Low-temperature preparation of Si3N4 whiskers bonded/reinforced SiC porous ceramics via foam-gelcasting combined with catalytic nitridation

Abstract

Porous α-Si3N4 whiskers bonded/reinforced SiC (Si3N4(w)/SiC) ceramics were successfully prepared at as low as 1473K for 2h, via a combined foam-gelcasting and catalytic nitridation route using commercial Si and SiC powders containing some Fe impurity as the main raw materials. Small pores (0.03–5μm) left by the packing of raw material particles and interlocking of in-situ formed Si3N4 whiskers coexisted with large ones (8–400μm) resultant mainly from the foaming process. The impurity Fe from the raw materials Si and SiC acted as an internal catalyst, accelerating the nitridation of Si by increasing the bond length and weakening the bond strength in the N2 molecules adsorbed on it. As-prepared Si3N4(w)/SiC porous ceramics contained 71.53% porosity and had flexural and compressive strengths of 5.60±0.69MPa and 12.37±1.05MPa, respectively.