Preparation and characterization of transparent alumina aerogel monolith with high temperature resistance

Aluminum oxide (Al 2 O 3 ) aerogel has attracted considerable attention in the field of high-performance thermal insulation materials due to their high-temperature stability and low thermal conductivity. However, phase transformations at high temperatures often lead to a loss of transparency and insulation performance, limiting their application in high temperature. Herein, transparent Al 2 O 3 aerogel monoliths with sustained high-temperature performance were prepared by sol-gel method combined with the CO 2 supercritical drying. By systematically tuning the molar ratios of propylene oxide (PO), ethanol (EtOH) and water (H 2 O), an optimal formulation was determined as Al: PO: EtOH: H 2 O = 1 : 10: 12 : 45. This composition yielded a homogeneous boehmite-derived network with a low density (0.060 g/cm 3 ), a high surface area (618 m 2 /g) and a visible transmittance of 90.3% at 550 nm. The structural evolution of Al 2 O 3 aerogel at heat treatment temperature (600–1200 °C) was systematically studied. It was found that, Al 2 O 3 aerogel experienced a series of phase transformation (boehmite → γ → δ → θ → α) with gradual densification and pore shrinkage, avoiding catastrophic collapse. Consequently, the aerogel retained a specific surface area of 141 m 2 /g, a thermal conductivity of 0.066 W/(m·K), and a transmittance of 49.6% even at 1100 °C, demonstrating excellent high-temperature thermal insulation and optical properties. This work provides a promising strategy for the efficient preparation of high-performance transparent insulation materials that can operate in high-temperature environments.