GRAPHITE is a GRAPHITE MATERIAL with coherent crystallographic domains of limited size regardless of the perfection and preferred orientation (texture) of their crystalline structure.
See: GRAPHITE MATERIAL.
Notes
The common use of the term POLYCRYSTALLINE GRAPHITE for POLYGRANULAR GRAPHITE is in line with this definition but may be inexact because usually all grains of POLYGRANULAR GRAPHITE are polycrystalline themselves.
POLYCRYSTALLINE GRAPHITE can exhibit a random orientation, more or less preferred orientation, or a highly oriented texture as in some PYROLYTIC GRAPHITES.
There is no sharp transition, however, between the typical polycrystalline texture and the “single crystal‐like” texture of HIGHLY ORIENTED PYROLYTIC GRAPHITE (HOPG).
See: HIGHLY ORIENTED PYROLYTIC GRAPHITE, POLYGRANULAR GRAPHITE, PYROLYTIC GRAPHITE.
Polygranular Carbon
Description
POLYGRANULAR CARBON is a CARBON MATERIAL composed of grains, which can be clearly distinguished by means of optical microscopy.
See: CARBON MATERIAL.
Notes
Industrial CARBON MATERIALS (such as electrodes) are mostly polygranular, but special grades are agranular materials, such as GLASS‐LIKE CARBON, CARBON FIBERS, or PYROLYTIC CARBON. Such materials are covered by the term AGRANULAR CARBON.
See: AGRANULAR CARBON, CARBON FIBERS, CARBON MATERIAL, GLAS‐LIKE CARBON, PYROLYTIC CARBON
Polygranular Graphite
Description
POLYGRANULAR GRAPHITE is a GRAPHITE MATERIAL composed of grains, which can be clearly distinguished by means of optical microscopy.
See: GRAPHITE MATERIAL.
Notes
From the viewpoint of crystallinity, a POLYGRANULAR GRAPHITE is always a POLYCRYSTALLINE GRAPHITE, but not vice versa. Most industrial GRAPHITE MATERIALS are polygranular. Monogranular materials consist mostly of NON‐GRAPHITIC CARBON; such materials are called monolithic or AGRANULAR CARBONS.
See: AGRANULAR CARBON, GRAPHITE MATERIAL, NON‐GRAPHITIC CARBON, POLYCRYSTALLINE GRAPHITE.
Premium Coke
Description
PREMIUM COKE is an extremely well graphitizing carbon with a high degree of optical anisotropy (isochromatic areas of optical texture above about 100 μm) and is characterized by a combination of the following properties that differ significantly from those of REGULAR COKE: high real density, low reversible thermal expansion, and low ash content combined, in most cases, with low sulfur content.
See: REGULAR COKE.
Notes
PREMIUM COKE is mainly produced from tars or residues from petrochemistry by the DELAYED COKING PROCESS. Also refined COAL‐TAR PITCHES are used as precursors for PREMIUM COKE production.
See: COAL‐TAR PITCH, DELAYED COKING PROCESS, REGULAR COKE.
Puffing
Description
The term PUFFING describes an irreversible expansion of some CARBON ARTIFACTS during GRAPHITIZATION HEAT TREATMENT between 1650 and 2700 K.
See: CARBON ARTIFACT, COKE, GRAPHITIZATION HEAT TREATMENT.
Notes
PUFFING is caused by the release of heteroatoms, for instance, sulfur atoms, from the COKE in association with specific microstructural rearrangements.
See: COKE, POLYGRANULAR CARBON, PUFFING INHIBITOR.
Puffing Inhibitor
Description
PUFFING INHIBITORS are metals or metal compounds with a high chemical affinity for the heteroatoms in the carbons. They are distributed as fine particles within the CARBON MATERIALS to be graphitized.
See: CARBON MATERIAL.
Notes
Iron and iron compounds are most frequently used as PUFFING INHIBITORS when PUFFING is related to sulfur.
See: PUFFING.
Pyrolytic Carbon
Description
PYROLYTIC CARBON is a CARBON MATERIAL deposited from gaseous hydrocarbon compounds on suitable underlying substrates (CARBON MATERIALS, metals, ceramics) at temperatures ranging from 1000 to 2500 K (chemical vapor deposition).
See: CARBON MATERIAL.
Notes
A wide range of microstructures, e.g. isotropic, lamellar, substrate‐nucleated, and varied content of remaining hydrogen, can occur in PYROLYTIC CARBONS, depending on the deposition conditions (temperature, type, concentration, and flow rate of the source gas, surface area of the underlying substrate, etc.).
“Pyrocarbon” that is synonymous with PYROLYTIC CARBON was introduced as a trademark and should not be used as a term.
The term PYROLYTIC CARBON does not describe the large range of CARBON MATERIALS obtained by thermal degradation (thermolysis, pyrolysis) of organic compounds when they are not formed by chemical vapor deposition (CVD). Also CARBON MATERIALS, obtained by physical vapor deposition (PVD), are not covered by the term PYROLYTIC CARBON.
See: CARBON MATERIAL.
