Preparation of fine, hollow, spherical NiFe2O4 powders

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Abstract
Aerosol droplets of a dilute aqueous solution of Ni(II) and Fe(III) nitrates were used to synthesize fine nickel ferrite powders by pyrolysis at temperatures ranging from 450 °C to 810 °C. The aerosol product was characterized by thermal analysis, x-ray diffraction, scanning electron microscopy, and BET surface area determination. At low temperature (480 °C), very active fine, hollow, noncrystalline spheres were formed. As the pyrolysis temperature increased, sintering occurred, larger particles with broader size distribution were obtained, and a higher degree of crystallinity of nickel ferrite was produced. The products at pyrolysis temperatures of 660 °C and above exhibited magnetic properties. The powders prepared from the aerosolization process at low temperatures had high reactivity and crystallized rapidly. The effect of the initial solution concentration was also studied, and dilute solutions produced spheres with fine size and narrow size distribution.