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

In the present work, the oxidation reactions: CO + (1)/O-2(2) --> CoO, 3CoO + (1)/O-2(2) --> Co3O4 and Ni + (1)/O-2(2) --> 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.