 Discovery Information
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| Who: Smithson Tenant, A.F.Fourcory, L.N.Vauquelin, H.V.Collet-Descoltils
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| When: 1804 |
| Where: England/France |
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| Name Origin
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| Latin: iris, iridis (rainbow) as many of its salts are stronly coloured. |
| "Iridium" in different languages. |
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| Sources
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| Found in gravel deposits with platinum. Naturally occurring iridium alloys include iridiosmium and osmiridium, both of which are mixtures of iridium and osmium. Although rare on Earth, iridium is common in meteorites.
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| Canada is the main producer of iridium. Around 3 tons are produced annually. |
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| Abundance
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| Universe: 0.002 ppm (by weight) |
| Sun: 0.002 ppm (by weight) |
| Carbonaceous meteorite: 0.55 ppm |
| Earth's Crust: 4 x 10-4 ppm
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| Seawater: n/a ppm |
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| Uses
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| Used with osmium to tip gold pen points, to make crucible and special containers (that require high temperature resistance). Used to make alloys used for standard weights and measures, and heat-resistant alloys. Also used in cancer irradiation, hypodermic needles, helicopter spark plugs and as hardening agent for platinum.
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| History
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| Iridium was discovered in 1803 by British scientist Smithson Tennant in London, England along with osmium in the dark-coloured residue of dissolving crude platinum in aqua regia (a mixture of hydrochloric and nitric acid). The element was named after the Latin word for rainbow (iris; iridium means
"of rainbows") because many of its salts are strongly coloured.
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| An alloy of 90% platinum and 10% iridium was used in 1889 to construct the standard metre bar and kilogramme mass, kept by the International Bureau
of Weights and Measures near Paris. The metre bar was replaced as the definition of the fundamental unit of length in 1960
(see krypton), but the kilogram prototype is still the international standard of mass.
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| Notes
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| Due to its extreme hardness and brittle properties, iridium is difficult to machine, form, or work. Iridium is the most corrosion-resistant
metal known. Iridium cannot be attacked by any acids or by aqua regia, but it can be attacked by molten salts, such as NaCl and NaCN.
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| The global demand for iridium in 2007 was 3,700 kg, out of which 780 kg were used for electrical applications such as spark
plugs; 1,100 kg for electrochemical applications such as electrodes for the chloralkali process; 750 kg for catalysis; and
1,100 kg for other uses.
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| Iridium is rare on Earth, but relatively common in meteorites. |
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| Hazards
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| Iridium metal is generally non-toxic, but its compounds should be regarded as highly toxic.
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