Binary Pb Alloy Structure And Properties Of Molecular Dynamics Simulations And Vacuum Distillation Experiments

Molecular dynamics has become one of the key methods in researching the structure of the melt because it can simulate the macroscopic properties and can collective lots of microcosmic information. Microstructure, thermodynamic and transmission properties of the alloy at high temperature are all important parameters for the structure and properties of solid state alloy, and also effect the separation and purification progress of the alloy and become the focus of the present molecular dynamics reserch. Microstructures, clusters, thermodynamic properties, and diffusion properties of Pb-Cu, Pb-Au, Pb-Ag and Pb-Mg alloy were simulated at this research. And also did systemic vacuum distillation experiments for Pb-Cu, Pb-Ag and Pb-Au binary alloy to explore the effcte of Microstructures and diffusion properties on vacuum distillation of binary alloy. The central work and conclusion of this paper includes:Firstly, we simulate the melting process for Pb-Cu, Pb-Ag, Pb-Au and Pb-Mg binary alloy. The pair correlation function, correlation radius, coordination number and atomic number of the cluster were calculated. With the parameter of the pair correlation function, atmic interaction was analyzed. The vatiations of the coordination number with content of Pb are discussed, and compared the bond of homologous and heterologous atom by coordination number. With the correlation radius the cluster and the vatiations of the disorderd region in binary alloy with content of Pb are discussed. The height of the first peak in the partial pair correlation function was used to analyze the content of Pb dependence of crystallization of Cu cluster.Enthalpy of formation, cohesive energy and formation energy at different temperature were calculated and agreed well with the experimental value. Formation energy of Pb-Cu, Pb-Au and Pb-Ag alloy at the same temperature and the same lead content was compared, formation energy of Pb-Ag and Pb-Cu alloy are positive so the alloy belong to positive deviation system, the Pb-Au alloy belong to negative deviation system. With the temperature increased, the deviation degree decreased and the alloy approaches to ideal melt. Formation energy of Pb-Cu alloy is higher than that of Pb-Ag alloy at the temperature, namely the deviation degree of Pb-Cu alloy is higher than that of Pb-Ag alloy.Diffusion properties of liquid pure Cu, Ag, Au and Pb were calculated and compared with the experimental ones, calculation errors of four pure metals are less than 1.9% near the melting point. Activation energy and pre-factor of self diffusion were calculated and agree well with the experimental values, high calculation precision of self diffusion coefficient appears in this paper.A new method to calculate the mutual diffusion coefficient was proposed based on molecular dynamics and NRTL thermodynamic equation. At first, self diffusion coefficient was calculated with molecular dynamics, then thermodynamic factor was calculated with NRTL equation, mutual diffusion coefficient was obtained with Darken equation. Mutual diffusion coefficients of Pb-Cu, Pb-Mg, Pb-Au and Pb-Ag alloy at different temperature were obtained in this paper and the calculated value agrees well with the experimental one. Influencing factors to diffusion coefficient was analyzed with crystallization, cluster and the bond of atom influence the self and mutual diffusion coefficients. The relevance of the two component was calculated, we can obtian form the result that the relevance of the two component are determined by the number of heterologous atom bond, the more numbers of heterologous atom bond the stronger relevance we have.Vacuum distillation experiments were carried out with Pb-Cu,Pb-Ag and Pb-Au binary alloy, from the result we can see Pb-Cu,Pb-Ag and Pb-Au binary alloy can separate well with vacuum distillation method, some special experiment phenomena were observed, and analysed with microstructure of melt and diffusion coefficients.The mass flux and evaporation velocity of Pb in binary alloy were calculated and compared, when the concentration difference of Pb in residuum is 1%-5%, the mass flux and evaporation velocity is similar, the evaporation velocity of Pb in binary alloy was controlled by the mass flux. When the concentration difference of Pb is 5%-10%, the mass flux is less than the evaporation velocity of Pb, but the differences between them are not so significant, so the evaporation velocity of Pb in binary alloy was controlled by the mass flux and the temperature, and the effect of the mass flux makes a big difference compared with that of the temperature. When the concentration difference of Pb is more than 10%, the mass flux is much less than the evaporation velocity of Pb, which means the evaporation velocity of Pb in binary alloy was controlled by the temperature.