Microstructure

Glassy carbon SIGRADUR® is a form of carbon with a highly disordered structure. Recent research has shown that glassy carbon has a fullerene-related structure. The sp2 bonded carbon atoms are arranged in planes with a hexagonal symmetry. Non-six-membered rings (pentagons, heptagons) bend the hexagonal carbon planes. As a result of these observations, a model was proposed for the structure of glassy carbon which consisted of discrete fragments of curved carbon planes, in which pentagons and heptagons were dispersed randomly throughout networks of hexagons. Figure a and b show typical TEM images of glassy carbon SIGRADUR® K and SIGRADUR® G.

Such a structure model would explain the many interesting properties of glassy carbon like the low reactivity, the high strength and hardness, the low density and the impermeability.

Peter Harris, Fullerene-related structure of commercial glassy carbons
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