Silicon carbide (SiC), also known as carborundum, is a semiconductor containing silicon and carbon. It occurs in nature as the extremely rare mineral moissanite. Synthetic SiC powder has been mass-produced since 1893 for use as an abrasive.
SiC exists in different crystalline structures, referred to as polytypes. Each polytype is denoted by a number which stands for the number of layers in one period of its crystal lattice, and a letter that signifies the type of crystal lattice. The two most common polytypes of silicon carbide are “alpha” (α-SiC) and “beta” (β-SiC).
- Alpha Silicon Carbide (α-SiC): Alpha silicon carbide is the most common polytype, which is characterized by a hexagonal crystal structure (similar to a wurtzite crystal structure). It is formed at temperatures greater than 1700 °C and has a hardness slightly less than that of boron carbide, but it is still harder than most other materials. At present, the silicon carbide produced by China’s industry is divided into black silicon carbide and green silicon carbide, both of which are hexagonal crystals and belong to α-SiC.
- Beta Silicon Carbide (β-SiC): Beta silicon carbide, on the other hand, has a cubic crystal structure (similar to a zinc blende crystal structure). It is formed at temperatures below 1700 °C and is often used in the semiconductor industry due to its good thermal conductivity, low thermal expansion, wide band gap, and excellent electron mobility.
It is important to note that these polytypes share the same chemical formula (SiC), but the difference in crystal structure gives them slightly different physical properties. This allows for the material to be used in a wide range of applications, such as in abrasives, structural ceramics, automotive parts, electrical components, and even in aerospace applications.