Ionic diffusion coefficients

First, when a large excess of inert elec trolyte is present, the electric field will be small and migration can be neglected for minor ionic components Eq. (22-19) then applies to these minor components, where D is the ionic-diffusion coefficient. Second, Eq. (22-19) apphes when the solution contains only one cationic and one anionic species. 

Figure 5.4 The intrinsic conduction electron concentration as a function of temperature and band gap energy together with the values of the ionic diffusion coefficient which would provide an equal contribution to the conduction...

Nemst, 1888). This eqnation is valid in dilnte solntions. An analogous equation including activity coefficients can be derived, bnt for the reasons outlined above, it again is not sufficiently accnrate in describing the experimental data in concentrated soluhons. Equahon (4.6) is of great valne becanse it can be nsed to evaluate ionic diffusion coefficients from valnes of Uj which are more readily measnred. 

The diffusive and convective terms in Eq. (20-10) are the same as in nonelectrolytic mass transfer. The ionic mobility Uj, (g mol cm )/(J-s), can be related to the ionic-diffusion coefficient D, cmVs, and the ionic conductance of the ith species X, cmV(f2-g equivalent) ... 

Noda, A., Hayamizu, K., and Watanabe, M., Pulsed-gradient spin-echo H and NMR ionic diffusion coefficient, viscosity and ionic conductivity of non-chloroaluminate room-temperature ionic liquids, /. Phys. Chem. B, 105, 4603,2001. 

In this chapter we deal with the ionic diffusion coefficient, the ionic association, and the interaction between ions in ionic liquids. We employ self-diffusivity to interpret the ionic transport behavior and aim at evaluating the ionicity and the ionic states of the ionic liquids. 

In most investigations where gas absorption takes place into a liquid containing several species of ions, the investigators have ignored the need to use ionic diffusion coefficients. The relationships presented above should, of course, be used only in the absence of experimental data. A comprehensive tabulation of experimentally measured diffusivities for electrolytes has been presented by Robinson and Stokes (R12). 

Recently, several interesting studies of the electrochemical properties of electrodes coated with thin films of Nafion have been reported. These chemically modified electrodes are prepared using low-EW polymers which are alcohol soluble, or using a solution of a 1100-EW polymer which has been dissolved at high pressure and temperature. Electrochemical studies for cations such as the Ru(bpy)3 couple yielded estimates of ionic diffusion coefficients in the polymer films. However, results also indicate that these films are far more porous than conventional Nafion membranes, so it is not possible to compare values directly with those discussed above. 

Figure 15 shows the change in the ionic diffusion coefficients of tetra-alkylammonium ions in strong acid cation resins as a function of mean effective pore diameter of the resins.l As the pore diameter is increased, the penetrability of the resins with respect to the large ions also increased. 

Membrane Diffusion in Dilute Solution Environments. The measurement of ionic diffusion coefficients provides useful information about the nature of transport processes in polymer membranes. Using a radioactive tracer, diffusion of an ionic species can be measured while the membrane is in equilibrium with the external solution. This enables the determination of a selfdiffusion coefficient for a polymer phase of uniform composition with no gradients in ion or water sorption. In addition, selfdiffusion coefficients are more straightforward in their interpretation compared to those of electrolyte flux experiments, where cation and anion transport rates are coupled. 

The temperature and viscosity dependence of the ionic diffusion coefficient can be estimated from... 

This system is the Na-K chabazite system, which was studied in detail by them (20). The results computed using the extended theory of Brooke and Rees disagree badly with their experimental results. The Helfferich-Plesset equation disagrees just as badly. Brooke and Rees have themselves suggested that in addition to the variation of ionic activities, the variation of ionic diffusion coefficients with concentration must be considered, and perhaps water transport. 

Here, the ionic diffusion coefficient of Cl—, D, is equal to the ionic diffusion coefficient of K+, D+, and hence to the electrolyte diffusion coefficient, D of KCI. The boundary conditions for the solution of Equation 6 are... 

This is the rule by which the individual ionic diffusion coefficients combine to yield the diffusion coefficient of the electrolyte. The oo superscript emphasizes that the relation is correct only at infinite dilution. 

It is possible to show that, if one considers the correct description of ionic diffusion coefficient suction of a crystal, the value obtained for the ionic coefQcient on the surface is abnormally high in the nanoscale compared with the microscale... 

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