Graphitizing and non-graphitizing carbons

Graphitizing and non-graphitizing carbons (alternatively graphitizable and non-graphitizable carbon) are the two categories of carbon which are produced by pyrolysis of organic materials. They were first identified by Rosalind Franklin in a 1951 paper for Proceedings of the Royal Society . In this paper she defined graphitizing carbons as those which could be transformed into crystalline graphite by heating to a temperature of 3000°C, while non-graphitizing carbons could not be transformed into graphite at any temperature. Among the precursors which produced graphitizing carbon were polyvinyl chloride (PVC) and petroleum coke, while polyvinylidene chloride (PVDC) and sucrose produced non-graphitizing carbon. The 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 the production of graphitizable carbons.