paper presents a study of the interaction of water vapor with Silica is an important component of thermal insulation used in a thermally cycled silica.
aerospace transport vehicles. Although normally hydrophilic and
Hydrophobicity and wetting of surfaces are the results of requiring rewaterproofing after flight, silica insulation has been attractive forces between the solid surface and water (4).
reported to become hydrophobic on heating and cooling in a vac-Silica surfaces consist of different functional groups. A numuum and, therefore, potentially hydrophobic after reentry. To unber of articles (5, 6) have shown that some of these, the derstand and model these processes, the rates of desorption and hydroxyl functional groups, play a major role in the hydroadsorption of water on silica were studied by thermogravimetry, phobicity of the surfaces. Silica surfaces, like those of other Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy. Silica powders with a high surface area were heated oxides, are normally hydrophilic, but can be treated chemiin vacuo in the temperature range 200-1000ΠC, infrared abcally or exposed to high temperatures to dehydroxylate. Such sorbance spectra were obtained at various temperatures, and surtreated surfaces will be hydrophobic for a time depending face structure was examined by X-ray photoelectron spectroscopy. on their environment. This is due to the interaction between A kinetic sorption model was developed based on a Langmuir rate water and surface hydroxyl groups. The interaction of water expression. Activation energies for adsorption and desorption were and hydroxyl groups on silica surfaces has been the focus determined by fitting the experimental results numerically. The of several studies (6-9). It has been proposed that under study found adsorption of water on the heat-treated silica occurs normal atmospheric conditions silica surfaces have mainly within seconds, implying hydrophobicity is lost rapidly after the two types of hydroxyls as silanol groups: free-vibrational heat-treated silica is exposed to water.