The synergistic effect of iodide and sodium nitrite on the corrosion inhibition of mild steel in bicarbonate-chloride solution

Abstract

The effect of potassium iodide (KI) and sodium nitrite (NaNO2 inhibitor on the corrosion inhibition of mild steel in chloride bicarbonate solution has been studied using electrochemical techniques. Potentiodynamic polarisation data suggest that, when used in combination, KI and NaNO2 function together to inhibit reactions at both the anode and the cathode, but predominantly anodic. KI/NO2- concentration ratios varied from 2:1 to 2:5; inhibition efficiency was optimized for a ratio of 1:1. The surface morphology and corrosion products were analysed using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The latter shows that the addition of I-to NO2 facilitates the formation of a passivating oxide (γ-Fe2O3) as compared to NO2- alone, decreasing the rate of metal dissolution observed in electrochemical testing. The synergistic effect of KI/NO2- inhibition was enhanced under the dynamic conditions associated with testing in a rotating disc electrode.