|Jmol-3D images||Image 1|
|Molar mass||64.099 g/mol|
|Appearance||White powder to grey/black crystals|
|Melting point||2,160 °C (3,920 °F; 2,430 K)|
|Boiling point||2,300 °C (4,170 °F; 2,570 K)|
|Solubility in water||decomposes|
|Crystal structure||Tetragonal |
|Space group||D174h, I4/mmm, tI6|
|Std enthalpy of
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
The pure material is colorless, however 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.
- 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 20°C temperature). Impurities present in the carbide include phosphide, which produces phosphine when hydrolysed.
This reaction was an important part of the industrial revolution in chemistry, and was made possible in the USA as a result of massive amounts of inexpensive hydroelectric power produced at Niagara Falls before the turn of the 20th century.
Production of acetylene
- CaC2 + 2 H2O → C2H2 + Ca(OH)2
This reaction was the basis of the industrial manufacture of acetylene, and is the major industrial use of calcium carbide.
Today acetylene is mainly manufactured by the partial combustion of methane or appears as a side product in the ethylene stream from cracking of hydrocarbons. Approximately 400,000 tonnes are produced this way annually (see Acetylene Preparation).
In China, acetylene derived from calcium carbide remains a raw material for the chemical industry, in particular for the production of polyvinyl chloride. Locally produced acetylene is more economical than using imported oil. Production of calcium carbide in China has been increasing. In 2005 output was 8.94 million tons, with the capacity to produce 17 million tons.
Production of calcium cyanamide
Calcium carbide reacts with nitrogen at high temperature to form calcium cyanamide:
- CaC2 + N2 → CaCN2 + C
Calcium carbide is used:
- in the desulfurisation of iron (pig iron, cast iron and steel)
- as a fuel in steelmaking to extend the scrap ratio to liquid iron, depending on economics.
- as a powerful deoxidizer at ladle treatment facilities.
Calcium carbide is used in carbide lamps, in which water drips on the carbide and the acetylene formed is ignited. These lamps were usable but dangerous in coal mines, where the presence of the flammable gas methane made them a serious hazard. The presence of flammable gases in coal mines led to miner safety lamps such as the Davy lamp, in which a wire gauze reduces the risk of methane ignition. However, carbide lamps were still used extensively in slate, copper, and tin mines, where methane is not a serious hazard, but most miner's lamps have now been replaced by electric lamps.
Carbide lamps are still used for mining in some less wealthy countries, for example in the silver mines near Potosí, Bolivia. Carbide lamps are also still used by some cavers exploring caves and other underground areas, although they are increasingly being replaced in this use by LED lights.
In the artificial ripening of fruit, calcium carbide is sometimes used as source of acetylene gas, which is a ripening agent similar to ethylene. However, this is illegal as consumption of fruits artificially ripened using calcium carbide can cause serious health problems in those who partake them.
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- IUPAC name ethene, chemical formula of C2H4
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