The Synergistic Effect of Iodide and Sodium Nitrite on the Corrosion Inhibition of Mild Steel in Bicarbonate-Chloride Solution

Gaius Debi Eyu; Geoffrey Will; Willem Dekkers; Jennifer MacLeod

doi:10.3390/ma9110868

The Synergistic Effect of Iodide and Sodium Nitrite on the Corrosion Inhibition of Mild Steel in Bicarbonate-Chloride Solution

Materials (Basel). 2016 Oct 26;9(11):868. doi: 10.3390/ma9110868.

Authors

Gaius Debi Eyu¹, Geoffrey Will², Willem Dekkers³, Jennifer MacLeod⁴

Affiliations

¹ Department of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane QLD 4000, Australia. gaius.eyu@qut.edu.au.
² Department of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane QLD 4000, Australia. g.will@qut.edu.au.
³ Department of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane QLD 4000, Australia. w.dekkers@qut.edu.au.
⁴ Department of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane QLD 4000, Australia. jennifer.macleod@qut.edu.au.

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.

Keywords: EIS; bicarbonate solution; iodide ion; mild steel; passivation; polarization.