Iridium

Iridium (osmium. Iridium is notable for being the most corrosion-resistant element known and for its significance in the determination of the probable cause of the extinction, by a meteorite strike, of the dinosaurs. It is used in high-temperature apparatus, electrical contacts, and as a hardening agent for platinum.

Characteristics

A NaCN.

The measured kg/m³ for iridium versus 22,610 kg/m³ for osmium. Definitive selection between the two is therefore not possible at this time.

Applications

The principal use of iridium is as a hardening agent in platinum alloys. Other uses:

• Crucibles and devices that require high temperatures.
• Electrical contacts (notable example: Pt-Ir spark plugs).
• Osmium-iridium alloys are used for compass bearings.
• Iridium is commonly used in complexes like Ir(mppy)₃ and other complexes in polymer LED technology to increase the efficiency from 25% to almost 100% due to triplet harvesting.
• Used as a source of radioactivity (Ir-192) for the treatment of cancer (in particular High Dose Rate prostate brachytherapy)
• Iridium is used as a acetic acid
• Iridium is used in supercolliders in the production of antimatter, specifically antiprotons

At one time iridium, as an alloy with platinum, was used in bushing the vents of heavy ordnance, and in a finely powdered condition (iridium black), for painting porcelain black.

Iridium was used to tip some early-twentieth-century fountain pen nibs. The tip material in modern fountain pens is still conventionally called "iridium," although there is seldom any iridium in it. An exception to this are the JML Fountain pens, sold in the UK.

History

Iridium was discovered in 1803 by British scientist salts are strongly coloured.

An alloy of 90% platinum and 10% iridium was used in 1889 to construct the krypton), but the kilogram prototype is still the international standard of mass.

K-T boundary

Main article: Cretaceous–Tertiary extinction event

Main article: K–T boundary

The K–T boundary of 65 million years ago, marking the temporal border between the Cretaceous and Tertiary eras of geological time, was identified by a thin stratum of iridium-rich clay. A team led by Luis Alvarez (1980) proposed an extraterrestrial origin for this iridium, attributing it to an asteroid or comet impact. Their theory is widely accepted to explain the demise of the dinosaurs. A large buried impact crater structure with an estimated age of about 65 million years was later identified near what is now Yucatán Peninsula. Dewey M. McLean and others argue that the iridium may have been of volcanic origin instead. The Earth's core is rich in iridium, and Piton de la Fournaise on Réunion, for example, is still releasing iridium today.

Occurrence

Iridium is found uncombined in nature with platinum and other platinum group metals in alluvial deposits. Naturally occurring iridium alloys include nickel mining and processing.

Iridium is the rarest non-radioactive, non-noble gas element in the Earth's crust, but it is relatively common in meteorites. Iridium and osmium are the densest elements, and both are believed to have dropped below the Earth's crust toward the core when the Earth was young and molten. The concentration of iridium in meteorites matches the concentration of iridium in the Earth as a whole.

Isotopes

Main article: isotopes of iridium

There are two natural beta decays into platinum-192, while most of the other radioisotopes decay into osmium.

Precautions

Iridium metal is mostly non-toxic due to its relative unreactivity.

References

• Los Alamos National Laboratory: Iridium