promoting the sustainable and responsible use of cobalt in all forms

Physico-Chemistry

The physico-chemical properties of cobalt allow for a hard wearing, wear-resistant metal with unique valency properties. These qualities make it unsubstitutable in a number of key sustainable and strategic applications.

Cobalt is a transition metal appearing in the fourth period of the periodic table between iron and nickel.

The ground state atom is 1s2 2s2 2p6 3s2 3d7 4s2.

Cobalt’s most common valency is therefore Co2+, due to the removal of two 4s electrons. Other valencies also exist however, such as in the more complex salts. For example mixed valencies, Co2+ and Co3+, are present in Co3O4.

Cobalt is a shiny, grey, brittle metal with a close packed hexagonal (CPH) crystal structure at room temperature. At 421°C, the CPH crystal structure changes to a face centred cubic form (FCC).

The metal is rarely used as a structural material in the pure form but almost always as an alloy or a component of another system.

Physical constants of cobalt metal

Density 8.85 g/cm3
Melting Point 1,493oC (2719oF)
Boiling Point 2,870oC (5612oF)
Coeff. of Linear Expansion 10-6 per oC = 12.5 (to 100oC)
Coeff. of Volume Expansion 10-6 per oC = 35.6 (to 100oC)
Transition temp. CPH to FCC ~421oC
Curie Point 1,121oC
Atomic Number 27
Valencies +2, +3
Saturation Induction 18,700 Gauss (1.87T)

Table 1 The physical constants of cobalt metal