Electrical and Shielding Properties of Epoxy Composites with Combined Fillers (SiO2-Fe2O3)/CNT and (SiO2-Fe3O4)/CNT

The paper presents the results of investigation of multi-component epoxy composites containing silica gel globules coated with Fe oxide particles (SiO2-Fe oxide) and multi-wall carbon nanotubes (CNTs). The structure and phase composition of (SiO2-Fe oxide) globules were examined by XRD analysis, scanning electron microscopy, FTIR and Raman spectroscopy. It was found that the combination of SiO2 particles, (SiO2-Fe oxide) particles and conductive carbon nanotubes in epoxy composites leads to a sufficient increase in electrical conductivity compared to two-phase CNT/epoxy CM. For all samples of SiO2/CNT- and 22 wt.%(SiO2-Fe oxide)/2%CNT/epoxy CMs the negative temperature coefficient of electrical resistance (TCR) is observed. The coating of SiO2 globules with Fe oxides slightly influences the shielding properties. The addition of 2 wt.% CNT along with (SiO2-Fe oxide) filler into epoxy resin results in an increase of electromagnetic interference (EMI) shielding efficiency SET\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$SE_{T}$$\end{document} up to 8–12 dB in the frequency range 26–54 GHz with a shield thickness of ~ 2 mm. The sufficient increase of SET\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$SE_{T}$$\end{document} with the frequency indicates the prevailing part of EMI shielding due to absorption compared with reflection, SEA/SET\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{SE_{A} } \mathord{\left/ {\vphantom {{SE_{A} } {SE_{T} }}} \right. \kern-0pt} {SE_{T} }}$$\end{document} ratio reaches the values of 0.78–0.87 in the frequency range 36–54 GHz.