Nanostructured Ceramic Oxides Containing Ferrite Nanoparticles and Produced by Mechanical Milling.
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Nanostructured Ceramic Oxides Containing Ferrite Nanoparticles and Produced by Mechanical Milling. A. Huerta-Ricardo1, K. Tsuchiya2, T. Umemoto2 and H. A. Calderon1 1 Departamento de Física, ESFM-IPN, UPALM Ed. 9, Zacatenco D.F. Mexico. 2 Dept. Prod. Systems Eng., Toyohashi University of Technology, Toyohashi Aichi 441 Japan. ABSTRACT This investigation deals with the production process and the characterization of ceramic materials consisting of magnetic particles in an insulating matrix. Composites made of magnetite particles (Fe3O4 or MgFe2O4) in a wüstite or magnesiowüstite matrix (FexO or Mg1-xFexO), respectively, have been produced by means of mechanical milling and spark plasma sintering. As-milled powders have a nanocrystalline structure in both systems. As a function of milling time, low energy milling gives rise to an increasingly higher volume fraction of wüstite in the FexO-Fe3O4 system while it promotes increasing amounts of magnesiowüstite (MgxFe1-xO). Sintering is performed from 673 to 1273 K in vacuum. Sintering at low temperatures allows retention of nanosized grains containing a fine dispersion of magnetic particles in a wüstite and magnesiowüstite matrix. Measurement of magnetic properties reflects the constitution of the sintered samples and the effect of grain size. It also allows determination of the transformation sequence both during mechanical milling and sintering INTRODUCTION Oxide ceramics are under intense investigation for their technological advantages in magnetization, dielectric response and chemical stability in such diverse applications as magnetic recording media, induction cores and microwave resonant circuits [1, 2]. Several researchers have mixed iron oxides with other ceramics as MgO, NiO, and ZnO to improve mechanical and magnetic properties [2, 3]. In such systems, the matrix (NaCl-type structure) has paramagnetic behavior and ferromagnetism is provided by precipitation of a second phase (spinel structure). Groves and Fine have shown that precipitation of a coherent spinel-structure in a NaCl-structure matrix may occur merely by rearrangement of the concentration of cations and the interstitial– site occupancy [4]. This transformation gives an octahedral precipitate morphology. However, clear evidence regarding the phase transformation mechanism in oxide ceramics is not well known. These materials are normally produced by conventional techniques, for example by diffusing iron into the matrix and thermal treatment to induce precipitation. The present investigation deals with the production of magnetite precipitates (Fe3O4) in a wüstite matrix (FexO) and magnesioferrite precipitates (MgFe2O4) in a magnesia matrix (MgO). The matrix phases have a NaCl structure and the precipitates a cubic inverse spinel structure. In such systems, the phase decomposition process occurs by the rearrangement of the cations in the continuous oxygen lattice. The combination of a nonconductive matrix and magnetic particles is interesting due to the expected magnetic and physical properties. The spati
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