Structure, Thermodynamic Properties, and Shock Compression of Bismuth–Lead Melts and Correlation Effect during Diffusion. Molecular Dynamics

Abstract

The models of Bi–Pb solutions were constructed by molecular dynamics at temperatures of up to 30 000 K and pressures of up to 282 GPa. The embedded atom model (EAM) potentials for pure components and the Lennard-Jones potential for pairs 12 are used. The density isobar at normal pressure and the solution formation heat isotherm at 700 K were in good agreement with experiment. The thermodynamic (density, energy, heat capacity, compression modulus, sound velocity, and Gruneisen coefficients), structural, and diffusion properties of the eutectic Bi₅₅Pb₄₅ melt at normal pressure and temperatures of up to 2900 K and under conditions of shock compression were calculated. At elevated pressure, the negative deviations from ideality change to positive ones. A molecular-dynamic calculation of the mutual diffusion coefficients at 550–928 K was performed on the melt models. The interdiffusion coefficients found by the molecular dynamics method are smaller than those measured experimentally by the capillary method by a factor of 1.25–1.64. The correlation effect during diffusion in melts similar to the cataphoretic effect in ionic solutions is confirmed. In Bi–Pb solutions with negative deviations from ideality, the correlation factor is substantially smaller than unity. In the equation for the interdiffusion coefficient, the thermodynamic factor and the correlation factor partially cancel each other.