Langmuir adsorption, the gibbs adsorption isotherm, and interfacial kinetics in liquid metal systems

Abstract

The adsorption of strongly surface active solutes is considered in terms of the ideal site-fillageor Langmuir isotherm. The resulting equation for the depression of surface tension of a liquid metal by such a solute is σ P −σ = RTΓ i Emphasis>/o In (1 +Ka i) where σ p − σ is the depression of surface tension of the pure liquid metal, Γ i Emphasis>/o is the saturation coverage by the solute,a i is the bulk activity of the solute, andK is a coverage independent adsorption coefficient. The isotherm is found to give a very good description of the available data for Group VI solutes on several metals. The derived values of the adsorption coefficient are applied to several kinetic studies and they are found to give good relative and possibly absolute measures of the interference by such solutes on interfacial reaction rates. The iron-sulfur system appears to differ, but only by a factor of two. The application of these adsorption coefficients in aiding the interpretation of kinetic studies is considered.