Abstract
Mn 3 O 4 hausmannite, which is a normal spinel with the Mn 2+ in the tetrahedral site and the Mn 3+ in the tetrahedral site, is one of the most stable manganese oxides. Variation in the valence of Mn ions (2+, 3+ and 4+) contributes to several different structures of manganese oxides. The autoxidation of precipitated manganese hydroxide in an alkaline solution is a practical approach to synthesize hausmannite (Mn 3 O 4 at low temperature. During the process, the particle size and morphology of derived products were totally different from the precursors even though nanometer-sized Mn(OH) 2 crystals were fabricated at first. It was observed that the variation was resulted from the accumulation of produced Mn 3 O 4 crystallites which departed from the original crystals. This study has not only discussed the influence of reactant concentrations on the particle size and morphology of derived powders, but also revealed the morphological transformation of crystals involved in autoxidation with the aid of electron micrographs.