Selective dissolution of brass in salt water

The selective dissolution of brass was studied using potentiodynamic polarization, coloumetric analysis and electrochemical impedance spectroscopy ( EIS). Using coloumetric analysis, the partial currents i(Zn) and i(Cu) were measured under various potentials and chloride concentrations. Chloride ions promote the dissolution of Zn and Cu and hence increase the rate of dissolution of the alloy. At active potentials, zinc dissolves preferentially leaving the alloy surface enriched in copper. Under this condition, the polarization resistance of the interface and its double layer capacity increase with the time and extent of dissolution of the alloy. As the chloride concentration increases and/ or the potential shifts in the noble direction, the rate of copper dissolution increases so that simultaneous dissolution of both components is observed. This increase in the rate of copper dissolution is enhanced by the higher stability of the copper chloride complex ( CuCl2-) compared to zinc chloride ( ZnCl2).