Rhenium
Title: Rhenium
CAS Registry Number: 7440-15-5
Literature References: Re; at. wt 186.207; at. no. 75; valences 1-7; the heptavalent state is the most stable. Group VIIB(7). Two naturally occurring isotopes: 185 (37.07%); 187 (62.93%); the latter is radioactive, T½ ~1011 years. Artificial, radioactive isotopes: 177-184; 186; 188-192. Occurs in gadolinite, molybdenite, columbite, rare earth minerals, and some sulfide ores. Average concn in earth's crust 1 ´ 10-9 (0.001 ppm). Discovered by Noddack et al., Naturwissenschaften 13, 567, 571 (1925). Prepn of metallic rhenium by reduction of potassium perrhenate or ammonium perrhenate: Hurd, Brim, Inorg. Synth. 1, 175 (1939). Prepn of high purity rhenium: Rosenbaum et al., J. Electrochem. Soc. 103, 518 (1956). Reviews: Melaven in Rare Metals Handbook, C. A. Hampel, Ed. (Reinhold, New York, 1954) pp 347-364; Peacock in Comprehensive Inorganic Chemistry vol. 3, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 905-978; P. M. Treichel in Kirk-Othmer Encyclopedia of Chemical Technology vol. 20 (Wiley-Interscience, New York, 3rd ed., 1982) pp 249-258.
Properties: Hexagonal close-packed crystals, black to silver-gray. d 21.02. mp 3180°. bp 5900° (estimated). Specific heat 0-20° 0.03263 cal/g/°C. Specific electrical resistance: 0.21 ´ 10-4 ohm/cm at 20°. Brinell hardness: 250. Latent heat of vaporization 152 kcal/mol. Reacts with oxidizing acids, nitric and concd sulfuric; not with HCl.
Melting point: mp 3180°
Boiling point: bp 5900° (estimated)
Density: d 21.02
Use: Electron tube and semiconductor applications, in alloys for electrical contacts, as catalyst; possibly in high temp thermocouples and to improve the workability of tungsten and molybdenum alloys; plating jewelry, medical instruments, high vac equipment, mirror backings.

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