Cobalt (Co) – Properties, Applications

Topics Covered

Chemical Properties
Physical Properties
Mechanical Properties
Thermal Properties


Cobalt is a chemical element with Co as its symbol. It belongs to group 9, periodic number 4 of the periodic table. Its atomic number is 27.

Cobalt is silver-white in color with a bluish tinge. It is a hard, ferromagnetic, brittle element. The primary ores of cobalt are cobaltite, smaltite and erythrite. It can also be obtained as a byproduct of lead, nickel, silver, copper and iron mining and refining processes. Evidence also indicates that it is present in meteorites. Major cobalt producers are DR Congo, Zambia, China, Russia and Australia.

Cobalt is stable in air and is not affected by water. It is active chemically and dissolves in dilute sulfuric acid, nitric or hydrochloric acid. Alkalis have an effect on it as well.

Chemical Properties

The chemical properties of cobalt are provided in the table below.

Chemical Data
CAS number 7440-48-4
Thermal neutron cross section 34.8 barns/atom
Electrode potential -0.280 V
Ionic radius 0.630 Å
Electronegativity 1.88
X-ray absorption edge 1.608 Å
Electrochemical equivalent 1.1 g/A/h

Physical Properties

The following table discusses the physical properties of cobalt.

Properties Metric Imperial
Density 8.80 g/cm3 0.318 lb/in3
Melting point 1493 °C 2719 °F
Boiling point 2927 °C 1603°F

Mechanical Properties

The mechanical properties of cobalt are tabulated below.

Properties Metric Imperial
Yield strength 225 MPa 32600 psi
Poisson’s ratio 0.32 0.32
Modulus of elasticity 211 GPa 30600 ksi
Shear modulus 82.6 GPa 12000 ksi
Hardness, Brinell 125 125
Hardness, Vickers 253 253

Thermal Properties

The thermal properties of cobalt are tabulated below.

Properties Metric Imperial
Thermal expansion co-efficient (@20-100°C/68-212°F) 12.5 µm/m°C 6.94 µin/in°F
Thermal conductivity 69.21 W/mK 480.3 BTU in/hr.ft².°F


The following are the application areas of cobalt:

  • In producing alloys
  • In magnets and magnetic recording media
  • As catalysts for petroleum and chemical industries
  • As drying agents for paints and inks

Cobalt blue is used in stained glass, tiles, porcelain, pottery, and enamel jewelry.

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