1-(benzyloxy)-1-oxopropan-2-aminium 4-methylbenzenesulfonate (BOPAMS) and 4-(benzyloxy)-4-oxobutan-1aminium 4-methylbenzenesulfonate (BOBAMS) were prepared and confirmed through spectroscopic methods (FT-Infrared, Carbon 13-NMR and Proton-NMR). BOPAMS and BOBAMS were evaluated as unharmful inhibitors for aluminium corrosion. The anti-corrosive properties, inhibition mechanism, inhibitor-metal adsorption behaviour and corrosion inhibition efficiency were evaluated by employing approaches like gravimetric, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). FT-IR demonstrated functional groups that are responsible for the binding of BOPAMS and BOBAMS with surfaces of aluminium. BOPAMS and BOBAMS resemble a semi-chemisorption/physisorption mechanism, obeying Langmuir binding model. The mechanism of binding adopted by BOPAMS and BOBAMS was proposed.
The anticorrosive properties of six (6) selected sulphonamide derivatives on the aluminium surface were investigated in order to reveal their mechanism and mode of adsorption on Al/HCl interface, as well as the strength of the interactions between the inhibitor and Al surface. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques were utilised to evaluate the inhibition efficiencies of the selected compounds, while scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy techniques were utilised to understand the surface morphology of Al and adsorption sites of the sulphonamides. Density functional theory (DFT) calculations were utilised to investigate the strength of interactions between the inhibitor molecules and Al. Corrosive electrolyte of 1 M hydrochloric acid was employed in the study. All the studied sulphonamides showed excellent corrosion inhibition efficiencies with maximum values of up to 95%-97% at the optimum concentrations (4 × 10-5 M - 4 × 10-5 M), based on EIS measurements. The EIS parameters further revealed adsorbed film of the sulphonamides on the Al surface with capacitive-inductive characters. All the six sulphonamides reduced the corrosion current densities for both anodic and cathodic half-reactions and shifted the corrosion potentials to some anodically nobler values as revealed by the PDP data. Adsorption of the sulphonamides at the Al/HCl interface was described by the Langmuir isotherm model. Surface protection properties of the sulphonamides were further confirmed by SEM plates that showed less damaged surface of Al for the inhibited process compared to the uninhibited one. DFT results suggest that the binding energy for the inhibitors on the Al surface results in an energy that is less than 30 kJ/mol, which is an indication that the interactions are van der Waal type of interaction, suggesting physisorption mechanism.
SYNOPSIS The effectiveness of two synthesized ionic liquids, 1-(benzyloxy)-1-oxopropan-2-aminium 4-methylbenzenesulfonate (1-BOPAMS) and 4-(benzyloxy)-4-oxobutan-1-aminium 4-methylbenzenesulfonate (4-BOBAMS), were evaluated for mild steel corrosion inhibition in 1.0 M hydro-chloric acid solution, using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and gravimetric techniques. Organic moieties responsible for the adsorption process on mild steel surface were investigated using Fourier transform infrared spectroscopy (FTIR). Gravimetric analysis revealed that the inhibition efficiency of 1-BOPAMS and 4-BOBAMS increased with concentration, with maximum inhibition values of 90.32% and 97.91%, respectively, at the highest concentration of the inhibitors. Gibbs free energy (nG°ads) values indicated a strong interaction between the mild steel surface and the molecules of the ionic liquids, and that the adsorption process was spontaneous. These values also show that the inhibitive nature of ionic liquids against mild steel corrosion is caused by a mixedtype of adsorption film formed on the steel surface. The Langmuir adsorption isotherm was used to describe the adsorption of ionic liquid molecules onto the mild steel surface. Polarization curves showed that 1-BOPAMS and 4-BOBAMS have a similar effect on both the anodic and cathodic half-reactions, indicating that they prevent the dissolution of mild steel through both physical and chemical process. Nyquist plots were defined by incomplete semicircle capacitive loops, showing that the charge transfer mechanism controls the corrosion of mild steel in acidic solution. Keywords: corrosion inhibition, ionic liquids, mild steel, adsorption isotherm.
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