Evaluation of (di)ethanolamine-based protic ionic liquids as corrosion inhibitors

Abstract

Corrosion can be defined as a deterioration process in which material loss is due to electrochemical reactions with the external environment. Corrosion is responsible for damage in various areas of industry, such as failures in pipelines, tubes, tanks, and boilers, causing significant financial and environmental damage. Thus, to deal with this adversity, a solution used by the sector would be to use techniques to combat corrosion, among which corrosion inhibitors are highlighted because they are considered more practical and profitable. This technique is extremely efficient in terms of protecting metallic materials, even though some inhibitors commonly found in the industry have toxic compounds in their composition, thus being considered inappropriate for society due to the high environmental risk. Given this ecological precaution, the search for new ecologically sustainable alternatives is present in the study of corrosion mitigation. This work comprises an application for protic ionic liquids as inhibitors, defined as organic salts originating from Bronsted-Lowry acid-base neutralization reactions. Owing to their different properties, these compounds are of extreme scientific interest, such as thermal and electrical conductivity, high viscosity, high solvation power, and low toxicity. In this study, the inhibitory action of Protic Ionic Liquids (LIPs) on the corrosion of ASTM A36 carbon steel in a 3.5% NaCl medium was investigated. From this perspective, ionic liquids were chemically characterized using specific techniques such as Thermogravimetric Analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), and Nuclear Magnetic Resonance (NMR). The corrosion inhibition efficiency was evaluated through electrochemical tests, Open Circuit Potential Monitoring (PCA), Potentiodynamic Polarization (PP), Electrochemical Impedance Spectroscopy (EIE), and surface evaluation using specific techniques such as Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (SAM). Mass loss tests were carried out using the same electrolyte (NaCl 3.5%) at pH 7 at different temperatures (35, 40, 50, and 60 C) and acidification (pH 2 and 4). Also, morphology tests will be carried out for a more in-depth evaluation of the surface, through the technique of Raman Spectroscopy and the oxides produced on the surface by X-Ray Diffraction. Finally, the protic ionic liquids will be characterized through physicochemical evaluation for a better understanding of the properties of the tested material. Thus, from the preliminary results, it is possible to state that the evaluated LIPs can be used as corrosion inhibitors, emphasizing the LIPs that contain bases (Ethanolamine and Diethanolamine) in combination with the smallest acids. These compounds showed the highest values of inhibition efficiency, above 80%, at the highest concentrations evaluated (500 and 1000 ppm). Finally, the results showed that the studied molecules behave as corrosion inhibitors of the anodic and mixed types because of the results of dynamic potential polarization and are still adsorbed on the surface via physisorption with van der Waals interactions.