Lightweight mullite fiber-reinforced SiCnw/SiOC composites for efficient insulation and electromagnetic wave absorption

Owing to their excellent thermal insulation properties and chemical stabilities, ceramic aerogels are widely employed in thermal protection structure; however, their potential as electromagnetic wave (EMW) absorbers remains underdeveloped. Aerogels that provide both high-temperature thermal insulation and EMW absorption are difficult to obtain. Herein, a new mullite/SiC/SiOC (MCS) composite aerogel was grown in situ using a sol–gel process with a mullite nanofiber sponge as reinforcement. The pores in the fiber sponge are filled with numerous SiC nanowires and SiOC aerogel, forming a multiscale porous nanostructure. The semiconductor insulator composition and specific nanostructure endow MCS with excellent impedance-matching characteristics and strong EMW loss capability. The minimum reflection loss reaches −35.12 dB at a thickness of 2.5 mm and the effective absorption bandwidth almost covers the X-band. Meanwhile, the composite is lightweight (0.13–0.15 g cm⁻³) with a low thermal conductivity (0.03–0.036 W m⁻¹ K⁻¹), offering excellent thermal insulation performance. Overall, MCS composites are promising for applications requiring thermal insulation and EMW absorption.