Published: 2000
Total Pages:
Get eBook
The objective of this thesis is to study the phase equilibria ofbinary mixtures using molecular simulation. Vapor-liquid, vapor-solid, liquid-liquid, and liquid-solid coexistence lines arecalculated for binary mixtures of Lennard-Jones spheres using MonteCarlo simulation and the Gibbs-Duhem integration technique. Completephase diagrams, i.e., showing all types equilibrium betweenvapor, liquid, and solid phases are constructed. The calculations presented in this thesismark the first time that molecular simulation hasbeen used to obtain phase diagrams describing all types of equilibriabetween vapor, liquid, and solid phases. We present complete phase diagrams for binary Lennard-Jones mixtureswith diameter ratios ranging from 0.85 to 0.95 and attractivewell-depth ratios ranging from 0.45 to 1.6, at reduced pressuresranging from 0.002 to 0.1. The Lorentz-Berthelot combining rules areused to calculate the cross-species interaction parameters. Wesystematically explore how the complete phase diagrams change as afunction of the diameter ratio, well-depth ratio, binaryinteraction parameter, and system pressure. We first calculate complete phase diagrams for several binary mixtures at a single pressure and find that for well-depth ratios of unity (equal attractions among species) there is no interference between the vapor-liquid and solid-liquid coexistence regions. As the well-depth ratio increases or decreases from unity, the vapor-liquid and solid-liquid phase envelopes widen and interfere with each other, leading to the appearance of a solid-vapor coexistence region. For diameter ratios of 0.95, the solid-liquid lines have a shape characteristic of a solid solution (with or without a minimum melting temperature); as the diameter ratio decreases the solid-liquid lines fall to lower temperatures until they eventually drop below the solid-solid coexistence region, resulting in either a eutectic or peritectic three-phase line. We then vary the binary interaction parameter in th.