Dielectric and microwave absorption properties of SiC ceramics derived from pre-oxidized polycarbosilane precursor

SiC ceramics were obtained by pyrolyzing oxidation cured polycarbosilane (PCS) from 800 to 1 200℃ in vacuum. The oxidation curing PCS powders at different temperature and pyrolysis product were characterized by FT-IR and Raman spectrum, respectively. The dielectric properties of SiC ceramics are investigated by measuring their complex permittivity using rectangle wave guide method in the frequency range of 8.2-12.4 GHz, and the reflection loss of samples were calculated based on the transmission line theory. The results show that Si-H and Si-CH₃ groups are oxidized to form Si-OH bonds during the oxidation curing process. The order of free carbon increases with the increase of pyrolysis temperature, which can contribute to the increasing of the real and imaginary parts of permittivity of SiC ceramics. When the sample thickness is 3.5 mm, the peak value of SiC ceramics derived from PCS after cured at 170℃ and pyrolyzed at 1 200℃ is -18 dB, and the reflection loss exceeded -10 dB in the whole frequency, which exhibits best absorbing performance.