Electrochemical, surface and 1018-steel corrosion product characterization in sulfuric acid with new imidazole-derived inhibitors

In the present work, three imidazole-derived ionic liquids (ILs) were evaluated as corrosion inhibitors (CIs) of AISI 1018 steel in 0.5 and 1.0 M H₂SO₄. The ILs were: 1-methyl-3-benzylimidazolium chloride (MBIC), 1-methyl-3-hexylimidazolium imidazolate (MIDI) and 1-butyl-3-benzylimidazolium acetate (BBIA). The inhibition efficiency (IE) was calculated from potentiodynamic tests whose results confirmed that the IE of the ILs was directly proportional to the concentration, obtaining the maximal IE (60 %) at 100 ppm with the inhibitor MBIC at 45 °C. The analysis of the electrochemical results revealed that these new ILs displayed the behavior of mixed-type CIs. In addition, the adsorption process of the IL molecules on the steel surface obeyed the Temkin adsorption model. On the other hand, the low IEs were explained through the analysis of electrochemical and thermodynamic parameters (ΔG°_ads, ΔH°_ads and ΔS°_ads). The surface characterization of the samples protected with CIs was carried out by means of the Mössbauer technique, which helped to conclude that the main corrosion products were rozenite, goethite and akaganeite/lepidocrocite. Finally, the corrosion inhibition mechanism performed by the ILs is proposed.