Microwave absorbing property of gelcasting SiC-Si3N4 ceramics with hierarchical pore structures

In this work, X-band microwave absorbing properties of gelcasted SiC-Si3N4 ceramics with different hierarchical pore structures at both room temperature and high temperature were reported for the first time. Effects of pore structures, sample thickness and temperature on complex permittivity and microwave absorption performance of SiC-Si3N4 ceramics were investigated systemically. The results suggested that the introduction of appropriate hierarchical pore structure was beneficial to improve the absorbing performance of the material. The minimum reflection loss value can reach -59.2 dB for the 3.8 mm thick sample at 8.35 GHz and room temperature. By elevating the temperature, the effective absorption bandwidth of porous SiC-Si3N4 with a thickness of 3.0 mm covers the entire X-band. The excellent microwave absorbing property of porous SiC-Si3N4 ceramics was attributed to the multiple reflections brought about by the existence of hierarchical pores, interfacial polarization between SiC and Si3N4 grains, and defect dipole polarization in grains and grain boundaries. The good absorbing property and the clarification of absorbing mechanism of porous gelcasted SiC-Si3N4 ceramics will provide a solid foundation for the development of porous SiC-based absorbing parts.