Molecular Dynamics Simulations Of Common-Cation Alkali Halide Molten Salt

Fused alkali halide is of technological and theoretical importance and as such has attracted considerable interest. But due to its high temperature and severe cauterization, its structure and properties are difficult to accurately describe through some conventional physical or chemical methods. As calculating and computer techniques are developing fast, people shift more and more attention to research into the structure and properties of molten salt liquor by computer simulations. Molecular dynamics (MD) method, an important way of computer simulations, can not only help apprehend and explain the experimental data on a micro level, but also excel when such a simulation can't be done laboratorially or when the laboratorial cost is too high. MD has become a vital implement for the research on the molten salt and its liquor theory. The simulation results are very important for understanding the interaction and structure between the particles in the molten salt and its liquor.In 1970's and 1980's, comprehensive investigation has been done on molten pure alkali halides using MD. Micro details on an atomic level and statistical thermodynamics properties obtained from MD have given a valuable insight on experimental results and validated the theories about pure alkali halide melts. MD simulations on the mixing effects of binary molten alkali halides are mainly concentrated on common-anion systems and there is satisfactory coincident with experimental and theoretical results. But there is very little investigation on common-cation systems, and that there are many discrepancies between experimental and simulation results. Furthermore, the experimental observation is inconsistent with that of theoretic analysis. As yet, the mixing effect of commom-cation molten alkali halides is still in doubt.The main work of this dissertation is to put forward the sound modification through potential functions. By using the potential functions, Md simulation of three binary common-cation molten alkali halides KF-KCl, NaF-NaCl and KF-KI is done. The simulation has revealed that the problem can be solved qualitatively, and the quantification can be accorded. Contents of this thesis are following:In Chapter 1, the development and the status quo of molecular dynamics method and alkali halide are reviewed.In Chapter 2, aspects of MD methods to be adopted in the simulation,including the concepts, hypothesis, arithmetic techniques, data analysis methods, steps and procedures are analyzed.In chapter 3, the Fumi-Tosi potential function of alkali halide and its general potential parameters are analyzed in detail for their vital roles in MD which indicates the Mayer's Van der Waals coefficient Cij,Dij is small and thehardness parameter of short range repulsive potential needs revised. We introduced a new series of Van der Waals coefficient and had the repulsive parameter recalculated. The basic radius which we got is consistent with Fumi-Tosi's while the short range repulsive potential hardeness parameter changed. Meanwhile, we discussed methods of achieving mixing alkali halide's potential parameter.In chapter 4, the mixing effects in molten KF-KCK NaF-NaCl and KF-KI mixtures are studied at 1273K over the full concentration range by MD simulation, respectively. Two series parameters are adopted in the simulation.Calculations of the excess mixing enthalpy reveal: if by Tosi-Fumi's and Mayer's parameters, the excess mixing enthalpy is consistent with the Kleppa's experiment at the big ion end; if by Tosi-Fumi's and Jain et al's parameters, the excess mixing enthalpy accords with the Kleppa's experiment at both ends. Three conclusion may be drawn from these preliminary results: (1) the contribution of coulomb force and non-coulomb force to the excess mixingenthalpy are equivalent, which is consistent with Kleppa's experiments on binary alkali halide containing fluoride; (2) the former underestimates non-coulomb force's contribution to the enthalpy mixture, which accords with Ree and Holt's theoretical analysis and also with our disc...