Electrochemical and surface analytical study of the formation of oxide films on monel-400 and copper in alkaline media

The nature of the oxide films formed on monel-400 and copper in presence of NaOH and N-methylpyrrolidine (a volatile amine) at pH 9.5 and in 0.1 M KNO3 medium were investigated. The oxide films were grown by applying an anodic potential of +0.4 V (vs saturated calomel electrode) for 30 min. The compositions of the surface oxide films were analysed by X-ray photoelectron spectroscopy. In the case of copper in NaOH medium, Cu(0) and a very small amount of copper hydroxide were observed. However, in amine medium, Cu(0) and Cu-amine complex were found. For monel in NaOH, the anodic film was found to contain hydroxides of both copper and nickel. After sputtering, this film showed a small amount of metal oxide below the hydroxide layer as confirmed by the oxygen peak. In amine medium the anodic film was found to contain only nickel hydroxide and metallic copper. The depth profile analysis of films showed that the film developed was very thin and the nickel hydroxide was sputtered very easily from the film.