The Characteristic Curve in Physical Adsorption

Abstract

The concept of the characteristic curve in physical adsorption and the rule of its temperature invariance is traced from the potential theory of adsorption by Polanyi to the Frenkel–Halsey–Hill equation, the theory of volume filling of micropores by Dubinin et al. and the theory of adsorption on heterogeneous surfaces. A computer simulation of an irregular atomic configuration at the surface of amorphous carbon is presented. In the submonolayer region, the isotherms of argon adsorption simulated on that surface are shown to correspond to the Freundlich equation and are close to the experimental isotherms on a diamond dust sample. Simulated isosteric heats of adsorption are also reasonably close to the experimental data for argon on a real carbon black. The BET C constant for the simulated isotherm is lower than for the real isotherm on untreated carbon black. However, the isotherms at two temperatures can be described by one absolute isotherm of adsorption.