Fabrication of Fe-, Ni- and FeNi-coated Al 2O 3 core-shell microspheres by heterogeneous precipitation

Abstract

The precursors with NiCO 3·2Ni(OH) 2·2H 2O-, Fe 2O 3· nH 2O-, or both of NiCO 3·2Ni(OH) 2·2H 2O- and Fe 2O 3·nH 2O-coated alumina microspheres were prepared, respectively, by the aqueous heterogeneous precipitation using metal salts, ammonium hydro-carbonate and α-Al 2O 3 micropowders as the starting materials. Subsequently, magnetic metallic Ni-, α-Fe- and γ-FeNi-coated alumina core-shell structural microspheres were successfully obtained by thermal reduction of the as-prepared precursors at 700 °C for 2 h, respectively. Optimized precipitation processing parameters of the concentration of alumina micropowders (15 g/L), the rate of adding reactants (5 mL/min) and pH value were determined by a trial and error method. Powders of the precursors and the resultant metal (Ni, α-Fe, γ-FeNi alloy)-coated alumina micropowders were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The experimental results show that it is possible to adjust metal coating thicknesses and fabricate multilayer structured metal/ceramics core-shell microspherical powder materials and these materials may be applied for high performance of functional materials and devices.