Forming Mechanism of Compact Layer on the Surface of MgO/Si_3N_4 Composite

It was found that MgO/Si3N4 composite possesses a self-impedient performance to oxidation. A compact layer on the surface, which is an anti-oxidation and anti-corrosion layer, formed spontaneously in MgO/ Si3N4 composite in the process of oxidation, and the thickness and density of the compact layer increased by adding Si or Al into the composite. On the basis of the results, the forming mechanism, the composition and structure of the compact layer of the composites with or without Si or Al were studied. The transform oxygen partial pressure was proposed as a standard for evaluating the escape intensity of gaseous SiO and A12O. It will show using the thermodynamics and the standard that gaseous SiO and A12O can produce inside the composite and they reoxidize and react with other oxides in the outside layer to form the compact layer.