Anode partial reaction

In electrolytic corrosion, an anodic partial reaction takes place according to Eq. (2-3)... 

If U is assumed to be the protection potential U, the velocity of the anodic partial reaction according to Eq. (2-21) is so fast that the concentration Cg is maintained. At the same time, Eq. (2-51) represents the highest value for Cg. Therefore it follows from Eqs. (2-51) and (2-52) that ... 

Correspondingly, amphoteric aluminum materials suffer active corrosion by the anodic partial reaction ... 

A relatively high degree of corrosion arises from microbial reduction of sulfates in anaerobic soils [20]. Here an anodic partial reaction is stimulated and the formation of electrically conductive iron sulfide deposits also favors the cathodic partial reaction. 

An important consequence of ion migration is the formation of cells where the coated surface acts as a cathode and the exposed metal at the damage acts as an anode (see Section 4.3). The reason for this is that at the metal/coating interface, the cathodic partial reaction of oxygen reduction according to Eq. (2-17) is much less restricted than the anodic partial reaction according to Eq. (2-21). The activity of such cells can be stimulated by cathodic protection. 

With anodic polarization, the anodic partial reaction predominates at defects so that OH" ions formed according to Eq. (2-17) are combined in the corrosion... 

Inhibitors are materials that reduce either one or both of the partial corrosion reactions as in Fig. 2-5. Anodic or cathodic inhibitors inhibit the anodic or cathodic reaction respectively so that the rest potential becomes either more positive or more negative. Most inhibitors, however, inhibit the anodic partial reaction. This is because the transfer of metal ions can be more easily restricted than that of electrons. 

Large Anodic Current. When r] has large positive values, the second exponential term in Eq. (6.45) (corresponding to the cathodic partial current density) decreases while the first term (corresponding to the anodic partial reaction) increases, resulting in i. Thus, the smaller term. 

Mechanism, The overall anodic partial reaction, Eq. (8.5), usually proceeds in at least two elementary steps (like the cathodic partial reaction) formation of an electroactive species, and charge transfer. The formation of electroactive species (R) usually proceeds in two steps through an intermediate (Redinterm)-... 

The most studied anodic partial reaction is the oxidation of formaldehyde. Red = H2CO. The overall reaction of the electrochemical oxidation of formaldehyde at the copper electrode in an alkaline solution proceeds as... 

Kinetics. The major factors determining the rate of the anodic partial reaction are pH and additives. Since OH ions are reactants in the charge-transfer step [e.g., Eq. (8.23)], the effect of pH is direct and significant (see, e.g.. Ref. 32). Additives may have an inhibiting or an accelerating effect. 

The electrode potentials E Ef) are given in mV and the current densities / in mA/cm. Determine (a) E, the mixed potential (b) / ep, the rate of deposition for this process and (c) the transfer coefficients a for the cathodic and anodic partial reactions. Solve this problem algebraically by finding an intersection of two strait fines do not plot any E = fii) functions. 

Relationships of other type are observed in the case where both the conjugated reactions proceed through the same band (Fig. 13b). For example, the cathodic reaction (42b) can take place with the participation of valence electrons rather than conduction electrons, as was assumed above. Thus, reduction of an oxidizer leads to the injection of holes into the semiconductor, which are used then in the anodic reaction of semiconductor oxidation. In other words, the cathodic partial reaction provides the anodic partial reaction with free carriers of an appropriate type, so that in this case corrosion kinetics is not limited by the supply of holes from the bulk of a semiconductor to its surface. Here the conjugated reactions are in no way independent ones. 

Three anodic partial reactions are considered active dissolution of two metals M and M with different kinetics in the absence of their ions in bulk solution and decomposition of water with the evolution of oxygen. The kinetics of the latter process is so slow on most corroding metals that only at very negative potentials can oxygen present in the solution be electroreduced and this eventually becomes limited by mass transport due to the limited solubility of oxygen in water. At even more negative potentials, hydrogen evolution takes place on the electrode surface. The cathodic reduction of some metal ions present on the electrode surface as a consequence of corrosion is also considered in Fig. 13(b). 

It is well established that the overall electroless deposition reactions are basically electrochemical in nature, consisting of cathodic and anodic partial reactions occurring simultaneously on the same substrate surface ... 

These rate laws demonstrate that Cu(II) is not involved in the anodic partial reaction, whereas both HCHO and OH are involved in the cathodic copper deposition reaction. It is interesting to note that HCHO acts as an inhibitor of the partial cathodic reaction. The above rate laws suggest that the mechanisms are more complex than indicated by simple combination of two independent partial reactions. 

The experimental evidence described above clearly shows that the cathodic and anodic partial reactions interact with each other, and that such interactions are an essential part of the mechanism of electroless copper deposition. It should be noted that the interdependence of partial reactions has also been demonstrated by Bindra et al. [127], based on their results of kinetic and mechanistic analysis. 

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