Carbide, in chemistry, a compound of carbon with another element. The introduction of the electric furnace into practical chemistry was followed by the preparation of many metallic carbides previously unknown, some of which, especially calcium carbide, are now of great commercial importance. Carbides of the following general formulae have been obtained by H. Moissan (M denotes an atom of metal and C of carbon):—
M3C = manganese, iron; M2C = molybdenum; M3C2 = chromium; MC = zirconium; M4C3 = beryllium, aluminium; M2C3 = uranium; MC2 = barium, calcium, strontium, lithium, thorium, &c.; MC4 = chromium.
The principal methods for the preparation of carbides may be classified as follows:—(1) direct union at a high temperature, e.g. lithium, iron, chromium, tungsten, &c.; (2) by the reduction of oxides with carbon at high temperatures, e.g. calcium, barium, strontium, manganese, chromium, &c.; (3) by the reduction of carbonates with magnesium in the presence of carbon, e.g. calcium, lithium; (4) by the action of metals on acetylene or metallic derivatives of acetylene, e.g., sodium, potassium. The metallic carbides are crystalline solids, the greater number being decomposed by water into a metallic hydrate and a hydrocarbon; sometimes hydrogen is also evolved. Calcium carbide owes its industrial importance to its decomposition into acetylene; lithium carbide behaves similarly. Methane is yielded by aluminium and beryllium carbides, and, mixed with hydrogen, by manganese carbide. The important carbides are mentioned in the separate articles on the various metals. The commercial aspect of calcium carbide is treated in the article Acetylene.
