The inhibition of benzimidazole derivatives on corrosion of iron in 1 M HCl solutions

The inhibitive action of some benzimidazole derivatives namely 2-aminobenzimidazole (AB), 2-(2-pyridyl)benzimidazole (PB), 2-aminomethylbenzimidazole (MB), 2-hydroxybenzimidazole (HB) and benzimidazole (B), against the corrosion of iron (99.9999%) in solutions of hydrochloric acid has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). At inhibitor concentration range (10⁻³-10⁻² M) in 1 M acid, the results showed that these compounds suppressed both cathodic and anodic processes of iron corrosion in 1 M HCl by adsorption on the iron surface according to Langmuir adsorption isotherm. The efficiency of these inhibitors increases in the order AB>PB>MB>HB>B. Both potentiodynamic and EIS measurements reveal that these compounds inhibit the iron corrosion in 1 M HCl and that the efficiency increases with increasing of the inhibitor concentration. Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit. A correlation between the highest occupied molecular orbital E_HOMO and inhibition efficiencies was sought.     

Corrosion inhibition of mild steel by alkylimidazolium ionic liquids in hydrochloric acid

The acid corrosion inhibition process of mild steel in 1 M HCl by 1-butyl-3-methylimidazolium chlorides (BMIC) and 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO₄) has been investigated using electrochemical impedance, potentiodynamic polarization and weight loss measurements. Potentiodynamic polarization studies indicate the studied inhibitors are mixed type inhibitors. For both inhibitors, the inhibition efficiency increased with increase in the concentration of the inhibitor and the effectiveness of the two inhibitors are in the order [BMIM]HSO₄ > BMIC. The adsorption of the inhibitors on mild steel surface obeyed the Langmuir's adsorption isotherm. The effect of temperature on the corrosion behavior in the presence of 5 × 10⁻³ M of inhibitors was studied in the temperature range of 303-333 K. The associated activation energy of corrosion and other thermodynamic parameters such as enthalpy of activation (ΔH), entropy of activation (ΔS), adsorption equilibrium constant (K_ads) and standard free energy of adsorption (ΔG_ads) were calculated to elaborate the mechanism of corrosion inhibition.     

Inhibition of mild steel corrosion in hydrochloric acid solution by triazole derivatives: Part I. Polarization and EIS studies

A comparative study of 5-amino-1,2,4-triazole (5-ATA), 5-amino-3-mercapto-1,2,4-triazole (5-AMT), 5-amino-3-methylthio-1,2,4-triazole (5-AMeTT) and 1-amino-3-methylthio-1,2,4-triazole (1-AMeTT) as inhibitors for mild steel corrosion in 0.1 M HCl solution at 20 °C was carried out. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were applied to study the metal corrosion behaviour in the absence and presence of different concentrations of these inhibitors under the influence of various experimental conditions. Measurements of open circuit potential (OCP) as a function of time till reaching the steady-state potentials (E_st) were also established. The studies have shown that 5-AMT was the most efficient inhibitor reaching values of inhibition efficiency (IE%) up to 96% at a concentration of 10⁻³ M. Polarization curves showed that the four studied compounds act as mixed inhibitors. The potential of zero charge (PZC) of mild steel was determined in 0.1 M HCl in the absence and presence of the studied inhibitors. The effect of chemical structure of the four tested inhibitors was discussed. Results obtained from OCP versus time, polarization and impedance measurements are in good agreement.     

Carboxymethylchitosan + Cu mixture as an inhibitor used for mild steel in 1 M HCl

The inhibition effect of Carboxymethylchitosan (CMCT), Cu²⁺, and CMCT + Cu²⁺ mixture on the corrosion of mild steel in 1 M HCl has been investigated using gravimetric and electrochemical techniques. CMCT + Cu²⁺ mixture acts much more effectively than the inhibiting action of each additive separately. In addition, higher efficiency is achieved for the mixture of 20 mg L⁻¹ CMCT + 10⁻⁴ M Cu²⁺. The efficiency of the optimal mixture increases with the temperature in the range 298-353 K. Activation energy of corrosion reaction in the presence of the optimal mixture of the inhibitors is much lower than that exhibited in 1 M HCl solution. The inhibition mechanism proposed in this paper is based on the results of conductometric investigations.     

Investigation of the inhibitive effect of ortho-substituted anilines on corrosion of iron in 1 M HCl solutions

The inhibitory activity of some o-substituted anilines on iron corrosion in hydrochloric acid (HCl) was studied in relation to inhibitor concentration using potentiodynamic and electrochemical impedance spectroscopy (EIS) measurements. O-substituted anilines were found to act as mixed type inhibitors. The results showed that o-substituted anilines suppressed both cathodic and anodic processes of iron corrosion in 1 M HCl by its adsorption on the iron surface according to Langmuir adsorption isotherm. Potentiodynamic and EIS measurements reveal that these compounds inhibit the iron corrosion in 1 M HCl and that the efficiency increases with increasing of the inhibitor concentration. Data obtained from EIS are analyzed to model the corrosion inhibition process through equivalent circuit.     

Preparation and characterization of thiocyanate-selective electrodes based on new complexes of copper(II) as neutral carriers

The complexes of hydroxycitronellal (o-aminobenzoic acid) copper(II) (Cu(II)-HXAB) and salicylaldehyde (o-aminobenzoic acid) copper(II) (Cu(II)-SHAB) were used as neutral carriers in PVC-based membrane ion-selective electrodes. The electrode based on Cu(II)-HXAB exhibited near-Nernstian potential response to thiocyanate (SCN⁻) in a linear range of 1.0 × 10^− 6 to 1.0 × 10^− 1 M with a detection limit of 8.5 × 10^− 7 M and a slope of − 57.3 mV/decade in 0.01 M phosphate buffer solution (pH 5.0). The electrode exhibited high selectivity to SCN⁻ over other tested anions with an anti-Hofmeister selectivity sequence. The selectivity behavior might be discussed in terms of UV-Vis spectrum and infrared spectrum. The transfer process of thiocyanate across the membrane interface was investigated by making use of the AC impedance technique. The electrode containing Cu(II)-HXAB could be applied to thiocyanate analysis in waste water with satisfactory results.     

Investigation of adsorption and inhibitive effect of 2-mercaptothiazoline on corrosion of mild steel in hydrochloric acid media

The inhibition effect of 2-mercaptothiazoline (2MT) on the corrosion behavior of mild steel (MS) in 0.5 M HCl solution was studied in both short and long immersion times (120 h) using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques. For long-term tests, hydrogen gas evolution (VH₂−t) and the change of the open circuit potential with immersion time (E_ocp − t) were also measured in addition to the former three techniques. The surface morphology of the MS after its exposure to 0.5 M HCl solution with and without 1.0 × 10⁻² M 2MT with the different immersion times was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermal stability of the inhibitor film was investigated by thermogravimetric analysis (TGA). The value of activation energy (E_a) for the MS corrosion and the thermodynamic parameters such as adsorption equilibrium constant (K_ads), free energy of adsorption (ΔG_ads), adsorption heat (ΔH_ads) and adsorption entropy (ΔS_ads) values were calculated and discussed. The potential of zero charge (PZC) of the MS in inhibited solution was studied by the EIS method, and a mechanism for the adsorption process was proposed. The results showed that 2MT performed excellent inhibiting effect for the corrosion of the MS. Finally, the high inhibition efficiency was discussed in terms of adsorption of inhibitor molecules and protective film formation on the metal surface. TGA results also indicated that the inhibitor film on the surface had a relatively good thermal stability.     

Comparison of inorganic inhibitors of copper, nickel and copper-nickels in aqueous lithium bromide solution

The electrochemical behavior of copper, nickel and two copper-nickel (Cu90/Ni10 and Cu70/Ni30) alloys in 850 g/L LiBr solution in the absence and presence of three different inorganic inhibitors (chromate CrO₄²⁻, molybdate MoO₄²⁻, and tetraborate B₄O₇²⁻) has been studied. Differences in inhibition efficiency are discussed in terms of potentiodynamic and cyclic measurements.The best protection is obtained by adding chromate to the 850 g/L LiBr solution while the inhibition efficiencies of molybdate and tetraborate ions were not markedly high. Very aggressive anions, such as bromides, in the present experimental conditions, notably reduce the action of the less efficient molecules (molybdate and tetraborate), but not that of the most efficient ones (chromate).The results of the investigation show that the inhibiting properties depend on the nickel content in the alloy; this element improves the general corrosion resistance of the material in the sense that it shifts free corrosion potential towards more noble values and density corrosion currents towards lower levels. The nickel content in the alloy also enlarges the passivating region of the materials in chromate and molybdate-containing solution; furthermore it decreases the current passivating values to lower values. Nickel addition improves the localized corrosion resistance in the bromide media.     

Inhibition of copper corrosion in acidic pickling solutions by N-phenyl-1,4-phenylenediamine

Inhibition of copper corrosion by N-phenyl-1,4-phenylenediamine (NPPD) has been investigated in de-aerated, aerated, and oxygenated aqueous 0.50 M HCl solutions by using potentiodynamic polarization, potentiostatic current-time, electrochemical impedance spectroscopy, and weight-loss measurements, along with scanning electron microscopic (SEM) and energy dispersive X-ray (EDX) experiments. Potentiodynamic polarization measurements showed that the NPPD molecules significantly decrease cathodic, anodic, and corrosion currents in all these solutions. Potentiostatic current-time measurements as well as SEM and EDX investigations of the copper surface revealed that NPPD suppresses the copper dissolution current due to its adsorption on the copper surface as a Cu(I)-NPPD complex. Impedance measurements also supported the results obtained from both the potentiodynamic and potentiostatic experiments. The inhibition efficiencies measured from polarization, electrochemical impedance spectroscopy (EIS), and weight-loss experiments are all internally consistent with each other. These results together showed that NPPD is a good mixed-type inhibitor for copper corrosion in all solutions studied.     

The influence of some new 2,5-disubstituted 1,3,4-thiadiazoles on the corrosion behaviour of mild steel in 1 M HCl solution: AC impedance study and theoretical approach

The new 2,5-disubstituted 1,3,4-thiadiazoles were investigated as corrosion inhibitors of mild steel in 1 M HCl using AC impedance technique. Four of these compounds exhibit good inhibition properties, while two of them, 2,5-bis(4-nitrophenyl)-1,3,4-thiadiazole and 2,5-bis(4-chlorophenyl)-1,3,4-thiadiazole, stimulate the corrosion process especially at low concentrations. 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. Possible correlations between experimental inhibition efficiencies and quantum chemical parameters such as dipole moment (μ), highest occupied (E_HOMO) and lowest unoccupied (E_LUMO) molecular orbitals were investigated. The models of the inhibitors were optimised with the Density Functional Theory formalism (DFT) using hybrid B3LYP/6-31G (2d,2p) as a higher level of theory. The Quantitative Structure Activity Relationship (QSAR) approach has been used and composite index of some quantum chemical parameters were constructed in order to characterize the inhibition performance of the tested molecules.     

Inhibitory effect of non-ionic surfactants of the TRITON-X series on the corrosion of carbon steel in sulphuric acid

The corrosion inhibition characteristics of non-ionic surfactants of the TRITON-X series, known as TRITON-X-100 and TRITON-X-405, on stainless steel (SS) type X4Cr13 in sulphuric acid were investigated by potentiodynamic polarisation measurements. It was found that these surfactants act as good inhibitors of the corrosion of stainless steel in 2 mol L⁻¹ H₂SO₄ solution, but the inhibition efficiency strongly depends on the electrode potential. The polarisation data showed that the non-ionic surfactants used in this study acted as mixed-type inhibitors and adsorb on the stainless steel surface, in agreement with the Flory-Huggins adsorption isotherm. Calculated ΔG_ads values are −57.79 kJ mol⁻¹ for TRITON-X-100, and −87.5 kJ mol⁻¹ for TRITON-X-405. From the molecular structure it can be supposed that these surfactants adsorb on the metal surface through two lone pairs of electrons on the oxygen atoms of the hydrophilic head group, suggesting a chemisorption mechanism.     

Inhibition of magnesium localised corrosion in chloride containing electrolyte

An in situ Scanning Vibrating Electrode Technique (SVET) is used to investigate the inhibition of localised corrosion occurring on unpolarised magnesium (Mg) samples immersed in 5% (w/v) aqueous sodium chloride electrolyte. In uninhibited electrolyte, localised corrosion features taking the form of dark, radially expanding discs are shown to consist of a strongly cathodic interior, surrounded by a ring of anodic activity. A range of potential anionic inhibitors, selected on the basis of their ability to form insoluble precipitates with aqueous Mg²⁺ ions, are systematically investigated and compared with chromate additions. Of the anions evaluated only phosphate additions markedly decrease the extent of localised corrosion observed and provide a comparable level of inhibition to chromate. The onset of profound corrosion inhibition is achieved at threshold concentrations of 10⁻² and 2 × 10⁻⁴ mol dm⁻³ for chromate and phosphate additions respectively. Phosphate inhibition efficiency increases markedly when the pH of the electrolyte is decreased. Consequently at phosphate concentrations of ≥10⁻³ mol dm⁻³, in the pH 4-7 range, Mg is able to withstand over 4 h immersion with little evidence of breakdown. From the empirical evidence presented, it is proposed that phosphate principally acts to inhibit hydrogen evolution at focal cathodic sites, where elevated pH produces sufficient PO₄³⁻ speciation to form a surface precipitate by combining with free Mg²⁺.     

A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite and its application for electrochemical supercapacitor

A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite [MnO₂/P(An-co-oAs)] was successfully synthesized by a delamination/reassembling process using P(An-co-oAs) ionomer and layered manganese oxide in aqueous solution. This nanocomposite obtained was then characterized by Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), electron microscopy (SEM), and thermogravimetric (TG) analysis. X-ray diffraction and electron microscope analysis showed that the MnO₂/P(An-co-oAs) nanocomposite had a lamellar structure with increasing interlayer spacing. The MnO₂/P(An-co-oAs) nanocomposite exhibited substantially improved conductivity, which was near 100 times greater than that of its pristine MnO₂ (3.5 × 10⁻⁷ S cm⁻¹). The specific capacitance of the MnO₂/P(An-co-oAs) nanocomposite reached 262 F g⁻¹ in 1 M Na₂SO₄ at a current density of 1 A g⁻¹, which was significantly higher than that of either of its two pristine materials [MnO₂ (182 F g⁻¹) or P(An-co-oAs) (127 F g⁻¹)] owing to the synergic effect between the two pristine components. The fabrication mechanism of the nanocomposite was also proposed and discussed in this paper.     

Localized electrochemical study of corrosion inhibition in microdefects on coated AZ31 magnesium alloy

In the present work corrosion inhibition in microdefects of protective coatings on magnesium alloy was studied by SVET (scanning vibrating electrode technique) and SIET (scanning ion-selective electrode technique) in 0.05 M NaCl. Mg²⁺- and pH-selective microelectrodes were developed to be used by SIET. The microelectrodes were characterized from the standpoint of properties important for corrosion applications, aiming at the reliable functioning during measurements. The combination of SVET and SIET demonstrated to be a useful approach to investigate the inhibition of corrosion processes in microdefects on coated AZ31. In this paper the corrosion inhibiting properties of 1,2,4,-triazole, F⁻ and Ce³⁺ on AZ31 alloy were analyzed. According to the results, 1,2,4-triazole in concentration of 0.01 M showed the highest inhibition efficiency among the studied inhibitors and was able to prevent the increase of pH in the corroding defects, by keeping the corrosion activity on a very low level during the tested immersion period.     

Synthesis of undecanoic acid phenylamides as corrosion inhibitors

Non‐substituted or mono‐substituted 11‐cyano or 11‐thiocyanato undecanoic acid phenylamide derivatives were synthesized and characterized with their FT‐IR and ¹H‐NMR spectra. Thereafter, their corrosion prevention efficiencies were investigated. All compounds were tested with steel coupons in acidic medium by a gravimetric method. Acidic tests were done with a medium concentration of 2 M HCl for 5 h at variable temperatures and inhibitor concentrations. The corrosion prevention efficiencies of the inhibitors were compared according to their chemical structures and the corrosion inhibition mechanism was also discussed. The synthesized compounds showed promising corrosion inhibition efficiencies under the outlined test conditions. Best inhibitions were obtained at 27°C and 100 ppm concentration of corrosion inhibitors.     

Novel Amide-Based Cationic Surfactants as Efficient Corrosion Inhibitors for Carbon Steel in HCl and H2SO4 media

A variety of surface active compounds were synthesized by the quaternization of some straight chain amide derivatives with triethylamine or pyridine. Their structure FT-IR and ¹H-NMR spectra were recorded. In addition their physical properties and corrosion prevention efficiencies were investigated. All compounds were tested with steel coupons in acidic media by the gravimetric method. As acidic media 1.5 M HCl and 1.5 M H₂SO₄ were used and the corrosion inhibition tests fulfilled at room temperature for 24 h. Almost all prepared cationic surfactants showed efficient inhibition around their critical micelle concentrations. The effects of HCl concentration on corrosion inhibition of some synthesized compounds were also investigated. The corrosion tests were supported by contact angle measurements.     

Electrochemical and quantum chemical study of purines as corrosion inhibitors for mild steel in 1 M HCl solution

The purines and its derivatives, such as, guanine, adenine, 2,6-diaminopurine, 6-thioguanine and 2,6-dithiopurine, were investigated as corrosion inhibitors for mild steel in 1 M HCl solution by weight loss measurements, electrochemical tests and quantum chemical calculations. The polarization curves of mild steel in the hydrochloric acid solutions of the purines showed that both cathodic and anodic processes of steel corrosion were suppressed. The Nyquist plots of impedance expressed mainly as a depressed capacitive loop with different compounds and concentrations. For all these purines, the inhibition efficiency increased by increasing the inhibitor concentration, and the inhibition efficiency orders are 2,6-dithiopurine > 6-thioguanine > 2,6-diaminopurine > adenine > guanine with the highest inhibiting efficiency of 88.0% for 10⁻³ M 2,6-dithiopurine.The optimized structures of purines, the Mulliken charges, molecular orbital densities and relevant parameters were calculated by quantum chemical calculations. The quantum chemical calculation results inferred that the adsorption belong to physical adsorption, which might arise from the π stacking between the π electron of the purines and the metal surface.     

Electrochemical behavior of nickel in nitric acid and its corrosion inhibition using some thiosemicarbazone derivatives

The adsorption and corrosion inhibition behavior of three selected thiosemicarbazone derivatives, namely 3-pyridinecarboxaldehyde thiosemicarbazone (META), isonicotinaldehyde thiosemicarbazone (PARA) and 2-pyridinecarboxaldehyde thiosemicarbazone (ORTHO) at the nickel surface were studied electrochemically by Tafel and impedance methods and computationally by carrying out Monte Carlo searches of configurational space on nickel/thiosemicarbazone derivative system. Electrochemical measurements showed that the inhibition efficiency of these compounds increased with increase in their concentration. The recorded inhibition efficiencies of the three tested thiosemicarbazone increase in the order: META > PARA > ORTHO. Polarization studies showed that these compounds act as mixed-type inhibitors for nickel corrosion in 1.0 M HNO₃ solutions. Results obtained from Tafel and impedance methods are in good agreement. Thiosemicarbazone derivatives have been simulated as adsorbate on Ni (1 1 1) substrate and the adsorption energy, binding energy and the low energy adsorption sites have been identified on nickel surface.     

The ultrasonic electropolymerization of an 5-[o-(4-bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) film electrode and its electrocatalytic properties to dopamine oxidation in aqueous solution

5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H₂SO₄ between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s⁻¹. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L⁻¹ phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10⁻⁷ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹. The electrode had a detection limit of 6.0 × 10⁻⁸ mol L⁻¹(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s⁻¹, the transfer coefficient α = 0.709, the electron number involved in the rate determining step n_α = 0.952, and the diffusion coefficient D_o = 3.54  10⁻⁵ cm² s⁻¹ were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.