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Transport equations of electrodiffusion processes in the laboratory reference frame.

Authors
  • Garrido, Javier
Type
Published Article
Journal
The Journal of Physical Chemistry B
Publisher
American Chemical Society
Publication Date
Feb 23, 2006
Volume
110
Issue
7
Pages
3276–3280
Identifiers
PMID: 16494340
Source
Medline
License
Unknown

Abstract

The transport equations of electrodiffusion processes use three reference frames for defining the fluxes: Fick's reference in diffusion, solvent-fixed reference in transference numbers, and laboratory fluxes in electric conductivity. The convenience of using only one reference frame is analyzed here from the point of view of the thermodynamics of irreversible processes. A relation between the fluxes of ions and solvent and the electric current density is deduced first from a mass and volume balance. This is then used to show that (i) the laboratory and Fick's diffusion coefficients are identical and (ii) the transference numbers of both the solvent and the ion in the laboratory reference frame are related. Finally, four experimental methods for the measurement of ion transference numbers are analyzed critically. New expressions for evaluating transference numbers for the moving boundary method and the chronopotentiometry technique are deduced. It is concluded that the ion transport equation in the laboratory reference frame plays a key role in the description of electrodiffusion processes.

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