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Iridium - Properties and Applications

Iridium is considered to be a rare, precious metal which is brittle and hard along with a low ductility, which makes it a difficult material to work. In appearance, iridium is a lustrous, silvery metal. It has an abundance in the earth's crust of almost 3x106 ppm.

As might be anticipated from its position in the periodic table, iridium is stable to water and air and is not attacked by any acids, including "aqua regia", which is used for separate iridium from various other platinum group metals.

However, fused NaOH will indeed attack iridium. It is extremely corrosion resistant and is employed as an alloying agent with metals such as osmium and gold in order to develop alloys which are very hard and have good corrosion resistance.

Iridium is also employed in spark plugs, and its radioactive isotope, €92Ir is a medium energy gamma emitter applicable for industrial radiography.


Iridium was first discovered by tenant in 1803 who found it in the residue left behind after the dissolution of crude platinum in aqua regia.

The name iridium was derived from the fact that its salts are highly coloured.


Iridium can be found uncombined in nature. Most commonly it is found associated with other platinum group metals in alluvial deposits.

It is also produced as a by-product of nickel and platinum refining.

Key Properties

Iridium is:

  • Silvery-white in colour, with a yellowish cast
  • It is very hard and brittle and hence difficult to machine and work
  • It is the most corrosion resistant metal known and oxidises only slowly at high temperatures
  • It is not attacked by any acids or aqua regia
  • It is attacked by molten salts such as NaCl and NaCN
  • It resists attacked by fused bases and molten metals
  • Competes with Osmium for the mantle of the densest material known to man with a density of about 22.6 g/cm3
  • Fluorine and chlorine attack iridium at red heat
  • Has a face centred cubic structure


Iridium’s main use is as a hardening agent for platinum.

It is also used for making:

  • Crucibles and other equipment that operate at high temperatures
  • Fountain pen nibs (alloyed with Osmium)
  • Pivot bearings
  • Scientific and other specialised equipment


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