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 ?49.19%of open porosity) was about 30MPa, the residual strength ratio
was more than 70% after 1300?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.