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Character and Structure of Graphite

Character and Structure of Graphite

Graphite is the carbon crystalline mineral. Its crystal flame is hexagon layered lattice. The distance between planes is 3.40A. The distance between two carbon atoms in the same layer is 1.42A.

Graphite is the carbon crystalline mineral. Its crystal flame is hexagon layered lattice. The distance between planes is 3.40A. The distance between two carbon atoms in the same layer is 1.42A. Graphite has complete layered cleavage. The cleavage surface is molecule bonds mainly, with weak attractive for molecule, so graphite has good native floatability.
   Graphite, dark and grey, with a flexible texture and oily feeling, can pollute paper. The hardness of graphite is 1 to 2. With the increasing of impurities along vertical direction, the hardness can increase to 3 to 5. Its specific gravity is 1.9 to 2.3. Under without oxygen conditions, its melting point is more than 3000?. Graphite is one of the highest temperature resistant minerals.
   In nature, there is no pure graphite. Graphite often has SiO2?Al2O3?FeO?CaO?P2O5?CuO and other impurities, in the form of quartz, iron pyrite, carbonate and other minerals. Besides, graphite contains water, asphalt, and gases, such as CO2,H2 ,CH4,N2.  Therefore, when we analyze graphite, besides fixed carbon content, volatile components and ash components must be tested.
   The technique properties are mainly decided by its crystalline form. Graphite minerals with different crystalline forms have different industrial values and uses. Industrially, according to different crystalline forms, natural graphite can be divided into three kinds.
1.       Compact crystalline graphite 
 It is also called block graphite. The crystal of this kind graphite is very clear, and can be seen by eyes. The diameter of the grain is more than 0.1mm.The crystals are in disorder, with compact block shape. Its character is high grade, with 6060% carbon content, sometimes 8098%, while its plasticity and lubricity are not as good as flake graphite.
2.       Flake graphite 
 The crystal of flake graphite is flake shaped, formed by deterioration under high strength pressure, with two kinds——large flake and fine flake. Its character is low grade, generally between 23% or 10025%. Flake graphite is one of minerals with the best floatability. After multigrinding and multiselecting, it becomes high grade concentrate ore. The floatability, lubricity and plasticity are all higher than other kinds of graphite, so the industrial value of flake graphite is the highest.
3.       Cryptocrystalline graphite
 Cryptocrystalline graphite is also called noncrystal graphite or earthy graphite. The diameter of the crystal is less than 0.1mm. The graphite is the collection of microcrystal graphite, and only can be seen under the microscope. This graphite has the following characteristics: earthy-shaped surface, lustre poverty, bad lubricity, high grade, generally 6080%,few reaching more than 90% ,and poor core quality.
 Among natural graphite, block and flake graphite are the best and have the widest use. China has not found massive block graphite mine, but flake and cryptocrystalline graphite have large mine bed and form large-scale exploitation base.
   Graphite has many excellent properties, so it is widely used in many departments of national economy, especially in metallurgy, machinery, electric appliance, chemical industries.
   Graphite owns excellent high and low temperature resistance property, with low expandable coefficient and stable measurement, so graphite can resist the extreme temperature changes. The high temperature resistance of graphite is different from that of general metals. When the temperature increases, graphite will not become softer, but stronger.