graphite, mineral consisting of carbon. Graphite has a greasy feel and leaves a black mark, thus the name from the Greek verb graphein, &#;to write.&#;
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Graphite has a layered structure that consists of rings of six carbon atoms arranged in widely spaced horizontal sheets. Graphite thus crystallizes in the hexagonal system, in contrast to diamond, another form of carbon, that crystallizes in the octahedral or tetrahedral system. Such pairs of differing forms of the same element usually are rather similar in their physical properties, but not so in this case. Graphite is dark gray to black, opaque, and very soft (with a Mohs scale hardness of 1.5), while diamond may be colorless and transparent and is the hardest naturally occurring substance (with a Mohs scale hardness of 10). Graphite is very soft because the individual layers of carbon atoms are not as tightly bound together as the atoms within the layer. It is an excellent conductor of heat and electricity. For detailed physical properties of graphite, see native element (table).
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carbon: Properties and uses
Before the discovery in that graphite when burned in air forms carbon dioxide, graphite was confused with both the metal lead and a superficially similar substance, the mineral molybdenite.
Graphite is formed by the metamorphosis of sediments containing carbonaceous material, by the reaction of carbon compounds with hydrothermal solutions or magmatic fluids, or possibly by the crystallization of magmatic carbon. It occurs as isolated scales, large masses, or veins in older crystalline rocks, gneiss, schist, quartzite, and marble and also in granites, pegmatites, and carbonaceous clay slates. Small isometric crystals of graphitic carbon (possibly pseudomorphs after diamond) found in meteoritic iron are called cliftonite.
Naturally occurring graphite is classified into three types: amorphous, flake, and vein. Amorphous is the most common kind and is formed by metamorphism under low pressures and temperatures. It is found in coal and shale and has the lowest carbon content, typically 70 to 90 percent, of the three types. Flake graphite appears in flat layers and is formed by metamorphism under high pressures and temperatures. It is the most commonly used type and has a carbon content between 85 and 98 percent. Vein graphite is the rarest form and is likely formed when carbon compounds react with hydrothermal solutions or magmatic fluids. Vein graphite can have a purity greater than 99 percent and is commercially mined only in Sri Lanka.
Graphite was first synthesized accidentally by Edward G. Acheson while he was performing high-temperature experiments on carborundum. He found that at about 4,150 °C (7,500 °F) the silicon in the carborundum vaporized, leaving the carbon behind in graphitic form. Acheson was granted a patent for graphite manufacture in , and commercial production started in . Since petroleum coke, small and imperfect graphite crystals surrounded by organic compounds, has been the major raw material in the production of 99 to 99.5 percent pure graphite.
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Learn Morepencil with graphite
A pencil with graphite, the form of carbon that makes up the central core of a pencil.
Graphite is used in pencils, lubricants, crucibles, foundry facings, polishes, brushes for electric motors, and cores of nuclear reactors. Its high thermal and electrical conductivity make it a key part of steelmaking, where it is used as electrodes in electric arc furnaces. In the early 21st century, global demand for graphite has increased because of its use as the anode in lithium-ion batteries for electric vehicles. About 75 percent of graphite is mined in China, with significant amounts mined in Madagascar, Mozambique, and Brazil.
Unless you have ever needed a specialty or replacement part, you may have never heard of carbon graphite before. Carbon graphite is a material that is used for replacement and specialty parts because when prepared properly it offers wear resistance, high-temperature capabilities, self-lubricating properties, and the ability to be used with corrosive materials.
Carbon graphite components are most often made from two things: powders and binders. Powders consist of natural or synthetic graphite, petroleum coke, carbon black, or other forms of carbon. The common binder used in carbon graphite materials is coal tar pitch.
When the powders and the binders are mixed they will then be moved into the next phase of carbon graphite production which is molding or extrusion. There are several methods of molding but the most common are Iso-molding, Extrusion, and Compression Molding. The type of molding or extrusion that is chosen is dependent on the end product being created.
When successful molding has taken place, the carbon graphite parts will then be baked. Baking is a vital part of the process because up until this point, the binder is simply holding the powders together, but not providing the strength carbon graphite parts are known for. This is where a very controlled, oxygen-free baking process is important, as it works to carbonize the binder and turn what is known as &#;green&#; material into a strong carbon graphite. Again, inspections are done constantly and baking temperatures are monitored closely to ensure a standardized product that will perform as expected.
Interestingly, as the green material is baked, a process known as outgassing will occur. This is a result of extreme baking temperatures and involves the hydrocarbons in the binder being driven out of the material. The result? Carbon graphite materials that are porous. The porous nature of the carbon allows for manufacturers to impregnate it with other substances and create unique material characteristics. The type of impregnation will be determined by what the part will be used for, but it can combine characteristics such as strengthening, improving wear resistance, better heat and chemical resistance and making the material impermeable.
Carbon graphite is used in the manufacturing of many different elements because it handles dry running conditions, high temperatures, and also has good thermal and electrical conductivity. When impregnated with phenolic resin, metals, inorganic salt, or other materials, the applications for carbon graphite becomes even more extensive.
Because of these properties, carbon graphite has many applications including but not limited to:
This is just a quick sampling of the applications for carbon graphite, all of which can be found here. Such a versatile material is sure to continue to be used in a growing number of applications now and in the future.
If you have ever looked for a replacement part you may have come across the opportunity to have the part custom made for you using carbon graphite. It is a great choice for specialty parts because the material offers a combination of strength, hardness, and wear resistance while also offering natural lubricity.
The material is thermally stable and is a natural choice in both chemical and corrosive applications. Additionally, carbon graphite is a great choice for specialty parts because it can be impregnated with resins, metals, and oxidation inhibitors to make it even more versatile. With proper machining or manufacturing, it can be used to create even the most obscure, out of stock or out of production parts that will stand the test of time.
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