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 [1473 K (1200 °C)] for 3 hours with the addition of 3 wt pct Cr₂O₃ NPs. First-principle calculations suggested that the electron transfer from Cr₂O₃ to N₂ 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 [1673 K (1400 °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.