Abstract
The following experimental approach was used to obtain nitrogen and argon standard isotherms at the boiling temperature of the adsorbates. The surface of hydrated fume silicas and silica gels of widely differing structures were covered by the densest monomolecular organosiloxy layer. The specific surface area of these surface-modified samples was obtained in two different ways. First, it was calculated by assuming the uniform globular model for the structure of the silicon dioxide starting material. Second, within a group of silicas covered by the same substituent, relative surface areas were determined by direct comparison of the adsorption isotherm of a sample with that measured on one of the silicas elected as a standard. Calculated surface areas gave excellent correlation with those obtained by direct comparison. Reference isotherms were derived by this study giving the complete information necessary for the determination of specific surface areas of powders having similar surface properties to those studied in the present work.
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