Transport-Controlled Deposition and Dissolution of Metals

Metal deposition and dissolution usually involve more than a simple discharge or formation of hydrated metal ions. In most practical cases, reactions of complex dissociation or formation occur simultaneously as well as deposition and incorporation of foreign substances (impurities or additives), etc. They all affect the structure and appearance of the deposit obtained. In particular, the shape of the deposit, the surface roughness, and surface coarseness (see Section 2) are found to depend strongly on the path of the flow of the electric current (traditionally termed “primary current distribution”) and the path and rate of flow of the species involved, directly or indirectly, in the electrolytic process. Thus, the last factor has a profound effect on the morphology of the deposit and may be a cause of seemingly unrelated phenomena: (a) Amplification of surface irregularities has been known to appear in electrode processes of high specific rate when deposition is carried out at low concentrations of simple ions in solution.1,2 A special example of such a case is shown in Figure 1.