Abstract
The pyrolysis of the surface-treated silica gels with several alcohols, whose surfaces had been confirmed to have a hydrophobic nature, was studied by the analysis of the vapors evolved at each temperature up to 800°C through the Quadru Pole Mass Spectrometer. It was found that the pyrolysis of the surface group was performed at 450°C and the silica gels thus thermally decomposed reverted to a hydrophilic nature. The surface area of the original silica gel activated at the temperature up to 500°C was found to be invariant, whereas that of the silica gels activated at higher temperature decreased by the sintering or solidification with increasing temperature. The silica gel activated at 1000°C had a quarter of the surface area of the original silica gels. The surface area of silica gels treated with the alcohols was small in comparison with that of original silica gels, but it increased after the activation at 250°and 350°C. When these surface-treated silica gels were heated at 450°C, they had the nearly same surface area as the one of original silica gel. The argon adsorption isotherms at 77°K on these silica gels showed a good agreement with the one of the original silica gel over whole range of relative pressure. Therefore it was considered that the geometric surface structure like pore of the substrate was invariant through the surface-treatment, and the nature of the surface of silica gel was changed from hydrophilic to hydrophobic through these treatments.
