Study of Protic Ionic Liquids as Sustained Corrosion Inhibitors for Mild Steel in Saline Solution with Acidic pH and Temperature Variations

The industry's principal objective is to comprehend the optimal application of each metal alloy in terms of corrosion resistance. A key focus lies in exploring alternative approaches to address this corrosive process in a manner that is both sustainable and economically feasible. The major strategy to mitigate this contest involves the utilization of inhibitors. However, it is imperative to note that certain inhibitors pose environmental risks. This study explores the effect of the addition of protic ionic liquids (PILs) on the corrosion of carbon steel (A36) in a saline solution (3.5 wt% NaCl), considering variations in pH and temperature. It focuses on understanding the effects of pH and temperature on the PILs' ability to protect the steel surface. Notably, changes in pH do not affect the protective capacity of the inhibitors. Efficiency values exceeding 72% were achieved under both acidic conditions tested. The study reveals two scenarios: At 40 °C, the PILs effectively protect the steel, with an efficiency of approximately 74% at concentrations of 500 and 1000 ppm. However, at 60 °C, efficiency decreases notably, reaching a maximum of 51% at a concentration of 500 ppm. Afterward, to evaluate the protective effectiveness of these compounds, gravimetric and electrochemical impedance spectroscopy (EIS) serve as the main methods, accompanied by optical and atomic force microscopy (AFM) for evaluating the surface. In electrochemical tests, PILs 1 and 2 exhibit superior efficiency, with film formation, while PILs 3 to 6 demonstrate comparatively lower values.

Keywords:
A. Protic Ionic Liquids; B. Corrosion Inhibitor; C. Mild Steel A36; D. Electrochemistry