Fabrication of Si3N4 reticulated porous ceramics reinforced by needle-like β-Si3N4

Si3N4 reticulated porous ceramics (RPC) were prepared by twice-sintering and replication techniques. The α-Si3N4 and Si powder in raw materials were partially transformed into needle-like β-Si3N4 when the samples were sintered. The compressive strength of the Si3N4 RPC could be remarkably improved by these needle β-Si3N4 crystals because these needle crystals integrate with the liquid glass phase and other phases into a whole during a twice-sintered process. This is similar to a whisker-reinforced mechanism. This mechanism was testified by SEM, EDS and XRD analyses. The influence of pretreatment of polyurethane sponge precursors as well as the viscosity of the slurry on green bodies was also investigated. The Si3N4 RPC with 30 wt% Si and 5 wt% Al2O3 yielded the compressive strength of 2.2 MPa and no deformation.