Thermodynamic Optimization And Calculation Of Phase Diagrams Related To The Rare Earth Halides And The Alkali Metal Ones

By using CALPHAD (Calculation of Phase Diagrams) technique the optimization and calculation of the binary systems related to rare earth halide and the alkali metal one were carried out in this thesis. Due to the characters of stronger interactivities of those systems (NdCl₃—MCl (M=Li, Na, K, Rb, Cs), TmCl₃—MCl (M= Na, K, Rb, Cs), LaBr₃—MBr (M=Na, K, Rb, Cs), DyCl₃-NaCl, LaF₃—NaF, YF₃-LiF), the new modified quasichemical model in the pair-approximation for short-range ordering developed by Pelton et al. was used. And for the first time the model was applied to the systems of REB3-MB (RE=Rare Earth, M=Alkali metal, B=Bromide, Fluoride). The calculated phase diagrams and thermodynamic properties are self-consistent. Based on database and literature data, some basic computer programs were employed in the course of optimization and calculation. According to the theory of self-consistence between thermodynamic parameters and phase diagrams, some thermodynamic models were chosen and constructed firstly. Then the measured phase equilibria data and experimental thermo-chemical properties were evaluated, at last the phase diagrams were optimized and described rationally. By comparing the calculated results and the experimental ones, we checked up some parts of experimental phase diagrams and mixing enthalpies in this work, and predicted completely mixing enthalpies of TmCl₃-MC(lM=Na, K, Rb, Cs)and parts of LaF₃—NaF, YF₃-LiF systems. Meanwhile the thermodynamic functions of some intermediate compounds were gotten. Further discussions about the calculated and experimental enthalpy of mixing in the systems were made: the enthalpy of mixing decreases with the increasing of the radius of alkali metal ion from Li⁺ to Cs⁺; moreover, the broad minimum values of the interactive coefficients were found at the 25% mole fraction of rare earths halides, which represented the characters of short-range ordering.