© A.W.Marczewski 2002
A Practical Guide to Isotherms of ADSORPTION on Heterogeneous Surfaces
Barret-Joyner-Halenda scheme (1955) formula:
The "adsorbed"/"desorbed" amount is the sum of adsorption/desorption from open pores and evaporation from/condensation in the pores changing their state between being filled-up and containing only adsorbed film (compare Figs. below)
The smallest pore is already filled up (or still filled-up if you are on desorption isotherm branch), other pores contain some adsorbate as an adsorbed liquid film with thickness given by a full equation (both meniscus radius and pressure dependent) or a simplified one (only pressure dependence up to condensation / below evaporation point) - e.g. HJ or FHH.
The smallest and medium sized pores are already filled up (or still filled-up if you are on desorption isotherm branch), larger pores contain some adsorbate as an adsorbed liquid film with thickness given by a full equation (both meniscus radius and pressure dependent) or a simplified one (only pressure dependence up to condensation / below evaporation point) - e.g. HJ or FHH.
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