Carbon foams modified with in-situ formation of Si₃N₄ and SiC for enhanced electromagnetic microwave absorption property and thermostability

High-performance electromagnetic (EM) absorbing property and excellent thermostability of three-dimensional (3D) hierarchical carbon foams (CFs) modified with in-situ formation of Si₃N₄ and SiC were herein fabricated for the first time. The crystallinity of the carbon films could be tunable from amorphous carbon to graphite-shape carbon nanosheet by heat treatment of the as-received hybrid foams. Compared with those of pristine CFs, the multiscale hybrid CFs with in-situ formation of Si₃N₄ and SiC could achieve stronger EM microwave absorption performance with a minimum reflection loss (RL) value of − 43.2 dB at 4.7 GHz at 5.0 mm, and the maximum effective absorption bandwidth (EAB) could be up to 4 GHz (11.8–15.8 GHz) at a thickness of 2.0 mm. The absorption mechanism of the hybrid foams is discussed in detail from the point of the structure and composition transformation, of interfacial polarization and multiple reflections effects and of polarization relaxation effects. The hybrid foams could be thermostable in air atmosphere beyond 1000 °C with above 93% weight retentions, suggesting that the multiscale hybrid CFs could be used as promising absorber materials with strong EM wave absorption performance in harsh environments.