Thermodynamic modeling of motlen salt solutions with multivalent cations having multiple coordination numbers

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Thermodynamic and phase equilibrium modeling of multicomponent systems is of great industrial importance nowadays. The metallurgical and chemical industries commonly use thermochemical packages to simulate chemical reactions and phase equilibria for process development. Multicomponent multivalent salts systems are widely used for the production and processing of metals. Al electrolysis, coating of refractory metals, the next generation of nuclear reactors, promising electrolytes for Ti production all depend on molten salt chemistry. The thermodynamic and phase equilibrium modeling of multicomponent salt systems consists in expanding the Gibbs energy of a phase as a function of T, P and composition and finding a global energy minimum. Model parameters of the Gibbs energy functions are obtained by optimizing their values to best reproduce simultaneously the experimental data found in the literature (enthalpy, liquidus, etc.). Parameters form a database and the models are used to predict phase equilibria and thermodynamic properties in the multicomponent system. The Gibbs energy models must agree with the ionic structure of the multicomponent melt (oxidation states and coordination of ions), especially for complex chloro-fluoride melts dissolving some oxide components with cations of variables valency as the NaF-KF-NaCl-KCl-TiFx-TiClx (x=2, 3, 4) system. The proposed project consists in developing models and databases of parameters for the prediction of phase equilibria (liquidus and eutectic temperatures, stable products, vapor pressures) and thermodynamic properties (activities, enthalpy, Cp) of multicomponent reciprocal salts systems of industrial importance, with the novelty of taking into account the coordination numbers and oxidation states of the ions as they changes with composition. Models will be developed for the NaF-KF-NaCl-KCl-TiF2-TiCl2-TiF3 -TiCl3-TiF4-TiCl4 and the AF-BeF2-ThF4-UF3-UF4-UF6 (where A is an alkali) systems. Solid solutions and pure compounds will also be integrated in the model. For the liquid solution, Ti and U will have several coordination numbers (4-8) and their relative stabilities with composition will be calibrated on measurements.