Electrochemical study of three new morpholine-based inhibitors for P460N steel in 3.5 wt. % NaCl solution

Abstract

BackgroundCorrosion of steel occurs due to the rough working environment in which it is used. It accelerates the deterioration of the steel components and results in substantial financial loss. Continuous research has been carried out to prevent or reduce the corrosion of steel and other metals because these materials have so many industrial applications. MethodsThe inhibition performance of three new organic substances, N1-(3-morpholinopropyl)-N1-((pyridine-2-yl)methyl)propane-1,3-diamine (I1), 2‑methoxy-6-(((3-((3-morpholinopropyl)(pyridin-2-ylmethyl)amino)propyl)imino)methyl)phenol (I2), and its reduced form, 2‑methoxy-6-(((3-((3-morpholinopropyl)(pyridin-2-ylmethyl)amino)propyl)imino) methyl) phenol (I3), on corrosion of the P460N in 3.5 wt.% NaCl solution was investigated by potentiodynamic polarization (PDP), EIS, immersion tests, and SEM techniques. Significant findingsA novel material exhibiting superior corrosion protection capabilities for steel was synthesized, and its efficacy was validated through both electrochemical and non-electrochemical testing methods. Comparing the OCP values in the blank and inhibitor-containing solutions shows a negative shift. According to PDP experiments, the highest value of icorr occurs with the P460N electrode in the inhibitor-free solution (79.4 μA.cm−2). Meanwhile, in the case of the highest concentration of I1, I2, and I3 inhibitors, a significant reduction in the corrosion rate was observed, with reductions of 6, 17, and 22 times, respectively. Notably, the reduced form (I3) exhibited exceptional protection against corrosion. PDP results confirmed that the inhibition efficiency reached the highest value of 84.1, 94.3, and 95.5% for I1, I2, and I3 at 2.0 mM concentration. From the EIS measurements, the inhibition performance of inhibitors follows the order I3 > I2 > I1 at equal concentration. Based on the immersion test results and SEM-EDS evaluation, the reduced sample (I3) demonstrated significantly lower corrosion over an extended period, indicating excellent long-term stability in the 3.5% NaCl solution. The electrochemical (PDP and EIS), and non-electrochemical (immersion tests) data confirmed that the inhibition efficiency of the inhibitor of I3 was better than the two other compounds. SEM and EDS analysis showed severe corrosion for the P460N surface without an inhibitor, and corrosion products such as iron oxide and trapped NaCl in porosity appeared very uneven, with different shapes. The study explored four absorption mechanisms: Langmuir, Temkin, Freundlich, and Frumkin. The three new inhibitors were found to adhere to the Langmuir adsorption isotherm with a high correlation coefficient of approximately 0.999. Moreover, these inhibitors demonstrated mixed inhibition behavior for P460N steel in a 3.5% NaCl solution.