Investigations on porous silicon nitride ceramics prepared by the gel-casting method

Due to their special structure and many excellent properties, porous Si 3 N 4 ceramics have a wide range of potential applications as a new structural and functional integrated material. In the present study, porous Si 3 N 4 ceramics with excellent bending properties and satisfactory porosity were prepared by the gel-casting method. The variations in porosity, bending strength, fracture morphology and phase composition of the porous Si 3 N 4 ceramics with different weight fractions of La 2 O 3 –MgO sintering additive were investigated. The results showed that the density of porous Si 3 N 4 ceramics increased linearly with the increase of sintering additive content. When the content of sintering additive increased from 2.5 wt.% to 10 wt.%, the porosity of porous ceramics decreased from 30 % to 10 %. With the increase of sintering additive content, the bending strength of the samples first increased and then decreased. When the sintering additive content was 5.0 wt.%, the average bending strength of the samples reached a maximum of 240.88 MPa, and scanning electron microscopy and X-ray diffractometry results showed that β-Si 3 N 4 particles with well-developed pores and a maximum aspect ratio of 5.8 were formed in the porous silicon nitride ceramics. This study provides a reference for the preparation of porous Si 3 N 4 ceramics with good bending properties and porosity.