Effects of Zn and Pb as alloying elements on the electrochemical behaviour of brass in borate solutions

Abstract

The electrochemical behaviour of brasses with various Zn content (5.5–38) and brass (Cu–38Zn) with different Pb content (1.3–3.3) in borate solution, pH 9.0, was investigated. The effects of applied potential and the presence of aggressive Cl− ions were also studied. Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedence spectroscopy (EIS) were used. Increase in zinc content decreases the corrosion rate of brass in borate solution exponentially. Long immersion of leaded brasses and alloys with different Zn content improves their stability due to the formation of a passive film. The passive film formation under open-circuit and potentiostatic conditions proceeds via dissolution–precipitation mechanism. The addition of a low concentration of Cl− ion (0.01 M) to the borate solution increases the corrosion rate of Cu–38Zn due to dezincification. Increase in Cl− ion concentration (0.01–0.2 M) decreases the corrosion rate of the brass exponentially due to formation of insoluble CuCl. For Cl− ion concentrations >0.2 M the corrosion rate of the brass increases again due to the formation of the soluble CuCl2 − complex.