Carbide is a durable metal that is often compared to diamonds in terms of hardness. It is used in many different applications due to its resistance to corrosion, heat, scratches and pitting. The chemical composition of carbide depends on the element it is made from. For example, calcium carbide (CaC2) is a key raw material for the production of acetylene while silicon carbide, also known as carborundum, is used in ceramics and cutting tools. Iron carbide, also called cementite, is an important component of steel and cast iron.
There are two main types of carbide: interstitial and covalent. Interstitial carbides form when the lattice of a metal with low electronegativity differences attracts carbon atoms to itself. This creates a bond between the carbon and the metal atoms with both pi-bonds and sigma bonds. This type of carbide has a relatively high melting point and is very refractory. Examples of interstitial carbides include TiC, ZrC, HfC, VC, NbC, TaC and WC.
Covalent carbides are formed by the combination of low electronegativity elements like silicon and boron. These carbides exhibit a low electronegativity difference and have sp-d hybridization with each carbon carrying one lone pair. Examples of covalent carbides are boron carbide and silicon carbide, or carborundum.
Complex carbides have a more complicated crystalline structure and are usually much harder than simple carbides. They have a trigonal prism of carbon atoms surrounded by a tetrahedral arrangement of metal atoms with more complicated structures. The stoichiometry of these carbides can vary, and they are typically more stable than the interstitial carbides. The most common examples of complex carbides are titanium carbide (TiC), tungsten carbide (Wc) and vanadium carbide (Vc).