Substitutional adsorption isotherms and corrosion inhibitive properties of some oxadiazol-triazole derivative in acidic solution

A newly synthesized oxadiazol-triazole derivative (TOMP), was investigated as corrosion inhibitor of mild steel in 0.5 M H₂SO₄ solution using weight loss measurements, polarization and electrochemical impedance spectroscopy (EIS) methods. Results obtained revealed that TOMP is effective corrosion inhibitor for mild steel in sulphuric acid and its efficiency attains more than 97.6% at 298 K. The number of water molecules (X) replaced by a molecule of organic adsorbate was determined from the substitutional adsorption isotherms applied to the data obtained from the weight loss experiments performed on mild steel specimen in acidic solution in the 298-333 K range.     

On the inhibition of mild steel corrosion by 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol

The corrosion inhibition of mild steel in a 2.5 M H₂SO₄ solution by 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol (APTT) was studied at different temperatures, utilising open circuit potential, potentiodynamic and impedance measurements. The results indicate that APTT performed as an excellent mixed-type inhibitor for mild steel corrosion in a 2.5 M H₂SO₄ solution and that the inhibition efficiencies increased with the inhibitor concentration but decreased proportionally with temperature. The kinetic and thermodynamic parameters for adsorption of APTT on the mild steel surface were calculated. A chemisorption mechanism of APTT molecules on the mild steel surface was proposed based on the thermodynamic adsorption parameters.     

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.     

Inhibiting effects of butyl triphenyl phosphonium bromide on corrosion of mild steel in 0.5 M sulphuric acid solution and its adsorption characteristics

Butyl triphenyl phosphonium bromide (BuTPPB) has been evaluated as a corrosion inhibitor for mild steel in 0.5 M H₂SO₄ solutions using galvanostatic polarisation and potentiostatic polarisation measurements. The study was also complemented by infra red (IR) spectroscopy, scanning electron microscopy (SEM) and quantum chemical calculations. Galvanostatic polarisation measurements showed that the presence of BuTPPB in aerated 0.5 M H₂SO₄ solutions decreases corrosion currents to a great extent and the corrosion rate decreases with increasing inhibitor concentration at a constant temperature. At 298K, inhibition efficiency was found to be 94.5% for 10⁻⁷ M BuTPPB which increased to about 99% for the BuTPPB concentration of 10⁻² M. The effect of temperature on the corrosion behaviour of mild steel was studied at five different temperatures ranging from 298 to 338K. The polarisation curves clearly indicate that BuTPPB acts as a mixed type inhibitor. Adsorption of BuTPPB on the mild steel surface follows the Langmuir isotherm.Potentiostatic polarisation measurements showed that passivation was observed only for lower BuTPPB concentrations (10⁻⁵ and 10⁻⁷ mol l⁻¹) for the mild steel in 0.5 M H₂SO₄. IR and SEM investigations also confirmed the adsorption of BuTPPB on the mild steel surface in 0.5 M H₂SO₄ solutions. The molecular parameters obtained using PM3 semi-empirical method, were correlated with the experimentally measured inhibitor efficiencies.     

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.     

Experimental and theoretical studies of thiazoles as corrosion inhibitors for mild steel in sulphuric acid solution

The inhibition effects of 2-amino-5-mercapto-1,3,4-thiadiazole (2A5MT) and 2-mercaptothiazoline (2MT) on mild steel corrosion in 1.0 M H₂SO₄ were studied with potentiodynamic polarization, linear polarization resistance and electrochemical impedance spectroscopy techniques. It was shown that both 2A5MT and 2MT act as good corrosion inhibitors for mild steel protection. The high inhibition efficiencies were attributed to the simple blocking effect by adsorption of inhibitor molecules on the steel surface. The effects of the presence of extra NH₂ group and N atom in 2A5MT on the ability to act as corrosion inhibitors were investigated by theoretical calculations.     

The inhibition of mild steel corrosion in acidic medium by 1-methyl-3-pyridin-2-yl-thiourea

The effect of 1-methyl-3-pyridin-2-yl-thiourea on the corrosion resistance of mild steel in H₂SO₄ solution was investigated by different techniques. The results show that the inhibition efficiency increases with the increase of inhibitor concentration. This compound affects both the anodic dissolution of steel and the hydrogen evolution reaction in 0.5 M H₂SO₄. The adsorption of this inhibitor is also found to obey the Langmuir adsorption isotherm. From the adsorption isotherm, value of the ΔG_ads for the adsorption process was calculated. From the corrosion rate obtained at 25-45 ± 1 °C E_a, ΔH_a and possible mechanism have been proposed.     

A study of 4-carboxyphenylboronic acid as a corrosion inhibitor for steel in carbon dioxide containing environments

4-Carboxyphenylboronic acid (CPBA) has been found to be an efficient carbon dioxide (CO₂) corrosion inhibitor for steel in aqueous media. The results indicate that the addition of CPBA to CO₂ containing sodium chloride solutions at a low concentration is able to retard corrosion anodic reactions, reduce corrosion current densities, increase charge transfer and total resistances, resulting in more uniform and smoother steel surfaces. These effects are attributed to the formation of a barrier layer on steel surface, which provides metal surface protection. The inhibitor was also found to mitigate corrosion by promoting random distribution of minor anodes.     

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.     

Corrosion monitoring of mild steel in sulphuric acid solutions in presence of some thiazole derivatives – Molecular dynamics, chemical and electrochemical studies

The physical behavior of three selected thiazole derivatives, namely 2-Amino-4-(p-tolyl)thiazole (APT), 2-Methoxy-1,3-thiazole (MTT) and Thiazole-4-carboxaldehyde (TCA) at iron (1 1 0) surface dissolved in aqueous solution were studied via molecular dynamics (MD) simulations. From the calculated binding energies, APT showed preferred adsorption on the steel surface among the three tested thiazole derivatives. The inhibition performance of the three thiazoles on the corrosion of mild steel in 0.5 M H₂SO₄ solutions was investigated at 25 °C. Measurements were conducted under various experimental conditions using weight loss, Tafel polarization and electrochemical impedance spectroscopy. Electrochemical frequency modulation (EFM) technique was also employed here to make accurate determination of the corrosion rates and test validation of the Tafel extrapolation method for measuring corrosion rates. Polarization curves showed that the three thiazole derivatives were of mixed-type inhibitors for mild steel corrosion in 0.5 M H₂SO₄ solution. EFM results were in agreement with other traditional chemical and electrochemical techniques used in corrosion rate measurements. Chemical and electrochemical measurements are consistent with computational study that APT is the most effective inhibitor among the tested thiazoles.     

The effect of temperature and concentration on the corrosion inhibition mechanism of an amphiphilic amido-amine in CO2 saturated solution

The corrosion inhibition mechanism of the N-[2-[(2-aminoethyl)amino]ethyl]-9-octadecenamide on mild steel surface in CO₂-saturated 5% NaCl solution has been studied. The inhibition efficiency decreases with increasing temperature. Adsorption of the inhibitor studied is found to follow the Frumkin adsorption isotherm. EIS results show that the mechanism of its corrosion inhibition at concentrations higher than critical micelle concentration is by forming a protective porous bi-layer. The activation energy, thermodynamic parameters and electrochemical results reveal a change in the adsorption mode of the inhibitor studied: the inhibitor could primarily be physically adsorbed at low concentrations, while chemisorption is favoured as concentration increases.     

Effect of Geobacter sulfurreducens on the microbial corrosion of mild steel, ferritic and austenitic stainless steels

The influence of Geobacter sulfurreducens was tested on the anaerobic corrosion of four different steels: mild steel 1145, ferritic steel 403 and austenitic steels 304L and 316L. Within a few hours, the presence of cells induced a free potential (E_oc) ennoblement around +0.3 V on 1145 mild steel, 403 ferritic steel and 304L austenitic steels and slightly less on 316L. The kinetics of E_oc ennoblement depended on the amount of bacteria in the inoculum, but the final potential value depended essentially on the nature of the material. This effect was due to the capacity of G. sulfurreducens to create a direct cathodic reaction on steel surfaces, extracting the electrons directly from material. The presence of bacterial cells modified the corrosion features of mild steel and ferritic steel, so that corrosion attacks were gathered in determined zones of the surface. Local corrosion was significantly enhanced on ferritic steel. Potential ennoblement was not sufficient to induce corrosion on austenitic steels. In contrast G. sulfurreducens delayed the occurrence of pitting on 304L steel because of its capability to oxidize acetate at high potential values. The electrochemical behaviour of 304L steel was not affected by the concentration of soluble electron donor (acetate, 1–10 mM) or the amount of planktonic cells; it was directly linked to the biofilm coverage. After polarization pitting curves had been recorded, microscopic observations showed that pits propagated only in the surface zones where cell settlement was the densest. The study evidenced that Geobacter sulfurreducens can control the electrochemical behaviour of steels in complex ways that can lead to severe corrosion. As Geobacteraceae are ubiquitous species in sediments and soils they should now be considered as possible crucial actors in the microbial corrosion of buried equipment.     

Corrosion of X65 steel in CO2-saturated oilfield formation water in the absence and presence of acetic acid

Electrochemical corrosion behavior of X65 steel in CO₂-saturated formation water in the absence and presence of acetic acid was studied by electrochemical measurements, scanning vibrating micro-electrode (SVME), localized electrochemical impedance spectroscope (LEIS) and surface analysis techniques. It is found that, when steel is immersed in formation water, the dissolution of Fe dominates the anodic process and the steel is in active dissolution state. Adsorption of intermediate product on the electrode surface results in generation of an inductive loop in the low frequency range of EIS plot. As corrosion proceeds, the concentration of Fe²⁺ in the solution increases. When the product of [Fe²⁺] × [] exceeds solubility product of FeCO₃, FeCO₃ will deposit on the electrode surface, and protects the steel substrate from further corrosion. The steel is in a “passive” state. When the electrode surface is completely covered with FeCO₃ film, the inductive loop in the low frequency range disappears. In the presence of acetic acid in formation water, the cathodic reaction will be enhanced due to the direct reduction of undissociated acetic acid. Addition of acetic acid degrades the protectiveness of corrosion scale, and thus, enhances corrosion of steel by decreasing the FeCO₃ supersaturation in solution.     

Corrosion of N80 carbon steel in oil field formation water containing CO2 in the absence and presence of acetic acid

Corrosion behaviour of N80 carbon steel in formation water containing CO₂ was studied by polarization curve technique, electrochemical impedance spectroscopy, weight loss test, scanning electron microscope, and X-ray diffraction. Effects of temperature and acetic acid concentration on the corrosion behaviour of N80 carbon steel were discussed. The results showed that increasing temperature not only enhanced the dissolution of steel substrate, but also promoted the precipitation of FeCO₃, the addition of acetic acid enhanced localized corrosion attack on N80 carbon steel. FeCO₃ was the main corrosion product. And there was a transition region between CO₂ corrosion control and HAc corrosion control.     

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.     

Water soluble conducting polymer composite of polyvinyl alcohol and leucine: An effective acid corrosion inhibitor for mild steel

A new corrosion inhibitor namely poly(vinyl alcohol‐leucine) composite (PVAL) has been synthesized and its influence on corrosion inhibition of mild steel in 1 M hydrochloric acid solution has been studied by weight loss and potentiodynamic polarization techniques. The composite (PVAL) showed more than 95% inhibition efficiency (IE) at an optimum concentration of 0.6% by weight. The inhibition efficiency of inhibitor has been found to vary with inhibitor concentration, solution temperature, and immersion time. Various kinetic and thermodynamic parameters (E_a, ΔH_o, ΔS_o for corrosion and ΔG_ads, ΔH_ads, ΔS_ads for adsorption) reveal a strong interaction between inhibitor and mild steel surface. The negative values of ΔG_ads indicate the spontaneous adsorption of the inhibitor on mild steel surface. Potentiodynamic polarization studies showed PVAL as mixed type inhibitor. It inhibits mild steel corrosion by blocking the active sites of the metal. Electrochemical impedance spectroscopic (EIS) techniques were also used to investigate the mechanism of corrosion inhibition.     

Synergistic effect of polyaspartic acid and iodide ion on corrosion inhibition of mild steel in H2SO4

The inhibition effect of polyaspartic acid (PASP) and its synergistic effect with KI on mild steel corrosion in 0.5 M H₂SO₄ solution are studied by weight loss and electrochemical methods. The inhibition efficiency increases with the concentration of PASP and increases further with the presence of 1 mM KI. Result of the zero charge potential measurement shows that iodide ion promotes the film formation of PASP greatly. The mild steel surfaces after immersion test were analyzed using scanning electron microscopy and X-ray photoelectron spectroscopy. An adsorption model is proposed to elucidate the synergistic mechanism of synergistic effect.     

Investigation of the inhibiting effect of N-[(Z)-1-phenylemethyleidene]-N-{2-[(2-{[(Z)-1phenylmethylidene]amino}phenyl)disulfanyl]phenyl} amine and its derivatives on the corrosion of stainless steel 304 in acid media

The effect of newly synthesized S₂N₂-Schiff bases is investigated on stainless steel 304 corrosion in 15% hydrochloric acid. The Tafel curves of the steel in hydrochloric acid containing Schiff bases show inhibition for both cathodic and anodic processes. Moreover, double layer capacitance and charge transfer resistance values are derived from Nyquist plots. The inhibition efficiency of Schiff bases increases with the increase in inhibitor concentration and temperature. Moreover, Langmuir adsorption isotherm is suitable to fit experimental data of the studied inhibitors. Effect of temperature on the efficiency of the corrosion inhibition shows chemisorption of inhibitors on the surface of metal.     

Adsorption and inhibitive properties of some new Mannich bases of Isatin derivatives on corrosion of mild steel in acidic media

Adsorption of four derivatives of piperidinylmethylindoline-2-one on mild steel surface in 1 M HCl solution and its corrosion inhibition properties has been studied by a series of techniques, such as polarization, electrochemical impedance spectroscopy (EIS), weight loss and quantum chemical calculation methods. The values of activation energy (E_a) for mild steel corrosion and various thermodynamic parameters were calculated and discussed. Potentiodynamic polarization measurements showed that all inhibitors are mixed type. The degree of surface coverage was determined by using weight loss measurements and it was found that adsorption process of studied inhibitors on mild steel surface obeys Langmuir adsorption isotherm.     

Inhibition effects of 2,5-dimercapto-1,3,4-thiadiazole on the corrosion of mild steel in sulphuric acid solution

The effect of 2,5-dimercapto-1,3,4-thiadiazole (DMTD) on the corrosion of mild steel (MS) in 1.0 M H₂SO₄ was investigated. DMTD acted as a mixed-type inhibitor without change of the mechanism of hydrogen evolution. The inhibition efficiency increased with the increase in concentration of DMTD but decreased with the increase of temperature. Adsorption of the inhibitor on the MS surface obeyed the Langmuir adsorption isotherm. The potential of zero charge suggests MS surface is positively charged in 1.0 M H₂SO₄. Thermodynamics and quantum chemical calculations reveal that the adsorption process of DMTD includes electrostatic interaction and electron donor–acceptor interactions.