Effect of diatomite additive on the mechanical and dielectric properties of porous SiO sub(2)-Si sub(3)N sub(4 ) composite ceramics

Porous SiO sub(2)-Si sub(3)N sub(4 ) composite ceramics with high porosity and excellent mechanical properties were fabricated by pressureless-sintering at relatively low temperature of 1 500 degree C using diatomite as pore forming agent. The effects of diatomite on flexural strength, fracture toughness, shrinkage, porosity and phase transformation of the porous ceramics were investigated in detail. Compared with that of the ceramic without adding diatomite, the porosity of the ceramic with 10% diatomite is increased by about 27.4%, the flexural strength and fracture toughness reaches 78.04 MPa and 1.25 MPa.m super(1/2), respectively. As the porosity increases, the dielectric constant of porous SiO sub(2)-Si sub(3)N sub(4 ) ceramic decreases obviously from 3.65 to 2.95.