|Jmol-3D images||Image 1|
|Molar mass||64.099 g/mol|
|Appearance||White powder to grey/black crystals|
2160 °C, 2433 K, 3920 °F
2300 °C, 2573 K, 4172 °F
|Solubility in water||decomposes|
|Crystal structure||Tetragonal |
|Space group||D174h, I4/mmm, tI6|
|Std enthalpy of
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.). Because of presence of PH3 (phosphine), NH3 (ammonia), and H2S (hydrogen sulfide), the smell of technical-grade calcium carbide is part of the process or production and is produced intentionally to be unpleasant in larger concentrations, and noticeable in smaller ones, as a part of warning system for unwanted leaks, fires or explosion.
It is illegally used for ripening fruits in India, consumption of which can lead to cancer.
- 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. 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 cancer and other serious health problems in those who partake them.
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- "Caving equipment and culture (from Te Ara Encyclopedia of New Zealand)".
- Clemmer, Gregg (1987). American Miners' Carbide Lamps: A Collectors Guide to American Carbide Mine Lighting. Westernlore Publications.
- IUPAC name ethene, chemical formula of C2H4
- F. B. Abeles and H. E. Gahagan, III (1968). "Abscission: The Role of Ethylene, Ethylene Analogues, Carbon Dioxide, and Oxygen". Plant Physiol. 43 (8): 1255–1258. doi:10.1104/pp.43.8.1255. PMC 1087003. PMID 16656908.
- Calcium Carbide & Acetylene at The Periodic Table of Videos (University of Nottingham)
- Calcium Carbide Manufacturing
- 2008 Material Safety Data Sheet