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Graphite

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Graphite is like diamond, It is a form of native carbon crystalline with its atoms arranged in a hexagonal structure that is opaque and dark gray to black. It occurs as hexagonal crystals, flexible sheets, scales, or large masses. It may be earthy, granular, or compact. Graphite forms from the metamorphism of carbonaceous sediments and the reaction of carbon compounds with hydrothermal solutions. It occurs naturally in this form and is the most stable form of carbon under standard conditions. Under high pressures and temperatures it converts to diamond. It looks dramatically different from diamond and is at the other end of the hardness scale. It’s softness is due to the way carbon atoms are bonded to each other rings of six carbon atoms are arranged in widely spaced horizontal sheets. The atoms are strongly bonded within the rings but very weakly bonded between the sheets. It is used in pencils and lubricants. Its high conductivity makes it useful in electronic products such as electrodes, batteries, and solar panels.

Name: From the Greek to write, in allusion to its use as a crayon.

Association: A wide variety of minerals stable in the metamorphic conditions under which graphite forms. In meteorites, in nodules with troilite, silicates

Polymorphism & Series: Polymorphous with chaoite, diamond, and lonsdaleite.

Chemical Properties

Chemical Classification Native element
Formula C

Graphite Physical Properties

Color Steel gray to black
Streak Black
Luster Metallic, sometimes earthy
Cleavage Perfect in one direction
Diaphaneity Opaque
Mohs Hardness 1 to 2
Crystal System Hexagonal
Tenacity Flexible
Density 2.09 – 2.23 g/cm3 (Measured)    2.26 g/cm3 (Calculated)
Fracture Micaceous

Graphite Optical Properties

Anisotropism Extreme
Color / Pleochroism Strong
Optic Sign Uniaxial (-)
Birefringence extreme birefringence

Graphite Occurrence

It is formed by metamorphism of sedimentary carbonaceous material by reduction of carbon compounds; primary component in igneous rocks. It occurs in metamorphic rocks as a result of the reduction of sedimentary carbon compounds during metamorphic rocks. It is also seen in magmatic rocks and meteorites. It-related minerals are quartz, calcite, mica and tourmaline. China, Mexico, Canada, Brazil and Madagascar are the main export sources of mined.

Synthetic Graphite

Synthetic graphite is a material consisting of graphitic carbon which has been obtained by graphitizing of non-graphitic carbon, by CVD from hydrocarbons at temperatures above 2500 K, by decomposition of thermally unstable carbides or by crystallizing from metal melts supersaturated with carbon.

The term artificial it is often used synonymously with synthetic graphite. However, the term synthetic graphite is preferred since their crystals are thought to be composed of carbon macromolecules. The term synthetic graphite is used predominantly for graphitized carbon, although the term CVD includes pyrolytic graphite as well as carbide decomposition residues. Such common uses are the same as the definition above. Synonyms for this most important type of synthetic graphite are Acheson graphite and electrograph.

Uses Area

  • Natural graphite is mostly used for refractories, batteries, steelmaking, expanded graphite, brake linings, foundry facings and lubricants.
  • Crucibles began using very large flake graphite, and carbon-magnesite brick requiring not quite so large flake graphite; for these and others there is now much more flexibility in the size of flake required, and amorphous graphite is no longer restricted to low-end refractories.
  • The use of graphite in batteries has increased in the last 30 years. Natural and synthetic are used to construct electrodes in major battery technologies.
  • The demand for batteries, As an example, a lithium-ion battery in a fully electric Nissan Leaf contains nearly 40 kg of graphite.
  • Natural graphite in steelmaking mostly goes into raising the carbon content in molten steel, and can also be used to lubricate the dies used to extrude hot steel.
  • Natural amorphous and fine flake graphite are used in brake linings or brake shoes for heavier (nonautomotive) vehicles, and became important with the need to substitute for asbestos.
  • A foundry facing mold wash is a water-based paint of amorphous or fine flake. Painting the inside of a mold with it and letting it dry leaves a fine graphite coat that will ease separation of the object cast after the hot metal has cooled.

Use of synthetic graphite

  • High-focal pyrolytic graphite (HOPG) is the highest quality synthetic form of graphite. In scientific research, it is used as the length standard for scanner calibration, especially on a scanning probe microscope.
  • It electrodes carry electricity that melts scrap iron and steel in electric arc furnaces, the majority of steel furnaces, and sometimes melts directly reduced iron (DRI). They are made from petroleum coke after being mixed with coal tar tar.
  • Electrolytic aluminum smelting also uses graphite carbon electrodes. On a much smaller scale, synthetic discharge electrodes are used to make injection molds for plastics in the electrical discharge process (EDM).
  • Special grades of synthetic graphite, such as gilsocarbon, find utility as a matrix and neutron moderator in nuclear reactors. The low neutron cross section also recommends the use in recommended fusion reactors.
  • It (carbon) fiber and carbon nanotubes are also used in carbon fiber reinforced plastics and heat-resistant composites such as reinforced carbon-carbon (RCC). Commercial structures made of carbon fiber graphite composites include fishing rods, golf club shafts, bicycle frames, sports car body panels, the body of the Boeing 787 Dreamliner and the body of the pool marker bars.
  • Modern smokeless powder is coated with graphite to prevent the accumulation of static charge.
  • It was used in at least three radar absorbing materials. Sumpf and Schornsteinfeger used in U-boat snorkels to reduce radar cross-sections were mixed with rubber. F-117 Nighthawk was also used on the tiles on the secret strike fighters.
  • Graphite composites are used as absorbers for high energy particles (eg, in the LHC beam dump).

Graphite recycling

The most common way of graphite recycling occurs when synthetic graphite electrodes are produced and cut into pieces or discard lathes, or when the electrode (or other) is used up to the electrode holder. A new electrode replaces the old one, but most of the old one remains. This is crushed and sized and the resulting graphite powder is mostly used to increase the carbon content of the molten steel. It-containing refractories are sometimes recycled, but often not because of graphite: the largest bulk materials such as carbon-magnesite bricks containing only 15-25% graphite often contain very little graphite. However, some recycled carbon-magnesite bricks are used as the basis for furnace repair materials, while broken carbon-magnesite bricks are used in slag air conditioners. The crucibles have a high graphite content, while the crucibles used and then recycled have a small volume.

A high quality flake graphite product very similar to natural leaf graphite can be made from steelmaking. Kish is a large volume of molten waste filtered from the molten iron feed into a basic oxygen furnace and consists of a mixture of graphite (precipitated from supersaturated iron), lime-rich slag and some iron. The iron is recycled in place and a mixture of graphite and slag is left. The best recovery process uses hydraulic grading (using water flow to separate minerals by specific gravity: graphite is light and almost precipitates) to obtain a 70% graphite concentrate. Leaching of this concentrate with hydrochloric acid yields a 95% graphite product with a flake size down to 10 sieves.

Distribution

Numerous localities, but only a few afford well-crystallized examples.

  • In the USA, at Monroe and Ticonderoga, Essex Co., New York; at Franklin and Sterling Hill, Ogdensburg, Sussex Co., New Jersey.
  • In Canada, commercially significant occurrences in Quebec, at Buckingham and Grenville, and in adjacent parts of Ontario.
  • In Russia, from Nizhni Tunguski, east of Turukhansk, near the Yenisei River, Siberia; at Shunga, Karelia.
  • Around Ratnapura, Matara, and Kurunegale, Sri Lanka, large deposits of pure material.
  • At Passau, Bavaria, Germany.
  • From Pargas, Finland.
  • In England, at Barrowdale, near Keswick, Cumbria.
  • In Mexico, at Santa Maria, Sonora, formed by metamorphism of coal beds.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019). Graphite: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
  • Smith.edu. (2019). Geosciences | Smith College. [online] Available at: https://www.smith.edu/academics/geosciences [Accessed 15 Mar. 2019].
Cite this article as: Geology Science. (2019). Graphite. [online] Available at: http://geologyscience.com/minerals/graphite/ [5th December 2019 ]
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