Microstructure And Properties Of H-BN/Si₃N₄ Porous Composite Ceramics

Using activated carbon as a pore-forming agent, we have fabricated porous h-BN/Si₃N₄ composite ceramics by cold isostatic process (CIP) followed pressureless sintering. The effects of h-BN content, porosity and sintering aids on the microstructure, mechanical properties, thermal properties and dielectric properties of h-BN/Si₃N₄ ceramic were investigated by XRD, SEM techniques and three points bending tests.By systematic research on CIP, we got the optimal green compact forming conditions including the binder content, grain composition, molding pressure and pressure-holding time etc. By investigating pore-forming removal in muffle furnace, we obtained the optimal conditions for pore-forming agent removal processing such as the heating rate, calcine temperature and holding time, and porous h-BN/Si₃N₄ composite ceramics were prepared.The effects of h-BN content, porosity, sintering aids on the microstructure and properties were investigated. It was found that the mechanical properties, thermal properties, dielectric properties and machinability of Si₃N₄ ceramics could be highly improved with the introduction of h-BN. The porosity was controlled by pore-forming agent content, and the pore shape was determined by the pore-forming agent shape, the thermal properties and dielectric properties were correlated with the porosity. When Al2O3+Y2O3 was used as sintering aids, the composite porous ceramic have a better sintering ability, more excellent bending fracture strength and thermal properties were achieved, but the dielectric properties was slightly aggravated compared with that when La2O3+Y2O3 was used as sintering aids.The investigating results in this paper will be good for the development of the relevant porous composite ceramics with excellent mechanical properties, thermal properties and dielectric properties.