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Alloy

Alloy

An alloy is a mixture of two or more elements, at least one of which is metallic, that itself has metallic properties (ductility, conductivity, etc.). Compounds that involve metals but do not have metallic properties are not alloys. Alloying occurs naturally; most raw gold, for example, is alloyed with silver, and natural nickel-iron alloys occur both in terrestrial rocks and as a common ingredient of meteorites. However, all alloys used for modern technological purposes are created industrially. This is necessary both because most raw metals exist as chemical compounds in rocks and because the balance of ingredients in a useful alloy must be precise.

In a given alloy, one metal is usually present in higher concentration than any other element; this is termed the parent metal or solvent of the alloy. Most alloys are solid at room temperature , and are assumed to be in the solid state when their properties are specified. Three common alloys are steel (parent metal iron , main additive carbon ), bronze (parent metal copper, main additive tin), and brass (parent metal copper, main additive zinc).

The nature of the mixing in an alloy depends on the chemical properties of its ingredients. The atoms of the different elements in an alloy can be roughly classed as indifferent to each other, as attracting each other, or as repelling each other. If all atoms in an alloy are indifferent to each other, they mix randomly and produce an alloy that is uniform at all levels above the atomic. Such an alloy is termed a random solid solution. If the atoms of unlike elements in an alloy attract each other, some orderly pattern develops when the alloy cools from its molten to its solid state. Such a solid is termed a superlattice or ordered solid solution. For example, a half-copper, half-aluminum alloy is an ordered solid solution in which planes of aluminum atoms alternate with planes of copper atoms. However, if the unlike atoms in a substance are attracted by strong electrical forces, the result is not an ordered solid solution with metallic properties but a true chemical compound. Salt, for example (sodium chloride, NaCl), is considered an ionic compound, not an alloy of sodium.

If the unlike atoms in an alloy attract each other less than the like atoms, the elements tend to segregate into distinct crystal domains upon solidification. The alloy is then a mass of pure, microscopic crystals of its component elements and is termed a phase mixture.

See also Crystals and crystallography; Industrial minerals; Metals; Precious metals; Phase state changes

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Alloy

Alloy

An alloy is a mixture of two or more metals. Some familiar examples of alloys include brass, bronze, pewter, cast and wrought iron, steel, coin metals, and solder (pronounced SOD-der; a substance used to join other metallic surfaces together). Alloys are usually synthetic materials, developed by scientists for special purposes. They generally have specially desirable properties quite different from the metals from which they are made. As an example, Wood's metal is a mixture of about 50 percent bismuth, 10 percent cadmium, 13 percent tin, and 27 percent lead that melts at 70°C (160°F). This low melting point makes Wood's metal useful as a plug in automatic sprinkler systems. Soon after a fire breaks out, the heat from the flames melts the Wood's metal plug, releasing water from the sprinkler system.

Important Alloys, Their Composition, and Typical Uses

Alloy Composition Uses
Babbitt metal tin: 90% used in bearings because of its low measure of fricti with steel
antimony: 7%
copper: 3%
bell metal copp 77% casting of bells
tin : 23%
brass copper with up to 50% zinc inexpensive jewelry; hose nozzles and couplings; piping; stamping dies
bronze copper with up 12% tin coins and medals; heavy gears; tools; electrical hardware
coin metal copper: 75% U.S. coins
nickel
duralumin aluminum: 95% aircraft, boats, railroad cars, and machinery because of its high strength and resistance to corrosion
copper: 4%
manganese: <1%
magnesium: 0.5%
monel nickel 60% corrosion-resistant containers
copper: 33%
iron: 7%
Nichrome® nickel: 80-85% heating elements in toasters, electric heaters, etc.
chromium: 15-20%
phosphor bronze bronze with a small amount of phosphorus springs electrical springs, boat proellers
solder lead: 50% joining two metals to each other
tin: 50%
sterling silver silver: 92.5% jewelry, art objects
copper: 7.5%
type metal lead: 75-95% used to make type for printing because it expands as it cools
antimony: 2-18%
tin: trace

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alloy

alloy (ăl´oi, əloi´) [O. Fr.,=combine], substance with metallic properties that consists of a metal fused with one or more metals or nonmetals. Alloys may be a homogeneous solid solution, a heterogeneous mixture of tiny crystals, a true chemical compound, or a mixture of these. Alloys are used more extensively than pure metals because they can be engineered to have specific properties. For example, they may be poorer conductors of heat and electricity, harder, or more resistant to corrosion. Alloys of iron and carbon include cast iron and steels; brass and bronze are important alloys of copper; amalgams are alloys that contain mercury; and chromium is an important additive in stainless steel. Because pure gold and silver are soft, they are often alloyed with one another or with other metals. New alloys are being engineered for use in new technology, including materials for the space program. Metallic glasses and crystalline alloys have also been developed, and metal alloys are sometimes bonded with ceramics, graphites, and organic materials as composites.

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alloy

al·loy • n. / ˈaˌloi/ a metal made by combining two or more metallic elements, esp. to give greater strength or resistance to corrosion: an alloy of nickel, bronze, and zinc. ∎  an inferior metal mixed with a precious one. • v. / ˈaˌloi; əˈloi/ [tr.] mix (metals) to make an alloy: alloying tin with copper to make bronze. ∎ fig. debase (something) by adding something inferior.

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"alloy." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 17 Aug. 2017 <http://www.encyclopedia.com>.

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alloy

alloy Combination of two or more metals. An alloy's properties are different from those of its constituent elements. Alloys are generally harder and stronger, and have lower melting points. Most alloys are prepared by mixing when molten. Some mixtures that combine a metal with a non-metal, such as steel, are also referred to as alloys.

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"alloy." World Encyclopedia. . Encyclopedia.com. 17 Aug. 2017 <http://www.encyclopedia.com>.

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alloy

alloy sb. XVI. — (O)F. aloi, f. OF. aloier, earlier aleier :- L. alligāre, f. AL-1 + ligāre bind (cf. ALLY2, LIEN).
So alloy vb. XVII; superseded †allay sb. and vb. (XIV) — OF. alei(er).

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"alloy." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. 17 Aug. 2017 <http://www.encyclopedia.com>.

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alloy

alloyahoy, alloy, Amoy, annoy, boy, buoy, cloy, coy, destroy, employ, enjoy, Hanoi, hoi polloi, hoy, Illinois, joy, koi, oi, ploy, poi, Roy, savoy, soy, toy, trompe l'œil, troy

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