Diffusion ionic

In theory, diffusion coefficients can be measured for any ion. In practice, however, most studies of ionic diffusion in glasses have been restricted to highly mobile ions which have a convenient radioactive isotope for use in tracer measurements. As a result, a majority of the data for ionic diffusion deals with sodium, with lesser amounts of data for potassium, rubidium, and cesium. Studies of lithium are very limited due to the lack of a radioactive isotope of lithium, while studies of divalent and other, more highly charged, ions are restrieted by the very low mobilities of these ions as compared to those of the monovalent ions. 

Diffusion of an ion which is a primary component of a glass, as discussed above, is termed self-diffusion. We can also measure diffusion of an ion which is not present in the glass, e.g., potassium diffusion in a sodium silicate glass. The results of such measurements for a set of R20-3Si02 glasses, where R is Na, K, Rb, or Cs, reveals that the diffusion coefficient is always greatest for the ion which is the component of the glass. The diffusivity of the impurity ions decreases as the difference 

Addition of a divalent modifier such as Ca to a sodium silicate glass decreases the diffusivity of Na ions. The much less mobile divalent ions occupy interstices in the network and block the diffusion of the more mobile monovalent ions. This effect on diffusivity is at least partially responsible for the improvement in chemical durability of alkali silicate glasses which occurs when alkaline earth oxides are added to the composition. 

Electrochemical impedance spectroscopy (EIS) was used for the characterization. The results showed that a great amount of the lithium ions remains on the solid electrolyte interphase layer of the mesocarbon microbeads half ceU with fluoro-o-phenylenedimaleim-ide additive, indicating that the ion moves easily because of high diffusion (32). 

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G. H. Frishat, Ionic Diffusion in Oxide Glasses Trans Tech Pubbcations, Bay Village, Ohio, 1975. 

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...

An example of a journal hovering between broad and narrow spectrum is Journal of Alloys and Compounds, subtitled an interdiciplinary journal of materials science and solid-state chemistry and physics. One which is more restrictively focused is Journal of Nuclear Materials (which I edited for its first 25 years). Ceramics has a range of journals, of which the most substantial is Journal of the American Ceramic Society. Ceramics International is an example of an international journal in the field, while Journal of the European Ceramic Society is a rather unusual instance of a periodical with a continental remit. More specialised journals include Solid State Ionics Diffusion and Reactions, and a new Journal of Electroceramics, started in 1997. 

G. Schulz, M. Martin. Computer simulations of pattern formation in ionconducting systems. Solid State Ionics, Diffusion and Reactions 101-103AM,... 

The data given should serve only as reference values following the rule, the higher the ionic potential, the thicker the hydration layer of the water molecules around the ion, and the slower the ionic diffusion. Cations generally diffuse more rapidly than anions. 

Home, R. A., Day, A. F., and Young, R. P. (1969). Ionic diffusion under high pressure in porous solid materials permeated with aqueous, electrolytic solution. /. Phys. Chem. 73,2782-2783. 

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) ... 

The quantity D, cannot be derived from molecular diffusivities at infinite dilution the calculated ionic diffusivity of Cu2+ is approximately 20% lower than the molecular diffusivity of CuS04. 

Effective ionic diffusivities at a rotating-disk electrode are calculated from the Levich equation as derived for constant physical properties, used here in inverted form ... 

The use of excess inert electrolyte so as to reduce differences in transport properties of the solution at the electrode surface and in the bulk. In such a solution, the ionic diffusivity of the reacting ion, for example, Cu2 + or Fe(CN)g, should be employed in the interpretation of results, and not the molecular diffusivities of the compounds, for example, CuS04 or K3Fe(CN)6. 

Table VII should be 1.939 for the ratio k = 0.5. Part of the 17% discrepancy between the results of Lin et al. (L9) and Eq. (27) may be ascribed to the use of incorrect diffusivities. An estimate of the errors is possible for part of their experiments. The value of the product nD/T of K3Fe(CN)6 based on the electric mobility at infinite dilution as used by Lin et al. is 11% too high, according to more recent measurements of the effective ionic diffusivity of Fe(CN)(% by Gordon et al. (G5). Similarly, the mobility product of K4Fe(CN)6 is 16% too high, and that of 02 no less than 26% too high, compared with data of Davis et al. (D7) (see Table III). According to Eq. (27) the value of D would have to be 27% too high to account fully for a coefficient that is 17% too high consequently, the discrepancy cannot be attributed entirely to incorrect diffusivities.

Diffusion in solution is the process whereby ionic or molecular constituents move under the influence of their kinetic activity in the direction of their concentration gradient. The process of diffusion is often known as self-diffusion, molecular diffusion, or ionic diffusion. The mass of diffusing substance passing through a given cross section per unit time is proportional to the concentration gradient (Fick s first law). 

If both ionic conductivity and ionic diffusion occur by the same random-walk mechanism, a relationship between the self-diffusion coefficient, D, and the ionic... 

The fluoride ion interstitials again lead to an increase in ionic conductivity. At lower temperatures this increase is modest because the interstitials aggregate into clusters, thus impeding ionic diffusion. At higher temperatures the clusters tend to dissociate, resulting in a substantial increase in conductivity. 

It 1s well known that water absorption bears a direct relation with the number of polar groups in the polymer and that Ionic diffusion occur via "hopping" along hydrophilic sites. Therefore, the hydrophilic/ hydrophobic characteristics of the Inhibitor exert a profound effect on dissolution rate. 

Figure 10. Three-dimensional AFM images of (a) Pt/polished AI2O3, (b) Pt/etched Ni, and (c) Pt/unpolished AI2O3 electrodes. Reprinted from J. -Y. Go et al., A study on ionic diffusion towards self-affine fractal electrode by cyclic voltammetry and atomic force microscopy, J. Electroanal. Chem., 549, p. 49, Copyright 2003, with permission from Elsevier Science.

Then, ionic diffusion towards self-affine fractal electrode was experimentally investigated by using cyclic voltammetry in a mixture of 30 wt % glycerol and 70 wt % (0.01 M K4[Fe(CN)6] + 0.5 M Na2S04) solution. The cyclic voltammograms obtained... 

In summary, from the above theoretical and experimental results, it is concluded that ionic diffusion towards self-affine fractal electrode should be described in terms of the apparent selfsimilar fractal dimension rather than the self-affine fractal dimension. In addition, the triangulation method is one of the most effective methods to characterize the self-similar scaling property of the self-affine fractal electrode. 

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