© A.W.Marczewski 2002

A Practical Guide to Isotherms of ADSORPTION on Heterogeneous Surfaces

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Barret-Joyner-Halenda (BJH) calculation scheme images

Barret-Joyner-Halenda scheme (1955) formula:
Barret-Joyner-Halenda scheme for k-th adsorption point
Pore 'i' filled Pore 'i+1' filled

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.
Pore 'i' filled

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.
Pore 'i+1' filled


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