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Cobalt

Iron - Cobalt - Nickel
Co
Rh  
 
 
General
Name, Symbol, NumberCobalt, Co, 27
Chemical series Transition metals
Group, Period, Block9 , 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]3d3d74s2
e- 's per energy level2, 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 ×1010-3 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
isoNAhalf-life DMDE MeVDP
56Co{syn.}77.27 days e capture4.56656Fe
57Co{syn.}271.79 dayse capture0.83657Fe
58Co{syn.}70.86 dayse capture2.30758Fe
59Co100%Co is stable with 32 neutrons
60Co{syn.}5.2714 yearsβ-2.82460Ni
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

Use in Medicine

Cobalt-60 (Co-60 or 60Co) is a radioactive metal that is used in radiotherapy. It produces two gamma X-rays with energies of 1.17 MeV and 1.33 MeV. The cobalt-60 source is about 2cm 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 Co-60 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. The first Co-60 therapy machine (the "cobalt bomb") was built and first used in Canada. In fact the first machine is on display in the Saskatoon Cancer Centre - look up when entering the lobby. The second machine is out beside the walkway into the Centre.

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.

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

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, like 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 oxidation states, there is an abundant number of compounds. Oxides 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 (59Co). 22 radioisotopes have been characterized with the most stable being 60-Co with a half-life of 5.2714 years, 57-Co (57Co) with a half-life of 271.79 days, and 56-Co (56Co) with a half-life of 77.27 days, and 58-Co (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 (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 radiotherapeutic units.


External Links