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Iron nanoparticles with a thin amorphous iron oxide layer synthesized by a gas-based method were used for silica coating, which was realized by a microemulsion method in an organic solvent. These core−shell nanocomposites showed improved antioxidation properties as confirmed by thermogravimetry and differential thermalgravimetric (TG-DTA) analysis in air. Further thermal treatment of the nanocomposites in N 2 resulted in the crystallization of amorphous iron oxide and formation of the Fe@Fe 3 O 4 @SiO 2 structure. Fe@SiO 2 nanostructures were obtained for the reduction of iron oxides to iron metal by treatment in N 2 /H 2 . Although different weight gain values were obtained for the Fe@Fe 3 O 4 @SiO 2 and Fe@SiO 2 powders, both of them exhibited almost the same peak temperature caused by oxidation of the iron core component. This result implies that the silica layer rather than the iron oxide layer determines antioxidation behavior. The silica-coated iron nanoparticles and iron nanoparticles showed strong ferromagnetism at room temperature. The nanocomposites treated with N 2 /H 2 exhibited improved saturated magnetization for the reduction of iron oxide by H 2 .
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Leng et al. (2009) studied this question.
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