Oxidation mechanism of MoSi sub 2 particles dispersed in mullite

The oxidation of silicide carbide dispersed phases in oxide matrices has been shown to proceed by oxygen diffusion. Silica formed by the reaction of oxygen with silicon can react with the matrix oxide to form a silicate, which may control the rate of diffusion of oxygen to the reaction interface. Two dispersed phase systems with compositionally similar reaction products, but with distinctly different activation energies for diffusion, have been studied to elucidate the oxidation mechanism. The oxidation of SiC particulates with the liberation of CO gas was found to occur totally at the reaction-product/bulk-material interface. The oxidation of MoSi{sub 2} particulates was found to occur in three stages represented by three zones in the reaction product. Mechanical separation of phases was observed to occur with the silicide dispersion because of the extrusion of the viscous silicate to the surface via gaseous evolution.