Electromagnetic property of SiO2-coated carbonyl iron/polyimide composites as heat resistant microwave absorbing materials

Heat resistant microwave absorbing materials were prepared by compression molding method, using polyimide resin as matrix and SiO2 coated carbonyl iron (Cl) as filler. The SiO2 coated CI particles were prepared by Sober process. The microwave absorbing properties and the effect of heat treatment on the electromagnetic properties of SiO(2)coated CI/polyimide composites were investigated. When the content of SiO2 coated Cl is 60 wt%, the value of minimum reflection loss decreases from -25 dB to -33 dB with the thickness increases from 1.5 mm to 2.1 mm. According to the thermal-gravimetric analyses (TGA) curves, the polyimide matrix can be used at 300 degrees C for long time. The complex permittivity of the composites slightly increases while the complex permeability almost keeps constant after heat treatment at 300 degrees C for 10 h, which indicating that the composites can be used at elevated temperature as microwave absorbing materials at the same time have good heat resistance and microwave absorption. (C) 2014 Elsevier B.V. All rights reserved.