REACTIVITY TOWARD OXYGEN AND CATION DISTRIBUTION IN COPPER-MANGANESE FERRITE SPINELS FINE POWDERS

The thermal behaviour of CuyMnxFe3-y-xO4 spinels (0 less than or equal to x less than or equal to 1, x + y approximate to 1) obtained at low temperature has been investigated over the temperature range of 50-70 0 degrees C mainly by thermogravimetry and infrared spectroscopy. Belo w 600 degrees C, Cu-Mn ferrites partly oxidized in cation deficient sp inels, CuyMnxFe3-yO4+delta, showing an incomplete oxidation of the tet rahedral divalent manganese ions. A quantitative analysis by DTG based on an oxide-reduction mechanism and on a difference of reactivity of copper, iron and manganese ions in relation to the occupied site (octa hedral or tetrahedral site) permits a cation distribution to be propos ed. For x > 0.70, the vacancies were found to occupy octahedral sites with a vacancy cation ratio closely of 1/5 similar to gamma-Fe2O3. Sub sequent oxidation of Mn2+ ions required higher temperature and was acc ompanied by a phase change.