Particle size effects on the oxidation-reduction behavior of Mn3O4 hausmannite

The oxidation of hausmannite, Mn3O4, of different particle sizes has been studied by thermogravimetry with a large range of linear heating programs under an oxygen pressure of 10 5 Pa. For high heating rate (600C/h) and whatever the particle size, Mn3O4 was converted to a-Mn2O3. For small particle size (32 nm) and low heating rate (3C/h) the oxidation shows the formation of two metastable manganese oxides, a cation deficient spinel of the formula Mn 2O2:92 with Mn 2C ions oxidation and Mn5O8 associated to Mn 3C ions oxidation. The difference in the kinetic behavior of Mn 2C and Mn 3C ions is interpreted with regard to a structural change from the cation deficient spinel to Mn5O8 initiated by the oxidation temperature. © 2001 Elsevier Science B.V. All rights reserved.