The Microstructure and Mechanical Properties of Porous Silicon Nitride Ceramics Prepared via Novel Aqueous Gelcasting

A novel aqueous gelcasting technique was employed to prepare porous silicon nitride ceramics using water‐soluble copolymer of isobutylene and maleic anhydride (Isobam) as both dispersant and gelling agent. The effects of fabrication parameters, including sintering additives, the second phase ( BN ), and pore‐forming agent (corn starch), on the microstructure and mechanical properties were separately investigated. The sample with Yb 2 O 3 as sintering additive, having a porosity of ~48.6%, showed a high flexural strength of 233 MP a and a high fracture toughness of 2.72 MPa·m 1/2 . With addition of 2.5wt% BN , the sample exhibited a high flexural strength of 211 MPa due to the uniform microstructure with β‐Si 3 N 4 grains. A high porosity of ~60% and a flexural strength of 110 MPa were obtained by adding 20wt% starch into the sample.