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alloy





Chrysler Building in New York
The entire crown of the Chrysler Building in New York is clad with "Enduro KA-2" metal, a stainless steel alloy developed in Germany
A combination of a metal with one or more other metals or non-metals, such as carbon or phosphorus. An alloy may be a compound of the metals, a solid solution of them, a heterogeneous mixture, or any combination of these. The resultant physical properties differ from those of the components. Alloys are general harder and stronger, and have lower melting points, than their constituent elements. Combinations with the lowest melting point are called eutectic mixtures. In the table of alloys below, 26 elements are involved.

Alloys are useful because their properties can be adjusted as desired by varying the proportions of the constituents. Very few metals are used today in a pure state. Alloys are formed by mixing their molten components. The structures of alloys consisting mainly of one component may be substitutional or interstitial, depending on the relative sizes of the atoms. The study of alloy structures in general is complex.

The commonest alloys are the different forms of steel, which all contain a large proportion of iron and small amounts of carbon and other elements. Brass and bronze, two well-known and ancient metals, are alloys of copper, while pewter is an alloy of tin and lead. The very light but strong alloys used in aircraft construction are frequently alloys of aluminum and magnesium. Solders contain tin with lead and bismuth; type metal is an alloy of lead, tin, and some antimony. Among familiar alloys are those used in coins: modern "silver" coinage in most countries is an alloy of nickel and copper. Special alloys are used for such purposes as die-casting, dentistry, high-temperature applications, and for making thermocouples, magnets, and low-expansion materials.


Superalloys

So-called superalloys are alloys of cobalt and nickel used as surface materials for spacecraft to withstand the rapid heating and high temperatures caused by the passage through the Earth's atmosphere particularly on re-entry from space. These alloys oxidize in air above 700°C (1,300°F) but the oxide coating initially formed prevents further oxidation.


A selection of alloys
Name Composition expressed as percentages Properties and uses
alnico Fe 60, Ni 20, Al 10, Co 10 permanent magnet
Babbitt metal Sn (predominates), Sb, Cu (+Pb) used for bearings, anti-friction metal
brass Cu with 20–35 Zn decorative
bronze Cu with 5–8 Sn primitive tools, coinage
carboloy W2C2 with 10 Cu very hard alloy, grinding tools
cast iron impure Fe, C up to 4½ with Mn, P, Si, and S traces decorative work, weights
cupronickel Cu 80, Ni 20 (coinage 25-75) coinage
delta metal Cu 55–60, Zn c. 40, Fe 2–4 bearings, marine propellers
dow metal Al, Mg aircraft and car parts
dental alloy Ag, Cu, Zn, Sn tooth fillings
duralumin Al 93–95½, Cu 3½–5½, Mn ½–¾, Mg ½–¾ aircraft frames
Dutch metal Cu with 30–35 Zn bronze in gold leaf form
E-alloy Al 78, Zn 20, Cu 2; Al 96, Zn 2, Cu 2 castings
electrum Au with 15–45 Ag coins (ancient times)
Frary metal Pb 97, Ba 2, Ca 1 bearings
German metal Cu 56–65, Zn 24–28, Ni 7–20 metal fittings, metal ware (often electroplated)
gun metal Cu 88, Sn 8–10, Zn 2–4 ordnance
hiduminium Al with small Cu, Ni, Mg, Si additions aircraft parts
illium complex of Co, Cr, Fe, Mn, Mb, Ni, and W acid resistant
Jae metal Ni 70, Cu 30 shunts on magnetic instruments
Lipowitz's alloy Bi 50, Pb 27, Sn 13, Cd 10 very low melting point (60°C)
magnolia metal Pb 80, Sb 15, Sn 5 medium duty bearings
monel metal Ni 68, Cu 29½, Fe 1¼, resistant to steam corrosion
Muntz metal, yellow metal Cu 60, Zn 40 resistant to seawater corrosion
nichrome Ni 60, Fe 20, Cr 20 filament wires
nickel silver Cu 55–63, Ni 10–30, Zn 7–35 electroplated articles, hence E.P.N.S.
pewter Sn 80, Pb 20, traces of Sb modern pewter Pb replaced by Sb with some Cu and Bi
permalloy Ni 77.5, Fe 22.5 (sometimes with traces of Co, Cr, Cu, and Mo) magnetic properties, transformers, submarine cable parts
phosphorbronze Cu 90, Sn 9½, P ½28 castings, bearings, and rsilient strip
pinchbeck Cu 89–93, Zn 7–11 imitation gold, jewellery
"silver" alloy Hg–Sn amalgam "silver" backing for mirrors
solder Sn½, Pb 33½ plumbing
speculum Cu 60–70, Sn 30–40 high polish surfaces, plating
stainless steel Fe 78–86, Cr 12–20, Ni 2 corrosion resistant culinary, sterile vessels, decorative
steel essentially Fe with C ½–1½ with special purpose additices of Cr, Mn, Mb, Ni, Si, Al, Cu, Co, Ti, W, V multifarious
stellite Co 43, Cr 43, W 14 et al. surgical and other cutting tools
tombac Cu 71–90, Zn 10–29 cartridge cases
type metal Pb 80–86, Sb 11–20, Sn 3–11 lino-, mono-, and stereotype fonts
white gold Au with Ni platinum substitute
Woods metal Bi 50, Pb 25, Sn 12½, Cd 12½ low melting point, fire sprinklers
X-40 Co 55, Cr 25, Ni 9, W 7, C ½, Fe ½, traces of Mn, Si non-creep at high temperatures, gas turbine rotor blades
Y-alloy Al 93, Cu 4, Ni 2, Mn 1  


Related categories

   • INDUSTRIAL CHEMISTRY
   • INORGANIC CHEMISTRY