Study On The Electromagnetic Wave Absorbing Properties Of Multi-walled Carbon Nanotube/Cement Composites

Carbon nanotubes (CNTs) are a nano-scale material which has high aspect ratio, large specific surface area and superior electric conductivity, and they have become one of the hotspots in the research fields of electromagnetic interference (EMI) prevention for meeting the requirement of thin thickness, low density, broad bandwidth and strong absorption. The preparation technology of carbon nanomaterials reinforced cement based composites was first studied in this study. The effect of dry mechanical mixing method and silicon fume on the dispersion of multi-walled carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) in the cement materials was investigated through mechanical properties and micro measurement and analysis methods. Moreover, MWCNT/cement composite samples were fabricated through MWCNT suspensions prepared by an ultrasonic processing method, and the electromagnetic wave absorbing properties of samples were investigated. The influence of MWCNT content and sample thickness on the electromagnetic wave reflectivity was discussed and analyzed in the frequency ranges of2-8GHz and8-18GHz, respectively. Additionally, we investigated the influence of0.6%MWCNTs mixed with ferrite and manganese dioxide respectively on the absorbing properties of cement composites. MWCNT/cement composites filled with rubber powder were prepared as well, the microwave loss characteristics of rubber powder and wave absorption performance of MWCNT/rubber powder cement samples were studied. The main results are as follows:(1) The effect of dry mechanical mixing method on the dispersion of carbon nanomaterials in the cement materials was little, making the strength of cement samples decrease sometimes. Contrarily, silicon fume can improve the dispersion of carbon nanomaterials in the cement materials. Carbon nanomaterials mixed with silicon fume can enhance the strength of cement composites effectively.(2) The performance of absorbing electromagnetic waves of the specimens is greatly improved by the incorporation of MWCNTs. In the frequency range of2-8GHz, the electromagnetic waves close to the absorbing peaks of cement matrix composites with0.6%MWCNTs can be remarkably absorbed. In the range of8-18GHz, the bandwidth of cement mortar filled with0.9%MWCNTs below-10dB reaches7.1GHz. and the reflectivity of the0.6%MWCNTs incorporated cement mortar with sample thickness of35mm varies stably between-8and-10dB, exhibiting a beneficial performance of broadband wave absorption. Compared with cement composites incorporated with only0.6%MWCNTs. the electromagnetic reflectivity peak value of MWCNTs/ferrite cement composites decreases remarkably, however, the fluctuation change of sample reflectivity becomes larger at the same time. MWCNTs/manganese dioxide absorber can improve the absorption properties of cement composites evidently. When the manganese dioxide content is10%. the minimum reflectivity of MWCNTs/manganese dioxide cement composites is-11.2dB and the bandwidth below-10dB reaches4.0GHz in the range of8-18GHz.(3) The addition of MWCNTs and rubber powder can enhance the absorbing properties of cement-based materials and broaden sample bandwidth. The electromagnetic waves close to the absorbing peaks of cement matrix composites with0.9%MWCNTs and8%rubber powder can be remarkably absorbed in the frequency range of2-8GHz. When the MWCNT content is0.6wt%and rubber powder content is8wt%, the minimum reflectivity value of sample was-13.6dB and the bandwidth below-10dB reaches4.7GHz. The wave absorption performance was both better than that of composite filled with MWCNTs or rubber powder individually.