What Is Silicon Carbide?
Silicon carbide (SiC) consists of silicon (Si) and carbon (C). It is not found naturally on Earth, but rather in meteorites. Due to its high hardness and wear resistance, it is extensively utilized in abrasives and refractory materials. While pure silicon carbide is colorless and transparent, it is typically black when used industrially.
High-purity silicon carbide is notably gaining traction as a superior material for power semiconductors, aimed at outperforming traditional silicon semiconductors.
Applications of Silicon Carbide
Characterized by its high hardness, wear resistance, thermal conductivity, and corrosion resistance, silicon carbide is ideal for use in mechanical seals, shafts, and other sliding parts. It also serves in the manufacture of classifier and crusher parts, as well as in heat-resistant components like high-temperature test equipment and metal-melting crucibles.
In addition, SiC power semiconductors are employed in hybrid electric vehicles (HEV).
Properties of Silicon Carbide
Silicon carbide is insoluble in water, sublimating at 2,545°C, and thermally decomposing at temperatures above 2,800°C. It ranks 9.5 on the Mohs hardness scale, making it second only to diamond and boron carbide. Its large refractive index of 2.65 allows large crystals to have mirror-like reflectivity.
Although pure silicon carbide is transparent, industrial variants are green or black, with the color fading as the purity increases. Impurities such as aluminum and nitrogen in the crystal lattice account for its coloring. Green silicon carbide, due to its higher electrical resistance, is often used in heating elements.
As silicon atoms are larger than carbon atoms, the interatomic distance in SiC is greater than in carbon, resulting in lower thermal conductivity and increased softness.
Structure of Silicon Carbide
Silicon and carbon in silicon carbide are covalently bonded, yet exhibit ionic characteristics due to their differing electronegativity, stabilizing as a 1:1 compound. Its molar mass is 40.097 g/mol, with a density of 3.22 g/cm3.
Atoms are tetrahedrally arranged around each other, with over 200 varieties based on the layer structure’s repetition pattern. Primarily, there are two types: alpha (hexagonal) and beta (cubic).
α-Type silicon carbide powder can be produced by heating coke and silica stone above 2,100°C in an electric furnace, while β-type is obtained by heating carbon black and silicon to 1,800°C in an argon atmosphere.
Other Information on Silicon Carbide
1. History of Silicon Carbide
In 1891, Edward Goodrich Acheson in the US synthesized silicon carbide by heating a coke and clay mixture with a carbon arc lamp, leading to the establishment of Carborundum Abrasives Co. and the industrial production of what is sometimes known as carborundum.
In 1905, Ferdinand Frédéric Henri Moissan discovered silicon carbide in a meteorite in Arizona, where it is also referred to as Moissanite in mineralogy.
2. Reactions of Silicon Carbide
Chemically inert, silicon carbide is insoluble in water, acids, and alkalis, and does not react with aqua regia or concentrated nitric acid. It remains unreactive towards N2, H2, or CO, but oxidizes at temperatures above 800°C in air, forming a protective SiO2 layer that slows further oxidation. It reacts with Cl2 above 800°C, producing C and SiCl4.