Sorption and dielectric behaviour of benzene on silica gel

Abstract

Sorption isotherms have been determined for nitrogen (–195°) and benzene (25°) on a purified commercial “chromatographic” silica gel. Their analysis indicated a distribution of pore radii mostly within the range 16–56 Å, with less than 8 % of the specific surface (355 m²/g) contributed by micropores of width < 7 Å.

The dielectric isotherm (1 Mc/sec, 25°) for benzene comprised three linear regions. The first extended from close to the origin to the B.E.T. monolayer value a_m, and was thus associated with monolayer adsorption. The second linear region was of lower slope than the first and corresponded to capillary condensation in the smaller pores, following monolayer completion. A third linear region, of intermediate slope between those of the first and second regions, occurred at an amount adsorbed close to 2a_m, and has been associated with capillary condensation in wider pores, after the adsorbed film is two layers thick.