| Description |
Iridium metal was detected in the black residue of aqua regia extract of platinum and identified as an element by British chemist Smithson Tennant in 1803. Around the same time, existence of this new metal was proposed by Vauquelin and deFourcroy in France in the course of their extraction of platinum by aqua regia. Tennant named this element Iridium after the Greek word, Iris, meaning rainbow.
Iridium occurs in small amounts in native platinum or platinum metal alloys. Iridium and osmium together constitute “osmiridium,” which is resistant to chemical attack and is a byproduct of platinum extraction. |
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| Uses |
The most important use of iridium is as an alloying metal for platinum and palladium. Such alloys are used for jewelry, decorative purposes, electrical contacts, thermocouples, crucibles, electrodes, hypodermic needles, and medical accessories. Iridium enhances resistance of platinum to chemical attack and corrosion. It also enhances hardness and tensile strength. The radioisotope Ir-192 is used in examination of ferrous welds and in other radiographic applications. |
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| Reactions |
At ordinary temperatures iridium exhibits strong resistance to chemical attack. At elevated temperatures of about 600°C, iridium metal combines with oxygen to form a coating of iridium dioxide, IrO2. Similarly, the metal reacts with halogens only at elevated temperatures. It reacts with fluorine at 250°C, forming iridium hexafluoride, IrF6, and, to a lesser extent, iridium tetrachloride IrCl4. Heating with chlorine at 600°C produces iridium trichloride, IrCl3. Iridium forms alloys with several metals—mostly platinum group metals.
Iridium does not react with concentrated acids or with molten alkalies. |
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| Chemical Properties |
Black Powder |
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| Uses |
In manufacturing crucibles; in hardening platinum; in making nibs for fountain-pen points. |
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| Purification Methods |
Iridium is a silver white hard solid which oxidises on the surface in air. Scrape the outer tarnished layer until silver clear and store it under paraffin. It is stable to acids but dissolves in aqua regia. [Gilchrist Chem Rev 32 277 1943.] |
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