Combustion synthesis of tantalum carbides TaC and Ta2C

The preparation of tantalum monocarbide TaC and hemicarbide Ta2C was conducted by self-propagating high-temperature synthesis (SHS) from elemental powder compacts in this study. Effects of starting stoichiometry, initial sample density, preheating temperature, and dilution by the final product on the combustion characteristics, as well as on the product composition were studied. Experimental observations indicate that with the progression of self-sustained combustion wave, the compact with a molar ratio of Ta:C = 1:1 experiences substantial structure delamination, leading to considerable elongation of the burned sample. In contrast, the powder compact made up of Ta:C = 2:1 almost retained its original shape after combustion. The flame-front propagation velocity was found to increase with initial sample density and temperature, but to decrease with diluent content. For both types of carbides, formation of the single-phase product was improved by increasing the sample green density. Complete conversion yielding TaC and Ta2C from the compacted samples with an initial density of 45% TMD was verified by the XRD analysis of end products. In addition, raising the sample temperature by prior heating was also proved to be effective in the enhancement of phase conversion. Based upon the dependence of flame-front velocity on combustion temperature, activation energies of 187.4 and 299.3 kJ/mol were deduced for the formation of TaC and Ta2C by SHS, respectively.