Specific Surface Area of Hydrated Silicon Dioxide Measured by Chemisorption

Abstract
Various methods of specific surface area determinations have been compared: the BET-method, Sing's αs-method and the calculation from the monolayer capacity of dense chemisorbed trimethylsiloxy and (3,3-dimethylbutyl)-dimethyl-siloxy layers. It was shown that fume silicas as well as xerogels precipitated from water gave consistent results if the samples underwent a 70 h hydrothermal treatment in boiling water. The methods were calibrated on a similarly hydrated, low surface area fume silica. Slight differences in behaviour were observed between the two classes of silica. Surprisingly, the results disproved any serious dependence of the form of the nitrogen adsorption isotherm on surface curvature.