Assessment of Temperature and Pressure Dependence of Molar Volume and Phase Diagrams of Binary Al–Si Systems

Abstract

This article reports the thermodynamic assessment of the temperature and pressure dependence of the molar volume of Al–Si binary systems, as well as P–T unary and high pressure binary phase diagrams based on the CALPHAD methodology. The molar volumes of stable fcc–Al, diamond–Si, and liquid phases as a function of temperature were directly assessed from the data reported in the literature whereas that of metastable fcc–Si was determined by extrapolating composition dependent volume data for Al–Si and Cu–Si fcc solid solutions through extrapolation to pure Si at atmospheric pressure. The Brosh equation of state, which incorporates the quasi-harmonic model, was implemented to avoid spurious estimations of negative heat capacity and thermal expansion at high pressure; it was subsequently used to predict the corresponding values for these properties. Additionally, the temperature and composition dependence of the molar volume as well as phase diagrams for the binary system at high pressure were calculated. Good agreement was reached between calculated results and experimentally estimated thermodynamic values.