Effect of Iodide Ions on Corrosion Inhibition of Mild Steel in 0.5 M H2SO4 by Poly(4-Vinylpyridine)

The effect of iodide ions on the corrosion inhibition of mild steel in 0.5 M sulfuric acid in the presence of poly(4-vinylpyridine) (P4VP) was studied by weight loss and different electrochemical techniques such as electrochemical impedance spectroscopy, potentiodynamic polarization and polarization resistance measurements. The obtained results showed that poly(4-vinylpyridine) effectively reduces the corrosion rate of mild steel. The addition of potassium iodide (KI) enhanced the inhibition efficiency (P%). The synergism parameter (Sp) calculated from inhibition efficiency was found to be greater than unity, suggesting that the phenomenon of synergism exists between P4VP and iodide ions. The adsorption of P4VP alone and in combination with KI followed Frumkin adsorption isotherm. The effect of temperature indicated that the inhibition efficiency of P4VP decreases with increasing temperature. Study of temperature effect showed also that inhibition efficiency of (P4VP + KI) does not depend on temperature. The apparent activation energies in the absence and in the presence of P4VP and ( P4VP + KI ) were determined.