Chemical State Analysis of Tin Oxide Films by Voltammetric Reduction

A new voltammetric method for the determination of corrosion products on tin surfaces has been proposed. In a borate buffer solution, which has frequently been used as the supporting electrolyte for this purpose, no well-separated reduction current peaks for tin oxides were obtained, while in an ammonia buffer solution (0.5 M NH 4 OH + 0.5 M NH 4 Cl), well-defined reduction peaks for anhydrous SnO and hydrated SnO 2 (denoted as SnO 2 • n H 2 O) were observed in a voltammogram. The potentials at these current peaks were separated by ∼0.3 V. Using this suitable electrolyte, we found that the main corrosion products formed on tin in air were SnO and SnO 2 • n H 2 O. These tin oxides were confirmed by X-ray diffraction analysis. It was also found that SnO was formed in air at a temperature higher than 100°C, while SnO 2 • n H 2 O was formed at a temperature below 100°C and at a higher relative humidity 90%.