Phosphate ions as environmentally friendly corrosion inhibitors for copper and aluminium brass in contact with tap water

M.B. VALCARCE; M. VÁZQUEZ

Cancun, México.

Congreso; XVII Internacional Materials Research Congress.; 2008

NACE International Mexican Section

Copper and copper alloys are materials broadly used in drinking distribution systems. In soft waters with slightly acidic pH, the metal can be actively dissolved releasing important quantities of Cu2+, which can be harmful for the health of the consumers. Corrosion inhibitors have been used to prevent the dissolution of copper. These inhibitors should be innocuous for human consumption and they should not present a negative impact on the environment. A compound that is frequently employed for this purpose is sodium orthophosphate.  When the electrolyte composition and pH allows the development of a superficial protective layer on the metal, Cu2+ release to the medium is minimum. However, this layer can suffer localized rupture or pitting that can lead to pipes perforation. Sodium orthophosphate used as corrosion inhibitor, can favour the development of a more resistant superficial layer that minimizes copper dissolution, and also it can act by decreasing the susceptibility to localized corrosion. Therefore, the protective characteristic of the superficial layers that are formed on copper and aluminum brass in drinkable water containing sodium orthophosphate are studied. All the experiments are carried out using artificial tap water (ATW) pH 7.6, comparing copper, zinc and brass electrodes. Electrochemical techniques such as cyclic voltamograms, potentiodynamic reduction and anodic polarization curves are used to evaluate the effect of various inhibitor concentrations (5, 10 and 20 mg l-1 P). These techniques are complemented with in-situ UV-visible reflectance spectroscopy. The results on copper indicate changes taking place in the surface layer composition that lead to higher pitting potentials, even when the lowest inhibitor concentration was tested.