Available online at www.sciencedirect.com Thermochimica Acta 469 (2008) 86–90 The combined effect of mechanical and thermal energy on the solid-state formation of NiFe 2 O 4 from the system 2NiCO 3 ·3Ni(OH) 2 ·4H 2 O–FeC 2 O 4 ·2H 2 O Vittorio Berbenni ∗ , Chiara Milanese, Giovanna Bruni, Amedeo Marini CSGI, Dipartimento di Chimica Fisica dell’Universit` a di Pavia, Via Taramelli 16, 27100 Pavia, Italy Received 10 September 2007; received in revised form 26 November 2007; accepted 27 November 2007 Available online 15 December 2007 Abstract Spinel-type ferrites MFe 2 O 4 (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 [V. Sepelak, I. Bergmann, A. Feldhoff, P. Heitjans, F. Krumeich, D. Mmenzel, F.J. Litterst, S.J. Campbell, K. Becker, J. Phys. Chem. C 111 (2007) 502612; S. Bid, P. Sahu, S.K. Pradhan, Physica E 39 (2007) 175] a mixed synthetic route that uses both mechanical and thermal energy. In the present work the strategy is applied to the preparation of NiFe 2 O 4 starting from mixtures of 2NiCO 3 ·3Ni(OH) 2 ·4H 2 O–FeC 2 O 4 ·2H 2 O subjected to both mechanical and thermal annealing. TG/DSC mea- surements allowed to obtain information on the reaction mechanism and also a H for the reaction between the constituent oxides yielding NiFe 2 O 4 in good agreement with the deduced from the data of G ◦ versus T. The XRPD of the samples recovered after the TG/DSC runs shows the reflexions of NiFe 2 O 4 only when starting from milled mixture. NiFe 2 O 4 can be prepared by thermal treatment of physical mixtures 2NiCO 3 ·3Ni(OH) 2 ·4H2O–10FeC 2 O 4 ·2H 2 O by 36 h at 1100 ◦ C. On the contrary 12 h at 400 ◦ C yield XRPD-phase pure NiFe 2 O 4 . Samples of NiFe 2 O 4 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 NiFe 2 O 4 can be obtained by a 12 h annealing at 450 ◦ C of the mechanically activated mixture. © 2008 Published by Elsevier B.V. Keywords: Solid-state synthesis; NiFe 2 O 4 ; Mechanical activation; TG/DSC; Heat capacity 1. Introduction Spinel ferrites MFe 2 O 4 (M = Ni, Zn, Mn, Co, Mg) are among the most important magnetic materials and have been widely used for various applications. In particular Ni ferrite powders (NiFe 2 O 4 ) have been extensively investigated for several appli- cations such as ferrofluids, catalysts, microwave devices and magnetic materials [1–3]. Usually NiFe 2 O 4 powders are prepared by solid-state reac- tion method and this approach requires heating at very high temperatures for long periods of time so that the energy con- sumption is high and the production rate quite limited. For these reasons, alternative routes have been searched for. So, ∗ Corresponding author. Tel.: +39 02 987211; fax: +39 0382 987575. E-mail address: berbenni@matsci.unipv.it (V. Berbenni). for example, the synthesis of powder of Ni ferrite has been accomplished by a self-propagating high-temperature synthe- sis [4] and, moreover, several wet chemical methods have been developed to synthesize oxide ceramic powders to improve their properties. Indeed hard- and soft-magnetic ultrafine fer- rite powders have been synthesized using a combination of coprecipitation and mechanical milling [5] and low-temperature synthesis of NiFe 2 O 4 has been performed by hydrothermal methods [6–8]. Furthermore Rashad and Fouad [9] synthe- sized Ni ferrite powders from fly ash via a chemical synthesis route (coprecipitation method) where the precursor had to be treated at T > 800 ◦ C for 2 h to obtain NiFe 2 O 4 . Again nickel ferrite powders were synthesized by pulse wire dis- charge method and characterized for their magnetic properties [10]. It has however to be noted that these methods have also draw- backs: high pH sensitivity, stringent drying conditions, complex 0040-6031/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.tca.2007.11.025