Synergism between Tartaric acid and Zinc ions under hydrodynamic conditions for corrosion inhibition of steel in cooling water solution-electrochemical impedance and morphological studies

A study of the St37 steel rotating disc electrode/cooling water interface was carried out using an environmentally friendly inhibitor mixture including Tartaric acid (TaA) and Zinc sulfate. Electrochemical Impedance Spectroscopy measurements were performed in the absence and presence of inhibitor in cooling water under static conditions and at different rotation speeds. TaA did not show good inhibition efficiency at quiescent conditions. However, its performance became significantly better in the presence of Zn2+ ions. The increase in electrode rotation speed also enhanced the inhibition efficiency of TaA and its mixture with Zn2+ ions. The synergism between TaA and Zn2+ ions and the solution hydrodynamics promoted the formation and adsorption of Tartrate-Zn2+ complexes on the metal surface, leading to a highly protective layer formed on metal surface as a barrier against diffusion of corrosive ions. Analysis by scanning electron microscopy and energy dispersive X-ray analysis was presented for both the corroded and protected metal surfaces. Based on results, a mechanism for corrosion inhibition and the synergism between two components was proposed.