Difference in the inhibitive effect of some Schiff base compounds containing oxygen, nitrogen and sulfur donors

2-(2-Hydroxybenzylideneamino)-2-methylpropane-1,3-diol (BAMP), 2-((2-hydroxynaphthalen-1-yl)methyleneamino)-2-methylpropane-1,3-diol (NAMP), 2-((pyridin-2-ylimino)methyl)phenol (PMP) and N-(thiophen-2-ylmethylene)pyridin-2-amine (TMP) were investigated as corrosion inhibitors of mild steel in 2 M HCl solution using weight loss, polarization and electrochemical impedance spectroscopy techniques. All measurements show that all compounds under study exhibit inhibitor properties for mild steel. Although the effect of molecular size on inhibition efficiency is observed from the results obtained between BAMP and NAMP, the introduction of heteroatoms into the structure is seen to be more pronounced eventhough the molecular size is diminished. TMP is seen to show the highest inhibitor efficiency of 97%.     

A preliminary investigation of corrosion inhibition of mild steel in 0.5 M H2SO4 by 2-amino-5-(n-pyridyl)-1,3,4-thiadiazole: Polarization, EIS and molecular dynamics simulations

The efficiency, as steel corrosion inhibitors in 0.5 M H₂SO₄, of two thiadiazole derivatives, 2-amino-5-(3-pyridyl)-1,3,4-thiadiazole (3-APTD) and 2-amino-5-(4-pyridyl)-1,3,4-thiadiazole (4-APTD), was investigated by polarization and electrochemical impedance spectroscopy. The protection efficiency increases with increasing inhibitors concentration, but the temperature has hardly effect on the inhibition efficiency of APTD. The adsorption of APTD on iron surface obeys the Langmuir isotherm. The experimental results show that the inhibition efficiency of 4-APTD is higher than that of 3-APTD, and the molecular dynamics (MD) simulations show that the adsorption of 4-APTD on iron surface has the higher binding energy than that of 3-APTD.     

Inhibition of the corrosion of steel in hydrochloric acid solution by some organic molecules containing the methylthiophenyl moiety

The corrosion inhibition effect of 2-[4-(methylthio) phenyl] acetohydrazide (HYD), 2-{[4-(methylthio) phenyl] acetyl} hydrazinecarbothioamide (TAD) and 5-[4-(methylthio) benzyl]-4H-1,2,4-triazole-3-thiol (TRD) on steel in 1.0 M HCl was investigated by mass loss and electrochemical methods. The effect of concentration, temperature and immersion time was studied. The results indicated that the compounds are efficient, mixed type and pursue Flory–Huggins adsorption isotherm. The inhibition efficiency at lower concentration of inhibitor decreased with temperature while at higher concentration, it is retained and the calculated free energy attributes this to comprehensive adsorption. The efficiency stands in the order TRD > TAD > HYD and is confirmed by the Quantum studies.     

Mono- and dicationic benzothiazolic quaternary ammonium bromides as mild steel corrosion inhibitors. Part I: Gravimetric and voltammetric results

Seven quaternary ammonium bromides of different heterocyclic compounds were investigated as corrosion inhibitors of mild steel in 1 M HCl using gravimetric and polarisation techniques. For comparison gravimetric experiments were carried out in 1 M H₂SO₄ as well. The inhibitor efficiency was found to depend on both concentration and molecular structure of the inhibitor. The polarisation curves revealed that the inhibitors were of mixed type. The adsorption of almost all inhibitors was well described by the Frumkin isotherm. The adsorption isotherm parameters were determined. Conformational changes in the molecular structure favour the adsorption and thus increase the inhibitive effect.     

Electrochemical and quantum chemical studies of 3,4-dihydropyrimidin-2(1H)-ones as corrosion inhibitors for mild steel in hydrochloric acid solution

The inhibition effect of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) on the corrosion of mild steel in hydrochloric acid medium has been investigated using weight loss measurements, electrochemical impedance spectroscopy, potentiodynamic polarization and quantum chemical study. Among the compounds studied, DHPM-3 exhibited the best inhibition efficiency η (%) 99% at 10 mg L⁻¹ at 308 K. Polarization measurements indicate that all the examined compounds are of mixed-type inhibitor. The adsorption of studied compounds obeyed the Langmuir’s adsorption isotherm. The electronic properties obtained using quantum chemical approach, were correlated with the experimental inhibition efficiencies.     

Corrosion inhibition of mild steel by ethylamino imidazoline derivative in CO2-saturated solution

The corrosion inhibition and adsorption behaviour of 2-undecyl-1-ethylamino imidazoline (2UEI) on N80 mild steel in CO₂-saturated 3% NaCl solutions was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy techniques and SEM observation. Inhibitor efficiency increased with increase in 2UEI concentration. Temperature studies revealed an increase in inhibition efficiency with rise in temperature and corrosion activation energies decreased in the presence of 2UEI. A mechanism of chemical adsorption of 2UEI on the metal’s surface is proposed. The adsorption characteristics of the inhibitor were approximated by Temkin isotherm. The inhibition efficiency of 2UEI was enhanced in the presence of iodide ions.     

Quantum chemical studies on corrosion inhibition of some lactones on mild steel in acid media

Study of the efficacy of some lactones to counter iron corrosion in 1 M hydrochloric acid using ab initio quantum chemical deductions and its comparison with the available experimental data forms a part of this research. It is believed that the inhibition efficiency has lucid correlation with the charge of oxygen atoms of inhibitor molecules. Furthermore, thermo-chemical calculations for oxepan-2-one (L3) on iron cluster result in adsorption energies close to experimental values. However, the interaction energies of L3 and iron cluster with the natural bond orbital are also reported. Furthermore, interaction energy of hydrogen ion and inhibitor with iron surface is investigated.     

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.     

A study of the inhibition of iron corrosion in HCl solutions by some amino acids

The performance of three selected amino acids, namely alanine (Ala), cysteine (Cys) and S-methyl cysteine (S-MCys) as safe corrosion inhibitors for iron in aerated stagnant 1.0 M HCl solutions was evaluated by Tafel polarization and impedance measurements. Results indicate that Ala acts mainly as a cathodic inhibitor, while Cys and S-MCys function as mixed-type inhibitors. Cys, which contains a mercapto group in its molecular structure, was the most effective among the inhibitors tested, while Ala was less effective than S-MCys. The low inhibition efficiency recorded for S-MCys compared with that of Cys was attributed to steric effects caused by the substituent methyl on the mercapto group. Electrochemical frequency modulation (EFM) technique and inductively coupled plasma atomic emission spectrometry (ICP-AES), were also applied to make accurate determination of corrosion rates. Validation of the Tafel extrapolation method for measuring corrosion rates was tested. Rates of corrosion rates (in μm y⁻¹) obtained from Tafel extrapolation method are in good agreement with those measured using EFM and ICP methods. Some theoretical studies, including molecular dynamics (MD) and density functional theory (DFT), were also employed to establish the correlation between the structure (molecular and electronic) of the three tested inhibitors and the inhibition efficiency. Adsorption via hydrogen bonding was discussed here based on some theoretical studies. Experimental and theoretical results were in good agreement.     

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.     

Corrosion inhibition of mild steel in hydrochloric acid solution by Schiff base furoin thiosemicarbazone

A heterocyclic Schiff base furoin thiosemicarbazone was tested for its corrosion inhibition towards mild steel in 1 M HCl solution using weight loss, Tafel polarization and electrochemical impedance spectroscopy techniques. Furoin thiosemicarbazone revealed good corrosion inhibition efficiency even at low concentrations towards mild steel in HCl medium. Comparison of corrosion inhibition efficiency of Schiff base and its parent amine and effect of temperature on inhibition efficiency were also investigated. The adsorption of furoin thiosemicarbazone on mild steel surface obeys Langmuir isotherm.     

Electrochemical effect of cationic gemini surfactant and halide salts on corrosion inhibition of low carbon steel in acid medium

In this paper, the corrosion inhibition of cationic gemini surfactant, in the absence and presence of halide salts (NaCl, NaBr and NaI) on steel in HCl was investigated at 20 ± 1 °C. The effects of pH, immersion time and salt concentration on the corrosion inhibition of steel were studied using weight loss, open circuit potential and electrochemical impedance spectroscopy. Inhibition efficiency increases by increasing surfactant concentration. Synergistic effect between surfactant and salts was studied. The inhibition efficiency increases by increasing salt concentration. This composite inhibitor containing gemini surfactant and halide was efficient and low-cost for steel corrosion inhibition in HCl.     

Corrosion control of copper in nitric acid solutions using some amino acids - A combined experimental and theoretical study

Inhibition performance of three amino acids, namely l-methionine (MIT), l-methionine sulfoxide (MITO) and l-methionine sulfone (MITO2), as corrosion-safe inhibitors for copper surface in 1.0 M nitric acid was investigated by weight loss, dc polarization and ac impedance techniques. A significant decrease in the corrosion rate of copper was observed in the presence of the investigated compounds. The reactivates of the compounds under investigation were analyzed through Fukui functions, to explain their inhibition performance. Simulation techniques incorporating molecular mechanics and molecular dynamics were used to simulate the adsorption of l-methionine derivatives, on copper (1 1 1) surface in nitric acid.     

The effect of electrolyte flow on the performance of 12-aminododecanoic acid as a carbon steel corrosion inhibitor in CO2-saturated hydrochloric acid

The effect of flow and flow pattern of CO₂-saturated HCl on the corrosion inhibition of carbon steel (CS) by 12-aminododecanoic acid (AA) was investigated in a square duct, rotating disk electrode (RDE), and jet impingement cell configuration. 3 mM AA provided high corrosion inhibition efficiency in the square duct and RDE configuration. However, in 1 mM AA the inhibition efficiency decreased with an increase in Re, due to desorption of AA from the CS surface. AA was found to poorly protect CS in the impingement-jet configuration at low Re, while at high Re, acceleration of CS corrosion was recorded.     

Nicotinic acid as a nontoxic corrosion inhibitor for hot dipped Zn and Zn-Al alloy coatings on steels in diluted hydrochloric acid

The inhibition effect of nicotinic acid for corrosion of hot dipped Zn and Zn-Al alloy coatings in diluted hydrochloric acid was investigated using quantum chemistry analysis, weight loss test, electrochemical measurement, and scanning electronic microscope (SEM) analysis. Quantum chemistry calculation results showed that nicotinic acid possessed planar structure with a number of active centers, and the populations of the Mulliken charge, the highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) were found mainly focused around oxygen and nitrogen atoms, and the cyclic of the benzene as well. The results of weight loss test and electrochemical measurement indicated that inhibition efficiency (IE%) increased with inhibitor concentration, and the highest inhibition efficiency was up to 96.7%. The corrosion inhibition of these coatings was discussed in terms of blocking the electrode reaction by adsorption of the molecules at the active centers on the electrode surface. It was found that the adsorption of nicotinic acid on coating surface followed Langmuir adsorption isotherm with single molecular layer, and nicotinic acid adsorbed on the coating surface probably by chemisorption. Nicotinic acid, therefore, can act as a good nontoxic corrosion inhibitor for hot dipped Zn and Zn-Al alloy coatings in diluted hydrochloric acid solution.     

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.     

Electrochemical investigation and modeling of corrosion inhibition of aluminum in molar nitric acid using some sulphur-containing amines

Chemical and electrochemical measurements incorporated with quantum chemical calculations and molecular dynamics simulations were used to study the corrosion inhibition characteristics of some thiosemicarbazone derivatives on the inhibition of aluminum corrosion in 1.0 M HNO₃. Polarization curves demonstrated that the thiosemicarbazone derivatives were of mixed-type inhibitors. EIS plots indicated that the addition of thiosemicarbazone derivatives increases the charge-transfer resistance of the corrosion process, and hence the inhibition performance. The molecular dynamics simulation results show that the three thiosemicarbazone derivatives can adsorb on the A₂O₃ (1 1 1) surface through the sulphur and nitrogen atoms as well as π-electrons in the pyridyl structure.     

A theoretical study of some hydroxamic acids as corrosion inhibitors for carbon steel

The corrosion inhibition characteristics of two hydroxamic acids, i.e., oxalyl-dihydroxamic acid (C2) and pimeloyl-1,5-di-hydroxamic acid (C7), on carbon steel has been studied using density functional theory (DFT). Quantum chemical parameters such as highest occupied molecular orbital energy (E_HOMO), lowest unoccupied molecular orbital energy (E_LUMO), and energy gap (ΔE) have been calculated using B3LYP/6-31 + G∗∗ basis set. The relationship between the inhibition efficiency and quantum chemical parameters has been discussed in order to elucidate the inhibition mechanism of these compounds.     

Evaluation of corrosion inhibition at sand-deposited carbon steel in CO2-saturated brine

The adsorption of four CO₂ corrosion inhibitors on silica sand and their subsequent inhibition activity at sand-deposited steel has been investigated. The presence of a sand deposit affects the performance of inhibitors at carbon steel due to their competitive adsorption on sand. Sulfur-containing organic compounds show minimal adsorption on sand compared to pyridinium surfactants and provide the highest inhibition efficiency at the sand-deposited steel. The extent of inhibitor adsorption onto sand is discussed in relation to their chemical structures. The significance of determining the adsorption affinity to sand in the selection of inhibitors to mitigate under-deposit corrosion is demonstrated.