PREPARATION OF FINE, HOLLOW, SPHERICAL BAFE12O19 POWDERS

Aerosol droplets of a 2 wt% aqueous solution of Ba and Fe(III) nitrates were used to prepare fine Ba-ferrite powders by pyrolysis at temperatures 800 K and 1300 K. The particles are spherical with a mean size of 0.1-mu-m, with the constituent nanocrystals taking on a characteristic hollow structure. Both as-received and heat-treated powders were characterized by X-ray diffraction, thermal analysis, transmission electron microscopy, and magnetic hysteresis measurements. Composition analysis shows that the particles prepared at 800 K have a multiphase structure formed by unreacted Ba nitride and Fe oxide. As the synthesis temperature is increased up to 1300 K the prepared powder exhibits chemical homogeneity for the Ba-ferrite and hexagonal crystallographic structure. Additional thermal treatment (sintering) improves magnetic characteristics. Increase of magnetic saturation, remanence and coercivity were observed as an effect induced by the annealing process, and consequent upon the growth of hexagonal platelet like nanocrystals of ferrite.