PREPARATION OF ALUMINA AEROGEL FILMS BY LOW-TEMPERATURE CO2 SUPERCRITICAL DRYING PROCESS

Alumina aerogel thin films were formed by a new synthesis route. Sols were prepared by the Yoldas process. Gels were formed by sol evaporati on in a few hours. Films were prepared by dip coating glass or alumina substrates into both the sols and the gels. Aerogel films with specia l morphology were produced for the first time by exchanging the film s olvent with acetone after the dip coating, followed by supercritical d rying. The morphology of the films, studied by SEM and TEM, consists o f fiber-like network of round chains (similar to 0.1 mu m thick), and pores (0.1-0.5 mu m 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 al umina-water-acetone system in a 2D him geometry. A conceptual model fo r the film development is proposed.