gold alloys

(metallurgy) Any alloy containing gold.

Combinations of gold and other metals. Pure gold is soft. The addition of copper hardens the gold, and ultimately gold-copper alloys became standard for coinage. Gold coins in the United States contained 10% copper, the balance gold.

Pure gold is weak, having a tensile strength of less than 20,000psi (138 megapascals) when annealed; however, by alloying with copper, sometimes in conjunction with silver or nickel, and often a little zinc, gold alloys with strengths of 60,000–100,000 psi (414–690 MPa) may be made. Addition of these metals changes the color of gold so that red, yellow, greenish, and white golds result. The proportion of gold in solid gold jewelry is designated in karats (k); pure gold is 24 k, 18 k is 18/24 or 75% pure gold, and 14 k is 14/24 or 58.3% pure gold.

Industrial uses of gold depend primarily upon the corrosion resistance and secondarily upon the strength that can be secured by alloying alone or by alloying and heat treating. Many alloys used in dentistry contain gold, silver, and copper, often with small amounts of platinum and palladium; these alloys can be heat-treated to develop strengths above 150,000 psi (1.0 gigapascal). The latter have good spring properties. Alloys of this type find many electrical uses as contacts, particularly where rubbing is involved. Gold electroplate, often thin, is employed on high-frequency conductors, such as those in radar equipment, because of the high electrical conductivity and tarnish resistance of gold. For the same reason gold is employed in the construction of many transistors, microcircuits, printed circuits, and integrated circuits. Most such devices are so small that the cost of gold is relatively unimportant.

Because gold does not oxidize when heated in air, appropriate gold compounds can be decomposed by heat to liberate the metal. Compounds of this type are used in the decoration of china and also for the production of printed electrical circuits on ceramics. These materials, known as liquid bright golds, are applied in the form of varnish, which is dried and then heated to redness, leaving a thin film of gold firmly attached to the underlying ceramic. See also Gold; Gold metallurgy.

Any alloy that contains gold; usually alloyed with copper, silver, platinum, palladium, and zinc. The alloying of gold enhances certain properties such as hardness, or creates a lower melting point for gold solder.