CORROSION INHIBITION AND ADSORPTION BEHAVIOR OF MALACHITE GREEN DYE ON ALUMINUM CORROSION

Malachite green dye (MG) was studied as a corrosion inhibitor for aluminum in 1.0 mol dm^?3 HCl and 0.5 mol dm^?3 KOH using the gravimetric technique. The results revealed an inhibiting effect of MG, which was highly restrained in 0.5 M KOH and pronounced in 1.0 M HCl. MG inhibited the corrosion reaction in the acidic medium by adsorption on the metal/solution interface following the Flory-Huggins isotherm. Inhibition efficiency increased with MG concentration and synergistically increased in the presence of iodide ions, but decreased with a rise in temperature. The local reactivity of the MG molecule was analyzed theoretically using the density functional theory to explain the adsorption characteristics, while molecular dynamics simulations were performed to illustrate the adsorption structure of MG at a molecular level. The theoretical predictions showed good agreement with experimental results.     

Performance evaluation of poly (methacrylic acid) as corrosion inhibitor in the presence of iodide ions for mild steel in H2SO4 solution

The inhibition performance of poly (methacrylic acid) (PMAA) and the effect of addition of iodide ions on the inhibition efficiency for mild steel corrosion in 0.5 M H₂SO₄ solution were investigated in the temperature range of 303–333 K using electrochemical, weight loss, scanning electron microscopy (SEM), and water contact angles measurements. The results show that PMAA is a moderate inhibitor for mild steel in 0.5 M H₂SO₄ solution. Addition of small amount of KI to PMAA significantly upgraded the inhibition efficiency up to 96.7%. The adsorption properties of PMAA and PMAA + KI are estimated by considering thermodynamic and kinetic parameters. The results reveal that PMAA alone was physically adsorbed onto the mild steel surface, while comprehensive adsorption mode characterized the adsorption of PMAA + KI. Adsorption of PMAA and PMAA + KI followed Temkin adsorption isotherm. The SEM and water contact angle images confirmed the enhanced PMAA film formation on mild steel surface by iodide ions.     

Corrosion inhibition of mild steel in acidic media by Basic yellow 13 dye

The inhibition performance of Basic yellow 13 dye on mild-steel corrosion in hydrochloric acid solution was studied at 25 °C using weight loss and electrochemical techniques. The effect of inhibitor concentration on inhibition efficiency has been studied. Inhibition efficiency increased with increase of Basic yellow 13 concentration. The results showed that this inhibitor had good corrosion inhibition even at low concentrations (95% for 0.005 M Basic yellow 13) and its adsorption on mild-steel surface obeys Langmuir isotherm. ΔG _ads was calculated and its negative value indicated spontaneous adsorption of the Basic yellow 13 molecules on the mild-steel surface and strong interaction between inhibitor molecules and metal surface. The value of ΔG _ads was less than 40 kJmol⁻¹, indicating electrostatic interaction between the charged inhibitor molecules and the charged metal surface, i.e., physical adsorption.     

Corrosion of the zinc negative electrode of zinc–cerium hybrid redox flow batteries in methanesulfonic acid

Corrosion of zinc in aqueous methanesulfonic acid has been evaluated over a wide range of concentrations of acid (0.5–5 mol dm^?3), dissolved zinc (0.5–2 mol dm^?3), and electrolyte temperature (22–50 °C). The corrosion rate of zinc, in terms of weight loss and the volume of hydrogen evolved, varied with time and it was found to be highly dependent on the surface state and electrolyte conditions. With an initial active layer of zinc present, the corrosion rate rapidly increased following a decline when the proton concentration in the solution decreased to ca. 0.56 mol dm^?3. Organic and inorganic inhibitors were added to the electrolyte to suppress the zinc corrosion in 1 mol dm^?3 methanesulfonic acid. The strong adsorption and blocking effects of cationic organic adsorption inhibitors, such as cetyltrimethyl ammonium bromide and butyltriphenyl phosphonium chloride, led to a significant decrease in zinc corrosion over a 10 h immersion period. With the addition of indium and lead ions inhibitors, the zinc surface showed less activity. Zinc corrosion continued to a smaller extent in the presence of these metallic inhibitors during the first few hours, but the metallic layer of the inhibitors did not cover the surface completely resulting in continued hydrogen evolution and making the inhibitors less effective at longer times.     

The electrochemical characteristics of commercial aluminium alloy electrodes for Al/air batteries

To develop new materials for Al/air batteries, the evaluation and characterisation of commercial aluminium alloys, namely, Al2000, Al2000Clad and Al7000, as anodes in alkaline electrolyte batteries has been performed. Their self-corrosion rate, hydrogen evolution rate and electrochemical properties, including open circuit potentials, polarisation characteristics and potentiodynamic measurements, were examined in a 4 M KOH solution. Among the tested alloys, Al2000 was found to be the most promising because it exhibits a high open circuit potential, a good anode efficiency and a minimum corrosion rate. Al2000/NiOOH and Al2000/air batteries were tested. Electrolyte concentrations between 0.01 and 4 M KOH were studied, and discharge currents between 0.8 and 20 mA cm^?2 were imposed to analyse the evolution of the E_cell. Conversely, the Al7000 alloy exhibited the highest corrosion rate and H₂ evolution compared to the other alloys.     

Synergistic effect of halide ions and polyethylene glycol on the corrosion inhibition of aluminium in alkaline medium

The corrosion inhibition of aluminium in alkaline medium was studied at 30 and 40°C in the presence of polyethylene glycol (PEG) using gravimetric (weight loss) and thermometric techniques. The effect of halides (KCl, KBr, and KI) on the inhibitory action of PEG was also studied. It was found that PEG acted as inhibitor for aluminium corrosion in the alkaline medium. Inhibition efficiency increased with increasing inhibitor concentration. An increase in temperature led to increase in both the corrosion rate and inhibition efficiency in the absence and presence of inhibitor and halides. Phenomenon of chemical adsorption mechanism is proposed from the values of E_a, Q_ads, and ΔG obtained. The adsorption of PEG on the surface of aluminium was found to obey Flory–Huggins and Temkin adsorption isotherms. The synergism parameter, S₁ evaluated was found to be greater than unity indicating that the enhanced inhibition efficiency caused by the addition of halides is synergistic in nature. The inhibition efficiency, surface coverage and synergism parameter increased in the order; I^?> Br^?> Cl^? showing that a joint adsorption of PEG and halide ions on aluminium plays a significant role in the adsorption process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Studies on the influence of iodide ions on the synergistic inhibition of the corrosion of mild steel in an acidic solution

The synergistic action caused by iodide ions on the corrosion inhibition of mild steel in 0.5 M H₂S0₄ in the presence of dicyclohexylamine (DCHA) has been investigated using potentiodynamic polarization, linear polarization and a.c. impedance techniques. DCHA inhibits the corrosion of mild steel in 0.5 m H₂SO₄ even at lower concentrations. The inhibition efficiency decreases with increase in the concentration of the amine. The addition of iodide ions enhances the inhibition efficiency to a considerable extent. The adsorption of this compound is also found to obey Langmuir's adsorption isotherm, thereby indicating that the main process of inhibition is by adsorption. The increase in surface coverage values in the presence of iodide ions indicates that DCHA forms an insoluble complex at lower amine concentrations by undergoing a joint adsorption. The synergism parameter (S) is defined and calculated both from inhibition efficiency and surface coverage values. This parameter in the case of DCHA is found to be more than unity, indicating that the enhanced inhibition efficiency caused by the addition of iodide ions is only due to synergism and there is a definite contribution from the inhibitor molecule. Thus, DCHA is then adsorbed by coulombic attraction on the metal surface where the I^– is already chemisorbed and thus reduces the corrosion rate.     

INFLUENCE OF K+ AND NA+ IONS ON DIRECT ELECTROSYNTHESIS OF SOLID K2FEO4 AND COMPARISON OF THE PHYSICOCHEMICAL PROPERTIES OF K2FEO4 SAMPLES

The influence of K⁺ and Na⁺ ions on the direct electrosynthesis of solid K₂FeO₄ was investigated in 14 M OH^? solutions. At 50 or 60°C, the maximum current efficiency of electrosynthesis is obtained in 9 M KOH +5 M NaOH solution. The maximum current efficiency of 64.9% is obtained at 60°C in 9 M KOH +5 M NaOH solution, similar to the maximum value of 63.9% at 70°C in 14 M KOH solution in the temperature ranges studied. The result shows that the temperature at which the maximum current efficiency is obtained in 9 M KOH +5 M NaOH is much lower than that in 14 M KOH. Solid K₂FeO₄ powders directly electrosynthesized in 9 M KOH +5 M NaOH and 14 M KOH solutions were characterized by Fourier transform-infrared spectrometry (FT-IR), scanning electron microscopy (SEM), and X-ray diffraction (XRD), and their electrochemical performance was investigated by means of galvanostatic discharge. The result shows that the two samples have similar physical properties and discharge performance.     

CORROSION INHIBITION OF CuNi10Fe ALLOY WITH PHENOLIC ACIDS

The purpose of this study was to investigate the efficiency of two phenolic acids, namely p-hydroxybenzoic acid (HBA) and protocatechuic acid (PCA), as corrosion inhibitors for CuNi10Fe alloy in a 0.5 mol dm^?3 NaCl solution. In these investigations, open circuit potential measurements, potentiodynamic polarization measurements, and the linear polarization method have been used. It was found that both phenolic acids had similar corrosion inhibition effects on the CuNi10Fe alloy dissolution. The inhibition efficiency (IE) increased with increase in inhibitor concentration. The polarization shows that both compounds functioned as cathodic corrosion inhibitors by adsorption on the surface of CuNi10Fe alloy according to the Freundlich adsorption isotherm. The numerical values of free energies of adsorption indicate physical adsorption of the compounds on the electrode surface. DFT-based quantum chemical computations and molecular dynamics (MD) simulations revealed identical electronic and adsorption structures for both HBA and PCA, which could account for the similarities in the experimentally observed inhibiting effects.     

Synergistic effect of 2-mercapto benzimidazole and KI on copper corrosion inhibition in aerated sulfuric acid solution

2-Mercapto benzimidazole (MBI) was used as a copper corrosion inhibitor in aerated 0.5 mol L^–1 H₂SO₄ solutions. The inhibition efficiency (IE) increased with increasing MBI concentration to 74.2% at the 1 mM level. A synergistic effect existed when MBI and iodide ions were used together to prevent copper corrosion in sulfuric acid. It was found that IE reached 95.3% in 0.5 mol L^–1 H₂SO₄ solutions containing 0.75 mmol L^–1 MBI and 0.25 mmol L^–1 KI. X-ray photoelectron spectroscopy (XPS) analysis of the copper samples showed that a (Cu⁺MBI) complex film formed on the surface to inhibit the copper corrosion and the iodide ions did not participate in the formation of the inhibitor film. The synergistic effect was attributed to the adsorption of iodide anions on the copper surface, which then facilitated the adsorption of protonated MBI and the formation of an inhibitive film.     

Effect of Temperature on Kinetics and Adsorption Profile of Endothermic Chemisorption Process: –Tm(III)–PAN Loaded PUF System

Abstract

The sorption behavior of 3.18×10^?6 mol l^?1 solution of Tm(III) metal ions onto 7.25 mg l^?1 of 1‐(2‐pyridylazo)‐2‐naphthol (PAN) loaded polyurethane foam (PUF) has been investigated at different temperatures i.e. 303 K, 313 K, and 323 K. The maximum equilibration time of sorption was 30 minutes from pH 7.5 buffer solution at all temperatures. The various rate parameters of adsorption process have been investigated. The diffusional activation energy (ΔE_ads) and activation entropy (ΔS_ads) of the system were found to be 22.1±2.6 kJ mol^?1 and 52.7±6.2 J mol^?1 K^?1, respectively. The thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) were calculated and interpreted. The positive value of ΔH and negative value of ΔG indicate that sorption is endothermic and spontaneous in nature, respectively. The adsorption isotherms such as Freundlich, Langmuir, and Dubinin–Radushkevich isotherm were tested experimentally at different temperatures. The changes in adsorption isotherm constants were discussed. The binding energy constant (b) of Langmuir isotherm increases with temperature. The differential heat of adsorption (ΔH_diff), entropy of adsorption (ΔS_diff) and adsorption free energy (ΔG_ads) at 313 K were determined and found to be 38±2 kJ mol^?1, 249±3 J mol^?1 K^?1 and –40.1±1.1 kJ mol^?1, respectively. The stability of sorbed complex and mechanism involved in adsorption process has been discussed using different thermodynamic parameters and sorption free energy.     

Understanding the inhibitory effect of sodium oleate on the corrosion of Al and Al–Cu alloys in 1.0 M H<Subscript>3</Subscript>PO<Subscript>4</Subscript> solution—Polarization studies

Polarization measurements were employed, as a first step towards studying the corrosion behaviour of Al and two Al–Cu alloys, namely Al–4.5%Cu, and Al–7.5%Cu alloys in deaerated stirred 1.0 M H₃PO₄ solution at 25 °C. Inhibition of Al and Al–Cu alloys corrosion in 1.0 M H₃PO₄ solution, using sodium oleate (SO) as an anionic surfactant inhibitor, was also studied. Polarization curves showed that SO acted as a mixed-type inhibitor to Al corrosion, while it acted mainly as a cathodic inhibitor to the acid corrosion of Al–4.5%Cu, and Al–7.5%Cu alloys. Inhibition is accomplished by inhibitor adsorption on the electrode surface without detectable changes in the chemistry of corrosion. The relationship between surfactant concentration, surfactant critical micellar concentration (CMC), and corrosion inhibition is also discussed based on the Langmuir isotherm assumption, commonly applied in corrosion inhibition evaluations. The protection efficiency increases with increase in surfactant concentration and %Cu in Al samples. Maximum protection efficiency of the surfactant is observed at concentrations around its CMC. The mechanism of adsorption is discussed based on the surface charge of the electrode surface.     

Effect of amino acids containing sulfur on the corrosion of mild steel in phosphoric acid solutions polluted with Cl−, F− and Fe3+ ions–behaviour near and at the corrosion potential

Research on non‐toxic inhibitors is of considerable interest in investigations into the replacement of hazardous classical molecules. This paper reports the action of four amino acids containing sulfur on the corrosion of mild steel in phosphoric acid solution with and without Cl^?, F^? and Fe³⁺ ions near and at the corrosion potential (E_corr) using both the polarization resistance method and electrochemical impedance spectroscopy (EIS). Both cysteine and N‐acetylcysteine (ACC) showed higher inhibition efficiency than methionine and cystine. Adsorption of methionine onto a mild steel surface obeys the Frumkin adsorption isotherm and has a free energy of adsorption value (ΔG °_ads) lower than those obtained in the presence of cystine, cysteine and ACC whose adsorption isotherms follow that of Langmuir. Both F^? and Fe³⁺ ions stimulate mild steel corrosion while Cl^? ions inhibit it. The binary mixtures of methionine, cysteine or ACC with Cl^? or F^? ions are effective inhibitors (synergism) while the combinations of the amino acid with Fe³⁺ or the ternary Cl^?/F^?/Fe³⁺ mixture have low inhibitive action (antagonism). EIS measurements revealed that the charge transfer process mainly controls the mechanism of mild steel corrosion in phosphoric acid solution in the absence and presence of the investigated additives. The mechanism of corrosion inhibition or acceleration is discussed. © 2002 Society of Chemical Industry     

Synergistic effect of iodide ions on inhibitive performance of 2,5-bis(4-methoxyphenyl)-1,3,4-thiadiazole during corrosion of mild steel in 0.5?M sulfuric acid solution

The synergistic effect of iodide ions on the corrosion inhibition of mild steel in 0.5 M H₂SO₄ solutions by 2,5-bis(4-methoxyphenyl)-1,3,4-thiadiazole (4-MTH) has been studied using electrochemical impedance spectroscopy (EIS) and the Tafel polarisation method. The results showed that the inhibition efficiency increased with 4-MTH concentration while the potential of desorption (E _d) remained unchanged. The addition of potassium iodide (KI) in the acid solution stabilized the adsorption of 4-MTH molecules on the metal surfaces and, therefore, enhanced the inhibition efficiency of 4-MTH and increased the value of E _d. The synergistic effect was observed between KI and 4-MTH with an optimum mass ratio of [4-MTH]/[KI] = 5/5. The calculated values of synergism parameter (S _θ) from the coverage of the surface were found to be more than unity in most cases. This clearly showed the synergistic influence of iodide ions on the corrosion inhibition of mild steel in 0.5 M H₂SO₄ by 4-MTH. The adsorption of this inhibitor alone and in combination with iodide ions followed Langmuir’s adsorption isotherm.     

Effect of iodide ions on corrosion inhibition of mild steel by 3,5-bis(4-methylthiophenyl)-4H-1,2,4-triazole in sulfuric acid solution

The synergistic effect of iodide ions on the corrosion inhibition of mild steel in 0.5 M sulfuric acid (H₂SO₄) in the presence of 3,5-bis(4-methylthiophenyl)-4H-1,2,4-triazole (4-MTHT) was investigated using weight loss measurements and different electrochemical techniques such as potentiostatic polarization curves and electrochemical impedance spectroscopy (EIS). The inhibition efficiency (E, %) increased with 4-MTHT concentration, but the desorption potential (E _d) remained unchanged with increasing 4-MTHT concentration. The addition of potassium iodide (KI) enhanced E considerably and increased the value of E _d. A synergistic effect was observed between KI and 4-MTHT with an optimum mass ratio of [4-MTHT]/[KI] = 4 × 10^–2. The synergism parameters (S ) calculated from surface coverage were found to be more than unity. This result clearly showed the synergistic influence of iodide ions on the corrosion inhibition of mild steel in 0.5 M H₂SO₄ by 4-MTHT. The adsorption of this inhibitor alone and in combination with iodide ions followed Langmuir's adsorption isotherm.     

Influence of H+ and Cl− ions on inhibitive performance of poly(aniline) for iron corrosion in acid

The inhibition effect of poly(aniline) on pure iron corrosion in 1M HCl and with various H⁺ ions and Cl^? ions concentrations was investigated by the polarization and electrochemical impedance spectroscopy methods. The results showed that poly(aniline) suppressed both cathodic and anodic processes of iron dissolution in 1M HCl by its adsorption on the iron surface according to Langmuir's adsorption isotherm. The inhibition efficiency of poly(aniline) was found to increase with the inhibitor concentrations. Further, it was observed that, there was no significant variation in corrosion potential (E_corr) values in the presence of inhibitors suggesting that, this polymer behaved as mixed type inhibitor. Similar studies for the inhibitor at 500 ppm in various concentrations of H⁺ and Cl^? ions, have shown that the inhibition efficiency decreases with decrease in concentrations of H⁺ ions and Cl^? ions in aqueous solution. It reveals that, the adsorption of inhibitor on iron surface is by more cationic form of inhibitor and higher efficiency at higher H⁺ and Cl^? ions is due to enhanced adsorption of cat ionic form of inhibitor molecules. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Inhibition of Steel Corrosion in Nitric Acid by Sulfur Containing Compounds

The inhibitive mechanism, thermodynamics, and adsorptive properties of thiobarbituric acid (TBA) and thiourea (TU) on the corrosion of mild steel in 0.5 M HNO₃ solution have been investigated using potentiodynamic, electrochemical impedance spectroscopy techniques, and quantum chemical calculations. Both inhibitors showed good inhibition efficiency in nitric acid solution. TU was the most effective inhibitor and its inhibition efficiency increases with increasing concentration to attain 99% at 6 × 10^?3 mol · L^?1 at 30°C. Theoretical fitting of different isotherms, Langmuir, Flory–Huggins, Temkin, and the kinetic-thermodynamic models were tested to clarify the nature of inhibitors adsorption on mild steel surface. The obtained experimental data fitted all the applied adsorption isotherms except Langmuir. The thermodynamic activation parameters were determined to provide evidence of the inhibitory effect of TBA and TU. To determine the surface charge at the steel surface in nitric acid solution the potential of zero charge was measured using AC measurements at different potentials. Quantum chemical parameters were calculated and explained. The data clarified that the inhibition of steel in nitric acid by TU or TBA takes place through physicochemical adsorption mechanism.     

Influence of halide ions on the adsorption of diphenylamine on iron in 0.5 M H2SO4 solutions

Halide ions are found to enhance the inhibition performance of amines due to enhanced adsorption of amines by the adsorbed halide ions on the metal surface. In this work, the synergistic action of halide ions on the corrosion inhibition of iron in 0.5 M H₂SO₄ by diphenylamine has been found out by electrochemical impedance and polarization methods. Analysis of impedance data has been made with equivalent circuit with constant phase angle element for calculation of double layer capacitance values. Experiments have been carried out in the concentration range of 100-1000 ppm of diphenylamine in the presence of 0.5-1.0 × 10⁻³ M of halide ions. Diphenylamine is found to be a cathodic inhibitor and the inhibition efficiency of about 65% is obtained at 1000 ppm. The anodic and cathodic Tafel slopes in the presence of diphenylamine alone and with halide ions are 65 ± 5 and 105 ± 5 mV, respectively. Diphenylamine inhibits corrosion by adsorption and the surface coverage values are increased considerably in the presence of halide ions. In the presence of iodide ions, the inhibition efficiency of diphenylamine at 100 ppm is increased to more than 90%. In the case of other halide ions, the inhibition efficiency of diphenylamine in increased to 80% at 1000 ppm. The order of synergism of halide ions is I⁻ ? Br⁻ > Cl⁻. The highest synergistic effect of iodide ions is due to chemisorption with metal surface due to its larger size and ease of polarizability.     

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.