[en] Graphical abstract: Equilibrium adsorption configurations of 2-amino-5-bromopyrazine (ABP) on Fe (1 1 0) surface using molecular dynamics (MD) simulations. - Highlights: • DFT and molecular dynamics studies of pyrazine derivatives used as corrosion inhibitor. • The correlation of inhibition effect and reactivity parameters was discussed. • We model the interactions of some pyrazine derivatives on Fe (1 1 0) surface. • Excellent correlation exist between inhibition efficiency and binding energy. - Abstract: The adsorption properties of three pyrazine compounds namely, 2-methylpyrazine (MP), 2-aminopyrazine (AP) and 2-amino-5-bromopyrazine (ABP), for steel corrosion was investigated by quantum chemical calculation and quenched force-field molecular dynamics simulation. Global reactivity parameters such as E_HOMO, E_LUMO, the energy gap (E_LUMO − E_HOMO), dipole moment, have been calculated and discussed. Fukui indices were calculated to describe the local reactive sites of the molecules. The equilibrium adsorption behaviour of these pyrazine molecules on Fe (1 1 0) surface was investigated using molecular dynamics simulation. The binding energy followed the order: ABP > AP > MP, which is in agreement with experimental results

[en] The inhibition of mild steel corrosion in 1 M HCl aqueous solution by 3-amino-2-methylbenzylalcohol (AMBA) was investigated using weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) and cyclic voltammametry (CV) techniques. Attenuated total reflectance infrared spectroscopy (ATR-IR), contact angle (CA) and scanning electron microscopy (SEM) measurements were carried out to confirm the adsorption of AMBA on mild steel surface. Computer simulations using density functional theory (DFT) and Monte Carlo methodologies were further employed to provide insights into the mechanism of interaction between the inhibitor and the steel surface. All the results confirmed that AMBA is a good corrosion inhibitor for mild steel in 1 M HCl. The addition of NaI was found to increase the inhibition effect of AMBA on mild steel to a considerable extent. DFT results reveal that the N atom together with the π-systems in the aromatic ring were the active sites for the interaction of AMBA with steel surface. Furthermore, the negative value of the adsorption energy obtained from the Monte Carlo simulation indicates the stability of the adsorbed inhibitor film on the steel surface. - Graphical abstract: EIS spectra and adsorption configuration of AMBA on Fe (110). - Highlights: • 3-amino-2-methylbenzylalcohol inhibit mild steel corrosion in acid medium. • ATR-IR, contact angle, SEM, were used for steel surface characterization. • DFT and Monte Carlo simulations provide atomic and molecular level insights. • The theoretical data clearly support the experimental results obtained.

[en] A theoretical study of benzimidazole (BI) and two of its derivatives namely 2-methylbenzimidazole (2-CH₃BI) and 2-mercaptobenzimidazole (2-SHBI) recently used as corrosion inhibitors for mild steel in 1 M HCl was undertaken by considering Density Functional Theory (DFT) at the B3LYP/6-311G++(d,p) level. The properties most relevant to their potential action as corrosion inhibitors has been calculated in the neutral and protonated form: E_HOMO, E_LUMO, energy gap (ΔE), dipole moment (μ), electronegativity (χ), global hardness (η) and the fraction of electrons transferred from the inhibitor molecule to the metallic atom (ΔN). The theoretical results are in agreement with the experimental data.

[en] Research highlights: → Alloxazine (ALLOX) is found to be a good inhibitor for the corrosion of mild steel in 0.5 M H₂SO₄. → The adsorption of ALLOX on mild steel surface was found to accord with the Temkin adsorption isotherm and also follows the first-order reaction. → The corrosion inhibition is satisfactorily discussed by both thermodynamic and kinetic parameters. → The inhibitive mechanism is explained by UV-Visible spectroscopy and quantum chemical calculation results. - Abstract: Alloxazine (ALLOX) was tested as corrosion inhibitor for mild steel in 0.5 M H₂SO₄ solution using non-electrochemical technique (gravimetric and UV-Visible spectrophotometric measurements) at 303-333 K. ALLOX acts as inhibitor for mild steel in acidic medium. Inhibition efficiency increases with increase in concentration of ALLOX but decrease with rise in temperature. The adsorption of ALLOX was found to follow Temkin adsorption isotherm model. Both the activation and thermodynamic parameters governing the adsorption process were calculated and discussed. The adsorption follows a first-order kinetics. DFT study gave further insight into the mechanism of inhibition action of ALLOX.

[en] Indeno-1-one [2,3-b] quinoxaline (INQUI), synthesized in our laboratory, was tested as inhibitor for the corrosion of mild steel in 0.5 M H₂SO₄ using gravimetric method at 30 ^oC. The inhibitor (INQUI) showed about 81% inhibition efficiency (E (%)) at an optimum concentration of 10 x 10^-6 M. The inhibition efficiency increases with increase in inhibitor concentration but decreases with increase in immersion time. The adsorption of the inhibitor on the mild steel in the acid solution was found to accord with Temkin's adsorption isotherm. The calculated value of the free energy for the adsorption process, ΔG_ads, reveals a strong chemisorbed bond between the inhibitor and mild steel surface and a spontaneous adsorption of the inhibitor on the mild steel surface. Density functional theory (DFT) proves that INQUI molecule is adsorbed on the mild steel surface by the most negatively charged nitrogen and oxygen atoms.

[en] 2,3-diphenylbenzoquinoxaline (2,3DPQ) has been synthesized and its inhibiting action on the corrosion of mild steel in 0.5 M H₂SO₄ has been assessed by weight loss method at 30 deg. C. The results of the investigation show that this compound has excellent inhibiting properties for steel corrosion in sulphuric acid. Inhibition efficiency increases with increase in the concentration of the inhibitor. The adsorption of 2,3DPQ onto the mild steel surface followed the Langmuir adsorption model with the free energy of adsorption ΔG_ads⁰ of -11.4 kJ mol^-1. Quantum chemical calculations were employed to give further insight into the mechanism of inhibition action of 2,3DPQ.

[en] Ketoconazole (KCZ) has been evaluated as a corrosion inhibitor for mild steel in aerated 0.1 M H₂SO₄ by gravimetric method. The effect of KCZ on the corrosion rate was determined at various temperatures and concentrations. The inhibition efficiency increases with increase in inhibitor concentration but decrease with rise in temperature. Adsorption followed the Langmuir isotherm with negative values of ΔG_ads⁰, suggesting a stable and a spontaneous inhibition process. Quantum chemical approach was further used to calculate some electronic properties of the molecule in order to ascertain any correlation between the inhibitive effect and molecular structure of ketoconazole.

[en] The inhibitive capabilities of Clotrimazole (CTM) and Fluconazole (FLC), two antifungal drugs, on the electrochemical corrosion of aluminium in 0.1 M HCl solution has been studied using weight loss measurements at 30 and 50 deg. C. The results indicate that both compound act as inhibitors in the acidic corrodent. At constant acid concentration, the inhibition efficiency (%I) increased with increase in the concentration of the inhibitors. Increase in temperature increased the corrosion rate in the absence and presence of the inhibitors but decreased the inhibition efficiency. CTM and FLC adsorbed on the surface of aluminium according to the Langmuir adsorption isotherm model at all the concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameter obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. The reactivity of these compounds was analyzed through theoretical calculations based on AM1 semi-empirical method to explain the different efficiencies of these compounds as corrosion inhibitors. CTM was found to be a better inhibitor than FLC.

[en] Highlights: • The inhibition performance of three Schiff bases on steel were studied theoretically. • The adsorption energies of the Schiff bases with Fe (110) were high and negative. • BDTC adsorbed more stronger on Fe than BMTC and BHTC. • DFT modeling and Monte Carlo simulations provided molecular level insights. • Theoreical evaluation and experimental results were in good agreement. DFT and Monte Carlo simulation were performed on three Schiff bases namely, 4-(4-bromophenyl)-N^′-(4-methoxybenzylidene)thiazole-2-carbohydrazide (BMTC), 4-(4-bromophenyl)-N^′-(2,4-dimethoxybenzylidene)thiazole-2-carbohydrazide (BDTC), 4-(4-bromophenyl)-N^′-(4-hydroxybenzylidene)thiazole-2-carbohydrazide (BHTC) recently studied as corrosion inhibitor for steel in acid medium. Electronic parameters relevant to their inhibition activity such as E_HOMO, E_LUMO, Energy gap (ΔE), hardness (η), softness ($\sigma$), the absolute electronegativity (χ), proton affinity $\left(\mathrm{PA}\right)$ and nucleophilicity (ω) etc., were computed and discussed. Monte Carlo simulations were applied to search for the most stable configuration and adsorption energies for the interaction of the inhibitors with Fe (110) surface. The theoretical data obtained are in most cases in agreement with experimental results.

[en] The effect of iodide ions on the inhibitive performance of 2,3-diaminonaphthalene (2,3-DAN) in 1 M HCl for aluminium corrosion has been studied using hydrogen evolution (gasometry) measurements at 30 and 40 deg. C. Results obtained showed that the presence of 2,3-DAN molecules in the corrosive medium (1 M HCl solution) inhibits the corrosion process of aluminium and as the concentration of 2,3-DAN increases the inhibition efficiency also increased at the studied temperatures. A synergistic effect was observed between KI and 2,3-DAN. The experimental results suggest that the presence of iodide ions in the solutions stabilized the adsorption of 2,3-DAN molecules on the metal surfaces and, therefore improve the inhibition efficiency of 2,3-DAN. Phenomenon of physical adsorption is proposed for the inhibition and the process followed the Freundlich adsorption isotherm. The activation energy (E_a), heat of adsorption (Q_ads) and free energy of adsorption for the corrosion process (ΔG_ads) have been evaluated at the different temperatures and the values support the results obtained. Some quantum chemical parameters and the Mulliken charge densities for 2,3-diaminonaphthalene were calculated by the AM1 Semi-empirical method to provide further insight into the mechanism of inhibition of the corrosion process