Abstract
The precursors for nanosized α-Fe- and Al 2O 3–Fe-coated cenospheres were synthesized by the aqueous heterogeneous precipitation using ferrous(II) sulfate, ammonium bicarbonate, ammonium aluminum sulfate and cenospheres as main raw materials. Subsequently, the composite microspheres with magnetic coatings of α-Fe in grain sizes of about 50 nm were successfully obtained by reduction of the as-prepared precursors in an H 2/N 2 atmosphere at 720 °C for 2 h. The morphology, composition, phases of the precursors and the derived composite microspheres were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD). The magnetic properties of the nanosized α-Fe- and Al 2O 3–Fe-coated cenospheres were measured by vibrating sample magnetometer (VSM). On the basis of tests, optimized processing parameters for fabrication of nanosized α-Fe- and Al 2O 3–Fe-coated cenospheres were determined and the multilayered Al 2O 3/20 wt.%Fe/cenospheres exhibited a very higher coercivity value of approximate 203 Oe compared about 79 Oe of the 20%Fe/cenospheres.
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