STRESSES AND STRAINS IN ADSORBENT–ADSORBATE SYSTEMS: V. THERMODYNAMIC THEORY OF ADSORPTION-EXTENSION PHENOMENA

Abstract

The extensive thermodynamic variables of solids having large surface–volume ratios are usually not homogeneous functions of first degree in one another. In such systems mutual thermodynamic field potentials usually exist as between surface and interior regions. In general, mutual Helmholtz field potentials are not additive. When the lack of additivity of the Helmholtz potentials in adsorbate–adsorbent systems is independent of the quantity adsorbed, the changes in potentials of adsorbent and of adsorbate, due to adsorption, are additive and the equilibrium resembles the equilibrium of purely mechanical stresses. In such cases the adsorption potential is measured largely by the partial reversible relaxation of compressive and shear self-strain potentials of the solid adsorbent.