Fabrication and properties of porous Si3N4–SiO2 ceramics with dense surface and gradient pore distribution

For fabricating porous Si3N4–SiO2 ceramics with good moisture resistance and mechanical and dielectric properties, a technique combining oxidation–bonding, sol–gel directional infiltration and sintering is explored. The sol–gel infiltration time has great effect on the microstructure and properties of the porous Si3N4–SiO2 ceramics. As the infiltration time increases, the porous Si3N4–SiO2 ceramics improve obviously in mechanical properties and decline little in dielectric properties. With the increase of infiltration time from 0.5 to 2.0 h, the porous Si3N4–SiO2 ceramics increase obviously in flexural strength from 46 to 121 MPa and in Vickers hardness from 2.4 to 5.3 GPa, increase slightly in dielectric constant from 3.32 to 3.76 and in dielectric loss from 3.36×10−3 to 3.65×10−3. Due to their dense surface, the porous Si3N4–SiO2 ceramics possess good resistances to moisture and mechanical shock.