The permeation of hydrogen and nitrogen through a metal wall is analyzed for the case where surface adsorption is rate limiting in addition to volume diffusion. By applying equilibrium thermodynamics plus a minimum of kinetic theory, an expression is derived for steady state permeation. The expression reduces to the familiar Richardson equation in the limit of negligible surface resistance. In addition, unsteady permeation with slow adsorption is examined by solving appropriate finite difference equations. The results accurately predict anomalies commonly encountered in permeation and diffusion data at low temperatures and pressures, e.g., thepnanomaly wherengsim;1/2, curvature or droop in Arrhenius plots, and anomalously low diffusivities. The analysis is useful not only in understanding the influence of surface effects on permeation, but also in applying permeation membranes to the study of surface phenomena.
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