Enhanced corrosion resistance of mild steel in normal sulfuric acid medium by 2,5-bis(n-thienyl)-1,3,4-thiadiazoles: Electrochemical, X-ray photoelectron spectroscopy and theoretical studies

The inhibitive action of some thiadiazole derivatives, namely 2,5-bis(2-thienyl)-1,3,4-thiadiazole (2-TTH) and 2,5-bis(3-thienyl)-1,3,4-thiadiazole (3-TTH) against the corrosion of mild steel in 0.5 M H₂SO₄ solution has been investigated using weight loss measurements, Tafel polarisation and electrochemical impedance spectroscopy (EIS) techniques. The experimental results obtained revealed that these compounds inhibited the steel corrosion in acid solution. The protection efficiency increased with increasing inhibitors concentration and the ability of the molecule to adsorb on the steel surface was dependent on the position of the sulphur atom on the thienyl substituent. Inhibition efficiency values obtained from various methods employed were in reasonable agreement. Potentiodynamic polarisation studies clearly showed that 2-TTH and 3-TTH acted as mixed inhibitors. Adsorption of these inhibitors on steel surface obeyed to Langmuir adsorption isotherm. X-ray photoelectron spectroscopy and the thermodynamic data of adsorption showed that inhibition of steel corrosion in normal sulphuric solution by n-TTH is due to the formation of a chemisorbed film on the steel surface. Molecular modelling was used to gain some insight, about structural and electronic effects in relation to the inhibiting efficiencies.     

Electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy study of the corrosion behaviour of galvanized steel and electroplating steel

The efficiency of a formula containing 2-{(2-hydroxyethyl)[(4-methyl-1H-1,2,3-benzotriazol-1-yl)methyl]amino}ethanol (tolyltriazole) and decanoic acid as corrosion inhibitor for galvanized steel and electroplating steel in aqueous solution have been determined by electrochemical impedance spectroscopy (EIS) techniques. The experimental data obtained from this method show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. The corrosion behaviour in the presence of different concentration of decanoic acid (DA) in the formula was also investigated by EIS. Results obtained reveal that, the formula is a good inhibitor for galvanized steel and electroplating steel in aqueous solution, the better performance was obtained in the case of galvanized steel. The ability of the inhibitor to be adsorbed on the surface was dependent on the nature of metal. X-ray photoelectron spectroscopy surface analysis with inhibitor shows that it's chemisorbed at the galvanized and electroplating steel/aqueous solution interface.     

Corrosion behaviour of galvanized steel and electroplating steel in aqueous solution: AC impedance study and XPS

The efficiency of a new triazole derivative, namely, 2-{(2-hydroxyethyl)[(4-methyl-1H-1,2,3-benzotriazol-1-yl)methyl]amino}ethanol (TTA) has been studied for corrosion inhibition of galvanized steel and electroplating steel in aqueous solution. Corrosion inhibition was studied using electrochemical impedance spectroscopy (EIS). These studies have shown that TTA was a very good inhibitor. Data obtained from EIS show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. The corrosion behaviour of galvanized steel and electroplating steel in aqueous solution was also investigated in the presence of 4-methyl-1H-benzotriazole (TTA unsubstituted) by EIS. These studies have shown that the ability of the molecule to adsorb on the steel surface was dependent on the group in triazole ring substituent. X-ray photoelectron spectroscopy surface analysis with TTA shows that it chemisorbed on surface of galvanized steel and electroplating steel.     

An electroactive co-polymer as corrosion inhibitor for steel in sulphuric acid medium

The corrosion behavior of mild steel in sulphuric acid solution containing various concentrations of a co-polymer formed between maleic anhydride and N-vinyl-2-pyrrolidone (VPMA) was investigated using weight-loss, polarization and electrochemical impedance techniques. The polymer acts as an effective corrosion inhibitor for steel in sulphuric acid medium. The inhibition process is attributed to the formation of an adsorbed film of co-polymer on the metal surface which protects the metal against corrosion. Scanning electron microscopy (SEM) studies of the metal surfaces confirmed the existence of an adsorbed film. The adsorption followed the Langmuir isotherm. The protection efficiency increased with increase in inhibitor concentration and decreased with increase in temperature and acid concentration. The thermodynamic functions of the adsorption and dissolution processes were evaluated.     

Enhanced corrosion resistance of mild steel in molar hydrochloric acid solution by 1,4-bis(2-pyridyl)-5H-pyridazino[4,5-b]indole: Electrochemical, theoretical and XPS studies

The inhibition effect of the new pyridazine derivative, namely 1,4-bis(2-pyridyl)-5H-pyridazino[4,5-b]indole (PPI) against mild steel corrosion in 1 M HCl solutions was evaluated using weigh loss and electrochemical techniques (potentiodynamic polarisation curves and impedance spectroscopy). The experimental results suggest that PPI is a good corrosion inhibitor and the inhibition efficiency increased with the increase of PPI concentration, while the adsorption followed the Langmuir isotherm. X-ray photoelectron spectroscopy (XPS) and theoretical calculation of electronic density were carried out to establish the mechanism of corrosion inhibition of mild steel with PPI in 1 M HCl medium. The inhibition action of this compound was, assumed to occur via adsorption on the steel surface through the active centres contained of the molecule. The corrosion inhibition is due to the formation of a chemisorbed film on the steel surface.     

Electrochemical, theoretical and XPS studies of 2-mercapto-1-methylimidazole adsorption on carbon steel in 1 M HClO4

The inhibition of the corrosion of carbon steel in 1 M HClO₄ by 2-mercapto-1-methylimidazole (MMI) has been investigated in relation to the concentration of the inhibitor as well as the temperature using weight loss and electrochemical measurements. The effect of the temperature on the corrosion behaviour with addition of different concentrations of MMI was studied in the temperature range 30-60 °C. Polarization curves reveal that MMI is a mixed type inhibitor. The inhibition efficiency of MMI is temperature independent but increases with the inhibitor concentration. Changes in impedance parameters (charge transfer resistance, R_t, and double-layer capacitance, C_dl) were indicative of adsorption of MMI on the metal surface, leading to the formation of a protective film. Adsorption of MMI on the carbon steel surface is found to obey the Langmuir adsorption isotherm. Some thermodynamic functions of dissolution and adsorption processes were also determined. The X-ray photoelectron spectroscopy (XPS) of the carbon steel indicated that MMI is chemically adsorbed on the steel surface. Moreover, the electronic properties such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels and molecular orbital densities were calculated.     

Chemical and electrochemical investigations of high carbon steel corrosion inhibition in 10 % HCl medium by quinoline chalcones

The corrosion inhibitive effect of 3-(3-oxo-3-phenyl-propenyl)-1H-quinolin-2-one (PPQ) and 3-(3-oxo-3-phenyl-propenyl)-1H-benzoquinolin-2-one (PPBQ) on high carbon steel (HCS) in 10 % HCl media was evaluated by chemical (weight loss) and electrochemical (electrochemical impedance spectroscopy and potentiodynamic polarization technique) measurements. The inhibition efficiencies obtained from weight loss and electrochemical measurements were in good agreement. The inhibition efficiency was found to increase with the increase in inhibitor concentration but decreased with rise in temperature. Potentiodynamic polarization studies revealed the mixed mode inhibition of inhibitors. The adsorption behavior of these inhibitors on the HCS surface was found to obey the Langmuir adsorption isotherm. The thermodynamic parameter values of free energy of adsorption (?G _ads) and enthalpy of adsorption (?H _ads) revealed that the inhibitor was adsorbed on the HCS surface via both chemisorption and physisorption mechanisms. The adsorption mechanism of inhibition was supported by spectroscopic techniques (UV–visible, FT-IR, and wide-angle X-ray diffraction), surface analysis (SEM–EDS), and adsorption isotherms.     

Tween-40 as corrosion inhibitor for cold rolled steel in sulphuric acid: Weight loss study, electrochemical characterization, and AFM

The inhibition action of a non-ionic surfactant of tween-40 on the corrosion of cold rolled steel (CRS) in 0.5-7.0 M sulphuric acid (H₂SO₄) was studied by weight loss and potentiodynamic polarization methods. Atomic force microscope (AFM) provided the surface conditions. The inhibition efficiency increases with the tween-40 concentration, while decreases with the sulphuric acid concentration. The adsorption of inhibitor on the cold rolled steel surface obeys the Langmuir adsorption isotherm equation. Effect of immersion time was studied and discussed. The effect of temperature on the corrosion behavior of cold rolled steel was also studied at four temperatures ranging from 30 to 60 °C, the thermodynamic parameters such as adsorption heat, adsorption free energy and adsorption entropy were calculated. A kinetic study of cold rolled steel in uninhibited and inhibited acid was also discussed. The kinetic parameters such as apparent activation energy, pre-exponential factor, rate constant, and reaction constant were calculated for the reactions of corrosion. The inhibition effect is satisfactorily explained by both thermodynamic and kinetic parameters. Polarization curves show that tween-40 is a cathodic-type inhibitor in sulphuric acid. The results obtained from weight loss and potentiodynamic polarization are in good agreement, and the tween-40 inhibition action could also be evidenced by surface AFM images.     

Establishment of equivalent circuits from electrochemical impedance spectroscopy study of corrosion inhibition of steel by pyrazine in sulphuric acidic solution

This paper describes the use of the electrochemical impedance spectroscopy technique (EIS) in order to study the corrosion inhibition process of steel in 0.5 M H₂SO₄ solution at the open circuit potential (OCP). Diethyl pyrazine-2,3-dicarboxylate (Prz) as a non-ionic surfactant (NS) inhibitor has been examined. The Nyquist diagrams consisted of a capacitive semicircle at high frequencies followed by a well-defined inductive loop at low frequency values. The impedance measurements were interpreted according to suitable equivalent circuits. The results obtained showed that the Prz is a good inhibitor. The inhibition efficiency increases with an increase in the surfactant concentration to attain 80% at the 5 × 10⁻³M. Prz is adsorbed on the steel surface according to a Langmuir isotherm adsorption model.     

1,3-Bis(3-hyroxymethyl-5-methyl-1-pyrazole) propane as corrosion inhibitor for steel in 0.5 M H2SO4 solution

The effect of addition of 1,3-bis(3-hyroxymethyl-5-methyl-1-pyrazole) propane (M = 264 g). HMPP on steel corrosion in 0.5 M sulphuric acid is studied by weight-loss, electrochemical polarisation and electrochemical impedance spectroscopy (EIS) measurements at various temperatures. The results obtained showed that HMPP acts as a good corrosion inhibitor. The inhibition efficiency increases with the bipyrazole compound to attain 88%. It acts as a mixed-type inhibitor. Trends in the increase of charge-transfer resistance and decrease of capacitance values also show the adsorption of the molecule on the metal surface. The bipyrazole adsorbs on the steel surface according to the Langmuir isotherm adsorption model. Effect of temperature indicates that inhibition efficiency decreases with temperature between 25 and 85 °C.     

Berberine as a natural source inhibitor for mild steel in 1 M H2SO4

Berberine was abstracted from coptis chinensis and its inhibition efficiency on corrosion of mild steel in 1 M H₂SO₄ was investigated through weight loss experiment, electrochemical techniques and scanning electronic microscope (SEM) with energy disperse spectrometer (EDS). The weight loss results showed that berberine is an excellent corrosion inhibitor for mild steel immersed in 1 M H₂SO₄. Potentiodynamic curves suggested that berberine suppressed both cathodic and anodic processes for its concentrations higher than 1.0 × 10⁻⁴ M and mainly cathodic reaction was suppressed for lower concentrations. The Nyquist diagrams of impedance for mild steel in 1 M H₂SO₄ containing berberine with different concentrations showed one capacitive loop, and the polarization resistance increased with the inhibitor concentration rising. A good fit to Flory-Huggins isotherm was obtained between surface coverage degree and inhibitor concentration. The surface morphology and EDS analysis for mild steel specimens in sulfuric acid in the absence and presence of the inhibitor also proved the results obtained by the weight loss and electrochemical experiments. The correlation of inhibition effect and molecular structure of berberine was then discussed by quantum chemistry study.     

Investigation of the inhibitive effect of triphenyltin 2-thiophene carboxylate on corrosion of steel in 2 M H3PO4 solutions

A new organic compound was synthesised and tested as corrosion inhibitor of steel in phosphoric acid medium using gravimetric, electrochemical polarisation and electrochemical impedance spectroscopy (EIS) measurements. Results obtained show that the inhibitor studied is a good cathodic inhibitor. EIS results show that the change in the impedance parameters (R_T and C_dl) with concentration of triphenyltin 2-thiophene carboxylate (TTC) is indicative of the adsorption of molecules leading to the formation of a protective layer on the surface of steel. The effect of the temperature on the steel corrosion in 2 M H₃PO₄ and with addition of various concentrations of TTC in the range of temperature 298-348 K was studied. The associated apparent activation corrosion energy has been determined.     

The inhibition effect of some amino acids towards Pb-Sb-Se-As alloy corrosion in sulfuric acid solution

The inhibition effect of three amino acids towards the corrosion of Pb-Sb-Se-As alloy in 1.28 s.g. H₂SO₄ solution was investigated with linear polarization and weight loss measurements methods. The results drawn from two different techniques are comparable. The used amino acids were tryptophane, proline and methionine. The effect of inhibitor concentration and temperature against inhibitor action was investigated. It was found that these inhibitors act as good inhibitors for the corrosion of lead alloy in H₂SO₄ solution. Increasing inhibitor concentration increases the inhibition efficiency. It was found that adsorption of used amino acids on lead alloy surface follows Langmuir isotherm.     

The inhibition of corrosion of mild steel in 0.5 M sulfuric acid solution in the presence of benzyl triphenyl phosphonium bromide

Benzyl triphenyl phosphonium bromide (BTPPB) has been evaluated as a corrosion inhibitor for mild steel in aerated 0.5 M sulfuric acid solution by galvanostatic polarization and potentiostatic polarization methods. The effect of BTPPB on the corrosion current is measured at various temperatures and concentrations. The inhibitor efficiencies, effective activation energies and heat of adsorption have been calculated. The inhibition efficiency increases with increase in inhibitor concentration to reach 99.3% for 10⁻² M. The nature of adsorption of BTPPB on the metal surface has also been examined. Probable mode of adsorption on the metal surface has been proposed using infrared spectroscopic studies. The electrochemical results have also been supplemented by surface morphological studies and quantum chemical analysis.     

Corrosion inhibition of steel in 0.5 M H2SO4 by [(2-pyridin-4-ylethyl)thio]acetic acid

The influence of [(2-pyridin-4-ylethyl)thio]acetic acid (P1) and pyridine (P2) on the corrosion inhibition of steel in sulphuric acid solution is studied using weight loss, potentiodynamic polarisation and linear polarisation resistance (R_p) and electrochemical impedance spectroscopy (EIS) measurements. Results obtained show that P1 is the best inhibitor and its inhibition efficiency (E%) increases with the increase of concentration. The highest E% of 82% is observed at 5 × 10⁻³ M. Potentiodynamic polarisation studies clearly reveal that P1 acts as a mixed inhibitor. The inhibitor studied reduces the corrosion rates. E% values obtained from various methods used are in good agreement. Adsorption of P1 on steel surface obeys to Langmuir adsorption isotherm. Effect of temperature indicates that E% decreases with temperature between 298 and 353 K.     

Surface Analysis of Inhibitor Film Formed by 4-Amino-N-(1,3-thiazol-2-yl) Benzene Sulfonamide on Carbon Steel Surface in Acidic Media

Inhibitive properties of the antibacterial sulfa drug sulfathiazole—IUPAC name being 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide—on the corrosion of carbon steel in 1.0 M HCl solution were investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Sulfathiazole is a good adsorption inhibitor, and the inhibition efficiency increases with increasing concentration. Adsorption is spontaneous and is best described by Temkin isotherm. XPS analysis showed, at this stage, that the main product of corrosion is a nonstoichiometric Fe³⁺ oxide/oxyhydroxide consisting of a mixture of Fe₂O₃, α, and γ-FeO(OH) and/or Fe(OH)₃, where α, γ-FeO(OH) is the main phase.     

Attenuated total reflectance spectroscopy of simultaneous processes: Corrosion inhibition of cuprous oxide by benzotriazole

Attenuated total reflectance (ATR) spectroscopy was used to perform in situ studies of the corrosion inhibition of cuprous oxide (Cu₂O) by benzotriazole (BTA) in aqueous solution at concentrations from 1 to 20 μM. Because two separate processes occur simultaneously, that of Cu₂O corrosion and corrosion inhibition by BTA adsorption, the spectral information was subjected to deconvolution by a conjugate gradient minimization algorithm. Under these conditions, a solution phase concentration of 7-10 μM BTA nearly completely inhibited the corrosion of Cu₂O in deionized water. Using a Langmuir adsorption model, this represented only 25% of the maximally covered surface area.     

Structurally selective protection of steel against oxygen corrosion by 1-hydroxyethylidenediphosphonatozincate

A method for protecting steel against oxygen corrosion in water solutions using an inhibitor that selectively reacts with a metal surface in corrosion centers is proposed. 1-hydroxyethylidenediphosphonatozincate, which contains a localized π bond between its phosphorus and oxygen atoms, is used as the inhibitor in combination with magnesium ions at an oxygen concentration of 0.1 to 6.0 mg dm^?3 and pH in a water solution of 5.8 to 11.1. A 91–93% degree of protection is achieved at an inhibitor concentration of 6 mg dm^?3.     

Pyridine–pyrazole compound as inhibitor for steel in 1 M HCl

The influence of 3,5-dimethyl-1H-pyrazole (P1), pyridine (P2) and 2-(3-methyl-1H-pyrazol-5-yl) pyridine (P3) on the corrosion inhibition of steel in molar hydrochloric acid solution is studied using weight-loss, potentiodynamic and EIS measurements. Results obtained shows that P3 is the best inhibitor and its inhibition efficiency increases with the increase of concentration to attain 89% since 10⁻³ M. Potentiodynamic polarisation studies clearly reveal that it acts essentially as a cathodic inhibitor. The inhibitor studied reduces the corrosion rates. E (%) values obtained from various methods used are in good agreement. Adsorption of P3 on steel surface has an S-shaped adsorption isotherm.     

Inhibitive action of <Emphasis Type="Italic">Clematis gouriana</Emphasis> extract on the corrosion of mild steel in acidic medium

The inhibitive action of Clematis gouriana (CG) on mild steel (MS) corrosion in 1.0 M HCl solution was studied. Inhibition efficiency of CG was carried out by using various weight loss methods, potentiodynamic polarisation, and electrochemical impedance spectroscopy. Inhibition efficiencies of up to 95.70% for CG can be obtained. Adsorption of CG on the MS surface was found to obey the Langmuir adsorption isotherm. Free energy of adsorption calculated from the temperature studies revealed the possibility of both chemisorptions and physisorption. The adsorbed film on the MS surface containing the CG inhibitor was also characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope and energy-dispersive spectrum. The possible active ingredient responsible for the anticorrosion effect is identified as aporphine alkaloid which is isolated and screened for the anticorrosion effect using electrochemical studies. The possible mode of corrosion inhibition of aporphine alkaloid is also derived using FTIR studies.