Metal-solution interphase

Before discussing metal-solution interphase, we shall discuss the relevant properties of the individual components of an interphase. These individual components are at the same time also basic components of an electrodep)osition cell (excluding the pKJwer supply). The basic components of an electrodeposition cell are, as shown in Figure 2.1, two metal electrodes (Mj and M2), water containing dissolved ions, and two metal-solution interfaces Mj-solution and M2-solution. 

We show that the electric field in the metal-solution interphase is very high (e.g., 10 or lO V/cm). The importance of understanding the structure of the metal-solution interphase stems from the fact that the electrodepKJsition processes occur in this very thin region, where there is a very high electric field. Thus, the basic characteristics of the electrodeposition processes are that they proceed in a region of high electric field and that this field can be controlled by an external power source. In Chapter 6 we show how the rate of deposition varies with the potential and structure of the double layer. 

Figure 4.2. Formation of metal-solution interphase equilibrium state n = %.

The simplest model of the structure of the metal-solution interphase is the Helmholtz compact double-layer model (1879). According to this model, all the excess charge... 

Let us consider the general electrochemical cell shown in Figure 5.2. The potential difference across the electrochemical cell, denoted , is a measurable quantity called the electromotive force (EMF) of the cell. The potential difference in Figure 5.2 is made up of four contributions since there are four phase boundaries in this cell two metal-solution interphases and two metal-metal interfaces. The cell in Figure 5.2 can be represented schematically as Pt/M7S/M/Pt. 

Equality of i and i on an atomic scale means that a constant exchange of charge carriers (electrons or ions) takes place process the metal-solution interphase. Figure 6.3... 

Figure 6.3. RedOx interphase at equilibrium an equal number of electrons crossing in both directions across the metal-solution interphase.

Thus, the overall reaction [Eq. (8.2)] is the outcome of the combination of two different partial reactions, Eqs. (8.4) and (8.5). As mentioned above, these two partial reactions, however, occur at one electrode, the same metal-solution interphase. The equilibrium (rest) potential of the reducing agent, E eq,Red [Eq. (8.5)] must be more negative than that of the metal electrode, E eq,M [Eq. (8.4)], so that the reducing agent Red can function as an electron donor and as an electron acceptor. This is in accord with the discussion in Section 5.7 on standard electrode potentials. 

One possible, although speculative explanation of the effect of the addition of sulfamic acid or sodium sulfate may be based on Eq. (4.9). According to this equation, the variation in the concentration c of a nonreacting electrolyte changes the thickness of the metal-solution interphase, the double-layer thickness It appears that as the thickness of the double layer, decreases, the coercivity of the Co(P) deposited decreases as well. 

Adsorption of Polymers, The three major characteristics of polymers in the metal-solution interphase of interest in metal deposition are the polydispersity, large number... 

The book is divided into 18 chapters, presented in a logical and practical order as follows. After a brief introduction (Chapter 1) comes the discussion of ionic solutions (Chapter 2), followed by the subjects of metal surfaces (Chapter 3) and metal solution interphases (Chapter 4). Electrode potential, deposition kinetics, and thin-fihn nucleation are the themes of the next three chapters (5-7). Next come electroless and displacement-type depositions (Chapter 8 and 9), followed by the chapters dealing with the effects of additives and the science and technology of alloy deposition... 

It is clear that the adsorption of species in the metal-solution interphase region needs a subtle analysis. The unraveling of the complex situation and the building up of a basic picture of the accumulation and depletion of species at an electrified interface is one of the principal achievements of the new electrochemistry and is largely due to the American electrochemist, Grahame. 

Fig. 6.96. Deformation of the adsorbed ion due to the electric field at the metal-solution interphase. (Reprinted from J. O M. Bockris, M. Gamboa-Aldeco, and M. Szklarczyk, J. Electroanal. Chem. 339 355, copyright 1992, Fig. 16, with permission from Elsevier Science.)...

The simplest model of the structure of the metal-solution interphase is the Helmholtz compact double-layer model (1879). According to this model, all the excess charge on the solution side of the interphase, qs. is lined up in the same plane at a fixed distance away from the electrode, the Helmholtz plane (Fig. 4.4). This fixed distance xH is determined by the hydration sphere of the ions. It is defined as the plane of the centers of the hydrated ions. All excess charge on the metal, qM, is located at the metal surface. 

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