Preparation of Si3N4 porous ceramics via foam-gelcasting and microwave-nitridation method

Si3N4 porous ceramics with improved mechanical strength were fabricated for the first time by a combined foam-gelcasting and microwave-nitridation method at 1273-1373 K. The Si3N4 porous samples prepared at 1373 K/20 min with the porosity of 68.9% had respectively flexural and compressive strength as high as 8.1 and 20.8 MPa, which values were comparable or even superior to those of Si3N4 porous ceramics prepared previously by the conventional heating technique at a much higher temperature of 1773-1973 K, indicating that present preparation strategy is feasible to prepare high quality Si3N4 porous ceramic at a much milder condition. Moreover, the thermal conductivity of as-prepared Si3N4 porous ceramics at 1073 K was as low as 1.697 W/(m K), suggesting it could be a potentially good heat insulating material for aluminum electrolyte cells.