Types and grades of graphite. Types, grades and general technical requirements
In accordance with GOST 17022-81 “Graphite. Types, grades and general technical requirements” highlight the following mineralogical types of graphite:
- – crystalline
- – cryptocrystalline.
The same GOST provides for the following grades of graphite: GSM-1, GSM-2, GAK-1, GAK-2, GAK-3, GK-1, GK-2, GK-3, GS-1, GS-2, GS- 3, GS-4, P, EUZ-M, EUZ-II, EUZ-III,EUT-I, EUT-II, EUT-III, GT-1, GT-2, GT-3, GE-1, GE- 2, GE-3, GE-4, GL-1, GL-2, GL-3, EUN, GLS-1, GLS-2, GLS-3, GLS-4.
They correspond to the following types of use (consumption) of graphite:
- – special low-ash graphite,
- – battery graphite,
- – pencil graphite,
- – lubricating graphite,
- – crystalline electrocarbon graphite,
- – crucible graphite,
- – elemental graphite,
- – crystalline foundry graphite,
- – graphite cryptocrystalline electrocarbon,
- – cryptocrystalline foundry graphite.
Graphite properties:
– the electrical conductivity of graphite is anisotropic (i.e., it depends on the direction within the graphite itself). It conducts electricity well in a direction parallel to the basal plane. In this case, its electrical conductivity is close to metallic. In the perpendicular direction, the electrical conductivity is hundreds of times less.
– has low hardness. Mohs school hardness 1.
– relatively soft. After exposure to high temperatures, it becomes slightly harder and very brittle,
– density 2.08-2.23 g / cm³,
– easy to machine, – color from iron-black to steel-gray, metallic luster, – infusible, stable when heated in the absence of air, – greasy (slippery) to the touch, leaves a mark on paper and fingers,
– when rubbed, graphite stratifies into separate flakes (this property is used in pencils),
– has a fairly high thermal conductivity. The thermal conductivity of graphite is anisotropic. It ranges from 100 to 354.1 W / (m * K) and depends on the grade of graphite, on the direction relative to the basal planes and on temperature,
– the coefficient of thermal expansion of graphite is also anisotropic and depends on temperature. Up to 700 K, the coefficient of thermal expansion of graphite is negative in the direction of the basal planes (graphite shrinks when heated), its absolute value decreases with increasing temperature. Above 700 K the coefficient of thermal expansion becomes positive. In the direction perpendicular to the basal planes, the coefficient of thermal expansion is positive, practically does not depend on temperature, and is more than 20 times higher than the average absolute value for the basal planes,
– high diamagnetism
– chemically inactive,
– has chemical resistance
– acid-resistant,
– reacts with oxygen at high temperatures, burning to carbon dioxide,
– forms an inclusion compound with alkali metals, salts