Amorphous SiOC-coated submicron mullite aerogels with excellent thermal and structural stability up to 1500 ℃

Mullite aerogel is considered a promising candidate for thermal protection. However, structural collapse and poor temperature resistance limit its application at high temperature. Herein, amorphous SiOC-coated mullite aerogels (MAs) were prepared by high-temperature calcination, using Al₂O₃ nanorods and SiO₂ particles as precursor units. The one-dimensional submicron skeleton prevents weak pearl chain connections and high surface energy, while the nanoscale amorphous SiOC layer protects the encapsulated mullite skeleton, ensuring a strong skeleton and pores at high temperatures. MAs exhibit a low thermal conductivity of 0.0375 W/(m·K) at room temperature, a robust compressive strength of 0.369 MPa, and good thermal stability: after 30 min of annealing at 1500 ℃, the minimal linear shrinkage of MAs was 0.72 %. Interestingly, the amorphous SiOC layer grew into nanowires under a butane flame, which reconstructed the network and impeded the heat flow. Thus, the novel MAs exhibit considerable thermal insulation advantages in harsh environments.