Thermodynamic assessment of TbBr3 unary and NaBr-TbBr3 binary system

As a basis for the design and development of molten salt mixtures, thermodynamic calculations of the phase diagram and thermodynamic properties were carried out on the TbBr3 unary and NaBr-TbBr3 binary systems over the entire temperature and composition range, respectively. The Gibbs energy of TbBr3 was evaluated using an independent polynomial to fit the experimental heat capacity, the thermodynamic parameters for each phase in the NaBr-TbBr3 system were optimized by using available experimental information on phase diagram and thermodynamic properties. A two sub-lattice ionic solution model (Na+)P: (Br−, TbBr63−, TbBr3)Q for the liquid phase and Neumann-Kopp rule for the stoichiometric compound Na3TbBr6 were adopted to reproduce the experimental data with reasonable excess Gibbs energy. Comparisons between the calculated phase diagram and thermodynamic quantities show that all reliable experimental information is satisfactorily accounted for by the present thermodynamic description.