COLLOIDAL COBALT HYDROUS OXIDES PREPARATION AND PROPERTIES OF MONODISPERSED CO3O4

Monodispersed cubic crystals (∼0.1 μm in edge length) of cobalt(II,III) oxide, Co3O4, have been obtained by heating cobalt acetate solutions (10-3-10-2 M) at ∼100°C for a few hours. Bubbling of oxygen prior to aging was found to greatly increase the yield in Co3O4. No precipitates have been obtained from other cobalt salt solutions (CoSO4, Co(NO3)2 and CoCl2) when these were treated in a similar manner. When sodium persulfate was used instead of oxygen as an oxidizing agent, the particles obtained on aging the cobalt(II) salt solutions at 100°C had a composition of CoO(OH) and were irregular in shape. Heating cobalt(II) salt solutions at 300°C in an autoclave yielded Co23O4 in all cases; in the presence of acetate ions the resulting particles were of cubic morphology but polydispersed, whereas other cobalt salts yielded irregularly shaped solids. © 1979.