Friday 20 November 2015

Iridium Element Facts

The main use of iridium is as a hardening agent for platinum alloys. With osmium, it forms an alloy that is used for tipping pens, and compass bearings. Iridium is used in making crucibles and other equipment that is used at high temperatures.

Iridium Element Facts

Data Zone | Discovery | Facts | Appearance & Characteristics | Uses | Abundance & Isotopes | References


  Iridium rich layer (K-T boundary) which marks the demise of the dinosaurs.
Iridium rich layer (K-T boundary) which marks the demise of the dinosaurs. Image Ref. (1)

77
Ir
192.2

Data Zone
Classification: Iridium is a transition metal
Color: silvery-white
Atomic weight: 192.22
State: solid
Melting point: 2447 oC, 2720 K
Boiling point: 4430 oC, 4703 K
Electrons: 77
Protons: 77
Neutrons in most abundant isotope: 116
Electron shells: 2,8,18,32,15,2
Electron configuration: [Xe] 4f14 5d7 6s2
Density @ 20oC: 22.56 g/cm3
Show more, including: Heats, Energies, Oxidation, Reactions, Compounds, Radii, Conductivities

Discovery of Iridium
Iridium was discovered in 1803, by English chemist Smithson Tennant in London.

He found it in the residue left when crude platinum had been dissolved in aqua regia (a mixture of hydrochloric acid and nitric acid).

Smithson Tennant also discovered osmium at the same time.

Iridium’s name comes from the Latin word ‘iris’, meaning rainbow, because many of its salts are highly colored.

Abnormally high amounts of iridium have been found in rocks dating to the K-T boundary between the Cretaceous and Tertiary periods (65 million years ago).

This has led to a widely held view that an iridium-containing comet struck the Earth at that time, which led to the extinction of the dinosaurs and many other forms of life.

Iridium

Iridium metal. Photo by Dschwen.


Appearance and Characteristics
Harmful effects:

Iridium is considered to be of low toxicity.

Iridium in powder form is a known irritant and is a fire hazard.

Characteristics:

Iridium is a rare, hard, lustrous, brittle, very dense platinum-like metal.

Chemically it is very unreactive.

It is the most corrosion-resistant metal known and it resists attack by any acid.

Iridium is attacked by molten salts such as sodium chloride (NaCl) and sodium cyanide (NaCN).

Iridium is generally credited with being the second densest element (after osmium) based on measured density, although calculations involving the space lattices of the elements show that iridium is denser.


Uses of Iridium
The main use of iridium is as a hardening agent for platinum alloys.

With osmium, it forms an alloy that is used for tipping pens, and compass bearings.

Iridium is used in making crucibles and other equipment that is used at high temperatures.

It is also used to make heavy-duty electrical contacts.

Iridium was used in making the international standard kilogram, which is an alloy of 90% platinum and 10% iridium.

Radioactive isotopes of iridium are used in radiation therapy for the treatment of cancer.


Abundance and Isotopes
Abundance earth’s crust: 0.4 parts per billion by weight, 0.05 parts per billion by moles

Abundance solar system: 2 parts per billion by weight, 0.01 parts per billion by moles

Cost, pure: $4200 per 100g

Cost, bulk: $2300 per 100g

Source: Iridium is found in natural alloys with platinum and osmium in alluvial deposits. Commercially, iridium is recovered as a by-product from the nickel mining industry.

Isotopes: Iridium has 34 isotopes whose half-lives are known, with mass numbers from 165 to 198. Naturally occurring iridium is a mixture of two isotopes: 191Ir and 193Ir with natural abundances of 37.3% and 62.7% respectively.


References
1. U.S. Geological Survey


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