Fabrication and properties of Si2N2O ceramics for microwave sintering furnace

The Si2N2O ceramics with low dielectric constant, low thermal diffusivity and high thermal shock resistance were successfully prepared by vacuum sintering. The amorphous Si3N4 was used as raw material with Li2CO3 as sintering additive. The phase, microstructure, oxidized resistance, mechanical and dielectric properties of the Si2N2O ceramics were investigated. XRD analysis showed that the suitable content of Li2CO3 could promote the generation of Si2N2O ceramics. However, the excess or insufficient amount of Li2CO3 additive would cause decomposition of Si2N2O phase. The Li2O volatilized at high temperature leaving highly pure (99.63%) porous Si2N2O ceramics. The flexural strength of the porous Si2N2O ceramics (with approximate to 49.19% of open porosity) was about 30 MPa, the residual strength ratio was more than 70% after 1300 degrees C quenching in air. The SiO2 layer formed by oxidization could prevent Si2N2O ceramics from further oxidizing. Therefore, these Si2N2O ceramics will be excellent thermal insulation and wave-transparent materials for high temperature microwave sintering furnace.