Roughness effective, solids layer

Both of these methods may be applied to nonplanar electrodes if the results are obtained at electrolysis times sufficiently short that the diffusion layer remains thin in comparison to the radius of curvature of the nonplanar electrode surface. For example, the spherical hanging-mercurcy-drop electrode provides chronoamperometric data that deviate less than 1-2% from the linear-diffusion Cottrell equation out to times of about 1 s. With solid wire electrodes of cylindrical geometry, similar conclusions apply, but at short times surface roughness effects yields a real surface area that is larger than the geometric area. 

When we consider many particles settling, the density of the fluid phase effectively becomes the bulk density of the slurry, i.e., the ratio of the total mass of fluid plus solids divided by the total volume. The viscosity of the slurry is considerably higher than that of the fluid alone because of the interference of boundary layers around interacting solid particles and the increase of form drag caused by particles. The viscosity of a slurry is often a function of the rate of shear of its previous history as it affects clustering of particles, and of the shape and roughness of the particles. Each of these factors contributes to a thicker boundary layer. 

In addition to the effect of the nonideality of the metal on the electrolyte phase, one must consider the influence of the electrolyte phase on the metal. This requires a model for the interaction between conduction electrons and electrolyte species. Indeed, this interaction is what determines the position of electrolyte species relative to the metal in the interface. Some of the work described below is concerned with investigating models for the electrolyte-electron interaction. Although we shall not discuss it, the penetration of water molecules between the atoms of the metal surface may be related3 to the different values of the free-charge or ionic contribution to the inner-layer capacitance found for different crystal faces of solid metals. Rough calculations have been done to... 

Figure 3.3. Various features of diffusion and convection associated with crystal growth in solution (a) in a beaker and (b) around a crystal. The crystal is denoted by the shaded area. Shown are the diffusion boundary layer (db) the bulk diffusion (D) the convection due to thermal or gravity difference (T) Marangoni convection (M) buoyancy-driven convection (B) laminar flow, turbulent flow (F) Berg effect (be) smooth interface (S) rough interface (R) growth unit (g). The attachment and detachment of the solute (solid line) and the solvent (open line) are illustrated in (b).

In NiV intermetallics, Ni has been identified as providing the active sites, and it has been found that the as-prepared materials are less active because they are partially passivated by surface oxides. A treatment with HF greatly improves the activity, which is mainly related to the formation of a surface porous layer enriched with Ni as proven by AES analysis (Fig. 31). However, when NiV and Raney Ni are compared, for both the activity has been found to vary proportionally to the surface roughness factor, but the specific activity is much higher for NiV [542]. This indicates that synergetic effects are real in this case this recalls the observations made in the cases of Ni—Mo and Ni—Mo-Cd solid solutions [141, 518]. 

Thus, in the metal/YSZ systems of solid-state electrochemistry, AC-impedance spectroscopy provides concrete evidence for the formation of an effective electrochemical double layer over the entire gas-exposed electrode surface. The capacitance of this metal/gas double layer is of the order of 100-500 pF cm-2 of superficial electrode surface area and of the order 2-10 pF cm-2 when the electrode roughness is taken into account and, thus, the true metal/gas interface surface area is used, comparable to that corresponding to the metal/solid electrolyte double layer. Furthermore AC-impedance spectroscopy... 

In order to understand the relevance of the surface state in the stopping power, we also present results in which the contribution of the surface state in the calculation of Xo(Qt j j is neglected (short-dashed line). In the inner part of the solid, both calculations give roughly the same values of the stopping. However, in the outer part the stopping is clearly underestimated when the effect of the surface state is not considered. Moreover, comparison between the two curves (solid and short-dashed) shows that the last maximum of the stopping obtained within the complete calculation, that appears outside the top-most layer, is due to the presence of the surface state. 

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