Diffusion in electrolyte solutions

Pinto-Graham Pinto and Graham studied multicomponent diffusion in electrolyte solutions. They focused on the Stefan-Maxwell equations and corrected for solvation effects. They achieved excellent results for 1-1 electrolytes in water at 25°C up to concentrations of 4M. 

It is characteristic for the actual diffusion in electrolyte solutions that the individual species are not transported independently. The diffusion of the faster ions forms an electric field that accelerates the diffusion of the slower ions, so that the electroneutrality condition is practically maintained in solution. Diffusion in a two-component solution is relatively simple (i.e. diffusion of a binary salt—see Section 2.5.4). In contrast, diffusion in a three-component electrolyte solution is quite complicated and requires the use of equations such as (2.1.2), taking into account that the flux of one electrically charged component affects the others. 

Several topics in diffusion have arbitrarily been excluded from the following discussion diffusion in electrolytic solutions (F3, G9, HI, 02, R3, Yl), diffusion in ionized gases (K4), diffusion in macromolecular systems (W2), diffusion through membranes (F14), use of diffusional techniques in isotopic separations (S18), diffusion in metals (S8), and neutron diffusion (F2, G5, H15, W15). 

Churchill, London (1946), Chapter 1 8) H.S, Harned, ChemRevs 40, 461-522 (1947) (Quantitative aspect of diffusion in electrolytic solutions) 9) R.B. Dean, ChemRevs 41, 503-23(1947) (Effects produced by diffusion in aqueous systems containing membranes) 10) D.A. Hougen K.M. Watson, "Chemical Process principles , Part 3, "Kinetics Catalysts , Wiley, NY (1947), Chap 20 11) Perry (1950), pp 522-59 (by... 

R. Mills and V.M.M. Lobo, Self-diffusion in electrolyte solutions, Elsevier, Amsterdam, 1989. 

The treatment of diffusion given in this section is valid only for the analysis of solutions in the limit of inifinite dilution. We return to the question of diffusion in several sections of this book. In Section 9.2 a simple theory of diffusion in electrolyte solutions is discussed. In Section 10.6 the coupling between diffusion and heat conduction is treated in some detail. In section 11.6 a microscopic description of diffusion is given. Finally in Sections 13.5 and 13.6 a detailed treatment of diffusion in binary and ternary solutions of nonelectrolytes and electrolytes is presented. The concentration-dependence of the diffusion coefficient is considered in Section 13.5. These sections are based on the theory of nonequilibrium thermodynamics and are thus relegated to the chapter on this subject. Particular attention should be given to these sections by any reader interested in the analysis of diffusion. 

Electrolytic solutions. Diffusion in electrolyte solutions is more complicated by dissociation of molecules into ions (cations and anions) and the resulting effects of the charge producing forces between these ions, the solution and ion clusters. 

Bernard O, Kunz W, Turq P, Blum L (1992) Self-diffusion in electrolyte solutions using the mean spherical approximation. J Phys Chem 96 398 03 Conductance in electrolyte solutions using the mean spherical approximation, ibid 96 3833-3840... 

Mills R. and Lobo V.M.M., Self-diffusion in Electrolyte Solutions, Elsevier,... 

The rotating disk electrode is becoming one of the most powerful methods for studying both diffusion in electrolytic solutions and the kinetics of moderately fast electrode reaction because the hydrodynamics and the mass-transfer characteristics are well understood and the current density on the disk electrode is supposed to be uniform. Levich [179] solved the family of equations and provided an empirical relationship between diffusion limiting current (id) and rotation rate ( >) as shown in Eq. (9.42). In particular applications in fuel cells, the empirical relationship which is given by Levich was also used in linear scan voltammetry (LSV) experiment performed on a RDE to study the intrinsic kinetics of the catalyst [151,159,180-190]. However, it is more appropriate to continue the discussion later in detail in the LSV section. 

No theory on diffusion in electrolyte solutions is capable of giving generally reliable data on D. However, for estimating purposes, when no experimental data are available, we suggest ... 

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