Experimental and theoretical study on the inhibition performance of triazole compounds for mild steel corrosion

A relationship between quantum chemical parameters for three triazole compounds and their inhibition ability was studied using electrochemical measurements (potentiodynamic polarization and EIS), molecular dynamic method and quantum chemical calculations. Electrochemical measurements results revealed that the inhibition efficiencies increased with the concentration of inhibitors. The molecular dynamic method results showed that the higher interaction potential between the inhibitor and metal surface, the higher the inhibition efficiency. The quantum chemical calculation results showed that the triazole ring is the active site in these inhibitors and they can absorb on Fe surface by donating electrons to Fe d-orbital.     

Temperature effect on mild steel corrosion in acid media in presence of azoles

The inhibiting properties of four azoles (indole, benzimidazole, benzotriazole, benzothiazole) were investigated in case of mild steel corrosion in 1 M HCl. The effect of temperature was followed. Impedance spectroscopy, polarization resistance, gravimetric and polarization curves methods were applied. An adequate structural model of the interface in inhibitors presence is offered and the values of the corresponding parameters are calculated. The apparent activation energy of the process taking place in an inhibitor presence was determined on the ground of five temperature values in the range from 20 °C to 60 °C using the data obtained by two independent methods. Comparative investigations were carried out in 1 M H₂SO₄ aiming to elucidate the effect of the acid’s anion. The generalization of the data obtained provided to make conclusions concerning the mechanism of the inhibitors’ adsorption.     

Effect of 2,2′ benzothiazolyl disulfide on the corrosion of mild steel in acid media

2,2′ benzothiazolyl disulfide (BTDS) has been synthesised and their inhibiting action on mild steel corrosion in 1 M HCl and 0.5 M H₂SO₄ at 308 K has been investigated using weight loss, EIS, polarization and SEM study. BTDS showed better efficiency in 0.5 M H₂SO₄ compared to 1 M HCl. Polarization studies revealed that BTDS is a mixed type inhibitor in both acids predominantly cathodic in 1 M HCl where as predominantly anodic in 0.5 M H₂SO₄. Thermodynamic parameters i.e. free energy of adsorption, enthalpy, entropy and activation energy were calculated, the values of these parameters showed good interaction.     

Quantum chemical studies on the corrosion inhibition of some sulphonamides on mild steel in acidic medium

Quantum chemical calculations using the density functional theory (DFT) and some semi-empirical methods were performed on four sulphonamides (sulfaguanidine, sulfamethazine, sulfamethoxazole and sulfadiazine) used as corrosion inhibitors for mild steel in acidic medium to determine the relationship between molecular structure and their inhibition efficiencies. The results of the quantum chemical calculations and experimental %IE were subjected to correlation analysis and indicate that their inhibition effect are closely related to E_HOMO, E_LUMO, hardness, polarizability, dipole moment and charges. The %IE increased with increase in the E_HOMO and decrease in E_HOMO − E_LUMO. The negative sign of the E_HOMO values and other kinetic and thermodynamic parameters indicates that the data obtained support physical adsorption mechanism.     

Experimental and molecular dynamics studies on corrosion inhibition of mild steel by 2-amino-5-phenyl-1,3,4-thiadiazole

The corrosion inhibition of mild steel in 0.5 M H₂SO₄ and 1.0 M HCl by 2-amino-5-phenyl-1,3,4-thiadiazole (APT) has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results show that the inhibition efficiency increases with the increase of APT concentration in both acids, and the higher inhibition efficiency is obtained in 0.5 M H₂SO₄. The adsorption of APT molecules on the steel surface obeys Langmuir adsorption isotherm in both acids, and occurs spontaneously. The molecular dynamics method has also been used to simulate the adsorption of ATP molecule and solvent ions on the iron surface. The results show that with the adsorption of sulfate ions the Fe + anion + APT system has the higher negative interaction energy comparing to the case of the adsorption of chloride ions.     

Electrochemical and quantum chemical studies of some azomethine compounds as corrosion inhibitors for mild steel in 1 M hydrochloric acid

The corrosion inhibition effect of new azomethine compounds: PhNNC (COCH₃)NC₆H₄Y {Y = OCH₃ (SB₁), CH₃ (SB₂), H (SB₃), Br (SB₄) and Y = Cl (SB₅)} on mild steel in 1 M HCl, was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and quantum chemistry analysis. It has been found that the inhibition efficiency increased with increasing inhibitor concentration. The polarization curves showed that these Schiff bases function as mixed inhibitors. The adsorption of studied compounds on mild steel surface was found to follow the Langmuir isotherm. Molecular modeling was used to correlate corrosion inhibition properties and calculated quantum chemical parameters.     

Quantum chemical study of some cyclic nitrogen compounds as corrosion inhibitors of steel in NaCl media

Corrosion inhibition efficiencies of 3-amino-1,2,4-triazole (3-ATA), 2-amino-1,3,4-thiadiazole (2-ATDA), 5-(p-tolyl)-1,3,4-triazole (TTA), 3-amino-5-methylmercapto-1,2,4-triazole (3-AMTA) and 2-aminobenzimidazole (2-ABA) as corrosion inhibitors on steel in sodium chloride media were investigated by using semiempirical PM3 and density functional theory (DFT) methods. Quantum chemical parameters such as highest occupied molecular orbital energy (E_HOMO), lowest unoccupied molecular orbital energy (E_LUMO), energy gap (ΔE) and dipole moment (μ) have been calculated for these compounds by using semiempirical PM3 and 6-31G(d), 6-311G(d,p) DFT methods. It was found that theoretical data support the experimental results.     

Theoretical investigation of corrosion inhibition effect of imidazole and its derivatives on mild steel using cluster model

Interaction energies of imidazole and its seven derivatives on the surface of mild steel were calculated via a cluster model by using quantum chemical calculations at density functional theory level. The mild steel surface and its adsorption sites were considered as some clusters taken from two-layered (0 0 1) planes and the quantum chemical calculations which were carried out consist of adsorption of the inhibitor molecules on the surface of these clusters. It is shown that 90% of inhibition variations of the imidazole derivatives are described by considering perpendicular interaction of the inhibitors by iron atom in the mild steel unit cell.     

Investigation on some Schiff bases as corrosion inhibitors for mild steel

In the present work, the effect of some newly synthesized Schiff bases containing sulphur nitrogen as heteroatom was investigated on mild steel corrosion in acidic media. Electrochemical studies of the mild steel samples were performed in an aerated solution of 0.1 M HCl + dimethyl sulphoxide (DMS) as co-solvent. DMS is also behaving as a corrosion inhibitor for mild steel. At low inhibitor concentration and short immersion time one can see only the inhibitive effect of DMS as anodic inhibitor for mild steel. At high concentration and long immersion time inhibition efficiencies are increased and cathodic inhibition is observed.     

Experimental and theoretical studies for mild steel corrosion inhibition in 1 M HCl by two new benzothiazine derivatives

The inhibition effect of new heterocyclic compounds, namely 2-aryl-benzothiazin-3-one (P1) and 3-aryl-benzothiazin-2-one (P2) on mild steel corrosion in 1 M HCl was investigated using electrochemical measurements. The results indicated that the inhibition efficiency depends on concentration and molecular structure of the investigated compounds. It is also found that the inhibition of P1 is greater than P2. The molecular structure effect on the corrosion inhibition efficiency was investigated using DFT calculations. The structural and electronic parameters were calculated and discussed. The obtained results show that the experimental and theoretical studies agree well and confirm that P1 is the better inhibitor.     

Inhibitive effect of diethylcarbamazine on the corrosion of mild steel in hydrochloric acid

Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), weight loss measurements and atomic force microscopy techniques were used to investigate the inhibitory effect of diethylcarbamazine (DECM) on corrosion of mild steel in HCl solution. The inhibitor showed >90% inhibition efficiency at 5.01 × 10⁻⁴ M. Results obtained revealed that inhibition occurs through adsorption of inhibitor molecules on metal surface without modifying the mechanism of corrosion process. Potentiodynamic polarization studies suggested that it is a mixed type inhibitor, predominantly controls cathodic reaction. Activation parameters (E_a, ΔH and ΔS) and thermodynamic parameters (, and ) were calculated to investigate mechanism of inhibition.     

Evaluation of the inhibitive effect of some plant extracts on the acid corrosion of mild steel

Corrosion inhibition of mild steel in 2 M HCl and 1 M H₂SO₄ by extracts of selected plants was investigated using a gasometric technique at temperatures of 30 and 60 °C. The studied plants materials include leaf extracts Occimum viridis (OV), Telferia occidentalis (TO), Azadirachta indica (AI) and Hibiscus sabdariffa (HS) as well as extracts from the seeds of Garcinia kola (GK). The results indicate that all the extracts inhibited the corrosion process in both acid media by virtue of adsorption and inhibition efficiency improved with concentration. Synergistic effects increased the inhibition efficiency in the presence of halide additives. Inhibition mechanisms were deduced from the temperature dependence of the inhibition efficiency as well as from assessment of kinetic and activation parameters that govern the processes. Comparative analysis of the inhibitor adsorption behaviour in 2 M HCl and 1 M H₂SO₄ as well as the effects of temperature and halide additives suggest that both protonated and molecular species could be responsible for the inhibiting action of the extracts.     

Thermodynamic, electrochemical and quantum chemical investigation of some Schiff bases as corrosion inhibitors for mild steel in hydrochloric acid solutions

The corrosion inhibition of mild steel in 1.0 M HCl solution by four Schiff bases was investigated using weight loss and electrochemical measurements and quantum chemical calculations. All compounds showed >90% inhibition efficiency at their optimum concentrations. The activation energy (E_a) of corrosion and other thermodynamic parameters were calculated to elaborate the mechanism of corrosion inhibition. The adsorption of the inhibitors on the mild steel surface follows Langmuir isotherm model. Polarization studies indicated that all studied inhibitors are mixed type. The computed quantum chemical properties viz., electron affinity (EA) and molecular band gap (ΔE_MBG) show good correlation with experimental inhibition efficiencies.     

The effects of pharmaceutically active compound doxycycline on the corrosion of mild steel in hydrochloric acid solution

Corrosion inhibition of mild steel in hydrochloric acid solution by doxycycline has been studied by weight loss measurements, polarization resistance, Tafel polarization and electrochemical impedance spectroscopy. The inhibitor showed more than 95% inhibition efficiency at optimum concentration 9.02 × 10⁻⁴ M. Potentiodynamic polarization suggests that it is a mixed type of inhibitor. Electrochemical impedance spectroscopy was used to investigate the mechanism of corrosion inhibition. Thermodynamic parameters were calculated to investigate mechanism of inhibition. The compound follows Langmuir adsorption isotherm. AFM studies of mild steel surface with and without inhibitor were performed and calculated roughness also supported the inhibition data.     

Effect of hexamethylpararosaniline chloride (crystal violet) on mild steel corrosion in acidic media

The corrosion inhibition of mild steel in 0.5 M H₂SO₄ and 1 M HCl by hexamethylpararosaniline chloride (HMPC) was investigated using the gravimetric technique in the temperature range 303–333 K. The results indicate that HPMC inhibited the corrosion reaction in both acid media at all temperatures and inhibition efficiency increased with HMPC concentration. The inhibiting action is attributed to general adsorption of protonated and molecular HPMC species on the corroding metal surface. Adsorption followed a modified Langmuir isotherm and the Temkin isotherm, with very high negative values of the free energy of adsorption (). An increase in temperature reduced the inhibition efficiency of HPMC in 0.5 M H₂SO₄ but increased efficiency in 1 M HCl. Activation parameters such as activation energy (E_a), activation enthalpy (ΔH^∗) and activation entropy (ΔS^∗) as well as the adsorption heat (Q_ads) were evaluated from the effect of temperature on corrosion and inhibition processes.     

The inhibition action of ammonium salts of O,O′-dialkyldithiophosphoric acid on carbon dioxide corrosion of mild steel

Ammonium salts of O,O′-dialkyldithiophosphoric acids (RО)₂ Р(S) S⁻ HN⁺, were synthesized and tested as inhibitors for carbon dioxide corrosion of mild steel using weight loss, polarization curves, electrochemical impedance spectroscopy and scanning electron microscopy methods. High inhibition efficiency has been found for all compounds (η = 70–99%) at very low concentrations (0.25–5) mg l⁻¹. Polarization curves show that the title compounds can be considered as inhibitors of the mixed type. The absorption of inhibitor molecules on the mild steel surface obeys the Langmuir isotherm. Inhibition efficiency for some ammonium salts increases with temperature. The activation energy and some thermodynamic parameters were computed.     

Synergistic effect of potassium iodide with phthalazone on the corrosion inhibition of mild steel in 1.0 M HCl

The effects of phthalazone (PTO) and its synergistic effect with KI on the corrosion of mild steel in 1.0 M HCl solution were studied using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The inhibition efficiency increases with the concentration of the inhibitor and increased further with the presence of 6.02 mM KI. The synergistic effect of 6.02 mM KI at different concentrations of PTO was determined by calculating the synergism parameters, which showed that a cooperative mechanism exists between the iodide anion and PTO cations.     

A comparative study of the corrosion inhibition of mild steel in sulphuric acid by 4,4-dimethyloxazolidine-2-thione

The corrosion protection of mild steel in a 2.5 M H₂SO₄ solution by 4,4-dimethyloxazolidine-2-thione (DMT) was studied at different temperatures by measuring changes in open circuit potential (OCP), potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Corrosion current densities calculated from EIS data were comparable to those obtained from polarisation measurements. Results showed that DMT inhibited mild steel corrosion in a 2.5 M H₂SO₄ solution and indicated that the inhibition efficiencies increased with the concentration of inhibitor, but decreased proportionally with temperature. Polarisation curves showed that DMT is a mixed-type inhibitor. Changes in impedance parameters suggested the adsorption of DMT on the mild steel surface, leading to the formation of protective films. The DMT adsorption on the mild steel surface followed the Langmuir adsorption isotherm. The kinetic and thermodynamic parameters for dissolution and adsorption were investigated. Comprehensive adsorption (physisorption and chemisorption) of the inhibitor molecules on the mild steel surface was suggested based on the thermodynamic adsorption parameters.     

Lignin terpolymer for corrosion inhibition of mild steel in 10% hydrochloric acid medium

Lignin terpolymer has been obtained by grafting copolymerization of both dimethyl diallyl ammonium chloride (DMDAAC) and acrylamide (AM) onto lignin. The corrosion inhibition properties of the terpolymer were tested. The results showed that the highest corrosion inhibition percentage was over 95% in 10% HCl acid medium at 25 °C and 80 °C. The lignin terpolymer inhibitor adsorption followed Temkin isotherm at 25 °C and 80 °C, and the adsorption capability was in reverse proportion to the temperature according to −ΔG_ads. The effects of corrosion inhibition are the comprehensive synergistic effect through the graft reaction among lignin, AM and DMDAAC.     

Tryptamine as a corrosion inhibitor of mild steel in hydrochloric acid solution

The inhibitor effect of tryptamine on the corrosion of mild steel in 0.5 M hydrochloric acid at 30 °C was investigated using linear polarization, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency increases with an increase in concentration of tryptamine. At 500 ppm tryptamine the inhibition efficiency calculated by these techniques is around 97%. Cathodic and anodic polarization curves of mild steel in the presence of different concentrations of tryptamine at 30 °C reveal that it is a mixed type inhibitor. Tryptamine follows Langmuir adsorption with adsorption free energy of −35.07 kJ mol⁻¹.