions and the excess Gibbs function for the solid solution was calculated by a sublattice model. The quaternary eutectic was determined and a set of pseudo-ternary systems with fixed ratio of LaF 3 was calculated in order to find the optimal composition for a molten salt fuel.