Preparation of tantalum carbonitride by self-propagating high-temperature synthesis of Ta-C system in nitrogen

An experimental investigation on the preparation of tantalum carbonitrides by self-propagating high-temperature synthesis (SHS) was conducted using compacted samples of tantalum and carbon powders ignited in gaseous nitrogen. Effects of the carbon content and nitrogen pressure on the combustion characteristics and the degree of nitridation were studied. Experimental observation shows that the SHS process is characterized by the steady propagation of a self-sustained combustion front. The flame-front propagation velocity was found to increase with an increase in the carbon content of the compact. For the samples of Ta + 0.3C and Ta + 0.5C, after the passage of the combustion front the reaction continues lengthily in an afterburning stage, leading to a moderate increase in the nitridation percentage with nitrogen pressure and a comparable degree of nitridation for these two types of samples. However, due to the lack of afterburning combustion, the degree of nitridation of the Ta + 0.7C sample was greatly affected by the pressure of nitrogen. The XRD analysis of final products indicates that in addition to the dominant phase of Ta(C,N), there exists a small amount of Ta left unreacted.