OXIDATION BEHAVIOR OF ALUMINUM NITRIDE

The evaluation of the thermal stability of three different fully dense AlN materials in the temperature range of 600-degrees-C to 1400-degrees-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 almost-equal-to 1350-degrees-C. The kinetics are linear (1100 less-than-or-equal-to T less-than-or-equal-to 1400-degrees-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 less-than-or-equal-to T less-than-or-equal-to 1200-degrees-C are followed by parabolic kinetics at higher temperatures (T > 1250-degrees-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.