Iridium Articles from CALABASASINN.COM Free Article Directory

Search our Site:

Iridium (pronounced /?'r?di?m/) is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000&_160;°C. Although only certain molten salts and halogens are corrosive to solid iridium, finely divided iridium dust is much more reactive and can even be flammable. The most important iridium compounds in terms of use are the salts and acids it forms with chlorine, though iridium also forms a number of organometallic compounds used in catalysis and in research. 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.

Iridium was discovered in 1803 by Smithson Tennant among insoluble impurities in natural platinum from South America. It is one of the rarest elements in the Earth's crust, with annual production and consumption of only three tonnes. However, iridium does find a number of specialized industrial and scientific applications. Iridium is employed when high corrosion resistance and high temperatures are needed, as in spark plugs, crucibles for recrystallization of semiconductors at high temperatures, electrodes for the production of chlorine in the chloralkali process, and radioisotope thermoelectric generators used in unmanned spacecraft. Iridium compounds also find applications as catalysts for the production of acetic acid.

Iridium has been linked with the extinction of the dinosaurs and many other species 65&_160;million years ago. The unusually high abundance of iridium in the clays of the K–T geologic boundary was a crucial clue that led to the theory that the extinction was caused by the impact of a massive extraterrestrial object with Earth—the so-called Alvarez hypothesis. Iridium is found in meteorites with an abundance much higher than its average abundance in the Earth's crust. It is thought that due to the high density and siderophilic ("iron-loving") character of iridium, most of the iridium on Earth is found in the inner core of the planet.

One of the lesser-known members of the platinum group metals, iridium is white, resembling platinum, but with a slight yellowish cast. It possesses quite remarkable chemical and physical properties. Due to its hardness, brittleness, and very high melting point (the tenth highest of all elements), solid iridium is difficult to machine, form, or work, and thus powder metallurgy is commonly employed instead.^[1] It is the only metal to maintain good mechanical properties in air at temperatures above 1600&_160;°C.^[2] Iridium has a very high boiling point (11th among all elements) and becomes a superconductor under 0.14&_160;K.^[3]

Iridium Subcategories Iridium Articles