Grain boundary segregation of ceramic aerogels for reliable thermal insulation at extreme conditions

Thermal insulation under extreme conditions requires materials to have high thermal stability and insulating properties to guarantee the critical system functionality and safety in aerospace, military, and high-temperature industries. Ceramic aerogels are the most attractive candidate to date, but due to the grain growth effect at high temperatures, they still suffer from insufficient structural stability and degraded thermal insulation that can lead to catastrophic failures. Here, we report an unusual grain boundary segregation in Y₆Zr₁O₁₁ fibrous aerogels with zirconium segregated at the yttria-zirconia grain boundary to inhibit boundary migration for fine-grain enhancement. The aerogel, fabricated by an airflow-assisted centrifugal spinning method, exhibits a grain size of only 172 nm and high thermal stability with volume shrinkage <3% at 1,500 °C in air, as well as near-infrared reflectivity up to 98.12% and low thermal conductivity of only 89 mW m^-1 K^-1 at 1,000 °C under a density of 50 mg cm^-3. This work not only establishes a set of grain boundary segregation considerations in material design of ceramic aerogels, but also promotes the large-scale and low-cost practical applications of such aerogels for reliable thermal insulation at extreme conditions.