Iridium

The iridium is a chemical element periodic Tableau, of symbol Ir and Atomic number 77.

It is a Métal of transition from the family of the Métaux of the group of platinum, very hard, heavy, breakable and of silver plated white aspect.
Il is used in the alloys high-strength and being able to tolerate high temperatures. One finds it in alloy nature with the Platine or the Osmium. Among the known elements, iridium is most resistant to the Corrosion. Its presence in extreme cases of the geological layers Cretaceous-Tertiary sector is associated with two theories on the disappearance of the dinosaurs. It is used in devices having to tolerate high temperatures, in the electrical contacts and like hardening agent of platinum.

Characteristics

Iridium is white, resembles platinum, but with a light yellowish key. Because of its extreme hardness and its inelasticity, it is difficult to machine, format or to work.

Iridium is the known metal most corrosion resistant. It can be attacked by no Acide nor even by the Eau levels, but can the being by salts in fusion, such as the Sodium chloride (NaCl) and the Cyanure of sodium (Na CN).

Iridium has a very high density, hardly higher than that of osmium, the 2 natural elements densest known. However, calculations of density since space will be able to produce more reliable results and precis that those current, which are of 22.610 kg/m ³ for osmium against 22.650 kg/m ³ for iridium. Their final classification is thus not possible for the moment.

Applications

Iridium is mainly used as agent hardening in platinum alloys. Here of other uses:

• in the crucibles and the equipment supporting of the high temperatures,
• in the electrical contacts, whose in particular candles of the engine spark-ignition , alloy
• with the Osmium, in the points of Stylo plucks and in the stages of compass.
• to treat the surface of the glasses of ski (what causes the effect of mirror)

History

Iridium was discovered in 1803 by Smithson Holding with London, England, at the same time as osmium in the residues of the dissolution of platinum in water levels. Its name comes from Latin iris meaning “Arc-en-ciel”, because of its salts which are very coloured.

An alloy of 10% of iridium and platinum 90% was used like material for the standards of the Mètre and the Kilogram, preserved by the International office of the weights and measures at Sevres, close to Paris, France.

The limit K-T, marking the temporal border between the eras of the secondary (period of the Cretaceous) Cretaceous and of the Tertiary sector (period of the Paleogene) Tertiary, was identified by a fine Strate of clay fat in iridium. According to much of scientists, such as Luis Walter Alvarez, this iridium has an extraterrestrial origin, brought by a Astéroïde or a Comet which would have struck the Earth close of what is now the valley of the Yucatan, with the Mexico. According to others, such as Dewey Mr. McLean of Virginia Polytechnic Institute, this iridium has a volcanic origin. Indeed the terrestrial core is rich, and the Piton of the Furnace of the Réunion for example in slackening still today.

Occurrence

Iridium is in nature at the same time as platinum and other metals of the same family. It is recovered commercially like a by-product of the mines of Nickel.

Isotopes

There exist two natural isotopes and much of radioisotopes. Most stable among the latter is the ¹⁹²Ir with a Demi-vie 73,83 days. It disintegrates in ¹⁹² Pt while the majority of the others disintegrate out of osmium.

Risks

Iridium in its metal form is generally not toxic because of its chemical not-reactivity, but its compounds must be regarded as highly toxic.

See too

• Metals of the group of platinum