Alloy

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If a metal is combined with other chemical elements (metallic or nonmetallic) to form a solution or compound, and if the combination has metallic properties, the resulting material is called an alloy. Generally, a number of properties of the alloy are significantly different from those of its components. An alloy with two components is called a binary alloy; one with three is a ternary alloy; one with four is a quaternary alloy.

Steel is an extremely useful alloy, with iron as its major component and a carbon content between 0.02% and 1.7% by weight.

Some common alloys are brass, bronze, and steel. Some alloys are named after their primary constituent. For example, the "silver" used in jewelry and the "aluminum" used as a structural building material are actually alloys. Alloys of gold are rated on a scale of carats—for instance, 14 carat gold is 58% gold. The term "alloy" is sometimes used loosely as a synonym for "aluminum alloy." An example of such usage is the "alloy wheels" fitted on automobiles.

General properties

Alloys are usually designed to have properties that are more desirable than those of their constituents. For instance, steel is stronger than iron, its main element. The alloy "inherits" some of the characteristics of the elements it was made from—usually properties such as density, reactivity, and electrical and thermal conductivity. By contrast, properties such as tensile strength, Young's modulus, and shear strength can differ vastly from those of its constituent materials. These differences are caused by various factors, including the packing of atoms of differing sizes within the alloy. Larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors. Consequently, an alloy tends to resist deformation more than a pure metal, in which the atoms are freer to move.

Unlike pure metals, most alloys do not have a sharp melting point. Instead, they melt over a temperature range in which the material is a mixture of the solid and liquid phases. The temperature at which melting begins is called the solidus, and that at which melting is complete is called the liquidus. For most pairs of elements, however, there is a single, sharp melting point when the elements are in a particular ratio, called a eutectic mixture.

Some common alloys

Amalgam

Any alloy of mercury is called an amalgam. Most metals are soluble in mercury, but some (such as iron) are not. Amalgams are commonly used in dental fillings because they have been relatively cheap, easy to use, and durable. In addition, until recently, they have been regarded as safe. They are made by mixing mercury with silver, copper, tin, and other metals. The mercury content of dental fillings has recently stirred controversy, based on the potentially harmful effects of mercury.

Mercury amalgams have also been used in the process of mining gold and silver, because of the ease with which mercury amalgamates with them. In addition, thallium amalgam is used as the liquid material in thermometers, because it freezes at -58°C, whereas pure mercury freezes at -38°C.

Brass

Bronze

Pewter

Solder

Steel

List of alloys

This is a list of alloys grouped by the main metallic constituent, in order of increasing atomic number of the main metal. Under these headings, the alloys are in no particular order. Some of the main alloying elements are optionally listed after the alloy names.

Alloys of aluminum

Alloys of potassium

Alloys of iron

Alloys of cobalt

Alloys of nickel

Alloys of copper

Alloys of gallium

  • Galinstan

Alloys of silver

Alloys of tin

Rare earth alloys

  • Mischmetal (various rare earths)

Alloys of gold

Alloys of mercury

Alloys of lead

Alloys of bismuth

  • Wood's metal
  • Rose metal
  • Field's metal
  • Cerrobend

Alloys of zirconium

  • Zircaloy

See also

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