Synthesis of core–shell iron nanoparticles from decomposition of Fe–Sn nanocomposite and studies on their microwave absorption properties

Core–shell iron nanoparticles have been synthesized by pyrolysis of nanocomposite of oxides of iron–tin (Fe–Sn). The core–shell nanoparticles of phase pure iron in carbonaceous shell are formed only at very low concentration of tin (0.0011 mol) in the nanocomposite sample. From different studies viz. X-ray diffraction, high-resolution transmission electron microscopy, atomic force microscopy, and Raman spectroscopy, it has been established that core–shell nanostructures have been formed with Fe as core and amorphous carbon as the shell. The heating of nanocomposite at different temperatures up to 900 °C revealed very interesting dynamics of formation of core–shell structure wherein above 650 °C the iron carbide phase decomposes and carbon atoms move out to form an amorphous shell around iron nanoparticles. This process of formation of core–shell structures is quite different from conventional way wherein synthesis of core material precedes formation of shell in two different steps. The microwave absorption properties of core–shell nanoparticles have been studied by making their composites in nitrile butadiene rubber. Reflection loss simulation studies show high values in the X and Ku bands of microwave region. The frequency of maximum return loss can be tuned through variation of composition and thickness of composite layer.