Rhenium is a chemical element with the symbol Re and atomic number 75. A silvery-white, rare, heavy, polyvalent transition metal, rhenium resembles manganese chemically and is used in some alloys. Rhenium is obtained as a by-product of molybdenum refinement and rhenium-molybdenum alloys are superconducting. It was the last naturally occurring element to be discovered and belongs to the ten most expensive metals on Earth (over US$ 7500.-/kg).
Rhenium is a silvery white metal, lustrous, and has one of the highest melting points of all elements, exceeded by only tungsten and carbon. It is also one of the most dense, exceeded only by platinum, iridium and osmium. Rhenium has the widest range of oxidation states of any known element: -3, -1, 0, +1, +2, +3, +4, +5, +6 and +7. The oxidation states +7, +6, +4, +2 and -1 are the most common.
Its usual commercial form is a powder, but this element can be consolidated by pressing and resistance-sintering in a vacuum or hydrogen atmosphere. This procedure yields a compact shape that is in excess of 90 percent of the density of the metal. When annealed this metal is very ductile and can be bent, coiled, or rolled. Rhenium-molybdenum alloys are superconductive at 10 K; tungsten-rhenium alloys are also superconductive, around 4-8 K depending on the alloy. Rhenium metal superconducts at 2.4 K.
|Symbol||Re||Ionic radius(6-coordinate)/pm IV||63|
|Atomic number||75||Density (25°C)/gcm-3||21|
|No. of naturally occurring isotopes||2||Melting point/ °C||3180|
|Atomic weight||186.207||Boiling point / °C||-5650|
|Ionic radius(6-coordinate)/pm VII||53||ΔHf(monoatomic gas)/kJmol-1||779(+/-8)|
|Ionic radius(6-coordinate)/pm VI||55||Electrical resistivity (20°C)/μohm cm||19.3|
|Ionic radius(6-coordinate)/pm V||58||Electronegativity χ||1.9|
|Temperature (oC) @Vap. Pressure||Techniques||Remarks|
|10-8 Torr||10-6 Torr||10-4 Torr||Electron Beam||Crucible||Coil||Boat|
|1928||2207||2571||Poor||-||-||-|| Fine wire will self-evaporate |
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