Carbides, Survey

Abstract

AbstractCarbon reacts with many elements of the Periodic Table to form a diverse group of compounds known as carbides, some of which are extremely important in technology. For example, calcium carbide, CaC2, is a source of acetylene; silicon carbide, SiC, and boron carbide, B4C, are used as abrasives; tungsten carbide, WC, titanium carbide, TiC, and tantalum (niobium) carbide, TaC(NbC), find use as structural materials at extremely high temperatures or in corrosive atmospheres. Cementite, Fe3C, and the multimetallic complexes (Co,W)6C, (Cr,Fe,Mo)23C6, and (Cr,Fe)7C3are the components in tool steels and Stellite‐type alloys responsible for their hardness, wear resistance, and excellent cutting performance. There are also emerging applications of these materials as catalysts. Binary compounds of carbon are divided into four main groups: the salt‐like, metallic, diamond‐like, and volatile compounds of carbon. The nature of the bonding is correspondingly of ionic, metallic, semiconductor, or covalent character, but these divisions are not rigid and there are a number of transitional cases. A number of compounds, although containing carbon, fit only marginally in the category of carbides. This includes the acetylides and the alkali metal–graphite compounds, the coordination and organometallic compounds, ML. Carbides are generally prepared by the direct reaction of carbon with metals or metal‐like materials at elevated temperatures. Their most outstanding properties are extreme hardness and physical strength combined with high temperature stability.