Fiber-reinforced alumina-carbon core-shell aerogel composite with heat-induced gradient structure for thermal protection up to 1800 °C

[Display omitted] •The support of multiscale skeleton leads to ultra-low carbonization shrinkage.•Hydrogen bonding induces in situ nano-doping of light-shading carbon layers.•Synergistic multiscale structure results in thermal superinsulation performance.•Heat induced gradient structure shows excellent ablation resistance under 1800 °C.•Al2O3 ceramic skeleton is the structural foundation for these excellent properties. High performance thermal insulation materials are urgently demanded for hypersonic spacecraft. Aerogels are considered as promising candidates owing to their low density and low thermal conductivity. However, some deficiencies, such as the unsatisfactory high-temperature thermal insulation properties and the non-exfoliation-resistant particle porous structure of ceramic aerogels, the ease of oxidation and large carbonization shrinkage of carbon aerogels, remain great challenges for their further applications in high-temperature aerobic ablation environments. Here, we report a multiscale fiber-reinforced Al2O3-carbon core–shell aerogel composites with low density (0.23–0.31 g·cm−3), excellent mechanical properties (4.89 MPa at 10% strain) and ultra-low carbonization shrinkage (as low as 1.33%). Benefiting from the synergistic effect of in situ nano-doped light-shading carbon layers, porous Al2O3 ceramic rod skeleton and oriented fibers, the composites demonstrate an extremely low high-temperature thermal conductivity (0.055 W·m−1·K−1 at 1200 °C) that is far superior to those of existing high-temperature insulating aerogel composites. In addition, the unique heat-induced gradient structure also confers outstanding thermal protection properties to the composite at 1800 °C with a liner ablation rate of 6.44 μm·s-1and a mass loss rate of 0.167 mg·s−1. This work not only opens a new path for the preparation of thermal superinsulating materials used for spacecraft, but also provides a simple solution to the difficulty of compatibility between low-density insulating porous skeleton and ablation-resistant tough structures, thereby enabling thermal insulation materials to possess desired ablation-resistant properties.