Cobalt

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Iron - Cobalt - Nickel Co Rh       Full table
General
Name, Symbol, Number	Cobalt, Co, 27
Chemical series	Transition metals
Group, Period, Block	9 [?], 4 , d
Density, Hardness	8900 kg/m3, 5.0
Appearance	metallic with grey tinge
Atomic Properties
Atomic weight	58.933200 amu
Atomic radius (calc.)	135 (152) pm
Covalent radius	126 pm
van der Waals radius	n/a pm
Electron configuration	[Ar]3d74s2
e- 's per energy level	2, 8, 15, 2
Oxidation states (Oxide)	2,3 (amphoteric)
Crystal structure	hexagonal
Physical Properties
State of matter	solid (ferromagnetic)
Melting point	1768 K (2723 °F)
Boiling point	3200 K (5301 °F)
Molar volume	6.67 ×10-3 m3/mol
Heat of vaporization	376.5 kJ/mol
Heat of fusion	16.19 kJ/mol
Vapor pressure	175 Pa at 1768 K
Velocity of sound	4720 m/s at 293.15 K
Miscellaneous
Electronegativity	1.88 (Pauling scale)
Specific heat capacity	420 J/(kg*K)
Electrical conductivity	17.2 106/m ohm
Thermal conductivity	100 W/(m*K)
1st ionization potential	760.4 kJ/mol
2nd ionization potential	1648 kJ/mol
3rd ionization potential	3232 kJ/mol
4th ionization potential	4950 kJ/mol
Most Stable Isotopes
iso NA half-life DM DE MeV DP 56Co {syn.} 77.27 days e capture 4.566 56Fe 57Co {syn.} 271.79 days e capture 0.836 57Fe 58Co {syn.} 70.86 days e capture 2.307 58Fe 59Co 100% Co is stable with 32 neutrons 60Co {syn.} 5.2714 years β- 2.824 60Ni
SI units & STP are used except where noted.

Cobalt is a chemical element in the periodic table that has the symbol Co and atomic number 27.

Table of contents 1 Notable Characteristics 2 Applications 3 History 4 Biological Role 5 Occurrence 6 Compounds 7 Isotopes 8 Precautions 9 External Links

Notable Characteristics

Cobalt is a hard ferromagnetic silver-white element. The Curie temperature is of 1388 K with 1.6~1.7 Bohr momentums 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 cristallographic 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 hardmetals) and diamond tools.
• Magnets and magnetic recording media.
• 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.
• Co-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.

History

Cobalt was known in ancient times through its compounds, which would color glass a rich blue.

George Brandt (1694-1768) is credited with the discovery of cobalt. The date of discovery varies depending on the source, but is between 1730 and 1737. He was able to show that cobalt was the source of the blue color in glasses, which previously had been attributed to the bismuth found with cobalt.

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

The word cobalt comes from the German kobalt or kobold, meaning evil spirit, the metal being so called by miners, because it was poisonous and troublesome (it polluted and degraded the other mined elements as Nickel).

Biological Role

Cobalt in small amounts is essential to many living organisms, including humans. Having 0.13 to 0.30 ppm 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 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 mainland China, Zambia, Russia and Australia.

Compounds

Due to the various oxydation states, there is an abundant number of compounds. Oxydes are both antiferromagnetic at low temperature CoO (Neel-temperature : 291 K) and Co3O4 (Neel-temperature : 40 K).

Isotopes

Naturally occurring cobalt is composed of 1 stable isotope; 59-Co. 22 radioisotopes have been characterized with the most stable being 60-Co with a half-life of 5.2714 years, 57-Co with a half-life of 271.79 days, and 56-Co with a half-life of 77.27 days, and 58-Co 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 lifes 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 (50-Co) to 73 amu (73-Co). The primary decay mode before the most abundant stable isotope, 59-Co, is electron capture and the primary mode after is beta emission. The primary decay products before 59-Co 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. All cobalt compounds should be regarded as toxic, unless there is evidence to the contrary. Most cobalt compounds are probably not very toxic.

Cobalt-60 is a powerful gamma ray emitter and exposure to 60-Co is therefore a cancer risk. Ingestion of 60-Co will lead to incorporation of some cobalt into tissues, and this incorporated cobalt is released very slowly. Cobalt 60 is a risk factor in a nuclear confrontation because neutron emissions will convert some iron into this radioactive isotope. Some nuclear weapon designs could intentionally increase the amount of Cobalt-60 dispersed as nuclear fallout - this is sometimes called a dirty bomb or cobalt bomb. The risk in the absence of a nuclear war comes from improper handling (or theft) of medical radiotheraputic units.

External Links

• WebElements.com - Cobalt (http://www.webelements.com/webelements/elements/text/Co/key)
• EnvironmentalChemistry.com - Cobalt (http://environmentalchemistry.com/yogi/periodic/Co)
• People affected by Cobalt 60 radiation to sue for compensation (http://www.terraper.org/English_part/NU62CO_1/NU6_3/NU63cobalt.htm)
• London celebrates 50 years of Cobalt-60 Radiotherapy (http://www.caro-acro.ca/caro/educ/publ/vig/vignettes/cobalt/Interactions.pdf)