- Structure
- Nomenclature
- Properties
- Physical state
- Molecular weight
- Melting point
- Boiling point
- Density
- Chemical properties
- Obtaining
- Applications
- In the production of acetylene
- In reducing CO emissions
- In obtaining calcium cyanamide
- In the metallurgical industry
- In various uses
- Discontinued use
- Risks
- References
The calcium carbide is an inorganic compound consisting of the elements calcium (Ca) and carbon (C). Its chemical formula is CaC 2. It is a solid that can be colorless to yellowish or grayish white, and even black depending on the impurities it contains.
One of its most important chemical reactions of CaC 2 is that which occurs with water H 2 O, in which it forms acetylene HC≡CH. For this reason it is used to obtain acetylene industrially. Due to the same reaction with water, it is used to ripen fruits, in false guns and in naval flares.
Solid calcium carbide CaC 2. Ondřej Mangl / Public domain. Source: Wikimedia Commons.
The reaction of CaC 2 with water also produces a sludge useful for preparing clinker (a component of cement), which produces less carbon dioxide (CO 2) compared to the traditional method of producing cement.
With nitrogen (N 2), calcium carbide forms calcium cyanamide, which is used as a fertilizer. CaC 2 is also used to remove sulfur from certain metal alloys.
Some time ago CaC 2 was used in so-called carbide lamps, but these are no longer very common because they are dangerous.
Structure
Calcium carbide is an ionic compound and is made up of the calcium ion Ca 2+ and the carbide or acetylide ion C 2 2-. The carbide ion is made up of two carbon atoms joined by a triple bond.
Chemical structure of calcium carbide. Author: Hellbus. Source: Wikimedia Commons.
The crystalline structure of CaC 2 is derived from the cubic one (like that of sodium chloride NaCl), but as the C 2 2- ion is elongated, the structure is distorted and becomes tetragonal.
Nomenclature
- Calcium carbide
- Calcium carbide
- Calcium acetylide
Properties
Physical state
Crystalline solid that when pure is colorless, but if it is contaminated with other compounds it can be yellowish white or grayish to black.
Calcium carbide CaC 2 with impurities. Leiem / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0). Source: Wikimedia Commons.
Molecular weight
64.0992 g / mol
Melting point
2160 ºC
Boiling point
CaC 2 boils at 2300ºC with decomposition. The boiling point must be measured under an inert atmosphere, that is, without oxygen or moisture.
Density
2.22 g / cm 3
Chemical properties
Calcium carbide reacts with water to form acetylene HC≡CH and calcium hydroxide Ca (OH) 2:
CaC 2 + 2 H 2 O → HC≡CH + Ca (OH) 2
Acetylene is flammable, therefore in the presence of humidity CaC 2 can be flammable. However, when it is dry it is not.
Calcium carbide CaC 2 with water forms acetylene HC≡CH, a flammable compound. Kristina Kravets / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0). Source: Wikimedia Commons.
Calcium carbide reacts with nitrogen N 2 to form calcium cyanamide CaCN 2:
CaC 2 + N 2 → CaCN 2 + C
Obtaining
Calcium carbide is produced industrially in an electric arc furnace starting from a mixture of calcium carbonate (CaCO 3) and carbon (C) that is subjected to a temperature of 2000 ° C. The reaction is summarized like this:
CaCO 3 + 3 C → CaC 2 + CO ↑ + CO 2 ↑
Or also:
CaO + 3 C → CaC 2 + CO ↑
In an electric arc furnace an arc of electricity is produced between two graphite electrodes, which resist the high temperatures that are formed. A calcium carbide with 80-85% purity is obtained.
Applications
In the production of acetylene
Industrially, the reaction of calcium carbide with water is used to produce acetylene C 2 H 2.
CaC 2 + 2 H 2 O → HC≡CH + Ca (OH) 2
This is the most important use of calcium carbide. In some countries, acetylene is highly valued, as it allows the production of polyvinyl chloride, which is a type of plastic. Furthermore, acetylene is used for welding at high temperatures.
HC≡CH acetylene flame for welding metals at very high temperatures. Author: Shutterbug75. Source: Pixabay.
In reducing CO emissions
The remains obtained from obtaining acetylene starting from CaC 2 (also called "calcium carbide sludge" or "calcium carbide residues") are used to obtain clinker or concrete.
Calcium carbide mud has a high content of calcium hydroxide (Ca (OH) 2) (around 90%), some calcium carbonate (CaCO 3) and has a pH greater than 12.
Calcium carbide residues can be used in the construction activity to prepare concrete, thus reducing the generation of CO 2 in this industry. Author: Engin Akyurt. Source: Pixabay.
For these reasons, it can react with SiO 2 or Al 2 O 3, forming a product similar to that obtained by the cement hydration process.
One of the human activities that produces the most CO 2 emissions is the construction industry. The CO 2 is generated by being released from the calcium carbonate during the reaction to form concrete.
Using calcium carbide sludge to replace calcium carbonate (CaCO 3) has been found to reduce CO 2 emissions by 39%.
In obtaining calcium cyanamide
Calcium carbide is also used industrially to obtain calcium cyanamide CaCN 2.
CaC 2 + N 2 → CaCN 2 + C
Calcium cyanamide is used as a fertilizer, because with the soil water it converts into cyanamide H2N = C = N, which provides nitrogen to plants, an essential nutrient for them.
In the metallurgical industry
Calcium carbide is used to remove sulfur from alloys such as ferronickel. The CaC 2 is mixed with the molten alloy at 1550 ° C. Sulfur (S) reacts with calcium carbide and produces calcium sulfide CaS and carbon C:
CaC 2 + S → 2 C + CaS
Sulfur removal is favored if mixing is efficient and the carbon content in the alloy is low. Calcium sulfide CaS floats on the surface of the molten alloy from where it is decanted and discarded.
In various uses
Calcium carbide has been used to remove sulfur from iron. Also as a fuel in the production of steel and as a powerful deoxidizer.
It is used to ripen fruit. Acetylene is generated from calcium carbide with water, which induces the ripening of fruits, such as bananas.
Bananas can be ripened using calcium carbide CaC 2. Author: Alexas Fotos. Source: Pixabay.
Calcium carbide is used in dummy guns to cause the loud bang noise that characterizes them. Here also the formation of acetylene is used, which explodes with a spark inside the device.
CaC 2 is used to generate signals offshore in self-igniting naval flares.
Discontinued use
CaC 2 has been used in so-called carbide lamps. The operation of these consists of dripping water on the calcium carbide to form acetylene, which ignites and in this way provides light.
These lamps were used in coal mines, but their use was discontinued due to the presence of methane gas CH 4 in these mines. This gas is flammable and the flame from the carbide lamp can cause it to ignite or explode.
CaC 2 calcium carbide lamp. SCEhardt / Public domain. Source: Wikimedia Commons.
They were widely used in slate, copper and tin rock mines, and also in early automobiles, motorcycles and bicycles, as headlights or headlights.
Currently they have been replaced by electric lamps or even LED lamps. However, they are still used in countries like Bolivia, in the silver mines of Potosí.
Risks
Dry calcium carbide CaC 2 is not flammable but in the presence of moisture it quickly forms acetylene, which it is.
To extinguish a fire in the presence of CaC 2, never use water, foam, carbon dioxide or halogen extinguishers. Sand or sodium or calcium hydroxide should be used.
References
- Ropp, RC (2013). Group 14 (C, Si, Ge, Sn, and Pb) Alkaline Earth Compounds. Calcium Carbides. In Encyclopedia of the Alkaline Earth Compounds. Recovered from sciencedirect.com.
- Pohanish, RP (2017). C. Calcium Carbide. In Sittig's Handbook of Toxic and Hazardous Chemicals and Carcinogens (Seventh Edition). Recovered from sciencedirect.com.
- Sun, H. et al. (2015). Properties of Chemically Combusted Calcium Carbide Residue and Its Influence on Cement Properties. Materials 2015, 8, 638-651. Recovered from ncbi.nlm.nih.gov.
- Nie, Z. (2016). Eco-Materials and Life-Cycle Assessment. Case Study: CO 2 Emission Analysis of Calcium Carbide Sludge Clinker. In Green and Sustainable Manufacturing of Advanced Material. Recovered from sciencedirect.com.
- Crundwell, FK Et al. (2011). Refining Molten Ferronickel. Sulfur Removal. In Extractive Metallurgy of Nickel, Cobalt and Platinum Group Metals. Recovered from sciencedirect.com.
- Tressler, RE (2001). Structural and Thermostructural Ceramics. Carbides. In Encyclopedia of Materials Science and Technology. Recovered from sciencedirect.com.
- Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.