Oxidation behavior of aluminum nitride

The evaluation of the thermal stability of three different fully dense AlN materials in the temperature range of 600 °C to 1400 °C in air indicates the strong effect of the starting composition on the oxidation process. The oxidation resistance of pure AlN and Y₂O₃-doped AlN was found to be good up to ≍1350 °C. The kinetics are linear (1100 ≤ T ≤ 1400 °C) and the process is governed by a surface reaction that gives rise to the formation of a porous, nonprotective oxide scale, where Al₂O₃ and Y-aluminates (i.e., AlN–Y₂O₃) have been found as crystalline reaction products. For AlN-CaC₂, higher oxidation rates indicate that the outward migration of Ca modifies the reaction mechanisms. Linear kinetics in the range 1100 ≤ T ≤ 1200 °C are followed by parabolic kinetics at higher temperatures (T > 1250 °C); with regard to the latter behavior, an activation energy of 160 kJ/mole could indicate the diffusion of oxygen through the oxidation scale as the rate-controlling mechanism.