Physical adsorption of gases on porous solids. I. Comparison of loose powders and porous plugs

Abstract

For the first time, comparison has been made of adsorption on a given surface both as a free surface and as the internal surface of a porous plug. In this way it has been possible to provide direct evidence both for capillary condensation and for blockage of capillaries with adsorbed layers in porous solids. Blockage produced well-marked effects only where the surface was of the order of 1000 m. 2 /g. and the porosity was less than 0·6. Where it was observed, it was to be noted that (i) molecules tended to be attracted into blocked capillaries, producing swelling, (ii) monolayer capacities and hence surface areas determined by the B. E. T. method were values which corresponded only to the unblocked surface area when the monolayer is nearly complete. At the low-pressure end of adsorption isotherms, plug and powder gave identical results within the limits of experimental error, i. e. better than 1%, so that, until blockage or capillary condensation was manifested, the total particle surface was accessible to adsorption. In agreement with this, the total pore volume was also accessible, since the volume adsorbed at saturation was not less than the pore volume.