Pore structure analysis by water vapor adsorption. II. Analysis of five silica gels

Abstract

Complete pore structure analyses were performed for five silica gels, applying the micropore analysis method and the “corrected modelless” method, developed by Brunauer and his coworkers, to water vapor adsorption-desorption isotherms. The same five silica gels were analyzed by the same methods, using nitrogen adsorption-desorption isotherms. The cumulative pore volume and pore surface results obeyed the criteria of correct analysis both for water vapor and nitrogen, and the results obtained by the two adsorbates were in good agreement. This was possible because the entire pore system was accessible to both adsorbates. The pore volume distribution curves, however, were different for the two adsorbates, though not very different. The differences indicate that the pore structure curves are not functions of the adsorbent alone but of both the adsorbent and adsorbate. Complete micropore analysis cannot be performed when the filling of a part of the micropores occurs simultaneously with capillary condensation in some of the larger pores. A method is offered for circumventing this difficulty.