摘要
Porous Si 3 N 4 ceramics were fabricated by combining gelcasting and pressureless sintering. The roles of sintering temperatures and sintering additives (Y 2 O 3 , Al 2 O 3 , and Y 2 O 3 -Al 2 O 3 ) in regulating phase composition, microstructure, sintering, mechanical, and dielectric properties of porous Si 3 N 4 ceramics were systematically studied. Compared with Y 2 O 3 and Al 2 O 3 , owing to the lower eutectic temperature, Y 2 O 3 -Al 2 O 3 was more effectively in promoting the particle rearrangement and dissolution-diffusion-reprecipitation processes during high-temperature sintering, leading to higher phase transformation degree of α→β-Si 3 N 4 , larger aspect ratio of columnar β-Si 3 N 4 grains, and higher densification of porous Si 3 N 4 ceramics. Furthermore, the increasing sintering temperature and the present β-Si 3 N 4 seeds within the raw powders were also conducive to phase transformation of α→β-Si 3 N 4 , β-Si 3 N 4 growth, and developing highly interlocking microstructure contributing to strengthening mechanical properties. At 10 wt% Y 2 O 3 and 5 wt% Al 2 O 3 , the complete phase transformation of α→β-Si 3 N 4 and sufficient β-Si 3 N 4 growth were achieved by pressureless sintering at 1750 ℃ for 1 h. The apparent porosity, bulk density, flexural strength , and fracture toughness of porous Si 3 N 4 ceramics reached 2.7%, 2.98 g/cm 3 , 450.9 MPa, and 4.35 MPa·m 1/2 , respectively, exhibiting superior mechanical properties. At 2 wt% Y 2 O 3 and 1 wt% Al 2 O 3, the resulting porous Si 3 N 4 ceramics had dielectric constant of 4.28–4.38 and dielectric loss tangent of 2.1 × 10 −3 -3.2 × 10 −4 throughout X-band, showing good microwave transmission properties. This study indicates that the gelcasting combined with pressureless sintering was proved to be a feasible method to prepare high-strength and low-dielectric porous Si 3 N 4 ceramics using Y 2 O 3 -Al 2 O 3 as sintering additives.
危险品化学品经营许可证（带存储）