Molecular Dynamics Simulation And Vacuum Distillation Of Pb - Sb Alloy

It will be of great importance to recycle Pb-Sb and Pb-Sb-Sn alloys produced from the smelting process and their consumption process. Vacuum distillation has many advantages such as short flow sheet, pollution-free and high metal recoveries and so on, which makes it widely applied in the area of secondary material recovery. Pb, Sb and Sn can be obtained by treating the Pb-Sb-Sn alloy with the method of vacuum distillation, however, the mechanism concerning how the alloy of Pb-Sb and Pb-Sb-Sn changes during the distillation process is yet to be thoroughly investigated. And some phenomena like the separation of Pb and Sb is affected by the azeotropy of Pb-Sb alloy are yet to be explained. Consequently, it will be of great scientific values for the vacuum distillation of Pb-Sb alloy by conducting researches investigating the structure and properties of Pb-Sb alloy and the electronic properties of Pb-Sb alloy. In this thesis, with the help of computer simulation, the structure and property of Pb-Sb, Pb-Sb-Sn liquid state alloy was investigated by adopting ab initio molecular dynamic, furthermore, comparison and verification of the results was performed by the Pb-Sb alloy vacuum distillation experiments.Activity and activity coefficients for Pb-Sb under different temperatures (923K,973K, 1073K,1173K,1273K and 1373K) were predicted by MIVM. Pb-Sb activity coefficients were used to calculate separation coefficient and vapor-liquid phase equilibrium composition, which decide whether Pb-Sb could be separated by vacuum distillation in thermodynamics. When the pressure was maintained at 10Pa and the temperature was set during 923-1373K, the evaporation rate of Pb-Sb alloy was calculated, and the instantaneous gas composition under the same conditions was predicted accordingly.Furthermore, dynamic simulation concerning the liquid state structure, surface structure of Pb-Sb binary alloy as well as the liquid structure of Pb-Sb-Sn ternary alloy was conducted by employing the ab initio molecular dynamic. And structure optimization of Pb-Sb binary alloy gas state cluster was performed. What’s more, dynamic simulation of the stable cluster obtained was also conducted. The result indicates that when the pressure was maintained at 10Pa, the temperature was kept at 1073K,1173K,1273K and 1373K, the maximum atom force and highest stability of Pb-Pb, Sb-Sb and Pb-Sb could be achieved when the liquid structure of Pb-Sb binary alloy was distributed during the range of Pb-22%Sb, Pb-15%Sb, Pb-20.5%Sb, Pb-11.8%Sb and Pb-17.7%Sb. The stable components of alloy melt changes according to the change of temperaure, and it is difficult to separate the Pb-Sb alloy by vacuum distillation when these stable components exist under these conditions. The stability of Pb-22%Sb in Pb-Sb binary alloy surface structure was higher than that of Pb-17.7%Sb when the pressure was miantained at 10Pa and temperature ws kept at 1073K, which is consistent with the simulation results of liquid state Pb-Sb alloy. When the temperature was maintained at 1223K and 1373K, the first peak of the radial distribution function among the atoms of Pb-Sb-Sn in the Pb-Sb-Sn ternary alloy liquid state structure of Pb-Sb-Sn increased from 2.11 to 2.15, the coordination number increased from 2.64 to 2.72. The first peak of structure factor decreased from 1.80 to 1.68, the diffusion coefficient increased from 0.95 to 1.23, resulting in a reduction of the alloy order degree and the decreasing stablity of the alloy. viz. it is easier to separate Pb-Sb-Sn ternary alloy. Furthermore, when the temperature is constant, the stability of the alloy melt tends to increase with increasing Pb atomic numbers in Pb-Sb-Sn alloy. In addition, structural optimization was carried out for the gas phase cluster PbmSbn (m+n≤9), stable structures were obtained. The result indicates that Pb and Sb in volatile exist in stable clusters of Pb4Sb2 (Pb-22.7%Sb).The atomic potential of Pb, Sb and Pb-Sb alloys were constructed by the embedded atom potential model. And the potential parameters of Pb, Sb and Pb-Sb alloys were obtained by using the experimental data of the lattice constant, the cohesive energies, the formation energy of a vacancy, the elastic constants, the bulk modulus, the shear modulus and the anisotropy ratio to fit the EAM. They support to represent the microscopic structure of Pb-Sb alloy at the atomic level.Finally, the vacuum distillation researches on Pb-Sb alloy was carried out. The result indicates that the azeotropic composition was 16.5% Sb for Pb-Sb alloy at 1073 K, while the azeotropic composition was distributed between 15%Sb and 20%Sb at 1173 K. The azeotropic point varied accoding to the change of temperature.The innovativeness of this thesis can be described as follows:(1) The melt structural information of Pb-Sb, Pb-Sb-Sn was gained using ab initio molecular dynamic for the first time. The azeotropic point for Pb-Sb alloy vacuum distillation was obtained, which provides a novel research method for the vacuum distillation of alloys.(2) Furthermore, the potential parameters of Pb, Sb and Pb-Sb alloy were constructed, which provides a much systematic theory basis for the vacuum distillation further theoretical research of Pb-Sb.