Synthesis and electromagnetic properties of Fe/SiO₂ yolk/shell nanospheres with improved oxidation resistance

Nearly monodispersed Fe/SiO₂ yolk/shell nanospheres with an average diameter of about 250 nm were synthesised by hydrogen-thermal reduction of Fe₃O₄/SiO₂ precursor nanospheres. The morphology of products and precursors was characterised in three stages of preparation. Electrical conductivity magnetic properties and electromagnetic properties in the microwave band of Fe/SiO₂ yolk/shell nanospheres were investigated. The eddy current effect in Fe/SiO₂ yolk/shell nanospheres was effectively suppressed because of separation of ultrafine iron particles by silica shells, indicating that the eddy current effect can be suppressed only by separating iron particles and it is not related to the interface of iron and sillica. A reflection loss of -12.5 dB and an effective absorption band with a bandwith of 3.3 GHz were simultaneously obtained for Fe/SiO₂ yolk/shell nanospheres-containing coatings with thickness of 2 mm. Compared with bare Fe particles obtained from Fe₃O₄ precursor nanospheres, oxidation resistance of Fe/SiO₂ yolk/shell nanospheres was improved because of the existence of silica shells.