The ratio of coarse, medium, and fine SiC should be 5:1:4. Black SiC is generally used as the raw material for manufacturing silicon carbide bricks, with the following chemical composition: SiC 98.0%, free C 0.5%, Fe 0.2%, and free SiO2 0.6%. The manufacturing process varies depending on the bonding method. A simplified process for different bonding methods is as follows:
Silicon nitride-bonded silicon carbide bricks: A green body formed from coarse, medium, and fine silicon carbide particles and fine silicon powder is produced at 1370℃ in pure N2 gas, resulting in a silicon nitride-bonded silicon carbide brick with a 26α-SiC skeleton and 26α and 26β-Si3N4 as the matrix. A small amount of residual silicon and SiO2N2 remains in the matrix; the relative content of these components varies depending on the manufacturing plant.
Bound silicon carbide bricks: SiC, silicon powder, and carbon powder are mixed in a certain ratio, formed, and fired in a reducing atmosphere at 1400℃. In most cases, carbon embedding and firing are employed. During firing, a type of SiC brick with a SiC-β-Si3N4 bond is produced, consisting of a SiC-β-SiC framework and a fine-grained SiC matrix. The SiC-β-SiC is formed during firing through the reaction of fine silica powder and fine carbon powder; this product also contains small amounts of residual silicon and carbon.
Silicon oxynitride bonded silicon carbide bricks: In the formulation of this type of brick, the proportion of fine silica powder is less than that of silicon carbide.
