Enhancing corrosion resistance of XC38 steel using sulfur and nitrogen-containing phenyl thiosemicarbazone: A comprehensive experimental and computational analysis

Background

This research explores the effectiveness of a novel Schiff base compound as an organic corrosion inhibitor for XC38 steel immersed in a 1M hydrochloric acid solution. The study aims to identify the inhibitor's ability to reduce corrosion under controlled experimental conditions.

Methods

The synthesis and characterization of the Schiff base inhibitor were meticulously confirmed through FTIR, XRD, and NMR techniques. The efficacy of this inhibitor in curbing the corrosion of XC38 carbon steel in a 1M hydrochloric acid solution was rigorously evaluated using gravimetric analysis, Electrochemical Impedance Spectroscopy (EIS), and Potentiodynamic Polarization (PDP), with a specific focus on the impacts of varying concentrations and temperatures. Surface interaction mechanisms were thoroughly investigated using SEM, EDS, AFM, ATR-FTIR, and XRD. These studies were complemented by activation thermodynamics and adsorption isotherm assessments, providing a comprehensive understanding of the thermodynamic properties of the inhibitor. Additionally, computational studies, including DFT, NCI analysis, and MC simulations, were employed to delve into the dynamics of inhibitor-surface interactions, offering detailed insights into the molecular interactions at play.

Significant findings

The novel Schiff base inhibitor demonstrated remarkable efficacy, achieving up to 98.14 % effectiveness at a concentration of 100 ppm in protecting XC38 steel in a corrosive environment as determined by weight loss measurements. Gravimetric analysis revealed a significant reduction in mass loss and corrosion rate, corresponding with an increase in DMTS concentration. PDP measurements indicated an inhibition efficiency (EI%) of up to 94 %. EIS results showed an inhibition efficiency (EI%) of up to 93.53 %. The inhibitor's performance was notably enhanced at lower temperatures (303, 313, and 323 K) and higher concentrations. Activation thermodynamics and adsorption isotherm studies showed negative $\Delta G_{ads}^{\circ }$ values, indicating spontaneous adsorption. Advanced EIS and Tafel polarization studies identified the compound as a mixed-type inhibitor, effectively modulating both cathodic and anodic reactions. Surface analyses using SEM, EDS, AFM, and XRD confirmed the formation of a protective layer on the steel surface, preventing the formation of iron oxides and thus mitigating corrosion. Complementary DFT calculations, including analyses of Mulliken charge, FMOs, DOS, ESP, and ELF analyses, provided detailed insights into potential electron donation and acceptance sites crucial for its inhibitory action. NCI analysis shed further light on the nature of inhibitor-metal surface interactions, enhancing our understanding of the adsorption mechanisms. MC simulations robustly supported these theoretical insights, which depicted the inhibitor's adsorption behavior on the Fe(110) surface, demonstrating a compelling alignment between theoretical forecasts and empirical observation.