Transient diffusion kinetics in media exhibiting axial variation of diffusion properties. Part 1.—Sorption kinetics

Abstract

Transient uni-dimensional sorption of a penetrant in a medium exhibiting a gradation in diffusion properties along the diffusion axis is considered. The effect of the mode and extent of the variation in diffusion properties on the kinetics of both ‘symmetrical’ and ‘unsymmetrical’ sorption processes is investigated systematically by numerical solution of a number of carefully chosen representative cases. A previous asymptotic analytical treatment is reconsidered, corrected where necessary, and further developed. Its practical usefulness is then assessed by comparison with the corresponding numerical results. The insight thus gained should permit a much more systematic and informative analysis of the transient sorption kinetic behaviour of experimental non-homogeneous solid–penetrant systems.