P. Simon et al., CHARACTERIZATION BY ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY OF PASSIVELAYERS FORMED ON LEAD-TIN ALLOYS, IN TETRABORATE AND SULFURIC-ACID-SOLUTIONS, Journal of power sources, 55(1), 1995, pp. 63-71
Lead-tin alloys (up to 2.5 wt.% Sn) were passivated in de-aerated sodi
um tetraborate solution (pH=9.1). Voltammetry measurements showed that
alloying tin had the effect of inhibiting the oxidation of lead into
PbO or PbO2, but did not hinder the formation of an intermediate compo
und, PbOx. By impedance spectroscopy measurements, it was found that t
he polarization resistance of the passivated electrodes increased when
the alloying tin content increased. Pure lead and Pb-0.5 wt.% Sn allo
y exhibited a semi-conducting behaviour, while surface films formed on
tin-rich alloys were found more electronically conducting. These feat
ures were related to the important enrichment of the passive layers wi
th corrosion-resistant SnO2. The same alloys were passivated in sulfur
ic acid solutions in experimental conditions to develop an oxide film
under the sulfate layer. It was found that for pure lead and Pb-0.5wt.
%Sn, the oxide layer behaved as a semi-conductor. With alloying tin (g
reater than or equal to 1 wt.%), the composite lead-tin oxide was elec
tronic conducting and non-ionic conducting in a solution of pH=9.1, bu
t in sulfuric acid tin oxide was unstable and increased the ionic cond
uctivity of the passive layers.