Study on the oxidation process of cobalt hydroxide to cobalt oxides at low temperatures

The transformation process of cobalt hydroxide (Co(OH)(2)) to cobalt oxides (Co3O4/CoOOH) in aqueous solution was studied in the temperature range of 50-90 degrees C. The crystalline structures and morphologies of the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) analysis. The OH-: Co2+ ratio and aging time influenced the transformation process from Co(OH)(2) to final products. And the formation of hydrotalcite-like phase intermediate ([(Co1-xCoxIII)-Co-II(OH)(2)](NO3)(x)center dot nH(2)O) is a crucial factor for synthesizing Co3O4. When the OH-: Co2+ ratio was in the range of 1.0 : 1-1.8 : 1, alpha-Co(OH)(2) was oxidized to [(Co1-xCoxIII)-Co-II(OH)(2)](NO3)(x)center dot nH(2)O at first, and then transformed to Co3O4 crystals. When the OH-: Co2+ ratio was in the range of 2.0 : 1-50.0 : 1, without the appearance of soluble Co(OH)(4)(2-) ions in the reaction system before oxidation, fast conversion from alpha-Co(OH)(2) to beta-Co(OH)(2) resulted in the formation of only CoOOH crystals, without the appearance of [(Co1-xCoxIII)-Co-II(OH)(2)](NO3)(x)center dot nH(2)O or Co3O4 crystals.