Phosphate and Borate Ions as Inhibiting Agents for Cu–10Al–10Zn Corrosion in Saline Solution

Abstract

In this article, the inhibitive effects of di-sodium borate and tri-sodium phosphate on the Cu–10Al–10Zn alloy corrosion in NaCl solutions are investigated. Polarization techniques and electrochemical impedance spectroscopy (EIS) were used. Surface examination and morphological studies were employed. All investigations were carried out in stagnant naturally aerated neutral 3.5% NaCl solution containing different concentrations of PO4 3− and B4O7 2− ions. Polarization measurements reveal that phosphate and borate ions have the large effect on the corrosion current density of Cu–10Al–10Zn in 3.5% NaCl solution. As PO4 3− concentrations increase, the current density decreases till 0.05 M PO4 3− and starts to increase again in contrast to B4O7 2− where the latest amount (0.01 M) decreases the current density to its minimum value and then increases as B4O7 2− concentration increased. EIS measurements have shown that a more resistive passive film is formed on the Cu–10Al–10Zn alloy in the presence of PO4 3−. The formation of such passive film on the alloy surface was discussed. The impedance data were fitted to equivalent circuit model that explains the different electrochemical processes occurring at the electrode/electrolyte interface. Phosphates and borates can be considered as effective corrosion inhibitors for the corrosion of Cu–10Al–10Zn alloy in 3.5% NaCl solution