Fractal Surface Analysis by Using Capillary Condensation Data

Abstract

Both the Neimark equation and the recently proposed modified version (Wang and Li, Ind. Eng. Chem. Res. 1997, 36, 1598) were used to determine the surface fractal dimension D of coprecipitation methods, and low water sol−gel processes derived alumina and aluminum borate samples calcined at different temperatures. It was found that both Da (from the adsorption isotherm) and Dd (from the desorption isotherm) values obtained from the Neimark equation are larger than those evaluated from its modified version, respectively, and the scaling range, where fractal behavior is observed, of the Neimark method is smaller than that of its modified version. However, both methods indicated that thermal effects may decrease D for all examined porous samples and pointed out that Dd < Da in our samples, which is in contrast to the earlier fractal surface analysis report for some porous solids with the modified thermodynamic method (Wang and Li). The relative magnitude between Dd and Da, and then, the applicability of the relation Dreal (real surface fractal dimension) = Dm (from mercury intrusion data) − (Dd − Da) proposed by Wang and Li were discussed.