DETERMINATION OF THE SURFACE FRACTAL DIMENSION OF ACTIVE CARBONS BY MERCURY POROSIMETRY

Mercury porosimetry has been used to characterize the macroporosity of several carbon materials activated by steam or carbon dioxide and the ir surface fractal dimension is determined. The first part is devoted to the analysis of the differential volume versus pressure curves in o rder to distinguish between mechanical effects resulting from the merc ury pressure and true pore filling. It is shown, in the second part, t hat the macropore volume is not strongly affected by the activation pr ocess, but it depends mainly on the initial texture of the carbon. On the other hand, the fractal dimension varies largely with the activati on conditions and burn-off. The experimental results suggest that the fractal dimension tends to increase with the degree of burn-off in ste am, whereas the opposite occurs during activation by carbon dioxide. T hese observations are discussed in relation to the mechanisms of activ ation. (C) 1994 Academic Press, Inc.