Definitions of carbon forms and processes

Graphite is defined as a material consisting mainly of graphitic carbon which has been abtained by means of graphitization heat treatment of a non-graphitic carbon or by chemical vapor deposition (CVD) from hydrocarbons at temperatures above 1800C to give a deposit with the graphite structure.

Non-graphitic carbons:

Non-graphitic carbons are all varieties of substances consisting mainly of the element carbon with two dimensional long-range order of the carbon atoms in planar hexagonal networks, but without any measurable crystallographic order in the direction perpendicular to the planes (c-direction). Many non-graphitic carbons can be converted to graphite by graphitization heat treatment to 2200C or above. Non-graphitizable carbons are those which cannot be transformed into graphitic carbon solely by heat treatment at temperature of 3000C or above under atmospheric or lower pressures.

Pitches:

Pitches are carbonaceous materials derived from organic precursors by relatively low temperature processes below 400C such as distillation. They are oligomers containing a wide range of molecular types and masses. Most pitches melt on heating to yield an isotropic fluid. Continued heating above 375C results in the alignment of lamellar molecules leading to nematic discotic liquid crystals. The further development of this liquid crystal or mesophase system provides the basic microstructure of the final carbon product, dictating its optical texture.

Volatile matter is released from the bulk of the pitch material through-out the carbonization process which, together with the complex packing within and between the carbonized particles, results in porosity in the final product. The degree and nature of the porosity depend upon the precursor and the conditions of the carbonization process. Two principal types of pitch are used as matrix precursors. Coal-tar pitch is a product of coal distillation, generally containing fused aromatic ring systems with minimal aliphatics. Petroleum pitches are the heavy residues of petroleum processing, consisting mainly of alicyclic rings with some aromatic, methylene and alkyl groups. Petroleum pitch cokes are generally the more graphitizable of the two.

Cokes:

A coke is a highly ordered carbonaceous product of the pyrolysis of organic material, at least parts of which have passed through a liquid…

 

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