The effect of various halide ions on the passivity of Cu, Zn and Cu–xZn alloys in borate buffer

Cu and Zn metals and four of their alloys, Cu–10Zn, Cu–20Zn, Cu–30Zn and Cu–40Zn, were studied in borate buffer, pH = 9.2, in the presence of the halides, NaF, NaCl, NaBr and NaI. Electrochemical polarization and SEM/EDS methods were used in the study. The mechanism of corrosion of copper and copper alloys induced by iodide ions differed fundamentally from that induced by other halide ions. Iodide ions promote the general type of corrosion during which very slowly soluble CuI is formed. F−, Cl− and Br− ions promote localized corrosion attack. All halide ions induce localized corrosion on the passive layer on zinc. The breakdown potentials of Cu, Zn and four Cu–xZn alloys were measured as a function of concentration and type of halide ions.