Corrosion of Zinc as a Function of pH

Anodic and cathodic polarization of zinc was carried out in 0.1 M sodium chloride (NaCl) solution with pH ranging from 1 to 13. The electrochemical data was then contrast to thermodynamic chemical equilibrium diagrams. The analysis shows that, in general, variations in corrosion of zinc with pH are associated with the cathodic currents. In acidic solutions, the active form of corrosion occurring is controlled by the kinetics of the cathodic reaction (predominantly hydrogen evolution). In the pH range (7 to 10), the lowered cathodic reaction rate reduces overall zinc corrosion rates. The surface oxides thermodynamically predicted to form in this pH (7 to 10) do not form an effective corrosion protection barrier. In alkaline conditions corrosion occurs chiefly by the formation of zinc hydroxide complexes or zinc oxides that could protect the surface depending on local pH and potential at the metal surface. This work expands the knowledge on zinc electrode kinetics over a wide range of pH and augments the existing literature on zinc corrosion.