High-Temperature-Resistant Aerogels Based on Amorphous Al ₂ O ₃ and SiO ₂ Nanoparticle Composites for Thermal Insulation

To address the challenge that Al 2 O 3 aerogels undergo phase transformation and pore collapse above 1000 °C, leading to thermal-insulation failure. This study employs an ambient pressure drying (APD) platform to construct a composite strategy. This strategy integrates chitosan (CTS) three-dimensional soft template combined with functionalized silicon sources and in situ TEOS deposition reinforcement. The effects of different functional groups (−CH 3 and −(CH 2 ) 3 NH 2 ) on the nanoscale microstructure, high-temperature phase evolution, and thermal stability of Al 2 O 3 –SiO 2 aerogels (ASA) were systematically elucidated. Compared with samples without carbon-containing silicon sources, the methyl-functionalized ASA-M effectively reduced capillary stress during APD, retained nanopores smaller than 10 nm, and generated a higher proportion of Al–O–Si hybrid bonds, maintaining a continuous nanoscale framework and mesoporous network even after heat treatment at 1400 °C. In contrast, the aminopropyl-functionalized ASA-A promoted secondary TEOS deposition through weak-base catalysis and exhibited preferential cristobalite growth at 1200 °C. Among them, ASA-M demonstrated superior anticrystallization capability and thermal stability, preserving an intact skeleton and mesostructure at 1400 °C. This strategy successfully produced crack-free monolithic aerogels under ambient-pressure condition and maintained nanostructural integrity at ultrahigh temperatures, providing a pathway for developing high-performance oxide aerogels for extreme-environment applications.