silicon carbide

silicon carbide. It is a compound of silicon and carbon known for its exceptional hardness and thermal stability. This semiconductor material occurs naturally as the rare mineral moissanite, but is predominantly produced synthetically for industrial use. Its unique combination of properties has made it critical in applications ranging from abrasives to advanced electronics.

Properties

Silicon carbide exhibits extreme hardness, ranking 9 on the Mohs scale, just below diamond. It possesses high thermal conductivity, which is superior to many metals, and maintains its mechanical strength at temperatures exceeding 1600°C. The material is chemically inert and resistant to oxidation and corrosion from many acids and alkalis. Its wide band gap allows it to function as a semiconductor under high-temperature, high-voltage, and high-frequency conditions where silicon fails. These properties are derived from its strong covalent bonds within a stable crystal lattice.

Production

The primary industrial method for producing silicon carbide is the Acheson process, developed by Edward Goodrich Acheson in the 1890s. This involves heating a mixture of silica sand and petroleum coke in a resistive furnace to temperatures above 2200°C. More modern techniques include the Lely process, which yields high-purity single crystals, and chemical vapor deposition for creating thin films. Companies like Saint-Gobain and Cree (now Wolfspeed) are major producers. The synthesis process must carefully control impurities, as they significantly affect the electrical properties of the final material.

Applications

Historically, its primary use has been as an abrasive in grinding wheels, sandpaper, and cutting tools, often marketed under the trade name Carborundum. In metallurgy, it serves as a deoxidizing agent in steel production, such as in processes at ArcelorMittal. In electronics, it is a key material for high-power devices like Schottky diodes and MOSFETs used in electric vehicles from Tesla, Inc. and power grids. It is also used in ceramic matrix composites for brake discs in high-performance cars from Porsche and in protective cladding for nuclear fuel rods in reactors like those operated by Westinghouse Electric Company.

History

The natural form, moissanite, was first identified in 1893 by Ferdinand Henri Moissan in the Canyon Diablo meteorite in Arizona. Edward Goodrich Acheson accidentally synthesized the material in 1891 while attempting to create artificial diamonds, leading to the founding of the Carborundum Company. Its value as an industrial abrasive was immediately recognized, revolutionizing machining and grinding. During World War II, it was a strategic material for armor plating. The late 20th century saw its emergence as a critical semiconductor, with pioneering research conducted at institutions like North Carolina State University and commercialized by companies such as Infineon Technologies.

Crystal structure

Silicon carbide is notable for its polymorphism, existing in many different crystal structures called polytypes. The most common polytypes are the hexagonal 6H-SiC and the cubic 3C-SiC (also known as beta-silicon carbide). These structures are composed of tetrahedrally coordinated silicon and carbon atoms, with the stacking sequence of the close-packed layers determining the polytype. The different polytypes have varying electronic properties; for instance, 4H-SiC is preferred for many power semiconductor devices. The study of these structures has been advanced by work at laboratories like the Lawrence Berkeley National Laboratory.