A rotating ring-disk stripping technique has been used to analyze Sn-Pb alloys plated from methane sulfonic acid solutions with and without a proprietary additive and to construct associated current-potential curves. The deposition of both pure Sn and pure Pb was polarized by the additive, but the polarization was much greater for Pb. For alloys plated without the additive, the potential dependence of the partial currents iSn and iPb was essentially the same as that of the pure metals. The alloy compositions were very different from the solution ratios Sn(II):Pb(II) and could be either tin-rich or lead-rich compared to the solution. In the presence of the additive, on the other hand, the alloy compositions approximated the solution compositions of the metal ions; both Pb and Sn deposition were polarized in the alloy compared to deposition of the pure metals, but the extent of polarization caused by the codepositing metal was much greater for Sn. The electrodissolution of Sn-Pb alloys in HCl shows a complex oscillatory behavior, which is produced by the selective dissolution of Sn but which may also be sustained by the formation and redissolution of sparingly soluble surface films. The oscillatory behavior disappears at low dissolution current and low rotation rate, which favor a higher surface concentration of the dissolving metals. Composition determinations are essentially the same under conditions with and without oscillations.
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IBM Journal of Research and Development
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06 April 2010
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