Fabrication of magnetic nanosized α-Fe- and Al2O3–Fe-coated cenospheres

The precursors for nanosized α-Fe- and Al2O3–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 H2/N2 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 Al2O3–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 Al2O3–Fe-coated cenospheres were determined and the multilayered Al2O3/20 wt.%Fe/cenospheres exhibited a very higher coercivity value of approximate 203 Oe compared about 79 Oe of the 20%Fe/cenospheres.

Graphical abstractThe nanosized α-Fe- and Al2O3–Fe-coated cenospheres have been fabricated using the heterogeneous precipitation–thermal reduction method and basically maintain the spherical morphology of cenospheres with little aggregations or agglomerations. These powder materials with a core-shell structure have a uniform coating with no cracks. The shell consists of nanosized α-Fe for the nanosized α-Fe-cenospheres and multilayered, nanosized Al2O3–Fe for the Al2O3–Fe-coated cenospheres.Figure optionsDownload full-size imageDownload as PowerPoint slide