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 c onditions using electrochemical impedance spectroscopy (EIS). Corrosio n under open-circuit conditions was caused mainly by the dissolved oxy gen depolarizer, copper (I) chloride (CuCl) or copper (I) sulfate (Cu2 SO4), together with some surface oxides, which were assumed to be corr osion products, leading to electrode passivation. Impedance spectra in the form of Nyquist plots consisted of depressed semicircles with dif ferent degrees of depression. These depressions increased with dilutio n of the electrolyte rather than with immersion time. This behavior wa s attributed partially to inhomogeneities and surface roughness, Data were analyzed in terms of the constant phase element model, which redu ced to infinite Warburg diffusion in neutral solutions. At high cathod ic overpotentials, reduction of hydrogen (H+) in acid media and of oxy gen in neutral media seemed to be rate controlling. Potentiostatic pol arization at potentials > -0.5 V led to selective dissolution of zinc and accumulation of corrosion products. At potentials > -0.2 V, pittin g occurred.