Thermodynamics of the Al2O3–Al4C3 system: I. Thermochemical functions of Al oxide, carbide and oxycarbides between 298 and 2100 K

A consistent set of thermochemical functions are proposed for aluminium oxide (Al2O3), carbide (Al4C3) and oxycarbides (Al4O4C, Al2OC), including Gibbs free energies, enthalpies and entropies of formation as well as heat capacities, between 298 and 2100 K. Heat capacities of the base components of the Al–O–C system are also given. All equations are compared with existing functions in terms of relative errors, pointing important discrepancies for aluminium carbide and aluminium oxycarbide Al2OC. When some are used to determine equilibrium partial pressures of carbon monoxide in classical high temperature solid–gas reactions, these discrepancies are confirmed or amplified. As a consequence, the present equations are suggested to describe the thermodynamic behaviour of aluminium carbide and aluminium oxycarbide Al2OC.