High-strength porous Si 3 N 4 ceramics prepared by freeze casting and silicon powder nitridation process

Abstract Porous Si3N4 ceramics with uniform morphology were fabricated via freeze casting and silicon powder nitridation process. Because of the interlocking grains, Si3N4 porous ceramics obtained high porosity of 70.51% and high flexural strength of 16.3 MPa despite of its nitridation degree 88.8%. With SiC addition, a much higher nitridation degree 97.9% was achieved. But the relatively low porosity of 66.7% with low flexural strength of 9.6 MPa was gained owing to the restrained growth and deflection of grains. After post-sintering, the increased aspect ratio of grains gave rise to the improved flexural strength for Si3N4 porous ceramics, while the contrary phenomenon was observed with SiC addition.