Study of corrosion behavior of API 5L X52 steel in sulfuric acid in the presence of ionic liquid 1-ethyl 3-methylimidazolium thiocyanate as corrosion inhibitor

The inhibition effect of ionic liquid (IL) 1-ethyl-3- methylimidazolium thiocyanate (EMIM)(+) (SCN)(-) on the corrosion of API 5L X52 steel in 0.5 M H2SO4 solution at different temperatures were studied, using gravimetrical, electrochemical, spectroscopic and simulation methods. The highest efficiency and the optimal concentrations were 90.1% and 75 ppm of the IL respectively. Scanning electron microscopy characterization reveals less surface damage in the corroded samples confirming the effectiveness of the IL, while X-ray photoelectron spectroscopy analysis evidenced the formation of an interfacial protective layer, composed by the inhibitor molecules and corrosion products. Polarization measurements showed that the IL is a mixed-type inhibitor, retarding the dissolution of mild steel and hydrogen evolution reactions, enhancing its efficiency as a function of its concentration; besides a minor influence of the temperature in the inhibition efficiency is recorded by weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy techniques. A competitive chemisorption process is observed on steel obeying a Langmuir isotherm. Ultraviolet-visible spectroscopy confirmed chemical interaction between IL and metal surface. The density functional theory and molecular dynamic (MD) simulation were used to correlate with the experimental results and determine the adsorption energy of the inhibitor in different substrate's crystallographic planes. Furthermore, from the results of the interaction between the inhibitor molecules in the presence of water on the steel surface using MD on seven most compact planes of BCC system, it was capable of establishing a correlation between adsorption energies of the inhibitor and the crystallographic texture and the surface roughness of the studied steel. (C) 2019 Elsevier B.V. All rights reserved.