Production of nanostructured CoO, Co₃O₄ and NiO particles by mechanically induced reactions

In the present work, the oxidation reactions: Co + 1/2O₂ → CoO, 3CoO + 1/2O₂ → Co₃O₄ and Ni + 1/2O₂ → NiO were induced by mechanical milling. These oxidation reactions were carried out under air atmosphere and with the addition of methanol as a process control agent to avoid excessive agglomeration of the original metallic powders. Characterization of product phases has been done using x-ray diffraction, scanning electron microscopy, transmission electron microscopy and microanalysis by energy dispersive x-ray spectrometry. Oxidation of cobalt produced CoO and Co₃O₄ phases; the addition of methanol delayed the formation of the Co₃O₄ phase. For nickel, the product phases were NiO and a residual amount of Ni. Cobalt powders were more easily oxidized than Ni powders, probably as a result of their smaller initial particle size. The resulting crystallites in the oxide particle had sizes smaller than 20nm in both cases.