Tennant discovered iridium in 1804 in the residue obtained on attacking impure platinum with aqua regia. Its name is derived from the Greek ιρις (rainbow) and reflects the various colours of its salts.
- One of the platinum-group metals.
- Like platinum, it is a white metal, though with a glint of yellow.
- Very hard and brittle.
- Its volumic mass (22,420 kg/m3) is only slightly less than that of osmium (22,570 kg/m3).
- Iridium has catalytic properties which enable its use in hydrogenation.
- In the automotive industry, iridium is used mainly as a component of exhausts for direct injection (GDI) engines and, to a lesser extent, in spark plugs. In the form of alloys with ruthenium, the metal is used in the manufacture of electrodes for the production of chlorine by electrolysis.
- Iridium has also been used since 1995 as a catalyst in the production of acetic acid.
- Iridium linings and fabrications are also used in glass production because the metal is inert in contact with molten glass
- Other applications include crucibles used to grow synthetic single crystals for LED and data-storage technologies.
- Iridium also serves as an alloying element to harden the platinum used in pacemakers, medical probes and other applications of this type.
- The 90% Pt–10 Ir alloy has an extremely low thermal expansion coefficient. It was selected to make the standard metre kept at the “Pavillon de Sèvres” in France.
Recycling accounts for a small proportion of the metal produced globally each year.