Investigations on the MnO2-Fe2O3 system roasted in air atmosphere

Abstract

Solid-state reaction method is a common and effective technique to synthesize ferrites. This work investigated the phase transformation of MnO2 and Fe2O3 system roasted at 500–1400°C in air atmosphere to understand the formation process of manganese ferrite. The results showed that the formation of manganese ferrite (MnxFe3−xO4) was derived from the reaction between Fe2O3 and Mn3O4 (the decomposition product of MnO2). Below 900°C, MnO2 firstly decomposed to Mn2O3 and then to Mn3O4, and Fe2O3 was seldom reacted with Mn2O3 and Mn3O4. When the temperature went up to 1000°C, Fe2O3 easily reacted with Mn3O4 to generate manganese ferrite. The reaction degree was enhanced dramatically with the rising of temperature. Moreover, the x value in the MnxFe3−xO4 increased from 0 to 1 from 900°C to 1400°C. In other words, the higher the temperature was, the closer the MnxFe3−xO4 was to MnFe2O4. Thermodynamic analysis of MnO2-Fe2O3 system under different O2 partial pressures was carried out to further explain the formation mechanism.