Over potential anodic dissolution

It appears that in several nonaqueous systems, the difference between the potentials of the A13+/A1 couple and that of other couples, such as Zn2+/Zn, Sn2+/ Sn, Cu2+/Cu, and others is much lower than in aqueous solutions [456-458], Consequently, electroplating of Al alloys from nonaqueous solutions is feasible and may even be advantageous over metallurgical processes of alloy formation [456,459,460], Anodic dissolution of aluminum electrodes has also been investigated [461-465], It appears that reversible behavior of the A13+/A1 couple may be obtained in a number of nonaqueous systems (see next section). 

A final constraint on selection of electrode materials is frequently imposed by the problem of their corrosion, or oxidation. Thus accepting that a reduction such as that of ethene occurs over the potential range + 0.1 V to — 0.1 V, a number of metals such as Fe, Co, and Ni will not be stable, at least in more acidic solutions, but will corrode by means of the anodic dissolution reactions-... 

It was found that electropolishing occurs in systems which, under anodic dissolution, exhibit a limiting current characteristic of diffusion control, i.e., currents are dependent on flow rate of the electrolyte past the anode, as shown in Figure 24. Over a certain range of potentials at the limiting current plateau, at which maximum brilliance is obtained, oscillations of potential occur at a virtually constant current density, with an amplitude of over 0.40 V, and without appreciable damping. Also, a significant photoelectrochemical effect is found. 

Fig. 1.39 Schematic anodic polarisation curve for a metal. Region AB describes active dissolution of the metal. BC is the active/passive transition, with passivation commencing at B. Passivation is complete only at potentials higher than C. The metal is passive over the range CD...

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