Influence of the heat treatment conditions on the formation of CuFe2O4 from mechanical milled precursors oxides
Résumé
Stoichiometric mixture of CuO and alpha-Fe2O3 milled in air up to 30 h was subjected to different heat treatments. The evolution of the heat treated milled powders was investigated by X-ray diffraction (XRD). The CuFe2O4 was partially obtained by milling, the material consisting in a mixture of phases. By applying different heat treatments in air and in vacuum, for 2-6 h, in 500-800 A degrees C temperature range the phases composition of the milled samples is changed. A heat treatment at 500 A degrees C in vacuum favours the formation of delafossite (CuFeO2) and tenorite (CuO) phases. If the same heat treatment is made in air, the CuFe2O4 phase formation with a cubic structure is favoured. Differential scanning calorimetry (DSC) investigation realised in Ar atmosphere revealed two large exothermic peaks. The first one is associated with the formation of the delafossite and tenorite phases and the second one with the formation of CuFe2O4. The XRD patterns of the samples subjected to the DSC measurements present maxima corresponding to the delafossite and cuprospinel (CuFe2O4) phases. For the heat treatment at 600 A degrees C in air the phases present in the sample are the same as for the annealing performed at 500 A degrees C: CuFe2O4, alpha-Fe2O3 and CuO. The heat treatment in air at 800 A degrees C leads to the complete reaction between the different phases and the formation of CuFe2O4 phase in whole the sample volume. The CuFe2O4 ferrite crystallises after this heat treatment in two crystal systems: cubic and tetragonal.