Ir - Iridium

Properties

Iridium is a hard, brittle, lustrous, silvery metal belonging to Group 9 of the Periodic Table. It is the 84th most abundant element within the Earth’s crust, meaning it is very rare. Iridium, along with the likes of platinum, is considered a precious metal. It is one of the hardest and most corrosion resistant metals known, and is the 2nd most dense metal after osmium, being 20 times denser than water. Iridium is unaffected by air, water and acids, and the only two substances that will dissolve it are molten sodium cyanide and potassium cyanide.

History

Iridium has been implicated as a factor in the extinction of life 65 million years ago, as its abundance is far higher in meteorites than within the Earth’s crust.  Indeed, the metal’s presence within the Earth could have only originated from space.

An Englishman, Smithson Tennant, is credited with the discovery of iridium. He came across it whilst analysing a specimen of crude platinum, which when dissolved in dilute aqua regia did not all go into solution, with some remaining as a powder. This powder he then tested by using a combination of acid and alkali treatments, eventually separating into two new metals which he called osmium and iridium. The name iridium comes from the Latin word for rainbow ‘Iris’, due to its highly coloured salts.

Sources

The annual production and consumption of  iridium is only 3 tonnes. 191Ir and 193Ir are the only two naturally occurring isotopes of iridium, as well as the only stable isotopes; the latter is the more abundant of the two.

Uses

Presently, 37% of iridium is consumed by the electronics industry, due its high corrosion (highest) and heat (10th highest) resistance qualities.  Around 25% of iridium is used by the chemical industry, another 25% is used in the electrical industry, the electro-chemical industry, and in particular the chlor-alkali industry, also around 25%. The remaining 25% finds use in outlets such as for crucibles, spark plugs and alloys. Iridium is used as an additive to platinum, creating alloys that increase the hardness of the platinum. The fact that it has a high resistance to corrosion makes it useful for items such as hypodermic needles and rocket engines, and the aerospace industry uses iridium to produce alloys that will give a long life to certain engine parts, as well as being used to make corrosion resistant deep water pipes.