Iridium belongs to the platinum group of metals and is highly dense and resistant to corrosion. It was discovered in 1803.
History and Discovery
Ancient South Americans and Ethiopians have used platinum along with iridium. Iridium was discovered as an impurity in platinum metal by Smithson Tennant in 1803. When platinum was dissolved in aqua regia, iridium appeared as dark insoluble residue, which was later identified as a new metal. The name iridium was given by Tennant after the Greek goddess Iris (Goddess of rainbow), as the newly discovered metal formed varying color compounds and salts .
|Periodic Table Classification||Group 9
|State at 20C||Solid|
|Electron Configuration||[Xe] 4f14 5d7 6s2|
|Electron Shell||2, 8, 18, 32, 15, 2|
|Density||22.4 g.cm-3 at 20°C|
|Atomic Mass||192.22 g.mol -1|
|Electronegativity according to Pauling||2.20|
Iridium is an extremely rare element. And is present in about 0.001 ppm in crustal rocks. Iridium is an element of space and is more abundant on meteorites than in Earth’s crust and has an average abundance of 0.5 ppm . Traces of iridium from core samples of Pacific Ocean and Cretaceous-Paleogene boundary support the hypothesis that massive meteorites showers led to extinction of dinosaurs around 66 million years ago. Due to its low reactivity, iridium is found in its elemental form or in the form of natural alloys, including iridium-osmium alloys (idrosmine and osmiridium). Some minerals of iridium have also been found, but they are quite rare, such as cuproiridsite and irarsite. The annual production and consumption of iridium is only three tons.
Iridium is a whitish silver transition metal. It is brittle solid at standard temperature and pressure. It is a significantly dense metal and is considered as the 2nd densest element (22.56 g/cm3). Iridium is considered as the most corrosion-resistant metal and does not react with water or oxygen even at high temperatures . In powdered form, iridium is highly flammable. Indium has very high boiling and melting points. It can become a super conductor at temperature lower than 0.14K [?]. Indium has an extraordinary ability to withstand deformation and is very stiff. Indium is resistant to most acids and alkalis. It is a very costly metal.
Iridium is considered as a Nobel metal due to its low reactivity. It does not react with molten metals, acids or silicate. However, certain salts, including potassium and sodium cyanide can react with iridium at high temperature. Iridium also reacts with fluorine at high temperature .
Significance and Uses
- Iridium is widely used in electronic industry and is primarily used as a coating agent.
- Iridium is used as a catalyst in various chemical industries, such as Cativa process that involves the formation of acetic acid from methanol by carbonylation.
- Alloys of osmium-iridium are used to make compass bearings, tips of fountain pen and balances used for precision.
- Iridium alloys are used to make electrical contact points in spark plugs.
- Iridium is used to make aircraft engines due to its high resistant to corrosion and heat.
- Iridium radioactive isotope, iridium-192 is used in making energy generators.
Indium is a highly flammable metal. However, it is not considered very toxic. Exposure to indium can lead to minor irritation of eyes and ingestion can lead to slight stomach disorder.
Isotopes of Iridium
Iridium has only two naturally occurring isotopes, iridium-191 and iridium-193 . And has around 34 artificially occurring isotopes, that range in mass number from 164 to 199. The most stable radioactive artificial isotope is irdium-192 (73 days).
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