Abstract
A new voltammetric method for determination of the oxides on tin was proposed. In an ammonia buffer solution (0.5 M NH4OH+0.5 M NH4Cl), well-defined reduction peaks for SnO and hydrated SnO2 (denoted as SnO2･nH2O) were observed in a current-potential curve. The peak potentials were fully separated by -0.3 V, since NH4+ ions facilitated the reduction of SnO2･nH2O. On the other hand, in a borate buffer solution, which has been frequently used as the supporting electrolyte for this purpose, and in 1 M KCl containing higher concentration of ions, the peak of SnO2･nH2O was not detected. By using the ammonia buffer solution, we found that the main corrosion products formed on tin in air were SnO and SnO2･nH2O. It was also found that SnO was formed in air at a temperature higher than 100℃, while SnO2･nH2O was formed at a temperature below 100℃ with a higher relative humidity of 90%. The amounts of the respective oxides increased with temperature and relative humidity. In addition, the film thicknesses of tin oxides estimated from the areas of reduction peaks were close agreement with FIB/SEM data.
