Interactions and Inhibition Effect of Urea-Derived Mannich Bases on a Mild Steel Surface in HCl

Cost-effective
new Mannich bases 1-(pyridin-4-yl­(pyrrolidin-1-yl)­methyl)­urea
(UPyP), 1-(morpholino­(pyridin-4-yl)­methyl)­urea (UMP), and 1-(piperidin-1-yl­(pyridin-4-yl)­methyl)­urea
(UPP) were synthesized, characterized, and examined as corrosion inhibitors
for the corrosion of a mild steel surface in 1.0 M hydrochloric acid
(HCl) solution using weight loss, potentiodynamic polarization, and
electrochemical impedance spectroscopy (EIS) measurements. The X-ray
structures of UMP and UPP are reported. The inhibition efficiency
increases with increasing inhibitor concentration and decreases with
increasing solution temperature. Potentiodynamic polarization measurements
showed that all inhibitors are mixed type. The values of thermodynamic
and activation parameters were calculated and discussed. Adsorption
of inhibitors on the mild steel surface in the presence of HCl follows
Langmuir’s adsorption
isotherm. The relationship between molecular structure and their inhibition
efficiencies has been studied using density functional theory (DFT)
calculations. Experimental and theoretical results are in good agreement.