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 hard metals) 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 enamelss.
- Pigments (cobalt blue and cobalt green).
- 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.
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