Contoured electrodes

Investigations are being made into alternative zinc electrode configurations. Contoured electrodes containing PTFE powder have been found to extend cell life, and the use of surface-active agents has been reported to be successful. 

Utilizing Eqs. (34) to (39) in Eq. (33), the potential energy surface for the iodide ion-iodine system as a function of distance x from the electrode and the normalized solvent coordinate qig was determined as given in Fig. 15 as a contour plot. It is observed that far from the electrode surface, the ionic and the atomic states are separated by an energy barrier... 

Figure 50. (a) Primary potential distribution surrounding a disk-shaped electrode. (Reprinted with permission from ref 47. Copyright 2004 John Wiley Sons.) (b) Finite-element calculation of the 2D primary potential profile near an electrode with regular periodic contact to the electrolyte

contour plot are lines of constant potential vertical lines follow the current path. 

It should be understood that even for micro surface features the potential is uniform and the ohmic resistance through the bath to peaks and valleys is about the same. Also, electrode potential against SCE will be uniform. What is different is that over micro patterns the boundary of the diffusion layer does not quite follow the pattern contour (Fig. 12.3). Rather, it thus lies farther from depth or vias than from bump peaks. The effective thickness, 8N, of the diffusion layer shows greater variations. This variation of 8N over a micro profile therefore produces a variation in the amount of concentration polarization locally. Since the potential is virtually uniform, differences in the local rate of metal deposition result if it is controlled by the diffusion rate of either the depositing ions or the inhibiting addition (leveling) agents. 

It was also demonstrated that ssDNA is better adsorbed onto the GC electrode than dsDNA. The dsDNA molecule has some difficulty reaching the surface contours of the rough GC electrode surface, while ssDNA can approach closer to the electrode surface because of its greater flexibility. 

Figure 3.9 Quadrupole mass analyzer with hyperbolic-shaped rods. A potential of + 0 is applied to the electrodes in the x direction and — 0 to the electrodes in the direction. The potential at the centre is zero. Equipotential contours have a hyperbolic shape.

The solid/liquid interfacial energy is reduced on applying a voltage V between the droplet and a counter-electrode below the insulator. This decreases 0and leads to improved wetting of the solid by the droplet (dashed contour) [98] (by courtesy of RSQ. 

Fig. 3. Heat production is an important consideration for devices using electric fields in the liquid near cells. This figure shows the theoretical distribution of heat production in and around a spherical cell at the centre of a quadrupole electrode chamber in a solution of low electrical conductivity (top) and high conductivity (bottom). The heat production is given by gE2 where g is the conductivity of the solution or cell component and E is the (local) electric field strength. The contour interval is 7% of the maximum in each case. The cell is modelled as an electrically conductive sphere enveloped by an insulating but capacitive membrane.

Because the generator electrodes must have a significant voltage applied across them to produce a constant current, the placement of the indicator electrodes (especially if a potentiometric detection system is to be used) is critical to avoid induced responses from the generator electrodes. Their placement should be adjusted such that both the indicator electrode and the reference electrode occupy positions on an equal potential contour. When dual-polarized amperometric electrodes are used, similar care is desirable in their placement to avoid interference from the electrolysis electrodes. These two considerations have prompted the use of visual or spectrophotometric endpoint detection in some applications of coulometric titrations. 

Formation or consumption of reacting species at the electrode surface causes concentration distribution of electroactive species in the solution phase during electrolysis. Equi-concentration contours stand for a concentration profile. A concentration profile can be measured by detecting current or potential by use of a small probe electrode at various locations near a target large electrode. A typical method is scanning electrochemical microscopy. See also diffusion layer, - scanning electrochemical microscope. 

Anodes and cathodes need not be separate electrodes but can be areas on the same piece of metal. O Halloran et al. [4] have developed a technique in which isopotential contours on the corroding electrode may be mapped (see Fig. 1). As the technique involves gathering a large number of data points, a microprocessor is used. A small reference electrode is passed across a corroding specimen close to its surface and the potential differences relative to another fixed reference electrode are recorded. The potential profile reflects the ion current density in the vicinity of the corroding surface and... 

Contour maps of apparent resistivity can be misleading. Electrode spacing should not be considered to have a linear relationship with depth of penetration. 

Figure 31. Contour projection of the 3D-adiabatic potential energy surfaces in thermodynamic equilibrium for the Volmer reaction as a function of the solvent coordinate q and the distance to the electrode dei for a Au(l 11) surface and an infinite, monoatomic Au nanowire (Data obtained from Ref 61.)... 

This has been justified by the stereochemistry of the DNA double helix in comparison with the ribbon-like feature of the ssDNA that can follow the electrode contours more easily. The roughness of a solid electrode surface also means that double helix DNA has some difficulty in following the surface contours, whereas single-stranded unwound DNA molecules fit more easily into the grooves on the surface of the electrode because of their greater flexibility. 

In the second approach, the required localization of metal dissolution is achieved by other means. Some of them were considered in the previous sections. Here, TEs of several types are used [92-97] (1) An electrode with the shape and dimensions corresponding to the required cavity in the WP (2) a TE in the form of a wire or needle, which penetrates into the WP at the expense of its local anodic dissolution and moves according to a certain program, in order to obtain a given contour and (3) a high-speed jet beam of electrolyte from a micronozzle. 

Figure 2.36 Simulations of feature filling of correspond to those anticipated for the catalyst pre-treated electrodes. Interface motion derivatization treatments specified in is displayed using colorized contour lines to Figure 2.35. The feature filling times reflect the local catalyst coverage. Each corresponding to the last growth contour are ...

As discussed in Section 4.4.1, it is possible to reduce the critical voltage by changing the wettability of the electrode-electrolyte interface, which can be achieved by adding surfactants to the electrolyte. An example is shown in Fig. 7.9(a). Liquid soap was added to 30 wt% NaOH [129]. The critical voltage is reduced from around 30 to about 14 V. The critical current density and the gas film formation time are also reduced. Machining at lower voltages becomes possible. An example of successive drillings of microholes at 20 V is illustrated in Fig. 7.9(b). Very well-defined contours are achieved. The fluctuation of the mean diameter is less than 5 Xm (computed from a set of 50 microholes), which... 

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