Resilient Si₃N₄@SiO₂ nanowire aerogels for high-temperature electromagnetic wave transparency and thermal insulation

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 m^2·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.