rhodium (redirected from atomic number 45)

rhodium (rō`dēəm), metallic chemical element; symbol Rh; at. no. 45; at. wt. 102.9055; m.p. about 1,966°C;; b.p. 3,727±100°C;; sp. gr. 12.41 at 20°C;; valence +2, +3, +4, +5, or +6. Rhodium is a lustrous, silver-white, chemically resistant metal in the so-called platinum group of metals in Group 9 of the periodic table. It has a face-centered cubic crystalline structure. It is insoluble in most acids, including aqua regia, but is dissolved in hot concentrated sulfuric acid. Rhodium compounds include halides, oxides, sulfates, sulfites, a nitrate, and a sulfide. The salts form rose-colored aqueous solutions. Rhodium is found associated with other platinum metals in river sands and in compounds in such minerals as rhodite and sperrylite. It is obtained as a byproduct in the refining of nickel sulfide ores mined near Sudbury, Ont., Canada. The major use of the metal is in alloys with platinum and iridium; it gives improved high-temperature strength and oxidation resistance. These alloys are used in pen nibs, phonograph needles, high-temperature thermocouple and resistance wires, bearings, and electrical contacts and as a catalyst. The metal itself, because of its brilliance and resistance to tarnish, is used to plate jewelry and the reflectors of searchlights. Rhodium was discovered in 1804 by W. H. Wollaston in crude platinum ore.

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rhodium

Metallic chemical element, one of the transition elements, chemical symbol Rh, atomic number 45. Chemically related to platinum, it is a precious, silver-white metal mainly used as an alloying agent for the latter element. Rhodium added to platinum in small amounts yields alloys that are harder and that lose mass at high temperatures more slowly than pure platinum. Such alloys are used for laboratory furnace crucibles, spark-plug electrodes, catalysts in very hot chemical environments (including automobile catalytic converters), and high-temperature thermocouples. Because rhodium resists tarnishing at ordinary temperatures and is highly reflective, it is in demand as a surface electroplating for jewelry and other decorative articles. The plated metal is also used for reflecting surfaces in optical instruments.