Preparation and high-temperature microwave absorbing properties of 6H-SiC/MWCNT/silicon resin composites

Microwave absorbing materials (MAMs) have been widely used in the military and industrial fields. Recently, considerable efforts have been made to develop hybrid composition, multilayer structure absorbers to meet requirements such as strong absorption characteristics, wide absorption frequencies, light weights and oxidation resistance. In this study, a series of flexible composites consisting of 6H-SiC powder (40–50 wt.%), silicon resin (60–50 wt.%) and multiwalled carbon nanotubes (MWCNTs, additional 0.05–0.2 wt.%) were prepared and applied to produce high-temperature microwave absorbers via the spray coating method. The prepared composites were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the microwave absorbing properties of the composites were measured in the 4–18 GHz frequency range by the free space measurement method. The TGA thermograms indicated that the thermal stabilities of the prepared composites increased with increases in the 6H-SiC content but were less affected by increases in the MWCNT content. The actual measurement results showed that the optimum composition was 50 wt.% 6H-SiC, 50 wt.% silicon resin and an additional 0.2 wt.% MWCNT. The minimum reflection loss (RL) value of –58.9 dB was observed at 9.7 GHz with a thickness of 1.6 mm, and the effective absorption bandwidth (RL < –10 dB, for 90% microwave absorption) reached 2.3 GHz. At a high temperature of 450 °C, the absorption peak was located at 10.0 GHz with a reflection loss of – 13.7 dB, and the effective frequency bandwidth still reached 1.6 GHz.