Electrochemical behavior of tin in sodium borate solutions and the effect of halide ions and some inorganic inhibitors

The corrosion of tin electrode in sodium borate (Na₂B₄O₇) solutions was investigated using cyclic voltammetry and potentiostatic current transient techniques. In absence of halide ions, the E/j response exhibits active/passive transition. The active region involves one anodic peak corresponding to the formation of Sn(OH)₂ and/or SnO. Addition of Cl⁻, Br⁻ or I⁻ (C ? 0.01 M) ions inhibits the active dissolution of tin, but higher concentrations enhance the active dissolution and tend to breakdown the passive film and induce pitting attack. The effect of , , and as inorganic inhibitors on the pitting corrosion of tin in (0.1 M Na₂B₄O₇ + 0.1 M NaCl) solution has also been studied. The presence of these anions (except ) inhibits pitting corrosion. Chronoamperometry measurements showed that nucleation of pit takes place after an incubation time (t_i). The rate of pit nucleation () increases with increasing halide ions concentration and applied potentials, but decreases with increasing the concentration of the inorganic inhibitors (except ). The inhibition efficiency of these inhibitors decreases in the order:

     

The effect of counter anions on corrosion resistance of steel covered by bi-layered polypyrrole film

The bi-layered polypyrrole (PPy) coatings were investigated for corrosion prevention of a carbon steel. The inner layer was doped with the Keggin structure anions of (PMo₁₂) and anions for stabilization of the passive oxide film at the metal-polymer interface, and the outer layer was doped with four organic anions of dihydroxynaphthalenedisulfonate (DHNDS), naphthalenedisulfonate (NDS), anthraquinonedisulfonate (AnqDS) or dodecylsulfate (DoS) for inhibition of the decomposition and release of PMo₁₂. The corrosion tests were performed in 3.5 wt.% NaCl aqueous solution. The corrosion resistance of the steels covered by the bi-layered PPy films was found in the following order: PPy-PMo₁₂/PPy-DHNDS < PPy-PMo₁₂/PPy-NDS < PPy-PMo₁₂/AnqDS < PPy-PMo₁₂/PPy-DoS. The performance of corrosion protection related to the oxidized state of the polymer was discussed.     

Influence of alloy chemistry on microstructure and properties in NiCrBSi overlay coatings deposited by plasma transferred arc welding (PTAW)

The microstructures and performance of two NiCrBSi alloy overlays deposited by plasma transferred arc welding are studied. The coatings consist of a γ-Ni primary dendritic phase with harder Ni + Ni₃B or Ni + Ni₃Si eutectics and Cr-based particles (CrB, Cr₃C₂, and Cr₇C₃) situated at the interdendritic regions. It was found that the volume fraction of the soft primary dendritic phase drastically decreased and the proportion of chromium borides and carbides increased with an increase of C, B, Si, and Cr content. Microhardness testing revealed that the primary Ni dendrite, interdendritic, and Cr-particle phases had average hardness values of 405, 860, and 1200 HV respectively. An increase in the volume fraction of hard eutectics and Cr-particles lead to a substantial increase in hardness and wear resistance.     

Photoelectron spectroscopy study of the inhibition of mild steel corrosion by molybdate and nitrite anions

Passive films formed on mild steel in aqueous 8.6 mM NaCl solutions (pH 8), containing either or , have been studied with X-ray photoelectron spectroscopy. For either anion these films are ∼5 nm deep, and the primary chemical state of iron is Fe³⁺. Following exposure to , the film consists of a sub-layer (∼4.1 nm) composed largely of ferric oxide/hydroxide, overlaid by Fe₂(MoO₄)₃ (∼0.6 nm). As regards , spectra are consistent with the film being closely related to γ-Fe₂O₃. Furthermore, a reduction product of , potentially N₂, is present, displaying a depth profile comparable to that of molybdate.     

On the fundamentals of electrochemical corrosion of X65 steel in CO2-containing formation water in the presence of acetic acid in petroleum production

Electrochemical corrosion behavior of X65 steel in CO₂-containing oilfield formation water in the presence of acetic acid (HAc) was investigated by various electrochemical measurements and analyses as well as thermodynamic calculations of ionic concentrations, reaction rate constants and equilibrium electrode potentials. A conceptual model was developed to illustrate corrosion processes of steel in oilfield formation water system. The anodic reactions of the steel contain a direct dissolution of Fe, Fe → Fe²⁺ + 2e, and the formation of corrosion scale, FeCO₃, by Fe + → FeCO₃ + H⁺ + 2e. The cathodic processes contain the reduction of H⁺, , H₂O and HAc, where reduction of HAc has the least negative equilibrium potential and thus dominates the cathodic process. With addition of HAc in the solution, both cathodic and anodic reaction rates increase remarkably. It is attributed to the fact that HAc inhibits or degrades the formation of protective scales due to the decrease of solution pH. Upon electrode rotation, the measured impedance decreases with the increase in HAc concentration. The FeCO₃ scale will not form on electrode surface. When HAc concentration is less than 1000 ppm, the adsorbed intermediate product is not significant, resulting in generation of a low-frequency inductive loop in EIS plots. When HAc concentration is more than 3000 ppm, the adsorption of intermediate product is significant, generating overlapped capacitive semicircles in EIS measurements.     

Semiconducting and passive film properties of nitrogen-containing type 316LN stainless steels

The semiconducting property of passive films of nitrogen-containing type 316LN stainless steels in different electrolytic media (0.5 M NaCl, borate buffer and borate buffer + 0.5 M NaCl) was investigated by electrochemical impedance spectroscopy (EIS). The nitrogen effect on the chemical composition of the passive films was investigated using X-ray photoelectron spectroscopy, (XPS). Based on capacitance results, the semiconducting parameters obtained from the Mott-Schottky plots indicated a decrease in the donor and acceptor density (N_D and N_A) with increase in nitrogen content, and variation in the flat band potential (E_FB), depending on the electrolytic media. Thus indicating that the oxide layers of the passive film are modified by nitrogen addition. The presence of nitrogen and in the passive film was confirmed by the XPS analysis of the passive film. Cyclic polarization for pitting and repassivation corrosion studies indicated a decrease in hysteresis loop with increase in nitrogen content in 0.5 M NaCl solution. In the highest nitrogen-containing alloy (0.556 wt.% N), the hysteresis loop was small and negligible indicating that the pit initiation is minimum in this alloy. Based on the results obtained, an attempt was made to correlate the semiconducting nature of the passive films with pitting corrosion resistance.     

The application of electrochemical noise resistance to evaluate the corrosion resistance of AISI type 304 SS in nitric acid

The paper presents the application of noise resistance to evaluate the corrosion behaviour of sensitized AISI type 304 SS in nitric acid of varying concentration (4 N, 12 N, 16 N) and temperature (298 K, 323 K, 348 K). Electrochemical noise data was acquired from a three identical electrode configuration in the required conditions at open circuit potential. The noise resistance was evaluated as the ratio of the standard deviation of the potential to that of the current noise after removing the DC component. The inverse relationship between noise resistance and corrosion rate was exploited to qualitatively assess the corrosion behaviour of AISI type 304 SS in nitric acid. Noise resistance decreased with increase in concentration implying an increase in corrosion rate with increase in nitric acid concentration. An increase in temperature from 298 K to 323 K and 348 K decreased the noise resistance in 4 N and 12 N nitric acid implying higher corrosion rates at higher temperatures. The corrosion rates were similar at 323 K and 348 K in these concentrations. The simultaneous measurement of current and potential noise facilitated the evaluation of the frequency dependence of the noise data to determine the spectral noise resistance (R_sn) and the DC limit of the spectral noise resistance . The results from R_sn and also indicated higher corrosion rates at higher concentration and temperature. Also R_n and correlated well in 4 N and 12 N nitric acid at 323 K and 348 K while disparity was observed at room temperature in 4 N and 12 N nitric acid.     

Improvement of healing treatment with NaNO3 for a passivated iron electrode covered with an ultrathin polymer coating to prevent iron corrosion in some solutions containing aggressive anions

An ultrathin and ordered polymer coating was prepared on a passivated iron electrode by modification of a 16-hydroxyhexadecanoate ion self-assembled monolayer with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octyltriethoxysilane C₈H₁₇Si(OC₂H₅)₃. Further, the passivated and polymer-coated electrode was healed by treatment in 1.0 M NaNO₃ for 4 h. Prevention of passive film breakdown and iron corrosion for the passivated, polymer-coated and healed electrode was examined by monitoring of the open-circuit potential and repeated polarization measurements in oxygenated 0.1 M KClO₄, 0.1 M Na₂SO₄ and 0.1 M NaCl for many hours. The values of the time for passive film breakdown, t_bd were >240, 22.2 and 9.5 h in these solutions, respectively. The protective efficiencies for the electrode were extremely high, more than 99.9% before t_bd, indicating complete protection of substrate iron against corrosion in these solutions, unless passive film breakdown occurred. The presence of on the passive surface by treatment in 1.0 M NaNO₃ was detected by X-ray photoelectron and FTIR reflection spectroscopies. The self-healing activity of adsorbed to suppress passive film breakdown was discussed.     

Enhancement of corrosion resistance of Mg-9 wt.% Al-1 wt.% Zn alloy by a calcite (CaCO3) conversion hard coating

A calcite (CaCO₃) coating on Mg alloy, formed by chemical conversion treatment, was investigated. Aqueous with Ca²⁺ concentration of ∼220 ppm was employed in the chemical conversion treatment. Cross-sectional microstructures of the coated sample after 2 h of treatment revealed a two-layer coating structure. The corrosion current density (I_corr) of the coated sample was approximately two orders of magnitude lower than that of the untreated sample. Electrochemical impedance spectroscopy (EIS) and an appropriate equivalent circuit suggested that each of the layers of the two-layer coating effectively protects Mg alloy against corrosion.     

Inhibitive effect of diethylcarbamazine on the corrosion of mild steel in hydrochloric acid

Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), weight loss measurements and atomic force microscopy techniques were used to investigate the inhibitory effect of diethylcarbamazine (DECM) on corrosion of mild steel in HCl solution. The inhibitor showed >90% inhibition efficiency at 5.01 × 10⁻⁴ M. Results obtained revealed that inhibition occurs through adsorption of inhibitor molecules on metal surface without modifying the mechanism of corrosion process. Potentiodynamic polarization studies suggested that it is a mixed type inhibitor, predominantly controls cathodic reaction. Activation parameters (E_a, ΔH and ΔS) and thermodynamic parameters (, and ) were calculated to investigate mechanism of inhibition.     

Bis-isoxazolidines: A new class of corrosion inhibitors of mild steel in acidic media

Two new bis-isoxazolidines were synthesized in excellent yields via cycloaddition reaction of 1-pyrroline 1-oxide with 2,7-di(10-undecenyloxy)naphthalene and 1,4-di(10-undecenyloxy)benzene. One of the bis-isoxazolidines, on reaction with two equivalents of 1-bromododecane, afforded a bis-quaternary ammonium salt. All three inhibitor molecules in the presence of 400 ppm at 60 °C achieved inhibition efficiencies (IE) in the ranges 97-98% and 92-96% as determined by gravimetric method for corrosion of mild steel in 1 M HCl and 0.5 M H₂SO₄, respectively. The results obtained by the electrochemical methods using Tafel plots and electrochemical impedance spectroscopy corroborated the findings of the weightloss method. Both bis-isoxazolidines demonstrated remarkable efficiency in the lower range of inhibitor concentrations - in the presence of a meager 1.5 ppm of the inhibitor molecules, IEs of ∼70% in 1 M HCl were achieved. Thermodynamic parameters (, , ) for the adsorption process in the presence of the bis-isoxazolidines were determined. The values of around -90 kJ/mol in 1 M HCl and −50 kJ/mol in 0.5 M H₂SO₄, pointed towards the chemisorption of the inhibitor molecules, especially in HCl media. While the corrosion inhibition by these molecules was predominantly under cathodic control in 1 M HCl, the inhibition in 0.5 M H₂SO₄ was found to be under anodic control. The bis-isoxazolidines were found to provide a suitable inhibition mechanism for the corrosion inhibition in HCl as well as in H₂SO₄ media.     

Corrosion of niobium in sulphuric and hydrochloric acid solutions at 75 and 95 °C

New Pourbaix diagrams were calculated at 25, 75 and 95 °C for the Nb-H₂O system. The species and were considered. Potentiodynamic polarization and mass loss experiments (14 days) were conducted in concentrated H₂SO₄ (20, 40 and 80 wt%) and HCl (20 and 38 wt%) solutions at 75 and 95 °C. Nb forms a metastable pentoxide (Nb₂O₅) in H₂SO₄ and HCl solutions which dissolves as . Corrosion rates decrease between the 40% and the 80% H₂SO₄ solutions. SEM micrographs show generalized pitting in the 20% and 40% H₂SO₄ solutions. Mass loss corrosion rates did not exceed 306 μm/yr. Corrosion rates estimated by Tafel extrapolation were within two orders of magnitude of those measured by mass loss and it is shown that this finding is consistent with the thickening of the oxide.     

Influence of 1,2-diaminoethane on the mechanism of aluminium corrosion in sulphuric acid solutions

The influence of 1,2-diaminoethane (DAE) on aluminium corrosion in H₂SO₄ solutions (pH 3) was investigated. In pure H₂SO₄, rapid uniform corrosion is followed by inhibition due to the formation of stable Al-sulphate binuclear bidentate metal bound surface complexes via a ligand exchange mechanism with two neighbouring sites. Metastable pitting is also observed. DAE acts as a strong corrosion inhibitor for both uniform and localised corrosion, due to the formation of Al-DAE monodentate hydrogen-bond surface complexes either by direct adsorption of the protonated molecule on Al-OH sites or via a ligand exchange mechanism with the proton of an site.     

Inhibition of mild steel corrosion in acid solution by Pheniramine drug: Experimental and theoretical study

Inhibition of mild steel corrosion in 1 M HCl solution by Pheniramine drug was studied using weight loss, electrochemical impedance spectroscopy, linear polarization resistance, and potentiodynamic polarization measurements. The values of activation energy (E_a) and different thermodynamic parameters such as adsorption equilibrium constant (K_ads), free energy of adsorption , adsorption enthalpy and adsorption entropy were calculated and discussed. The adsorption process of studied drug on mild steel surface obeys the Langmuir adsorption isotherm. Potentiodynamic polarization measurements showed that Pheniramine is mixed-type inhibitor. Further, theoretical calculations were carried out and relations between computed parameters and experimental inhibition efficiency were discussed.     

2,2′-Dithiobis(3-cyano-4,6-dimethylpyridine): A new class of acid corrosion inhibitors for mild steel

The title compound (PyS)₂ has been synthesized and its inhibiting action on the corrosion of mild steel in 1-5 M H₂SO₄ solutions at 35-50 °C has been investigated by polarization resistance (R_p), polarization curves and electrochemical impedance spectroscopy (EIS). (PyS)₂ showed excellent performance and its efficiency did not affect either by increasing the acid concentration or rise of temperature. Polarization curves indicated that (PyS)₂ behaves mainly as anodic inhibitor in 1 M H₂SO₄ solutions and as a mixed-type inhibitor in 3 and 5 M H₂SO₄ solutions at different temperatures. Adsorption of (PyS)₂ on the steel surface followed Temkin’s adsorption isotherm with a very high negative value of the free energy of adsorption . The activation parameters of the corrosion process were calculated. EIS showed that the charge transfer controls the corrosion process in the uninhibited and inhibited solutions.     

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.     

Inhibition of iron corrosion in acid solutions by Cefatrexyl: Behaviour near and at the corrosion potential

The corrosion inhibition of iron in HCl, HClO₄, H₂SO₄ and H₃PO₄ solutions (1M for each) by cefatrexyl has been studied by polarization resistance (R_p) and electrochemical impedance spectroscopy (EIS) at the corrosion potential. The results obtained at 30 °C revealed that cefatrexyl acts as a weak inhibitor in HCl solution while it shows excellent inhibition performance in the remaining acids. Adsorption of cefatrexyl in HCl solution obeys Langmuir’s isotherm with a very low value of the free energy of adsorption (physisorption) while its adsorption in the other acids follows Temkin’s isotherm with very high negative values of (chemisorption). Data obtained from EIS measurements were analyzed to model the corrosion inhibition process through appropriate equivalent circuit models. The calculated values of the apparent activation energy (E_a) and the pre-exponential factor (λ) indicate that cefatrexyl blocks nearly the whole active centers of iron surface in H₃PO₄ solution even at elevated temperatures. The inhibition mechanism of cefatrexyl was discussed.     

Effects of inorganic additions on the performance of manganese-based conversion treatments

The electrochemical behaviour of permanganate-based no-rinse conversion coatings on AA3003-H14 aluminium alloy shows that they have promise as an alternative to toxic chromate-based coatings. A selection of inorganic additions has been made here to a simple 0.1 M KMnO₄ formulation investigated previously. The performance of the different coatings has been evaluated from potential-time and polarisation measurements in 0.5 wt % (0.085 M) NaCl solution for periods up to 3 days. The addition of fluoride ions produced no benefit, whereas Al(NO₃)₃ shows an improvement when added in small amounts. Tests with the individual ions reveal that it is Al³⁺ cations, rather than anions, which produce the greatest benefit.     

Experimental and theoretical investigation of organic compounds as inhibitors for mild steel corrosion in sulfuric acid medium

Three synthesized organic compounds were tested as corrosion inhibitors for mild steel in sulfuric acid medium by potentiostatic polarization, FTIR spectroscopy and SEM techniques. Quantum chemical parameters were also calculated to characterize adsorption mechanism. Acceptable correlations were obtained between inhibition efficiency and the calculated quantum chemical parameters. It was found that the investigated compounds exhibit a good inhibition effect especially at 8-10 ppm range concentration, which makes them commercially important. The adsorption of inhibitors on the surface obeys Langmuir adsorption isotherm. The values of activation energy and the thermodynamic parameters, such as K_ads, , and were calculated.     

Effects of temperature and aggressive anions on corrosion of carbon steel in potable water

Experiments on the corrosion of carbon steel in three kinds of artificial potable waters containing different concentrations of aggressive anions, Cl⁻ and , open to air in the temperature range from 5 to 60 °C were conducted using weight loss and electrochemical methods. The corrosion rate increased in proportion to the concentration of aggressive anions and with increasing temperature. At lower concentrations of aggressive anions and temperatures, the corrosion rate was lower and the corrosion potential was higher, at intermediate concentrations and temperatures, the corrosion rate increased logarithmically with decreasing potential, and at higher concentrations and temperatures, the corrosion rate was higher and the potential was lower. The corrosion behavior in potable water can be determined by the balance between inhibitive action of oxygen (passive film formation) and aggressive action of Cl⁻ and ions.