Platinum Group Metals (PGMs)
These noble metals are close to each other on the periodic table.
The platinum group metals (PGMs) are six transitional metal elements that are chemically, physically, and anatomically similar. The PGMs are the densest known metal elements. Exceptionally rare, the six metals naturally occur in the same ore bodies. They are highly durable and, due to their high value, often recycled, giving them long life cycles.
These noble metals are close to each other on the periodic table, and are all referred to as "transition metals." They can be further divided into sub-groups: the iridium-group platinum group elements (IPGEs) and the palladium-group platinum group elements (PPGEs).
The six PGMs are:
The IPGEs comprise osmium, iradium, and ruthenium, while the PPGEs are rhodium, platinum, and of course, palladium.
Characteristics of Platinum Group Metals
Platinum is probably the best known of this group of metals, due in large part to its use in jewelry making. It is dense, stable, and rare, and widely used in medical and electronic devices and applications.
Palladium is a soft, silvery-white metal valued for its catalytic properties. It has a high melting point but the lowest melting point of all the PGMs.
Both platinum and palladium are often used as catalysts, meaning they speed up chemical reactions without themselves being chemically altered in the process.
Iridium considered the most corrosion-resistant pure metal, can resist salts, oxides, and mineral acids, but is affected by sodium chloride and sodium cyanide. It has a high melting point and is resistant to deformation, making it an excellent alloy strengthener.
Rhodium and iridium are harder and more difficult to work with, although chemical compounds of these two metals are valued in a number of alloy applications. Rhodium is valued as a catalyst material and has high reflectance. It also has a low electrical resistance and a low and stable contact resistance.
Ruthenium and osmium are hard and brittle, and have poor resistance to oxidation, but are valuable alloy additives and catalysts.
Applications for Platinum Group Metals
PGMs are most often used as catalysts because of their chemical stability, but they are not limited to this role. According to the International Platinum Group Metals Association (IPA), one-quarter of all goods manufactured either contain a PGM or had a PGM play a key role in its production.
Some examples of end-use applications include: as catalysts for the petroleum industry (palladium and platinum), in pacemakers and other medical implants (iridium and platinum), as a stain for fingerprints and DNA (osmium), in the production of nitric acid (rhodium), and in chemicals, such as cleaning liquids, adhesives, and paints (ruthenium).
Properties of Platinum Group Metals
|Melting point (°C)||1,769||1,554||1,960||2,443||2,310||3,050|
|Vickers hardness no.*||40||40||101||220||240||350|
(microhm.cm at 0°C)