Fabrication of magnetic nanosized γ-FeNi-coated ceramic core-shell microspheres by heterogeneous precipitation and thermal reduction

Precursors with NiCO3-2Ni（OH）2.2H2O- and Fe203.nH20-coated alumina, graphite and cenosphere were synthesized by precipitation using ferrous sulfate, nickel sulfate, ammonium bicarbonate, alumina, graphite and cenosphere as the main starting materials. Magnetic γ-FeNi-coated alumina, graphite and cenosphere core-shell structural microspheres were subsequently prepared by thermal reduction of the as-prepared precursors at 600℃ for 2 h. Precipitation parameters, e.g. concentration of ceramic micropowders （lOg/L）, sulfate solution （0.2mol/L）, rate of adding reactants （3 mL/min） and pH value were optimized by a trial-and-error method. Powders of the precursors and the resulting coating of γ-FeNi with grain size below 40 nm on alumina, graphite and cenosphere microspheres were characterized by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）. The magnetic properties of the nanosize γ-FeNi-coated alumina, graphite and cenosphere microspheres were measured by vibrating sample magnetometer （VSM）. The results show that the core-shell structural γ-FeNi-coated ceramic microspheres exhibited higher coercivity than pure γ-FeNi powders, indicating that these materials can be used for high-Derformance functional materials and devices.