OXIDATION OF TIC AT LOW-TEMPERATURES

The isothermal oxidation of TiC powders was carried out at low temperatures of 350-500-degrees-C at oxygen pressures of 3.9, 7.9 and 16 kPa under a static total pressure of 39.5 kPa, achieved by mixing with argon, using an electro-microbalance. The oxidation kinetics are described by the one-dimensional diffusion equation. It was found that oxidation consists of four steps, I (fast step), II (slow step), III (fast step) and IV (slow step), at all the pressures. Two activation energies were obtained in steps II-IV: 125-150 kJ mol-1 below about 420-degrees-C and 42-71 kJ mol-1 above that temperature. The low- and high-temperature oxidation mechanisms are discussed in connection with the formation of oxycarbide/titanium suboxides and the crystallization of anatase, followed by the generation of cracks in the grains.