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Preparation of Alumina Aerogel Films by Low Temperature CO2 Supercritical Drying Process 总被引:1,自引:0,他引:1
G.S. Grader Y. Rifkin Y. Cohen S. Keysar 《Journal of Sol-Gel Science and Technology》1997,8(1-3):825-829
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 (≈0.1 μm thick), and pores (0.1–0.5 μm 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. 相似文献
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Keysar S. Cohen Y. Shagal S. Slobodiansky S. Grader G.S. 《Journal of Sol-Gel Science and Technology》1999,14(2):131-136
Alumina gels were synthesized by catalyzed gelation of aluminum sec-butoxide (ASB) via the Yoldas process. The gels were aged for up to 6 months and then supercritically dried (SCD) with CO2. The molar ratio of acid to ASB was in the range of 0.01–0.6. Viscosity measurements of the gels showed a shear thinning and plastic behavior with no response up to a limiting yield stress. The gel rheology obeys the Casson model. Analysis of the viscosity as a function of the acid to alkoxide molar ratio, showed that the average molecular weight of the gels is inversely proportional to the acid to alkoxide molar ratio.The viscosity of all the gels increased with aging time for a period of about 6 months reaching an asymptotic value after 1–2 weeks. The viscosity is shown to correlate with the microstructure of these nanomaterials during aging. Aging gives rise to a nearly constant surface area of 350 m2/g regardless of acid to alkoxide ratio in an aging period of about 6 months. 相似文献
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