Thermoanalytical study on oxidation of TaC1−xNx powders by simultaneous TG-DTA-MS technique

Thermal analysis of non-isothermal and isothermal oxidation of the carbonitride solid solution TaC1−xNx powder (x=0–1.0 with variation of every 0.2) was performed using simultaneous TG-DTA-MS technique. Sintered TaC1−xNx bodies were prepared by spark plasma sintering of powder mixtures of TaC and TaN at 1800 °C. The crushed powder was oxidized non-isothermally by heating to 1000 °C or isothermally at 700–800 °C in a flowing mixed gas of Ar and O2 (pO2=20 kPa). The dependency of the oxidation of TaC1−xNx on the composition x was investigated from the standpoint of initiation temperature, completion temperature, and maximum rate. It was suggested that the oxidation kinetics are represented by either a diffusion-limited rate equation or a first-order reaction rate equation, depending on the composition and temperature. DTA-MS analysis in the very early stage of oxidation showed that N2 gas evolves in advance of CO2 with the respective exothermal effect.