Surface Films Formed on Copper and Brass at Open Circuit Potential

R. PROCACCINI; W. SCHREINER; M.B. VALCARCE; M. VAZQUEZ; S. CERÉ

Niza, Francia

Congreso; 61st Meeting of the International Society of Electrochemistry; 2010

The corrosion resistance of Cu-Zn alloys, strongly depends on the quality of the protective passive film. This study focuses on the influence of Zn on the composition of the surface layer. Thus, the growth of oxide films on copper and brass (Cu77Zn21Al2) in borax 0.1 mol L-1 solution was investigated. Al pH 9.2 the solubility of copper oxides is minimal. The effect of the presence of chloride ions (0.01 mol L-1) in the electrolyte was also evaluated. Both systems were studied using a set of different electrochemical, optical and surface techniques, among which cyclic voltammetry, differential reflectance, impedance spectroscopy and X-ray photoelectron spectroscopy and Raman spectroscopy can be mentioned. It was evident that the incorporation of Zn as an alloying element changes the composition and thickness of the surface films resulting a more porous and dielectric film than on copper. Also, the formation of a duplex layer of Cu2O/CuO on copper at potentials positive to the open circuit potential (OCP) is demonstrated. In the case of brass, zinc compounds are incorporated to the surface film. By comparing the reflectance spectra for copper and brass at open circuit potential it was observed that brass showed lower transmittance than copper, indicating that the surface film on brass is thicker than that on copper. This is in agreement with the potentiodynamic and chronopotentiometric curves. It also became evident that a surface film can be formed on these materials even at potentials negative to the OCP and that zinc(II) species are the main constituents of these films growth on brass, while copper oxides are incorporated to surface film when approaching the OCP. Raman spectroscopy and XPS spectra confirmed that Cu2O and CuO/Cu(OH)2 are present in the surface films formed on the aged materials. The presence of chloride ions at low concentrations contributes to the dissolution of the oxo-hydroxides formed during the early stages of the ageing process at open circuit potential. Also copper chloro-compounds are formed, as shown by Raman spectroscopy for both copper and brass electrodes.