Investigation of corrosion and stability of lead-brass alloy in acid and neutral solutions using electrochemical impedance spectroscopy

The corrosion behavior of a lead-brass alloy (58% Cu, 1.8% Pb, and 42.2% Zn) was investigated in naturally aerated acid and neutral chloride and sulfate solutions under open-circuit and potentiostatic control conditions using electrochemical impedance spectroscopy (EIS). Corrosion under open-circuit conditions was caused mainly by the dissolved oxygen depolarizer, copper (I) chloride (CuCl) or copper (I) sulfate (Cu2SO4), together with some surface oxides, which were assumed to be corrosion products, leading to electrode passivation. Impedance spectra in the form of Nyquist plots consisted of depressed semicircles with different degrees of depression. These depressions increased with dilution of the electrolyte rather than with immersion time. This behavior was attributed partially to inhomogeneities and surface roughness, Data were analyzed in terms of the constant phase element model, which reduced to infinite Warburg diffusion in neutral solutions. At high cathodic overpotentials, reduction of hydrogen (H+) in acid media and of oxygen in neutral media seemed to be rate controlling. Potentiostatic polarization at potentials > -0.5 V led to selective dissolution of zinc and accumulation of corrosion products. At potentials > -0.2 V, pitting occurred.