“…The electrochemical kinetic parameters such as the corrosion free potential ( E corr ), corrosion current density ( i corr ), the polarization resistance ( R p ) and the cathodic and anodic Tafel slopes ( ß c and ß a , respectively) which are obtained by the Tafel extrapolation method are listed in Table 3. The corrosion rates are calculated using Equation 10 assuming that the whole surface of the C-steel is attacked by the aggressive media, and no localized corrosion is detected 62,63 .Figure 5Potentiodynamic polarization curves for C-steel at a scan rate of 0.3 mV s −1 in 0.5 M HCl in the presence of 0, 20, 30, 35, 40 μmol L −1 of AEO7 corrosion inhibitor at ( A ) 20, ( B ) 30, ( C ) 40 and ( D ) 50 °C.…”
The impact of AEO7 surfactant on the corrosion inhibition of carbon steel (C-steel) in 0.5 M HCl solution at temperatures between 20 °C and 50 °C was elucidated using weight loss and different electrochemical techniques. The kinetics and thermodynamic parameters of the corrosion and inhibition processes were reported. The corrosion inhibition efficiency (IE%) improved as the concentration of AEO7 increased. In addition, a synergistic effect was observed when a concentration of 1 × 10−3 mol L−1 or higher of potassium iodide (KI) was added to 40 µmol L−1 of the AEO7 inhibitor where the corrosion IE% increased from 87.4% to 99.2%. Also, it was found that the adsorption of AEO7 surfactant on C-steel surface followed the Freundlich isotherm. Furthermore, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements indicated that AEO7 was physically adsorbed on the steel surface. The surface topography was examined using an optical profilometer, an atomic force microscope (AFM), and a scanning electron-microscope (SEM) coupled with an energy dispersion X-ray (EDX) unit. Quantum chemical calculations based on the density functional theory were performed to understand the relationship between the corrosion IE% and the molecular structure of the AEO7 molecule.
“…The electrochemical kinetic parameters such as the corrosion free potential ( E corr ), corrosion current density ( i corr ), the polarization resistance ( R p ) and the cathodic and anodic Tafel slopes ( ß c and ß a , respectively) which are obtained by the Tafel extrapolation method are listed in Table 3. The corrosion rates are calculated using Equation 10 assuming that the whole surface of the C-steel is attacked by the aggressive media, and no localized corrosion is detected 62,63 .Figure 5Potentiodynamic polarization curves for C-steel at a scan rate of 0.3 mV s −1 in 0.5 M HCl in the presence of 0, 20, 30, 35, 40 μmol L −1 of AEO7 corrosion inhibitor at ( A ) 20, ( B ) 30, ( C ) 40 and ( D ) 50 °C.…”
The impact of AEO7 surfactant on the corrosion inhibition of carbon steel (C-steel) in 0.5 M HCl solution at temperatures between 20 °C and 50 °C was elucidated using weight loss and different electrochemical techniques. The kinetics and thermodynamic parameters of the corrosion and inhibition processes were reported. The corrosion inhibition efficiency (IE%) improved as the concentration of AEO7 increased. In addition, a synergistic effect was observed when a concentration of 1 × 10−3 mol L−1 or higher of potassium iodide (KI) was added to 40 µmol L−1 of the AEO7 inhibitor where the corrosion IE% increased from 87.4% to 99.2%. Also, it was found that the adsorption of AEO7 surfactant on C-steel surface followed the Freundlich isotherm. Furthermore, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements indicated that AEO7 was physically adsorbed on the steel surface. The surface topography was examined using an optical profilometer, an atomic force microscope (AFM), and a scanning electron-microscope (SEM) coupled with an energy dispersion X-ray (EDX) unit. Quantum chemical calculations based on the density functional theory were performed to understand the relationship between the corrosion IE% and the molecular structure of the AEO7 molecule.
“…5,6 The -dependent crevice corrosion behavior of a metal can be predicted from its potentiodynamic polarization curve. Figure 1 is a schematic of a metal with a crevice and the corresponding polarization curve.…”
The study of localized corrosion is hindered by the inability to characterize electrolyte compositions inside crevices and pits during the corrosion process. This paper describes the development of a microelectrode system for in situ monitoring of the pH in artificial crevices and small recesses. This system permits determination of the pH gradient inside a crevice, even in the presence of a pronounced potential drop. The pH sensor, consisting of a palladium hydride electrode, can be positioned at any desired depth into the crevice while observing the position of the passive to active transition. With increasing time of crevice corrosion, one finds a pronounced pH change in the crevice electrolyte. This work lends further insight toward understanding of crevice corrosion and other localized corrosion phenomena. Crevice corrosion is a form of localized corrosion in which metal within a small space between the metal and another material corrodes at a faster rate than the outside surface of the metal. This particular type of corrosion is considered particularly insidious because it attacks alloys that generally exhibit excellent corrosion resistance. Another characteristic of crevice corrosion is that it takes place in areas that are not immediately visible, which can lead to unexpected catastrophic failure of the metal in service. Mitigation of crevice corrosion requires an in-depth understanding of the crevice corrosion process.Knowledge of crevice corrosion is limited by the inability to completely characterize the crevice environment. Various techniques have been used in an attempt to quantify the crevice environment, including the extraction of crevice solution with a syringe, 1 the placement of electrode in the path of an advancing crack, placing electrodes at fixed distances along the crevice wall, 2 capillary electrophoresis, 3 freezing and extraction of localized corrosion electrolyte, 4 and the incorporation of microelectrodes in crevice formers. All these techniques are unable to obtain information at an arbitrary position within the crevice while at the same time observing the position of the passive to active transition on the crevice wall.The IR potential drop mechanism of crevice corrosion begins with the increase in potential, , within the electrolyte, as the anodic and cathodic reactions separate from one another. 5,6 The -dependent crevice corrosion behavior of a metal can be predicted from its potentiodynamic polarization curve. Figure 1 is a schematic of a metal with a crevice and the corresponding polarization curve.The metal surface at x ϭ 0 is in the passive ͑oxide-protected͒ region of the polarization curve, but the separation of anodic and cathodic reactions produces a potential drop, ⌬. This potential drop equals the decrease of the electrode potential, E(x), from its value at the (x ϭ 0) outer surface. Where E(x) on the crevice wall is more negative than the passivation potential, E pass , high rates of dissolution ͑i.e., crevice corrosion͒ occur. In this x Ͼ x pass region of the crevice ...
“…The IR potential drop mechanism of crevice corrosion begins with the increase in potential, φ, within the electrolyte as the anodic and cathodic reactions separate from one another. , The φ-dependent crevice corrosion behavior of a metal can be predicted from its potentiodynamic polarization curve. Figure is a schematic of a metal with a crevice and the corresponding polarization curve…”
Electrochemical microprobes for monitoring of the electrochemical conditions inside recesses are needed to
better understand how localized corrosion and other charge-transfer processes occur in confined spaces. The
electrode potential distribution can be routinely measured in cavities of greater than 100 μm opening dimension,
but the ability to measure the concentrations of chemical species and their change with time in the presence
of potential gradients is only recently becoming possible. Microprobes for potential, pH, and chloride ion
will be described, and results with these sensors will be presented and discussed for creviced iron samples in
aqueous electrolytes. Results reveal that these species change in concentration and distribution with time,
with the greatest ionic concentrations corresponding to locations of highest metal dissolution rate on the
crevice wall. These new physical chemistry insights provide a better understanding of the passive-to-active
behavior in crevices.
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