Oxidation bonding of porous silicon nitride ceramics with high strength and low dielectric constant

Silica (SiO2) bonded porous silicon nitride (Si3N4) ceramics were fabricated from α-Si3N4 powder in air at 1200–1500 °C by the oxidation bonding process. Si3N4 particles are bonded by the oxidation-derive SiO2 and the pores derived from the stack of Si3N4 particles and the release of N2 and SiO gas during sintering. The influence of the sintering temperature and holding time on the Si3N4 oxidation degree, porosity, flexural strength and dielectric properties of porous Si3N4 ceramics was investigated. A high flexural strength of 136.9 MPa was obtained by avoiding the crystallization of silica and forming the well-developed necks between Si3N4 particles. Due to the high porosity and Si3N4 oxidation degree, the dielectric constant (at 1 GHz) reaches as low as 3.1.