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Cobalt

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                27                 iron ← cobalt → nickel
                 -
                ↑
                Co
                ↓
                Rh

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                       Name, Symbol, Number cobalt, Co, 27
                                         Chemical series transition metals
                                              Group, Period, Block 9, 4, d
                                       Appearance metallic with gray tinge
                                           Atomic mass 58.933195 (5) g/mol
                                     Electron configuration [Ar] 3d^7 4s^2
                                           Electrons per shell 2, 8, 15, 2
                                                       Physical properties
                                       Density (near r.t.) 8.90 g·cm^−3
                                    Liquid density at m.p. 7.75 g·cm^−3
                                                     Melting point 1768  K
                                                    (1495 ° C, 2723 ° F)
                                                      Boiling point 3200 K
                                                    (2927 ° C, 5301 ° F)
                                         Heat of fusion 16.06 kJ·mol^−1
                                     Heat of vaporization 377 kJ·mol^−1
                          Heat capacity (25 °C) 24.81 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 1790 1960 2165 2423 2755 3198

                                                         Atomic properties
                                               Crystal structure hexagonal
                                                     Oxidation states 2, 3
                                                       ( amphoteric oxide)
                                    Electronegativity 1.88 (Pauling scale)
                                                       Ionization energies
                                           ( more) 1st: 760.4 kJ·mol^−1
                                                    2nd: 1648 kJ·mol^−1
                                                    3rd: 3232 kJ·mol^−1
                                                      Atomic radius 135 pm
                                              Atomic radius (calc.) 152 pm
                                                    Covalent radius 126 pm
                                                          Miscellaneous–
                                           Magnetic ordering ferromagnetic
                               Electrical resistivity (20 °C) 62.4 nΩ·m
                        Thermal conductivity (300 K) 100 W·m^−1·K^−1
                       Thermal expansion (25 °C) 13.0 µm·m^−1·K^−1
                               Speed of sound (thin rod) (20 °C) 4720 m/s
                                                   Young's modulus 209 GPa
                                                      Shear modulus 75 GPa
                                                      Bulk modulus 180 GPa
                                                        Poisson ratio 0.31
                                                         Mohs hardness 5.0
                                                 Vickers hardness 1043 MPa
                                                  Brinell hardness 700 MPa
                                             CAS registry number 7440-48-4
                                                         Selected isotopes

                  CAPTION: Main article: Isotopes of cobalt

                                iso   NA   half-life   DM  DE ( MeV)  DP
                               ^56Co syn  77.27 d      ε   4.566     ^56Fe
                               ^57Co syn  271.79 d     ε   0.836     ^57Fe
                               ^58Co syn  70.86 d      ε   2.307     ^58Fe
                               ^59Co 100% Co is stable with 32 neutrons
                               ^60Co syn  5.2714 years β^- 2.824     ^60Ni

                                                                References

   Cobalt ( IPA: /ˈkəʊbɒlt/) is a hard, lustrous, silver-gray metal, a
   chemical element with symbol Co. It is found in various ores, and is
   used in the preparation of magnetic, wear-resistant, and high-strength
   alloys. Its compounds are used in the production of inks, paints, and
   varnishes.

Notable characteristics

   Cobalt is ferromagnetic with atomic number 27. The Curie temperature is
   of 1388 K with 1.6~1.7 Bohr magnetons per atom. It is frequently
   associated with nickel, and both are characteristic ingredients of
   meteoric iron. Mammals require small amounts of cobalt salts.
   Cobalt-60, an artificially produced radioactive isotope of cobalt, is
   an important radioactive tracer and cancer-treatment agent. Cobalt has
   a relative permeability two thirds that of iron. Metallic cobalt
   commonly presents a mixture of two crystallographic structures hcp and
   fcc with a transition temperature hcp→fcc of 722 K.

   Common oxidation states of cobalt include +2 and +3, though +1 is also
   seen.

Applications

     * Alloys, such as:
          + Superalloys, for parts in gas turbine aircraft engines.
          + Corrosion- and wear-resistant alloys.
          + High speed steels.
          + Cemented carbides (also called hard metals) and diamond tools.
     * Magnets and magnetic recording media.
          + Alnico magnets.
     * Catalysts for the petroleum and chemical industries.
     * Electroplating because of its appearance, hardness, and resistance
       to oxidation.
     * Drying agents for paints, varnishes, and inks.
     * Ground coats for porcelain enamels.
     * Pigments ( cobalt blue and cobalt green).

   Cobalt blue glass
   Enlarge
   Cobalt blue glass

     * Battery electrodes.
     * Steel-belted radial tires.
     * Cobalt-60 has multiple uses as a gamma ray source:
          + It is used in radiotherapy.
          + It is used in radiation treatment of foods for sterilization
            (cold pasteurization).
          + It is used in industrial radiography to detect structural
            flaws in metal parts.

   Co-60 is useful as a gamma ray source partially because it can be
   produced - in known quantity, and very large amounts - by simply
   exposing natural cobalt to neutrons in a reactor for a given time.

Use in medicine

   Cobalt-60 (Co-60 or ^60Co) is a radioactive metal that is used in
   radiotherapy. It produces two gamma rays with energies of 1.17 MeV and
   1.33 MeV. The ^60Co source is about 2 cm in diameter and as a result
   produces a geometric penumbra, making the edge of the radiation field
   fuzzy. The metal has the unfortunate habit of producing a fine dust,
   causing problems with radiation protection. The ^60Co source is useful
   for about 5 years but even after this point is still very radioactive,
   and so cobalt machines have fallen from favour in the Western world
   where linacs are common.

History

   Cobalt compounds have been used for centuries to impart a rich blue
   colour to glass, glazes, and ceramics. Cobalt has been detected in
   Egyptian sculpture and Persian jewelry from the third millennium BC, in
   the ruins of Pompeii (destroyed AD 79), and in China dating from the
   Tang dynasty (AD 618–907) and the Ming dynasty (AD 1368–1644).

   Swedish chemist Georg Brandt (1694–1768) is credited with isolating
   cobalt sometime between 1730 and 1737. He was able to show that cobalt
   was the source of the blue colour in glass, which previously had been
   attributed to the bismuth found with cobalt.

   During the 19th century, cobalt blue was produced at the Norwegian
   Blaafarveværket (70-80 % of world production), led by the Prussian
   industrialist Benjamin Wegner.

   In 1938, John Livingood and Glenn Seaborg discovered cobalt-60.

   The word cobalt is derived from the German kobalt, from kobold meaning
   "goblin", a term used for the ore of cobalt by miners, who thought it
   worthless and who found that it was poisonous and that it polluted and
   degraded other mined elements, mainly due to the arsenic and sulfur
   also found in the ore.

Biological role

   Cobalt in small amounts is essential to many living organisms,
   including humans. Having 0.13 to 0.30 mg/kg of cobalt in soils markedly
   improves the health of grazing animals. Cobalt is a central component
   of the vitamin cobalamin, or vitamin B-12.

Occurrence

   Cobalt ore
   Enlarge
   Cobalt ore

   Cobalt is not found as a free metal and is generally found in the form
   of ores. Cobalt is usually not mined alone, and tends to be produced as
   a by-product of nickel and copper mining activities. The main ores of
   cobalt are cobaltite, erythrite, glaucodot, and skutterudite. The
   world's major producers of cobalt are the Democratic Republic of the
   Congo, the People's Republic of China, Zambia, Russia and Australia. It
   is also found in Finland, Azerbaijan, and Kazakhstan. It is also
   produced in the town of Cobalt, Ontario as a byproduct of silver
   mining.

   see also Category:Cobalt minerals

Compounds

   There is a wide variety of cobalt compounds. The +2 and +3 oxidation
   states are most prevalent, however cobalt(I) complexes are also fairly
   common. Cobalt(II) salts form the red-pink [Co(OH[2])[6]]^2+ complex in
   aqueous solution. Adding excess chloride will also change the colour
   from pink to blue, due to the formation of [CoCl[4]]^2-. Cobalt oxides
   are antiferromagnetic at low temperature: CoO ( Neel temperature 291 K)
   and Co[3]O[4] (Neel temperature: 40 K).

   see also Category:Cobalt compounds

Isotopes

   Naturally occurring cobalt is composed of 1 stable isotope, ^59Co. 22
   radioisotopes have been characterized with the most stable being ^60Co
   with a half-life of 5.2714 years, ^57Co with a half-life of 271.79
   days, ^56Co with a half-life of 77.27 days, and ^58Co with a half life
   of 70.86 days. All of the remaining radioactive isotopes have
   half-lifes that are less than 18 hours and the majority of these have
   half lives that are less than 1 second. This element also has 4 meta
   states, all of which have half lives less than 15 minutes.

   The isotopes of cobalt range in atomic weight from 50 amu (^50Co) to 73
   amu (^73Co). The primary decay mode before the most abundant stable
   isotope, ^59Co, is electron capture and the primary mode after is beta
   decay. The primary decay products before ^59Co are element 26 (iron)
   isotopes and the primary products after are element 28 (nickel)
   isotopes.

Precautions

   Powdered cobalt in metal form is a fire hazard. Cobalt compounds should
   be handled with care due to cobalt's slight toxicity.

   ^60Co is a powerful gamma ray emitter and exposure to it is therefore a
   cancer risk. Ingestion of ^60Co will lead to incorporation of some
   cobalt into tissues, which is released very slowly. ^60Co is a risk
   factor in a nuclear confrontation because neutron emissions will
   convert ^59Co into this isotope. Some nuclear weapon designs could
   intentionally increase the amount of ^60Co dispersed as nuclear fallout
   – this is sometimes called a dirty bomb or cobalt bomb, once predicted
   by a leading scientist as being capable of wiping out all life on
   earth. The risk in the absence of a nuclear war comes from improper
   handling (or theft) of medical radiotherapeutic units. Nevertheless,
   the gamma radiation emitted from ^60Co is used to kill bacteria on
   fruit and vegetables thus increasing their shelf life. This process is
   referred to as irradiation.

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