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.
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