Microstructure and properties of porous silicon nitride ceramics prepared by gel-casting and gas pressure sintering

Wave-transparent porous Si3N4 ceramics were prepared by gel-casting and gas pressure sintering, and the effects of solid loading on microstructure, mechanical and dielectric properties were investigated. Microstructures with interlocked elongated β-Si3N4 grains and uniformly distributed pores were observed, while both the β-Si3N4 phase content and grain aspect ratio reduced as the solid loading increased due to the restrained anisotropic growth of β-Si3N4 grains. As the solid loading increased from 30 to 45 vol.%, the porosity of ceramics declined from 57.6% to 36.4%. The flexural strength increased linearly from 108.3 to 235.1 MPa, and the dielectric constant and loss tangent of ceramics increased from 2.63 and 2.85 × 10−3 to 3.68 and 3.56 × 10−3 (10 GHz), respectively.