Nucleus, electrocrystallization

The experimental data for the rate of stationary two-dimensional nucleation in electrocrystallization of cadmium on the surface of the Cd(OOOl) crystal face in 2.5 M CdS04 aqueous solution at 45 °C were presented [234]. The overpotential dependence of the nucleus size was determined. 

We now consider briefly how nucleus formation on an electrode surface, electrocrystallization, can be studied. Nucleation normally follows a first-order rate law... 

Apart from the purely thermodynamic analysis, the description of the electrocrystallization phenomena requires special consideration of the kinetics of nucleus formation [i-v]. Accounting for the discrete character of the clusters size alteration at small dimensions the atomistic nucleation theory shows that the supersaturation dependence of the stationary nucleation rate Jo is a broken straight line (Figure 2) representing the intervals of A p within which different clusters play the role of critical nuclei. Thus, [A//, A/l"] is the supersaturation interval within which the -atomic cluster is the critical nucleus formed with a maximal thermodynamic work AG (nc). 

Under these conditions, in the presence of an overpotential, metal ions may discharge on the surface of the crystal of bulk M. This type of electrodeposition is called electrochemical crystal growth or electrocrystallization on a like substrate and will be considered in Chapter 4. Polarization to a potential E < E may be also imposed on a foreign substrate. If this is the case then it is possible to form metal nuclei on its surface. A nucleus is a cluster of metal atoms that carries the physical properties of the new crystalline phase and it is the nucleus formation what we consider as a precursor of the overall electrociystaUization phenomenon. 

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