Graphitizing and non-graphitizing carbons (alternatively graphitizable and non-graphitizable carbon) are the two categories of

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

produced by

pyrolysis The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''p ...

of organic materials.

Rosalind Franklin Rosalind Elsie Franklin (25 July 192016 April 1958) was a British chemist and X-ray crystallographer whose work was central to the understanding of the molecular structures of DNA (deoxyribonucleic acid), RNA (ribonucleic acid), viruses, c ...

first identified them in a 1951 paper in ''

Proceedings of the Royal Society ''Proceedings of the Royal Society'' is the main research journal of the Royal Society. The journal began in 1831 and was split into two series in 1905: * Series A: for papers in physical sciences and mathematics. * Series B: for papers in life s ...

''. In this paper, she defined graphitizing carbons as those that can transform into crystalline graphite by being heated to 3000°C, while non-graphitizing carbons don't transform into graphite at any temperature. Precursors that produce graphitizing carbon include polyvinyl chloride (PVC) and petroleum coke.

Polyvinylidene chloride Polyvinylidene chloride, or polyvinylidene dichloride (PVDC), is a homopolymer of vinylidene chloride. History Ralph Wiley accidentally discovered polyvinylidene chloride polymer in 1933. He, then, was a college student who worked part-time at ...

(PVDC) and

sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refi ...

produce non-graphitizing carbon. Physical properties of the two classes of carbons are quite different. Graphitizing carbons are soft and non-porous, while non-graphitizing carbons are hard, low density materials. Non-graphitizing carbons are otherwise known as ''chars'', ''hard carbons'' or, more colloquially, charcoal. Glassy carbon is also an example of non-graphitizing carbon. The precursors for graphitizing carbons pass through a fluid stage during pyrolysis (

carbonization Carbonization is the conversion of organic matters like plants and dead animal remains into carbon through destructive distillation. Complexity in carbonization Carbonization is a pyrolytic reaction, therefore, is considered a complex proces ...

). This fluidity facilitates the molecular mobility of the aromatic molecules, resulting in intermolecular dehydrogenative polymerization reactions to create aromatic, lamellar (disc-like) molecules. These “associate” to create a new liquid crystal phase, the so-called mesophase. A fluid phase is the dominant requirement for production of graphitizable carbons.H. Marsh and M.A. Diez (1994) " Mesophase of Graphitizable Carbons" In: Shibaev V.P., Lam L. (eds) Liquid Crystalline and Mesomorphic Polymers. Springer, New York, NY Non-graphitizing carbons generally do not pass through a fluid stage during carbonization. Since the time of Rosalind Franklin, researchers have put forward a number of models for their structure . Oberlin and colleagues emphasised the role of basic structural units (BSU), made of planar aromatic structures consisting of less than 10-20 rings, with four layers or fewer. Cross-linking between the BSUs in non-graphitizing carbons prevents graphitization. More recently, some have put forward models that incorporate pentagons and other non-six-membered carbon rings.

References

{{reflist Allotropes of carbon

See also

References