Self-standing and compressible SiCnw/SiCnf composite aerogel via free carbon in-situ transformation mechanism: towards thermal and electromagnetic wave protection

SiC nanofiber-based composite aerogel represents a promising lightweight, high-temperature-resistant, and broadband-absorbing material. However, the residual carbon phase during the pyrolysis process would threaten the high-temperature oxidation tolerance. Herein, a free carbon in-situ transformation (FCIT) strategy was proposed to convert the amorphous free carbon on the surface of SiC nanofibers into SiC nanowires, constructing a multi-scale SiC nanowire/SiC nanofiber (SiCnw/SiCnf) composite aerogel. The SiCnw great broaden the inner fibrous framework, and the hierarchical network offers great enhancement for EM attenuation, compression resistance and thermal insulation. The self-standing composite aerogel possesses excellent flexibility (1500 cycles in 180°-bending test) and compression resistance (100 cycles at 40% strain). With only 10 wt% filler content, the SiCnw/SiCnf sample displays an effective absorption bandwidth (EAB) of 8.81 GHz (9.19-18.00 GHz) at a thickness of 2.94 mm. Even after enduring oxidation at 800 °C, the EAB still remains substantial at 6.92 GHz (11.08-18.00 GHz). Moreover, the outstanding mechanical performance were also retained under high temperature and oxidation environment due the reduced density and thermal conductivity. Therefore, the multifunctional SiCnw/SiCnf composite aerogel prepared by FCIT strategy could be served as efficient thermal and EMW protection candidate.