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Jai Ganesh

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Iridium

Iridium

Gist

Iridium (Ir) is a rare, hard, brittle, silvery-white transition metal in the platinum group, known for its exceptional corrosion resistance and high density. It is primarily used in alloys for electrical contacts, scientific equipment, and spark plugs. The element is also essential in catalysis, medical brachytherapy for cancer treatment (using Iridium-192), and as the basis for the global Iridium satellite constellation. 

Iridium is used in high-tech applications because of its extreme resistance to heat and corrosion, including in spark plugs, crucibles for high-temperature crystal growth, and catalysts for industrial chemical processes like acetic acid production. Iridium alloys are also vital for specialized tools, deep-sea pipes, and components in aerospace and electronic devices, with its radioactive isotope (Iridium-192) used in cancer treatment (brachytherapy).

Summary

Iridium is a chemical element; it has symbol Ir and atomic number 77. This very hard, brittle, silvery-white transition metal of the platinum group, is considered the second-densest naturally occurring metal (after osmium) with a density of 22.56 g/{cm}^{3} (0.815 lb/cu in) as defined by experimental X-ray crystallography. 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. It is one of the most corrosion-resistant metals, even at temperatures as high as 2,000 °C (3,630 °F).

Iridium was discovered in 1803 in the acid-insoluble residues of platinum ores by the English chemist Smithson Tennant. The name iridium, derived from the Greek word iris (rainbow), refers to the various colors of its compounds. Iridium is one of the rarest elements in Earth's crust, with an estimated annual production of only 6,800 kilograms (15,000 lb) in 2023.

The dominant uses of iridium are the metal itself and its alloys, as in high-performance spark plugs, crucibles for recrystallization of semiconductors at high temperatures, and electrodes for the production of chlorine in the chloralkali process. Important compounds of iridium are chlorides and iodides in industrial catalysis. Iridium is a component of some OLEDs.

Iridium is found in meteorites in much higher abundance than in the Earth's crust. For this reason, the unusually high abundance of iridium in the clay layer at the Cretaceous–Paleogene boundary gave rise to the Alvarez hypothesis that the impact of a massive extraterrestrial object caused the extinction of non-avian dinosaurs and many other species 66 million years ago, now known to be produced by the impact that formed the Chicxulub crater. Similarly, an iridium anomaly in core samples from the Pacific Ocean suggested the Eltanin impact of about 2.5 million years ago.

Details

Iridium (Ir) is a chemical element, one of the platinum metals of Groups 8–10 (VIIIb), Periods 5 and 6, of the periodic table. It is very dense and rare and is used in platinum alloys. A precious, silver-white metal, iridium is hard and brittle, but it becomes ductile and can be worked at a white heat, from 1,200° to 1,500° C (2,200° to 2,700° F). It is one of the densest terrestrial substances. In the massive state the metal is practically insoluble in acids and is not attacked even by aqua regia. It can be dissolved in concentrated hydrochloric acid in the presence of sodium perchlorate at 125° to 150° C (257° to 302° F).

Because of difficulties in preparation and fabrication, the pure metal has few applications. Iridium is chiefly used in the form of platinum alloys. Platinum-iridium alloys (5 to 10 percent iridium) are readily workable metals that are much harder and stiffer and more resistant to chemical attack than the soft pure platinum. Such alloys are used for jewelry, pen points, surgical pins and pivots, and electrical contacts and sparking points. The international prototype standard kilogram of mass is made from an alloy containing 90 percent platinum and 10 percent iridium.

Pure iridium probably does not occur in nature; its abundance in the Earth’s crust is very low, about 0.001 parts per million. Though rare, iridium does occur in natural alloys with other noble metals: in iridosmine up to 77 percent iridium, in platiniridium up to 77 percent, in aurosmiridium 52 percent, and in native platinum up to 7.5 percent. Iridium generally is produced commercially along with the other platinum metals as a by-product of nickel or copper production.

Iridium-containing ores are found in South Africa and Alaska, U.S., as well as in Myanmar (Burma), Brazil, Russia, and Australia. In the late 20th century South Africa was the world’s major producer of iridium.

The element was discovered in 1803 in the acid-insoluble residues of platinum ores by the English chemist Smithson Tennant; the French chemists H.-V. Collet-Descotils, A.-F. Fourcroy, and N.-L. Vauquelin identified it at about the same time. The name iridium, derived from the Greek word iris (“rainbow”), refers to the various colours of its compounds. Natural iridium consists of a mixture of two stable isotopes, iridium-191 (37.3 percent) and iridium-193 (62.7 percent). The chemistry of iridium centres on oxidation states of +1, +3, and +4, though compounds of all states from 0 to +6 are known with perhaps the exception of +2. Complexes in oxidation state +1 chiefly contain carbon monoxide, olefins, and phosphines as ligands. The anions hexachloroiridate, [IrCl6]2−, and hexabromoiridate, [IrBr6]2−, are the only notable chemical species containing iridium in the +4 oxidation state. Iridium is somewhat more reactive than ruthenium and osmium.

Element Properties

atomic number  :  77
atomic weight  :  192.2
melting point  :  2,410° C (4,370° F)
boiling point  :  4,527° C (8,181° F)
specific gravity  :  22.4 (20° C)
oxidation states  :  +1, +3, +4.

Additional Information:

Appearance

Iridium is a hard, silvery metal. It is almost as unreactive as gold. It has a very high density and melting point.

Uses

Iridium is the most corrosion-resistant material known. It is used in special alloys and forms an alloy with osmium, which is used for pen tips and compass bearings. It was used in making the standard metre bar, which is an alloy of 90% platinum and 10% iridium. It is also used for the contacts in spark plugs because of its high melting point and low reactivity.

Biological role

Iridium has no known biological role, and has low toxicity.

Natural abundance

Iridium is one of the rarest elements on Earth. It is found uncombined in nature in sediments that were deposited by rivers. It is commercially recovered as a by-product of nickel refining.

A very thin layer of iridium exists in the Earth’s crust. It is thought that this was caused by a large meteor or asteroid hitting the Earth. Meteors and asteroids contain higher levels of iridium than the Earth’s crust. The impact would have caused a huge dust cloud depositing the iridium all over the world. Some scientists think that this could be the same meteor or asteroid impact that wiped out the dinosaurs.

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