Flexible and Hierarchical Structured Alumina Boron Nitride Nanofibrous Aerogel for Thermal Superinsulation in Extreme Conditions

Abstract

Achieving effective thermal superinsulation at extremely high temperatures is paramount for aerospace, industrial operations, and societal advancements. Boron nitride (BN) aerogels, composed of nanoscale BN building units, are ultralight ceramics known for their excellent thermal and chemical stability, especially their high-temperature oxidation resistance. However, their vulnerability to oxidation and brittleness under specific high-temperature conditions poses challenges. This study introduces a practical and scalable method to synthesize alumina ceramic BN aerogels (ACBNAs), which offer flexibility, are lightweight, and offer exceptional thermal insulation. The preparation of an aerogel was accomplished through the use of the highly concentrated emulsion template method. This method involved dispersing and intertwining alumina fibers and boron nitride fibers within an emulsion. Polyvinyl acetate (PVA) was utilized as a self-sacrifice polymer agent to rearrange the structure. he distinctive hierarchical cellular architecture of these ceramic nanofibrous aerogels imparts an ultralow density of ∼25 mg cm^–3, an ultralow thermal conductivity of 26.17 mW m^–1 K^–1, and remarkable robustness across a wide temperature range from −196 to 1200 °C, with the capability for large-scale shape manipulation. Moreover, when ACBNA is used as a thermal insulation layer, in conjunction with Al foil, which acts as both a low-infrared-emission and high-infrared-reflection layer, ACBNA forms a composite structure capable of effectively concealing high-temperature targets. These advantageous multifaceted features position ACBNA as ideal for thermal insulation, thereby broadening its potential applications to harsh environments.