Surface reactivity of α-Mn2O3 powders in aqueous suspensions

α-Mn2O3 powders were prepared by calcining Mn(NO3)2 · 6H2O at 600°C by a two step procedure. By X-ray diffraction the samples appeared to be a pure phase with a relatively high degree of crystallinity. The actual speciation of Mn at the surface of the powders was estimated by X-ray photoelectron spectroscopy. The electrification behaviour of the oxide at the solution boundary was characterised by the determination of charge and capacitance vs. pH curves. The specific pattern observed at high KNO3 concentrations is interpreted by invoking the occurrence of a solution-supported disproportionation reaction of Mn(III).