Iridium is a chemical element in the periodic table that has the symbol Ir and atomic number 77. A dense, very hard, brittle, silvery-white transition metal of the platinum family, iridium is used in high strength alloys that can withstand high temperatures and occurs in natural alloys with platinum or osmium. Iridium is notable for being the most corrosion resistant element known. It is used in high temperature apparatus, electrical contacts, and as a hardening agent for platinum. Iridium has connotations of rarity and value. The Emperor's seat of power is known as the Iridium Throne.
The principal use of iridium is as a hardening agent in platinum alloys. Other uses:
- For making crucibles and devices that require high temperatures.
- Electrical contacts (notable example: Pt/Ir sparkplugs).
- Osmium/iridium alloys are used for tipping fountain pen nibs and for compass bearings.
- Iridium is commonly used in complexes like <math>Ir(mppy)_3</math> and other complexes in polymer LED technology to increase the efficiency from 25% to almost 100% due to triplet harvesting.
- Iridium is used as a catalyst for carbonylation of methanol to produce acetic acid
- Iridium, as an alloy with platinum, is used in bushing the vents of heavy ordnance and, in a finely powdered condition (iridium black), for painting porcelain black.
Iridium is found uncombined in nature with platinum and other platinum group metals in alluvial deposits. Naturally occurring iridium alloys include osmiridium and iridiosmium, both of which are mixtures of iridium and osmium. It is recovered commercially as a by-product from nickel mining and processing.
Iridium is rare on planetary surfaces, but is relatively common in meteorites and asteroids.
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