Amorphous coating enhanced Si₃N₄ nanoribbon aerogels with stable thermal insulation and mechanical properties in extreme conditions

Ultra-high-temperature ceramic aerogels exhibit low density, exceptional thermal stability, and superior thermal insulation capabilities, making them ideal candidates for thermal protection in next-generation high-end aerospace applications. However, the development of ceramic aerogels with enhanced structural and thermal stability in extreme environments remains a significant challenge. Although fibrous ceramic aerogels demonstrate improved flexibility compared to granular counterparts, they struggle to recover after large deformations due to the absence of inter-fiber constraints. Furthermore, existing elastic aerogels fail to provide reliable thermal protection in extreme harsh environments (ultra-high temperature aerobic) due to detrimental crystallization and oxidation at high temperatures. Here, we propose a strategy combining single-crystal ceramic nanoribbons and amorphous glassy coating to synthesize Si₃N₄/amorphous coating (Si₃N₄/AC) aerogels. The three-dimensional porous crosslinked network is formed by a combination of single-crystal Si₃N₄ nanoribbons and the amorphous coating that encapsulates and welds nanoribbons together. The inherent flexibility and thermal stability of Si₃N₄ nanoribbons, coupled with the displacement restriction and oxidation resistance effect of the amorphous coating, confer excellent compression recovery and thermal stability to the aerogels. Additionally, these aerogels exhibit ultralow thermal conductivity (∼29.7 mW m⁻¹ K⁻¹), attributable to the minimal solid heat transfer within the porous network and the rapid dissipation of thermal energy by the high interfacial thermal resistance at crystalline-amorphous phase boundaries. This robust thermal protection system material is compatible with lightweight (∼20 mg cm⁻³), large strain (60 %) recoverable compressibility, fatigue resistance, refractory performance, and excellent thermal stability over wide temperature range (−196–1600 °C), offering new options and possibilities for future deep-space exploration.