Surface characterization of copper, zinc and brass in contact with tap water inhibited with phosphate ions

The composition of the surface layers has been investigated on copper, zinc and brass in contact with moderately hard, highly carbonated and chloride rich artificial tap water (ATW). Cyclic voltammetry, reflectance spectroscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy have been used to identify the changes in composition that result from the incorporation of sodium orthophosphate to ATW. The results showed that when PO43− is added, the film changes its composition and it also becomes thinner, denser and more compact. On copper, the presence of CuO in the passive film can be correlated to the improvement in the corrosion behavior in the presence of phosphate ions. In the case of brass, the development of a thinner, compact and less porous Zn3(PO4)2 layer hinders Cu(I) dissolution. A mechanism explaining the effect of this inhibitor is proposed, which accounts for the experimental results.