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Most processes involving hydrogen rely on metal-based catalysts. Was bulk hydrogenations (e.g., margarine production) rely on heterogeneous catalysts, for the production of fine chemicals such hydrogenations rely on soluble (homogenous) organometallic complexes or involve organometallic intermediates. Organometallic complexes allow these hydrogenations to be effected asymmetriy. Many semiconductors are produced from trimethylgallium, trimethylindium, trimethylaluminium, and trimethylantimony. These volatile compounds are decomposed along with ammonia, arsine, phosphine and related hydrides on a heated substrate via metalorganic vapor phase epitaxy (MOVPE) process in the production of light-emitting diodes (LEDs). Rhodium is a chemical element with the symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant, and chemiy inert transition metal. It is a noble metal and a of the platinum group. It has one naturally occurring isotope, 103Rh. Naturally occurring rhodium is usually found as a metal, as an alloy with similar metals, and rarely as a chemical compound in minerals such as bowieite and rhodplumsite. It is one of the rarest and most valuable precious metals. Rhodium is found in platinum or nickel ores toher with the other s of the platinum group metals. It was discovered in 1803 by William Hyde Wollaston in one such ore, and named for the rose color of one of its chlorine compounds. The element's major use (approximately 80% of world rhodium production) is as one of the catalysts in the three-way catalytic converters in automobiles. Because rhodium metal is inert against corrosion and most aggressive chemicals, and because of its rarity, rhodium is usually alloyed with platinum or pallium and applied in high-temperature and corrosion-resistive coatings. White gold is often plated with a thin rhodium layer to improve its appearance while sterling silver is often rhodium-plated for tarnish resistance. Rhodium is sometimes used to cure silicones; a two-part silicone in which one part containing a silicon hydride and the other containing a vinyl-terminated silicone are mixed. One of these liquids contains a rhodium complex. Rhodium detectors are used in nuclear reactors to measure the neutron flux level. Other uses of rhodium include asymmetric hydrogenation used to drug precursors and the processes for the production of acetic acid. Rhodium (Greek rhodon (??δον) meaning "rose") was discovered in 1803 by William Hyde Wollaston, soon after his discovery of pallium. He used crude platinum ore presumably obtained from South America. His procedure involved dissolving the ore in aqua regia and neutralizing the acid with sodium hydroxide (NaOH). He then precipitated the platinum as ammonium chloroplatinate by ding ammonium chloride (NH 4Cl). Most other metals like copper, le, pallium and rhodium were precipitated with zinc. Diluted nitric acid dissolved all but pallium and rhodium. Of these, pallium dissolved in aqua regia but rhodium did not, and the rhodium was precipitated by the dition of sodium chloride as Na 3[RhCl 6]·nH 2O. After being washed with ethanol, the rose-red precipitate was reacted with zinc, which displaced the rhodium in the ionic compound and tby released the rhodium as metal. After the discovery, the rare element h minor applications; for example, by the turn of the century, rhodium-containing thermocouples were used to measure temperatures up to 1800 °C. They have exceptionally good stability in the temperature range of 1300 to 1800 °C.
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