Thermodynamic properties and phase diagram of the graphite-diamond-liquid carbon system

Abstract

We review work performed on a three-phase theoretical carbon equation of state. The algorithm has been used, with good success, in a chemical equilibrium code of mixtures (of solids, liquids, and gasses), in which the gas phase is modeled by a statistical mechanical theory of mixtures. We use simple Grüneisen models for the solid phases and compute the corresponding liquid phases with a “scaling” theory. A modified Lindemann model is used in the scaling theory to predict melting properties. The liquid carbon consists of a mixture of expanded graphitic and diamond-like forms. Terms that describe the electronic energy change of the liquid have been estimated with the INFERNO code. Both experimental and theoretical work has been used to determine the best equation of state parameters. The resulting model yields a phase diagram consistent with all known mutually consistent data. Significant uncertainties still exist in the melting data.

Key Words:

• Liquid carbon
• graphite
• diamond
• phase-change
• equation-of-state
• Lindemann law