Effect of dehydration on porous structure of monolithic aerogels based on fibrous aluminum oxyhydroxide |
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Authors: | O K Krasil’nikova A S Pogosyan T Yu Grankina N V Serebryakova |
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Affiliation: | 1.Frumkin Institute of Physical Chemistry and Electrochemistry,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | Aluminum oxide monolithic aerogels (PMAOs) with specific surfaces of up to 400 m2/g and densities of up to 0.004 g/cm3 were obtained by the direct oxidation of metallic aluminum by water vapors. Studies of the obtained aerogels using the methods
of scanning and transmission electron microscopy showed that a freshly prepared aerogel represents the amorphous structure
from alumina fibrous with a diameter of about 5 nm. Parameters of a porous aerogel structure were determined from the isotherms
of adsorption of nitrogen vapors at 77 K. It is shown that the specific surface area decreases by 50% upon the dehydration
of aerogel by temperature pretreatment at 900°C until the phase transition temperature is reached. At the same time, heat
treatment at temperatures above 1200°C results in a phase transition at which significant contraction of structure occurs
and the specific surface area decreases to 20 m2/g. The number of primary adsorption centers was obtained from comparative plots of water vapor adsorption. It was found that
preliminary dehydration only slightly affects the number of primary centers of water adsorption. |
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