COBALT(III) OXIDE BLACK

COBALT(III) OXIDE BLACK is used as a pigment; for glazing porcelain and pottery; and for coloring enamels.

COBALT(III) OXIDE BLACK is prepared by heating cobalt compounds at low temperatures in air.

Heating with hydrogen, carbon or carbon monoxide reduces the oxide to cobalt metal.
Co2O3 + 3H2→ 2Co + 3H2O
Co2O3 + 3CO→ 2Co + 3CO
2Co2O3 + 3C→ 4Co + 3CO2
Strong heating in air converts cobalt(III) oxide to tricobalt tetroxide.
Reactions with mineral acids produce their Co3+ salts:
Co2O3 + 6HCl → 2CoCl3 + 3H2O

Neither the oxide Co2O3 nor the hydroxide Co(OH)3 is definitely established. The oxidation of cobalt(II) hydroxide in aqueous suspension with, for example, peroxides, or the destruction of a cobalt(III) complex with alkali gives a brown or black powder Co2O3.aq which upon drying at 150° yields the monohydrate Co2O3.H2O; this is probably best formulated as CoO(OH). When heated further in attempts to dehydrate it, the "monohydrate" begins to evolve oxygen (as well as water) at 300° with the formation of black Co3O4. When heated to 100° in air cobalt(II) hydroxide is converted to dark brown CoO(OH).

Steel-gray or black powder.Soluble in concentrated acids; insoluble in water.

Grayish black powder; density 5.18 g/cm³; decomposes at 895°C; insoluble in water; soluble in concentrated mineral acids.

Pigment, coloring enamels, glazing pottery.

Cobaltic oxide (Co2O3) is also known as cobalt oxide or cobalt black. It is dark gray to black and is used in pigments, ceramic glazes, and semiconductors.

Cobalt(III) oxide is prepared by heating cobalt compounds at low temperatures in air.

Sometimes incorrectly called cobalt peroxide.

: Moderately toxic by intraperitoneal and subcutaneous routes. Questionable carcinogen. Violent reaction with hydrogen peroxide. The oxide increases the sensitivity of nitroalkanes (e.g., nitromethane, nitroethane, and 1 nitropropane) to heat or detonation. See also COBALT COMPOUNDS.