Chemical compound
Calcium carbide
Names
Preferred IUPAC name
Calcium acetylide
Systematic IUPAC name
Calcium ethynediide
Other names
- Calcium percarbide
- Calcium carbide
- Calcium dicarbide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard
100.000.772
EC Number
PubChem CID
UNII
CompTox Dashboard
(EPA)
- InChI=1S/C2.Ca/c1-2;/q-2;+2 YKey: UIXRSLJINYRGFQ-UHFFFAOYSA-N Y
- InChI=1/C2.Ca/c1-2;/q-2;+2Key: UIXRSLJINYRGFQ-UHFFFAOYAI
Properties
CaC2
Molar mass
64.100 g·mol−1
Appearance
White powder or colorless crystals, grey/brown/black crystals if impure
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)
Reacts to produce Acetylene
Structure
[1
]
Tetragonal (I phase)
Monoclinic (II phase)
Monoclinic (III phase)
I4/mmm (I phase)
C2/c (II phase)
C2/m (III phase)
6
Thermochemistry
Std molar
entropy
(S⦵298)
70 J/(mol·K)
Std enthalpy of
formation
(ΔfH⦵298)
−63 kJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Reacts with water to release acetylene gas
[2
]
GHS labelling:
Danger
H260
NFPA 704 (fire diamond)
305 °C (581 °F; 578 K) (acetylene)
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y (what is
YN ?)
Chemical compound
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.[3]
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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), C (carbon), etc.). In the presence of trace moisture, technical-grade calcium carbide emits an unpleasant odor reminiscent of garlic.[4]
Applications of calcium carbide include manufacture of acetylene gas, generation of acetylene in carbide lamps, manufacture of chemicals for fertilizer, and steelmaking.
Production
[edit]
Calcium carbide is produced industrially in an electric arc furnace from a mixture of lime and coke at approximately 2,200 °C (3,990 °F).[5] This is an endothermic reaction requiring 110 kilocalories (460 kJ) per mole[6] and high temperatures to drive off the carbon monoxide. This method has not changed since its invention in :
- 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 (68 °F) temperature). Impurities present in the carbide include calcium phosphide, which produces phosphine when hydrolysed.[7]
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.[8]
The electric arc furnace method was discovered in by T. L. Willson, and independently in the same year by H. Moissan.[9][10][11] In Jajce, Bosnia and Herzegovina, the Austrian industrialist Josef Kranz and his "Bosnische-Elektrizitäts AG" company, whose successor later became "Elektro-Bosna", opened the largest chemical factory for the production of calcium carbide at the time in Europe in . A hydroelectric power station on the Pliva river with an installed capacity of 8 MW was constructed to supply electricity for the factory, the first power station of its kind in Southeast Europe, and became operational on 24 March .[12]
Crystal structure
[edit]
Calcium carbide is a calcium salt of acetylene, consisting of calcium cations Ca2+ and acetylide anions −C≡C−. Pure calcium carbide is a colourless solid. The common crystalline form at room temperature is a distorted rock-salt structure with the C2−2 units lying parallel.[13] There are three different polymorphs which appear at room temperature: the tetragonal structure and two different monoclinic structures.[1]
Applications
[edit]
Production of acetylene
[edit]
The reaction of calcium carbide with water, producing acetylene and calcium hydroxide,[5] was discovered by Friedrich Wöhler in .
- CaC2(s) + 2 H2O(l) → C2H2(g) + Ca(OH)2(aq)
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.[14] Production of calcium carbide in China has been increasing. In output was 8.94 million tons, with the capacity to produce 17 million tons.[15]
In the United States, Europe, and Japan, consumption of calcium carbide is generally declining.[16] Production levels in the US during the s were 236,000 tons per year.[13]
Production of calcium cyanamide
[edit]
Calcium carbide reacts with nitrogen at high temperature to form calcium cyanamide:[5]
- CaC2 + N2 → CaCN2 + C
Commonly known as nitrolime, calcium cyanamide is used as fertilizer. It is hydrolysed to cyanamide, H2N−C≡N.[5]
Steelmaking
[edit]
Calcium carbide is used:
- in the desulfurization of iron (pig iron, cast iron and steel)[7]
- as a fuel in steelmaking to extend the scrap ratio to liquid iron, depending on economics.
- as a powerful deoxidizer at ladle treatment facilities.
Carbide lamps
[edit]
Main article: Carbide lamp
Calcium carbide is used in carbide lamps. Water dripping on carbide produces acetylene gas, which burns and produces light. While these lamps gave steadier and brighter light than candles, they were dangerous in coal mines, where flammable methane gas 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. Carbide lamps were still used extensively in slate, copper, and tin mines where methane is not a serious hazard. Most miners' 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,[17] although they are increasingly being replaced in this use by LED lights.
Carbide lamps were also used extensively as headlamps in early automobiles, motorcycles and bicycles, but have been replaced entirely by electric lamps.[18]
Other uses
[edit]
Calcium carbide is sometimes used as source of acetylene, which like ethylene gas, is a ripening agent.[19] However, this is illegal in some countries as, in the production of acetylene from calcium carbide, contamination often leads to trace production of phosphine and arsine.[20][21] These impurities can be removed by passing the acetylene gas through acidified copper sulfate solution, but, in developing countries, this precaution is often neglected.
Calcium carbide is used in toy cannons such as the Big-Bang Cannon, as well as in bamboo cannons. In the Netherlands calcium carbide is used around new-year to shoot with milk churns.[22]
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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.
Calcium carbide is used to determine the moisture content of soil. When soil and calcium carbide are mixed in a closed pressure cylinder, the water content in soil reacts with calcium carbide to release acetylene whose pressure can be measured to determine the moisture content.[23][24]
Calcium carbide is sold commercially as a mole repellent.[25] When it comes into contact with water, the gas produced drives moles away.[26]
References
[edit]
Carbide – A Hard, Durable Metal
Carbide is a hard material used in various industrial and machining applications. Its synthesis usually begins with synthesizing the respective metal hydride, which is then treated with carbonaceous materials to produce the carbides. The resulting carbides are extremely hard and wear-resistant.
Carbides: Metal-Based Carbon Compounds
Carbides are carbon-based compounds containing a less electronegative element, typically a metal or metal oxide, and have the symbol CB. Some common ones include calcium carbides, boron carbides, tungsten carbides, and silicon carbides, analyzed extensively below.
Calcium Carbide
Calcium carbide (CaC2) is a chemical compound that is a highly reactive material with numerous industrial applications.
When the compound reacts with water, it emits acetylene gas, a flammable gas used in welding and cutting torches. Acetylene gas can also be used to power carbide lamps and heating appliances. CaC2 is also used to manufacture calcium cyanamide, a fertilizer. It is also used to make vinyl chloride and to desulfurize iron.
Boron Carbide
Boron carbide (B4C), also known as black diamond, is an incredibly hard and durable material in many applications. It has a VHN score of 30 GPa, which makes it one of the hardest known substances on Earth, next to c-BN and diamond.
B4C powder is used as an abrasive in polishing and blasting, as knives and cutting tools, and as a neutron absorber in nuclear reactors. Its low density makes it ideal for use in bulletproof vests and body armor. The material is also used in tank armor to protect against high-velocity kinetic energy penetrators.
Tungsten Carbide
Tungsten Carbide (WC) is a chemical substance of tungsten and carbon in equal parts. It is a grey-colored, extremely hard material (Mohs hardness of 9-9.5, indicating that it is scratch-resistant) frequently used in industrial applications where durability and wear resistance are required.
WC is also used to manufacture cutting tools, drill bits, and other tools that are subject to high levels of wear and tear. In addition to its industrial uses, it is also used in producing jewelry and other consumer products. WC is an excellent neutron reflector in early studies of reactive nuclear species, especially for weapons.
Silicon Carbide
Silicon Carbide, also known as SiC, is a silicon and carbon compound. It occurs naturally in deposits as rare minerals such as moissanite. Still, it can also be generated by reheating grains with each other at high temperatures for hours on end – a process known as sintering- until they turn hard enough even to bond into durable ceramic materials used in a variety of industries such as car clutches, car brakes, and bulletproof vests where strength is critical.
The compound’s electronic applications, including light-emitting diodes (LEDs) and semiconductor power devices, are being designed for high-power application areas in the automotive and industrial markets.
Aluminum Carbide
Aluminum carbide is a chemical compound with the formula Al4C3. It generally occurs as pale yellow to brown particles and is stable up to degrees Celsius. When this material comes into contact with water, it decomposes and emits methane gas.
In addition, finely dispersed Al4C3 particles within an aluminum matrix can help reduce the molecule’s tendency to creep. This is particularly true in the presence of SiC particles. Finally, Al4C3 can be used in high-speed cutting tools as an abrasive. In terms of hardness, this substance is comparable to topaz.
Carbide Types
Carbides are classified broadly based on the chemical bonding between their constituent atoms. Carbides are classified into three types: salt-like or ionic, covalent, and interstitial.
Salt-like or Ionic Carbides
These compounds containing discrete carbon anions can take C4, also known as methanide.
Covalent Carbides
These are two completely covalent carbides. They are made up of the two elements that are the closest in size and electronegativity to carbon, boron, and silicon.
Interstitial Carbides
These combine large transition metals and carbides. Because (C4-) take up the empty spaces of the closed-packed metallic structure, they are extremely hard and brittle.
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Intermediate Transition Metal Carbides
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