Cobalt is a chemical element with the symbol Co and 27 is the atomic number of It. Like nickel, cobalt is found in the Earth’s crust only in chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.
The metal was isolated by Swedish chemist Georg Brandt, though cobalt compounds had been used for centuries to impart a blue colour to glazes and ceramics. It has been detected in Egyptian statuettes and Persian necklace beads of the 3rd millennium BCE, in glass found in the Pompeii ruins, and in China as early as the Tang dynasty (618–907 CE) and later in the blue porcelain of the Ming dynasty (1368–1644). The name kobold was first applied in 16th century to ores thought to contain copper but eventually found to be poisonous arsenic-bearing cobalt ores. Brandt finally determined in 1742 that the blue colour of those ores was due to the presence of cobalt.
It makes up only 0.001% of Earth’s crust. It is found in small quantities in terrestrial and meteoritic native nickel-iron, in the Sun and stellar atmospheres, and in combination with other elements in natural waters, in ferromanganese crusts deep in the oceans, in soils, in plants and animals, and in minerals such as cobaltite, linnaeite, skutterudite, smaltite, heterogenite, and erythrite. In animals, cobalt is a trace element essential in the nutrition of ruminants and in the maturation of human red blood cells in the form of vitamin B12, the only vitamin known to contain such a heavy element.
Physical and Chemical Characteristics of Cobalt
- Cobalt is one of the three metals that are ferromagnetic at room temperature. It dissolves slowly in dilute mineral acids, does not combine directly with either hydrogen or nitrogen, but will combine, on heating, with carbon, phosphorus, or sulfur.
- It is also attacked by oxygen and by water vapour at elevated temperatures, with the result that cobaltous oxide, CoO (with the metal in the +2 state), is produced.
- It has a relative permeability two-thirds that of iron. Metallic cobalt occurs as two crystallographic structures: hcp and fcc.
- It is 27th element of the Periodic Table, constitutes about 0.001% of the Earth’s crust, where it is widely distributed usually in association with nickel and arsenic.
- It is a hard bluish–white ferromagnetic metal, m.p. 1493 °C, b.p. 3100 °C. Cobalt is relatively unreactive. It dissolves slowly in dilute mineral acids but does not combine with hydrogen or nitrogen, probably because in air the metal is covered with a layer of CoO.