Effects of α-Si3N4 seeds and sintering additives on properties of porous silicon nitride ceramics fabricated by carbothermal reduction

In this paper, porous Si3N4 ceramics were fabricated by carbothermal reduction between silicon dioxide and carbon [1]. The influences of alpha-Si3N4 seeds and sintering additives on the microstructure and mechanical properties of porous Si3N4 ceremics were investigated. XRD analysis proved the complete formation of a single-phase beta-Si3N4. SEM analysis showed that the resultant porous Si3N4 ceramics had a fine microstructure and a uniform pore structure. The sintered sample with Lu2O3 as sintering additive showed finer, higher aspect ratio beta-Si3O4 grains. The addition of Eu2O3 accelerated the densification of porous Si3N4 ceramics, decreased the porosity and increased the flexural strength. The addition of alpha-Si3N4 seeds accelerated the formation of the alpha-Si3N4 phase at a low temperature and the alpha-beta phase transformation process at a high temperature. With an increase in the alpha-Si3N4 seeds content, the porosity decreased, and the flexural strength increased accordingly.