carbides

Carbides are compounds of carbon chemically bonded to a less electropositive element. They include binary metal carbides as well as carbides of metalloids such as silicon and boron. The term covers materials with a range of bonding types, from ionic and covalent to metallic, and many carbides are extremely hard and thermally stable.

Prominent examples include silicon carbide (SiC), tungsten carbide (WC), calcium carbide (CaC2), and boron carbide (B4C). These substances typically have high melting points, high hardness, and good chemical stability. Transition-metal carbides such as TiC, VC, and WC combine hardness with electrical conductivity, while covalent ceramics like SiC and B4C offer superior wear resistance.

Uses span cutting tools, grinding wheels, wear-resistant coatings, and refractories. Calcium carbide is industrially important as a precursor to acetylene gas. Boron carbide is used as an abrasive and as a neutron absorber in reactor control rods.

Production methods include direct synthesis by reacting carbon with a metal at high temperatures, or carbothermic reduction of metal oxides in carbon-containing atmospheres. Some iron carbides, such as cementite (Fe3C), form in steel and influence hardening and strength.