Flexible and Hierarchical\nStructured Alumina Boron\nNitride Nanofibrous Aerogel for Thermal Superinsulation in Extreme\nConditions

Achieving effective thermal superinsulation at extremely\nhigh temperatures\nis paramount for aerospace, industrial operations, and societal advancements.\nBoron nitride (BN) aerogels, composed of nanoscale BN building units,\nare ultralight ceramics known for their excellent thermal and chemical\nstability, especially their high-temperature oxidation resistance.\nHowever, their vulnerability to oxidation and brittleness under specific\nhigh-temperature conditions poses challenges. This study introduces\na practical and scalable method to synthesize alumina ceramic BN aerogels\n(ACBNAs), which offer flexibility, are lightweight, and offer exceptional\nthermal insulation. The preparation of an aerogel was accomplished\nthrough the use of the highly concentrated emulsion template method.\nThis method involved dispersing and intertwining alumina fibers and\nboron nitride fibers within an emulsion. Polyvinyl acetate (PVA) was\nutilized as a self-sacrifice polymer agent to rearrange the structure.\nhe distinctive hierarchical cellular architecture of these ceramic\nnanofibrous aerogels imparts an ultralow density of ∼25 mg\ncm<sup>–3</sup>, an ultralow thermal conductivity of 26.17\nmW m<sup>–1</sup> K<sup>–1</sup>, and remarkable robustness\nacross a wide temperature range from −196 to 1200 °C,\nwith the capability for large-scale shape manipulation. Moreover,\nwhen ACBNA is used as a thermal insulation layer, in conjunction with\nAl foil, which acts as both a low-infrared-emission and high-infrared-reflection\nlayer, ACBNA forms a composite structure capable of effectively concealing\nhigh-temperature targets. These advantageous multifaceted features\nposition ACBNA as ideal for thermal insulation, thereby broadening\nits potential applications to harsh environments.