Non-graphitizing Carbons

Non-graphitizing Carbons
Peter J F Harris, The Encyclopedia of Materials: Science and Technology, Elsevier, 2001

Abstract
It was demonstrated many years ago by Rosalind Franklin ( 1951) that carbons produced by the solid phase pyrolysis of organic materials fall into two distinct classes. The so-called ``graphitizing'' carbons tend to be soft and non-porous, with relatively high densities, and can be readily transformed into crystalline graphite by heating at temperatures in the range 2200-3000 °C. In contrast, ``nongraphitizing'' carbons are hard, low density materials which cannot be transformed into crystalline graphite even at temperatures of 3000 °C and above. The low density of nongraphitizing carbons is a consequence of a microporous structure, which gives these materials an exceptionally high internal surface area. This high surface area can be enhanced further by activation, i.e. mild oxidation with a gas or chemical processing, and the resulting ``activated carbons'' are of enormous commercial importance, primarily as adsorbents. Despite much research, however, the detailed structure of these carbons at the atomic level is still poorly understood. Early models assumed that the microstructure consisted either of short fragments of graphite cross-linked by bridging groups or of a twisted network of carbon layer planes. More recent work has suggested that fullerene-related elements may be involved.

Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, UK.

[This article was written for The Encyclopedia of Materials: Science and Technology, Elsevier, 2001.]