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

Porous alpha-Si3N4 whiskers bonded/reinforced SiC (Si3N4(w)/SiC) ceramics were successfully prepared at as low as 1473 K for 2 h, 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 (0.03-5 mu m) left by the packing of raw material particles and interlocking of in-situ formed Si3N4 whiskers coexisted with large ones (8-400 mu m) 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 N-2 molecules adsorbed on it. As-prepared Si3N4(w)/SiC porous ceramics contained 71.53% porosity and had flexural and compressive strengths of 5.60 +/- 0.69 MPa and 12.37 +/- 1.05 MPa, respectively.