Sources and Uses of Osmium
Osmium was first found in 1803 by English chemists Smithson Tennant (November 30, 1761 to February 22, 1815) and William Hyde Wollaston (August 6, 1766 to December 22, 1828) in London, England (Tennant, 1804). The discovery of osmium is intimately connected with that of platinum and the other metals of the platinum group.
Sources of Osmium
Osmium is the least abundant stable element in the Earth’s crust, with an average of 50 parts per trillion in the continental crust. Osmium is found in nature as a native element or in natural alloys; especially the iridium-osmium alloys,osmiridium (Os rich), and iridosmium (Ir rich). In nickel and copper deposits, the platinum group metals occur as sulfides (i.e., (Pt,Pd)S)), tellurides (e.g., PtBiTe), antimonides (e.g., PdSb), and arsenides (e.g., PtAs2); in all these minerals Pt is substituted by a small amount of Ir and Os. As with all the Pt-group elements, Os can be found naturally in alloys with Ni or Cu. Within the Earth’s crust, Os, like Ir, is found at highest concentrations in three types of geologic structure: igneous deposits (crustal intrusions from below), impact craters, and deposits reworked from one of the former
structures. The largest identified primary reserves are in the Bushveld Igneous Complex in South Africa, nevertheless the large Cu-Ni deposits near Norilsk in Russia, and the Sudbury Basin in Canada are also important sources of Os. Smaller reserves can be found in the United States. The alluvial deposits used by pre-Columbian people in the Choco´ Department, Colombia are even today a resource for Pt-group elements. The second large alluvial deposit was found in the Ural Mountains, Russia, which is currently being mined as well.
Uses of Osmium
Due to the volatility and extreme toxicity of its oxide, Os is seldom utilized in its pure state, but is instead frequently alloyed with other metals for high-wear applications. Os alloys such as osmiridium are very hard and, together with other Pt-group metals, are employed in, for example, fountain pen tips, instrument pivots, and electrical contacts, since they can resist wear from everyday operation. Historically they were utilized for the tips of phonograph styli during the late 78 rpm and early “LP” and “45” record era, between roughly 1945 and 1955. Os alloy tips were much more durable than steel and Cr needle points, but wore out much faster than competing, and more expensive, sapphire and diamond tips, consequently they were discontinued. OsO4 has been employed in fingerprint detection and in staining fatty tissue for optical and electron microscopy. Another Os compound, Os ferricyanide (OsFeCN), shows comparable fixing and staining action.
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