Hierarchically structured SiBCN/SiC@SiO₂ nanofiber composite aerogel for efficient electromagnetic wave absorption

The rapid development of hypersonic vehicles and next-generation weaponry has prompted an urgent need for lightweight, high-temperature-resistant, and high-efficiency electromagnetic wave (EMW)-absorbing materials. To this end, using a silicon boron carbon nitride (SiBCN) nanofiber aerogel as the matrix, we propose an in situ whisker reinforcement–interfacial oxidation strategy, whereby SiC nanowires are grown in situ within its three-dimensional network via carbothermal reduction, and SiO₂ shells are subsequently formed via oxidation, resulting in a hierarchically porous, core–shell synergistic SiBCN/SiC@SiO₂ nanofiber composite aerogel. Benefiting from this structural design, the aerogel exhibits excellent compressive resistance (0.69 MPa) and substantially enhanced EMW absorption performance. The fiber/nanowire hierarchical porous network extends the propagation path of EMWs via multiple scattering and synergistically enhances interfacial polarization and conduction losses. On this basis, the introduction of the SiO₂ shell further improves impedance matching and enhances the interfacial polarization effect. Consequently, the aerogel delivers a minimum reflection loss of −53.18 dB at a thickness of 2.0 mm and an effective absorption bandwidth of 6.32 GHz. Over the thickness range of 1.5–5.0 mm, the total effective absorption bandwidth reaches 13.52 GHz, covering almost the entire C, X, and Ku bands. This work provides a new strategy for the structure–function integrated design of high-performance EMW-absorbing materials suitable for extreme environments.