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General Properties
Cobalt was discovered in 1735 by Swedish chemist Georg Brandt. It is a lustrous, bluish-white metal that is both hard and brittle. It has been used since ancient Egyptian times to color glass a deep blue, although that effect was thought to be due to bismuth until the 18th century. According to Webelements.com, cobalt has high melting and boiling temperatures of 1,768 Kelvin and 3,200 Kelvin, respectively. Due to its relatively small atomic radius, cobalt has a high density of 8.9 grams per cubic centimeter. Like other metals, cobalt is a good conductor of heat and electricity. Cobalt is ductile, meaning it can easily be drawn into wires; but compared with other metals it has only moderate malleability.
Magnetism
Cobalt is one of only three metals to exhibit natural ferromagnetism. That phenomenon occurs in atoms such as cobalt that have unpaired electrons. If the electrons are positioned at just the right distance apart, each unpaired electron is able to influence the spin of nearby electrons. The alignment of individual spins results in a significant magnetic effect.
Ferromagnetic metals such as cobalt demonstrate a strong attraction to a magnetic field. At high temperatures, cobalt loses that ferromagnetic effect, as the thermal energy of the atoms is sufficient to overcome the interaction between neighboring electrons.
Alloys
Alloying cobalt with other metals can lead to the creation of very strong magnetic materials, such as alnico, which can be used in electric motors, microphones, loudspeakers and other applications requiring strong, permanent magnets. Cobalt is also often alloyed with small amounts of chromium to form the heat-resistant basis of a range of super-alloys, such as those used in the components of turbine engines. Cobalt is an important constituent of many materials used to make cutting tools due to its hardness and resistance to wear.
Catalyst
Like other transition metals, cobalt has partially filled electron energy levels that offer a number of useful chemical and physical properties, including the ability to act as a catalyst in chemical processes. The vacancies in the partially filled electron energy levels act as a site for the adsorption of reactants, and this physical phenomenon can lead to the facilitation of a number of chemical reactions. Cobalt catalysts are particularly important in the reactions of hydrocarbons.