Electrode Surface Coarsening

The general equation of the polarization curve for the flat part of an electrode is given by Eq. (1.13) and by Eq. (2.23) for the tip of a protrusion ( h, around which the lateral diffusion flux can be neglected. 

The rate of growth of the tip of a protrusion relative to the flat surface is given by 

It was shown earlier that at sufficiently high frequencies, the average current density in electrodeposition at a periodically changing rate produces the same concentration distribution inside the diffusion layer as a constant current density of the same intensity. Hence, Eq. (4.76) is valid for all cases of electrodeposition at a constant and periodically changing rate at sufficiently high frequencies. 

However, an increase in surface coarseness in a deposition using a rectangular pulsating overpotential or pulsating current is only possible during the pulses of current or overpotential [35] and the integral form of Eq. (4.76) can be written as  

The copper deposits obtained under activation and mixed controls as those shown in Fig. 2.4 are shown in Fig. 4.8c, d. A considerable decrease in the grain size of deposit obtained at the low current densities (in the activation controlled region Figs. 2.4ac and 4.8) due to the increase of the amplitude of the overpotential relative to the corresponding value in constant overpotential deposition can be seen. There is no qualitative change, however, in the structure of the deposit. 

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Popov Kl, Pavlovic MG, Pavlovic LjJ, Cekerevac MI, Removic GZ (1988) Electrode surface coarsening in pulsating overpotential copper electrodeposition. Surf Coat Technol 34 355-363... 

It is therefore pleasing to observe that the electric field or, equivalently, the potential, has a similar effect on the surface mobility as does the temperature. The term electrochemical annealing, which is often used to denote the coarsening of electrode surfaces that occurs at high potentials [16], alludes to this fact. 

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