Cobalt

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27 ironcobaltnickel
-

Co

Rh
General
Name, Symbol, Number cobalt, Co, 27
Chemical series transition metals
Group, Period, Block 94, d
Appearance metallic with gray tinge
Standard atomic weight 58.933195(5) g·mol−1
Electron configuration [Ar] 3d7 4s2
Electrons per shell 2, 8, 15, 2
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
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
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
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Cobalt (IPA: /ˈkəʊbɒlt/) is a hard, lustrous, silver-grey 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.

Contents

[edit] Notable characteristics

Cobalt is a silver or grey ferromagnetic element 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.

[edit] Applications

[edit] Naturally occurring cobalt uses

Cobalt blue glass
Cobalt blue glass


[edit] Radioisotopes of Cobalt

Main article: Isotopes of cobalt

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-lives 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 u (50Co) to 73 u (73Co). The primary decay mode for isotopes with atomic mass unit values less than that of the most abundant stable isotope, 59Co, is electron capture and the primary mode of decay for those of greater than 59 atomic mass units is beta decay. The primary decay products before 59Co are element 26 (iron) isotopes and the primary products after are element 28 (nickel) isotopes.

Cobalt Isotopes[1]
Isotope Decay mechanism Half life
Co-50 positron emission 44 millisecond
Co-51 positron emission unmeasured
Co-52 positron emission 0.12 second
Co-53 positron emission 0.24 second
Co-54 positron emission 193.2 millisecond
Co-55 positron emission 17.53 h
Co-56 electron capture, positron emission 77.3 d
Co-57 positron emission 271.8 d
Co-58 electron capture 70.88 d
Co-59 stable
Co-60 beta decay and gamma ray 5.271 yr
Co-61 beta decay 1.65 hr
Co-62 beta decay 1.5 min
Co-63 beta decay 27.5 second
Co-64 beta decay 0.30 second
Co-65 beta decay 1.17 second
Co-66 beta decay 0.190 second
Co-67 beta decay 0.43 second
Co-68 beta decay 0.20 second
Co-69 beta decay 0.22 second
Co-70 beta decay 0.13 second
Co-71 beta decay 0.21 second
Co-72 beta decay 90 millisecond

[edit] Use of Cobalt radioisotopes 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 favor in the Western world where linacs are common.

Cobalt-57 (Co-57 or 57Co) is a radioactive metal that is used in medical tests; it is used as a radiolabel for vitamin B-12 uptake. It is useful for the Schilling's test.[2]

[edit] Industrial uses for radioactive isotopes

Cobalt-60 (Co-60 or 60Co) is useful as a gamma ray source because it can be produced—in predictable quantity, and high activity—by simply exposing natural cobalt to neutrons in a reactor for a given time. It is used for

[edit] History

Cobalt compounds have been used for centuries to impart a rich blue color 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)[3]. Cobalt glass ingots have been recovered from shipwrecks dating to the time of the Minoans[citation needed].

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 color 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. The first attempts at smelting the cobalt ores to produce cobalt metal failed, yielding cobalt(II) oxide instead; not only that, but because of cobalt's curious affinity for arsenic, the primary ores of cobalt always contain arsenic, and upon smelting the arsenic oxidized into the highly toxic As4O6, which was breathed in by workers.

[edit] 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.

[edit] Occurrence

Cobalt ore
Cobalt ore
Cobalt output in 2005
Cobalt output in 2005
World production trend
World production trend

Cobalt is not found as a native metal but 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.

In 2005, the Democratic Republic of the Congo was the top producer of cobalt with almost 40% world share followed by Canada, Zambia, Russia, Brazil and Cuba, reports the British Geological Survey.

see also Category:Cobalt minerals

[edit] 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(OH2)6]2+ complex in aqueous solution. Adding excess chloride will also change the colour from pink to blue, due to the formation of [CoCl4]2-. Cobalt oxides are antiferromagnetic at low temperature: CoO (Neel temperature 291 K) and Co3O4 (Neel temperature: 40 K), which is analogous to magnetite (Fe3O4), with a mixture of +2 and +3 oxidation states. The oxide Co2O3 is probably unstable; it has never been synthesized. Other than Co3O4 and the brown fluoride CoF3 (which is instantly hydrolyzed in water), all compounds containing cobalt in the +3 oxidation state are stabilized by complex ion formation.

see also Category:Cobalt compounds

[edit] 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 high-energy gamma ray emitter. Acute high-dose exposures to the gamma emissions, such as can occur when irradiation equipment is inadvertently diverted into scrap, can cause severe burns and death. Extended exposures increase the risk of morbidity or mortality from cancer.[4]

Nuclear weapon designs could intentionally incorporate 59Co, some of which would be activated in a nuclear explosion to produce 60Co. The 60Co, dispersed as nuclear fallout, creates what is sometimes called a dirty bomb or cobalt bomb, once predicted by physicist Leó Szilárd as being capable of wiping out all life on earth.

[edit] References & notes

  1. ^ Nuclides and Isotopes: Chart of the Nuclides, 16th Edition, by Edward Baum, Harold Knox, and Thomas Miller; Knolls Atomic Power Laboratory; 2002
  2. ^ JPNM Physics Isotopes
  3. ^ Encyclopedia Britannica Online.
  4. ^ The Juarez accident

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