Cathodic Tafel Slopes Research Articles

On the Corrosion Mechanism of Borided X12CrNiMoV12-3 Steel Immersed in a Neutral Aqueous Solution Containing Chloride and Sulfate Ions

The corrosion behavior of borided X12CrNiMoV12-3 steel immersed during 5 days in a 0.1 M NaCl + 0.04 M Na2SO4 aqueous solution was obtained. The boride layer (FeB/Fe2B) formed on the surface of the material was developed using the powder-pack boriding process at 1223 K during 6 hours of exposure. Some corrosion electrochemical parameters such as the polarization resistance, the current density, the anodic and cathodic Tafel slopes were determined by means of the potentiodynamic polarization technique, in which the corrosion resistance values of the borided stainless steel were compared with those estimated for the non-borided X12CrNiMoV12-3 steel (reference material).The corrosion behavior of the borided X12CrNiMoV12-3 steel was associated with the development of B2S3 and Fe2O3 on the surface of the boride layer as well as for the presence of texture fibers such as {020}//ND and {021}//ND (estimated from crystallographic texture analysis), which drastically reduced the corrosion resistance values of the boride layer exposed to the aqueous solution. Finally, the electrochemical reactions produced during the immersion of the borided X12CrNiMoV12-3 steel in the neutral chloride-sulfate aqueous solution were proposed.

Aluminum Deposition and Dissolution in [EMIm]Cl-Based Ionic Liquids–Kinetics of Charge–Transfer and the Rate–Determining Step

The kinetics of the dissolution and deposition of aluminum from a first generation ionic liquid consisting of AlCl3/1-ethyl-3-methylimidazolium chloride (molar ratio 2:1) was studied. Electrochemical impedance spectroscopy shows that the double layer capacitance and the charge–transfer resistance depend on the state of the electrode surface. The impedance spectra are strongly influenced by mass transport. The rate–determining step of the aluminum deposition, as determined from the cathodic Tafel slope evaluated from current step experiments, was found to be either a chemical step, releasing the complexing agent chloride, while aluminum is in the divalent oxidation state (AlCl3− → AlCl2 + Cl−) or an electron transfer from the divalent to the monovalent aluminum occurring twice for the overall reaction to occur once (Al2+ + e− → Al+). The rate–determining step for aluminum dissolution was found to be the transfer of an electron from elemental aluminum to the monovalent oxidation state (Al0 → Al+ + e−). A linear slope in the low cathodic overpotential region of the Tafel plot suggests a change in the cathodic rate–determining step. The Tafel slope indicates a chemical step, releasing the complexing agent chloride, after the last electron transfer (AlCl− → Al0 + Cl−) to be the rate–determining step for overpotentials below 50 mV. Density functional theory calculations support the proposed reduction and oxidation mechanisms.

Corrosion behavior of coupled active and passive reinforcing steels in simulated concrete pore solution

The present study aimed to investigate the corrosion behavior of coupled active and passive steels in concrete simulated environment. Three different active-to-passive area (A/P) ratios (i.e. A/P = 1/1, 1/3, 1/20) were studied by changing the exposed area of the active steel while keeping the passive steel constant. For each group of A/P ratio, three cells were prepared: individual cell with active steel specimens, individual cell with passive steel specimens, and a coupled cell which connected active and passive steels. All specimens were immersed in a simulated concrete pore solution for 14 days. Afterwards, 3 wt% NaCl was added to the cells. Different electrochemical measurement techniques were used to assess the influence of galvanic coupling and A/P ratio on the corrosion behavior of the steel specimens. Results indicated that coupling changed the corrosion behavior of the active steel. In the case of A/P = 1/1, the corrosion was mostly observed in the form of localized corrosion, whereas in the case of A/P = 1/20, a more general and severe corrosion was observed. In addition, coupling increased the anodic and cathodic Tafel slopes which are closely related to the iron oxidation rate (i.e. corrosion rate).

Theoretical and Experimental Study of the Acid Corrosion Inhibition of Copper by Aspirin (Acetylsalicylic Acid)

The inhibition efficiency of aspirin (acetylsalicylic acid-ASA) against copper corrosion was investigated in 0.5 M HCl solution at room temperature by using electrochemical techniques. Furthermore some quantum chemical calculations were done to explain the inhibition mechanism of ASA. It was found that ASA has a promising inhibitory action against corrosion of copper in the medium investigated. The polarization curves of ASA were obtained from electrochemical measurements. According to potentiodynamic results, ASA inhibits the corrosion process of the copper cathodically and its ability as a corrosion inhibitor is enhanced as its concentration is increased. The Tafel extrapolation method was used to calculate some corrosion parameters, such as corrosion potential (Ecorr), corrosion current (Icorr), cathodic Tafel slope (βc) and anodic Tafel slope (βa). Additionally, Langmuir adsorption isotherm was used to explain the adsorption behavior of ASA on copper surface. The adsorption equilibrium constant (Kads) and the standard free energy of adsorption ($$\Delta G_{{{\text{ads}}}}^{^\circ }$$) were calculated from Langmuir adsorption isotherm. It can be concluded that the adsorption of ASA on the copper surface contains mostly physisorption but also chemisorption thereby it is so called a mixed. The quantum chemical calculations have been performed on ASA for neutral and protonated forms by using density functional theory (DFT) in gas and aqeuous phases to explain the behavior of ASA as a corrosion inhibitor. These calculated quantum chemical parameters were compared to each other and the relationship between calculated parameters and corrosion inhibition mechanism of ASA is analysed.

Corrosion Inhibition Comparison of the Effect of Green Inhibitor on the Corrosion Behavior of 316L and 904L Austenitic Stainless Steels in Chloride Environment

Corrosion behavior of austenitic stainless steels type 904L and 316L in 3.5% NaCl solution was studied using eggshell powder (ESP) as an inhibitor. The experimental testing method was carried out using gravimetric and potentiodynamic polarization techniques. The testing results showed lower corrosion rate values with ESP, indicating the stainless steels corrosion resistance was influenced by the inhibitor and the chemical composition of 904L and 316L respectively. The morphological changes on stainless steel are checked with and without ESP, at its optimal concentration. Stainless steel 904L has higher impedance magnitude compared to stainless steel 316L at all concentrations of inhibitor studied in the sodium chloride solution. It was concluded that ESP is mixed type in nature; this conclusion was achieved by comparison of changes in the cathodic and anodic Tafel slope values.

Influence of Lavandula latifolia and Ricinus communis Oils on the Corrosion Control of Mild Steel in HCl Solution

Influence of the combined admixture of Lavandula latifolia and Ricinus communis oils (LACA) on the corrosion inhibition of mild steel immersed in 0.5 M HCl media was evaluated at an operating temperature of 25 °C by weight loss and potentiodynamic polarization methods. Observation shows inhibition efficiency increased with an increase in concentration. At 336 h of the experiment, the concentration of the 2, 4, 6 and 8 per 200 mL HCl concentrations exhibited minimal but stable weight loss till 144 h. In 2 mL HCl solution, weight loss value of 0.307 g was obtained at 312 h. HCl concentration of 12 mL exhibited optimal performance at 312 h with weight loss and corrosion rate value of 0.088 g and 0.48 mm/y. The corresponding inhibition efficiency is 88%. Results of cathodic and anodic Tafel slope indicate mixed-type inhibition effect. Adsorption isotherm showed that the inhibitor protection mechanism followed both the Frumkin and the Freundlich models more than the Langmuir isotherm model.

Effects of w/b ratio, fly ash, and chloride content on corrosion of reinforcing steel

To predict the corrosion of reinforcing steel, the electrochemical properties of reinforcing steel with different concrete mix proportions and chloride content were studied. The water to binder ratio of concrete was varied (0.45 and 0.60). Coal fly ash was used to replace OPC (0 and 30% by weight of the total binder). The initial chloride was 0, 2, and 4% by weight of concrete. Potentiodynamic polarization testing was conducted by controlling the moisture of specimens. The Tafel slope, corrosion potential, and corrosion rate were analyzed from the testing results. Results show that chloride content significantly affects the electrochemical properties of reinforcing steel. The anodic Tafel slope decreased as chloride content increased. The cathodic Tafel slope increased when the water to binder ratio decreased, or when the fly ash content increased due to a denser concrete pore structure, limiting oxygen diffusion. Results from this study can be used to simulate the corrosion of reinforcing steel and predict the service life of reinforced concrete structures. Also, the electrochemical compatibility between existing and repaired sections can be evaluated to ensure the durability of repaired RC structures.

The Current-Voltage Characteristics and Partial Pressure Dependence of Defect Controlled Electrochemical Reactions on Mixed Conducting Oxides

Electrochemical reactions at solid|gas interfaces of mixed ionic electronic conductors (MIEC), such as oxygen reduction or evolution, differ substantially from usual electrochemical reactions in aqueous solutions. Overpotentials do not directly translate to electrostatic surface potentials but act mainly by changing the concentration of point defects in the MIEC. This has severe consequences for the mechanistic interpretation of current voltage curves of MIEC electrodes. In this contribution it is shown how overpotential dependent defect concentrations affect the current-voltage curves of oxygen reduction and oxygen evolution at MIEC surfaces. Exemplarily, quantitative current-voltage curves are deduced from the known defect chemical data set (Brouwer diagram) of La0.6Sr0.4FeO3 − δ (LSF). Various curve shapes result, from Tafel-like exponential relations to essentially voltage independent limiting currents. Tafel slopes have a very different meaning compared to charge transfer limited reactions at metal electrode interfaces. It is shown how mechanistic information can be obtained from the difference of anodic and cathodic Tafel slopes or by comparing exchange current densities and ac resistances. Moreover, partial pressure dependences of anodic and cathodic currents are deduced, showing that exponents of power laws often do not indicate whether atomic or molecular oxygen species are involved in the rate limiting step.

Predicting the corrosion rate of steel in cathodically protected concrete using potential shift

The commonly accepted Cathodic Protection (CP) criterion i.e. 100 mV decay evolves from experimental investigations and may not always be accurate. Alternatively, corrosion rate monitoring can assess the adequacy of CP. This work examines the possibility of predicting the corrosion rate of steel in concrete using polarization data induced by known applied current density using Butler Volmer equation. For this, the value of cathodic Tafel slope (βc) plays an important role; decreasing βc from 210 to 60 mV, decreases the corrosion rate by 92% at 20 mA/m2 current density.The adequacy of the proposed method is evaluated by applying Impressed Current Cathodic Protection (ICCP) to concrete specimens which have a zinc rich paint (ZRP) as an external anode for a short duration of time. Results showed that to achieve at least 100 mV of depolarization, the applied current density should be at least 7 times the corrosion rate for the ZRP anode. However, this holds true, considering the short duration of the tests. Prediction of the corrosion rate of steel from potential shift forms the basis for the improved CP performance criterion for reinforced concrete structures.

Electrochemical and Theoretical Investigation for the Protection of Aluminum Corrosion in Hydrochloric Acid using Some Azole Derivatives

Three compounds of azole derivatives were investigated as inhibitors for the dissolution of aluminum (Al) in 0.5 M HCl solution using electrochemical techniques, e.g., potentiodynamic polarization, electrochemical impedance spectroscopy electrochemical frequency modulation (EFM). The surface of Al was examined in the absence and presence of the some azole derivatives using scanning electron microscopy (SEM). The potentiodynamic polarization suggests that these compounds act as mixed type inhibitors because they enhance both the anodic and cathodic Tafel slopes. The inhibition efficiency (%IE), increased with increasing the concentration of inhibitors. SEM proved the surface of Al is improved due to the adsorption of the azole compounds on the surface of Al. The adsorption of the azole compounds on the Al surface is obeyed Frumkin isotherm. The sequence of the %IE increases in the following order 1,2,3-benztriazole > methyl imidazole > imidazole. The extent of inhibition depends on the molecular size of the molecule and the electron density of the substituent groups.

The reduction reaction kinetics of vanadium(V) in acidic solutions on a platinum electrode with unusual difference compared to carbon electrodes

With the consideration of understanding the interplays between the electrolyte and electrode for the VO2+/VO2+ redox reactions at various electrodes and developing high-activity electrode materials for an all-vanadium redox flow battery, the reduction reaction kinetics of vanadium(V) ions on a platinum (Pt) electrode in comparison with that on carbon electrodes is investigated by steady-state potentiodynamic polarization and impedance spectroscopy measurements in sulfuric acid solutions with various pH and vanadium concentrations. No abnormal increase is observed neither in the cathodic Tafel slope nor the charge transfer resistance (Rct) at a transition potential (EK) on the Pt electrode. However, an abrupt change in the Tafel slope and Rct of vanadium(V) ions is observed on carbon electrodes. The above results indicate that the reduction reaction kinetics of vanadium(V) ions in acidic solutions on the Pt electrode show some unusual difference with that on carbon electrodes, and this is the first study to report such a new phenomenon. Additionally, possible mechanism pathways for the reduction reaction of vanadium(V) ions in acidic solutions are proposed for the above-mentioned carbon and Pt electrodes in this work.

The Effect of Grain Size on the Corrosion Behavior of Mg-RE Alloy ZE10A

Mg-RE alloy Electron717 (ZE10A, UNS M11600) has a nominal composition of 1.2wt % Zn, 0.25wt% Zr, <0.5%Zr, 0.007wt%Mn, 0.004wt %Fe,0.001wt%Ni and balanced Mg. Zirconium addition acts as a grain refiner, so it helps increase castability, mechanical properties and provide better corrosion resistance.1 ZE10A alloy may have better corrosion resistance than unalloyed Mg. Even though formation of Zn2Zr3 type precipitates has been suggested in this type of alloy, heat treatment in the temperature range of 200 – 300 ºC for different time periods did not show significant increase in the hardness. Therefore, this alloy is considered not age hardenable. Brady et.al showed that ZE10A alloy forms a dual layered passive film with inner layer rich in MgO and outer layer of Mg(OH)2.2 The formation of two layers make it more resistant to corrosion. This presentation will focus on the corrosion behavior of the ZE10A alloy as a function of grain size, and the hydrogen evolution behavior in different electrolytes. The alloy was investigated in three different heat-treated condition such as (1) As received (grain size of 7.90 µm), (2) Solution treated at 525oC for 8 hours (grain size of 26.24 µm) and (3) Solution treated at 525oC for 24 hours (grain size of 41.37 µm). Anodic and cathodic polarizations were carried out in three different electrolytes (pH unadjusted) such as: 1) 0.6M NaCl 2) 0.5M NaNO3 3) 0.1 M Na2SO4 Table 1.0 Summary of anodic and cathodic polarization results of ZE10A alloy in different heat-treated conditions and in three different solutions. Table 1 summarizes the polarization results. The polarization resistance decreased with increase in the grain size in all the electrolytes, in general. The corrosion current density increased with the grain size. Higher corrosion current densities were observed in the Na2SO4 solution than that in the other two electrolytes. The anodic Tafel slopes are found to be higher in the Na2SO4 solution than in NaCl and NaNO3, whereas, cathodic Tafel slopes did not reveal a clear trend of variation either with the grain size or type of electrolyte. The presentation will focus on how the microstructures in terms of grain size, and secondary phase distribution influence the corrosion behavior of the ZE10A alloy based on the experimental results and literature review. [1] N.T. Kirkland et.al JOM, 2011, 63(6)28-40 [2] M.P.Brady et. al Scripta Met. 106(2015) 38-41 Figure 1

Inhibition of corrosion of aluminum in alkaline solution by a novel azo-schiff base: Experiment and theory

The inhibition effect of a Schiff base with several functional groups on the corrosion of aluminum in alkaline solution is studied by experimental techniques and density function theory (DFT) calculations. The Schiff base are characterized by 1HNMR, 13CNMR, FT-IR, and CHN elemental analysis. In addition, different electrochemical and corrosion techniques such as weight loss, tafel polarization, electrochemical impedance spectroscopy (EIS) and optical microscopy images are performed to analyze the inhibiting performances. In the Tafel measurements the cathodic Tafel slopes values incurred small changes with increasing the inhibitor concentration, which revealed that the inhibitor was adsorbed on the aluminum surface. The inhibition efficiencies are calculated from weight loss measurement and electrochemical tests. The adsorption of the inhibitor onto the aluminum surface follows the Langmuir adsorption isotherm with the free adsorption energy of −8.66 kJ mol−1. The calculated adsorption energies and the amount of charge transfer obtained by DFT calculation revealed that corrosion inhibition effectively occurs with chemisorption, where new NAl bonds are formed between of N atoms in azo (–NN–) group and Al surface atoms, which is confirmed from ab initio molecular dynamics (AIMD) simulation.

Effect of Immersion Time and Cooling Mode on the Electrochemical Behavior of Hot-Dip Galvanized Steel in Sulfuric Acid Medium

In this work, we investigated the influence of galvanizing immersion time and cooling modes environments on the electrochemical corrosion behavior of hot-dip galvanized steel, in 1 M sulfuric acid electrolyte at room temperature using potentiodynamic polarization technique. In addition, the evolution of thickness, structure and microstructure of zinc coatings for different immersion times and two cooling modes (air and water) is characterized, respectively, by using of Elcometer scan probe, x-ray diffraction and metallography analysis. The analysis of the behavior of steel and galvanized steel, vis-a-vis corrosion, by means of corrosion characteristic parameters as anodic (βa) and cathodic (βc) Tafel slopes, corrosion potential (Ecorr), corrosion current density (icorr), corrosion rate (CR) and polarization resistance (Rp), reveals that the galvanized steel has anticorrosion properties much better than that of steel. More the immersion time increases, more the zinc coatings thickness increases, and more these properties become better. The comparison between the two cooling modes shows that the coatings of zinc produced by hot-dip galvanization and air-cooled provides a much better protection to steel against corrosion than those cooled by quenching in water which exhibit a brittle corrosive behavior due to the presence of cracks.

Inhibitor concentration on the corrosion behaviour of X70 steel in CO2 environments

PurposeThe purpose of this study is to investigate the corrosion behaviour of X70 steel in the presence and absence of various concentrations of inhibitor N-(2-o-Tolyl azophenyl)-acetamide (NTAA) in a CO2 environment.Design/methodology/approachThe temperature was set at 80°C, and the flow velocity was 1.5 m/s. The inhibitor concentrations were 10, 20, 30, 60 and 80 ppm, and the CO2 partial pressure was 0.8 MPa. Weight loss method, pitting depth measurement, scanning electron microscopy and electrochemical techniques were used to investigate the inhibitory effects of the inhibitor NTAA.FindingsThe results showed that a small peak emerged in the curve of the corrosion rate versus inhibitor concentration plot at 20-30 ppm. Polarisation studies revealed that the anodic Tafel slopes changed greatly in the presence of an inhibitor; NTAA behaved as an anode-type inhibitor. At concentrations of 20-30 ppm, the incomplete coverage of the metal surface by inhibitor molecules resulted in macroscopic galvanic corrosion.Originality/valueCorrosion behaviour of X70 steel in the presence and absence of various concentrations of an anode-type inhibitor was assessed. Cathodic Tafel slopes are almost unchanged, while the anodic Tafel slopes change significantly with the increase in inhibitor concentration. The corrosion rates of 20 and 30 ppm are almost three times of that of 10 ppm, which is because of the macroscopic galvanic corrosion caused by the inadequate coverage of inhibitor on steel surface.

Leaching and electrochemical dissolution of gold in the presence of iron oxide minerals associated with roasted gold ore

This study investigates the electrochemical interactions between gold and roasted gold ore (RGO), with its associated oxide minerals serving as slurry, in an electrolyte saturated with atmospheric oxygen. Conventional cyanidation yielded a decrease of ~40% in the gold leach rate with magnetite slurry, while increases of 25% and 10% were observed for hematite and maghemite, respectively. These gold leach rates were obtained by applying cathodic Tafel slopes only. SEM-EDS, in the case of magnetite slurry, exhibited a high accumulation of iron oxides on the gold surface, which is an indication of slowdown in the gold leach rate. In the case of roasted gold ore slurry, lower amounts of iron oxides were detected with the association of calcium-magnesium coating. XPS results also exhibited a small amount of gold in the slurry of magnetite particles after leaching, i.e., suggesting the adsorption of gold by magnetite, which also justifies the slowdown in the gold leach rate. Magnetic separation tests of cyanidation tailings containing 20% Au resulted in a 4% (mass-pull) magnetic concentrate sample with 72% non-leached Au. Roasted gold ore, magnetic tailings, and synthetic maghemite electrodes exhibited a cathodic peak, suggesting the reduction of ferric to ferrous ions, which could be responsible for the slowdown of leach kinetics, whereas magnetic concentrate did not. Furthermore, when oxygen was bubbled, this peak disappeared in the case of roasted gold ore and synthetic maghemite, though magnetic tailings still exhibited the peak.

The Mechanism of Alternating Current Corrosion of API Grade X65 Pipeline Steel

In the present work, corrosion rates of API grade X65 pipeline steel in sodium chloride solutions with and without alternating currents (AC) at different direct current (DC) potentials were measured using weight loss analysis. The results show that the effect of AC is most pronounced near the open-circuit potential; at more positive potentials, the rates approach those of the ohmic drop/mass transport-limited DC rates. Correspondingly, at negative potentials the rates decrease. Surprisingly, it was found that at all potentials, the AC corrosion rate was equal to the average AC current in the system. The data generated from weight loss experiments were compared with the results from a model for AC corrosion that was developed using a modified Butler-Volmer approach. The model considers the anodic and cathodic Tafel slopes, diffusion limited oxygen transport, interfacial capacitance, and solution resistance. Both experimental and model results showed the importance of the interfacial capacitance on the rate...

Effects of H2s and pH on Tafel Slopes in Electrochemical Corrosion of High Strength Carbon Steel S-135 in Alkaline Brines

Effects of H2S and pH on electrochemical corrosion of high-strength low-alloy carbon steel, Grade S-135, were investigated through Tafel slopes. Linear sweep voltammetry (LSV) was conducted in 5 %wt. NaCl solutions of pH 7.9, 10.7, and 12.4 with four H2S partial pressures (p H2S) ranging from 0 to 69 kPa at 85 oC after 60 hours of exposure. Anodic limiting current was observed without H2S, but disappeared at higher p H2S. Cathodic LSV plots did not show limiting currents, suggesting that H2O was the main reactant for the hydrogen evolution reaction at high pH. Both anodic and cathodic currents increased at 69 kPa p H2S compared to 0 kPa. Electrochemical reaction mechanisms were discussed based on anodic and cathodic Tafel slopes. The Tafel slopes from LSV were generally larger than those obtained from electrochemical frequency modulation. Different Tafel slopes could result in a discrepancy in corrosion rate by a factor of 5.

Fabrication and characterization of three-dimensional silver nanodomes: Application for alkaline water electrolysis

A novel approach to fabricate three-dimensional (3D) silver nanodomes (AgNDs) based on combination of soft lithography and nanosphere lithography was reported. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used for the characterization of the 3D nanostructures. The 3D-AgNDs were evaluated for electrochemical hydrogen production in 6 M KOH solution by some electrochemical techniques. It was found that well-structured AgNDs have higher hydrogen evolution activity than Ag bulk. The hydrogen discharge potential (EH2) at the NDs lowered ∼150 mV with respect to that of the bulk Ag electrode which demonstrated that fabrication of NDs favors the hydrogen evolution kinetics and reduces the energy input for activating the HER. The cathodic Tafel slopes of bulk Ag and AgNDs were found to be 108 and 114 mV dec−1, respectively. The related charge transfer coefficients were very close to 0.5. In the case of AgNDs, resistance was reduced from 660 to 197.1 Ω cm2. This electrode was also characterized with higher current density at a fixed overpotential when compared to bulk Ag. The superior hydrogen evolution performance of AgNDs was assigned to their high roughness and large real surface area. Roughness factor (Rf) of the NDs was 22 times higher than that of bulk Ag.

Effects of H2s and pH on Tafel Slopes in Electrochemical Corrosion of High Strength Carbon Steel S-135 in Alkaline Brines

Effects of H2S concentration and pH on electrochemical corrosion of high-strength low-alloy steel, Grade S-135, in NaCl-based solutions containing H2S were investigated using linear sweep voltammetry (LSV). S-135 is often used as drill pipe in oil and natural gas exploration. LSV was conducted at a scan rate of 5 mV/s in 5 %wt. NaCl solutions of pH 7.9, 10.7, and 12.4 and with four H2S partial pressures (P H2S) ranging from 0 to 69 kPa at 85 oC after >60 hours of corrosion. Limiting current density was observed in the anodic LSV plots at lower P H2S (0 and 0.83 kPa) but disappeared at higher P H2S (8.3 and 69 kPa). The cathodic LSV plots did not show limiting current densities, suggesting that H2O was probably the main reactant for hydrogen evolution reaction at high pH. However, the cathodic current density increased in the presence of H2S. A modified Tafel analysis method was employed to obtain the Tafel slopes when the LSV plots were influenced by limiting current. Electrochemical reaction mechanisms have been discussed based on the anodic and cathodic Tafel slopes. Also, the corrosion rate values have been calculated using the Tafel slopes obtained from LSV and compared to those calculated with the Tafel slopes from electrochemical frequency modulation.