Robust and thermostable C/SiOC composite aerogel for efficient microwave absorption, thermal insulation and flame retardancy

• C/SiOC composite aerogel was prepared by a simple process for the first time. • The optimal reflection loss reaches −67.85 dB with absorption bandwidth of 6.88 GHz. • Superior mechanical, anti-oxidation and thermal insulation properties are obtained. Carbon aerogel (CA) has been generally regarded as a potential electromagnetic wave (EMW) absorber, but unsatisfactory microwave absorption, mechanical and anti-oxidation properties are still the primary challenges for its application. Herein, a novel C/SiOC composite aerogel (CSA) was successfully synthesized by a simple copolymerization of dual sols, ambient pressure drying and thermal treatment process for the first time. The morphology and performance of the as-prepared CSA could be tailored just by controlling the initial ratio of silane and phenolic resin (PR) to adjust the content of SiOC in CSA, whose density was in the range of 0.252 to 0.294 g·cm −3 with a low thermal conductivity from 0.061 to 0.067 W·m −1 ·K −1 . Notably, the EMW absorption capacity of CSA was greatly enhanced with the increase of SiOC content, with the optimal reflection loss (RL ) value of −67.85 dB and effective absorption bandwidth (EAB) of 6.88 GHz, which was dramatically improved than CA (–22.89 dB, 5.34 GHz) and mainly ascribed to the optimized impedance matching characteristics and strong attenuation capacity. Meanwhile, compared with CA (2.63 MPa) with a density of 0.248 g·cm −3 , the mechanical properties of CSA (3.30–5.12 MPa) were also remarkably improved, and the maximum compression strength was nearly doubled. Furthermore, CSA obtained superior oxidation resistance than CA and exhibited excellent flame-retardant properties. All the results indicated that CSA could be considered as a highly promising candidate for applications in extreme environments due to its lightweight, high strength and outstanding microwave absorption capacity along with good oxidation resistance, superior thermal insulation performance and high flame retardancy.