Preparation, Properties and Growth Mechanism of Low-Cost Porous Si3N4 Ceramics with High Levels of β-Si3N4 Powders

Abstract

Nowadays, porous Si3N4 ceramics are fabricated by high purity α-Si3N4 powders, resulting in a higher cost of production. To reduce cost and save energy, in this research, high levels of β-Si3N4 powders were effectively utilized to produce excellent and low-cost porous Si3N4 ceramics. The effects of high levels of β-Si3N4 powders on the microstructural evolution and properties were investigated in detail. The results suggested that, with the increase in β-Si3N4 powders from 0 wt.% to 80 wt.%, the aspect ratio of β-Si3N4 grains gradually decreased because of the anisotropic growth of grains significantly impinged by adjacent other β-Si3N4 grains. Additionally, the bending strength and dielectric constant of porous silicon nitride ceramics declined and their values were 685 MPa - 220 MPa, and 7.58–5.57, respectively, while the porosity increased from 5.9% to 28.5%. Similarly, the residual bending strength of Si3N4 ceramics degraded from 615 MPa to 172 MPa at 1000 °C for 20 h owing to the formation of SiO2 on the surface of silicon nitride ceramics after oxidizing.