Synthesis of monolithic aerogel-like alumina via the accumulation of mesoporous hollow microspheres

• Monolithic alumina aerogel-like presented extraordinary physical properties similar to aerogel.
• Monolithic alumina aerogel-like was synthesized at ambient condition.
• Monolithic alumina aerogel-like was formed via accumulation of mesoporous hollow microspheres.
• Monolithic alumina aerogel-like showed great stability up to 1200 °C.

Monolithic aerogel-like alumina was synthesized via the accumulation of mesoporous hollow microspheres through an epoxide-driven sol–gel method. The addition of propylene oxide to the solution controls the gelation process, while the aging time and H2O/ethanol molar ratio in the initial component determine the morphology of the gel. The bulk density of the as-prepared sample was 0.133 g/cm3, and the BET surface area was 505.6 m2/g, which were very close to the values for the common alumina aerogel synthesized through the supercritical drying method. The microstructural evolution of the aerogel-like material as a function of aging time was carefully studied by SEM and TEM. The transition from solid particles to urchin-like mesoporous hollow microspheres can be explained as a self-templating process according to the Ostwald ripening mechanism. In addition, the samples were heat treated to 800 °C, 1000 °C and 1200 °C for 2 h. With an increase of the heat treatment temperature, the crystalline phases of the aerogel-like alumina varied from γ-phase alumina to θ-phase alumina. The microstructures as well as the physical properties, such as the thermal conductivity and elastic modulus, of samples heat-treated at different temperatures were also measured and revealed that the samples exhibited excellent stability against high temperature.

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