Inhibition Effect of Thiourea Derivative for Mild Steel Corrosion in Acid Medium: Experimental and Theoretical Studies

Abstract

The corrosion inhibition efficiency of thiourea derivative 1-[morpholin-4-yl(phenyl)methyl]thiourea (MPMT) for mild steel in 0.5 M HCl was studied at temperatures 303 K, 313 K, 323 K, and 333 K using experimental techniques like potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements and density functional theory technique. The results suggest that thiourea derivative is an excellent corrosion inhibitor for mild steel. The study of inhibition efficiency of the inhibitor at various temperatures revealed that efficiency of the inhibitor increased up to 323 K and at 333 K inhibition efficiency decreased due to desorption of the inhibitor. The inhibitor MPMT shows maximum corrosion inhibition efficiency of 91.08% and 91.2% in 1000 ppm concentration at 323 K according to PDP and EIS measurement, respectively. PDP measurements showed that MPMT acts as a mixed-type inhibitor involving both physisorption and chemisorption. This is also supported by the standard free energy of adsorption values (− 31.14 to − 36.68 kJ mol−1). The adsorption of MPMT on to the MS surface is obeyed by Langmuir adsorption isotherm at all temperatures. The regression values (R2) obtained from the adsorption isotherm plot are near to unity. The surface morphology of the uninhibited and inhibited mild steel samples was analyzed using the scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and UV–Visible spectroscopy. The fraction of electron transfer ∆N value obtained from the theoretical study is 0.5417, indicating the higher ability of the inhibitor molecule to donate electrons to the metal surface. The results obtained from quantum chemical analysis well correlated with the experimental studies.