Microwave-absorbing and mechanical properties of carbonyl-iron/epoxy-silicone resin coatings

doi:10.1016/j.jmmm.2008.07.011

Journal of Magnetism and Magnetic Materials

Volume 321, Issue 1, January 2009, Pages 25-28

https://doi.org/10.1016/j.jmmm.2008.07.011 Get rights and content

Abstract

Coatings with flake carbonyl-iron particles as absorber and epoxy-silicone resins as matrix were prepared. The complex permittivity, complex permeability and microwave-absorbing properties were investigated in the frequency range of 2–18 GHz. Both the real part of permittivity and permeability were increased with carbonyl-iron weight concentration. The minimum reflection loss shifts to the low-frequency region with increase in carbonyl-iron weight concentrations. The minimum reflection loss value of −42.5 dB was obtained at 10.6 GHz for the coatings with 55 wt% carbonyl-iron. The values of adhesive power and impact strength are up to 24 MPa and 50 kg cm, respectively. These results show that the coatings possess good microwave-absorbing and mechanical properties.

Introduction

Electromagnetic (EM) waves have been widely used in both military and civil applications: radar, wireless communication tools, local area networks, personal digital assistant, etc. [1]. However, there are many problems caused by the increasing usage of EM waves. In order to provide solution to electromagnetic interference (EMI) and electromagnetic compatibility (EMC), the absorbers of EM waves are becoming very important, which have attracted much attention of many scientists [2], [3].

Polymers filled with soft magnetic particles with high relative permeability, appropriate permittivity and low core losses for gigahertz frequencies applications are attracting more and more the interest. These composite materials are possible to control the magnetic and dielectric properties and can be molded into complex shapes due to the resins [4].

For the purpose of the microwave absorber used as coating on the exterior surfaces of military aircraft and vehicles [5], it is necessary to develop coatings with good microwave-absorbing and mechanical properties. The mechanical properties of coatings depend mainly on their composition: the amount of carbonyl-iron (CI) particles, resin amount and manufacturing technology.

The goal of the work is investigation of the EM, microwave-absorbing and mechanical properties of the soft magnetic coatings with the epoxy-silicone resin matrix and CI particles.

Section snippets

Experimental procedures

The magnetic coatings were prepared from CI particles and epoxy-silicone resins. The plate-shaped (flake) particles of the CI have a size of 2–5 μm and about 1-μm thickness. The content of CI particles was 50–75 wt%. The amount of the matrix as well as the temperature and curing time of the polymer material decides the technological conditions of composite fabrication. The CI particles and the resins were mixed and then the mixture was kept under low vacuum by a mechanical rotary pump to remove

Morphology of CI particles and the coatings

Fig. 1 shows the morphology of CI particles. The CI particles are thin flakes of 2–5 μm in diameter and of blow 1 μm in thickness.

Fig. 2 represents the microstructures of the coatings with different CI weight ratios. SEM images show that the CI particles are well separated by epoxy-silicone resin. The iron particles get closer but do not markedly agglomerate when the contents of CI increase.

EM properties

The complex permittivities of the coatings with different CI weight concentrations are presented in Fig. 3.

Conclusion

The CI resin coatings were fabricated by CI particles as absorber and epoxy-silicone resins as matrix. High value of magnetic permeability could be obtained in the composites containing flake CI particles. The frequency dependence of the permittivity, permeability and absorber properties on the CI weight concentration is measured. It is useful to control ε_r and μ_r by the variation of the CI weight concentrations. The minimum reflection loss also moves toward the low-frequency region with

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Microwave-absorbing and mechanical properties of carbonyl-iron/epoxy-silicone resin coatings

Abstract

Introduction

Section snippets

Experimental procedures

Morphology of CI particles and the coatings

EM properties

Conclusion

Mater. Sci. Eng. B

J. Magn. Mater.

Radar Absorbing Materials

J. Appl. Phys.