Oxidation of Mo/Al2O3 hybrid materials at high temperatures

In the present work, the oxidation behaviour of 5 vol% Mo/Al2O3 hybrid materials was investigated at high temperatures in air. At oxidation temperature ranging from 600 to 800 deg. C, Al2(MoO4)3 and MoO3 were developed. The growth of the oxidized zone, at which metallic Mo was not observed, obeyed the parabolic manner. The apparent activation energy of the parabolic rate constant was equal to 95 kJmol-1. The microstructures showed that there were many voids in the oxidized zone. Significant cracks, which would be formed due to volume expansion of Mo particles via inward diffusion of oxygen, were not observed in oxidized zone. They must be the evidence of outward diffusion of cations, most likely Mo6+ at grain boundary. As the temperature over 800 deg. C, the evaporation of MoO3 occurred dramatically.