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).