High-temperature oxidation of MoSi2

Oxidation behavior of MoSi2 was investigated in air over the temperature range of 1400–1700 °C. Spallation of the SiO2 scale did not occur at any temperature, and Mo5Si3 formation did not happen below 1700 °C. A change in the rate-controlling mechanism was detected within the temperature range of this study. Activation energy for oxidation of MoSi2 at high temperatures was determined to be 204 kJ/mol. This value is less than the value of activation energy for oxidation of MoSi2 controlled by diffusion of O2 through amorphous SiO2 layer reported at lower temperatures. The decrease in activation energy is attributed to the increased degree of crystallization of amorphous silica to β-cristobalite at high temperatures resulting in enhanced O2 diffusion through SiO 4 −4 tetrahedral structure.