Preparation and characteristics of highly porous BN-Si3N4 composite ceramics by combustion synthesis

Nitride based ceramics are considered as a kind of promising material for structural and functional integration due to their robust structure, extreme environmental resistance and electromagnetically transparency. It is still challenging to prepare nitride based ceramics with homogeneous and controllable microstructure because of their low self-diffusion coefficient and difficulty in sintering. Here, we developed a gelcasting-SHS process by combining gelcasting forming and self-propagating high temperature synthesis (SHS) for the preparation of porous BN-Si 3 N 4 composite ceramics. First, carbon residue problem in the gelcasting -SHS process was studied. Based on the result, porous BN-Si 3 N 4 composite ceramics with high porosity (69.42 ~ 86.48%), high strength (21.7 ~ 81.0 MPa) and low dielectric constants (1.42 ~ 2.87) were synthesized. In addition, the thermal shock resistance of porous BN-Si 3 N 4 composite ceramics until 1000 ℃ was evaluated.