Reactivity towards oxygen and cation distribution of manganese iron spinel Mn3-xFexO4 (0≤x≤3) fine powders studied by thermogravimetry and IR spectroscopy

Abstract

The thermal behaviour in oxygen and the cation distribution of manganese iron spinels Mn _3-x Fe _x O ₄ (0≤x≤3) obtained by a soft chemistry method have been determined by thermogravimetry and IR spectroscopy . The existence of two different cation distributions as function of composition x is established from a quantitative analysis by derivative thermogravimetry. For x>1.50, the IR spectroscopy clearly distinguished the presence of Fe ²⁺ and Mn ²⁺ ions located in octahedral and tetrahedral sites, respectively. For x<1.50, this method is also efficient for the differentiation of the Mn ²⁺ ions located in both types of site of the spinel structure. Kinetic studies on the oxidation process of Mn ²⁺ ions show that the oxidation proceeds by way of a diffusion-controlled reaction or by a nucleation–growth mechanism. The difference in the kinetic behaviour is interpreted with regard to a structural change from the cation-deficient spinel to multi-phase oxides initiated by the oxidation temperature.