Calcium carbide

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Calcium carbide
Calcium Carbide
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Identifiers
CAS number 75-20-7 YesY
PubChem 6352
ChemSpider 6112 YesY
Jmol-3D images Image 1
Properties
Molecular formula CaC2
Molar mass 64.099 g/mol
Appearance White powder to grey/black crystals
Density 2.22 g/cm3
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
Structure
Crystal structure Tetragonal [1]
Space group D174h, I4/mmm, tI6
Coordination
geometry
6
Thermochemistry
Std molar
entropy
So298
70 J·mol−1·K−1
Std enthalpy of
formation
ΔfHo298
−63 kJ·mol−1
Hazards
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references
Calcium carbide.

Calcium carbide is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of acetylene and calcium cyanamide.[2]

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.[3]

Production[edit]

Calcium carbide is produced industrially in an electric arc furnace from a mixture of lime and coke at approximately 2000 °C. This method has not changed since its invention in 1888:

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.[4]

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.[5]

The method for the production in an electric arc furnace was discovered independently by T. L Willson and H. Moissan in 1888 and 1892.[6][7]

Crystal structure[edit]

Pure calcium carbide is a colourless solid. The common crystalline form at room temperature is a distorted rock-salt structure with the C22− units lying parallel.[8]

Applications[edit]

Production of acetylene[edit]

The reaction of calcium carbide with water, producing acetylene and calcium hydroxide, was discovered by Friedrich Wöhler in 1862.

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.[9] 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.[10]

In the USA, Europe, and Japan, consumption of calcium carbide is generally declining.[11] Production levels in the USA in 1990s were 236,000 tons per year.[8]

Production of calcium cyanamide[edit]

Calcium carbide reacts with nitrogen at high temperature to form calcium cyanamide:

CaC2 + N2 → CaCN2 + C

Calcium cyanamide is used as fertilizer. It is hydrolysed to cyanamide, H2NCN.[8]

Steelmaking[edit]

Calcium carbide is used:

Carbide lamps[edit]

Main article: Carbide lamp
Lit carbide lamp

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,[12] although they are increasingly being replaced in this use by LED lights.

Carbide lamps were also used extensively as headlights in early automobiles, motorcycles and bicycles, but have been replaced entirely by electric lamps.[13]

Other uses[edit]

In the artificial ripening of fruit, calcium carbide is sometimes used as source of acetylene gas, which is a ripening agent similar to ethylene.[14][15] However, this is illegal as consumption of fruits artificially ripened using calcium carbide can cause serious health problems in those who partake them.[16]

Calcium carbide is used in toy cannons such as the Big-Bang Cannon, as well as in bamboo cannons.

Calcium carbide, together with calcium phosphide, is used in floating, self-igniting naval signal flares, such as those produced by the Holmes' Marine Life Protection Association.

References[edit]

  1. ^ Massalimov, I. A.; Kireeva, M. S.; Sangalov, Yu. A. (2002). Inorganic Materials 38 (4): 363. doi:10.1023/A:1015105922260. 
  2. ^ Patnaik, Pradyot (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill. ISBN 0-07-049439-8. Retrieved 2009-06-06. 
  3. ^ Jeffrey Wayne Vincoli (25 November 1996). Risk Management for Hazardous Chemicals. CRC Press. p. 429. ISBN 978-1-56670-200-3. 
  4. ^ a b Calcium Carbide, Bernhard Langhammer, Ullmann's Encyclopedia of Industrial Chemistry, Wiley Interscience. (Subscription required)
  5. ^ Freeman, Horace (1919). "Manufacture of Cyanamide". The Chemical News and the Journal of Physical Science 117: 232. Retrieved 23 December 2013. 
  6. ^ J. T. Morehead, G. de Chalmot (1896). "The Manufacture of Calcium Carbide". Journal of the American Chemical Society 18 (4): 311–331. doi:10.1021/ja02090a001. 
  7. ^ H. Moissan (1892). "Chimie Minérale – Description d'un nouveau four électrique". Comptes rendus hebdomadaires des séances de l'Académie des sciences 115: 1031. 
  8. ^ a b c Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  9. ^ Ya Dun (2006-01-23). "Troubles in the PVC industry". Hong Kong Trade Development Council. 
  10. ^ "Government takes measures to curb development of calcium carbide sector". BusyTrade.com. 2007-05-16. 
  11. ^ Jamie Lacson, Stefan Schlag and Goro Toki (December 2004). "Calcium Carbide". SRI Consulting. 
  12. ^ "Caving equipment and culture (from Te Ara Encyclopedia of New Zealand)". 
  13. ^ Clemmer, Gregg (1987). American Miners' Carbide Lamps: A Collectors Guide to American Carbide Mine Lighting. Westernlore Publications. 
  14. ^ IUPAC name ethene, chemical formula of C2H4
  15. ^ 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. 
  16. ^ "Bet on it. Your mango is ripened using carbide". Daily News and Analysis. May 18, 2013. Retrieved 2013-05-19. 

External links[edit]