Category: 13. Electrodeposition

Up to this point we have assumed that the material being plated is highly conductive and essentially at a single potential; in other words, we have assumed that the conductivity of the material is sufficiently high that the potential gradient accompanying current flow in the material is very small and can be neglected. There are…

Side reactions are reactions that do not directly contribute to the formation of the desired deposit. For the deposition of metals from aqueous solutions, the most common side reaction is electrolysis of water or reduction of hydrogen ions, which results in the evolution of hydrogen gas at the cathodic potentials needed for deposition. The portion…

In the above discussion, we have implicitly characterized deposition by a single overpotential and rate for the surface of interest. In practice, however, the rate varies over the surface of the piece being plated, as illustrated schematically in Figure 13.12. To avoid the problems associated with deposition under mass-transport control, practical systems typically operate at…

Additives have been and continue to be a critical component of industrial plating baths. Most additive work has been done empirically, although recent years have seen increased fundamental understanding of these complex systems. A detailed treatment of additive effects is left to more specialized texts. Instead, we provide just a brief introduction to this important…

Description of the deposition process rapidly becomes more complex as we move from the isolated nuclei of initial growth to interacting growth sites and, finally, coalescence and layer growth. The fundamental processes described above, however, provide a basis for understanding the deposit morphologies that are observed in practice. They also help us to understand ways…

Early Growth of NucleiIn this section, we examine initial growth of deposits from distinct nuclei. The distinguishing factor in early growth is that the nuclei are far enough apart to behave independently. Under such conditions, the total deposition current can be estimated by summing the contributions from the individual nuclei. Here we consider both kinetically…

Above we treated the thermodynamics associated with stable cluster formation. We now turn our attention to the rate at which nuclei are formed. In doing this, we restrict ourselves to the classical expressions for the nucleation rate attributed to Volmer and Weber, noting that similar expressions can be derived from atomistic theory. Please refer to…

The formation of new sites or nuclei from which deposition may occur is called nucleation, and it is a critical aspect of electrodeposition. The number and type of nuclei strongly influence the morphology of the deposit. Both the growth rate of the deposit and the rate of nucleation increase with increasing overpotential. If the nucleation…

To this point, we have treated electrodeposition in a macroscopic way. However, deposit morphology and properties vary dramatically with the conditions under which the deposition takes place as illustrated in Figure 13.2, where current density is varied. In order to understand these different morphologies, we need to explore the fundamental processes that take place during…

An important aspect of electrodeposition is that the total amount deposited is directly related to the amount of charge passed in carrying out the desired reaction, and hence to the thickness of the plated layer. The mass of the deposit is (13.1)where Q is the charge passed due to the plating reaction. Assuming that the…