Theoretical Study Of Ab Initio Molecular Dynamics Simulation Of Tin-based Alloys

Vacuum metallurgy has many advantages compared with traditional metallurgy,such as environment friendly,simplified flow sheet,high metal recovery,simple equipment,low energy consumption.However,Sn and M(M=Cu,Ag,Sb,Bi and Pb)can coexist in recovered metal by separation of lead-based alloys using vacuum metallurgy.In addition,microstructures and properties of Pb-M alloys are scarcely investigated,thus the development of vacuum metallurgy has been limited.Therefore,in order to solve the problem of efficient separation of tin,antimony,copper,silver and other elements,it has become an urgent need to develop a new processing technology.In this thesis,the theoretical study of vacuum distillation is the main content.The diffusion coefficient and diffusion law of tin-based alloy are studied.The vacuum distillation effect of tin-based alloy is predicted.The theoretical research on tin-based binary,ternary and quaternary alloys is carried out.The main conclusions are as follows:(1)Using ab initio molecular dynamics(AIMD),simulating the alloys such as Sn-Bi,Sn-Sb,and Sn-Sb-Ag at temperatures of 673K-1673 K,and obtaining the mean square displacement,radial distribution function and partial density of states result,providing the basis for the theoretical study of crude tin alloy vacuum distillation.(2)For the ab initio molecular dynamics study of the binary alloy system,it is found that for the Sn-Sb system,when the Sb content reaches 6.4%,the interaction between the atoms of Sn-Sb is the weakest.Compared with Sn-4.8%Sb and Sn-8.0%Sb,the Sn-6.4% Sb alloy system is more easily separated during vacuum distillation as the temperature increases.In addition,the ab initio molecular dynamics calculations of Sn-Pb,Sn-Bi,and Sn-Ag show that the interaction between atoms in the Sn-Pb system is weakened with the increase of temperature,and the Sn atom in the Sn-Bi system.The force between the atoms and the Bi atoms is weakened and the system is easier to separate.For the Sn-Ag system,although the temperature increases,the diffusion coefficient of the system increases,but the system is still not easy toseparate.(3)The ab initio molecular dynamics study of the Sn-Sb-Bi,Sn-Sb-Ag,and Sn-Sb-Cu ternary alloy system systems,and the results of the mean square displacement and density of states obtained by analysis,we conclude In the existence of impurity elements Bi,Ag and Cu in the tin-based alloy,the diffusion of the system is more chaotic,the force between the atoms is significantly reduced,and the system is easier to separate.For the Sn-Pb-Ag alloy,the presence of Ag can destroy the atomic force between Sn-Pb,making the system easier to diffuse.(4)Establishing a model to calculate the ab initio molecular dynamics under NVT.We studied the diffusion behavior of the quaternary alloy system Sn-Sb-Cu-Ag.Compared with the binary Sn-Sb system,the simultaneous existence of Ag and Cu Does not make the alloy easier to separate.Compared with the ternary systems Sn-Sb-Cu and Sn-Sb-Ag,the quaternary system does not exhibit good diffusion behavior due to the interaction between Cu atoms and Ag.