A corrosion inhibition mechanism of API 5L X60 steel exposed to 1.0 M H 2 SO 4 was proposed from the evaluation of three vinylalkylimidazolium poly(ionic liquids) (PILs), employing electrochemical and surface analysis techniques. The synthesized PILs were classified as mixed-type inhibitors whose surface adsorption was promoted mainly by bromide and imidazolate ions, which along with vinylimidazolium cations exerted a resistive effect driven by a charge transfer process by means of a protective PIL film with maximal efficiency of 85% at 175 ppm; the steel surface displayed less surface damage due to the formation of metal−PIL complex compounds.

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 (∆G°a ds , ∆H°a ds and ∆S°a ds ). 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.

The present work deals with the corrosion inhibition mechanism of API 5L X52 steel in 1 M H2SO4 employing the ionic liquid (IL) decyl(dimethyl)sulfonium iodide [DDMS+I–]. Such a mechanism was elicited by the polarization resistance (R p), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) techniques, both in stationary and dynamic states. The electrochemical results indicated that the corrosion inhibition was controlled by a charge transfer process and that the IL behaved as a mixed-type corrosion inhibitor (CI) with anodic preference. The experimental results revealed maximal inhibition efficiency (IE) rates up to 93% at 150 ppm in the stationary state, whereas in turbulent flow, the IE fell to 65% due to the formation of microvortexes that promoted higher desorption of IL molecules from the surface. The Gibbs free energy of adsorption (ΔG°ads) value of −34.89 kJ mol–1, obtained through the Langmuir isotherm, indicated the formation of an IL monolayer on the metal surface by combining physisorption and chemisorption. The surface analysis techniques confirmed the presence of Fe x O y , FeOOH, and IL on the surface and showed that corrosion damage diminished in the presence of IL. Furthermore, the quantum chemistry calculations (DFT) indicated that the iodide anion hosted most of the highest occupied molecular orbital (HOMO), which eased its adsorption on the anodic sites, preventing the deposition of sulfate ions on the electrode surface.

In the present research work, the temperature effect on the corrosion inhibition process of API 5L X60 steel in 1 M H2SO4 by employing three vinylimidazolium poly(ionic liquid)s (PILs) was studied by means of electrochemical techniques, surface analysis and computational simulation. The results revealed that the maximal inhibition efficiency (75%) was achieved by Poly[VIMC4][Im] at 308 K and 175 ppm. The PILs showed Ecorr displacements with respect to the blank from −14 mV to −31 mV, which revealed the behavior of mixed-type corrosion inhibitors (CIs). The steel micrographs, in the presence and absence of PILs, showed less surface damage in the presence of PILs, thus confirming their inhibiting effect. The computational studies of the molecular orbitals and molecular electrostatic potential of the monomers suggested that the formation of a protecting film could be mainly due to the nitrogen and oxygen heteroatoms present in each structure.