Iridium - Properties and Applications

Considered a rare precious metal, iridium is brittle and hard with low ductility, making it a difficult material to work with. Visually, iridium is a lustrous, silvery metal. As can be seen from its position in the periodic table, iridium is stable to water and air and is not corroded by any acid, including "aqua regia," which is used to separate iridium from various other platinum group metals.
However, molten NaOH does attack iridium. It is extremely resistant to corrosion and can be used as an alloying agent for metals such as osmium and gold to develop very hard alloys with good corrosion resistance. Iridium is also used in spark plugs, and its radioactive isotope, 92 Euro, is a medium-energy gamma emitter suitable for industrial radiography.


Iridium was first discovered in 1803 by a tenant who found it in the residue left after the dissolution of crude platinum in aqua regia. The name iridium comes from the fact that its salt is highly colored.


Unbound iridium can be found in nature. It is most commonly found in alluvial deposits in association with other platinum group metals.

Key Properties

Silvery white with a slight yellow tint
It is very hard and friable, making it difficult to work and work with
It is the most corrosion-resistant metal known and only oxidizes slowly at high temperatures
It is not attacked by any acid or aqua regia
It is attacked by molten salts
Resists attack by molten alkalis and molten metals
Competes with osmium as the densest material known to man in the mantle, with a density of about 22.6 g/cm 3
Fluorine and chlorine erode iridium when red hot
Has a face-centered cubic structure


The primary use of iridium is as a hardener for platinum.

It is also used to make

Crucibles and other devices that operate at high temperatures
Fountain pen nibs
Pivot bearings
Scientific and other specialized equipment

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