Thermodynamics of the Al–C–O Ternary System

Thermodynamic calculations in the Al–C–O system were performed to understand the vaporization behavior of the alumina-carbon section in open conditions. The gaseous phase in equilibrium with the alumina-graphite system was analyzed by high-temperature mass spectrometry using an effusion cell: Al(g), , and CO(g) molecules were the only vaporizing species in the temperature range . The measured partial pressures were lower than those attended at equilibrium and second and third calculations for different vaporization reactions never agree, this means a hindered vaporization. As complementary chemical analysis of the samples after experiment by XRD and XPS show that alumina and graphite do not produce any oxycarbide and carbide, the deduced main vaporization reaction is . This confirms that the section vaporizes congruently with a kinetic barrier. The analysis of this behavior leads to correlated limited composition ranges for the gaseous and condensed phases which are evaluated.