Hierarchically structured mullite/SiC nanofiber composite aerogels featuring efficient infrared shielding and electromagnetic wave absorption properties

Mullite nanofiber aerogels (MNAs) exhibit promising potential for application in the thermal protection systems of hypersonic vehicles. However, the sharp increase in high-temperature thermal conductivity and limited functionality hinder their further development. Herein, hierarchical mullite/SiC nanofiber composite aerogels (MSNCAs) are constructed based on SiC hollow spheres and SiC nanowires, achieving multifunctional integration of infrared shielding and strong electromagnetic wave (EMW) absorption. SiC hollow spheres serve as closed-cell units to create a porous fiber skeleton, whereas SiC nanowires form a secondary reinforcing network between the fibers. Their synergistic effect endows MSNCAs with excellent infrared shielding and EMW absorption performance. The composite exhibits a thermal conductivity of only 0.0516  W/(m·K) at 1000 °C and achieves a reduction of 61.54% in infrared transmittance between 2.5 and 8 μm, demonstrating efficient high-temperature insulation. Moreover, the multiscale structure optimizes impedance matching and enhances dielectric loss. Consequently, MSNCA-15 exhibits a reflection loss of −54.85 dB with an effective absorption bandwidth of 4.88 GHz at a thickness of 1.8 mm. Simultaneously, the bridging effect of SiC nanowires improves the compressive strength of the aerogel to 0.41 MPa. This study provides a new structural design strategy for developing lightweight composite materials that feature efficient thermal insulation and electromagnetic stealth properties.