Iridium is a hard and brittle metallic element found in group 9 of the periodic table. It is rare and occurs in alloys with other noble metals. It has various uses, including hardening platinum and making specialized crucibles. Iridium is also used in the standard of weights and measures for the kilogram. Some speculate that iridium was a component of an asteroid that led to the extinction of the dinosaurs.
Iridium is a metallic element with atomic number 77 and symbol Ir. In the periodic table of elements it is found in group 9, between platinum and osmium. It is referred to as a “transition metal” and also as a “platinum metal”, along with ruthenium, rhodium, palladium, osmium and platinum itself.
Iridium is a metallic element that is both hard and brittle. Described as whitish-yellow or silvery, it is only slightly less dense than osmium, which is the densest element: 22,560 g/cm3 compared to 22.6 gm/cm3.
Iridium was discovered by Smithson Tennant, an English chemist, in London, England in 1803, and its name comes from the Latin iris, the goddess of the rainbow because of its colored salts. Tennant also discovered osmium.
It is found in gravel deposits and is believed to occur only in alloys with other noble metals, i.e. not in the uncombined state. Often found alloyed with osmium in compounds called osmiridium and iridiosmium, the origin of the names is obvious. It is, however, extremely rare, occurring at just 001 ppm in the earth’s crust.
Iridium has several uses. It is used to harden platinum, combined with osmium in making gold-tipped pens, and to make highly specialized crucibles. Iridium may be involved in the irradiation of cancer, as well as in the manufacture of hypodermic syringes and surgical pins. Other uses include helicopter spark plugs, pivot bearings and extrusion dies.
A very special use of iridium is its role in the standard of weights and measures for the kilogram, which is made up of an alloy of iridium (10%) and platinum (90%). Due to exceptionally high amounts of iridium in rocks dating from the Cretaceous to Tertiary periods, some speculate that iridium was a component of an asteroid that struck the Earth and led to the extinction of the dinosaurs.
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