Ceramics

Silicon carbide (SiC) has been found to occur naturally only as small green hexagonal plates in metallic iron. The same form of silicon carbide has been manufactured synthetically, however. In this process, SiO₂ sand is mixed with coke in a large elongated mound in which large carbon electrodes have been placed at either end. As electric current is passed between the electrodes, the coke is heated to about 3,992°F (2,200°C). The coke reacts with the SiO₂ to produce SiC plus CO gas. Heating continues until the reaction has completed in the mound. After cooling, the mound is broken up, and the green hexagonal SIC crystals, which are low in impurities and suitable for electronic applications, are removed. The lower purity material is used for abrasives. The outer layer of the mound is reused in the next batch. SiC can be formed from almost any source of silicon and carbon. It has been produced in the laboratory from silicon metal powder and sugar, and from rice hulls. SiC is used for high-temperature kiln furniture, electrical resistance heating elements, grinding wheels and abrasives, wear-resistance applications, and incinerator linings.