Silver diffusion coefficient

Table 3. Silver diffusion coefficients DAg-10 , m /s in AgAu-alloys calculated for solid-phase and mixed kinetics for an ideally smooth and rough electrodes...

Very low values of the silver diffusion coefficient, typical for the selective dissolution of Agl5Au and Ag20Au alloys at 298 K, provide so small displacement of the diffusion front in the solid phase during obtaining the potentiodynamic dependencies that this front repeats in fact the electrode surface microrelief Therefore, the voltammetric peak current is directly proportional to the roughness factor. 

The diffusion coefficient of oxygen in solid silver was measured with a rod of silver initially containing oxygen at a conceim ation cq placed end-on in contact with a calcia-zirconia electrolyte and an Fe/FeO electrode. A constant potential was applied across dre resulting cell... 

The experimental value for Agl is 1.97 FT cirT1 [16, 3], which indicates that the silver ions in Agl are mobile with nearly a thermal velocity. Considerably higher ionic transport rates are even possible in electrodes, by chemical diffusion under the influence of internal electric fields. For Ag2S at 200 °C, a chemical diffusion coefficient of 0.4cm2s, which is as high as in gases, has been measured... 

In the first case, the rate of deposition depends on the equilibrium concentration of ad-atoms, on their diffusion coefficient, on the exchange current density and on the overpotential. In the second case, the rate of deposition is a function, besides of the geometric factors of the surface, of the exchange current and the overpotential. This mechanism is valid, for example, in the deposition of silver from a AgN03 solution. 

A Goldberg, W Higuchi. Improved method for diffusion coefficient determinations employing the silver membrane filter. J Pharm Sci 57 1583, 1968. 

The diffusion coefficients of palladium in a Pd-Ag alloy and silver in a range of Pd-Ag alloys are known, and the diffusion of palladium and silver atoms in a 20% Pd-Ag alloy was calculated (30) for t = 3600 sec representing the film preparation time. At temperatures of 100°, 200°, 300°, and 400°C, silver atoms would diffuse in this time distances of 3 X 10-4, 0.15, 9, and 150 A, respectively whereas at the corresponding temperatures, palladium atoms would diffuse 26, 460, 3000, and 11,000 A. Palladium atoms can thus penetrate the alloy lattice at moderate temperatures, whereas silver atoms have a probability of diffusing distances equivalent to a few unit cells only when the substrate temperature is greater than 300°-400°C. 

Figure 4.42 Self-diffusion coefficient in single and polycrystalUne silver, illnstrating the effect of grain boundary diffnsion, especially at lower temperatnres. From K. M. RaUs, T. H. Conrtney, and J. Wulff, Introduction to Materials Science and Engineering. Copyright 1976 by John Wiley Sons, Inc. This material is nsed by permission John Wiley Sons, Inc.

Another type of apparently pseudo -reference electrode involves the use of A1 wires in contact with solutions containing AlCb ions [41], A further group of researchers simply use conventional aqueous solution-based calomel or silver/silver chloride/aqueous chloride ion reference electrodes [42-44], These are included in Table 11.1 for illustration and completeness. The use of such electrodes is highly likely to lead to the introduction of water into the RTIL system in contact with the reference electrode, as well as to unknown problems in respect of LJPs. Properties such as voltammetric windows, diffusion coefficients and RTIL viscosity are all likely to be highly sensitive to trace amounts of water [45]. 

Figure 4.6. Normalized autocorrelation function. Autocorrelation function for collagen single molecules. The autocorrelation function G(nAt) is normalized by dividing all points by the first experimental point G(l). The autocorrelation function decays to a value of the average squared intensity of scattered light divided by G(l). The average squared intensity is proportional to the weight average molecular weight, whereas the rate of decay is related to the translational diffusion coefficient. Reproduced from Silver, 1987.

Figure 4.7. Determination of translational diffusion coefficient. Plots of ln[(G(nAf))/B) - 1] versus time for collagen a chains (top) and mixtures of a chains and P components (bottom). The translational diffusion coefficient is obtained by dividing the slope of each line by -2Q2, where Q is the scattering vector. B is the baseline of the autocorrelation function. Note for single molecular species, the slope is constant, and for mixtures with different molecular weights, the slope varies (molecular weight for a chains is 95,000 and for y components is 285,000). (reproduced from Silver, 1987).

Table 4.3. Determination of translational and rotational diffusion coefficients for connective tissue macromolecules from quasi-elastic light scattering reproduced from Silver, 1987...

Figure 4.10. Theoretical dependence of translational diffusion coefficient of rods on location of bends. Theoretical relationships shown between translational diffusion coefficient (a), particle scattering factor at a scattering angle of 175.5° (b), and bend angle obtained using bead model with bends at ID and 2D from the end. Points above horizontal lines shown for D o,w and P(175.5°) are significantly different from those values for a straight rigid rod. The total rod length is 4.41). (reproduced from Silver, 1987).

Quantitative measurements of diffusion coefficients under bombardment, made recently, substantiate the existence of an enhancement. In lead (122a), a flux of 3 x lO a cm 2 sec i increased the self-diffusion coefficient by a factor of about 100 at 20° and 10 at 40°. The effect was a dynamic one, not the result of permanent damage, since the original rate was again observed after the radiation source was removed. Heit-kamp, Biermann, and Lundy (122b) found an increase in the diffusion coefficient of lead in silver under alpha bombardment, and the increase agrees satisfactorily with that for lead in lead. Thus a flux of 1 X lO i cm 2 sec i gave rise to an 8.8% increase in diffusion coefficient for lead in silver at 438°, and one of 3 x lO o to an increase of 3.3% for lead in lead at 84°. 

The fastest diffusing substance in alumina is hydrogen (H2). Fast-diffusing cations are sodium, copper, silver, with hydroniums (H30+) the fastest of these monovalent cations. Many other di- and trivalent cations have diffusion coefficients intermediate between these fast-diffusing ions and the slowest diffusers, the lattice elements aluminum and oxygen, which have about the same diffusion coefficients. 

Kholyavenko and Rubanik (143) investigated the effect of internal diffusion on the ethylene oxidation rate, using the diaphragm method, and calculated the effective diffusion coefficients for ethylene and carbon dioxide diffusing through a silver diaphragm. 

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