Kinetic studies of oxidation of γ-AlON–TiN composites

Abstract

The present article deals with the investigation of the oxidation kinetics of γ-aluminum oxynitride–Titanium Nitride composites (AlON–TiN) in the temperature range of 1100–1300 °C by thermogravimetry. Oxidation experiments with AlON–TiN composite plates have been carried out in air both in isothermal and nonisothermal modes. The results showed that the rate of oxidation was negligible below 1000 °C, and showed an increase with increasing temperature at higher temperature. Both isothermal studies as well as experiments with ramped temperature clearly indicated that the mechanism of the reaction changes around 1400 °C. In the nonisothermal mode, the oxidation curve showed an increased reaction rate in this temperature range. Oxidation of AlON–TiN composite results in α-Al 2O 3 and TiO 2 at a low temperature and Al 2TiO 5 at higher temperature. The buildup of the product layer leads to diffusion controlled kinetics. In the nonisothermal experiments, the phase transformation from Al 2O 3 and TiO 2, to a Al 2TiO 5 product layer at higher temperature would lead to crack formation, thereby leading to direct chemical reaction. From the experiments for the isothermal oxidation of AlON–TiN composite plates, the overall reactions are separated into three stages: chemistry reaction-controlling stage; chemical reaction- and diffusion-mixed-controlled stage; diffusion-controlled stage. The apparent activation energy for the experiments were calculated to be 10.109, 2.19 and 5.614 kJ mol −1, respectively, in the above three stages.