Role of excess Al on the combustion reaction in the Al-TiO₂-C system

Of various systems that utilize a self-propagating high-temperature synthesis, the Al-TiO₂-C system is representative of in-situ production of metal matrix composites reinforced with TiC and Al₂O₃. Contrary to common understanding, however, the following reaction 4Al + 3TiO₂ + 3C→3TiC + 2Al₂O₃ is infeasible in the Al-TiO₂-C system with the given stoichiometric composition of 4Al + 3TiO₂ + 3C. Experiments have shown that the formation of TiC and Al₂O₃ is feasible only in an Al-TiO₂-C system that contains a certain amount of excess Al. In this study, the mechanism of the reactions in the Al-TiO₂-C system was elucidated in order to explain why excess Al is needed to promote the formation of TiC and Al₂O₃. We also estimated the amount of excess Al that is necessary to promote the complete transformation of the Al-TiO₂-C powders to TiC and Al₂O₃.