Nucleation Of Lead Research Articles

Fundamental aspects of lead electrodeposition processes: Nucleation and growth

In this comprehensive study, the processes of nucleation and growth of lead from electrolytes of various kind and compositions have been analyzed. The processes of Pb nucleation were examined by the analysis of potentiostatic current transients, while the growth process was examined by the scanning electron microscopic (SEM) analysis of the obtained deposits. It was found that nucleation of lead follows Scharifker and Hills (SH) model based on the 3-D instantaneous nucleation with the diffusion controlled growth. Morphologies of lead particles starting from granules produced at the low overpotentials from the dilute electrolytes to very branchy dendrites at the higher ones were formed by the electrodeposition processes. The obtained surface morphologies were correlated with the corresponding polarization characteristics. It was found that regular hexagonal particles are formed by electrodeposition in the ohmic control, while irregular crystals denoted as precursors of dendrites and dendrites of various types (the needle-like, the primary (P) and the secondary (S) dendrites) were formed in the mixed ohmicdiffusion and diffusion controlled electrodeposition. The needle-like and primary (P) dendrites were primarily formed from the basic (nitrate), while the secondary (S) and the tertiary (T) dendrites were formed from the complex (acetate and hydroxide) electrolytes.

Electrochemical nucleation of lead and copper on indium-tin oxide electrodes

The nucleation process of Pb and Cu onto indium-tin oxide electrodes was studied by single potentiostatic steps using 0.1×10−4 mol L−1 Cu(NO3)2 and 2×10−2 mol L−1 Pb(NO3)2 solutions in aqueous 1.0 mol L−1 NaNO3. The current, I max, and the time, t max, corresponding to the maximum, were evaluated by 3D nucleation with a diffusion-controlled growth model for instantaneous and progressive nucleation. The non-dimensional plots of (I/I max)2 vs. t/t max showed that Cu and Pb nucleation closely followed the response predicted for instantaneous nucleation. Other parameters, such as I vs. t 1/2 and I 2 max t max, as well as nuclei micrographs, were analyzed, corroborating the results obtained.

Heterogeneous nucleation of lead on quasicrystals

Solidification of lead by heterogeneous nucleation on quasicrystals has been studied by embedding lead nanoparticles in an Al-Cu-Fe icosahedral matrix and an Al-Cu-Co decagonal quasicrystalline matrix. Solid lead was found to nucleate on the matrix phase with definite orientations. This orientation is not unique in the case of the icosahedral matrix for which three orientational relationships were determined. The orientation selected by the nucleating particle depends on the plane of the quasicrystal on which the nucleation occurs. When the matrix becomes periodic in one dimension, that is in the case of the decagonal matrix, the orientational relationship with the solidified lead particles becomes unique.

The deconvolution of nucleation and growth rates from electrochemical current–time transients

Two new algorithms have been developed for the deconvolution of nucleation and growth rates from electrochemical current–time transients. The first is called Bootstrap, and is based on the method of successive approximations. The second is called Simplefit, and utilizes a curve-fitting procedure based on the simplex method. Both are able to provide numerical estimates of the number of crystals as a function of time, to better than 2% accuracy, in the presence of significant noise. The advantage of the algorithms is that they produce accurate output under conditions where standard methods fail. In particular, the number of crystals versus time can be determined even when crystal growth switches from interfacial control to diffusion control on the timescale of measurements. The efficacy of the algorithms is demonstrated on two real systems, namely the nucleation of zinc on carbon, and the nucleation of lead on carbon. In both cases non-steady states of nucleation are readily observed in the presence of time-varying crystal growth rates. In addition, a new phenomenon is seen for which the name ''nucleation persistence'' is suggested. This is the transient continuation of a high rate of nucleation after a rapid decrease in overpotential. The phenomenon is attributed to the slow readjustment of the size distribution of microscopic nuclei on the electrode surface. Interestingly, the existence of nucleation persistence invalidates the double potential step technique, which has previously been regarded as the standard method for observing electrochemical nucleation and growth. Finally, the mathematical theory of nucleation persistence is briefly sketched.

Electrodeposition and Nucleation of Lead from Chloride Melts

Electrodeposition and Nucleation of Lead from Chloride Melts

Spatial distributions and saturation number densities of lead nuclei deposited on vitreous carbon electrodes

The nucleation of lead onto vitreous carbon electrodes has been investigated. Diffusion-controlled growth of nuclei inhibits nucleation, giving rise to saturation with nuclei and introducing correlations in their location on the electrode surface. Similar nuclear number densities were obtained from direct, microscopic observation of the surface and from analysis of potentiostatic current transients considering the development of nucleation exclusion zones around already established nuclei. At low overpotentials nuclei were found to be uniformly distributed on the surface, whereas at high overpotentials the results were found to be consistent with simulations of the process that allowed for the existence of exclusion zones around nuclei, with radii proportional to the square root of their age.

Three-dimensional nucleation with diffusion controlled growth: Part II. The nucleation of lead on vitreous carbon

The nucleation of lead onto vitreous carbon electrodes has been investigated. The number density of active sites for nucleation was found to vary with the overpotential but not with the concentration of lead ions in solution. The overpotential and concentration dependence of the nucleation rate were also studied, and the results interpreted according to both atomistic and classical theories. Due to the small size obtained for the critical nuclei, the latter was refined to incorporate the effect of the line tension along the contact line between the three phases involved. However, the atomistic theory seems to afford a better representation of this electrochemical nucleation process.

Two-dimensional nucleation of lead and thallium

Two-dimensional nucleation of lead and thallium

Erratum: Nucleation of Lead with Preferred Orientation

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Nucleation of Lead with Preferred Orientation

Nucleation of Lead with Preferred Orientation