Fabrication and Properties of Porous Si3N4 Ceramic with High Porosity

A novel process combining oxidation-bonding and sintering was developed to fabricate porous Si3N4 ceramic with high porosity. After sintering at 1800 degrees C, the SiO2 in porous Si3N4 ceramic transforms into Si2N2O because of the reaction of SiO2 and Si3N4. Due to the reaction of SiO2 and carbon, the porosity of porous Si3N4 ceramic increases obviously from 40.2% to 76.8% with the weight decreasing by 35.6%. As the porosity increases, the dielectric constant and loss of the porous Si3N4 ceramic decrease obviously from 3.08 to 1.61 and from 3.70x10(-3) to 0.74x10(-3), but due to the production of Si2N2O whose mechanical properties are much higher than SiO2 and the increase of the bonding strength among Si3N4 particles, the flexural strength and the fracture toughness of the porous Si3N4 ceramic decrease from 55 to 39 MPa and from 0.7 to 0.5 MPa.m(1/2), respectively, but its Vickers hardness increases from 1.2 to 1.3 GPa.