A comparative analysis of copper and brass surface films in contact with tap water

A study of the surface oxide films naturally grown on copper and brass in contact with drinkable water is presented. The investigation focuses on the influence of Zn as alloying element on the corrosion resistance of brass. Artificial tap water, employed as electrolyte, simulates a practical application of these materials. The surface films were grown at open circuit potential for 2 and 192 hours. Diverse in-situ techniques such as cyclic voltammetry, polarization curves, electrochemical impedance spectroscopy and UV-Vis reflectance spectroscopy were employed. Even when the surface layer is mainly composed of cuprous oxide, Zn(II) species are incorporated in the surface film grown on brass. At longer ageing times, the thickness increases, without affecting the composition of the surface films. The corrosion current was calculated for both materials using various techniques. The corrosion current density and the anodic currents in the polarization curves decreased as the ageing time increased, particularly in the case of brass. This improvement in the performance of the film on brass can be attributed to the incorporation of Zn(II) species into the surface layer, particularly as the film consolidates at longer times.