Silicon Carbide

Chemical Formula

SiC

Topics Covered

Background

Silicon carbide is a hard covalently bonded material predominantly produced by the carbothermal reduction of silica (typically using the Acheson process). Depending on the exact reaction conditions the resulting silicon carbide is either a fine powder or a bonded mass that requires crushing and milling to produce a usable feedstock.

Several hundred structures of silicon carbide (polytypes) have been identified which have different stacking arrangements for the silicon and carbon atoms. The simplest structure is a diamond structure which is designated b-SiC. Other structures are either hexagonal or rhombic and are referred to as a-SiC.

Discovery

The discovery of silicon carbide can best be described with the following excerpt.

“It started about 100 years ago. A struggling scientist, once employed by Thomas Edison, dreamed of becoming wealthy. What better way to riches, he reasoned, than by making artificial diamonds?

The determined young man attached one lead from a dynamo to a discarded plumber’s bowl, filled the bowl with clay and powdered coke, inserted the other lead into the mix and threw the switch. Nothing seemed to happen. He was disappointed until he noticed a few bright specks on the end of the leads. When he drew one lead across a pane of glass, it cut like a diamond.

This young scientist, Dr. Edward Goodrich Acheson, had invented silicon carbide (SiC), the first man-made abrasive and substance hard enough to cut glass. Acheson’s discovery became Carborundum, the trademark for silicon carbide and the name given to the company he started.” - Carborundum Corporation

Key Properties

The outline properties of Silicon Carbide are that it is a refractory material (high melting point), it has excellent thermal conductivity and low thermal expansion, consequently it displays good thermal shock resistance. In addition, the high hardness, corrosion resistance and stiffness lead to a wide range of applications where wear and corrosion resistance are primary performance requirements. Silicon carbide possesses interesting electrical properties due to its semiconductor characteristics, the resistance of different compositions varying by as much as seven orders of magnitude.

Commercial Grades of Silicon Carbide

Commercial silicon carbide products for engineering applications are commonly produced in three forms, sintered silicon carbide (SSC), nitride bonded silicon carbide (NBSC) and reaction bonded silicon carbide (RBSC). However, there are also several other types such as clay bonded silicon carbide and SiAlON bonded silicon carbide. The former is usually used for refractory applications, and many variations exist, depending on the manufacturer.