Use of Al4C3 for fabrication of alumina–niobium carbide composites by combustion synthesis

•SHS with aluminothermic reduction was performed for formation of NbC and Nb2C–Al2O3 composites.•Al4C3 prevents carbothermic reduction of Nb2O5, leading to improved product formation.•Optimum sample compositions were obtained for formation of NbC and Nb2C–Al2O3 composites.•Variations of combustion temperature and velocity with sample stoichiometry were presented.

Alumina–niobium carbide (Al2O3–NbC and Al2O3–Nb2C) composites were synthesized by incorporating aluminothermic reduction of Nb2O5 into a self-propagating combustion process. Starting materials of this study included Nb2O5, Al, Al4C3 and carbon powders. Experimental evidence indicated that combustion temperature and flame-front velocity decreased with increasing elemental carbon in the reactant mixture. The use of Al4C3 as the source of carbon was demonstrated to prevent carbothermic reduction of Nb2O5. As a result, the combustion exothermicity was increased and phase transformation and product densification were improved. According to the composition analysis, the carbon-free samples composed of Nb2O5:Al:Al4C3 = 3:2:2 and 3:6:1 successfully produced NbC and Nb2C–Al2O3 composites, respectively, with very few minor phases.