Microstructure and mechanical properties of porous Si3N4–SiO2 ceramics fabricated by a process combining carbothermal reduction and sol–gel infiltration–sintering

Porous Si3N4–SiO2 ceramics were fabricated at low–cost by combining carbothermal reduction and sol–gel infiltration–sintering. Using nano–sized diatomite grains as a silica source and dextrin as a carbon source, highly porous Si3N4 ceramics with micron–sized pores were fabricated by carbothermal reduction of diatomite preforms. Si3N4 ceramics fabricated from 20 wt% dextrin preforms at 1450 °C had the highest flexural strength (13.4 MPa), high porosity (80.1%) and small pore size (0.8 μm). Using the obtained porous Si3N4 ceramics as preforms, porous Si3N4–SiO2 ceramics were fabricated by silica sol–gel infiltration–sintering. These porous Si3N4–SiO2 ceramics possessed high flexural strength (48.7 MPa), high porosity (43.5%) and small pore size (0.4 μm).