Electrochemical polymerization and initial corrosion properties of polyaniline-benzoate film on aluminum

Electrochemical synthesis of polyaniline (PANI) on aluminum electrode from aqueous solution of 0.25 mol dm⁻³ aniline and 0.2 mol dm⁻³ sodium benzoate has been investigated under potentiodynamic and galvanostatic conditions. Initial corrosion behavior of aluminum and PANI coated aluminum electrode exposed to 3% NaCl has been investigated using electrochemical potentiodynamic and impedance spectroscopy technique (EIS). It was shown that PANI coating initially provide corrosion protection of aluminum, decreasing the corrosion current density at least 15 times.     

Corrosion control of Cu-Ni alloys in neutral chloride solutions by amino acids

The corrosion inhibition of Cu-Ni alloys was investigated in aqueous chloride solutions using amino acids as environmentally safe materials. The corrosion rate was calculated in absence and presence of the corrosion inhibitor using polarization and impedance techniques. The inhibition efficiency of the different amino acids was also calculated.The experimental results have shown that a simple amino acid like glycine can be used as efficient corrosion inhibitor for the Cu-Ni alloys in neutral chloride solutions. An inhibition efficiency of about 85% could be achieved at very low concentrations of the amino acid (0.1 mM). For low Ni content alloy (Cu-5Ni), 2.0 mM cysteine shows a remarkable high (∼96%) corrosion inhibition efficiency. The experimental impedance data were fitted to theoretical data according to a proposed equivalent circuit model for the electrode/electrolyte interface, and the mechanism of the corrosion inhibition process was suggested. Different adsorption isotherms were tested and the corrosion inhibition process was found to depend on the adsorption of the amino acid molecules and/or the deposition of corrosion products on the alloy surface. The adsorption free energy of cysteine on Cu-5Ni (−37.81 kJ mol⁻¹) reveals a strong physical adsorption of the inhibitor on the alloy surface.     

Carbon steel passivity examined in alkaline solutions: The effect of chloride and nitrite ions

The effect of chloride and nitrite ions on the passivity of steel in alkaline solutions was investigated. Four nitrite dosages were tested, resulting in various nitrite/chloride ratios. The behavior of steel was evaluated on electrodes aged during 1 and 90 days, measuring electrochemical parameters such as the corrosion, pitting and repassivation potentials, the corrosion current density, the weight loss and performing electrochemical impedance spectra. The presence of 0.8 mol l⁻¹ of chloride induced pitting only under polarization and when the chloride/hydroxyl ratio was not less than one. Nitrite ions behave as effective inhibitors of pit propagation for all the concentrations tested (0.2-0.8 mol l⁻¹). A nitrite/chloride ratio of 0.25 induces complete surface repassivation. Nevertheless, at open circuit potential, the high alkalinity guarantees passivation even in the presence of chlorides. In the event that the passive layer is damaged and pitting can be initiated, nitrite ions are effective in inhibiting pit propagation.     

Electrochemical stability of Cu-10Al-5Ni alloy in chloride-sulfate electrolytes

The electrochemical behavior of the Cu-10Al-5Ni alloy in simulated electrolytes like those used in the industrial processes under normal working conditions was investigated. Conventional electrochemical techniques including open circuit potential measurements, polarization techniques, and electrochemical impedance spectroscopy were used. The alloy was found to be more stable against corrosion when the chloride-sulfate solution had a pH of 7-9. A sulfate concentration of ≅0.1 M in the chloride-sulfate electrolyte leads to the passivation of the alloy surface. The activation energy of the corrosion process was found to be 8 kJ mol⁻¹ assigning a diffusion controlled reaction. The impedance measurements and impedance data fitting to equivalent circuit models have shown that the passive film posses a duplex nature.     

The Influence of Ni Content on the Stability of Copper—Nickel Alloys in Alkaline Sulphate Solutions

The electrochemical behaviour of copper–nickel alloys with different Ni content (5–65%) in sulphate solutions of pH 12 was investigated. The effects of temperature, immersion time, and concentration of sulphate ions were also studied. Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS) were used. Potentiodynamic measurements reveal that the increase in nickel content increases the corrosion rate of the alloy in sulphate solution linearly. Nevertheless, an increase in the nickel content along with increase in immersion time improves the stability of the Cu–Ni alloys due to the formation of a stable passive film. An equivalent circuit model for the electrode/electrolyte interface under different conditions was proposed. The experimental impedance data were fitted to theoretical data according to the proposed model. The relevance of the model to the corrosion/passivation phenomena occurring at the electrode/solution interface was discussed.     

Electrosynthesis of poly(neutral red) incorporated with ferrocenesulfonic acid

The electrochemical oxidation of neutral red in 0.5 mol dm⁻³ sulfuric acid and 0.2 mol dm⁻³ ferrocenesulfonic acid solution was carried out using repeated potential cycling between −0.20 and 1.40 V (versus SCE). The polymer film was electrochemically deposited on a platinum anode and had an electrochemical activity in the solution of 0.5 mol dm⁻³ Na₂SO₄ with pH ≤ 7.0. The result from the X-ray photoelectron spectroscopy (XPS) experiment shows that the anions can be doped into the polymer film during the electrochemical polymerization reaction of neutral red. The scanning electron microscopy (SEM) micrograph shows that the surface of the resulting polymer film formed on the platinum foil is covered with a compact surface consisting of micro fibers. The visible spectrum and infrared spectrum (IR) of the polymer are different from those of the corresponding monomer. A possible chemical structure of the resulting polymer was also proposed.     

Monitoring protein binding to phospholipid monolayers using electrochemical impedance spectroscopy

Biotin was incorporated into dioleoyl phosphatidylcholine (DOPC) monolayers as dioleoyl phosphatidylethanolamine (DOPE)-biotin, DOPE-caproyl-biotin and DOPE-polyethylene glycol (PEG)-biotin. Experiments were carried out in electrolyte KCl (0.1 mol dm⁻³) buffered with 0.001 mol dm⁻³ phosphate buffer to pH 6.9. Bovine serum albumin (BSA), avidin, biotinylated anti-haemoglobin (IgG) and haemoglobin were added to the solution. The frequency dependence of the complex impedance of the coated electrode surfaces was estimated between 65,000 and 0.1 Hz at potentials −0.4 V versus Ag/AgCl 3.5 mol dm⁻³ KCl. The capacitance of the monolayers was measured at 75 Hz between potentials −0.4 and −1.1 V. Both non-specific and specific binding of the soluble proteins to DOPC gave rise to the occurrence of low frequency relaxations in the impedance data. The non-specific binding of BSA to DOPC can be suppressed by the incorporation of DOPE-PEG into the DOPC monolayer. The nature of the effect of specific binding of neutravidin to biotin on the impedance data depended on the positioning of the biotin group in relation to the DOPC monolayer surface. Successive binding of proteins to the biotin and then to each other gave rise to an increase in the significance of low frequency relaxations in the impedance data respectively.     

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.     

Heterogeneous hydrogen evolution on corroding Fe-3 at.% Si surface observed by scanning electrochemical microscopy

Corrosion behavior of Fe-3 at.% Si alloy in 0.01 mol dm⁻³ HCl solution was investigated by using scanning electrochemical microscopy (SECM) as well as general electrochemistry. The rate of corrosion coupled with hydrogen evolution was initially 0.44 A m⁻² but decreased significantly with time. Localized hydrogen evolution on the specimen surface was probed by an SECM system in which a force sensor was mounted to determine the probe height from the specimen surface. SECM images revealed that hydrogen evolution took place heterogeneously on the specimen surface depending on crystallographic orientation of substrate single grains in the initial stage and then became relatively homogeneous. Finally, a heterogeneous hydrogen distribution corresponding to the appearance of localized corrosion sites was observed.     

Influence of Co and Cu on the phase composition of Zn-Ni alloy

Influence of Co²⁺ and Cu²⁺ on codeposition of Zn-Ni in acetate-chloride electrolyte have been investigated by the potentiodynamic stripping and XRD methods. In our earlier work it has been determined that the quantity of the η-phase in the alloy increased with decrease in the quantity of Ni when codeposition of Zn-Ni took place in acetate-chloride electrolyte. Meanwhile, both the quantity of Ni and that of the η-phase in the alloys decreased, when Co or Cu were incorporated in the alloy. Data of XRD have shown that the quantity of γ-phase in the alloy increased with increase in the quantities of Co²⁺ or Cu²⁺ in acetate-chloride electrolyte. When concentration of [Co²⁺] (0.15 mol dm⁻³) was approximately 19 times as high as that of [Cu²⁺] (0.008 mol dm⁻³), the influence of Co²⁺ and that of Cu²⁺ on the phase composition of alloys were nearly similar.     

Electrochemical corrosion behavior of a Ti-35Nb alloy for medical prostheses

Since the 1980s, the titanium alloys show attractive properties for biomedical applications where the most important factors are, firstly, biocompatibility, corrosion and mechanical resistances, low modulus of elasticity, very good strength to weight ratio, reasonable formability and osseointegration. The aim of this study was to investigate the effects of two different heat treatments; furnace cooling and water quenching, on the general electrochemical corrosion resistance of Ti-35 wt%Nb alloy samples immersed in a 0.9% NaCl (0.15 mol L⁻¹) solution at 25 °C and neutral pH range. The samples were obtained using a non-consumable tungsten electrode furnace with a water-cooled copper hearth under argon atmosphere. The microstructural pattern was examined by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). In order to evaluate the electrochemical corrosion behavior of such Ti-Nb alloy samples, corrosion tests were performed by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. Analyses of an equivalent circuit have also been used to provide quantitative support for the discussions and understanding of the corrosion behavior. It was found that water quenching provides a microstructural pattern consisting of an alpha-martensite acicular phase which decreases the material electrochemical performance due to the stress-induced martensitic transformation.     

Complexities of corrosion behaviour of copper-nickel alloys under liquid impingement conditions in saline water

Flow-assisted electrochemical corrosion of Cu-Ni disc electrodes, subjected to a submerged impinging jet in saline water, was evaluated and quantified using the anodic current densities (j_a), corrosion potentials (E_corr), interfacial capacitances (C) and polarization resistances (R_p). The Reynolds numbers in the range of applied impinging velocities suggested that the flow between the solution and the electrode is turbulent in the systems investigated.The role of Ni content in the resistance of spontaneously formed barrier oxide film and diethyldithiocarbamate inhibitor film on Cu-Ni alloys (10, 20, 30 and 40 at.% Ni) was examined and evaluated using electrochemical impedance spectroscopy in dependence of the impinging velocity and the immersion time.The results are discussed in terms of the corrosion mechanisms and their relevance to the use of Cu-Ni alloys in desalination plants and in the marine engineering field because fluid hydrodynamics plays an important role in Cu-Ni alloys application. Based on the analysis presented in the paper, it is anticipated that the Cu-10Ni alloy is the best choice for application in the marine environment.     

Electrochemical behavior of Mg and some Mg alloys in aqueous solutions of different pH

The electrochemical behavior of Mg, Mg-Al-Zn and Mg-Al-Zn-Mn alloys were investigated in aqueous acidic, neutral and basic solutions. Conventional electrochemical techniques such as open-circuit potential measurements, polarization methods and electrochemical impedance spectroscopy (EIS) were used. The results have shown that the rate of corrosion in acidic solution is relatively high compared to that in neutral or basic solutions. The presence of Al, Zn and Mn as alloying elements decreases the rate of corrosion of the alloy. The activation energy of the corrosion process occurring at the surface of Mg or Mg alloys in aqueous solutions is less than 40 kJ mol⁻¹. This value indicates a one electron transfer electrode as a rate controlling process. The impedance data were fitted to equivalent circuit models that explain the different electrochemical processes occurring at the electrode/electrolyte interface.     

Structure and electrochemical characteristics of TiV1.1Mn0.9Nix (x = 0.1-0.7) alloys

The structure and electrochemical properties of TiV_1.1Mn_0.9Ni_x (x = 0.1-0.7) solid solution electrode alloys have been investigated. It is found that these alloys mainly consist of a solid solution phase with body centered cubic (bcc) structure and a C14 Laves secondary phase. The solid solution alloys show easy activation behavior, high temperature dischargeability, high discharge capacity and favorable high-rate dischargeability as a negative electrode material in Ni-MH battery. The maximum discharge capacity is 502 mAh g⁻¹ at 303 K when x = 0.4. Electrochemical impedance spectroscopy (EIS) test shows that the charge-transfer resistance at the surface of the alloy electrodes decreases obviously with increasing Ni content.     

Effect of Al content on the corrosion behavior of Mg-Al alloys in aqueous solutions of different pH

The effect of systematic increase of Al content on the electrochemical behavior of the Mg-Al alloys in aqueous solutions of different pH was investigated. Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy, EIS, were used to investigate the electrochemical behavior of the alloys in aqueous solutions. The results have shown that Mg-5Al is easily corroded due to the microgalvanic effect between α-phase and β-phase, its corrosion rate is even higher than that of Mg itself. The increase of Al content increases the corrosion resistance of the alloy due to the formation of the β-phase (Mg₁₇Al₁₂) together with the Mg α-phase. The ranking of the corrosion rate of these alloys was Mg-5Al > Mg > Mg-10Al ≅ Mg-15Al. The corrosion rates of the alloys in acidic solutions are pronouncedly high compared to those measured in neutral or basic solutions. The impedance measurements are in consistence with the polarization techniques and the impedance data were fitted to theoretical data obtained according to an equivalent circuit model describing the electrode/electrolyte interface.     

The stability of an acidic tin methanesulfonate electrolyte in the presence of a hydroquinone antioxidant

The electrodeposition of tin at a (0.28 cm²) copper surface from 0.014 mol dm⁻³ SnSO₄ and 12.5 vol.% methanesulfonic acid (MSA 1.93 mol dm⁻³) at 296 K was studied. Hydroquinone concentrations of 0.005, 0.05 and 0.5 mol dm⁻³ (corresponding to a molar concentration ratio of hydroquinone to stannous ions of 0.36, 3.6 and 36, respectively) were used. Cyclic and linear sweep voltammetry served to characterise the electrochemical behaviour of tin deposition and stripping. The effects of potential sweep rate and electrode rotation speed on the voltammetry were studied. The stability of the electrolyte with storage time was quantified by changes in the limiting current density for tin deposition at a smooth rotating disc electrode and the peak current density at a static disc electrode. The influence of hydroquinone on mass transport controlled tin deposition and suppression of hydrogen evolution was evaluated.     

Electrochemical impedance spectroscopy and corrosion behaviour of Al2O3-Ni nano composite coatings

In this paper, the results on the electrochemical impedance spectroscopy and corrosion properties of electrodeposited nanostructured Al₂O₃-Ni composite coatings are presented. The nanocomposite coatings were obtained by codeposition of alumina nanoparticles (13 nm) with nickel during plating process. The coating thickness was 50 μm on steel support and an average of nano Al₂O₃ particles inside of coatings at 15 vol.% was present. The structure of the coatings was investigated by scanning electron microscopy (SEM). It has been found that the codeposition of Al₂O₃ particles with nickel disturbs the nickel coating's regular surface structure. The electrochemical behavior of the coatings in the corrosive solutions was investigated by polarization potentiodynamic and electrochemical impedance spectroscopy methods. As electrochemical test solutions 0.5 M sodium chloride and 0.5 M potassium sulphate were used in a three electrode open cell. The corrosion potential is shifted to more negative values for nanostructured coatings in 0.5 M sodium chloride. The polarization resistance in 0.5 M sodium chloride decreases in 24 h, but after that increases slowly. In 0.5 M potassium sulphate solution the polarization resistance decreases after 2 h and after 30 h of immersion the polarization resistance is higher than that of the beginning value. The corrosion rate calculated by polarization potentiodynamic curves obtained after 30 min from immersion in solution is smaller for nanostructured coatings in 0.5 M potassium sulphate (4.74 μm/year) and a little bit bigger in 0.5 M sodium chloride (5.03 μm/year).     

Study on the two dealloying modes in the electrooxidation of Au-Sn alloys by in situ Raman spectroscopy

The electrochemical processes in dealloying of Au-Sn alloys in a solution of 2 mol dm⁻³ HCl have been first investigated in detail by means of in situ potential-dependent and time-resolved Raman spectra. Two dealloying modes were found occurring within different potential regions in the electrooxidation of Au-Sn alloys. One is the mode known as classical dealloying, where Sn is selectively dissolved; and the other a so-called quasi-dealloying mode found here, in which Au re-deposits automatically after simultaneous dissolution with Sn. Meanwhile, nanoporous gold, thin layers of gold nanoparticles stacked on the surface, and colloidal gold in the solution can be prepared from the Au-Sn alloys simply by an electrochemical control of potential. Moreover, the quasi-dealloying manner of Au-Sn alloys has also been grafted onto a pure Au electrode with a tin overlayer by electrodeposition to construct the SERS substrate conveniently.     

The kinetics and mechanism of the electroreduction of Bi(III) ions from chlorates (VII) with varied water activity

The influence of water activity on the mechanism and kinetics of Bi(III) ions electroreduction at dropping mercury electrode in chlorates (VII) using voltammetric and impedance methods was examined. The kinetic parameters determined in the examined solutions were correlated with water activity. The values of transfer coefficients, standard rate constants and activation energy point at the slight influence of supporting electrolyte concentration on the kinetics of Bi(III) electroreduction in 1-3 mol dm⁻³ chlorates (VII). In the concentration range of 4-8 mol dm⁻³ the values of transfer coefficients and standard rate constants increase considerably, whereas the values of activation energy decrease what testifies to the increase of reversibility of Bi(III) ions electroreduction. The character of the rate constants changes in the function of potential points at multi-stage process of Bi(III) ions electroreduction as well as a different mechanism of Bi(III) electroreduction in the solutions with low water activity in comparison with the solutions with high water activity.     

Corrosion inhibition of steel using mesoporous silica nanocontainers incorporated in the polypyrrole

Mesoporous silica nanocontainer powders were applied as corrosion inhibitor hosts. These powders were dispersed in the polypyrrole matrix by electropolymerization technique. The protection properties of these composite coatings with and without inhibitor were studied in 2 g dm⁻³ chloride ion solutions at constant pH. Open circuit potential (OCP), inductive coupled plasma (ICP), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and Fourier transform infrared spectroscopy (FTIR) results showed that the substrates were protected due to the release of corrosion inhibitor from mesoporous silica in the chloride media compared to the coatings without corrosion inhibitor. The released corrosion inhibitor reacted with substrate and made a protective phase during corrosion. This phase can heal the corroded area as a self-healing compound.