Lightweight and thermally insulating polymer-derived SiBCN/SiCnw ceramic aerogel with enhanced electromagnetic wave absorbing performance

[Display omitted] •SiBCN/SiC nanowire aerogel was prepared by a simple process.•The enhanced electromagnetic absorbing performance is achieved.•Superior thermal insulation property with low thermal conductivity is obtained.•The resulted aerogel is highly promising for defense and high-speed vehicle. Electromagnetic wave (EMW) absorption materials with lightweight and thermal insulation properties are highly sought after in aircraft and military application, because they can simultaneously resist aerodynamic heating and display EMW stealth function. Herein, a polymer-derived SiBCN/SiC nanowire composite aerogel was prepared through in-situ synthesis of SiC nanowires in SiBCN ceramic aerogel by catalyst-assisted annealing. The phase composition, nanoscale architectures, and EMW absorbing property of the as-obtained aerogels could be regulated by tuning annealing temperature. The resulting composite ceramic aerogel annealed at 1400 °C, which is composed of amorphous SiBCN, SiC nanowires, and free carbon, exhibits excellent microwave absorbing performance (minimum reflection loss of −50.1 dB and effective bandwidth of 6.4 GHz) and low thermal conductivity of 0.052 W/mK with low density (0.142 g/cm3). The superior EMW absorption capability is primarily ascribed to the improved impedance matching, multi-reflection, as well as enhanced interfacial polarization caused by SiC nanowires. Owing to the integration of EMW absorption and thermal insulation properties, the SiBCN/SiC nanowire aerogels pave the way for the construction of thermal insulation material for EMW absorption in the application of military and daily life.