SHS of Highly Dispersed Si3N4–SiC Ceramic Composites from Si–NaN3–Na2SiF6–C Powder Mixture

Abstract

Highly dispersed ceramic composites Si₃N₄–SiC were prepared by SHS under 4 MPa of nitrogen pressure from powder mixtures containing silicon, halide salt Na₂SiF₆, carbon, and sodium azide (NaN₃) as a nitriding reagent. Variation in the silicon and carbon content in the green mixture affected the process parameters, structure, and phase composition of combustion products. It was found that the combustion product containing no more than 10% SiC represents a mixture of ultrafine equiaxed and fiber-like particles, and its composition coincides with the theoretically calculated one. At the SiC content more than 10%, the product compositions were distinctive from the theoretical compositions by a lower SiC content and had α- and β-Si₃N₄ in almost equal amounts. Their structure was shown to contain ultrafine (150–300 nm) and coarse (up to 5 μm) particles.