Graphite

The graphite is a Minéral which is, with the Diamant, the Lonsdaleite and the Chaoite, one of the natural allotropes of the Carbone; it is a native element which is especially in the Sédiment S of regional Métamorphisme but, according to the rocks, it can be also formed starting from the organic coal, of the magma or by reduction of the carbonates.

Its structure consists of noncompact hexagonal layers, named graphenes , separated from approximately 0,336 Nm along the direction of their normal. In each layer, the carbon atoms are strongly bound by covalent bonds of the sp2 type, while the connections between the layers are weak, of π type, which explains the Clivage and weak the hardness.

The word “graphite” is derived from the Greek radical of γράφειν “to write”, with addition of the suffix - ite .

Physical properties

Graphite is the stable shape of carbon at ordinary temperature and pressure.

The appearance of graphite is that of a black solid to the submetallic glare; its hardness is low, between 1 and 2 on the scale of Mohs.

Because of its structure in layers, all the physical properties of graphite are anisotropic. In particular, the electric Conductivité is very different in the plan from the layers and the perpendicular direction.

Polytypism

Graphite exists into two polytypes:

  • graphite-2 H , crystalline System hexagonal, crystalline Class dihexagonale-bipyramidale, Group of space P 63/ mmc , stacking of the type ABAB where the plan B is relocated of a/\ sqrt {3} compared to plan A. Although its structure is similar to that of metals which crystallize with compact hexagonal stacking, graphite is a Non-métal. It has a certain electric conductivity, its electrical resistance is of 50 µ Ω .m, that is to say 2900 times that of the Cuivre.
  • graphite-3 R , trigonal with network rhomboedric, stacking of the type ABCABC. The rhomboedric structure is unstable: it occurs by moulding and disappears during an annealing. One never finds it like forms pure, but only like tendency to stacking ABC in the primary education hexagonal crystals.

The coal exists in touts the intermediate states between coal Amorphe and hexagonal graphite. One speaks about graphite “lubricostratic” (Latin “lubrico” to make slipping ) when the layers are moved in parallel randomly, and of graphite “turbostratic” (Latin “turbo” swirl ) if they are also turned randomly.

Uses

Graphite has many industrial applications, in various natural or synthetic forms:
  • mechanical engineering: parts of friction, seals, products lubricating;
  • electrical engineering: balas of engines;
  • like reducing, in particular in Iron and steel industry (coke of the blast furnaces);
  • like electrode, for example in iron and steel industry (electric steel);
  • like cathode, for example in the industry of electrolysis of aluminum;
  • like moderating in nuclear reactors;
  • like adsorbent, in the filter S with “activated carbon”.

It is also used in medicine as adsorbent in the event of Intoxication by oral way.

In the Visual arts, it is used for the Dessin (Fusain). It is used in particular to manufacture pencils, often under the incorrect name of “Black lead”.

The use domesticates most current is the lead pencil.

Also can it be used as alloy composite (Titane/Glass fiber/Aluminum) in the manufacture of the executives of rackets of tennis.

Simple: Graphite

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