Chemical State Analysis of Tin Oxide Films by Voltammetric Reduction

Abstract

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 þ 0.5 M NH 4 Cl), well-defined reduction peaks for anhydrous SnO and hydrated SnO 2 (denoted as SnO 2 nH 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 nH 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 nH 2 O was formed at a temperature below 100 C and at a higher relative humidity 90%.

Tin passivation in alkaline media: Formation of SnO microcrystals as hydroxyl etching product

“…1b, inset). The potential of this peak is in agreement with the reported cathodic reduction of stoichiometric SnO [37]. For the oxide film grown at −0.7 V (C in Fig.…”

“…Sweeping the potential to a more anodic value of −0.5 V (D in Fig. 1a, inset) results in a slight cathodic shift of the SnO 2 ·nH 2 O peak most likely due to its dehydration to a more stoichiometric SnO 2 layer (E = −1.7 V) [37]. A substantial decrease in the SnO phase is also observed.…”

“…To come out with a rough chemical identification of the main oxide compounds formed during the slow potential scan, the voltammetric reduction method previously described by Nakayama et al [37] was used. Briefly, in this method, the Sn electrode surface is passivated in the working alkaline medium, removed under anodic potentiostatic conditions, washed with MilliQ water and electrochemically reduced in an ammonia buffer composed by 0.5 M NH 4 Cl and 0.5 M NH 4 OH.…”

“…Briefly, in this method, the Sn electrode surface is passivated in the working alkaline medium, removed under anodic potentiostatic conditions, washed with MilliQ water and electrochemically reduced in an ammonia buffer composed by 0.5 M NH 4 Cl and 0.5 M NH 4 OH. In such medium, the cathodic reduction of reference powders SnO, SnO 2 ·nH 2 O and SnO 2 have been identified at potentials of −1.2, −1.5 and −1.7 V vs. SSC respectively and the method has been proven to be a feasible strategy to identify tin oxide products [37]. A set of samples for voltammetric reduction was prepared in 0.1 M NaOH by anodically sweeping the potential to Fig.…”

“…Chemical identification by voltammetric reduction was performed in ammonia buffer (0.5 M NH 4 OH + 0.5 M NH 4 Cl) using a method described by Hakayama et al [37].…”