The combined effect of mechanical and thermal energy on the solid state formation of NiFe2O4 from the system 2NiCO3•3Ni(OH)2•4H2O – FeC2O4•2H2O

Spinel-type ferrites MFe2O4 (M = Ni, Zn, Mn, Co, Mg) are among the most important magnetic materials and they are prepared mostly by solid-state reaction at elevated temperatures. We proposed in the past a mixed synthetic route that uses both mechanical and thermal energy. In the present work the strategy is applied to the preparation of NiFe2O4 starting from mixtures of 2NiCO3•3Ni(OH)2•4H2O–FeC2O4•2H2O subjected to both mechanical and thermal annealing. TG/DSC measurements allowed to obtain information on the reaction mechanism and also a delta H for the reaction between the constituent oxides yielding NiFe2O4 in good agreement with the deduced from the data of delta G° versus T. The XRPD of the samples recovered after the TG/DSC runs shows the reflexions of NiFe2O4 only when starting from milled mixture. NiFe2O4 can be prepared by thermal treatment of physical mixtures 2NiCO3•3Ni(OH)2•4H2O–10FeC2O4•2H2O by 36 h at 1100 °C. On the contrary 12 h at 400 °C yield XRPD-phase pure NiFe2O4. Samples of NiFe2O4 obtained from the milled mixture show a surface area that decrease by increasing the synthesis temperature from 400 °C to 700 °C. On the basis of measurements of molar thermal capacity, it is demonstrated that NiFe2O4can be obtained by a 12 h annealing at 450 °C of the mechanically activated mixture.