Studies of nickel electrocrystallization on platinum ultramicroelectrodes

A.N Correia,S.A.S Machado

doi:10.1590/s0103-50531997000100013

Abstract

The electrocrystallization of nickel was studied on a platinum ultramicroelectrode (UME). The behaviour of the current transients pointed to an instantaneous nucleation process under kinetic control. The application of Abyaneh's model showed that nuclei grow in a spherical cap geometry with different values for both rate constants in the parallel and perpendicular directions. The parallel rate constants for nuclei growth varied from 5.97 x 10-7 to 1.92 x 10-7 mol cm-2 s-1 by increasing the step potential from -0.57 to -0.63 V, while the perpendicular rate constant remained constant around 1.44 x 10-7 mol cm-2 s-1. The relationships between these two constants give the contact angles of the crystallites, whose values also increased with potential from 27.5 to 87.6 degrees. Finally, the number of nuclei formed on the surface increased with potential from 0.43 x 10(7) to 379.09 x 10(7) cm-2.

Highlights

The initial stages in the electrodeposition of several metals onto different substrates frequently occur by the birth and three-dimensional growth of nuclei
Within a such time domain, if the rate determining step is the diffusion of ions towards the surface, potentiostatic transients should present a linear dependence of the rising currents on t1/2 or t2/3
This work reports for the first time, to the authors’ knowledge, experimental results from Ni electrocrystallization on Pt UMEs

Summary

Introduction

The initial stages in the electrodeposition of several metals onto different substrates frequently occur by the birth and three-dimensional growth of nuclei. During a short time interval after a potentiostatic pulse, applied to generate the nuclei, they grow free of interactions with neighbors Within a such time domain, if the rate determining step is the diffusion of ions towards the surface, potentiostatic transients should present a linear dependence of the rising currents on t1/2 or t2/3. A convenient model for describing such a process was developed by Hills et al.[1,2,3,4,5] for either the instantaneous (i vs t1/2) or the progressive (i vs t3/2) birth of a large number of nuclei This model was further generalized by Scharifker et al.[6,7,8,9] in a study of three-dimensional nucleation on a finite number of active sites followed by diffusion-controlled growth of nuclei. In the very initial time domain, the stability of newly-born nu-

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