Effect of iron concentration on the thermal behaviour of γ-Mn 2O 3

Abstract

Samples of γ-Mn 2O 3 with various iron contents are obtained by co-precipitation from appropriate amounts of manganese sulphate and ferric nitrate solutions by a concentrated (2.5 N) boiling solution of sodium hydroxide. Thermal analysis, X-ray diffraction and IR spectroscopy of the specimens reveal that the presence of iron in γ-Mn 2O 3 up to 15 to 25 at.% leads to formation of a single phase γ-Mn 2O 3 solid solution, which is partly reduced to Mn 3O 4 around 680 °C and finally transforms to the α-Mn 2O 3 phase on heating at or above 950 °C. With increasing iron concentration beyond 25 at.%, the formation of a ferrite phase has been detected in addition to the γ-Mn 2O 3 solid solution. However, this ferrite phase is thermally unstable and breaks down on heating around 600°C.