Potentiodynamic behaviour of tin in different buffer solutions

The anodic oxidation of tin in carbonate-bicarbonate solutions covering a wide range of pH and electrolyte composition has been studied by voltammetric techniques and scanning electron microscopy (SEM). The influence of switching potentials, potential scan rate, rotation speed and surface condition are reported, SEM micrographs of the electrode surface show considerable differences in the characteristics of the surface products, whether they were formed in the potential region of the elect ro formation of stannous oxide and hydroxide or Sn(IV)-containing species which dehydrates into the most stable species. From the dependence of the charges on the potential scan rate it may be inferred that a direct oxidation of Sn(0) to Sn(IV) exists besides the sequence Sn(O) to Sn(II), and Sn(II) to Sn(lV). The effect of the initial surface state on the anodic reactions is better recognized for a rotated electrode. Analysis of the first and second voltammetric cycles through the changes of the anodic current densities with rotation speed. suggests that the initial electrooxidation process at a freshly prepared electrode surface does not follow a dissolution-precipitation mechanism. The formation of soluble corrosion products is enhanced in the potential range of the secondary passivity as the ionic strength of the buffer increases. (C) 2001 Elsevier Science Ltd. All rights reserved.