Thermal insulating Si₃N₄@SiO₂ nanowire aerogel with excellent mechanical performance at high-temperatures up to 1300 °C

Ceramic aerogels with low dielectric are attractive due to its lightweight and ultralow thermal conductivity, while it can withstand complex mechanical loads and thermal shock for the randoms/windows of aerospace. In this work, Si₃N₄ nanowires were assembled as basic building blocks to fabricate the nanostructure-based ultralight ceramic aerogels by freeze-drying and subsequent heat treatment method. The SiO₂ shell was formed on the surface of Si₃N₄ nanowire core and the Si₃N₄/SiO₂ interface was applied to improve the mechanical and thermal insulation performance. Thanks to the core–shell structure of Si₃N₄@SiO₂ nanowire (SSN) and the ultra-high porosity, the as-obtained Si₃N₄@SiO₂ nanowire aerogels display robust mechanical and thermal stability, the compress strength up to 27.1 kPa, and the compress strength up to 4.6 kPa even after heat treatment up to 1300 °C for 9000 s. The compress strength retention rate is 58% for SSN aerogel after oxidation for 9000 s. The SSN aerogel also features low thermal conductivity of 0.029 W·m^–1·K–1 at room temperature. Furthermore, the dielectric property of SSN aerogel is low (an ultra-low real permittivity (ε′) of 1.02–1.04, the dielectric loss of 2 × 10^–3). This robust material system is ideal for thermal insulation for the randoms/windows of aerospace.