2007 Schools Wikipedia Selection. Related subjects: Chemical elements
|Name, Symbol, Number||rhenium, Re, 75|
|Chemical series||transition metals|
|Group, Period, Block||7, 6, d|
|Atomic mass||186.207 (1) g/mol|
|Electron configuration||[Xe] 4f14 5d5 6s2|
|Electrons per shell||2, 8, 18, 32, 13, 2|
|Density (near r.t.)||21.02 g·cm−3|
|Liquid density at m.p.||18.9 g·cm−3|
|Melting point||3459 K
(3186 ° C, 5767 ° F)
|Boiling point||5869 K
(5596 ° C, 10105 ° F)
|Heat of fusion||60.43 kJ·mol−1|
|Heat of vaporization||704 kJ·mol−1|
|Heat capacity||(25 °C) 25.48 J·mol−1·K−1|
|Oxidation states||7, 6, 4, 2, −2
(mildly acidic oxide)
|Electronegativity||1.9 (Pauling scale)|
| Ionization energies
|1st: 760 kJ·mol−1|
|2nd: 1260 kJ·mol−1|
|3rd: 2510 kJ·mol−1|
|Atomic radius||135 pm|
|Atomic radius (calc.)||188 pm|
|Covalent radius||159 pm|
|Electrical resistivity||(20 °C) 193 nΩ·m|
|Thermal conductivity||(300 K) 48.0 W·m−1·K−1|
|Thermal expansion||(25 °C) 6.2 µm·m−1·K−1|
|Speed of sound (thin rod)||(20 °C) 4700 m/s|
|Young's modulus||463 GPa|
|Shear modulus||178 GPa|
|Bulk modulus||370 GPa|
|Vickers hardness||2450 MPa|
|Brinell hardness||1320 MPa|
|CAS registry number||7440-15-5|
Rhenium ( IPA: /ˈɹiːniəm/) is a chemical element in the periodic table that has 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. This was the last naturally-occurring element to be discovered and belongs to the ten most expensive metals on Earth (over US$ 4000.-/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. The oxidation states of rhenium include -3,-1,+1,+2,+3,+4,+5,+6 and +7 oxidation states. 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 .
This element is used in platinum-rhenium catalysts which in turn are primarily used in making lead-free, high-octane gasoline and in high-temperature superalloys that are used to make jet engine parts. Other uses:
- Widely used as filaments in mass spectrographs and in ion gauges.
- An additive to tungsten and molybdenum-based alloys to increase ductility in these alloys.
- Rhenium catalysts are very resistant to chemical poisoning, and so are used in certain kinds of hydrogenation reactions.
- Electrical contact material due to its good wear resistance and ability to withstand arc corrosion.
- Thermocouples containing alloys of rhenium and tungsten are used to measure temperatures up to 2200 ° C.
- Rhenium wire is used in photoflash lamps in photography.
Rhenium (Latin Rhenus meaning "Rhine") was the last naturally-occurring element to be discovered. The existence of an as-yet undiscovered element at this position in the periodic table had been predicted by Henry Moseley in 1914. It is generally considered to have been discovered by Walter Noddack, Ida Tacke, and Otto Berg in Germany. In 1925 they reported that they detected the element in platinum ore and in the mineral columbite. They also found rhenium in gadolinite and molybdenite. In 1928 they were able to extract 1 g of element by processing 660 kg of molybdenite.
The process was so complicated and the cost so high that production was discontinued until early 1950 when tungsten-rhenium and molybdenum-rhenium alloys were prepared. These alloys found important applications in industry that resulted in a great demand for the rhenium produced from the molybdenite fraction of porphyry copper ores.
Rhenium is not found free in nature, and it was only recently that the first rhenium mineral was found. In 1994, Nature published a letter describing a rhenium sulfide mineral found condensing from a fumarole on Russia's Kudriavy volcano. This is not an economically viable source of the element. Rhenium is widely spread through the Earth's crust at approximately 0.001 ppm.
Commercial rhenium is extracted from molybdenum roaster-flue dusts obtained from copper-sulfide ores. Some molybdenum ores contain 0.002% to 0.2% rhenium. Total world production is between 40 and 50 tons/year; the main producers are in Chile, USA and Kazakhstan. Recycling of used Pt-Re catalyst and special alloys allow the recovery of another 10 tons/year.
The metal form is prepared by reducing ammonium perrhenate with hydrogen at high temperatures.
Naturally occurring rhenium is a mix of 185Re, which is stable, and 187Re, which is unstable but has a very long half-life. There are twenty-six other unstable isotopes recognized.
Little is known about rhenium toxicity so it should be handled with care.