Functional role of BMPT (1-butyl-4-methylpyridinium tetrafluoroborate) as a corrosion inhibitor for mild steel

Surfactant-based organic inhibitors are effective for corrosion control due to their ability to adsorb on metal surfaces and form protective interfacial films. This study examines the corrosion inhibition behaviour of the cationic surfactant 1-butyl-4-methylpyridinium tetrafluoroborate (BMPT) for mild steel (MS) in 1 M sulphamic acid medium. Electrochemical measurements indicate that BMPT provides significant protection, with a maximum inhibition efficiency of 88.59% at 1.0 g L−¹ and 318 K. Thermodynamic parameters reveal spontaneous adsorption, with free energy values (ΔGads) between −7.95 and −10.17 kJ mol−¹, suggesting a mixed adsorption behaviour and predominantly physical adsorption. The adsorption process follows the Freundlich isotherm, suggesting favourable multilayer coverage of the steel surface. Surface morphology analyses using SEM, EDS, and profilometry confirm the formation of a compact inhibitor film and a substantial reduction in surface degradation. Computational studies based on density functional theory (DFT) and Monte Carlo (MC) simulations further support strong and stable adsorption of BMPT on the mild steel surface. The results demonstrate the suitability of BMPT as an effective inhibitor for acidic steel-processing environments.