Oxidation Study of Pure Tin and Its Alloys via Electrochemical Reduction Analysis

The oxidation of pure Sn and high Pb-Sn alloys was investigated under different oxidizing conditions of temperature and humidity. Both the chemical nature and the amount of oxides were characterized using electrochemical reduction analysis by measuring the electrolytic reduction potential and total transferred electrical charges. For pure tin, SnO grew faster under humid condition than in dry air. A very thin (<10Å) layer of SnO2 was formed on the top surface under humid condition. The mixture of SnO and SnO2 was found for oxidation at 150oC. For oxidation of high Pb-Sn alloys, tin was preferentially oxidized on surface and tin content over solubility limit suppressed the formation of lead oxide. For evaporated Pb-3Sn alloy reflowed two times at 370oC under H2 atmosphere, tin was enriched on the surface as tin dendrites and lead oxide was formed in the tin-depleted region which surrounds tin dendrites.