A Novel Phenolic Resin Aerogel Modified by SiO₂-ZrO₂ for Efficient Thermal Protection and Insulation

Phenolic aerogel holds great promise for applications in thermal protection against ablation, and constructing inorganic-organic hybrid networks is an effective strategy to enhance its oxidation and ablation resistance. This study introduces a stepwise hybridization strategy for the preparation of SiO₂-ZrO₂-phenolic resin aerogels (SZPA). First, nano-silica sol and nanometer-scale zirconia were physically blended to form a uniformly dispersed mixture. Subsequently, the modified silica was incorporated into a phenolic resin solution to construct a three-dimensional hybrid silica-phenolic network framework. Nano-sized zirconia was then uniformly dispersed within the matrix as a physical reinforcing phase through high-shear dispersion. Finally, the SZPA with a hierarchical nanoporous structure was obtained via ambient-pressure drying. Owing to its unique hybrid network structure, the aerogel exhibits markedly improved properties: the thermal conductivity is as low as 0.0419-0.0431 W/(m·K) (a reduction of approximately 24%), and the specific surface area is as high as 190-232 m²/g (an increase of approximately 83%). Meanwhile, the inorganic network considerably enhances the residual mass at elevated temperatures, as well as the oxidation resistance and thermal stability of the matrix. Among the tested materials, the SZPA-4 exhibited outstanding thermal insulation capability at high temperatures; its back surface temperature reached only 74.4 °C after 600 s of exposure to a 1200 °C butane flame. This study provides a feasible route for the preparation of high-performance phenolic-based composite aerogels for aerospace thermal protection systems, thereby expanding their potential applications in extreme thermal environments.