Oxidation resistance and high-temperature mechanical properties of porous Si2N2O/Si3N4 composite ceramics

Si2N2O/Si3N4 composite ceramics were prepared by pressureless sintered a Si3N4 and SiO2 mixture with 2 mol% Sm2O3. The oxidation behavior and high-temperature strength of Si2N2O/Si3N4 composite materials have been examined. The typical oxidation isotherm of Si2N2O/Si3N4 ceramic is represented by an asymptotic law. The oxidation rate for Si2N2O/Si3N4 was low as compared with those for Si3N4 ceramic. Thin protective oxide scales formed after long exposures to air at 1400 degrees C and substantial crystallization of the intergranular glass phase with formation of Sm-10(SiO4)(6)N-2 occurred during oxidation. Besides, Si2N2O/Si3N4 composites showed excellent high-temperature strength like Si3N4 ceramic and the residual strength ratio can be up to 80 % at 1100 degrees C which is much higher than Si2N2O single-phase ceramic. The degradation of strength at higher temperature results from the increase of interganular glass phase due to diffusion of molecular oxygen.