Preparation of alumina aerogel films by low temperature CO2 supercritical drying process

Abstract

Abstract. Alumina aerogel thin films were formed by a new synthesis route. Sols were prepared by the Yoldas process. Gels were formed by sol evaporation in a few hours. Films were prepared by dip coating glass or alumina substrates into both the sols and the gels. Aerogel films with special morphology were produced for the first time by exchanging the film solvent with acetone after the dip coating, followed by supercritical drying. The morphology of the films, studied by SEM and TEM, consists of fiber-like network of round chains (N0.1/zm thick), and pores (0.1-0.5/zm in diameter). It is shown that the fibers contain a homogeneous arrangement of sol particles, 2-4 nm in size. Formation of this microstructure can be attributed to phase separation in the alumina-water-acetone system in a 2D film geometry. A conceptual model for the film development is proposed.

Comparison of the Structure and Porous Texture of Alumina Gels Synthesized by Different Methods

“…The morphology of these alumina aerogels can also be modified to a large extent. For instance, Grader et al made alumina aerogels with a fiber-like network texture by exchanging water for acetone in Yoldas type gels, followed by supercritical drying in CO 2 . Mizushima and Hori measured the evolution of the specific surface area of such aerogels during heat treatment, and they compared different types of aerogels. , Their results showed that the fibrous structure of the gels prepared by supercritical drying at high temperature (in alcohol) retards the formation of the α-alumina phase by hindering grain growth in α-alumina.…”

Sol-Gel Synthesis of Non-Silica Monolithic Materials

“…Aluminium alkoxides are very reactive and the addition of chelating agents to control both the hydrolysis and condensation rate is often required [50,51,52]. Aluminium isopropoxide and aluminium sec-butoxide, were both used to obtain high-surface-area monolithic aerogels [53,54,55,56,57,58,59]. The first gamma alumina xerogel monoliths with hierarchical porosity and hexagonally ordered mesopores within macroporous walls were prepared by Li et al [60].…”

Synthesis of low shrinkage monolith alumina aerogels by surface modification and ambient pressure drying

“…The synthesis of the alumina aerogel involves three major steps: (i) preparation of wet gel with nanoporous structure; (ii) ageing the gel to enhance the skeleton structure; and (iii) drying the wet gels to remove the trapped solvent from the pores of the gels. Supercritical drying, as a conventional method to prepare monolithic aerogel, requires high-pressure equipment with high risk and cost [17][18][19][20]. It severely restricts the industrial production of aerogel.…”