Thermodynamic Evaluation of the Al2O3-Al4C3 System and Stability of Al-oxycarbides

Thermodynamic properties of the pseudo-binary Al 2 O 3 - Al 4 C 3 system have been evaluated based on thermodynamic models. An ionic-liquid model was applied to the liquid slag phase and a compound-energy model to Al 2 OC. Both the models are with two sublattices and the latter one can be extended to describe the solid solution phases formed among Al 2 OC, AlN, and SiC. A description of the system was obtained and then used to calculate the Al 2 O 3 -Al 4 C 3 phase diagram which shows satisfactory agreement with experimental observation. A series of potential diagrams was also calculated for the Al-C-O system, which illustrate the effect of partial pressures of Al, CO, and CO 2 gas on the stability of Al 4 C 3 , Al 4 O 3 , Al 4 O 4 C, and Al 2 OC at different temperatures. These diagrams can provide an important basis for the carbothermic reduction of alumina to produce Al 4 C 3