Graphitizing and non-graphitizing carbons: Difference between revisions

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'''Graphitizing''' and '''non-graphitizing''' carbons (alternatively graphitizable and non-graphitizable carbon) are the two categories of [[carbon]] produced by [[pyrolysis]] of organic materials. [[Rosalind Franklin]] first identified them in a 1951 paper in ''[[Proceedings of the Royal Society]]''.<ref>{{cite journal|author= R.E. Franklin |title= Crystallite growth in graphitizing and non-graphitizing carbons |journal= Proceedings of the Royal Society A|volume=209|pages=196-218196–218 |year=1951 |issue= 1097 | authorlink = Rosalind Franklin| DOIdoi = 10.1098/rspa.1951.0197|s2cid= 4126286 }}</ref>. 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. [[Precursor (chemistry)|Precursors]] that produce graphitizing carbon include [[polyvinyl chloride]] (PVC) and petroleum coke. [[Polyvinylidene chloride]] (PVDC) and [[sucrose]] 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]]). 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.<ref name= Mesophase >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 {{DOI| 10.1007/978-1-4613-8333-8_7 }}</ref>

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<ref>{{cite journal|author= A. Oberlin |title= Carbonization and graphitization |journal= Carbon|volume=22|pages=521-541521–541 |year=1984|DOIissue= 6 |doi = 10.1016/0008-6223(84)90086-1}}</ref>. More recently, some have put forward models that incorporate pentagons and other non-six-membered carbon rings<ref>{{cite journal|author= P.J.F. Harris |title= Fullerene-like models for microporous carbon |journal= Journal of Materials Science |volume=48|pages=565–577|year=2013 |DOIissue= 2 |doi= 10.1007/s10853-012-6788-1|s2cid= 14903411 |url= http://centaur.reading.ac.uk/28956/1/Revised%20JMS%2031%20July%20For%20Centaur.pdf }}</ref>

==See also==