What are the properties of silicon carbide refractory products?
Because the raw material and main crystalline phase of silicon carbide refractory products are mainly silicon carbide, many properties of the products are those of silicon carbide. In this type of refractory products, silicon carbide is an impurity substance, which must be bonded into a whole by a bonding agent, so the nature and substitution form of the bonding agent have a considerable influence on the properties of the product.
Silicon carbide is a non-metallic carbide in which silicon and carbon are covalently bonded. It is divided into natural silicon carbide and synthetic silicon carbide. Natural silicon carbide is called moissanite, with very few reserves and no exploitation value. The silicon carbide used in industry is artificially synthesized.
Silicon carbide is the only binary compound in the silicon carbide binary system, and its atomic ratio is 1:1. The mass fraction of C is 29.97%, and the mass fraction of Si is 70.03%. Silicon carbide has two crystal types: β-SiC and α-SiC. β-SiC is a cubic crystal system, and it is slowly and irreversibly transformed into hexagonal α-SiC from 2100°C to 2400°C. The holding time at the conversion temperature is the conversion amount. The true density of β-SiC is 3.21g/cm³ and α-SiC is 3.22g/cm³. Usually, the silicon carbide refractory products are mostly α-SiC. It has very low thermal expansion, which is approximately one-half of mullite. It has high performance. The thermal conductivity is about 35W/(m·℃) at room temperature. It decreases slightly with the increase of temperature, but it is still very high at high temperature. For example, it is still 11W/(m ·℃) above.
