Mechanisms of the Volume Filling of Micropores during the Adsorption of Vapours

Abstract

The fundamental equation for the pressure p^al of the adsorbed phase is derived by the thermodynamic treatment of micropore volume filling (MVF) process which also takes into account the structural changes of the adsorbate in the field of adsorption forces. The introduction of the principle of hydro-dynamical and mechanical equilibria reveals that MVF mechanisms can be characterized and classified according to the values of the pressures p_f^al corresponding to the beginning of MVF. The values of these pressures are calculated on the basis of experimental measurements of the length changes of the adsorbent rods during vapour adsorption. It is concluded, that the validity of the potential theory for MVF is based on the equality of the p_f^al and the standard liquid state p_o^l pressures (mechanism MVF 1). The existence of negative pressures p^al is typical for the MVF 2 mechanism. The positive values of p_f^al are characteristic for the intrusion of liquids into the micropores of solids, not wetted by the liquid (mechanism MVF 3).