|Name, Symbol, Number||rhenium, Re, 75|
|Chemical series||transition metals|
|Group, Period, Block||7, 6, d|
|Appearance||grayish white |
|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/cm³|
|Liquid density at m.p.||18.9 g/cm³|
|Melting point||3459 K|
(3186 °C, 5767 °F)
|Boiling point||5869 K|
(5596 °C, 10105 °F)
|Heat of fusion||60.43 kJ/mol|
|Heat of vaporization||704 kJ/mol|
|Heat capacity||(25 °C) 25.48 J/(mol·K)|
|Oxidation states||7, 6, 4, 2, −2|
(mildly acidic oxide)
|Electronegativity||1.9 (Pauling scale)|
|1st: 760 kJ/mol|
|2nd: 1260 kJ/mol|
|3rd: 2510 kJ/mol|
|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·K)|
|Thermal expansion||(25 °C) 6.2 µm/(m·K)|
|Speed of sound (thin rod)||(20 °C) 4700 m/s|
|Speed of sound (thin rod)||(r.t.) 463 m/s|
|Shear modulus||178 GPa|
|Bulk modulus||370 GPa|
|Vickers hardness||2450 MPa|
|Brinell hardness||1320 MPa|
|CAS registry number||7440-15-5|
Rhenium (chemical symbol Re, atomic number 75) is a silvery-white, lustrous, rare metal. Obtained as a byproduct of molybdenum refinement, it is among the ten most expensive metals on Earth. It is extremely resistant to wear and has one of the highest melting points of all elements. Its alloys with molybdenum or tungsten are superconducting. In combination with platinum, it makes good catalysts for the preparation of high-octane gasoline. It is also a component of high-temperature superalloys for jet engine parts.
Rhenium is widely spread in the Earth's crust, at approximately 0.001 parts per million (ppm), but it is not found free in nature. Some molybdenum ores contain 0.002 percent to 0.2 percent rhenium. 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 mineral, however, is not an economically viable source of the element.
Commercial rhenium is extracted from molybdenum roaster-flue dusts obtained from copper sulfide ores. Total world production is between 40 and 50 tons/year; the main producers are Chile, the United States, and Kazakhstan. Recycling of used platinum-rhenium catalyst and special alloys allow the recovery of another ten tons/year.
The name rhenium is derived from the Latin word Rhenus, meaning "Rhine." Before this element was discovered, its existence was predicted by Henry Moseley in 1914, based on his examination of the periodic table. Its discovery is generally attributed to Walter Noddack, Ida Tacke, and Otto Berg in Germany. In 1925, they reported detecting the element in platinum ore and in the mineral columbite. They also found rhenium in gadolinite and molybdenite. In 1928, they succeeded in extracting one gram (g) of the element by processing 660 kilograms (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, resulting in a high demand for rhenium produced from the molybdenite fraction of porphyry copper ores.
Rhenium is classified as a transition metal. In the periodic table, it lies in group seven (former group 7B), below manganese and technetium. It thus resembles the latter two elements in chemical properties. In addition, rhenium is situated in period six, between tungsten and osmium.
The melting point of rhenium is among the highest of all elements, exceeded only by the melting points of tungsten and carbon. Rhenium is also one of the densest, exceeded only by the densities of platinum, iridium, and osmium. The oxidation states of rhenium include -3,-1,+1,+2,+3,+4,+5,+6 and +7. Of these, the most common are +7,+6,+4,+2 and -1.
The usual commercial form of rhenium is a powder, but it can be consolidated by pressing and resistance-sintering in a vacuum or hydrogen atmosphere. This procedure yields a compact shape that is more than 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 ten Kelvin (K), and tungsten-rhenium alloys are superconductive around four to eight K, depending on the alloy.
Naturally occurring rhenium is a mix of 185Re, which is stable, and 187Re, which is radioactive but has a very long half-life. Many other radioactive isotopes are known, with atomic mass numbers ranging from 160 to 194, but most of them are extremely short-lived.
- Ammonium perrhenate (APR, NH4ReO4): This salt of rhenium is the most common form in which rhenium is traded. Its rhenium content is around 69.0–69.4 percent. Pure rhenium powder can be produced from APR simply by reducing the latter with hydrogen.
- Perrhenic acid (HReO4): This is a strong acid that can attack metals, metal oxides, carbonates, and hydroxides. It is, however, non-oxidizing. It exists only in solution—the solid has not been isolated. It is a common precursor to other rhenium compounds, some of have applications in the petrochemical and fine chemical industries.
- Rhenium trioxide or rhenium (VI) oxide (ReO3): This oxide is a red solid with a metallic luster. It is the only stable trioxide of the Group seven elements (manganese, technetium, rhenium). It can be formed by reducing rhenium (VII) oxide (Re2O7) with carbon monoxide. Unlike most oxides, it exhibits very low resistivity. Instead, it behaves more like a metal in that its resistivity decreases as its temperature is lowered. In crystals of the oxide, each rhenium atom is surrounded by six oxygen atoms, forming a ReO6 octahedron.
Rhenium is combined with platinum to form catalysts that are used primarily for making lead-free, high-octane gasoline. It is also a component of high-temperature superalloys that are used to make jet engine parts. Additional uses of rhenium are given below.
- It is widely used for filaments in mass spectrographs and ion gauges.
- As an additive in tungsten and molybdenum-based alloys, it increases their ductility.
- Catalysts made with rhenium are very resistant to chemical poisoning and are used in certain types of hydrogenation reactions.
- Based on its good wear resistance and ability to withstand arc corrosion, rhenium is used in electrical contact material.
- 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.
Little is known about the toxicity of rhenium, but as a precautionary measure, it should be handled with care.
- Korzhinsky, M.A. and S. I. Tkachenko, K. I. Shmulovich, Y. A. Taran and G. S. Steinberg (2004-05-05). Discovery of a pure rhenium mineral at Kudriavy volcano. Nature 369: 51–52.
- The Superconductivity of Some Intermetallic Compounds Retrieved December 4, 2007.
- Chang, Raymond. 2006. Chemistry, 9th ed. New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031
- Cotton, F. Albert and Geoffrey Wilkinson. 1980. Advanced Inorganic Chemistry, 4th ed. New York: Wiley. ISBN 0-471-02775-8
- Greenwood, N.N. and Earnshaw, A. 1998. Chemistry of the Elements, 2nd Edition. Oxford, U.K.; Burlington, Massachusetts: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654
- Rhenium Los Alamos National Laboratory. Retrieved December 4, 2007.
All links retrieved July 28, 2019.
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