2002 Volume 51 Issue 12 Pages 1145-1151
The quantitative characterization of oxide films formed on copper is an important subject in corrosion research. So far, chronopotentiometry has been most frequently applied to the selective determination of cuprous oxide (Cu2O) and cupric oxide (CuO) in copper oxide films. However, it is time-consuming, and has a serious problem that there are two different doctrines about which oxide is reduced first. In this study, we prepared two standard samples of Cu2O film (Dumet wires) and CuO film (by treating a copper sheet with a commercial oxidizing agent) and also a real sample in which the two oxides coexist on a copper sheet. We then performed quantitative analyses of the oxide films using a recently proposed voltammetric technique, i.e., double-sweep cyclic voltammetry (DSCV). It was found that the use of a strongly alkaline solution (i.e., 6 M KOH+1 M LiOH) allowed a perfect separation between two cathodic peaks due to the reductions of Cu2O and CuO. One of the peaks, appearing at a less negative potential, was due to the reduction of CuO to Cu, whereas the other peak, appearing at a more negative potential, was due to the reduction of Cu2O to Cu. These peak assignments have been justified by analyses of standard samples by X-ray diffraction, inert-gas fusion analysis for oxygen, and scanning ion microscopy (SIM). Also, the thickness of the oxide layer of each standard sample, calculated from the peak area, was in fair agreement with that estimated by either gas analysis or the SIM image.
