Synthesis and Microwave Absorption of the Silica-coated Fe Nanocomposites

Silica-coated Fe nanocomposites were prepared by the DC arc plasma in a mixed atmosphere of hydrogen (H2) and argon (Ar). The phase structure, composition and morphology of silica-coated Fe nanocomposites were examined by X-ray diffraction(XRD), transmission electron microscope(TEM) and electron energy dispersive spectroscope(EDS). The results show that the mean size of silica-coated Fe nanocomposites is about 50nm, and the amorphous silica which cover BCC-Fe cores form nanorods with the length of 150-200nm. The growth mechanism of silicaa2coated Fe nanocomposites is governed by an extended vapora2liquida2solid mechanism and Fe nanoparticles acted as a catalyst for the growth of the nanorods. Its electromagnetic parameters are measured in the range from 2GHz to 18GHz. It is calculated that the maximum reflection loss of silica-coated Fe nanocomposites can reach -14.5dB at 15.4GHz with 1.79mm in thickness, and the bandwidth with a reflection loss less than -10dB is from 8-18GHz. The ina2depth study of relative complex permittivity and permeability reveals that the excellent microwave absorption properties are the consequence of a proper EM match in microstructure. And the loss mechanism is natural resonance, as the consequence of the increased surface anisotropic energy for nanosized particles.