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Atomic Number: 77
Atomic Symbol: Ir
Atomic Weight: 192.217
Melting Point: 4,435 F (2,446 C)
Boiling Point: 8,002.4 F (4,428 C)
Word origin: Iridium comes from the Latin word iris, meaning rainbow.
Discovery: British chemist Smithson Tennant discovered iridium in the residue left when crude platinum is dissolved by aqua regia in 1803.
Properties of iridium
Iridium is the most corrosive resistant metal known and one of the densest metals. It is a member of the platinum family and is white with a yellowish tinge. Iridium is very hard and brittle, making it difficult to machine, form, or work. [See Periodic Table of the Elements]
Sources of iridium
Native platinum has many of the platinum group of metals, including iridium. Iridium is commercially recovered as a by product in nickel mining. The element is named iridium for its colored salts.
Uses of iridium
Due to its resistance to corrosion, iridium was used in making the standard meter bar of Paris. The bar was made of 90 percent platinum and 10 percent iridium. However, it was replaced as a unit of measure in the 1960s when the meter was redefined by the orange-red spectral line of krypton-86.
Iridium is widely used to harden platinum, make devices requiring high temperatures, and in electrical contacts. It’s also used incoating optical lenses to reduce glare and enhance clarity. Osmiridium, a combination of the elements osmium and iridium, is used for fountain pens and compass bearings.
(Source: Los Alamos National Laboratory)