Low-temperature oxidation of Mn3O4 hausmannite

Hausmannite, Mn3O4, with a specific surface area of 10 m2/g has been oxidized at low temperatures (300°C < T < 425°C). In this temperature range both Mn2+ and Mn3+ cations are oxidized. The oxidation of Mn2+ to Mn3+ is governed by a diffusion process and the spinel structure is stable up to 425°C. Oxidation of Mn3+ to Mn4+ leads to the crystallization of the Mn5O8 phase. Careful oxidation studies show the formation of two metastable manganese oxides, Mn5O8 and a defect spinel of the formula Mn2O2.78. The coordination numbers and the cation–anion distances in Mn3O4, γ-Mn2O2.78, and α-Mn2O3 obtained by EXAFS (extended X-ray absorption fine structure) are compared.