Carbide

Carbides are usually a hydrocarbon group of binary of chemical compounds of an element E and the carbon C and the general formula ExCy. An exception is Tantalhafniumcarbid.

• 2.1 carbide lamp
• 2.2 Carbidschießen
• 2.3 Carbidfischen

General

Are manufactured Carbide usually of elemental carbon, which is converted at high temperatures with the corresponding element, elemental oxide or Elementcarbonat in a solid state reaction. The production of calcium carbide and calcium carbonate, for example, coke is carried out at 2000 ° C in an arc furnace.

Depending on the difference in electronegativity between the relevant element and carbon occur carbides of one of the three following types.

Ionic carbides

Ionic carbides ( salt-like carbides ) have a distinct character and salt are typically formed by the strongly electropositive elements of the alkali, alkaline earth and earth elements. They contain carbon as the electronegative component.

Typical examples are lithium carbide Li2C2, beryllium -2c, magnesium carbide Mg2C3, calcium carbide CaC2 or Al4C3 aluminum carbide. They contain in their ionic lattice the respective metal cation and the Carbidion, formally derived from various hydrocarbons. This results in a further differentiation of nonionic Carbide:

• Methanides, eg -2c and Al4C3 contain C4, derived from methane CH4
• Acetylides, eg Li2C2, CaC2 contains, C22, derived from ethyne ( acetylene) C2H2 and
• Allenide, eg Mg2C3 containing C34, derived from Allen C3H4.

Ionic carbides react with water to form the corresponding metal hydroxide and the hydrocarbon, caused by multiple protonation of the anion with water.

The best-known representative is the calcium carbide used in the carbide ( CaC 2 ), often simply called carbide which releases acetylene in the presence of water:

The gray color of the actually white calcium carbide resulted from contamination by elemental carbon from the manufacturing process ( see above). The typical smell of calcium carbide is due to the monophosphane PH3, which is formed in an analogous manner to acetylene by hydrolysis of calcium phosphide. Calcium phosphide formed in the manufacturing process, when the calcium carbonate used contains trace amounts of calcium phosphate as an impurity.

The hydrolysis of calcium carbide was until the 1930s the only method for the industrial production of Acetylene. Calcium carbide was thus an important starting material for the development of acetylene chemistry ( cf. Reppe chemistry). With the advent of the petrochemical industry, that Ethinquelle, however, has lost much of its importance.

Covalent carbides

Covalent carbides are formed between carbon and elements with approximately the same electronegativity. The two main examples are SiC ( silicon carbide, " Carborundum " ) and B4C ( boron carbide ). They have covalent bonds between carbon and the respective element. Very strong covalent bonds associated with a crystal structure very similar to those of other hard materials ( SiC has a diamond -like structure ) leads to a high mechanical stability. Accordingly find these carbides usually as hard materials ( coatings, abrasive) and for reinforcing plastics use. Silicon carbide is also known as carrier material for catalysts in the chemical industry, of interest because it has a high thermal conductivity and virtually no abrasion.

Metal -like carbides

These carbides can be of the elements of the 2nd - 5th Subgroup formed, typical examples are titanium and tungsten. They usually have no well-defined stoichiometry. Rather, the carbon atoms are incorporated into the tetrahedral holes and depending on the size ratio to the metal in the octahedral interstices of the metal lattice and form inclusion compounds or interstitial compounds. These substances are characterized by a high mechanical and thermal stability and high melting points ( 3000 to 4000 ° C) and serve as hard materials and ceramics in chemical engineering and plant construction as cutting and grinding tools. Cementite ( Fe3C ), is a component of the steel.

The ball of a ballpoint pen is composed for example of tungsten carbide.

Popular applications

In common parlance carbide is usually equated with calcium carbide. This reacts with water to form acetylene which can be used for various applications.

Davy lamp

Carbide lamps were in mining and caving, as well as vehicle lighting, widely used. 1 kg of calcium carbide having supplied 250 to 300 liters of ethyne ( acetylene ), which burns with a bright flame to water and carbon dioxide.

Carbidschießen

The tradition of Carbidschießens is mainly cultivated in the Netherlands and in some parts of north-western Germany and northern Bavaria by young men at weddings, New Year's Eve and New Year. In Upper Lusatia it is known as Easter shooting. Due to the high risk potential which Carbidschießen is prohibited in Germany and in the Netherlands permitted only New Year's Eve and New Year, but it is also still practiced in Germany for young people on New Years Eve or similar occasions. In the Netherlands, this veritable Carbidschießfeiern be held. In Carinthia ( Austria ) the Carbidschießen as Easter custom of blessing the food will take place on Holy Saturday until the resurrection on Easter Sunday celebration in the morning instead. If one Calciumcarbidstücke some in a milk jug and they drizzled with a little water, the result is in the sealed with a lid or football volume, an explosive gas mixture of acetylene and oxygen. The gas mixture is then ignited by a previously drilled hole in the ground. The explosion of the cap or football can be thrown as far as up to 70 m.

Carbidfischen

The same principle made ​​in the hunger period after the Second World War, the poor exploited, despite the ban by the occupying powers to make by explosion of a Carbiddose fish in waters rapidly many fish unable to swim and clear away. Carbide was then readily available because of the use of Ethinherstellung for welding work and because of the use in Carbide bicycle lamps.