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

MARÍA BEATRIZ VALCARCE; SUSANA R. DE SANCHEZ; MARCELA VAZQUEZ

JOURNAL OF MATERIALS SCIENCE

Springer

Año: 2006 vol. 41 p. 1999 - 2007

0022-2461

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 was used as electrolyte. Diverse in-situ techniques such as cyclic voltammetry, polarization curves, electrochemical impedance spectroscopy and UV-Vis reflectance spectroscopy were employed. The surface films were grown at open circuit potential for 2 and 192 hours. It was found that 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. Besides, the films on copper and brass grow at a similar rate. The impedance results were interpreted in terms of an equivalent circuit. The resistance associated to the oxide layer increases with time suggesting that the film becomes more compact. Both the increase and the absolute value of Ro are higher for brass, in agreement with the incorporation of Zn(II) oxo-hydroxides to the surface layer.For thicker films, an element accounting for the diffusion of a charged specie through the film has to be included in the equivalent circuit. The corrosion current was calculated for both materials using various techniques. The corrosion current density decreased as the ageing time increased, particularly in the case of brass.