Corrosion inhibition effect of sodium iodide for mild steel in 1 M hydrochloric acid: Gravimetrical and electrochemical studies

The corrosion inhibition behavior of mild steel in 1 M HCl was investigated in the absence and the presence of sodium iodide (NaI) as an inorganic corrosion inhibitor. The influence of temperature, time and inhibitor concentration was studied using weight loss technique and Tafel polarization technique. The results showed that NaI act as a powerful inhibitor and the inhibition efficiency increase with increase in inhibitor concentration, time and temperature. Maximum inhibition efficiency was 96.1% at a higher level of inhibitor concentration, time and temperature. The adsorption of NaI on mild steel surface was found to follow Langmuir adsorption isotherm. The values of the free energy of adsorption were between - 20 and - 40 kJ/mol that indicate the cooperative adsorption (physical and chemical adsorption). The activation energy of the corrosion process was evaluated using Arrhenius-type equation. Electrochemical studies confirmed the inhibition action of NaI. Corrosion current densities moved to lower value with the addition of NaI. Inhibition efficiency values were in a good agreement with weight loss results. The shift of corrosion potential by iodide anion was lower than 85 mV indicates that it inhibits the anodic reaction and the cathodic reaction, which confirm that sodium iodide act as a mixed - type inhibitor.