Experimental and theoretical insights into the corrosion mitigation efficacy of novel quinoline-based pyrazole and isoxazole derivatives

Abstract

Mild Steel (MS) is widely used in various industrial applications due to its excellent mechanical properties and cost-effectiveness. However, prolonged usage often results in scale formation on MS surfaces, significantly reducing equipment efficiency and leading to production losses and, in some cases, industrial accidents. Acid descaling, commonly using 15 % hydrochloric acid (HCl), is effective for scale removal but can also accelerate corrosion of the underlying metal. Application of corrosion inhibitors is an effective methodology to mitigate the acid induced corrosion. This study investigates the application of two novel Quinoline-based compounds as effective corrosion inhibitors for mild steel in 15 % HCl. The pyrazole derivative namely 2-chloro-6-methoxy-3-(5-(4-methoxyphenyl)-1H-pyrazol-3-yl) quinoline [CMMQ] had displayed superior efficiency of 99.7 % and the isoxazole derivative namely 3-(2-chloro-6-methoxyquinolin-3-yl)-5-(4-methoxyphenyl)isoxazole [CMMI] displayed the efficiency of 96.7 %. Both the corrosion inhibitors display strong adsorption capabilities upon the MS surface driven through Langmuir adsorption isotherm model. The observed value for ΔG_ads lies around −41 kJ mol⁻¹ underscoring their potential in high-temperature and low-dosage applications. The electrochemical analysis reveals the mixed type adsorption of the corrosion inhibitors and they effectively protect the cathodic and anodic sites of corrosion. The primary adsorption mechanism is attributed to the aromatic heterocyclic rings, enhancing both inhibitor stability and surface protection. Theoretical results obtained in the study provided further insights into the interaction of the corrosion inhibitor molecules the steel at the atomic level.