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Rhenium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                75               tungsten ← rhenium → osmium
                Tc
                ↑
                Re
                ↓
                Bh

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                      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] 4f^14 5d^5 6s^2
                                   Electrons per shell 2, 8, 18, 32, 13, 2
                                                       Physical properties
                                                               Phase solid
                                      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

   CAPTION: Vapor pressure

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 3303 3614 4009 4500 5127 5954

                                                         Atomic properties
                                               Crystal structure hexagonal
                                         Oxidation states 7, 6, 4, 2, −2
                                                     (mildly acidic oxide)
                                     Electronegativity 1.9 (Pauling scale)
                                                       Ionization energies
                                             ( more) 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
                                                             Miscellaneous
                                                      Magnetic ordering  ?
                                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
                                                        Poisson ratio 0.30
                                                         Mohs hardness 7.0
                                                 Vickers hardness 2450 MPa
                                                 Brinell hardness 1320 MPa
                                             CAS registry number 7440-15-5
                                                         Selected isotopes

                 CAPTION: Main article: Isotopes of rhenium

                             iso    NA    half-life   DM  DE ( MeV)   DP
                            ^185Re 37.4% Re is stable with 110 neutrons
                            ^187Re 62.6% 4.35×10^10 y α   1.653     ^183Ta
                                                      β^- 0.003     ^187Os

                                                                References

   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).

Notable characteristics

   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 .

Applications

   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.

History

   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.

Occurrence

   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.

Isotopes

   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.

Precautions

   Little is known about rhenium toxicity so it should be handled with
   care.

   Retrieved from " http://en.wikipedia.org/wiki/Rhenium"
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