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 are assembled as basic building blocks to fabricate the nanostructure-based ultralight ceramic aerogels by freeze-drying and subsequent heat treatment method. The SiO₂ shell is formed on the surface of Si₃N₄ nanowire core and the Si₃N₄/SiO₂ interface is applied to improve the mechanical and thermal insulation performance. Thanks to the core-shell structure of Si₃N₄@SiO₂ nanowire and the ultra-high porosity, the as-obtained Si₃N₄@SiO₂ nanowire (SSN) 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.