Catalytic Preparation of Si3N4-Bonded SiC Refractories and Their High-Temperature Properties

Effects of Cr2O3 nanoparticles (NPs) on the catalytic nitridation of Si powders were investigated, and the results showed that the Cr2O3 NP catalysts enhanced the nitridation of Si powders and promoted the formation of Si3N4 whiskers. The complete conversion of Si was achieved at [1473K (1200 degrees C)] for 3 hours with the addition of 3wt pct Cr2O3 NPs. First-principle calculations suggested that the electron transfer from Cr2O3 to N-2 molecules facilitates the Si nitridation. Moreover, Si3N4-bonded SiC refractories were also prepared using in-situ formed Cr2O3 NPs as catalysts, and the hot modulus of rupture at [1673K (1400 degrees C)] of as-prepared refractories was about three times higher than that of samples without catalysts; the corrosion resistance against molten cryolite of the former was remarkably lower than that of the latter. The improvement was attributed to the catalytic effects of Cr2O3 NPs for in-situ formation of a fund of Si3N4 whiskers, which formed a network structure in the samples.