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发表于 17-9-2006 11:27 AM
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Cobalt (symbol Co) is a hard, lustrous, silver-gray metal, a chemical element. 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.
Applications
* Alloys, such as:
o Superalloys, for parts in gas turbine aircraft engines.
o Corrosion- and wear-resistant alloys.
o High speed steels.
o Cemented carbides (also called hard metals) and diamond tools.
* Magnets and magnetic recording media.
o 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).
* Battery electrodes.
* Steel-belted radial tires.
* Cobalt-60 has multiple uses as a gamma ray source:
o It is used in radiotherapy.
o It is used in radiation treatment of foods for sterilization (cold pasteurization).
o 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.
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.
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] 3d7 4s2
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
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–
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
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