Lightweight and Thermally Insulating Alumina-Based Nanofiber Aerogels Assembled from SiO2-Doped Nanofibers

Lightweight alumina-based aerogels with high thermal stability are promising candidates for high-temperature thermal insulation; however, conventional particle-based aerogels suffer from severe sintering and structural degradation. In this work, controlled amounts of SiO2 were introduced into Al2O3-based nanofibers (NFs) as a secondary phase to regulate their thermal stability, and the obtained SiO2-containing NFs were further assembled into alumina-based nanofiber aerogels (AGs). The SiO2-containing NFs were assembled into three-dimensional porous aerogels via a direct foaming and freeze-drying process, followed by high-temperature calcination. The introduction of SiO2 within the nanofibers effectively suppresses grain growth and delays the γ-Al2O3 to α-Al2O3 phase transformation through a Zener-pinning effect, resulting in a stabilized fibrous skeleton. Consequently, the AGs exhibit reduced density, enhanced porosity, improved compressive strength, and lower thermal conductivity. For aerogels calcined at 1000 °C, higher SiO2 incorporation within the nanofibers markedly improves the compressive response at 40% deformation, increasing the strength from 2.9 to 16.9 kPa, while the thermal conductivity measured at 1000 °C declines to 0.03597 W/(m·K) from an initial value of 0.03903 W/(m·K). This work demonstrates an effective strategy for designing thermally stable and mechanically robust oxide nanofiber aerogels for high-temperature insulation applications by tailoring the SiO2 content in alumina nanofibers.