through the mesophase, which must not have too high a viscosity. A close control of temperature, time, and feedstock is essential. Lower grades, for instance, ISOTROPIC COKES, are used for CARBON ELECTRODES applied, for example, in the production of aluminum.
See: ISOTROPIC CARBON, NEEDLE COKE.
Diamond
Description
DIAMOND is an allotropic form of the element carbon with cubic structure (space group Oh7‐Fd3m), which is thermodynamically stable at pressures above 6 GPa at room temperature and metastable at atmospheric pressure. At low pressures DIAMOND converts rapidly to GRAPHITE at temperatures above 1900 K in an inert atmosphere. The chemical bonding between the carbon atoms is covalent with sp3 hybridization.
See: CARBON, GRAPHITE.
Notes
There is also the hexagonal diamond‐like structure of the element CARBON (Lonsdaleite).
See: CARBON.
Diamond by CVD
Description
DIAMOND BY CVD (chemical vapor deposition) is formed as crystals or as films from various gaseous hydrocarbons or other organic molecules in the presence of activated, atomic hydrogen. It consists of sp3‐hybridized carbon atoms with the three‐dimensional crystalline structure of the diamond lattice.
See: DIAMOND‐LIKE CARBON FILMS.
Notes
“CVD diamond” or “low‐pressure diamond” is synonyms of the term DIAMOND BY CVD.
DIAMOND BY CVD can be prepared in a variety of ways. Deposition parameters are total (low) pressure, partial hydrogen pressure, precursor molecules in the gas phase, and temperature for activation of the hydrogen and that of the surface of the underlying substrate. The energy supply for the hydrogen activation may be, for instance, heat, radio frequency, microwave excitation (plasma deposition), or accelerated ions (e.g. Ar+ ions). CVD diamond has also been obtained at atmospheric pressure from oxyacetylene torches and by other flame‐based methods.
Often CVD carbon films consist of a mixture of sp2‐ and sp3‐hybridized carbon atoms and do not have the three‐dimensional structure of the DIAMOND lattice. In this case they should be called HARD AMORPHOUS CARBON or DIAMOND‐LIKE CARBON FILMS.
See: DIAMOND, DIAMOND‐LIKE CARBON FILMS.
Diamond‐Like Carbon Films
Description
DIAMOND‐LIKE CARBON (DLC) FILMS are hard, amorphous films with a significant fraction of sp3‐hybridized carbon atoms, which can contain a significant amount of hydrogen. Depending on the deposition conditions, these films can be fully amorphous or contain DIAMOND crystallites. These materials are not called DIAMOND unless a full three‐dimensional crystalline lattice of DIAMOND is proven.
See: DIAMOND.
Notes
DIAMOND‐LIKE CARBON FILMS without hydrogen can be prepared by carbon ion beam deposition, by ion‐assisted sputtering from GRAPHITE, or by laser ablation of GRAPHITE. DIAMOND‐LIKE CARBON FILMS containing significant contents of hydrogen are prepared by chemical vapor deposition. The hydrogen content is usually over 25 atomic %. The deposition parameters are (low) total pressure, hydrogen partial pressure, precursor molecules, and plasma ionization. The plasma activation can be radio frequency, microwave, or Ar+ ions. High ionization favors amorphous films, while high atomic hydrogen contents favor DIAMOND crystallite formation. Because of the confusion about structure engendered by the term DIAMOND‐LIKE CARBON FILMS, the term HARD AMORPHOUS CARBON has been suggested as a synonym.
See: DIAMOND, GRAPHITE, HARD AMORPHOUS CARBON.
Electrographite
Description
ELECTROGRAPHITE is a SYNTHETIC GRAPHITE made by electrical heating of GRAPHITIZABLE CARBON.
See: GRAPHITIZABLE CARBON, SYNTHETIC GRAPHITE.
Exfoliated Graphite
Description
EXFOLIATED GRAPHITE is the product of very rapid heating (or flash heating) of graphite intercalation compounds, such as graphite hydrogen sulfate of relatively large particle diameter (flakes). The vaporizing intercalated substances force the graphite layers apart. The EXFOLIATED GRAPHITE assumes an accordion‐like shape with an apparent volume often hundreds of times that of the original graphite flakes.
Notes
EXFOLIATED GRAPHITE is usually prepared from well‐crystallized NATURAL flake GRAPHITE. It is used for the production of graphite foils. EXFOLIATED GRAPHITE is different from the deflagration product of graphite oxide (graphitic acid).
See: NATURAL GRAPHITE.
Fibrous Activated Carbon
Description
FIBROUS ACTIVATED CARBON is an ACTIVATED CARBON in form of fibers, filaments, yarns or rovings, and fabrics or felts. Such fibers differ from CARBON FIBERS used for reinforcement purposes in composites by their high surface area, high porosity, and low mechanical strength.
See: ACTIVATED CARBON, CARBON FIBERS.
Notes
Sometimes fabrics of FIBROUS ACTIVATED CARBON are named CHARCOAL cloths; a more precise term is “activated carbon cloth.”
See: ACTIVATED CHARCOAL, CHARCOAL.
Fibrous Carbon
Description
See: FILAMENTOUS CARBON.
Filamentous Carbon
Description
