Cobalt Dioxide, CoO₂

Cobalt Dioxide, Cobalt Peroxide, CoO₂, is obtained in the hydrated condition as a greenish black precipitate by treating aqueous solutions of cobaltous salts with iodine and sodium hydroxide. It is also obtained by acting on a cobaltous salt with a hypochlorite. It decomposes at 100° C., and when washed undergoes partial reduction.

McConftell and Hanes claim to have obtained the monohydrate or cobaltous acid, H₂CoO₃, by the action of hydrogen peroxide upon cobaltous hydroxide in aqueous suspension. If the acid can exist at all in the free state it is very unstable, although some of its salts are well defined.

The more important cobaltites are cobaltous cobaltite, CoCoO₃, more usually known as cobaltic oxide, Co₂O₃; and cobaltous dicobaltite, CoO.2CoO₂.2H₂O, which has been obtained as glistening hexagonal plates by fusion of cobaltous oxide with potassium peroxide and washing with water. Bayley had already indicated the existence of this substance in 1879, and believed that at least two other hydrates exist, gamely, CoO.2CoO₂.4H₂O and CoO.2CoO₂.3H₂O, and possibly the monohydrate, CoO.2CoO₂.H₂O.

Magnesium cobaltite, MgO.CoO₂; barium cobaltite, BaO.CoO₂, and dicobaltite, BaO.2CoO₂, and a potassium cobaltous cobaltite, K₂O.CoO.3CoO₂, have also been described.