Cobalt(II) oxide is an inorganic compound that has been described as an olive-green or gray solid. It is used extensively in the ceramics industry as an additive to create blue-colored glazes and enamels, as well as in the chemical industry for producing cobalt(II) salts. A related material is cobalt(II,III) oxide, a black solid with the formula Co3O4.
CoO crystals adopt the periclase (rock salt) structure with a lattice constant of 4.2615 Å.[1]
It is antiferromagnetic below 289 K.[2]
Cobalt(II) oxide is prepared by oxidation of cobalt powder with air or by thermal decomposition of cobalt(II) nitrate or the carbonate.
Cobalt(II,III) oxide decomposes to cobalt(II) oxide at 950 °C:[3]
2 Co3O4 → 6 CoO + O2
It may also be prepared by precipitating the hydroxide, followed by thermal dehydration:
CoX2 + 2 KOH → Co(OH)2 + 2 KX
Co(OH)2 → CoO + H2O
As can be expected, cobalt(II) oxide reacts with mineral acids to form the corresponding cobalt salts:
CoO + 2 HX → CoX2 + H2O
Cobalt(II) oxide has for centuries been used as a coloring agent on kiln fired pottery. The additive provides a deep shade of blue named cobalt blue. The band gap (CoO) is around 2.4 eV.It also is used in cobalt blue glass.