Iridium: Occurrence, Properties, Biological importance and Uses

An Introduction to Iridium Element

Iridium is the transition element located in group number 9 and period number 6 of the periodic table. Its atomic number is 77 and its atomic mass is 192.217. A single atom of iridium contains 77 electrons. The nucleus of iridium contains 116 neutrons. It is chemically represented by the symbol “Ir”.

Naming and History

The name iridium is derived from the Greek word “Iris”. This was the name of the Greek Goddess of the rainbow. It was named because of its highly colored salts.

  • Smithson Tennant

In 1803, an English chemist Smithson Tennant discovered iridium, who also discovered osmium at the same time.

He dissolved platinum in aqua regia – the mixture of nitric acid and hydrochloric acid and heated it till the solution. The black residue left was thought to be graphite but the tenant had working experience with carbon so he thought differently.

He prepared alkaline and acidic solutions of that residue and found two elements. Iridium was one of the two.

  • Humphry Davy
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In 1813, sir Humphry Davy proved that iridium can be melted like other metals. He used an array of batteries for this purpose so a powerful current could be generated.


Occurrence of Iridium

Iridium is found in an uncombined state in nature. It has been observed that dating rocks between cretaceous and tertiary periods contain iridium. The major ores containing iridium are iridosmine and osmiridium. The major supplier of iridium is south Africa. It is also obtained as a by-product of nickel mining.

Properties of Iridium

Iridium is a silverish-whitish, hard, very brittle when pure, corrosion resistant, lustrous, and very dense rare transition metal. It is very unreactive and highly resists the attacks of acids and water. It is the most corrosion-resistant metal.

Molten salts such as sodium cyanide r sodium chloride can attack iridium. It is the second most dense metal after osmium. The melting point of iridium is 2446°C and its boiling point is 4428°C. It has a density of 22.42 grams per cubic centimeter. It exists in the solid phase at room temperature.

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Biological importance of Iridium

There is no known function of iridium in living organisms and is considered to be very less toxic. The powdered iridium, however, is a fire hazard and considered as irritating agent.

Uses of Iridium

  1. Pure iridium is so brittle that it can not be machined. So, it is mostly alloyed with other metals. Iridium is alloyed with platinum to make it hard.
  2. These alloys are used to make high-temperature equipment and crucibles.
  3. Osmium and iridium alloys are used for nibs of high-quality fountain pens and bearings of the compass.
  4. It is used as a catalyst in the chemical industry.
  5. In the automotive and electronic industry, iridium is used to coat electrodes in Chlor-alkali process.
  6. Due to its low reactivity, it is widely used in spark plugs and electrical contacts.
  7. Due to its highly corrosion-resistant nature, it was used as a standard meter bar.
  8. It is also used in the jewelry industry.
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Isotopes of Iridium

There are almost 34 known isotopes of iridium whose mass number ranges from 165 to 198. The most stable and common is basically a mixture of two isotopes: Ir- 191 and Ir- 193. The abundance of the former is 37 % and the latter is 62.7 %.

  • The radioisotopes of iridium are used in the diagnosis and treatment of cancer.