Calcium carbide is a chemical compound with the chemical formula CaC2. Its appearance depends on the grade and ranges from black through to grayish white lumps. Its main use now is as a source of acetylene. In China, acetylene is a feedstock for the chemical industry, in particular for the production of polyvinyl chloride, PVC.
Locally produced acetylene is more economic than using imported oil. Production of calcium carbide in China has been increasing. In 2005
output was 8.94 million tons with capacity to produce 17 million tons. In the USA, Europe and Japan consumption is generally reducing. Production levels in the USA in 1990 were 236,000 tons pa.
Calcium carbide is produced industrially in an electric arc furnace loaded with a mixture of lime and coke at about 2000 °C, this method has not changed since its invention in 1888.Calcium carbide is formed:
Calcium carbide synthesis requires an extremely high temperature,
~2000 °C, which 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 a few mm up to 50mm. 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.
Calcium carbide was used in carbide lamps, in which water drips on carbide and the formed acetylene is ignited. These lamps were of no use in coal mines where the presence of the explosive gas methane made them a serious hazard. The presence of explosive gases in coal mines led to the miner safety lamp. However carbide lamps were used extensively in slate, copper and tin mines, but most have now been replaced by electric lamps.
Carbide lamps are still used by some cavers exploring caves and other underground areas, though they are increasingly being replaced in this use by LED lights. They were also used extensively as head lights in early automobiles, though in this application they are also obsolete, having been replaced entirely by electric lamps.
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.
In the ripening of fruit, it is used as source of acetylene gas, which is a ripening agent (similar to ethylene). It is still used in the Netherlands and Belgium for a traditional custom called Carbidschieten (Shooting Carbide). To create an explosion, carbide and water are put in a milk churn with a lid. Ignition is usually done with a torch. Some villages in the Netherlands fire multiple milk churns in a row as an oldyear tradition. The old tradition comes from the old pagan religion to chase off spirits.
Calcium carbide is also used in small carbide lamps called carbide candles, which are used for blackening rifle sights to reduce glare. These “candles” are used due to the sooty flame produced by acetylene.
|Toxicological information||Calcium carbide LD50: Not available. LC50: Not available|
|Physical and Chemical Properties|
|Molecular Weight||64.1 g/mole|
|Melting Point||2300°C (4172°F)|
|Specific Gravity||2.22 (Water = 1)|
|Specification item grade||Superfine Grade||First Grade||Second Grade|
|Total content of nitrogen min. %||
|Free calcium carbide max. %||
|Through 250 mesh max. %||