| Having consulted all the available literature on the subject, according the basic principal and method of design of radar absorbing materials, composites of epoxy resin (EP)-coated ultramicro iron, ultramicro iron-coated hollow glass bead, and hollow glass bead /ultramicro iron/ EP with three-layer structure were prepared. Microstructure of composites was characterized through SEM, TEM, XRD, FTIR, and Zeta potential; Thermal stability was investigated through DTA-TG; Complex permittivity and complex permeability were investigated by vector net analysis. Influence of microstructure of composites on electromagnetic properties was discussed.Composites of EP coating ultramicro iron were prepared using ATPU&Span60 as surface agent in DMF solvent by decomposing carbonyl iron and then vacuum distillation after adding epoxy resin (E-44). The results showed: Composites showed microstructure of EP coating ultramicro iron( α -Fe), which could enhance the ability of antioxidation of composites. Having investigated composites of EP coating ultramicro iron using ATPU as surface agent, results showed that with increasing amount of ATPU, density , complex permittivity ( ε ) and complex permeability (μ ) of composites decreased, and retentivity and coercivity increased. ε'μ' and μ" decreased with increasing frequency. Change of ε " with frequency was concerned with the amount of ATPU. When the amount of ATPU was less than 2.32%, ε " decreased with increasing frequency, but when the amount of ATPU was greater than 2.32%, influence of frequency on ε " was not obvious. Influence of concentration of carbonyl iron on static magnetism was not obvious. During discussing composites of EP-coated ultramicro iron through surface agent ATPU & Span60, we could find that with increasing the amount of Span60, density, ε decreased; μ decreased firstly and then increased; With increasing frequency, ε and μ decreased. In addition, with increasing the mount of ATPU, density of composites decreased, ε and μ decreased firstly and then increased. Density of composites was varied with the amount of organic and grain size of ultramicro iron. Influence of microstructure on ε and μ was discussed with the interface defectmechanism.Composites of ultramicro iron-coated hollow glass bead were in-suit prepared using ATPU as surface agent by decomposing carbonyl iron in hollow glass beads and DMF mixed solution. The results showed: The interaction of ether linkage (-CH2CH2-0-CH2CH2-)of ATPU and hydroxy group(-OH) of the surface of hollow glass bead formed hydrogen bond; Amino group and iron formed coordination bond. With increasing the amount of hollow glass beads, the ratio of ultramicro iron-coated hollow glass bead decreased. Having analyzed the influence of ATPU on compactness of composites, we could conclude that when the amount of ATPU was less, not only compactness of composites was poor, but also congregation of ultramicro iron was obvious. With increasing the amount of ATPU further more, change of grain size of ultramicro iron was not obvious, but compactness of composites decreased. With increasing the amount of hollow glass bead, ε and μ " decreased, μ ' increased firstly and then decreased. With increasing the amount of ATPU, V decreased, and ?decreased firstly and then increased; But when the concentration of ATPU was greater than 6.7mg/ml, change of ε " with increasing of concentration of ATPU was not obvious. It was pointed that density of composites decreased and ε and μ could be adjusted due to hollow structure.Composites of hollow glass bead /ultramicro iron/ EP with three-layer structure were prepared by coating EP on the surface of composites of ultramicro iron-coated hollow glass bead. The results showed: Composites had better compactness than composites of ultramicro iron-coated hollow glass bead. With increasing the amount of ATPU, grain size of ultramicro iron decreased, compactness of composites enhanced, ε decreased, and μ decreased firstly and then increased. But when frequency was greater...
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