Microstructure and mechanical properties of porous Si_3N_4-SiO_2 ceramics fabricated by a process combining carbothermal reduction and sol-gel infiltration-sintering

摘要

Porous Si_3N_4-SiO_2 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 Si_3N_4 ceramics with micron-sized pores were fabricated by carbothermal reduction of diatomite preforms. Si_3N_4 ceramics fabricated from 20 wt% dextrin preforms at 1450 ℃ had the highest flexural strength (13.4 MPa), high porosity (80.1%) and small pore size (0.8 μm). Using the obtained porous Si_3N_4 ceramics as preforms, porous Si_3N_4-SiO_2 ceramics were fabricated by silica sol-gel infiltration-sintering. These porous Si_3N_4-SiO_2 ceramics possessed high flexural strength (48.7 Mpa), high porosity (43.5%) and small pore size (0.4 μm).