Effect of sintering temperature on microstructure and mechanical properties of highly porous silicon nitride ceramics produced by freeze casting

Highly porous Si3N4 with macroscopically aligned pores were prepared by the unidirectional freeze casting process using liquid N2 as refrigerant. The increased sintering temperature had no obvious influence on the porosity, but significantly promoted α → β-Si3N4 phase transformation and the growth of fibrous β-Si3N4 grains, and changed the pore structure. The flexural strength and fracture toughness of the sample sintered at 1900 °C could reach 73 MPa and 1.1 MPam1/2, respectively.