Effect of Alkyl Chain Length on the Corrosion Inhibition Performance of Imidazolium-Based Ionic Liquids for Carbon Steel in 1 M HCl Solution: Experimental Evaluation and Theoretical Analysis

Abstract

In this study, five kinds of 1-alkyl-3-methylimidazolium bromide ([C X ami]­Br) ionic liquids with different alkyl chain lengths (8, 10, 12, 14, and 16) were selected as inhibitors. Then, their corrosion inhibition performances for Q235 steel in 1.0 mol L–1 HCl solution were investigated via a weight loss test, polarization curve method, and surface analysis techniques. The results show that these five imidazolium-based ionic liquids are all mixed-type inhibitors, and they can be spontaneously adsorbed onto the Q235 steel surface. The adsorption process follows the Langmuir model and involves mixed physical–chemical adsorption. Theoretical calculations confirm that the increase in alkyl chain length is conducive to the imidazolium-based ionic liquids exhibiting stronger chemical bonding abilities and forming denser adsorption films. The inhibition efficiency significantly increases below the critical micelle concentration (CMC) with an increase in alkyl chain length, and the highest inhibition efficiency is 95.17% for the [C16ami]Br inhibitor at the concentration of 0.005 mM. However, above the CMC, the inhibition efficiency is minimally affected by the alkyl chain length since all ionic liquid inhibitors have reached adsorption saturation on the steel surface.

Experimental and Theoretical Studies on Long Alkyl Chain-Bearing Dibenzotriazole Ionic Liquids as Eco-friendly Corrosion Inhibitors in Aqueous Hydrochloride Acid

“…The EIS fitting results are summarized in Table , where the corrosion inhibition efficiency (η EIS ) of the EIS test can be calculated according to the following relationship η normalE normalI normalS = R normalc normalt − R normalc normalt 0 R c t × 100 % where R ct 0 and R ct are the charge-transfer resistances without and with the addition of corrosion inhibitors, respectively.…”

“…The decrease of CPE dl values could be explained as follows. The double-layer capacitance could be estimated by the Helmholtz model ,, C normald normall = ε r · S d where ε r is the relative permittivity and d is the thickness of the electrical double layer. It is reasonable to deduce that the adsorption film formed by inhibitor molecules at the steel/solution interface would repel water molecules away.…”

“…The point of zero charge of Fe is much higher than the pH value of HCl solutions used in this work. Therefore, the steel surface was positively charged in the acidic solutions . The BTA anions tightly adhered on the steel surface by electrostatic attraction, as well as donor–acceptor interactions between π-electrons and vacant 3d orbitals of Fe atoms.…”

“…Several quantum chemistry descriptors, including ionization energy ( I ), electron affinity ( A ), electronegativity (χ), absolute hardness (δ), and fraction of electron transfer (Δ N ), could be obtained as follows − I = prefix− E normalH normalO normalM normalO A = prefix− E normalL normalU normalM normalO χ = I + A 2 δ = I − A 2 normalΔ N = χ normalF normale − χ normali normaln normalh 2 ( δ F e + δ int ) where the subscripts int and Fe represent inhibitors and iron atoms, respectively. The Fe (110) plane is the most close-packed plane with the lowest surface energy and thus was chosen as the base plane for theoretical calculation in the present study. ,,,,, δ Fe = 0 eV·mol –1 and χ Fe = 4.82 eV for the Fe (110) plane were used …”

“…They found that none of the molecular electronic parameters correlated well with the experimental results. It is more reasonable to study the effects of alkyl chains by MD simulations, which could reveal the adsorption configuration of ILs , and even the structure of adsorption films at the metal–electrolyte interface. The structure of an adsorption film, like thickness, surface coverage ratio, and compactness, is vital for determining the corrosion inhibition performance.…”