Influence of composition and oxidation temperature on thermal conductivity of Si-Ti-O-N porous ceramics

As a material for a heat insulation engine, the development of ceramics with high strength, low thermal conductivity and low thermal expansion coefficient has been required. And composite of reaction bonded ceramics was thought to be promising candidate. The influence of composition and oxidation temperature on the thermal conductivity of porous Si-Ti-O-N ceramics, reaction-sintered using Si and Ti as starting powders, were studied, and the following results were obtained. (1) The thermal conductivity of an as-nitrided specimen decreased with the amount of Ti in raw material. (2) Simple calculation showed that the thermal conductivity of the solid part in porous ceramics also decreased with increasing Ti amount. (3) The thermal conductivity was minimum when oxidized at 700°C. Above 700°C, it increased with increasing temperature. This behavior was explained by the phase change of TiN to TiO2 with lower thermal conductivity and by the decrease in porosity caused by the oxidation reaction. (4) The weight gain in oxidation showed increased linearly with increasing amount of Ti, suggesting that the oxidation of TiN0.9 occurred more preferentially than Si3N4.