Temperature-dependent dielectric and microwave absorption properties of SiC_f/SiC-Al₂O₃ composites modified by thermal cross-linking procedure

SiC_f/SiC-Al₂O₃ composites were modified by thermal cross-linking procedure during the PIP process to optimize the dielectric and microwave absorption properties in the temperatures of 25-700 °C at 8.2-12.4 GHz. Both complex permittivity and tanδ of the composites without and after cross-linking show obvious temperature-dependent behavior and increase with the increasing temperatures. The mechanisms for these corresponding enhancements are also proposed. The composites without cross-linking exhibit poor RL values in the experimental temperatures owing to the deviation of impedance matching caused by the high complex permittivity. After cross-linking, the complex permittivity of the composites is reduced to suitable levels and shows low increasing tendency and amplitude with the increasing temperatures. Thus, the microwave absorption properties of the composites are significantly enhanced over the whole temperature and frequency ranges. Particularly, results indicate that minimum RL values and bandwidth below -10 dB reach -41.71 dB and 3.4 GHz at 300°C, and -22.76 dB and 4.1 GHz at 400 °C, respectively.