Monolayer Adsorption of Ar and Kr on Graphite: Theoretical Isotherms and Spreading Pressures

✍ Scribed by A. Mulero; F. Cuadros

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 174 KB
• Volume: 186
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1996.4622

✦ Synopsis

cients do not depend on temperature and density, are desir-The validity of analytical equations for two-dimensional fluids able. Steele's theory (3) is a first approach to make a molecuin the prediction of monolayer adsorption isotherms and spreading lar description of a well-defined but oversimplified represenpressures of rare gases on graphite is analyzed. The statistical tation of monolayer films of simple fluids physically mechanical theory of Steele is used to relate the properties of the adsorbed onto perfectly flat surfaces. Steele used statistical adsorbed and two-dimensional fluids. In such theory the model of mechanics and introduced the so-called ''two-dimensional'' graphite is a perfectly flat surface, which means that only the first approximation: the surface is sufficiently uniform and the order contribution of the fluid-solid interactions are taken into temperature sufficiently high for the adsorbed fluid moleaccount. Two analytical equations for two-dimensional Lennardcules to be completely mobile in two dimensions, i.e., the Jones fluids are used: one proposed by Reddy-O'Shea, based in the fit on pressure and potential energy computer simulated re-vibrational motion (perpendicular to the surface) of the adsults, and other proposed by Cuadros-Mulero, based in the fit of sorbed molecules is negligible. By neglecting the second the Helmholtz free energy calculated from computer simulated and higher terms of the periodicity of the fluid-solid interacresults of the radial distribution function. The theoretical results tions, Steele obtained the theoretical perfectly-mobile-adare compared with experimental results of Constabaris et al. sorption isotherm equation (4), (J. Chem. Phys. 37, 915 (1962)) for Ar and of Putnam and Fort (J. Phys. Chem. 79, 459 (1975)) for Kr. Good agreement is found using both equations in both cases.