Rational design of a novel mullite aerogel with extremely high mechanical strength and anti-oxidation behavior for advanced thermal protection in extreme environments

Aerogels, with ultra-low density and thermal conductivity, are key materials for the development of high-efficient thermal insulations. Yet, their low compressive strength, oxidation behavior, and poor thermal stability limit their further development. Herein, we have prepared a novel monolithic mullite aerogel using the RF/ Al2O3-SiO2 aerogel organic/inorganic hybrid as the precursor, followed by the CO2 supercritical drying, and high-temperature mullitization. The resulting mullite aerogel displays typical "pearl-necklace" three-dimensional network, with the average pore size at around 10-20 nm, showing a large BET specific surface of 481 m2/g. The compressive strength of the mullite aerogel is as high as 15.5 MPa, much larger than those of the reported ceramic aerogels. The mullite aerogel exhibits excellent thermal insulation property, and the mass loss is only 2.5% after the butane torch evaluation with 1300 degrees C for 10 min under air, showing its rather excellent anti-oxidation performance, and the anti-oxidation mechanism is also proposed.