Oxidation of Mo/Al₂O₃ hybrid materials at high temperatures

In the present work, the oxidation behaviour of 5 vol% Mo/Al ₂O₃ hybrid materials was investigated at high temperatures in air. At oxidation temperature ranging from 600 to 800°C, Al ₂(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°C, the evaporation of MoO₃ occurred dramatically.