Cobalt

   

Cobalt is a brittle, hard, silver-grey transition metal with magnetic properties similar to those of iron (ferromagnetic). Cobalt is present in meteorites. Ore deposits are found in Zaire, Morocco and Canada. The isotope cobalt-60 (60Co) is an artificially produced isotope used as a source of γ rays (its high energy radiation is useful for sterilisation in medicine and of foods). Cobalt salts colour glass a beautiful deep blue colour. Cobalt compounds are important catalysts in a number of industrial processes. Cobalt is required in small amounts for life and is the only metal found in vitamins (cobalt is the critical component of vitamin B12.

Cobalt was discovered by Georg Brandt at 1735 in Sweden. Origin of name: from the German word "kobald" meaning "goblin" or evil spirit.
Minerals containing cobalt were of value to the early civilisations of Egypt and Mesopotamia for colouring glass deep blue.
Cobalt was announced to be an element by Georg Brandt about 1739 (or possibly 1735). He had been trying to demonstrate that the blue colour of glass was because of a new element, cobalt, rather than bismuth, an element often found in the same locations as cobalt.

                                                            *Atomic number-27
                                                            *Atomic mass- 58.9332 g.mol -1
                                                            *Electronegativity according to Pauling-1.8
                                                            *Density-8.9 g.cm-3 at 20°C
                                                            *Melting point-1495 °C
                                                            *Boiling point-2927 °C

Characterstics:
Cobalt is a bluish-white, lustrous, hard, brittle metal. It is ferromagnetic.
The metal is active chemically, forming many compounds.


Physical Properties:
 *Melting point: 1768 [or 1495 °C (2723 °F)] K
 *Boiling point: 3200 [or 2927 °C (5301 °F)] K
 *Density of solid: 8900 kg m-3

Cobalt is a hard, gray metal that looks much like iron and nickel. It is ductile, but only moderately malleable. Ductile means capable of being drawn into thin wires. Malleable means capable of being hammered into thin sheets.
Cobalt is one of only three naturally occurring magnetic metals. The other two are iron and nickel. The magnetic properties of cobalt are even more obvious in alloys. An alloy is made by melting and mixing two or more metals. The mixture has properties different from those of the individual metals.
The melting point of cobalt metal is 1,493°C (2,719°F), and the boiling point is about 3,100°C (5,600°F). The density is 8.9 grams per cubic centimeter.

Chemical Properties:
                    Cobalt is a moderately reactive element. It combines slowly with oxygen in the air, but does not catch fire and burn unless it is in a powder form. It reacts with most acids to produce hydrogen gas. It does not react with water at room temperatures.


Occurance in Nature:
                     Cobalt is a relatively abundant element at about 10 to 30 parts per million. This places it in the upper third of elements according to their abundance in the Earth's crust.
The most common ores of cobalt are cobaltite, smaltite, chloranthite, and linnaeite. The major suppliers of cobalt in the world are Zambia, Canada, Russia, Australia, Zaire, and Cuba. No cobalt is mined in the United States.
The word cobalt, from the German word Kobold , meaning "goblin" or "evil spirit," was used by miners to describe a mineral that was very difficult to mine and was damaging to their health.


Reactions:
Reaction with air:mild, w/ht ⇒ Co3O4                                   Reaction with 6 M HCl:mild ⇒ H2, CoCl2
Reaction with 15 M HNO3:vigorous, ⇒ Co(No3)2, Nox      Reaction with 6 M NaOH:


Applications:
Cobalt is used in alloys for aircraft engine parts and in alloys with corrosion/wear resistant uses.
Cobalt is widely used in batteries and in electroplating.
Cobalt salts are used to impart blue and green colors in glass and ceramics.
Radioactive 60Co is used in the treatment of cancer.
Cobalt is essential to many living creatures and is a component of vitamin B12.
Cobalt is used in many alloys (superalloys for parts in gas turbine aircrafr engines, corrosion resistant alloys, high-speed steels, cemented carbides), in magents and magnetic recording media, as catalysts for the petroleum and chemical industries, as drying agents for paints and inks. Cobalt blue is an important part of artists' palette and is used bu craft workers in porcelain, pottery, stained glass, tiles and enamel jewellery. The radioactive isotopes, cobalt-60, is used in medical treatment and also to irradiate food, in order to preserve the food and protect the consumer.


Health Effects of Cobalt:
                       As cobalt is widely dispersed in the environment humans may be exposed to it by breathing air, drinking water and eating food that contains cobalt. Skin contact with soil or water that contains cobalt may also enhance exposure.
Cobalt is not often freely available in the environment, but when cobalt particles are not bound to soil or sediment particles the uptake by plants and animals is higher and accumulation in plants and animals may occur.

Cobalt is beneficial for humans because it is a part of vitamin B12, which is essential for human health. Cobalt is used to treat anaemia with pregnant women, because it stimulates the production of red blood cells. The total daily intake of cobalt is variable and may be as much as 1 mg, but almost all will pass through the body unadsorbed, except that in vitamine B12.

However, too high concentrations of cobalt may damage human health. When we breathe in too high concentrations of cobalt through air we experience lung effects, such as asthma and pneumonia. This mainly occurs with people that work with cobalt.

When plants grow on contaminated soils they will accumulate very small particles of cobalt, especially in the parts of the plant we eat, such as fruits and seeds. Soils near mining and melting facilities may contain very high amounts of cobalt, so that the uptake by humans through eating plants can cause health effects.
Health effects that are a result of the uptake of high concentrations of cobalt are:

- Vomiting and nausea
- Vision problems
- Heart problems
- Thyroid damage

Health effects may also be caused by radiation of radioactive cobalt isotopes. This can cause sterility, hair loss, vomiting, bleeding, diarrhoea, coma and even death. This radiation is sometimes used with cancer-patients to destroy tumors. These patients also suffer from hair loss, diarrhea and vomiting.

Cobalt dust may cause an asthma-like disease with symptoms ranging from cough, shortness of breath and dyspnea to decreased pulmonary function, nodular fibrosis, permanent disability, and death. Exposure to cobalt may cause weight loss, dermatitis, and respiratory hypersensitivity. LD 50 (oral, rat)- 6171 mg/kg. (LD50 = Lethal dose 50 = Single dose of a substance that causes the death of 50% of an animal population from exposure to the substance by any route other than inhalation. LD50 is usually expressed as milligrams or grams of material per kilogram of animal weight (mg/kg or g/kg).)

Carcinogenicity- International Agency for Research on Cancer (IARC) haslisted cobalt and cobalt compounds within group 2B (agents which are possibly carcinogenic to humans). ACGIH has placed cobalt and inorganic compounds in category A3 (Experimental animal carcinogen- the agent is carcinogenic in experimental animals at a relatively high dose, by route(s), histologic type(s), or by mechanism(s) that are not considered relevant to worker exposure.) Cobalt has been classified to be carcinogenic to experimental animals by the Federal Republic of Germany.



                                               

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