Glassy carbon

Glassy carbon, also called vitreous carbon, is a non-graphitizing carbon which combines glassy and ceramic properties with those of graphite. The most important properties are high temperature resistance, extreme resistance to chemical attack and impermeability to gases and liquids. It has been demonstrated that the rates of oxidation of certain glassy carbons in oxygen, carbon dioxide or water vapour are lower than those of any other carbon. Thus, while normal graphite is reduced to a powder by a mixture of concentrated sulphuric and nitric acids at room temperature, glassy carbon is unaffected by such treatment, even after several months. Glassy carbon is widely used as an electrode material in electrochemistry, as well as for high temperature crucibles and as a component of some prosthetic devices.

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It was first produced by workers at the laboratories of The General Electric Company, UK, in the early 1960s, using cellulose as the starting material. A short time later, Japanese workers produced a similar material from phenolic resin. The preparation of glassy carbon involves subjecting the organic precursors to a series of heat treatments at temperatures up to 3000^oC.

The structure of glassy carbon has long been a subject of debate. Early structural models for assumed that both sp² and sp³ -bonded atoms were present, but it is now known that glassy carbon is 100% sp². A later model was based on the assumption that the molecular orientation of the polymeric precursor material is memorised to some extent after carbonization. Thus, it is assumed that the structure bears some resemblance to that of a polymer, in which the "fibrils" are very narrow curved and twisted ribbons of graphitic carbon. However, more recent research has suggested that glassy carbon has a fullerene-related structure.^[1]

Note that glassy carbon should not be confused with amorphous carbon. This from IUPAC: "Glass-like carbon cannot be described as amorphous carbon because it consists of two-dimensional structural elements and does not exhibit ‘dangling’ bonds." .

See also

• Graphite
• Electrochemistry
• Fullerenes

References