Carbide

Calcium carbide.

In chemistry, Carbide confusingly refers to three different things:

1. The polyatomic ion C₂²⁻, or any salt of such. There is a triple covalent bond between the two carbon atoms.

2. The monatomic ion C⁴⁻, or any salt of such. This ion is a very strong base, and will combine with four protons to form methane: C⁴⁻ + 4 H⁺ → CH₄.

3. A carbon-containing alloy or doping of a metal or semiconductor, such as steel.

Contents

1 Examples
2 Types of carbides

2.1 Methides
2.2 Acetylides
2.3 Compounds that do not fit usual notions of valence or stoichiometry
2.4 Interstitial carbides
2.5 Some covalent compounds

3 Properties
4 External links

Examples

Sodium carbide (Na₂C₂)
Silicon carbide (SiC)
Tungsten carbide (often called simply carbide)
Cementite (iron carbide; Fe₃C)

See for a bigger list.

Types of carbides

Methides

A salt corresponding to the ion C⁴⁻ can be called a methide. Methides commonly react with water to form methane, however reactions with other substances are common.

Acetylides

A salt corresponding to the ion C₂²⁻ can be called an acetylide. Acetylides commonly react with water to form acetylene.

Compounds that do not fit usual notions of valence or stoichiometry

Interstitial carbides

These are formed with metals; they often have metallic properties.

Some covalent compounds

Elements that have similar electronegativity form mainly covalent compounds. For example, the compound silicon carbide is mostly covalent; it has similar structure to diamond.

Properties

Under conditions of standard temperature and pressure, metal carbides react strongly with water to form metal oxides or hydroxides and flammable acetylene gas, e.g.:

CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂

Carbide lamps, an important source of portable subterranean illumination for mining and caving, and in the past for lighthouse lamps, work through on-demand production and combustion of acetylene by the metered addition of water to calcium carbide.

Gas lighting, using acetylene gas generated from carbide, was used in some homes before the incandescent lamp came into widespread use. It was also the main source of lighting on bicycles and carriages before the widespread availability of electric lamps and batteries. The carbide was prepared industrially by the action of an electric arc furnace on a mixture of coke and limestone.

In the northern, eastern and southern regions of the Netherlands and in Belgium carbide is used as fireworks. 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.

External links

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