Surface Films on Cu and Brass Grown in Contact with Tap Water Containing Phosphate Ions

L. YOHAI; R. PROCACCINI; W. SCHREINER; M. VÁZQUEZ; M.B. VALCARCE

Niza

Encuentro; 61th Annual Meeting of the International Society of Electrochemistry; 2010

Copper and copper alloys are materials broadly used in drinking distribution systems. In soft waters with slightly acidic pH, they can actively dissolve, releasing important quantities of Cu2+ to the medium, which can be harmful for the health of the consumers [1]. In a hard tap water the development of a superficial protective layer on the metal, minimize Cu2+ releasing. However, this layer can suffer localized rupture or pitting that can lead to pipes perforation. Under this condition, sodium orthophosphate used as corrosion inhibitor acts by decreasing the susceptibility to pitting corrosion [2, 3]. This behaviour could be associated to changes in the surface film composition on copper and brass in a hard tap water. This investigation focuses on the influence of zinc as alloying element on the pitting corrosion resistance of brass. Therefore, a comparative study of the surface oxide films naturally formed on copper, zinc and brass in contact with drinkable water containing phosphate ions is presented. All the experiments were carried out using artificial tap water (ATW) pH 7.6. Cyclic voltammograms, potentiodynamic reduction curves and electrochemical impedance spectra were used to evaluate the effect of the inhibitor (10 mg L-1 as P) on the surface film grown on copper, brass and zinc at open circuit potential. These techniques were complemented with Raman and X-ray Photo spectroscopy. When copper is in contact with ATW the main component of the surface film is Cu2O. In the presence of phosphate as inhibitor, a more compact and thicker layer is developed. This layer is formed by a mixture of Cu2O, CuO and Cu(OH)2, in agreement with previous results [2]. In turn, the main components of the surface layer formed on brass are Cu2O and Zn oxo-hydroxides. When the inhibitor is incorporated to the water, the surface layer becomes thicker and more compact, with Cu2O and Zn3(PO)4 as the main components. This suggests that the presence of zinc as an alloying elements inhibits the participation of Cu(II) ions in the oxide film, which could be related to the differences in the pitting susceptibility [3]. References [1] M. M. Critchley, N. J. Cromar, N. C. McClure and H. J. Fallowfield; Journal of Applied Microbiology 94 (2003) 501-507 [2] M. B. Valcarce and M. Vázquez; Corrosion Science 52 (2010) 1413–1420 [3] M. B. Valcarce and M. Vázquez; VII International Nace Mexican Section Congress; Cancún, México; 2008