Microstructure and mechanical properties of porous Si3N4 ceramics prepared by freeze-casting

Porous silicon nitride (Si3N4) ceramics were prepared from water-based Si3N4 slurries via a freeze-casting process. The green body shows good replica of ice dendrites with uniform pore channels. The microstructure of porous Si3N4 ceramics could be controlled by the freezing temperature. After sintering, porous Si3N4 ceramics with uniform microstructure was obtained. At low freezing temperature, the pore size distribution was narrower and concentrated with pore morphology from tree-like to vimineous channels. Porous Si3N4 ceramics with a porosity of 51%, flexural strength of 77 MPa, and aspect ratio (AR) of 5.20 was obtained at 1850 °C with 3% sintering additives.