FRACTAL SURFACE-ANALYSIS BY USING CAPILLARY CONDENSATION DATA

Both the Neimark equation and the recently proposed modified version ( Wang and Li, Ind. Eng. Chem. Res. 1997, 36, 1598) were used to determi ne the surface fractal dimension D of coprecipitation methods, and low water sol-gel processes derived alumina and aluminum berate samples c alcined at different temperatures. It was found that both D-a (from th e adsorption isotherm) and D-d (from the desorption isotherm) values o btained from the Neimark equation are larger than those evaluated from its modified version, respectively, and the scaling range, where frac tal behavior is observed, of the Neimark method is smaller than that o f its modified version. However, both methods indicated that thermal e ffects may decrease D for all examined porous samples and pointed out that D-d < D-a in our samples, which is in contrast to the earlier fra ctal surface analysis report for some porous solids with the modified thermodynamic method (Wang and Li). The relative magnitude between D-d and D-a, and then, the applicability of the relation D-real (real sur face fractal dimension) = D-m (from mercury intrusion data) - (D-d - D -a) proposed by Wang and Li were discussed.