GENERAL-ASPECTS AND SURFACE-AREA IN SOLID-GAS ADSORPTION

A new form of Gibbs equation is proposed as a physical basis for the general interpretation of gas adsorption on solids. Two differential equations are defined as a mathematical basis of this approach. Both bases are defined with the help of a differential function psi(p(r)) having the form psi(p(r)) = psi(THETA) = (n(s)/p(r))/(dp(r)/dTHETA), where p(r) is the relative equilibrium pressure and n(s) is the amount adsorbed. The function psi(THETA) is the relative free energy of the surface at coverage THETA; therefore it characterizes the adsorption processes better than the measured isotherms themselves. This statement is especially valid for the type I isotherm, i.e. calculation of the function psi(p(r)) is unavoidable if one is to select the physically and mathematically appropriate isotherm equation. The function psi(p(r)) is also indispensible for the calculation of the specific surface area from type I and type II isotherms. The function can determine the multilayer plateau in the type I isotherms and can also distinguish the monolayer and multilayer domains of the type II isotherms.