Scanning studies on capillary condensation and evaporation of nitrogen. Part 2.—Analysis of ascending and descending scanning curves within B-type hysteresis loops

Abstract

The mechanism of emptying and filling of pore domains along the adsorption as well as the desorption boundary curve of the hysteresis loop was studied by the determination of a V–S curve derived from the tangents to primary scanning curves immediately after a pressure reversal at the boundaries of the hysteresis region. In all three cases studied, the V–S curve for the desorption process exhibits a discontinuity around p_g/p₀= 0.5, pointing to a sudden breakdown of the capillary-condensed state, which is not directly related to the detailed domain properties of the system. This breakdown of the capillary-condensed state invalidates in a number of cases the usual procedures for obtaining pore size distributions. The filling of slit-shaped pores was found to proceed most probably by additional sorption of one to two nitrogen molecules between adjacent adsorbed layers.