Nanocarbon/Co₃O₄/Epoxy Composites for Microwave Shielding and Absorption

The epoxy composite materials (CMs) with a random distribution of nanosized Co₃O₄ and carbon nanoparticles (graphite nanoplatelets GNP and carbon nanotubes CNT) are fabricated. Complex permittivity, permeability, and shielding properties of composite materials with 30 wt% of Co₃O₄ and (2–5) wt% of nanocarbon are measured in the frequency range of 1–67 GHz using the transmission–reflection method. A significant increase of microwave permittivity and presence of several peaks on the dependencies of the imaginary part of permittivity on the frequency are found for three‐phase nanocarbon/Co₃O₄/epoxy CMs. The observed microwave shielding efficiency of three‐phase epoxy composites is enhanced compared to two‐phase nanocarbon–epoxy composites. Such enhancement of shielding efficiency correlates with the increase of DC conductivity of these three‐phase composites. The measured complex permittivity and permeability spectra for nanocarbon/Co₃O₄/epoxy CMs are used for modeling the reflection loss for studied composites. It is shown that the most preferable for microwave absorption is the composites containing 2 wt% of nanocarbon filler for a sample thickness of 0.5–0.7 mm. The highest reflection loss = 30 dB with an absorption bandwidth of 15 GHz is found for epoxy composite filled with 2 wt% of GNP and 30 wt% of Co₃O₄ for a sample thickness of 0.5 mm.