Kinetics surface versus transport control

Guy, Ch. and Schott, J. (in press), Multisite Surface Reaction versus Transport Control during the Hydrolysis of a Complex Oxide, Chem. Geol. Kinet. (spec, issue). 

Erosion is typically characterized by either occurring on the surface or in the bulk. Surface erosion is controlled by the chemical reaction and/or dissolution kinetics, while bulk erosion is controlled by diffusion and transport processes such as polymer swelling, diffusion of water through the polymer matrix, and the diffusion of degradation products from the swollen polymer matrix. The processes of surface and bulk erosion are compared schematically in Fig. 1. These two processes are idealized descriptions. In real systems, the tendency towards surface versus bulk erosion behavior is a function of the particular chemistry and device geometry (Tamada and Langer, 1993). Surface erosion may permit the... 

Fig. 2.3 Rate-limiting steps in mineral dissolution (a) transport-controlled, (b) surface reaction-controlled, and (c) mixed transport and surface reaction control. Concentration (C) versus distance (r) from a crystal surface for three rate-controUing processes, where is the saturation concentration and is the concentration in an infinitely diluted solution. Reprinted from Sparks DL (1988) Kinetics of soil chemical processes. Academic Press New York 210 pp. Copyright 2005 with permission of Elsevier...

The multiphasic nature of the intra-particle diffusion plot confirms the presence of both surface and pore diffusion. In order to predict the actual slow step involved, the kinetic data were further analysed using Boyd kinetic expression. Equation A.22 was used to calculate B( values at different time t. The linearity of the plot of B( versus time was used to distinguish whether surface and intra-particle transport controls the adsorption rate. It... 

FIG. 37 Kinetics of irreversible adsorption under the diffusion controlled transport at a planar surface expressed as the versus (t/tch) dependencies (where t = l/(Sgit ) D is the... 

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