Iridium is the 83rd most abundant element and is found mixed with platinum, osmium,and nickel ores. The name iridium comes from the Latin word iris, meaning “rainbow,”īecause of the element’s highly colored salts. Theseunstable isotopes are all artificially produced. All the other 53 isotopes of iridium are radioactive with half-lives ranging froma few microseconds to a few hours or days and up to a few hundred years. Those two are Ir-191, which makes up 37.3% of theamount in the Earth’s crust, and Ir-193, which constitutes 62.7% of iridium’s existenceon Earth. There are 55 isotopes of iridium, two of which are stable and account for theelement’s total existence on Earth. Its melting point is 2,410☌, its boiling point is 4,130☌, and itsdensity is 22.560 g/cm 3. Iridium is highly resistant to attack by other chemicals and is one of the most dense elementsfound on Earth. Instead, the meter is now defined by scientists in termsof the length of the path traveled by light in a vacuum at the time of 1/299,792,458 of asecond. However, this metal bar is nolonger used as the standard meter. This platinum-iridiummeter bar, currently preserved in France, was for many years the standard unit of lengthin the metric system that is based on the decimal system.
A singleunit of this distance was then called a “meter” (“measure” in Greek). This distance was then divided into equal lengths of 1/10,000,000.
At about the time of the French Revolution, it was decided to determine the length ofthe meter bar by first calculating the distance from the North Pole to the equator runningthrough Paris. This is why it was used to make the standard meter barthat is an alloy of 90% platinum and 10% iridium. Iridium will only oxidize at high temperatures and is themost corrosive-resistant metal known. Iridium is a hard, brittle, white, metallic substance that is almost impossible to machine.It is neither ductile nor malleable. Iridium does not react with concentrated acids or with molten alkalies. Iridium forms alloys with several metals-mostly platinum group metals. Heating with chlorine at 600☌ produces iridium trichloride, IrCl3. It reacts with fluorine at 250☌, forming iridium hexafluoride, IrF6, and, to a lesser extent, iridium tetrachloride IrCl4. Similarly, the metal reacts with halogens only at elevated temperatures. At elevated temperatures of about 600☌, iridium metal combines with oxygen to form a coating of iridium dioxide, IrO2. The radioisotope Ir-192 is used in examination of ferrous welds and in other radiographic applications.Īt ordinary temperatures iridium exhibits strong resistance to chemical attack. It also enhances hardness and tensile strength. Iridium enhances resistance of platinum to chemical attack and corrosion. Such alloys are used for jewelry, decorative purposes, electrical contacts, thermocouples, crucibles, electrodes, hypodermic needles, and medical accessories. The most important use of iridium is as an alloying metal for platinum and palladium. Iridium may be the densest element discovered (Lide, 2006). Its resistance to high temperatures makes it attractive for making crucibles and other apparatuses that must withstand extreme temperatures. It is the most corrosion resistant metal known (Lide, 2006). Iridium (CASRN ) is a hard, brittle, yellowish- white metal that can withstand high temperatures and has a BP of 4428 ☌ (Lide, 2006). Iridium and osmium together constitute “osmiridium,” which is resistant to chemical attack and is a byproduct of platinum extraction. Iridium occurs in small amounts in native platinum or platinum metal alloys. Tennant named this element Iridium after the Greek word, Iris, meaning rainbow. Around the same time, existence of this new metal was proposed by Vauquelin and deFourcroy in France in the course of their extraction of platinum by aqua regia. Iridium metal was detected in the black residue of aqua regia extract of platinum and identified as an element by British chemist Smithson Tennant in 1803.