Glassy carbon

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. 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.

Production

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 °C.

It was first produced in the laboratories of The Carborundum Company, Trafford Park, Manchester, UK, in the mid 1950's by Bernard Redfern (BR) the inventor, a materials scientist and diamond technologist. He noticed that Cellotape he used to hold ceramic (rocket nozzle) samples in a furnace maintained a sort of structural identity after firing in an inert atmosphere. He searched for a polymer matrix to mirror a diamond structure and discovered a resole resin that would, with special preparation, set without a catalyst. Using this phenolic resin, crucibles were produced. Crucibles were distributed to organisations such as UKAEA Harwell. BR left the Carborundom Co., which officially wrote off all interests in the glassy carbon invention. Whilst working at the Plessey Company laboratory (a disused church!) in Towcester, UK, BR received a glassy carbon crucible for duplication from UKAEA. He identified it as one he had made from markings he had engraved into the uncured precursor prior to carbonisation. (It is almost impossible to engrave the finished product.) The Plessey Company set up a laboratory first in a factory previously used to make briar pipes, in Litchborough, UK, and then a permanent facility at Caswell, near Blakesly, UK. Caswell became the Plessey Research centre and then the Alan Clark research Centre. Glassy carbon arrived at the Plessey Company Limited as a fait accompli. BR was assigned two associates for the production of glassy carbon. F. C. Cowlard was an administrator who previously had some association with Silane and J. C. Lewis was a chemical assistant. Large sections of the precursor material were produced as castings or machined into a predetermined shape. Large crucibles and other forms were manufactured. Carbonisation took place in two stages. Shrinkage during this process is considerable but absolutely uniform and predictable. Some of the first ultrapure samples of Gallium Arsenide were zone refined in these crucibles. (Glassy carbon is extremely pure and unreactive to GaAs). Patents were filed and the name "Vitreous Carbon" presented to the product by the son of BR. Glassy/Vitreous Carbon was under investigation used for components for thermonuclear detonation systems and at least some of the patents surrounding the material were rescinded (in the interests of national security) in the 1960s.

Despite his majority contribution to the research, invention, development and production of glassy / Vitreous carbon, references to Bernard Redfern were not obvious in subsequent publications by Mssrs F. C. Cowlard and J. C. Lewis. (cf Cowlard, F. C., and Lewis, J. C., J. Materials Sci., 2, 507-512, (1967). )

Original boat crucibles and precursor samples exist.

Structure

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. However, more recent research has suggested that glassy carbon has a fullerene-related structure.

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." .

It exhibits a conchoidal fracture.

Electrochemical properties

Glassy carbon electrode (GCE) in aqueous solutions is considered to be an inert electrode for hydronium ion reduction:

H_3 O^{+}_{(aq)} +e^- text { } stackrel{GCE} {rightleftharpoons} text{ } H cdot_{(aq)}   Eo = −2.10 V versus NHE at 25 °C

Comparable reaction on platinum:

H_3 O^{+}_{(aq)} + Pt_{(s)} + e^- text { } rightleftharpoons text { } Pt:H_{(s)}   Eo = 0.000 V versus NHE at 25 °C

The difference of 2.1 V is attributed to the properties of platinum which stabilizes a covalent Pt-H bond.

See also

References

External links

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