Potential Helmholtz double layer

Part of the forces determining the formation of an apatite crystal are ionic in nature. In the interior of the crystals, the charges carried by each ion are neutralized by those carried by ions of opposite charge. In contrast, the charges of the surface ions are not neutralized, at least not by ions constitutive of the apatite crystal. When the crystal is suspended in water, a double-layer potential (Helmholtz double layer) develops at the solid-liquid boundary. The field surrounding each crystal can be divided into two different compart-... 

The potential for electrochemical corrosion in a boiler results from an inherent thermodynamic instability, with the most common corrosion processes occurring at the boiler metal surface and the metal-BW interface (Helmholtz double layer). These processes may be controlled relatively easily in smaller and simpler design boilers (such as dual-temperature, LPHW heating, and LP steam boiler systems) by the use of various anodic inhibitors. 

The potential between the Helmholtz double layer of a charged particle. Important for assessing the suitability of polyelectrolyte chemicals because it can be easily measured, unlike some other electrokinetic forces. 

On the basis of this argument, the mechanism for the current oscillation and the multilayer formation can be explained as follows. First note that U is kept constant externally with a potentiostat in the present case. In the high-current stage of the current oscillation, the tme electrode potential (or Helmholtz double layer potential), E, is much more positive than U because E is given hy E=U —JAR, where A is the electrode area, R is the resistance of the solution between the electrode surface and the reference electrode, andj is taken as negative for the reduction current. This implies that, even if U is kept constant in the region of the NDR, is much more... 

For moderately doped substrates, when the surface is free of oxide the change of potential is mostly dropped in the space charge layer and in the Helmholtz double layer. The reactions are very sensitive to geometric factors. The reaction that is kinetically limited by the processes in the space charge layer is sensitive to radius of curvature, while that limited by the processes in the Helmholtz layer is sensitive to the orientation of the surface. Depending on the relative effect of each layer the curvature effect versus anisotropic effect can vary. 

In the non-steady state, changes of stoichiometry in the bulk or at the oxide surface can be detected by comparison of transient total and partial ionic currents [32], Because of the stability of the surface charge at oxide electrodes at a given pH, oxidation of oxide surface cations under applied potential would produce simultaneous injection of protons into the solution or uptake of hydroxide ions by the surface, resulting in ionic transient currents [10]. It has also been observed that, after the applied potential is removed from the oxide electrode, the surface composition equilibrates slowly with the electrolyte, and proton (or hydroxide ion) fluxes across the Helmholtz layer can be detected with the rotating ring disk electrode in the potentiometric-pH mode [47]. This pseudo-capacitive process would also result in a drift of the electrode potential, but its interpretation may be difficult if the relative relaxation of the potential distribution in the oxide space charge and across the Helmholtz double layer is not known [48]. 

Fig. 4E Charge transfer across the Helmholtz double layer. The reactant is at the potential ( ), the product is at a potential (j) and the activated complex is at an intermediate position where the...

During anodic dissolution, the applied potential is partitioned between the space charge layer in the semiconductor, C/jc and the Helmholtz double layer, C/h ... 

Numerous models of the electrode-electrolyte interface have been developed. The simplest of these is the Helmholtz double-layer model, which posits that the charge associated with a discrete layer of ions balances the charge associated with electrons at the metal surface. The Helmholtz double-layer model predicts incorrectly that the interfacial capacitance is independent of potential. Nevertheless, cvurent models of the charge redistribution at electrode-electrolyte interfaces owe their terminology to the original Helmholtz model. 

FIGURE 1.3. Schematic illustration of the double layers in the semiconductor/electrolyte interface at an equilibrium condition. K is the potential drop across the space charge layer and Vh is the potential drop across the Helmholtz double layer. After Morrison. " ... 

The shift of the Mott-Schottky curve was explained by a trapping of electrons in surface states which leads to a change of the potential across the Helmholtz double layer by A(A( ). We have then according to Eq. (5.49)... 

If the moving colloidal particle is assumed to be cylindrical in shape, surrounded by a Helmholtz double layer, as shown in Fig. 12, and is situated in a motionless liquid in which there is a unit potential gradient, the forces acting on it will be just those effective on a thread of liquid... 

It will be recalled from Chapter 7 that has the dimensions of a reciprocal length and may thus be set equal to 1/8, 8 being the thickness of the Helmholtz double layer. Thus it may be seen that the expression utilized by Helmholtz for the potential of a parallel plate condenser... 

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