Brass corrosion in chlorinated tap water inhibited by phosphate ions

Abstract

The combined effect of phosphate ions as corrosion inhibitor and sodium hypochlorite as biocide is studied on aluminum brass in contact with artificial tap water. The interaction between phosphates and hypochlorite was evaluated by electrochemical techniques for films formed between 2 and 192 h and by weight loss tests for immersion times of 90 days. Raman spectroscopy and X-ray photoelectron spectroscopy were used to study the passive layer. When the biocide agent is present, dezincification is the predominant form of localized corrosion after long time exposures. When the inhibitor is present, a nobler pitting potential was found. Electrochemical impedance spectroscopy (EIS) results suggest the development of a compact passive layer, regardless of the presence of the biocide. No localized attack was detected on samples immersed for 90 days at open circuit potential in the presence of phosphates, even when NaClO is present. Weight loss analysis showed inhibition efficiencies higher than 90 % when phosphates and the biocide are present. The oxidative nature of NaClO could favor Zn dissolution and enhance the precipitation of Zn3(PO4)2 layer, producing a more compact surface layer.