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Rare Earth Elements
CommoditiesRare Earth ElementsGold |
As defined by IUPAC, rare earth elements or rare earth metals are a collection of seventeen chemical elements in the periodic table, namely scandium, yttrium, and the fifteen lanthanides. Scandium and yttrium are considered rare earths since they tend to occur in the same ore deposits as the lanthanides and exhibit similar chemical properties. Technological ApplicationsRare earth elements are incorporated into many modern technological devices, including superconductors, samarium-cobalt and neodymium-iron-boron high-flux rare-earth magnets, electronic polishers, refining catalysts and hybrid car components (primarily batteries and magnets). Rare earth ions are used as the active ions in luminescent materials used in optoelectronics applications, most notably the Nd:YAG laser. Erbium-doped fiber amplifiers are significant devices in optical-fiber communication systems. Phosphors with rare earth dopants are also widely used in cathode ray tube technology such as television sets. The earliest color television CRTs had a poor-quality red; europium as a phosphor dopant made good red phosphors possible. Yttrium iron garnet (YIG) spheres have been useful as tunable microwave resonators. Rare earth oxides are mixed with tungsten to improve its high temperature properties for welding, replacing thorium, which was mildly hazardous to work with.Discovery and Early HistoryRare earth elements became known to the world with the discovery of the black mineral ytterbite (also known as gadolinite) by Lieutenant Carl Axel Arrhenius in the year 1787, in a quarry in the village of Ytterby, Sweden. Many of the rare earths are named for the scientists who discovered or elucidated the elemental properties, or for their geographical discovery, or for Latin or Greek references, or for mythical references:
The ytterbite, renamed to gadolinite in 1800, of Lt. Arrhenius reached Johann Gadolin, a University of Turku professor, and his analysis yielded an unknown oxide (earth) which he called Ytteria. Anders Gustav Ekeberg isolated beryllium from the gadolinite but failed to recognize other elements which the ore contained. After this discovery in 1794 a mineral from Bastnäs near Riddarhyttan, Sweden, which was believed to be an iron-tungsten mineral, was re-examined by Jöns Jacob Berzelius and Wilhelm Hisinger. In 1803 they obtained a white oxide and called it ceria. Martin Heinrich Klaproth independently discovered the same oxide and called it ochroia. Thus by 1803 there were two known rare earth elements, yttrium and cerium, although it took another 30 years for researchers to determine that other elements were contained in the two ores ceria and ytteria (the similarity of the rare earth metals' chemical properties made their separation difficult). In 1839 Carl Gustav Mosander, an assistant of Berzelius, separated ceria by heating the nitrate and dissolving the product in nitric acid. He called the oxide of the soluble salt lanthana. It took him three more years to separate the lanthana further into didymia and pure lanthana. Didymia, although not further separable by Mosander's techniques was a mixture of oxides. In 1842 Mosander also separated the ytteria into three oxides: pure ytteria, terbia and erbia (all the names are derived from the town name "Ytterby"). The earth giving pink salts he called terbium; the one which yielded yellow peroxide he called erbium. So in 1842 the number of rare earth elements had reached six: yttrium, cerium, lanthanum, didymium, erbium and terbium. Nils Johan Berlin and Marc Delafontaine tried also to separate the crude ytteria and found the same substances that Mosander obtained, but Berlin named (1860) the substance giving pink salts erbium and Delafontaine named the substance with the yellow peroxide terbium. This confusion led to several false claims of new elements, such as the mosandrium of J. Lawrence Smith, or the philippium and decipium of Delafontaine.
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