Carbon-coated Fe [Fe(C)] nanocapsules were synthesized by a modified arc-discharge method, and their microstructure and electromagnetic (EM) properties (2–18 GHz) were investigated by means of transmission electron microscopy, Raman spectroscopy and a network analyser. The reflection loss R of less than −20 dB was obtained in the frequency range 3.2–18 GHz. A minimum reflection loss of −43.5 dB was reached at 9.6 GHz with an absorber thickness of 3.1 mm. The in-depth study of relative complex permittivity and permeability reveals that the excellent microwave absorption properties are a consequence of a proper EM match in microstructure, a strong natural resonance, as well as multi-polarization mechanisms, etc.

Nanofluids, a mixture of nanoparticles and fluid, have enormous potential to improve the efficiency of heat transfer fluids. Fe nanofluids are prepared with ethylene glycol and Fe nanocrystalline powder synthesized by a chemical vapor condensation process. Sonication with high-powered pulses is used to improve the dispersion of nanoparticles in the preparation of nanofluids. Nanofluids exhibit an enhancement of thermal conductivity after sonication. Thermal conductivity of a Fe nanofluid is increased nonlinearly up to 18% as the volume fraction of particles is increased up to 0.55 vol. %. Comparing Fe nanofluids with Cu nanofluids, we find that the suspension of highly thermally conductive materials is not always effective to improve thermal transport property of nanofluids.

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