Industrial Carbon and Graphite Materials. Группа авторов. Читать онлайн. Newlib. NEWLIB.NET

Автор: Группа авторов
Издательство: John Wiley & Sons Limited
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Жанр произведения: Техническая литература
Год издания: 0
isbn: 9783527674053
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of carbon are diamond, graphite, and amorphous carbon (Figure 2.2). These three allotropes are of industrial relevance. The most important by volume is amorphous carbon. Fullerenes represent a new allotropic form whose industrial breakthrough is still pending despite their extraordinary physical properties. The structural forms of the different allotropes are shown in Figure 2.3 [5, 6] and Figure 2.4 [6].

Property Boron Carbon Nitrogen
Atomic number 5 6 7
Classification Semimetal Nonmetal Nonmetal
State Solid Solid Gas
Density, g/cm3 2.46 G = 2.26, D = 3.53 0.00125
Mohs hardness 9.3 G = 0.5, D = 10
Melting point, K 2349 3773 (sublimation) 63.05
Boiling point, K 4203 5115 77.15
Heat of evaporation, kJ/mol 508 715 (sublimation) 5.58
Specific heat, J/kg K 1260 G = 709, D = 427 1040
Electrical conductivity, S/m 10−6 G = 2–3·105, ∥ 3.3 102, ⊥ D = ∼ 10−13 0
Thermal conductivity, W/mK 27.4 G = 119–165 D = 900–2300 25.8·10−3
Graph depicts the relative abundance of elements in the Earth's upper crust.

      The element carbon achieves in the form of graphite the highest sublimation point among all elements. In the allotropic form of diamond, carbon has the highest hardness. These outstanding properties are due to the formation of covalent bonds between the carbon atoms. In the case of diamond, four covalent bonds (sp3 hybridization) form a face‐centered cubic lattice with an interatomic distance of 0.154 nm. In the case of graphite, three covalent bonds form a hexagonal planar network with a bond length of 0.142 nm in the plane and an interplane distance of 0.335 nm. The fourth bonding p‐orbital overlaps with other adjacent p‐orbitals and creates the energy band for dislocated electrons (sp2 hybridization). The weak bonding between the layers is described as being of metallic character on the order of magnitude of van der Waals forces [7]. This results in a high electrical conductivity comparable with those of metals.

Schematic illustration of the hierarchical structure of allotropic modifications of the element carbon.

      Carbon is the sine qua non condition for life on Earth. The capability to form complex three‐dimensional molecules by single or double bonds between carbon atoms and the incorporation of heteroatoms such as nitrogen, oxygen, phosphorus, sulfur, and last but not least hydrogen open a tremendous biological diversity. Some examples of these complex molecules are proteins, vitamins, and the genetic makeup in DNA, RNA, and adenosine triphosphate (ATP), the most important molecule for energy transfer in living organisms. Others are carbohydrates like starch or sugar. The research on this group of molecules has once initiated the separation into organic and inorganic chemistry. Meanwhile also synthetic macromolecules, such as polymers, are considered to be organic molecules, formed by covalent bonds between carbon atoms and by incorporating heteroatoms. Fossils like crude oil and coals are ranked as organic substances metamorphosed from once‐living matter. By far the majority of carbon compounds are classified as organic molecules. Only a few ones are located under the group of carbon‐containing inorganic compounds. Examples are carbon monoxide (CO) and carbon dioxide (CO2), cyanides (CN), all carbides, and carbolic acid. The largest sources of inorganic carbon are limestone and dolomite.

Schematic illustration of the four most important allotropic forms of the solid element carbon and their main derivatives. Schematic illustration of the bonding hybridization and corresponding crystal structure of carbon allotropes.