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Graphite

Graphite

Graphite is a soft, black, metallic mineral composed of the element carbon . It is nontoxic and rubs off easily on rough surfaces, which is why graphite mixed with fine clay , rather than actual lead , is used to make pencil leads. The word graphite derives from the Greek gréphein, to write or draw.

Graphite has the same chemical formula as diamond (C), yet the two minerals could hardly be more unlike. Diamond is the hardest of minerals, graphite one of the softest; diamond is transparent, graphite opaque; and diamond is almost twice as dense as graphite. These radically different properties arise from the way the atoms are arranged in each substance. In graphite, carbon atoms are linked in hexagonal sheets resembling chicken-wire fencing. These sheets slide over each other easily, which accounts for graphite's slipperiness. In diamond, carbon atoms are linked in a potentially endless matrix of tetrahedra (four-cornered pyramids), an extremely strong arrangement. Surprisingly, however, graphite is stable under ordinary atmospheric conditions and diamond is not; that is, at standard temperature and pressure diamond transforms spontaneously to graphite. The rate of transformation is extremely slow because carbon atoms organized into diamond are separated from the lower-energy graphite state by an activation-energy barrier similar to that which keeps an explosive from going off until triggered by a spark.

The carbon in most graphite and diamonds derives from living things. The organic (carbon-containing) remains of organisms may be transformed into coal or into impurities in limestone ; under some conditions, metamorphosis of these rocks purifies these organic materials to produce graphite. Further metamorphosis under extremely high pressures, such as occur many miles underground, is needed to produce diamond.

Because graphite is resistant to heat and slows neutrons, it was used in the early years of nuclear-power research as a matrix to contain radioactive fuel elements and moderate their chain reaction. Early atomic reactors were termed atomic piles because they consisted mostly of large piles of graphite blocks. Graphite is used not only in pencils, but also as a lubricant for locksmiths and for bearings operating in vacuum or at high temperatures. Because it is both conductive and slippery, graphite is used in generator brushes. It is also employed in making metallurgical crucibles and electrical batteries. Most of the graphite used is manufactured from coal in electrical furnaces, not mined.

See also Chemical bonds and physical properties; Chemical elements

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graphite

graphite (grăf´īt), an allotropic form of carbon, known also as plumbago and black lead. It is dark gray or black, crystalline (often in the form of slippery scales), greasy, and soft, with a metallic luster. It is a good conductor of electricity and does not fuse at very high temperatures or burn easily. It occurs in nature in grayish-black masses, massive or crystalline, and is obtained in various parts of the world—in the United States (massive) in Nevada, Michigan, and Rhode Island and (crystalline) in Alabama and North Carolina; in Brazil; in the British Isles and on the Continent; and in Sri Lanka, Madagascar, and Siberia. It is also prepared artificially by treating hard coal in the electric furnace, a process discovered by E. G. Acheson. The uses of graphite are wide and diverse. The so-called lead of pencils is in reality a mixture of graphite with clay. Crucibles required to withstand high temperatures and also electrodes are commonly made of graphite. It is used also in stove polish, in some paints, and as a lubricant.

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"graphite." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 16 Aug. 2017 <http://www.encyclopedia.com>.

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graphite

graph·ite / ˈgraˌfīt/ • n. a gray, crystalline, allotropic form of carbon that occurs as a mineral in some rocks and can be made from coke. It is used as a solid lubricant, in pencils, and as a moderator in nuclear reactors. DERIVATIVES: gra·phit·ic / grəˈfitik/ adj. ORIGIN: late 18th cent.: coined in German (Graphit), from Greek graphein ‘write’ (because of its use as pencil “lead”).

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"graphite." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 16 Aug. 2017 <http://www.encyclopedia.com>.

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graphite

graphite (plumbago) Dark-grey, soft, crystalline form of carbon. It occurs naturally in deposits of varying purity and is made synthetically by heating petroleum coke. It is used in pencils, lubricants, electrodes, brushes of electrical machines, rocket nozzles, and as a moderator that slows down neutrons in nuclear reactors. Graphite is a good conductor of heat and electricity. Hardness 1–2; r.d. 2.1–2.3.

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"graphite." World Encyclopedia. . Encyclopedia.com. 16 Aug. 2017 <http://www.encyclopedia.com>.

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graphite

graphite Pure carbon, C; sp. gr. 2.1; hardness 2; greyish-black; feels soft and greasy; good basal cleavage; scaly, columnar, granular, or earthy; occurs in veins and may be disseminated through rocks as a result of metamorphism of original carbon-rich sediments. It is used as a lubricant, electrical conductor, and in the manufacture of crucibles and paint.

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"graphite." A Dictionary of Earth Sciences. . Encyclopedia.com. 16 Aug. 2017 <http://www.encyclopedia.com>.

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graphite

graphite XVIII. — G. graphit, f. Gr. gráphein write (the stuff being used for pencils); see -ITE.

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"graphite." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. 16 Aug. 2017 <http://www.encyclopedia.com>.

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graphite

graphite •graphite • prizefight • dogfight •cockfight • neophyte • saprophyte •bullfight • gunfight • firefight •gesundheit • Fahrenheit • malachite •blatherskite

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"graphite." Oxford Dictionary of Rhymes. . Retrieved August 16, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/graphite