With the development of aerospace technology, the Mach number of aircraft continues to increase, which puts forward higher performance requirements for high-temperature wave-transparent materials. Silicon nitrides have excellent mechanical properties, high-temperature stability, and oxidation resistance, but their brittleness and high dielectric constant impede their practical applications. Herein, by employing a template-assisted precursor pyrolysis method, we prepared a class of Si₃N₄@SiO₂ nanowire aerogels (Si₃N₄@SiO₂ NWAGs) that are assembled by Si₃N₄@SiO₂ nanowires with diameters ranging from 386 to 631 nm. Si₃N₄@SiO₂ NWAGs have low density of 12–31 mg∙cm⁻³, specific surface area of 4.13 m²∙g⁻¹, and average pore size of 68.9 μm. Mechanical properties characterization shows that the aerogels exhibit reversible compressibility from 60% compressive strain and good fatigue resistance even when being compressed 100 times at set strain of 20%. The aerogels also show good thermal insulation performance (0.032 W·m⁻¹∙K⁻¹ at room temperature), ablation resistance (butane blow torch), and high-temperature stability (maximum service temperature in air over 1200 ℃). The dielectric constant and loss of the aerogels are 1.02–1.06 and 4.3×10⁻⁵–1.4×10⁻³ at room temperature, respectively. The combination of good mechanical, thermal, and dielectric properties makes Si₃N₄@SiO₂ NWAGs promising ultralight wave-transparent and thermally insulating materials for applications at high temperatures.

SiC ceramics are attractive electromagnetic (EM) absorption materials for the application in harsh environment because of their low density, good dielectric tunable performance, and chemical stability. However, the performance of current SiC-based materials to absorb EM wave is generally unsatisfactory due to poor impedance matching. Herein, we report ultralight SiC/Si₃N₄ composite aerogels (~15 mg·cm⁻³) consisting of numerous interweaving SiC nanowires and Si₃N₄ nanoribbons. Aerogels were prepared via siloxane pyrolysis and chemical vapor reaction through the template method. The optimal aerogel exhibits excellent EM wave absorption properties with a strong reflection loss (RL, −48.6 dB) and a wide effective absorption band (EAB, 7.4 GHz) at a thickness of 2 mm, attributed to good impedance matching and multi attenuation mechanisms of waves within the unique network structure. In addition, the aerogel exhibits high thermal stability in air until 1000 ℃ and excellent thermal insulation performance (0.030 W·m⁻¹·K⁻¹). These superior performances make the SiC/Si₃N₄ composite aerogel promising to become a new generation of absorption material served under extreme conditions.