Cobalt

Cobalt is transition metal and was discovered in pure form in 1735. It is essential part of vitamin B12. Its compounds are known as cobalt blue used to color pottery and glass.

History and Discovery

Cobalt has been used as a coloring agent since Bronze Age. It has been found in Egyptian statuettes and in Persian jewelry of the 3rd millennium BCE. It was also used in China for pottery glazes as early as 618-907 CE. Cobalt in the form of metal was isolated by George Brandt in 1735. In 16th century kobold name was given to the ores that contain copper but in the end found that ores contain poisonous arsenic. Brandt in 1742 determined that in various ores, the blue color is due to the presence of cobalt. The word kobold derived from German word meaning ‘’goblin ore’’ [1].

Cobalt

Periodic Table ClassificationGroup 9
Period 4
State at 20CSolid
ColorBluish gray metal
Electron Configuration[Ar] 3d7 4s2
Electron Number27
Proton Number27
Electron Shell2, 8, 15, 2
Density8.9 g.cm-3 at 20°C
Atomic number27
Atomic Mass58.93 g.mol -1
Electronegativity according to Pauling1.88

Occurrence

Cobalt is widely present on the earth crust, in combination with other minerals and in natural water. It is the 32nd most abundant element present on the earth crust. It is present in the sun, in soil, and in bodies of plants and animals. Cobalt is mostly present in combination with nickel. In compound form, it occurs in minerals of in copper and nickel. Most common minerals of cobalt are cobaltite (cobalt sulfoarsenide mineral), linnaeite (sulfide mineral), skutterudite (series of cobalt and nickel mineral), and smaltite (cobalt, nickel arsenide). Cobalt is produced as a byproduct during the mining and refining nickel, silver, lead, copper and iron. Large deposits of cobalt are present in Canada, Australia, Zambia and Brazil.

Physical Characteristics

Refined or polished cobalt is a silvery white metal and have a faint bluish tinge.  Its physical properties resemble iron and nickel. Cobalt is a ferromagnetic (strongest magnet), up to 11210C. Its specific gravity is 8.9. Pure cobalt is obtained through smelting process, which is hard and lustrous and release vapors of arsenic. Cobalt is a is transition metal. It melts at 1495oC and its boiling temperature is 2927oC [2].

Chemical Characteristics

Cobalt is not very reactive metal. It is stable in air and is unaffected by water. Cobalt reacts slowly with dilute acids.  It combines with oxygen and produce Co3O4 and lose oxygen at higher temperature (900oC) and give monoxide (CoO). Cobalt does not catch fire in air and is resistant to burning, unless it is in powder form. Cobalt is weak reducing metal and protected from oxidation by formation of a passivating oxide film. It reacts with halogens and produce halides. Cobalt does not react with hydrogen and nitrogen gas even at high temperatures. At standard temperature it reacts with mineral acids. Cobalt exist in +2 and +3 oxidation state, although -3 to +5 oxidation states compounds are also formed. Cobalt oxides are antiferromagnetic at low temperature. Cobalt (II) oxide has a rock salt structure. In the form of halides, Cobalt (III) fluoride is used in fluorination reaction.

Significance and Uses

  • Cobalt is primarily used in the manufacturing of magnets.
  • Compounds of cobalt gives deep blue color to glass ceramics and inks.
  • It is also used to prepare wear resistant and high strength alloys.
  • 60Co isotope used as radioactive tracer for the production of gamma rays.
  • Cobalt is main part of Vitamin B12 called Cobalamin and in inorganic form it is a micronutrient for bacteria and algae.
  • Cobalt alloys are used in jet turbines and in gas turbines generator.
  • Salts of cobalt are used to give blue colors to porcelain and pottery.
  • It is used as a catalyst in petroleum and chemical industries.
  • Cobalt-60 is also used to irradiate the food in order to extent its shelf life.
  • Cobalt is used in making powerful magnets and magnetic recording media.

Health effects

Cobalt is necessary for human as it is a part of essential vitamin, B12. It stimulates the production of red blood cells and is widely used to treat anemia. In work place, when workers are exposed to high level of cobalt, they can suffer from lungs infections such as asthma and pneumonia. When plants grow on the soil near cobalt mining area, they take up high amount of cobalt which may eventually affect human health. The daily intake dose of cobalt is around 1mg.

Isotopes of Cobalt

Cobalt has one stable isotope 59Co. Cobalt-60 is a commercially important radioisotope that have a half- life of more than 5.2 years [3]. The isotopes of cobalt range in atomic weight from 50 to 73.

REFERENCES

[1]. Enghag, Per (2004). “Cobalt”. Encyclopedia of the elements: technical data, history, processing, applications. p. 667. I

[2]. Properties and Facts for Cobalt”. American Elements. Retrieved 2008-09-19.

[3]. http://www.chemistryexplained.com/elements/A-C/Cobalt.html