Resilient Si ₃N ₄@SiO ₂ 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 nitride has excellent mechanical properties, high-temperature stability, and oxidation resistance, but its brittleness and high dielectric constant impede its practical applications. Herein, by employing a template-assisted precursor pyrolysis method, we prepared a class of Si₃N₄@SiO₂ nanowires aerogels (Si₃N₄@SiO₂ NWAGs) that are assembled by Si₃N₄@SiO₂ nanowires with diameters ranging from 386 nm to 631 nm. The Si₃N₄@SiO₂ NWAGs have low densities (12-31 mg·cm^-3), a specific surface aerogel of 4.13 m²g^-1, and an 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 for 100 times at a set strain of 20%. The aerogels also show good thermal insulation performance (0.032 W·m^-1K^-1 at room temperature), ablation resistance (butane blow torch), and high-temperature stability (maximum service temperature in the air over 1200 °C). 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 the good mechanical, thermal, and dielectric properties makes Si₃N₄@SiO₂ NWAG a promising ultralight wave-transparent and thermally insulating material for application at high temperatures.