Kazuma Miura

Corrosion of tin alloys in sulfuric and nitric acids

Abstract To obtain a fundamental understanding of the corrosion behavior of lead-free solder, the corrosion behavior of tin-based eutectic alloys in sulfuric and nitric acids saturated with oxygen was investigated. The presence of bismuth in a Sn–Bi alloy (43Sn–57Bi (wt.%)) slightly accelerated the preferential dissolution of tin instead of dissolving itself in 0.05 M H 2 SO 4 and greatly accelerated, in 0.1 M HNO 3 compared with that of pure tin. In both acids, dissolution of both tin and zinc from a Sn–Zn alloy (91Sn–9Zn (wt.%)) occurred depending on the ratio of composition, and dissolution of tin from a Sn–Ag alloy (96.5Sn–3.5Ag (wt.%)) was accelerated. Dipping tests in H 2 SO 4 and HNO 3 of pH 4 showed that dissolution of only zinc and lead occurred, suggesting that the tin-based alloys investigated in this study are preferable to substitutes for lead solders in terms of corrosion resistance.

Corrosion products of tin in humid air containing sulfur dioxide and nitrogen dioxide at room temperature

Abstract To obtain a fundamental understanding of the corrosion behavior of tin in corrosive gas environments, in situ infrared reflection absorption spectroscopy measurements were carried out on tin in humid air containing SO2 and NO2 at room temperature. A series of time-resolved in situ IR spectra in air of 90% relative humidity (RH) containing 10–22 ppm SO2 suggested that the oxide films on tin specimens had a protective effect and that no significant corrosion occurred. The corrosion products in air of 80–90% RH containing 10–22 ppm NO2 were SnO2, SnO, nitrate and hyponitrite. The synergistic effect of SO2 and NO2 on corrosion of tin was not observed in humid air (RH of 90%) containing 0.84 ppm SO2 and 1.8 ppm NO2.