The application of some polydentate Schiff base compounds containing aminic nitrogens as corrosion inhibitors for mild steel in acidic media

The effect of three Schiff base compounds namely, (E)-2-(1-(2-(2-hydroxyethylamino)ethylimino)ethyl)phenol(I), 2,2′-(1E,1′E)-1,1′-(2,2′-azanediylbis(ethane-2,1-diyl)bis(azan-1-yl-1-ylidene))bis(ethan-1-yl-1-ylidene)diphenol(II) and 2,2′-((2E,12E)-3,6,9,12-tetraazatetradeca-2,12-diene-2,13-diyl)diphenol(III) on the corrosion behavior of steel in 2 M HCl solution has been investigated at 298 K by weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The inhibition efficiencies obtained from all methods employed are in good agreement. Results show compound III to be the best inhibitor with a mean efficiency of 93% at 10⁻² M additive concentration. Studies showed all three compounds to act as mixed type inhibitors and to obey the Langmuir adsorption isotherm.     

Aminic nitrogen-bearing polydentate Schiff base compounds as corrosion inhibitors for iron in acidic media: A quantum chemical calculation

Quantum chemical calculations based on DFT method were performed on three polydentate Schiff base compounds (PSCs) used as corrosion inhibitors for iron in acid media to determine the relationship between the molecular structure of PSC and inhibition efficiency. The structural parameters, such as the frontier molecular orbital energy HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), the charge distribution of the studied inhibitors, the absolute electronegativity (χ) values, and the fraction of electrons (ΔN) transfer from inhibitors to iron, were also calculated and correlated with inhibition efficiencies. The results showed that the inhibition efficiency of PSCs increased with the increase in E_HOMO and decrease in E_LUMO − E_HOMO; and the areas containing N atoms are most possible sites for bonding the metal iron surface by donating electrons to the metal.     

Electrochemical and theoretical investigation on the corrosion inhibition of mild steel by thiosalicylaldehyde derivatives in hydrochloric acid solution

Inhibitory effect of three Schiff bases 2-{[(2-sulfanylphenyl)imino]methyl}]phenol (A), 2-{[(2)-1-(4-methylphenyl)methylidene]amino}-1-benznethiol (B), and 2-[(2-sulfanylphen-yl)ethanimidoyl)]phenol (C) on corrosion of mild steel in 15% HCl solution has been studied using weight loss measurements, polarization and electrochemical impedance spectroscopy (EIS) methods. The results of the investigation show that the compounds A and B with mean efficiency of 99% at 200 mg/L additive concentration have fairly good inhibiting properties for mild steel corrosion in hydrochloric acid, and they are as mixed inhibitor. All measurements show that inhibition efficiencies increase with increase in inhibitor concentration. This reveals that inhibitive actions of inhibitors were mainly due to adsorption on mild steel surface. Adsorption of these inhibitors follows the Langmuir adsorption isotherm. Thermodynamic adsorption parameters (K_ads, ΔG_ads) of studied Schiff bases were calculated using the Langmuir adsorption isotherm. Activation parameters of the corrosion process such as activation energies, E_a, activation enthalpies, ΔH^∗, and activation entropies, ΔS^∗, were calculated by the obtained corrosion currents at different temperatures. Obvious correlation was found between the corrosion inhibition efficiency and the calculated parameters. The obtained theoretical results have been adapted with the experimental data.     

Bis-isoxazolidines: A new class of corrosion inhibitors of mild steel in acidic media

Two new bis-isoxazolidines were synthesized in excellent yields via cycloaddition reaction of 1-pyrroline 1-oxide with 2,7-di(10-undecenyloxy)naphthalene and 1,4-di(10-undecenyloxy)benzene. One of the bis-isoxazolidines, on reaction with two equivalents of 1-bromododecane, afforded a bis-quaternary ammonium salt. All three inhibitor molecules in the presence of 400 ppm at 60 °C achieved inhibition efficiencies (IE) in the ranges 97-98% and 92-96% as determined by gravimetric method for corrosion of mild steel in 1 M HCl and 0.5 M H₂SO₄, respectively. The results obtained by the electrochemical methods using Tafel plots and electrochemical impedance spectroscopy corroborated the findings of the weightloss method. Both bis-isoxazolidines demonstrated remarkable efficiency in the lower range of inhibitor concentrations - in the presence of a meager 1.5 ppm of the inhibitor molecules, IEs of ∼70% in 1 M HCl were achieved. Thermodynamic parameters (, , ) for the adsorption process in the presence of the bis-isoxazolidines were determined. The values of around -90 kJ/mol in 1 M HCl and −50 kJ/mol in 0.5 M H₂SO₄, pointed towards the chemisorption of the inhibitor molecules, especially in HCl media. While the corrosion inhibition by these molecules was predominantly under cathodic control in 1 M HCl, the inhibition in 0.5 M H₂SO₄ was found to be under anodic control. The bis-isoxazolidines were found to provide a suitable inhibition mechanism for the corrosion inhibition in HCl as well as in H₂SO₄ media.     

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.     

The corrosion protection of mild steel by polypyrrole/polyphenol multilayer coating

Electrochemical synthesis of very thin polyphenol (PPhe) film was achieved on polypyrrole coated mild steel electrode (MS/PPy) and a multilayer coating was obtained, cyclic voltammetry technique was used for the synthesis. The corrosion performance of this multilayer coating and single PPy coating were investigated in 0.05 M H₂SO₄ solution by using electrochemical impedance spectroscopy (EIS), anodic polarization curves and open circuit potential (E_ocp)-time curves were used. It was found that the multilayer coating could provide much better protection than the single PPy coating for corrosion of MS for much longer periods and an efficiency of 98.3% was determined for this coating after 340 h exposure time in corrosive medium. It is proposed that the very thin PPhe film coated on top of PPy coating lowered the porosity and improved the barrier effect of the coating significantly.     

Corrosion inhibition of mild steel in acidic medium by some sulfa drugs compounds

The inhibiting effect of four sulfa drugs compounds (e.g. sulfaguanidine, sulfamethazine, sulfamethoxazole and sulfadiazine) on mild steel corrosion in 1.0 M HCl solutions were evaluated using both galvanostatic polarization and weight loss techniques. All the examined sulfa drug compounds reduce the corrosion of mild steel. Among the compounds studied, sulfadiazine exhibited the best inhibition efficiency and sulfaguanidine the lowest. The inhibition efficiency goes through a maximum for sulfaguanidine while it increases continuously with concentration to a limit with sulfadiazine, sulfamethoxazole and sulfamethazine respectively. Galvanostatic polarization measurements indicate that all the examined compounds are of mixed inhibitor type with predominant cathodic effectiveness. Moreover, the results revealed a better performance for these compounds as corrosion inhibitors in HCl than in H₂SO₄ solutions. Also, the corrosion inhibition mechanism is discussed.     

Evaluation of 2-mercaptobenzimidazole as corrosion inhibitor for mild steel in phosphoric acid

The inhibiting action of 2-mercaptobenzimidazole on the corrosion of mild steel in phosphoric acid (H₃PO₄) solution has been investigated by weight loss and polarization. The studies reveal that the inhibitor is effective for the inhibition of mild steel over a wide concentration range of H₃PO₄ solutions and retards the anodic and cathodic corrosion reactions with emphasis on the former.     

Bis (benzimidazol-2-yl) disulphide: An efficient water soluble inhibitor for corrosion of mild steel in acid media

The inhibition effect of Bis (benzimidazol-2-yl) disulphide (BIMDS) on corrosion behavior of mild steel (MS) in 1.0 M HCl and 0.5 M H₂SO₄ was studied using different techniques. These studies have shown that studied compound is a good inhibitor for MS in 1.0 M HCl and 0.5 M H₂SO₄ solutions. Inhibitor showed better performance in 0.5 M H₂SO₄ solutions than 1.0 M HCl. Polarization measurements indicated that BIMDS is a mixed-type inhibitor in both acid media. Adsorption of inhibitor molecules on the mild steel surface showed Langmuir isotherm model in both acid media.     

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.     

Caffeic acid as a green corrosion inhibitor for mild steel

The inhibitor effect of the naturally occurring biological molecule caffeic acid on the corrosion of mild steel in 0.1 M H₂SO₄ was investigated by weight loss, potentiodynamic polarization, electrochemical impedance and Raman spectroscopy. The different techniques confirmed the adsorption of caffeic acid onto the mild steel surface and consequently the inhibition of the corrosion process. Caffeic acid acts by decreasing the available cathodic reaction area and modifying the activation energy of the anodic reaction. A mechanism is proposed to explain the inhibitory action of the corrosion inhibitor.     

Adsorption properties and inhibition of mild steel corrosion in hydrochloric solution by some newly synthesized diamine derivatives: Experimental and theoretical investigations

New diamine derivatives, namely 2-[{2-[bis-(2-hydroxyethyl)amino]ethyl}(2-hydroxyethyl)amino]ethanol (DAME) and 2-[{2-[bis-(2-hydroxyethyl)amino]ethyl}(2-hydroxyethyl)amino]propanol (DAMP) were synthesised and their inhibitive action against the corrosion of mild steel in 1 M HCl solution were investigated at 308 K. The detailed study of DAME is given using gravimetric measurements and polarization curves method. Results show that DAME is a good inhibitor and inhibition efficiency reaches 91.7% at 10⁻³ M. Tafel polarization study revealed that DAME acts as a mixed-type inhibitor. The inhibitor adsorption process in mild steel/DAME/hydrochloric acid system was studied at different temperatures (308-353 K) by means of weight loss measurements. The adsorption of DAME on steel surface obeyed Langmuir’s adsorption isotherm. The kinetic and thermodynamic parameters for mild steel corrosion and inhibitor adsorption, respectively, were determined and discussed. The comparative study of inhibitive performance of the two diamine derivatives revealed that DAME is more effective than DAMP. Quantitative Structure-Activity Relationship (QSAR) approach has been conducted in attempt to correlate the corrosion inhibition properties of these diamine derivatives with their calculated quantum chemical parameters.     

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.     

Evaluation of impedance measurements on mild steel corrosion in acid media in the presence of heterocyclic compounds

Five heterocyclic compounds, having a five atom ring, fused with the benzene ring (indole, benzimidazole, benzotriazole, benzothiazole and benzothiadiazole) were investigated as corrosion inhibitors of mild steel in 1 N HCl using impedance and polarisation resistance methods. Four of these compounds exhibit inhibition properties, while one of them, benzothiadiazole, stimulates the corrosion process. Adequate structure models of the interface are offered. The experimental data show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. At high inhibitor concentrations a second time constant is observed in the impedance spectra. The values of the polarisation resistance determined by the polarisation resistance method are well correlated with the sum of the separate resistances from the impedance measurements.     

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.     

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.     

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.     

Correlation between corrosion rate and AE signal in an acidic environment for mild steel

The AE method is an effective technique for inspecting corrosion damage of mild steel, such as tank bottom floors. However, the correlation between AE signals and corrosion behaviour for mild steel has not yet been fully clarified. In the present study, the authors considered that the corrosion regions of bottom floors become a strong acid environment by Cl⁻, as reported in a previous study. Thus, the polarization resistance for the test pieces of mild steel was measured with an AC impedance method under a strong acid environment. It was clear that the polarization resistance indicated the corrosion rate for a test piece of mild steel in the experiments. While measuring the AE signals, the corrosion rate was monitored with a test piece. As a result, the AE signal showed good correlation with the corrosion rates of the test pieces. The corrosion behaviour of the test pieces was then discussed with the corrosion potential measured during the experiments. Furthermore, the cathode current was changed to control the generated hydrogen gas volume. The volume of the hydrogen gas generated from the cathode reaction was correlated to the AE signals.     

Novel benzimidazole derivatives as corrosion inhibitors of mild steel in the acidic media. Part I: Gravimetric,electrochemical, SEM and XPS studies

Three novel benzimidazole derivatives, 2-aminomethyl benzimidazole (ABI), bis (2-benzimidazolylmethyl) amine (BBIA) and tri (2-benzimidazolylmethyl) amine (TBIA), have been studied as inhibitors for mild steel in 1.0 M HCl. The three compounds prevent mild steel from corrosion by adsorption on the steel surface and forming insoluble complex with ferrous species. Inhibition efficiency increases with the increase in the number of benzimidazole segments in the molecules (TBIA > BBIA > ABI). Protection efficiency of the inhibitors depends on concentration of inhibitor, temperature and concentration of hydrochloric acid.     

An investigation of benzimidazole derivative as corrosion inhibitor for mild steel in different concentration HCl solutions

The influences of a benzimidazole derivative, namely 1,8-bis (1-chlorobenzyl-benzimidazolyl) -octane (CBO) on the corrosion behaviour of mild steel in different concentration HCl solutions were studied by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements and SEM observations. The results showed that CBO acted as an excellent and a mixed-type inhibitor via strongly chemical adsorption onto mild steel surface to suppress simultaneously both anodic and cathodic processes according to the Langmuir adsorption isotherm. Inhibition efficiencies increased with increasing concentration of inhibitor and HCl. An inhibition mechanism was proposed in terms of strongly adsorption of inhibitor molecules on mild steel surface.