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Niobium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                41            zirconium ← niobium → molybdenum
                 V
                ↑
                Nb
                ↓
                Ta

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                      Name, Symbol, Number niobium, Nb, 41
                                         Chemical series transition metals
                                              Group, Period, Block 5, 5, d
                                                  Appearance gray metallic
                                            Atomic mass 92.90638 (2) g/mol
                                     Electron configuration [Kr] 4d^4 5s^1
                                       Electrons per shell 2, 8, 18, 12, 1
                                                       Physical properties
                                                               Phase solid
                                       Density (near r.t.) 8.57 g·cm^−3
                                                     Melting point 2750  K
                                                    (2477 ° C, 4491 ° F)
                                                      Boiling point 5017 K
                                                    (4744 ° C, 8571 ° F)
                                            Heat of fusion 30 kJ·mol^−1
                                   Heat of vaporization 689.9 kJ·mol^−1
                          Heat capacity (25 °C) 24.60 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 2942 3207 3524 3910 4393 5013

                                                         Atomic properties
                                     Crystal structure cubic body centered
                                                     Oxidation states 5, 3
                                                     (mildly acidic oxide)
                                     Electronegativity 1.6 (Pauling scale)
                                                       Ionization energies
                                           ( more) 1st: 652.1 kJ·mol^−1
                                                    2nd: 1380 kJ·mol^−1
                                                    3rd: 2416 kJ·mol^−1
                                                      Atomic radius 145 pm
                                              Atomic radius (calc.) 198 pm
                                                    Covalent radius 137 pm
                                                             Miscellaneous
                                                 Magnetic ordering no data
                                 Electrical resistivity (0 °C) 152 nΩ·m
                       Thermal conductivity (300 K) 53.7 W·m^−1·K^−1
                        Thermal expansion (25 °C) 7.3 µm·m^−1·K^−1
                               Speed of sound (thin rod) (20 °C) 3480 m/s
                                                   Young's modulus 105 GPa
                                                      Shear modulus 38 GPa
                                                      Bulk modulus 170 GPa
                                                        Poisson ratio 0.40
                                                         Mohs hardness 6.0
                                                 Vickers hardness 1320 MPa
                                                  Brinell hardness 736 MPa
                                             CAS registry number 7440-03-1
                                                         Selected isotopes

                 CAPTION: Main article: Isotopes of niobium

                             iso    NA   half-life  DM   DE ( MeV)    DP
                           ^91Nb   syn  6.8×10^2 y  ε   -            ^91Zr
                           ^91 mNb syn  60.86 d     IT  0.104 e      ^91Nb
                           ^92Nb   syn  10.15 d     ε   -            ^92Zr
                                                    γ   0.934        -
                           ^92Nb   syn  3.47×10^7y  ε   -            ^92Zr
                                                    γ   0.561, 0.934 -
                           ^93Nb   100% Nb is stable with 52 neutrons
                           ^93 mNb syn  16.13 y     IT  0.031 e      ^93Nb
                           ^94Nb   syn  2.03×10^4 y β^- 0.471        ^94Mo
                                                    γ   0.702, 0.871 -
                           ^95Nb   syn  34.991 d    β^- 0.159        ^95Mo
                                                    γ   0.765        -
                           ^95 mNb syn  3.61 d      IT  0.235        ^95Nb

                                                                References

   Niobium ( IPA: /niˈəʊbiəm, ˌnʌɪˈəʊbiəm/), or columbium ( IPA:
   /kəˈlʌmbiəm/) is a chemical element in the periodic table that has the
   symbol Nb and atomic number 41. A rare, soft, gray, ductile transition
   metal, niobium is found in niobite and used in alloys. The most notable
   alloys are used to make special steels and strong welded joints.
   Niobium was discovered in a variety of columbite (now called niobite)
   and was at first named after this mineral.

Notable characteristics

   Niobium is a shiny gray, ductile metal that takes on a bluish tinge
   when exposed to air at room temperature for extended periods. Niobium's
   chemical properties are almost identical to the chemical properties of
   tantalum, which appears below niobium in the periodic table.

   When it is processed at even moderate temperatures niobium must be
   placed in a protective atmosphere. The metal begins to oxidize in air
   at 200 ° C; its most common oxidation states are +3, and +5, although
   others are also known.

Applications

   Niobium has a number of uses: it is a component of some stainless
   steels and an alloy of other nonferrous metals. These alloys are strong
   and are often used in pipeline construction. Other uses;
     * The metal has a low capture cross-section for thermal neutrons and
       so finds use in the nuclear industries.
     * It is also the metal used in arc welding rods for some stabilized
       grades of stainless steel.
     * Appreciable amounts of niobium in the form of high-purity
       ferroniobium and nickel niobium are used in nickel-, cobalt-, and
       iron-base superalloys for such applications as jet engine
       components, rocket subassemblies, and heat-resisting and combustion
       equipment. For example, advanced air frame systems such as those
       used in the Gemini program used this metal.
     * Niobium is being evaluated as an alternative to tantalum in
       capacitors.
     * Because niobium metal and some niobium alloys are physiologically
       inert (and thus hypoallergenic), they are used in jewelry and in
       medical devices. Niobium metal treated with sodium hydroxide forms
       a porous layer that aids osseointegration.
     * Along with titanium, tantalum, and aluminium, Niobium can also be
       electrically heated and anodized to a wide array of colors using a
       process known as reactive metal anodizing. This makes it very
       attractive for use in jewelry.
     * Niobium is also added to glass in order to attain a higher
       refractive index, a property used in the optical industry to make
       thinner corrective glasses.

   Niobium becomes a superconductor when lowered to cryogenic
   temperatures. At atmospheric pressure, it has the highest critical
   temperature of the elemental superconductors: 9.3 K. In addition, it is
   one of the three elemental superconductors that are Type II (the others
   being vanadium and technetium), meaning it remains a superconductor
   when subjected to high magnetic fields. Niobium-tin and
   niobium-titanium alloys are used as wires for superconducting magnets
   capable of producing exceedingly strong magnetic fields. Niobium is
   also used in its pure form to make superconducting accelerating
   structures for particle accelerators.

History

   Niobium (Greek mythology: Niobe, daughter of Tantalus) was discovered
   by Charles Hatchett in 1801. Hatchett found niobium in columbite ore
   that was sent to England in the 1750s by John Winthrop, the first
   governor of Connecticut. There was a considerable amount of confusion
   about the difference between the closely-related niobium and tantalum
   that wasn't resolved until 1846 by Heinrich Rose and Jean Charles
   Galissard de Marignac, who rediscovered the element. Since Rose was
   unaware of Hatchett's work, he gave the element a different name,
   niobium. In 1864 Christian Blomstrand was the first to prepare the pure
   metal, reducing niobium chloride by heating it in a hydrogen
   atmosphere.

   Columbium (symbol Cb) was the name originally given to this element by
   Hatchett, but the International Union of Pure and Applied Chemistry
   (IUPAC) officially adopted "niobium" as the name for element 41 in 1950
   after 100 years of controversy. This was a compromise of sorts; the
   IUPAC accepted tungsten instead of wolfram, in deference to North
   American usage; and niobium instead of columbium, in deference to
   European usage. Not everyone agreed, however, and while many leading
   chemical societies and government organizations refer to it by the
   official IUPAC name, many leading metallurgists, metal societies, and
   most leading American commercial producers still refer to the metal by
   the original "columbium."

Occurrence

   Niobium metal
   Enlarge
   Niobium metal

   The element is never found as a free element but does occur in the
   minerals columbite ((Fe,Mn)(Nb,Ta)[2]O[6]), columbite-tantalite or
   coltan ((Fe,Mn)(Ta,Nb)[2]O[6]), pyrochlore ((Na,Ca)[2]Nb[2]O[6] OH,F),
   and euxenite ((Y,Ca,Ce,U,Th)(Nb,Ta,Ti)[2]O[6]). Minerals that contain
   niobium often also contain tantalum. Large deposits of niobium have
   been found associated with carbonatites (carbon- silicate igneous
   rocks) and as a constituent of pyrochlore. Brazil and Canada are the
   major producers of niobium mineral concentrates and extensive ore
   reserves are also in Nigeria, Democratic Republic of Congo, and in
   Russia. A large producer in Brazil is CBMM located in Araxá, Minas
   Gerais.

Isotopes

   Naturally occurring niobium is composed of one stable isotope (Nb-93).
   The most stable radioisotopes are Nb-92 with a half-life of 34.7
   million years, Nb-94 (half life: 20300 years), and Nb-91 with a half
   life of 680 years. There is also a meta state at 0.031
   megaelectronvolts whose half-life is 16.13 years. Twenty three other
   radioisotopes have been characterized. Most of these have half lives
   that are less than two hours except Nb-95 (35 days), Nb-96 (23.4 hours)
   and Nb-90 (14.6 hours). The primary decay mode before the stable Nb-93
   is electron capture and the primary mode after is beta emission with
   some neutron emission occurring in the first mode of the two mode decay
   of Nb-104, 109 and 110. It is worth 4 dollars a gram

Precautions

   Niobium-containing compounds are relatively rarely encountered by most
   people, but many are highly toxic and should be treated with care.
   Metallic niobium dust is an eye and skin irritant and also can be a
   fire hazard. Niobium has no known biological role.

   Retrieved from " http://en.wikipedia.org/wiki/Niobium"
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   with only minor checks and changes (see www.wikipedia.org for details
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