 ISSN 0235-7216 ISSN 2424-4538 (online) |
2009 m. Nr. 1 Influence of pH on the cathodic reduction of Sn(II) in sulfamic-fluoride solution
The influence of pH on cathodic reduction of Sn(II) in sulfamic-fluoride solutions was investigated using electrochemical and XPS techniques. Stable Sn(II) fluoride complexes were found to form in acid solutions with pH 1.0 and 2.5, and the reduction of these compounds was determined by diffusion and kinetic control. The surface of Sn electrode was active in these solutions. An increase in solution pH to 4.0 led to a slow settling of the equilibrium among various electroactive Sn(II) fluoride and hydroxofluoride complexes. An increase in temperature favoured the formation of mixed hydroxofluoride complexes. At pH = 4.0, the surface of Sn electrode interacted with solution components, and a layer of slightly soluble compounds was formed on the electrode surface, thus inhibiting the Sn(II) reduction process. The thickness of the passivating layer can exceed 40 nm, blocking the reduction of Sn(II) completely. Keywords: sulfamic-fluoride solutions, Sn electrode, Sn(II) fluoride complexes, cathodic process, passivation |
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