Synergistic effect of potassium iodide on corrosion inhibition of copper by tetraphosphonic acid in hydrochloric acid solution

Synergistic effect of KI on the corrosion inhibition efficiency of methylene bis [(2-hydroxy-5, 1-phenylene) bismethylene] tetraphosphonic acid (TPA) on corrosion of copper in 0.5 M HCl have been tested using weight loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The study show that copper is more efficiently inhibited by decreasing the concentration of TPA, and enhancement in inhibition efficiency was observed with an addition of 0.02 M potassium iodide due to synergism. The highest inhibition efficiency of 91% was observed for10−8 M TPA while an addition of 0.02 M KI to 10−8 M TPA improved the inhibition efficiency to 98%. Electrochemical test data prove that they are cathodic inhibitor and exhibit remarkable corrosion inhibition ability. The morphology confirms that the synergistic effect is due to coadsorption of iodide ions and TPA is co-operative in nature. Furthermore, the inhibition efficiency of (TPA + KI) does not depend on temperature. The adsorption of TPA alone or with iodide ions on the metal surface followed Frumkin adsorption isotherm. Thermodynamic parameters (Kads, ΔG°ads, ΔS°ads) were calculated using the adsorption isotherms from temperatures ranging from 25 to 55 °C. The experimental results were confirmed by density functional theory (DFT) and molecular dynamic simulation (MDS) calculation.