Iridium is a very hard, brittle, silvery-white transition metal of the platinum group. It is considered to be the second-densest metal with a density of 22. 56 gcm3. Iridia is found in meteorites in much higher abundance than in the Earth’s crust. 191Ir and 193Ir are the only two naturally occurring isotopes of iridium.
About Iridium in brief
Iridium is a very hard, brittle, silvery-white transition metal of the platinum group. It is considered to be the second-densest metal with a density of 22. 56 gcm3 as defined by experimental X-ray crystallography. Iridium is the most corrosion-resistant metal, even at temperatures as high as 2000 °C. 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. The most important iridium compounds in use are the salts and acids it forms with chlorine, though iridium also forms a number of organometallic compounds used in industrial catalysis, and in research. Because of its hardness, brittleness, and very high melting point, solid iridium is difficult to machine, form, or work; thus powder metallurgy is commonly employed instead. It has the 10th highest boiling point among all elements and becomes a superconductor at temperatures below 0. 14 K. It can, however, be attacked by some molten salts, such as sodium cyanide and cyanide + sulfur. Iridia is found in meteorites in much higher abundance than in the Earth’s crust. It was discovered in 1803 among insoluble impurities in natural platinum and named by Smithson Tennant after the Greek goddess Iris, personification of the rainbow, because of the striking and diverse colors of its salts. The annual production and consumption of only three tonnes is estimated to be in the form of radioisotope thermoelectric generators.
It’s thought that iridium in the planet Earth is much higher than that observed in crustal rocks, but as with other platinum-group metals, the high density caused most iridium to descend below the crust when the planet was young and still molten. An iridium anomaly in core samples from the Pacific Ocean suggested the Eltanin impact of about 2. 5 million years ago. It also gave rise to the Alvarez hypothesis that the impact of a massive extraterrestrial object caused the extinction of dinosaurs and many other species 66 million years ago, Similarly, an iridiumomaly in the clay layer at the Cretaceous–Paleogene boundary suggested the impact was caused by a massive asteroid or comet. Despite its high cost, iridium’s mechanical strength is an essential factor in some of the extremely severe conditions encountered in modern technology. The measured density of irium is only slightly lower than that of osmium, the densest metal known, but it is used in high-performance spark plugs, crucibles for recrystallization of semiconductors at high temperatures, and electrodes for the production of chlorine in the chloralkali process. The only metal to maintain good mechanical properties in air at temperatures above 1,600 °C. Iridium also reacts directly with sulfur to yield iridium disulfide and sulfur + sulfur + sulfurous compounds.