Anodic Reaction Rate Research Articles

Post treatment of silane and cerium salt as chromate replacers on galvanized steel

A complex film on hot-dip galvanized steel sheet (HDG) was prepared by immersing the sheet in 0.1wt.% Ce(NO 3) 3 solution and 5vol.% silane solution in turn. The corrosion protection of the complex film was evaluated by potentiodynamic linear polarization(LPR), electrochemical impendence spectra (EIS) and natural salt spray (NSS) tests and compared with that of single cerium film and silane film. The results showed that, the presence of these films on the zinc coating hindered corrosion reaction by reducing the rate of both anodic and cathodic reaction in the corrosion process, and the corrosion protection of the complex film was much better than that of single cerium film or silane film and closed to that of chromate film, because the polarization resistance R p and electrochemical impendence were increased markedly. Microstructure and chemical composition of these pretreated films were also investigated by scanning electron microscopy (SEM) and AES.

ダイカスト用 Zn-Al 合金の大気腐食特性に及ぼす第三元素添加の効果

The effects of third element addition on the atmospheric corrosion resistance of zinc die-cast alloys were investigated by using the cyclic wet and dry test which simulated a diurnal change in specimen temperature and relative humidity in an actual outdoor environment with a constant dew point of 301 K. The amount of chloride ion deposition on the specimen surface was adjusted to 1.0×10-3 g·m-2 by the formation of a uniform layer of diluted synthetic sea water. The addition of magnesium (Mg) improved the corrosion resistance of zinc alloys, while the addition of nickel (Ni) degraded the corrosion resistance. X-ray photoelectron spectroscopy measurements indicated that corrosion products formed on Mg-added alloys contained Mg compounds such as oxide, hydroxide, and carbonate. Electrochemical polarization curves of as-polished specimens indicated that the addition of Mg has little effect on anodic and cathodic reaction rates. On the contrary, the addition of Ni or Ti promoted cathodic reaction. The polarization curves measured on specimens after 1 cycle of the cyclic corrosion test indicated that the corrosion products formed on Mg-containing alloys leaded to anodic passivation and inhibited cathodic reaction, while those on Ni-containing alloys accelerated cathodic reaction. Scanning electron microscopic observation on specimens after 1 cycle of the cyclic corrosion test showed that Mg-containing alloys had smooth and uniform surfaces with dense corrosion products, while Ni- or Ti-containing alloys had rough surfaces. It is concluded that the formation of thin and dense corrosion product layer is responsible for the high corrosion resistance of Mg-containing alloys.

On the fundamentals of electrochemical corrosion of X65 steel in CO 2-containing formation water in the presence of acetic acid in petroleum production

Electrochemical corrosion behavior of X65 steel in CO 2-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 → Fe 2+ + 2e, and the formation of corrosion scale, FeCO 3, by Fe + HCO 3 - → FeCO 3 + H + + 2e. The cathodic processes contain the reduction of H +, HCO 3 - , H 2O 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 FeCO 3 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.

Size Effect on the Corrosion Behavior of Copper Wires in NaCl Solution

The influence of wire radius (0.04-0.82 mm) on the corrosion behavior of copper wires was investigated in naturally aerated 0.5 mol·L-1 NaCl solution (pH=7.4), by means of polarization and electrochemical impedance spectroscopy method. The results showed that the mass transfer process was significantly accelerated by non-linear diffusion when radius of copper wire was less than the thickness of diffusion layer (0.56 mm), and consequently, the cathodic and anodic reaction rates controlled by diffusion, as well as the corrosion current density, increased rapidly. It showed that the influence was accelerated with the decrease of wire radius. By comparing cathodic oxygen reduction reaction of platinum and stainless steel wires, the same results were obtained. Therefore, the size effect on corrosion behavior of copper wires is a widespread phenomenon.

Corrosion inhibition of copper in chloride media by 1,5-bis(4-dithiocarboxylate-1-dodecyl-5-hydroxy-3-methylpyrazolyl)pentane

The efficiency of 1,5-bis(4-dithiocarboxylate-1-dodecyl-5-hydroxy-3-methyl-pyrazolyl)pentane (BDTCPP) as copper corrosion inhibitor in 3.5% NaCl solutions was studied by electrochemical polarization methods (Tafel extrapolation and polarization resistance method), electrochemical impedance spectroscopy and immersion assays. Results obtained in this study reveal that BDTCPP is a good inhibitor and the potentiodynamic polarization studies clearly show that BDTCPP is a mixed-type inhibitor for copper in chloride solutions. It decreases the anodic reaction rate more strongly than the cathodic reaction rate and it renders the open circuit potential of copper more positive in 3.5% NaCl solutions. The UV analysis of the protective layer of BDTCPP after corrosion experiments shows that the inhibitor prevents copper corrosion by physisorption on the metal surface, followed by chemisorption of a protective Cu(II)-complex. This Cu(II) is generated by oxidation of the Cu(I) ion formed at the beginning of the corrosion process in the aerated solution of NaCl.

Bipolar Electrochemical Mechanism for the Propulsion of Catalytic Nanomotors in Hydrogen Peroxide Solutions

Bimetallic nanorods are propelled in aqueous solutions by the catalytic decomposition of hydrogen peroxide to oxygen and water. Several mechanisms (interfacial tension gradients, bubble recoil, viscous Brownian ratchet, self-electrophoresis) have been proposed for the transduction of chemical to mechanical energy in this system. From Tafel plots of anodic and cathodic hydrogen peroxide reactions at various metal (Au, Pt, Rh, Ni, Ru, and Pd) ultramicroelectrodes, we determine the potential at which the anodic and cathodic reaction rates are equal for each metal. These measurements allow one to predict the direction of motion of all possible bimetallic combinations according to the bipolar electrochemical (or self-electrophoretic) mechanism. These predictions are consistent with the observed direction of motion in all cases studied, providing strong support for the mechanism. We also find that segmented nanorods with one Au end and one poly(pyrrole) end containing catalase, an enzyme that decomposes hydrogen peroxide nonelectrochemically, perform the overall catalytic reaction at a rate similar to that of nanorods containing Au and Pt segments. However, in this case there is no observed axial movement, again supporting the bipolar electrochemical propulsion mechanism for bimetallic nanorods.

Hydrophobic ionic liquids based on the 1-butyl-3-methylimidazolium cation for lithium/seawater batteries

Two hydrophobic ionic liquids (room temperature molten salts) based on 1-butyl-3-methylimidazolium cation (BMI +), BMI +PF 6 − and BMI +Tf 2N −, were used in developing a highly efficient lithium anode system for lithium/seawater batteries. The lithium anode system was composed of lithium metal/ionic liquid/Celgard membrane. Both BMI +PF 6 −and BMI +Tf 2N − maintained high apparent anodic efficiency (up to 100%) under potentiostatic polarization (at +0.5 V versus open-circuit potential (OCP)) in a 3% NaCl solution. Eventually, traces of water contaminated the ionic liquid and a bilayer film (LiH and LiOH) on the lithium surface was formed, decreasing the rate of lithium anodic reaction and hence the discharge current density. BMI +Tf 2N − prevented traces of water from reaching the lithium metal surface longer than BMI +PF 6 − (60 h versus 7 h). However, BMI +PF 6 − was better than BMI +Tf 2N − in keeping a constant current density (∼0.2 mA cm −2) before the traces of water contaminated the lithium surface due to the non-reactivity of BMI +PF 6 − with the lithium metal that kept the bare lithium surface. During the discharge process, BMI +PF 6 − and BMI +Tf 2N − acted as ion transport media of Li +, Cl −, OH − and H 2O, but did not react with them because of the excellent chemical stability, high conductivity, and high hydrophobicity of these two ionic liquids. Both BMI +PF 6 − and BMI +Tf 2N − gels were tentative approaches used to delay the traces of water coming in contact with the lithium surface.

Electrochemical Properties of Steels in a Model Hydrogen Galvanic Couple

We study the effect of preliminary hydrogenation of carbon and low-alloy steels on their electrochemical behavior in a hydrogen galvanic couple “hydrogenated-nonhydrogenated steel.” The hydrogenation conditions being equal, the current of a hydrogen galvanic couple is determined not by its electromotive force but by the degree of polarization of the electrodes, which depends on the ratio between their areas. The polarization relations show that the electrochemical processes in a hydrogen galvanic couple obey the laws of electrochemical kinetics and have an activation nature. The current of a hydrogen galvanic couple is proportional to the concentration of absorbed hydrogen in steels, and, correspondingly, this dependence can serve as a basis of a new method for the nondestructive testing of hydrogen content in steel. As the hydrogen content in steels increases, their electrochemical properties approach the properties of a juvenile surface: the electrolytic potential becomes more negative, the polarization decreases, and the rate of anodic reactions grows sharply.

The effect of the dendritic microstructure on the corrosion resistance of Zn–Al alloys

The effect of microstructure on metallic alloys properties has been pointed out in various studies and particularly the influence of dendrite arm spacing upon the mechanical properties. It is well known that the dendrite fineness can be even of more importance in the prediction of mechanical properties than the grain size. It has also been reported in the literature that the structural morphology influences the corrosion resistance. The aim of this study is to investigate the influences of the secondary dendrite arm spacing and of solute redistribution during solidification on the corrosion resistance of hypoeutectic and hypereutectic Zn–Al alloys. Any metallic alloy possess within individual grains, a dendritic network with varying solute content. The investigation of the mechanism and kinetics of solute redistribution and dendrite arm size, which characterize solidification microstructures of hypo and hypereutectic alloys may also provide a better understanding of cathodic and anodic reaction rates. In order to obtain the casting samples of those alloys a vertical upward solidification apparatus was used. The corrosion resistance is analyzed by both the electrochemical impedance spectroscopy technique and Tafel extrapolation method conducted in a 3% NaCl solution at room temperature. It was found that the tendency of improvement on the corrosion resistance depends on both the cooling rate imposed during solidification, which affects dendrite arm size and the solute redistribution, and on the electrochemical behaviour of solute and solvent.

Deposition Behavior of Ni on Si(100) Surfaces in an Aqueous Alkaline Solution

The spontaneous deposition of Ni on Si(100) surface in aqueous alkaline solution was investigated under various conditions. In a 0.1 M solution containing 0.2-0.5 M the optimum pH for the homogeneous deposition at 60-80°C at each set of operating conditions shifted in the high-pH direction as both concentration and the operating temperature were decreased. The potential at which the deposition terminates and the deposition duration were determined from electrochemical open-circuit potential profiles. The different behaviors, observed at different pH levels, are discussed in terms of these potential measurements. Ultraviolet-visible absorption spectra of various Ni solutions used indicated that the deposition behavior was strongly affected by the composition of the Ni complex and the reactivity of Si surface. The deposition reaction efficiently proceeded when the Ni complex was present in a specific composition. The anodic reaction rate of Si decreased steeply when the solution temperature was lowered. The optimum condition for the homogeneous deposition was greatly affected by the reactivity of the Si surface rather than the composition of the complex, the higher pH favoring the overall reaction. © 2004 The Electrochemical Society. All rights reserved.

Effect of benzotriazole derivatives on the corrosion and dezincification of brass in neutral chloride solution

The effect of novel corrosion inhibitors, benzotriazole derivatives namely N,N-dibenzotriazol-1-ylmethylamine (DBMA), and 2-hydroxy ethyl benzotriazole (HEBTA) on the corrosion and dezincification of a 65/35 brass in 3% NaCl has been investigated by weight-loss, potentiodynamic polarization, electrochemical impedance and solution analysis techniques. Polarization studies clearly indicated that the benzotriazole derivatives behave as anodic inhibitors for brass in chloride solutions. They decrease the anodic reaction rate more strongly than the cathodic reaction rate and render the open circuit potential of brass more positive in NaCl solutions. Solution analysis revealed the decrease in dissolution of both copper and zinc in the presence of these inhibitors.

Influence of benzotriazole derivatives on the dezincification of 65–35 brass in sodium chloride

The effect of new corrosion inhibitors namely N-[1-(benzotriazol-1-yl)ethyl]aniline (BTEA), and N, N-dibenzotriazol-1-ylmethylaminoethane (DBME) on the dezincification of 65–35 brass in sodium chloride solution was investigated using weight-loss measurements and electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy. Results obtained revealed that these compounds were very good inhibitors and behaved better in NaCl solution. Polarization studies showed that the BTEA and DBME behave as a mixed-type of inhibitors for 65–35 brass in sodium chloride solution. They decrease the anodic reaction rate more strongly than the cathodic reaction rate and renders the open circuit potential of brass more positive in NaCl solutions. Solution analysis revealed the decrease in dissolution of both copper and zinc in the presence of these inhibitors.

Inhibition of copper corrosion by bis-(1-benzotriazolymethylene)-(2,5-thiadiazoly)-disulfide in chloride media

The effect of a novel corrosion inhibitor, bis-(1-benzotriazolymethylene)-(2,5-thiadiazoly)-disulfide (BBTD), on the corrosion of copper in 3% NaCl and 0.5 M HCl has been investigated. Results reveal that BBTD is a good inhibitor and behaves better in 3% NaCl than in 0.5 M HCl solution. Potentiodynamic polarisation studies clearly showed that BBTD is mixed-type inhibitor for copper in chloride solutions. It decreases the anodic reaction rate more strongly than the cathodic reaction rate and it renders the open circuit potential of copper more positive in either HCl or NaCl solutions. The FT-IR spectra indicated that BBTD prevented copper from corrosion by adsorption on the copper surface to form a protective complex with the Cu(I) ion.

Effect of heat treatment on electrochemical behaviour of aluminium alloy AA3005

The effect of heat treatment on the electrochemical properties of bare metal samples of aluminium alloy 3005 in an acidified sodium chloride solution was investigated. Annealing at increasing temperatures in the range 150–500°C causes negative potential transients of increasing magnitude and longevity for samples exposed at open circuit. Electrochemical characterisation shows the potential transients to be caused by an increased anodic reaction rate of the annealed material surfaces as compared to the cold rolled, hard temper substrate. It is suggested that this increased anodic activity during short time exposure of the bare metal samples may be attributed to changes in the protective properties of the surface oxide as a result of the high temperature heat treatment. The mechanisms controlling short term electrochemical properties of bare metal samples may not be identical to those controlling the filiform corrosion susceptibility of coated products and a cautious approach is recommended when using electrochemical techniques for predicting corrosion properties.

Studies on Electrochemical Behavior of Copper in Aerated NaBr Solutions with Schiff Base, N , N ′ ­ o-phenylen-bis(3-methoxysalicylidenimine)

The electrochemical behavior of copper in the aerated 0.5 mol dm−3 sodium bromide solutions with or without a Schiff base, -phenylen-bis(3-methoxysalicylidenimine) (V-o-Ph-V) were investigated by means of the steady-state polarization and impedance techniques. V-o-Ph-V acted as a mixed-type inhibitor in NaBr media, and it adsorbed easily on the copper surface at potentials near the corrosion potential. The adsorbed V-o-Ph-V formed a thin protective film which reduced both anodic and cathodic reaction rates significantly. The impedance spectra for copper measured at the corrosion potentials in the presence of V-o-Ph-V displayed two capacitive loops due to different influences of the protective film on the anodic and cathodic reactions occurring at the copper surface. V-o-Ph-V could self-assemble on the copper surface and the self-assembled film also exhibited a good inhibition on copper in halide solutions. The dissolution mechanism of copper and the inhibition mechanism of V-o-Ph-V on the copper in NaBr solution are interpreted. In addition, the inhibiting action of V-o-Ph-V is compared with that of the other two Schiff bases, -phenylen-bis (3-methoxysalicylidenimine) (V-p-Ph-V) and N-[(2-hydroxy-3-methoxyphenyl)methylene]-histidine (V-His) in order to investigate the effect of Schiff bases’ geometric structures on their inhibition ability. © 2001 The Electrochemical Society. All rights reserved.

Pitting corrosion of carbon steel caused by iron bacteria

Corrosion mechanism of 1020 AISI carbon steel was studied in iron bacteria contaminated water. A mixed culture of iron oxidizing bacteria, originally isolated from rust deposits of a clogged carbon steel heat exchanger was used. Weight loss and electrochemical measurements were carried out in 1 g l −1 NaCl solution with or without the addition of iron bacteria culture. The experimental results show that addition of the iron bacteria culture to 1 g l −1 NaCl solution induces a drastic ennoblement of corrosion potential ( E corr) from −0.75 to −0.25 V (SCE) and surface passivation. Through further exposure, E corr slowly shifted back and the steel underwent a severe pitting attack, an effect which was not observed with 1 g l −1 NaCl solution alone or when augmented with a nutrient medium. Electrochemical measurements show that the experimentally observed strong acceleration in pitting corrosion process occurred due to an increase in both cathodic and anodic reaction rates, induced by the iron bacteria.

Influence of gallic acid on the phase transformation in iron oxide layers below organic coatings studied with Moessbauer spectroscopy

The effect of gallic acid on the corrosion reactions underneath paint films on steel during immersion experiments in the presence and absence of oxygen is investigated using Moessbauer spectroscopy. The mass evolution as a function of immersion time is measured for different solid phases such as iron, lepidocrocite, magnetite and ferrous hydroxide. Results show that in the presence of oxygen, gallic acid enhances the initial dissolution of iron due to complexation with ferrous ion. The ferrous complex is subsequently oxidized into an insoluble ferric complex leading to a reduction in the anodic reaction rate. No magnetite is formed under these conditions. In the absence of oxygen, magnetite is formed by reduction of lepidocrocite on precorroded steel coated with films not containing gallic acid. When gallic acid is present in the paint film the reductive transformation of lepidocrocite to magnetite is inhibited.

ＳＯ４｀２−´イオンを含んだ溶液中でのアルミニウム合金の孔食発生に関する電気化学的検討

To investigate the effect of SO42- ion on pitting corrosion behavior of aluminum and aluminum alloy brazing sheets immersion corrosion test and electrochemical measurements were carried out in the solution of lower chloride concentration containing SO42- ion. As the SO42- ion reduced the anodic and cathodic reaction rate, the pitting corrosion resistance of aluminum increased. The pitting corrosion occurred even in solution containing SO42- when the cathodic reaction was high enough. In that case the pitting corrosion rate was much higher than that in the SO42- ion free solution. Higher pitting corrosion rate induced by SO42- ion was due to the lower pitting corrosion density which was closely related with the thicker oxide film formed on aluminum surface. The probability of pitting corrosion was estimated with the relation between Ecorr and Erep value in anodic polarization measurement in the solution.

Effect of Ionic Conductivity of Zirconia Electrolytes on the Polarization Behavior of Ceria‐Based Anodes in Solid Oxide Fuel Cells

The polarization behaviors of porous samaria‐doped ceria anodes coupled with zirconia electrolytes with various ionic conductivities (σion) were investigated. The exchange current density, j0, on such mixed‐conducting SDC anodes was not influenced by the σion at 900 and 1000°C, whereas j0 increased proportionally to σion at a lower temperature of 800°C. However, the dispersion of nanometer‐sized ruthenium catalysts on SDC particles resulted in an increase of j0 with increase in σion in the entire temperature range between 800 and 1000°C. The observations are well explained kinetically i.e., the anode performance is controlled by the rate of supply to the anode layer via the electrolyte, as the anodic reaction rate becomes sufficiently high due to highly dispersed Ru electrocatalysts. Consequently, it is clear that the use of high‐performance electrodes in combination with the solid electrolyte having high σion is a prerequisite to achieving high performance of solid oxide fuel cells.

Electrochemical aspects of the immersion treatment of aluminium

The processes occurring during zinc immersion plating of aluminium have been studied in alkaline medium. The mechanism of immersion zinc deposition on aluminium has been elucidated by studying the kinetics of the partial electrode reactions involved in this complex process. The diffusion of zincate ions has been shown to play a decisive role on the cathodic reaction kinetics as well as on the global (cathodic and anodic) reaction rate.