X. L. Dong

Microstructure and microwave absorption properties of carbon-coated iron nanocapsules

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.

Enhanced microwave absorption in Ni/polyaniline nanocomposites by dual dielectric relaxations

Ni/polyaniline (PANi) nanocomposites were prepared by chemical polymerization, and electromagnetic characteristics were then studied at 2–18GHz. The permittivity of the Ni/PANi nanocomposite presents dual dielectric relaxations with increasing content of PANi to over 15.6wt%, which is ascribed to a cooperative consequence of the core/shell interfaces and the dielectric PANi shells. Additionally, the permeability presents a strong natural resonance around 2–8GHz, which is dominant among microwave magnetic loss. The proper matching of the permittivity and the permeability contributes to enhanced microwave absorption.

Multidielectric polarizations in the core/shell Co/graphite nanoparticles

Hybrid core/shell Co/graphite nanoparticles synthesized by an arc-discharge method exhibit an enhanced dielectric loss property in the frequency range of 2–18 GHz. Complex permittivity expressed by Debye dipolar polarization approximate show that three kinds of dielectric polarizations coexist in this hybrid system. Combined with theoretical simulation, we further clarified that the dielectric polarizations are ascribed to the high defective graphite shells, and additional interfacial polarizations arising from the special core/shell architecture.

Characterization of Fe and Co nanoparticles synthesized by chemical vapor condensation

Abstract Magnetic nanoparticles of Fe and Co were synthesized by Chemical Vapor Condensation (CVC) using the precursors of iron carbonyl (Fe(CO) 5 ) and cobalt carbonyl (Co 2 (CO) 8 ) as the sources under a flowing helium atmosphere. Characteristics were investigated systematically by means of XRD, HRTEM and VSM. Typical particle sizes are on the order of 5 to 13 nm with uniform dispersion. A correlation between the process parameters of CVC and the resulting microstructure of the nanoparticles was investigated. Mechanism of forming the nanoparticles and the direction to improve the magnetic properties were discussed.

Transform between the permeability and permittivity in the close-packed Ni nanoparticles

We report an anomalously electromagnetic resonance in a simple Ni nanoparticle/paraffin system. The resonance, caused by the near-field interaction of nanoparticles, appears at ∼16u2002GHz as decreasing the interparticle distance down to ∼11u2002nm. It is associated with an unusual energy transfer from the permeability to permittivity, resulting in the enhanced dielectric and weakened magnetic attenuations. These experimental results can be well modeled by a numerical simulation, evidencing the enhanced electrical filed distribution as decreasing the interaction distance. This study enables us to first realize the permeability-to-permittivity transform of electromagnetic wave in nanocomposites.

Chemical synthesis of Co nanoparticles by chemical vapor condensation

Abstract Magnetic Co nanoparticles were synthesized by a chemical vapor condensation method using the precursor of cobalt carbonyl as the source under a flowing inert gas atmosphere. Characteristics of the resulting material were investigated systematically by means of X-ray diffraction, high resolution transmission electron microscopy, TEM, X-ray photoelectron spectroscopy, vibrating sample magnetometer and differential thermal analysis-thermogravimetry. A correlation between the preparation conditions and the resulting microstructure of the nanoparticles was studied.

Characterization and Microwave Absorption of “Core/Shell”-Type Nanoparticles

The carbon-coated Fe(C), Co(C) and Ni(C) nanocapsules were prepared by a modified arc-discharge method in methane atmosphere. The nanocapsule powder, 50 % by weight, was mixed uniformly with paraffin wax to form measurement samples. Their electromagnetic (EM) wave reflection loss of the composite samples was calculated using the relative complex permeability and permittivity measured in microwave frequency range of 2-18 GHz. It is indicated that Fe(C), Co(C) and Ni(C) nanocapsules show the broadband characteristics with strong absorption from 2 to 18 GHz for a coating thickness of about 2-3 mm. The excellent EM wave absorption properties are mainly attributed to the proper electromagnetic match in microstructure, strong natural resonance as well as multi-polarization mechanisms, etc. As an inspiration, we found this kind of nanocapsules with a dielectric shell and a ferromagnetic core are very promising for new EM wave absorption materials.