Improved microwave absorption properties of polycarbosilane-derived SiC core-shell particles by oxidation

Polycarbosilane-derived SiC (PCS-derived SiC) has been suggested as a promising candidate for particularly effective microwave absorption materials. To optimize the microwave absorption properties, while retaining the crystallinity of SiC, PCS-derived SiC ceramics were prepared by a combination of dehy-drogenation, appropriate oxidation, and pyrolysis. This study investigated microstructures, dielectric properties, and microwave absorption properties of as-prepared PCS-derived SiC. Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results demonstrate that dehydrogenation effectively prevented the breakage of Si-C bonds during the following oxidation. Furthermore, PCS-derived SiC with a similar core-shell structure was obtained after oxidation, the surface of which showed fewer SiC nanocrystals and shorter graphene-like carbon compared to the inner microstructure. Due to this unique microstructure, the oxidized PCS-derived SiC shows both better attenuation capability and impedance match than as-received PCS-derived SiC. Moreover, with extended oxidation time, the average epsilon' and epsilon" of PCS-derived SiC decreased from 13.0 to 5.2 to 10.5 and 4.4, respectively, which could be attributed to weakened polarization and decreased electrical conductivity. The minimum reflection loss of PCS-derived SiC could be significantly improved from -18 to -27 dB after oxidation, which indicates strong improvement in microwave absorption properties. (C) 2019 Elsevier B.V. All rights reserved.