Precious metals and precious alloys are rare metallic elements and alloys such as silver, gold, platinum, palladium, iridium, osmium, rhodium, and ruthenium. They possess unique characteristics that set them apart from other metals.
Types of Precious Metals and Alloys
There are a number of different precious metals that exist. The GlobalSpec SpecSearch Database contains searchable product information on gold, silver, palladium, platinum, and iridium metals and alloys.
- Gold is a dense, soft, shiny yellow metal that is the most malleable and ductile metal known. It has extremely high corrosion resistance, resulting in high-reliability electrical contacts even under light load conditions. Gold forms useful contact alloys with silver, copper, nickel, cobalt, platinum, and palladium. Major drawbacks are high cost, poor sliding friction characteristics, and low erosion resistance. Besides being used in jewelry and currency, it is used in industry for many specialty applications and electronics.
- Silver is a soft, white, lustrous transition metal. It has the highest electrical conductivity of any element and the highest thermal conductivity of any metal. Its high conductivity, low hardness, and high resistance to oxidation make silver an excellent choice for contact materials. Silver is strengthened with additions of copper, but this affects its conductivity. Fine silver is silver with very high purity (99.99% Ag). Pure or fine silver is too soft for most commercial applications, but is used as a starting component to form other silver-based alloys. Among many commercial and industrial uses, the electronics and power industries utilize silver’s excellent conductivity to achieve maximum electrical transfer efficiency.
- Palladium is a lustrous silvery-white metal that is the least dense and has the lowest melting point of the platinum group metals (PGM). It is soft and ductile when annealed and greatly increases its strength and hardness when cold-worked. It has good erosion resistance and high corrosion resistance with low material transfer. Palladium forms useful alloys with copper and ruthenium. It has the unique ability to absorb up to 900 times its own volume of hydrogen at room temperature. Major drawbacks are high cost and the development of high contact resistance films in the presence of organic vapors. The primary use of palladium is in catalytic converters but it is also used in electronics, hydrogen storage and purification, and jewelry.
- Platinum is a silvery-white, lustrous, ductile, and malleable metal. It has unnatural resistance to corrosion and does not oxidize at any temperature, although it is corroded by halogens, cyanides, sulfur, and caustic alkalis. Platinum forms useful alloys with iridium, ruthenium, and tungsten. Major drawbacks are high cost and the development of high contact resistance films in the presence of organic vapors. It is used in catalytic converters, laboratory equipment, electrical contacts and electrodes, and jewelry.
- Iridium is a very hard, brittle, silvery-white transition metal with a very high melting point. Iridium has the second highest density and modulus of elasticity and is the most corrosion-resistant metal, even up to temperatures of 2000°C. If forms useful alloys with platinum and osmium. It is used only in specialized applications because of its very high cost for materials that require either its heat-resistant properties or its corrosion resistance.
Specifications and Properties
Selecting metals and metal alloys requires an analysis of the desired specifications. Dimensions to consider include outer diameter (OD), inner diameter (ID), overall length, and overall thickness. Other specifications of importance (based on application) include product shape, tensile strength, yield strength, melting point, conductivity, corrosion resistance, ductility, and malleability. These properties differ based on the material or alloy composition.