The corrosion of Incoloy® alloy 800 TM (Ni32.5/Cr21/Fe) in 1.0 M HCl pickling solutions after varied exposure periods, namely, 0.5 h, 2.0 h, 4.0 h, and 24 h were reported. The work was also extended to include the corrosion of the alloy at 20 ºC, 30 ºC, 40 ºC, 50 ºC, and 60 ºC after 0.5 h immersion in the acid solution. The electrochemical impedance spectroscopy (EIS) measurements showed that the corrosion of Incoloy decreases when the exposure period increases and the highest surface and polarization resistances were recorded for the electrode after 24 h immersion. On the other hand, the increase of the temperature of the solution was found to highly increase the corrosion as a result of decreasing the resistance of the alloy under the increased corrosivity of the acid solution. The cyclic potentiodynamic polarization (CPP) measurements confirmed the EIS ones that the increase of immersion time decreases corrosion, while the increase of temperature pronouncedly increases it for the Incoloy in HCl solutions. This is because elongating the time of immersion leads to decreasing the values of j Corr and R Corr but rising the temperature greatly increases them. CPP curves also indicated
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The electrochemical corrosion behavior and prediction of corrosion rate for low alloy steel after tempering treatment in acid 3.5wt.% NaCl solution is investigated. First, the effects of tempering temperature on microstructures are analyzed by optical microscope (OM) and scanning electron microscopy(SEM). Then, the corrosion rate of alloy steel is calculated by accelerated corrosion tests, it indicates superior corrosion resistance. The polarization curve and electrochemical impedance spectroscopy (EIS) are applied to research the corrosion process. The proper time constants are chosen for equivalent circuit to fit experimental results. Finally, the results of EIS are in agreement with accelerated corrosion and potentiodynamic polarization measurements by relating to known physical parameters. Finally, the prediction model of corrosion rate is established by using grey system theory, simulations result shows that the obtained mathematical model is feasible, which can be well used to forecast corrosion rate for the low alloy steel .
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Self-healing coatings are a robust method of corrosion protection that can autonomically repair damage and prolong the useful life of the coating. Evaluation of the performance of self-healing coatings can be performed either globally or locally. The main disadvantages of the techniques used in evaluating self-healing performance are as follows: complexity in obtaining a stable potential due to the non-electrochemical nature of the coating as in OCP, limitations arising from the concentration polarization and IR drops as in PP and difficulty in the proper construction of the equivalent circuits as in the EIS. The electrochemical techniques PP and EIS provide quantitative results about the self- healing process where the protection efficiency and the rate of corrosion and therefore the rate of self- healing can be calculated using these techniques. These methods provide global information about the self-healing process and do not provide details of the local reactions occurring at the damage site. On the other hand, addressing the processes occurring locally at the solid/liquid interfaces may provide a key for investigating the mechanisms of the respective electrochemical reactions as well as the active species involved in the latter. For instance, SVET can measure the local distribution of fluxes but cannot differentiate the nature of the species that are responsible for generating the electric field. SIET can investigate the local activity of different ionic species however, it detects only a single specific ion in the medium. Therefore, a combination of SVET and SIET provides a powerful way of investigating both the distribution and type of the active species involved in the electrochemical process. Although, LEIS can probe valuable information about the changes of the impedance in a small area, it does not give information about the topology of the surface. SECM is capable of providing valuable information about the topology of the surface, it is highly specific and able to provide measurements of the smaller and faster phenomena. Moreover, SECM can give information about the kinetics and mechanisms of the electrochemical processes and therefore considered one of the best techniques for self-healing coating evaluation.
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Three electrochemical techniques, namely potentiodynamic polarization and linear polarization resistance (LPR), and AC-electrochemical impedance spectroscopy (EIS), were used to study the corrosion behavior of mild steel in absence and presence of inhibitor. All experiments were performed in conventional three electrode cell, using electrodes connected to Potentiostat/Galvanostat G300- 45050 (Gamry Instruments Inc., USA) Echem Analyst 5.0 software package was used for data fitting. Cell assembly consists of mild steel as working electrode with an exposed area of 1 cm 2 , platinum electrode as an auxiliary electrode, and standard calomel electrode (SCE) as reference electrode. All potentials were measured versus a standard calomel electrode (SCE) i.e. reference electrode. Tafel curves were obtained by changing the electrode potential automatically from −0.25 V to +0.25 V versus open corrosion potential at a scan rate of 1.0 mVs -1 . Linear Polarization Resistance (LPR) experiments were done from −0.02 V to +0.02 V versus open corrosion potential at the scan rate of 0.125mVs −1 . EIS measurements were performed under potentiostatic conditions in a frequency range from
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Nanocomposite coatings exhibit superior properties including corrosion and wear resistances compared to the plain non-composite ones. In this work, the deposition of polyvinyl chloride (PVC) and polystyrene (PS) nanofiber coatings on brass surface was carried out. The work was also extended to study the effects of PVC and PS on the corrosion passivation of brass in aerated 3.5 wt.% sodium chloride (NaCl) solutions. The PVC and PS coatings were prepared and deposited on brass surface using electrospinning technique. The nanofibers coating layers were characterized using optical (OM) and scanning electron (SEM) microscopes. The OM and SEM micrographs depicted that the PVC and PS coatings consist of dense and compact entangled nanofibers that completely cover up the brass surface. The corrosion measurements were performed by cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS) techniques on the uncoated and PVC and PS coated brass surfaces in NaCl solutions. Both CPP and EIS data confirmed that PVC and PS coatings protect the brass surface from being corroded through minimizing its corrosion current and corrosion rate and increasing its polarization resistance.
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The electrochemical behavior of lead in various aqueous media has attracted considerable attention from many investigators due to the instructive role of lead application in different areas, such as lead acid batteries, industrial hydrometallurgical processes, lead-silver alloys, etc. [1-7]. The electrochemical behavior of lead in acidic H 2 SO 4 solution , neutral Na 2 SO 4 solution, Na 2 HPO 4
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Non-Faradaic impedance biosensors perform impedance measurement in the absence of any redox probe. Bacteria detection is based on the impedance change upon the attachment of bacterial cells on an interdigitated microelectrode in the absence of any redox probe in the sample solution. An antigen-antibody complex is formed by the specific immunoreaction between Ab-Mb and Ag-Mb, where the latter functions as the complementary target of the former. The interfacial electron exchange at the interface of the solution and bioelectrode is interrupted by an immunocomplex-induced kinetic barrier. There is an increase in electron exchange resistance, together with a decrease in capacitance, with gradually impeded Faradaic reaction of the redox couple. The control group uses an Ag-Mb-free sample solution, with an R et value recorded as the control sample response. After aliquots of target
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Polypyrrole (PPy) was successfully electropolymerized potentiodynamically on prepassivated Fe electrode in an aqueous solution containing monomer and oxalic acid. Electropolymerization of PPy was performed between 0.3 V and 0.8 V vs SCE with a scan rate of 20 mV/s. Electrochemical properties of PPy coated Fe electrode were carried out using cyclic voltammetry, galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The maximum specific capacitance of PPy coated Fe electrode is 2280 F/g. This indicates the feasibility of the PPy coated Fe electrode for use in electrochemical capacitor. However, the PPy coated Fe system behaved like PAni and not as Ppy, exhibited high capacitance.
Inhibitors retard or prevent the corrosion of carbon steel by influencing the anodic or cathodic process of electrochemical corrosion reactions [10, 11]. Based on the inhibiting mechanism, inhibitors can be divided into three types: anodic-type inhibitors, cathodic-type inhibitors and mixed-type inhibitors. Anodic-type inhibitors such as nitrite, chromate and molybdate can effectively protect passive films of steel, but they may accelerate corrosion when pitting corrosion occurs [12, 13]. Cathodic-type inhibitors include organic compounds such as amines, amides, nitrogen-containing heterocycles and quinoline derivatives, which can absorb on the surface of steel and suppress the cathodic process [14-16]. Though they are eco-friendly, their inhibition performance is not as effective as that of anodic-type inhibitors [17, 18]. Efforts have been made to develop mixed-type inhibitors by synthesizing new chemicals because they contain the advantages of anodic-type and cathodic-type inhibitors. Organic compounds such as 4-(2’-amino-5’-methylphenylazo) antipyrine, 3 fatty acid triazoles, triazole and mercapto-triazole compounds have been proven to be as effective mixed-type inhibitors, that simultaneously act on the anodic and cathodic partial reaction of the corrosion process [19-25].
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Fig. 5 presents polarization curves for copper in simulated cooling water, in the absence and presence of Na-CMC at various concentrations. It is observed from the Tafel polarization curves (Fig.5) that both cathodic and anodic curves could show a lower current density in the presence of Na- CMC than those in the absence of Na-CMC. The anodic dissolution of copper and the cathodic reduction of oxygen are significantly inhibited. This suggests that Na-CMC is a mixed type (cathodic/anodic) of inhibitor . The corrosion kinetic parameters namely the corrosion potential (E corr ), corrosion current density (I corr ), anodic Tafel slope (β a ) and cathodic Tafel slope (β c ) are
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Fig. 7 shows the EIS spectra of X70 steel when it was corroded in contaminated silty soil at different pH values for 1 d and 14 d. From the plots, the impedance spectra are similar at various corrosion times and pH values, but the sizes are obviously different. In the non-contaminated silty soil, the impedance spectrum radius was the largest, and in the pH value of 1.50 was the smallest. In general, the impedance arc radius increased with an increase in pH in the two measured corrosive time. It can be seen that the sulfuric acid contaminated silty soil greatly influenced the corrosion processes of the X70 steel.
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So far, most of studies were carried out on composite electrodes [8-10] and thin-film electrodes [11-12], a single particle of micrometer size electrodes were also investigated with the aim of clarifying its electronic and ionic transport properties . Results deduced with composite electrodes are influenced by not only the electrochemical properties of the active materials but also the fabrication (i.e. organic binder, conductive additives, and porosity.) It is important to know the kinetic properties of lithium transport in the oxide host to determine the cycling performance, so, the stability of oxide during the charge/discharge process is desirable to be studied to enhance the performance of lithium ion batteries.
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The corrosion behavior of copper in 0.06 mol/L NaCl solution has been investigated in the previous study  which was focused on the effect of sampling frequency on the energy distribution plot and the PSD spectra was discussed. The aim of the present work is to compare the results of different electrochemical methods on monitoring the copper corrosion process, especially evaluate the effect of trend removal methods on the analysis of electrochemical noise data.
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The examination of the electrochemical parameters given in Table 2 reveals that the corrosion current densities i corr decreases considerably with rise of MPEO concentration. Correspondingly, the inhibition efficiency Tafel % increases to reach its maximum value of 85 % at 0.7 g L -1 of MPEO. This behavior suggests that the MPEO adsorption protective film formed onto the mild steel surface tends to be more and more complete and stable with increasing of MPEO concentration. The presence of MPEO causes a slight shift of corrosion potential when compared to that in the absence of inhibitor. In our study, E corr of mild steel shifts anodically in the range of 7-15 mV compared to the uninhibited solution. From reports in the literature, it has been revealed that if the displacement of E corr is more than 85 mV the inhibitor can be considered as a cathodic or anodic type inhibitor whereas when the displacement of
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The most common approach for the development of this technique is to measure the impedance of an electrochemical system by applying a single fre- quency alternating voltage to the interface. And thus, the system responds with a phase shift and amplitude between the applied voltage and the resulting current. This result is visualized in its real and imaginary components . There is a wide variety of commercial equipment to measure impedance as a function of frequency, in intervals of approximately 1 mHz to 80 MHz .
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signi ﬁ cantly by mixing the OEG SAM with small concentrations of 11-mercaptoundecanol (MUD). The monolayer properties and composition were characterized by means of impedance spectroscopy, water contact angle, ellipsometry and X-ray photoelectron spectroscopy. An equivalent circuit model is proposed to interpret the EIS data and to determine the conductivity of the monolayer. We ﬁ nd that for increasing MUD concentrations up to about 5% the resistivity of the SAM steadily increases, which together with a considerable decrease of the phase of the impedance, demonstrates signi ﬁ cantly improved dielectric properties of the monolayer. Such monolayers will ﬁ nd widespread use in applications which depend critically on good dielectric properties such as capacitive biosensor.
Anti-corrosive behavior of the synthesized poly(ACU-co-NTA) was characterized by electrochemical tecniqiues such as potentiodynamic polarization and electrochemical impedence. The potentiodynamic polarization curves of the different molar ratio of poly(ACU-NTA) coated and uncoated metal in 0.05M H 2 SO 4 solution. The Tafel plots of all the studied mole ratios of poly(ACU-co-NTA) have good corrosion
The EIS analysis is a powerful and informative technique which determines the rate that the electrode material can be charge/discharge , therefore an important factor in determining the power density and to evaluate the properties of conductivity and charge transport. In order to gain insight on the intrinsic electrochemical properties of the composite electrode, EIS measurement was carried within the probed frequency range of 100,000 to 0.1 Hz.
under the circumstances of Au–YSZ electrode is showed by electrochemical impedance measurements, which demonstrates that due to delocalization of YSZ's ionic conductivity to electrode response in the whole electrode volume, the electrochemical features of the oxygen electrode response can be optimized for the composite electrode of Au–YSZ only. Thus, it can be concluded that compared to pure gold electrode, in a YSZ-based sensor porous Au–YSZ composite electrodes display a beneficial effect.
curves indicated that the coating enhanced the degradation resistance of the alloy significantly. The bare metal showed a corrosion current density of 60 µA/cm 2 , whereas the coated alloy exhibited a current density of only 6 µA/cm 2 . Similar to the EIS results, when a small content of ethanol was added to the coating solution, the degradation resistance of the resulted coating increased. The 1E and 3E coatings showed a corrosion current density of 4µA/cm 2 and 2.5µA/cm 2 , respectively. But, further addition of ethanol decreased the degradation resistance i.e., the corrosion current density of the 5E and 7E coatings was 4µA/cm 2 and 18µA/cm 2 , respectively. A comparison of the corrosion current density of the coatings produced in different coating solutions suggests that the 3E coating performed better than the aqueous coating and also the 1E, 5E and 7E coatings.
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