Silicon carbide (SiC) is an extremely hard material that is extremely rare naturally, being found only within meteorites, but is widely manufactured.
In the pre-industrial world it was highly valued as a rare abrasive. The occurrence on the Greek island of Milos in the form of significant quantities of corundum (which contains traces of silicon carbide) has been cited as as factor in the advances made in statuary by the Ancient Greeks. Natural silicon carbide is known as moissanite after Ferdinand Henri Moissan who first discovered its presence in a meteorite in Arizona. Moissanite continues to be a term used in lapidiary and amongst jewellers for a subsititute for diamond.
The commercial manufacture of silicon carbide, known as the 'the Acheson process' consists of fusing sand and coke in an electric furnace at temperatures above 2,200°C. The reaction can be represented as:
SiO2 + 3C = SiC + 2CO
The manufactured product is known by various trade-names including 'Carborundum
' and 'Crystolon
As a material silicone carbide has a hexagonal crystalline structure. It is a hard, highly stable material, its hardness on the Mohs scale is 9 (2150-2950 absolute), compared to diamond at 10 (8000-8500 absolute). It has a high melting point and a very low thermal expansion coefficient making its use as a ceramic ideal for furnace parts and bearings. There is significant current interest in its use as a semiconductor, it is currently used for blue LEDs and as a substrate for other semiconductor materials such as gallium nitride. The electroluminescence of silicon carbide makes it valuable as an ultra violet detector. It is also used as a mirror surface for astronomy.