Calcium carbide

Calcium carbide, also known as calcium acetylide, is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of acetylene and calcium cyanamide. The pure material is colorless, while pieces of technical-grade calcium carbide are grey or brown and consist of about 80–85% of CaC2 (the rest is CaO (calcium oxide), Ca3P2 (calcium phosphide), CaS (calcium sulfide), Ca3N2 (calcium nitride), SiC (silicon carbide), etc.). In the presence of trace moisture, technical-grade calcium carbide emits an unpleasant odor reminiscent of garlic. Applications of calcium carbide include manufacture of acetylene gas, generation of acetylene in carbide lamps, manufacture of chemicals for fertilizer, and steelmaking. Calcium carbide is produced industrially in an electric arc furnace from a mixture of lime and coke at approximately . This is an endothermic reaction requiring per mole and high temperatures to drive off the carbon monoxide. This method has not changed since its invention in 1892: CaO + 3 C → CaC2 + CO The high temperature required for this reaction is not practically achievable by traditional combustion, so the reaction is performed in an electric arc furnace with graphite electrodes. The carbide product produced generally contains around 80% calcium carbide by weight. The carbide is crushed to produce small lumps that can range from a few mm up to 50 mm. The impurities are concentrated in the finer fractions. The CaC2 content of the product is assayed by measuring the amount of acetylene produced on hydrolysis. As an example, the British and German standards for the content of the coarser fractions are 295 L/kg and 300 L/kg respectively (at 101 kPa pressure and temperature). Impurities present in the carbide include calcium phosphide, which produces phosphine when hydrolysed. This reaction was an important part of the industrial revolution in chemistry, and was made possible in the United States as a result of massive amounts of inexpensive hydroelectric power produced at Niagara Falls before the turn of the 20th century.