A comparative study on the passivation and localized corrosion of α, β, and α + β brass in borate buffer solutions containing sodium chloride

Abstract

The passivation and localized corrosion of α-, β-, and (α + β)-brass in borate-boric acid buffer solutions (pH 9) containing different NaCl concentrations (c_NaCl) were studied comparatively using conventional electrochemical techniques at 25 °C. The passivation of brass in borate-boric acid buffer was due to the electroformation of a complex passive layer consisting of ZnO · xH₂O and Cu₂O—CuO. In NaCl-containing borate-boric acid buffer the breakdown of the passive layer occurs leading to pitting corrosion when the applied potential exceeds a certain critical value, E_b. For a given type of brass, the value of E_b is shifted negatively as c_NaCl is increased. At a constant c_NaCl the localized corrosion resistance of brass increases in the following order (α + β)-brass ≅ β-brass < α-brass. For all brass the localized corrosion resistance was lower than that of polycrystalline Cu, but considerably greater than that of polycrystalline Zn. Passive film composition and de-alloying can account for the localized corrosion resistance of these alloys.