Reduction behavior of barium hexaferrite into metallic iron nanocrystallites

Abstract

Barium hexaferrite (BaFe12O19) powder was prepared through the ceramic route by calcination of a stoichiometric mixture of barium carbonate and iron oxide at 1200 °C for 2 h. Compacts of synthesized BaFe12O19 powder were isothermally reduced in hydrogen atmosphere at 600-1000 °C. Based on thermogravimetric analysis, the reduction behavior of BaFe12O19 and reaction kinetics and mechanism were studied. The initial ferrite powder and the various reduction products were characterized by X-ray diffraction analysis,a scanning electron microscope and a vibrating sample magnetometer to reveal the effect of hydrogen reduction on composition, microstructure and magnetic properties. The reduction rate was found to be controlled by interfacial chemical reaction mechanism. Metallic iron was formed in nanosized regimes while grain growth and coalescence were observed at higher reduction temperatures. Magnetic measurements show diluted magnetic properties for the formed metallic iron, whereas coercivity values were in the range 14.1-55 Oe and saturation magnetization varied from 24.79 to 36.15 emu/g. These values have been ascribed to the formation and growth of nanosized metallic iron particles as the reduction treatment proceeded. © 2006 Elsevier B.V. All rights reserved.