An integral tool from the time we’re toddlers, graphite is most known as the active ingredient in lead pencils. It is one of the three familiar naturally occurring forms of the chemical element carbon, along with amorphous carbon (not to be confused with amorphous graphite) and diamond.
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Despite its popular use in writing instruments the material’s use is far outweighed by a myriad of other industrial applications whose performance depends on its unique chemical and physical properties. Graphite is a major additive to many industrial systems where it provides functionality as a refractory, lubricant, thermal conductor, electrical conductor, UV shield, electromagnetic pulse shield, corrosion shield, pigment, etc. The articles presented here are a qualitative introduction to graphite as a material that can provide formulators and manufacturers with an efficient means of adding value to their products and processes. The unique properties of graphite, its formation, and application will be described with emphasis on the eloquent relationship between molecular and crystallographic form and their effect on function.
Graphite is considered an archaic industrial mineral since it has been mined for its useful properties (lubrication, pigmentation, writing, etc.) for thousands of years. The word graphite is derived from the Greek word graphein, which means, to write. A version of the word graphein is still retained by carbon scientists as the word graphene, which is the term used to describe a single layer of a graphite crystal, the graphene layer. The documented use of graphite as a commercial writing material is traced to the area around Keswick in Cumberland Great Britain where a high quality deposit of writing graphite was discovered in the middle of the 1500s (Petroski).
During the late 1800s, while attempting to manufacture the refractory material silicon carbide, E.G. Acheson discovered that synthetic graphite formed as a result of this ultra-high temperature electric process. This discovery was the birth of the synthetic graphite industry. At approximately the same time that Mr. Acheson was experimenting with the manufacture of synthetic graphite electrodes, Mr. Riddle (the founder of Asbury Graphite Mills, Inc.) was converting a water-powered mill, formally used to grind flour, into a natural graphite grinding mill.
With the help of the Asbury Graphite Mills, Inc., today’s industrial society has the benefit of Asbury’s 110+ years of processing both natural and synthetic graphite products to strict size, purity, and performance specifications using the most up-to-date grinding and size-classification equipment.
Graphite materials fit into two primary classifications: natural graphite and synthetic graphite. Natural graphite can be further divided into three primary types: amorphous, flake, and crystalline vein. Each type has characteristic properties and is formed in a unique geologic setting. Synthetic graphite can be divided into many types with its ultimate properties dependent on the precursor carbon used in its manufacture, as well as the carbon’s precursor heat treatment history.
Regardless of type, all graphite materials share certain inherent characteristics, which are a reflection of the atomic structure and crystallographic arrangement of carbon atoms in the graphite crystal. Properties such as lubricity, thermal conductivity, electrical conductivity, color, etc., are all constants when applied to a single crystal of graphite. However when single crystals or crystallites combine to form macroscopic particles as in flakes, lumps, powders, or pieces of graphite, these properties see changes that reflect the way microscopic crystals are arranged in macroscopic particles. Crystal or crystallite orientation relative to neighbor domains, grain boundary effects, etc., all contribute to the overall bulk properties of the solid or powder which can be very different from those of the perfect crystal. This arrangement of crystals and crystallites, as well as the purity of a given graphite material, is what gives graphite of different types their respective properties. These differences result in the variation in performance characteristics observed for different graphite materials.
Next, learn more about the structure, bonding, morphology, and general properties of graphite as we delve further into the various forms available from Asbury Carbons.
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.”
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 1779 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.
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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 1896, and commercial production started in 1897. Since 1918 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.
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