Effects of Al content on formation of TaC, Ta2C, and Ta2AlC by combustion synthesis with aluminothermic reactions

Fabrication of TaC-, Ta2C-, and Ta2AlC-Al2O3 composites was conducted by incorporating aluminothermic reduction of Ta2O5 into self-propagating high-temperature synthesis (SHS). Starting materials of this study included Ta2O5, Al, Al4C3, and carbon black powders. The effect of elemental Al content was studied by adjusting the proportions of Al, Al4C3, and carbon. Experimental results showed that the increase of elemental Al facilitated the reduction of Ta2O5, increased the combustion exothermicity, and improved the evolution of carbide phases. Compared to Al4C3, elemental Al was demonstrated to be a more effective reductant for Ta2O5. Formation of Al2O3 -added TaC and Ta2C composites with trivial minor phases was achieved by the Al4C3-free samples with molar ratios of Ta2O5:Al:C = 3:10:6 and 3:10:3, respectively. For the production of the Ta2AlC-Al2O3 composite, a significant loss of Al occurred in the samples especially for those containing Al4C3. As a result, Ta2AlC and Ta2C were present as the main carbide phases. The increase of elemental Al improved the yield of Ta2AlC, and the need of excess Al was advised.