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.