Cobalt

Notable characteristics

It is Ferromagnétique with a Température of Curie of 1388 K and with one moment of 1.6~1.7 magnetons of Bohr (µ_B) by atom.
Il exists two crystallographic configurations about it hcp (hexagonal compact) and CFC (cubic with centered face). The temperature criticizes hcp→cfc between these two structures is of 722 K.
Les oxides Cobalt is antiferromagnetic at low temperature. CoO with a temperature of Néel of 291 K and Co₃O₄ with a temperature of Néel of 40 K.

Applications

In the Alloy S, such as:

the Super-alloy S, for certain parts in the Turbine S with gas.
corrosion resisting alloys
the Carbide S
high speed steels (for the realization of the cutting tools).
dental Alloy prosthesis (crown for example)

magnets and media of tape recording
Like Catalyst in chemical industry and oil
Like agent drying in paintings and inks
For certain electrodes of accumulator battery (positive nickel electrodes for alkaline batteries NiCd, NiMH and NiZn, and electrodes of accumulators to lithium).
cobalt-60 has many uses as source of rays beta, because of its relatively short half-life (thus easier to eliminate) compared to other transmitting isotopes such particles:

For the Radiotherapy
In the treatment by radiation of food for its sterilization.
In industrial radiography to locate the defects of the parts.

However, the cobalt-60 of synthesis (produced by natural cobalt exposure to the neutron radiations of a nuclear reactor) is not completely pure, and always contains other radioactive isotopes with disintegration epsilon, transmitter of dangerous gamma ray because this highly energy radiation destroys the cores and contaminates them in persistent radioactive elements. Moreover enrichment and the purification of cobalt-60 techniques of centrifugation similar require to those used for the enrichment of the isotopes of military use, techniques highly supervised because strategic with the international plan.
Also, one now prefers to use accelerators of electrons (similar to the cathode tubes of our monitors and television sets but to quite higher levels of acceleration) which produce flows much purer and well better controlled particles beta (but that requires equipment much heavier for its use than a simple cobalt-60 capsule, and this method is especially used in industrial environment, and also maintaining in medical environment).

History

One knows cobalt since antiquity thanks to his compounds which color glass of an intense blue . One allots to Georg Brandt (1694 - 1768) the discovery of cobalt. The date of the discovery varies according to the sources but is located between 1730 and 1737. It was the first to show that cobalt was the source of the color blue in glasses, whereas one previously attibuait this one with the Bismuth which one found with cobalt. During the 19th century, the blue cobalt was produced by the Norwegian factory Blaafarveværket (70 80% of the worldwide production) directed by the Prussian industrialist Benjamin Wegner. In 1938, John Livingood and Glenn Seaborg discovered cobalt-60.

Toxicity, ecotoxicity

With negligible amount, it is one oligoélément, present in the vitamin B 12, and used against anemia, because supporting the red globules. A toxicity of cobalt is however supposed for a long time; the word cobalt coming besides from German kobalt or Kobold ; a spirit malefic which haunted the mines in the Germanic tradition. Metal would have been thus named by the minors because it was toxic and caused problems; Moreover, it polluted and degraded the other elements mined like the Nickel.

It is due to its property chemical, but also to its radiotoxic properties, in Isotope S Radioactif S of the cobalt, of which the Cobalt 60, used for research and in nuclear medicine, for example in the form of needles to kill out of the cancer cells.
Il can act as synergy with other metals which often accompany it in nature (Arsenic, and moindrement Cuivre, Nickel, Manganèse).

In the ecosystems : Its toxicity varies according to the organizations, the individuals, the context and the chemical species considered (pure cobalt, in Nanoparticule, cobalt II or cobalt III, or salts organic and/or inorganic). Its toxicity and its mobility for the plants and animals increase with the acidity of the ground. The acid rains can accentuate of it mobility and the Biodisponibilité, with risk of Bioaccumulation and Bioturbation by certain plants, mushrooms and animals.

At the Man: the exposure to cobalt can induce lung diseases (respiratories difficulties possibly evolving/moving in asthma, or pneumonia in workers having breathed a cobalt air charged). In the Sixties, certain breweries added cobalt in their beers to stabilize foam of it, which caused in large beer drinkers of nauseas, vomiting and serious cardiac affections. One however did not note cardiac affections at the feeble ones and expectant mothers having been médicamentés with cobalt, but of the fetal anomalies are caused in animals exposed in laboratory to cobalt high rates at the time of the pregnancy.

It is classified like " cancerogenic possible " by the international research Center on cancer; because it causes a cancer when it is introduced into a muscle or under the skin, but it does not seem to be cancerogenic when inhaled by animals exposed via the air, food or water. This risk could increase if it is about Nanoparticule S, but he does not seem to have been the subject of research.

Environmental sources

natural Sources: (grounds, erosion, Volcano S, sea water and Forest fires. Average rate in the ground, in the world is of eight Ppm (left per million), but it varies of almost zero to 6.450 ppm even more near mines (In Ontario, 16 and 17 ppm of cobalt were respectively measured in rural parks and of old city parks)

anthropic Sources: (water, air and ground, and ecosystems are polluted by the mines and the industry of cobalt, smoke of the incinerators and resulting from the combustion of the coal and the oil which contain a small proportion of it, just as exhaust fumes from the vehicles and planes.

Except for the workers or people exposed to industrial or natural sources important, 99 p. 100 of cobalt which we absorb would come from food, rather than of water or the air).

Production

Its principal ores are in the form of arsenides, of sulfides and oxides. Currently, it is the Africa which holds the main part of the cobalt resources at the planetary level: the Democratic republic of Congo concentrates with it only half of the known reserves. The Zambia is the first producer in the cobalt world, but the ore can be molten and refined in various zones of the world. The group UMICORE is world leader in this field.

Figures of 2003, metal contained in the ores and concentrates, source: The state of the world 2005

See too

Heavy metals
metal Element-trace (ETM)
Blue

External bonds

Page on toxicology of cobalt (relative with its use in ceramics in particular).

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