Anodic Polarization Behavior Research Articles

Electrochemical Surface Nanostructuring of Ti47Cu38Fe2.5Zr7.5Sn2Si1Ag2 Metallic Glass for Improved Pitting Corrosion Resistance

Ti‐based bulk metallic glasses are envisioned for human implant applications. Yet, while their elevated Cu content is essential for a high glass‐forming ability, it poses biocompatibility issues, necessitating a reduction in near‐surface regions. To address this, surface treatments that simultaneously generate protective and bioactive states, based on nanostructured Ti and Zr‐oxide layers are proposed. An electrochemical pseudo‐dealloying process using the bulk glass‐forming Ti47Cu38Fe2.5Zr7.5Sn2Si1Ag2 alloy is defined. Melt‐spun ribbons are immersed in hot concentrated nitric acid solution, monitoring the anodic polarization behavior. From the current density transient measurements, together with surface studies (field‐emission scanning electron microscopy, transmission electron microscopy, and Auger electron spectroscopy), the surface reactions are described. This nanostructuring process is divided into three stages: passivation, Cu dissolution, and slow oxide growth, leading to homogenous nanoporous and ligament structures. By tuning the applied potential, the pore and ligament sizes, and thickness values are adjusted. According to X‐ray photoelectron spectroscopy, these nanoporous structures are Ti and Zr‐oxides rich in hydrous and nonhydrous states. In a simulated physiological solution, for those treated glassy alloy samples, complete suppression of chloride‐induced pitting corrosion in the anodic regime of water stability is achieved. This high corrosion resistance is similar to that of clinically used cp‐Ti.

Effect of magnesium on discharge behavior of Al-Sn-Ca-Mg anodes for Al-air batteries

In alkaline electrolytes, Mg elements affect the electrochemical properties and corrosion behaviors of Al-Sn-Ca alloys have been conducted. The results demonstrate that Mg improves the polarization behavior and further increases the anodic activity of Ca-containing Al anodes. Solid solubility Mg in the matrix is oxidized to Mg2+ during discharge. These ions boost the number of anion vacancies in the Ca-containing product layer, which encourages the diffusion of ions on the anodic surface, improves anodic polarization behavior, and allows it to operate at high current densities. Meanwhile, the "dissolution-redeposition" process of Sn is accelerated by the defects created by Mg2+, raising the overpotential of Al anodes for hydrogen evolution. As a result, Mg plays a significant role in Ca-containing Al alloys as anodes.

Ionic conductive cellulose-based hydrogels for Al-air batteries: Influence of the charged-functional groups on the electrochemical properties

Gel electrolytes for aluminum-air (Al-air) primary batteries were prepared based on hydroxyethyl cellulose (HEC) and acrylate monomers bearing differently charged functional groups (i.e., -COOCH2CH2N+(CH3)3Cl−, -COO- and -COOCH2CF3). The acrylate monomers were grafted from HEC backbone and crosslinked using methylenebisacrylamide (MBA) to obtain hydrogels with tuned mechanical (15–75 kPa), morphological (pore size 35–125 μm) properties and varied swelling degrees at alkaline electrolyte (900–2500%). Electrochemical measurements were performed on Al-air cells assembled from Al anode, gel electrolytes (in 1 M NaOH) and carbon-based air-cathodes containing silver fine particles (Ag-FPs). Hydrogels with quaternary ammonium salt (HEC-AEtMACl) showed very long discharge time (6.5 h) compared to 1.8 h with the fluorinated hydrogels (HEC-TFEMA) and 1.1 h with carboxylated hydrogels (HEC-AA). Also, HEC-AEtMACl showed the highest current peak (3.9 μA at 1.4 V). Polarization curves proved that the anodic polarization behavior is dominant resulting from the anodic parasitic reaction. The Electrochemical Impedance Spectroscopy (EIS) evidenced that HEC-TFEMA has ionic conductivity (34.4 mScm−1) higher than that of HEC-AEtMACl. However, the highest specific capacity was observed to HEC- AEtMACl 0.928 mA h/cm2 compared to 0.26 and 0.15 mA h/cm2 for HEC-TFEMA and HEC-AA respectively.

A novel electrocoagulation process with centrifugal electrodes for wastewater treatment: Electrochemical behavior of anode and kinetics of heavy metal removal

Anodic passivation is a key problem to impair the efficiency of in the electrocoagulation (EC) process. Process intensification of EC has attracted increasingly greater attention. In this work, a novel centrifugal electrode reactor was designed and applied in EC process to enhance the treatment of simulated heavy metal wastewater using aluminum anode. Results showed that the removal efficiency of heavy metals was significantly improved by the centrifugal electrodes, compared with the stationary electrodes. Electrochemical behavior of centrifugal electrodes was analyzed by an improved rotating disk electrode system. Anodic polarization behavior of aluminium showed a typical characteristic of dissolution in centrifugal electrodes, rather than passivation in static condition. Anode dissolution was controlled by the diffusion of Cl− ion that was enhanced by centrifugal electrodes. Thus, anode passivation was reduced. In addition, the kinetics analysis indicated that the removal of heavy metals in EC by centrifugal electrodes conformed to Variable-Order-Kinetic (VOK) model based on the Langmuir adsorption.

Anodic Polarization Study of Step Pulse Waveform for Machining Accuracy in Electrochemical Micromachining

Electrochemical micromachining (EMM) shows promise as a versatile process for machining chemically resistant metallic materials in microsystems applications. A traditional rectangular pulse pattern has been modified into a step pulse waveform with a series of short rectangular pulses with different amplitudes. By establishing the experimental setup, anodic polarization behavior has been investigated throughout the dissolution process with 0.1 M H2SO4 electrolyte solution at different applied voltages under the application of rectangular and step pulse waveforms. Utilizing the step pulse waveform, oscillation of the anode potential and transpassive state have been obtained during machining. Thus, from polarization studies, it has been observed that at 13 V, the current density is accelerated in a moderate range, i.e., 0 to 33 A cm−2, which can reduce the anodic dissolution rate during the active state. Alternatively, the stray current effects and micro-sparks can be controlled because the duration of the passive state is very small and the RMS voltage can be reduced by 20.65% as compared to the rectangular pulse waveform. Further, overcut and tapering effects have been reduced by 83.99% to 51.39% and by 98.66% to 44.48% at the applied voltage of 13 to 17 V, respectively.

Corrosion performance and degradation mechanism of a bi-metallic aluminum structure processed by wire-arc additive manufacturing

An Al-5Mg alloy (AA5083) block, deposited over an AA6061 substrate by wire-arc additive manufacturing, was electrochemically tested along two different cross-sectional planes by cyclic polarization in 3.5 wt.% NaCl. The deposited layers and the interlayer boundaries showed similar polarization behavior regardless of the cross-sectional direction. The corrosion of both the substrate and the deposited layers was mainly attributed to the presence of relatively coarse intermetallic Al(Fe, Mn)Si particles. In the substrate, corrosion was governed by deep crevices along the interfaces of directionally aligned Al(Fe, Mn)Si particles with the Al matrix. The deposited layers and the interlayer boundaries showed pitting around numerous Al(Fe, Mn)Si particles and/or Al(Fe, Mn, Cr, Ti)Si at the interlayer boundaries, which were much finer compared to those of the substrate. The abundance of the fine precipitates and their intergranular location caused surface material removal, which was more extensive along the interlayer boundaries. The perpendicular z-y and z-x planes of the deposited block did not show significant differences in anodic polarization behavior. Differences were more distinct in the case of cathodic polarization. Some anisotropy in polarization behavior was noted through the thickness of the z-y plane that complies with the obtained tensile behavior.

Electrochemical behavior of aluminium anode in super-gravity field and its application in copper removal from wastewater by electrocoagulation

Anodic passivation is a key problem to reduce the efficiency of electrocoagulation (EC) process. Super-gravity technology was introduced into EC process to enhance the treatment of heavy metal wastewater using pure aluminum electrode. The results showed that the removal ratio of Cu increased, and the cell voltage decreased with the increase of gravity coefficient, suggesting a promoting effect of super-gravity field on electrocoagulation process. Electrochemical behavior of aluminium anode in super-gravity field was analyzed by potentiodynamic polarization, cyclic voltammetry and electrochemical impedance spectroscopy. It was found that anodic polarization behavior of aluminium showed a typical characteristic of dissolution in super-gravity, rather than passivation in normal gravity. The type of anode dissolution changed from pitting corrosion to uniform corrosion in super-gravity field. The outer oxidized film of anode was thinning, and more Al3+ ions were released by anode dissolution, which was attributed to the super-gravity enhancement of the mass transfer process of Cl− ions. In addition, X-ray diffraction and Fourier transform infrared spectroscopy indicated that the flocs generated in super-gravity field had amorphous and looser Al–O framework structure. As a result, the efficiency of EC process was improved by super-gravity.

Characterization of a nanocrystalline NiCo electroformed sheet metal

A novel electroformed nanocrystalline nickel cobalt alloy (n-NiCo) developed for sheet metal applications was investigated in terms of microstructure, as well as mechanical, thermal stability, and corrosion properties. The as-received material with a grain size of 18 ± 5 nm exhibited enhanced hardness compared with conventional polycrystalline NiCo mainly due to the Hall–Petch strengthening effect. Differential scanning calorimetry and annealing treatment results revealed that the n-NiCo was stable up to 200 °C for at least 1 h, and the onset of abnormal grain growth was observed when the material was annealed to 250 °C. While low-temperature annealing treatment was shown to increase the hardness of the material slightly, annealing at temperatures of 300 °C and above resulted in a reduction in hardness due to rapid normal grain growth. The n-NiCo sheet exhibited mixed Ni/Co anodic polarization behavior in environments of varying pH.

Multiscale mechanical performance and corrosion behaviour of plasma sprayed AlCoCrFeNi high-entropy alloy coatings

The combination of technical advantages of high entropy alloys (HEAs) and manufacturing capabilities of thermal spray (TS) offer potential towards new protective coatings to address extreme engineering environments. In this research, equi-atomic AlCoCrFeNi HEA coatings were synthesized via atmospheric plasma spray (APS) using mechanically alloyed feedstock, and a correlation between microstructure and mechanical properties in terms of both hardness and wear were established at multiscale levels. In addition, electrochemical performance in sea water and the overall residual stress distribution in the HEA coatings were also assessed. Superimposition of scanning electron micrographs and statistically analysed heat and contour maps using nanoindentation datasets revealed deviations in localized properties within and across individual phases; which were supported by Weibull plots of individual phases. Scanning wear tests revealed superior nanowear resistance of oxide phases developed by in-flight oxidation during APS process. In comparison, the HEA phases in the coating exhibited significant localized plastic deformation. The outcome of macroscale wear testing postulated that plasma sprayed AlCoCrFeNi HEA coatings exhibited superior wear resistance at high temperature (500 °C) than at room temperature, signifying high thermal stability of the coating. Residual stress generated due to plasma spray was measured using neutron diffraction and was tensile in nature. The corrosion resistance of the coating was slightly lower than that of SS316L, however, the anodic and cathodic polarization behaviour of HEA coating were identical to that of SS316L, indicating that the AlCoCrFeNi-based HEAs have prospects as corrosion resistant materials.

Formation and Characterization of Dispersed Mixed Iron-titanium Oxide Systems by Electrochemical Method

Aims: Anodic polarization behavior of a combined iron-titanium electrode (two metals in electrical contact with each other) in aqueous solutions containing halide ions (F- and Cl-) was studied. Methods: he joint anodic dissolution of titanium and iron with subsequent thermal treatment makes it possible to obtain precursors of a highly dispersed mixed oxide system Fe2O3-TiO2. The phase and elemental composition and structural characteristics of obtained products were examined using X-ray diffraction and scanning electron microscopy. It has been experimentally confirmed that via changing the anode current density, hydrofluoric acid concentration in electrolyte and ratio of the working surface area of contacting metals, it is possible to effectively control the rate of anodic reactions and phase composition and morphology of anodic oxidation products for iron and titanium components in a combined electrode. Results: The main results of this study are as follows: Electrochemical method for the synthesis of complex dispersed oxide system Fe2O3-TiO2 based on joint anodic oxidation of contacting metals in aqueous media was suggested. Relationships between parameters of the electrochemical process and characteristics of the synthesized oxide system were revealed. Conclusion: By varying the parameters of the electrolysis process, it is possible to prepare complex oxyhydroxides with different ratios of iron and titanium, which makes it possible to synthesize precursors of iron titanates of preset composition and structure.

Corrosion Behavior and Inhibition Studies of AZ31B Magnesium Alloy With and Without Cl- in the Alkaline Electrolytes in Addition with Various Inhibitor Additives

The pitting corrosion and inhibition studies of AZ31B magnesium alloy were investigated in the alkaline solution (pH12) with chloride and inhibitors. The corrosion behavior of passive film with/without Cl- in the alkaline electrolyte were conducted by polarization curve and immersion tests in the presence of various additives (inhibitors) to clarify the inhibition efficiency of pitting corrosion at higher potential region. Critical concentration of pitting corrosion for Mg alloy was evaluated with 0.005 M NaCl in 0.01 M NaOH on the anodic polarization behavior. Critical pitting of AZ31B Mg alloy in 0.01 M NaOH is a function of chlorides; Epit = - 1.36 - 0.2 log [Cl-]. When the Sodium Benzoate (SB) was only used as an inhibitor, a few metastable pits developed on the Mg surface by an immersion test despite no pitting corrosion on the polarization curve meaning that adsorption of SB on the surface is insufficient protection from pitting corrosion in the presence of chloride. The role of SB and Sodium Dodecylbenzenesulfonate (SDBS) inhibitors for the Mg alloy surface in the presence of chloride was suppressed from pitting corrosion to co-adsorb on the Mg alloy surface with strong formation of passive film preventing pitting corrosion.

Anodic Polarization Behavior of Cold-Worked Austenitic Stainless Steel: A Newer Approach

The anodic potentiodynamic polarization behavior of various grades of cold-worked (rolling and machining) austenitic stainless steels were studied. Deformed specimens were characterized by Electron backscattered diffraction (EBSD) and Fourier transform infrared spectroscopy (FTIR)-imaging. The FTIR-imaging was used to quantify chromium oxide (Cr2O3) spectra. It was observed, average area under Cr2O3 spectra was decreased with increase in cold -working. The certain regions in deformed microstructure showed higher value of area under Cr2O3 spectra, indicated stability of passivation film that needs to be explored. There was no microstructurally different between machined specimens.

Preparation and electrochemical corrosion behaviour of 3D large-sized nanocrystalline copper bulk in solutions with chloride ions

ABSTRACTA 3D large-sized nanocrystalline (NC) copper bulk was prepared by inert gas condensation and in situ warm compress, the density of which was 99.51% of theoretical value. Electrochemical methods and XRD、EDS、SEM technique were used to investigate the anodic polarisation behaviour of NC copper in solutions with chloride ions. NC copper exhibited a different anodic polarisation behaviour from its coarse-grain (CG) counterpart in 0.47 wt-% NaCl solution. No second passivity was observed for NC copper, while there was a notable second passivity for CG copper. Compared with CG copper, the corrosion resistance of NC copper decreased. The anodic polarisation behaviour of NC copper changed significantly when 104 ppm Cl− was added in 0.3% Na2SO4 solution. Attributed to the CuCl protective film on NC copper, the critical current intensity decreased and the decreasing rate of anodic current intensity lowed notably in activity-passivity zone.

Effect of Fe-C alloy additions on properties of Cu-Zr-Ti metallic glasses

The effect of Fe-C alloy additions on thermal, mechanical and corrosive properties of (Cu50Zr40Ti10)1-x(Fe-C)x (x = 0–2.20 at%) alloys were systematically investigated. The results show that the Fe and C additions can enhance glass transition temperature Tg and onset crystallization temperature Tx, but narrow supercooled liquid region ΔTx. Work-hardening can be clearly observed for the Cu-based bulk metallic glasses (BMGs) containing Fe and C elements. The yield strength (σy), fracture strength (σf) and plastic strain (εp) are drastically increased by Fe-C alloy additions. The corrosion potential Ec increases and the corrosion current density ic decreases with increasing Fe and C contents. The studied Cu-based BMGs exhibit unique and novel anodic polarization behavior characterized by current platforms plus current serrations. The current serrations are much larger for the Cu-based BMGs with 0 ≤ x ≤ 1.32 at% than for those with 1.76 ≤ x ≤ 2.20 at%. The corrosion surface images are changed from the pits to the passive films by Fe-C alloy additions. The corrosion behavior gradually transforms from the pitting corrosion to the self-passivization with increasing Fe and C contents. The corresponding mechanisms are also discussed.

Composition design and properties of Cu–Zr–Ti bulk metallic glass composites

(Cu50Zr50)x(Cu73Ti27)100-x (x = 0.63–0.75 at.%) alloys are designed using the proportional mixing of Cu50Zr50 and Cu73Ti27 binary alloys. Their thermal, mechanical and corrosive properties as well as the glass forming ability (GFA) are systematically investigated. The results show that the studied Cu-based glass forming alloys are bulk metallic glass composites (BMGCs) with off-eutectic compositions and display work-hardening behavior. The glass transition temperature and the reduced glass transition temperature increase and then decrease with increasing x when x ≥ 0.74 at%, while on the contrary for the critical cooling rate and supercooled liquid region. Both yield strength and fracture strength firstly increase and then decrease with decreasing x when x ≤ 0.71 at%. The plastic strain of (Cu50Zr50)0.75(Cu73Ti27)0.25 BMGC is the largest among the studied Cu-based BMGCs. Potentiodynamic polarization measurements show that all studied BMGCs exhibit a step-like anodic polarization behavior, indicating two competitive procedures of pitting corrosion and self-passivization. The corrosion behavior gradually transforms from predominant self-passivization to the pitting corrosion with decreasing x. Both corrosion current density and onset passive current density of (Cu50Zr50)0.75(Cu73Ti27)0.25 BMGCs are two orders of magnitude lower than those of the other Cu-based BMGCs. The mechanisms for the GFA and the corrosion are also discussed. The present work would shed light on how to design and develop BMGCs with superior comprehensive performances.

Anodic Polarization Behavior of Iron in Phosphoric Acid Solution Under the Action of Magnetic Field

The effect of magentic field on anodic dissolution, passivation and dissolution-passivation transition of iron in sulfuric acid solutions have been investigated. The change of anodic dissolution in the dissolution-passivation transition region and the resultant shrinkage of the passive region due to applied magnetic field have been reported. Uneven dissolution of iron electrode after anodic dissolution in sulfuric acid solutions have been reported. In the represent work, the effect of magnetic field on anodic behavior of iron in 0.5 mol/L phosphoric acid is investigated. Potentiodynamic polarization curves and potentiostatic polarization measurements are conducted at 0T and 0.4T. The anodic polarization curves at 0T and 0.4T are shown in Fig. 1, and the electrode surfaces after the measurements are shown in Fig. 2. The anodic polarization curve at 0T exhibits typical anodic dissolution, dissolution-passivation transition, steady passivation and transpassivation behavior. There is no sgnificant effect of magentic field on the active dissolution at potentials lower than Emax, 0T. Magnetic field moves the dissolution-passivation transition potential to a more noble potential therefore narrows the steady passivation range. There is no passive range in the anodic polarizaiton curve at 0.4T, showing only the drastic drop of current at Emax, 0.4T and then an increase of current soon. There is a quasi-linear potential-current density relationship in a wide potential range, i.e. -0.45 to 0.90V(SCE) at 0T, and -0.45 to 1.85V (SCE). The electrode surfaces after the potentiodynamic polarization measurements up to 2.0V(SCE) at 100 mV/min are observed, indicating severe anodic dissolution. The uneven electrode surface shows the locally accelerated anodic dissolution at the left and right edges of the electrode. From the center of the electrode along the horizontal direction to the edge, the uneven dissolution of the electrode surface presents an aggravating tendency. The results are consistent with thoese observed for iron in sulfuric acid at 0.4T magnetic field. When potentiostatic polarization starts at 1.2V at 0T, passive state can be reached and the further applied 0.4T magnetic field decreased the measured current density, showing the potential-dependent rate determining step and the resultant magnetic field effect on selective electrochemical processes. Figure 1

Influence of Cations on Atmospheric Corrosion of Hot-Dipped Galvanized Steel

The zinc-coated sheets are widely used in auto industries, especially for body parts. Corrosion caused to the body parts by sea salts and deicing salts such as NaCl, MgCl2 and CaCl2 has raised concerns of the automakers. The role of Mg and Ca cations in is still intriguing [1], and the corrosion products formed under such condition could rather prolong the service life of galvanized steels. In this study, by combining the non-destructive electrochemical impedance spectroscopy (EIS) method and morphology observation, the benefit of alkaline metal cations on enhancing the corrosion resistance of galvanized steels has been investigated through accelerated lab test. A commercial hot-dip galvanized steel having the coating thickness of 10 μm was employed as the specimen. The amounts of chloride salts deposited on the specimen surface were 4.05 g/m2 for MgCl2, 4.75 g/m2 for CaCl2, and 5.00 g/m2 for NaCl so that the chloride amounts were fixed to be 3.05 g/m2. The salt coated specimens were exposed to the dry-wet cycling over 95 % RH (2 h) - 40 % RH (2 h) in the humidity chamber. EIS and polarization curves were measured at the certain intervals of the exposure to evaluate the stage of degradation of the coating. The corrosion products were examined by X-Ray diffraction (XRD) and scanning electron microscope with an energy dispersive X-ray detector (SEM-EDX). The specimens deposited with MgCl2 exhibited far better corrosion resistance than those with NaCl. Even after 15 weeks (630 cycles), the open circuit potential held at around -0.9 V (vs. SSE), indicating the remain of metallic zinc coating. The corrosion rate estimated by EIS results was also low. This high corrosion resistance was ascribed to a thin and homogenous corrosion product layer, which was mainly composed of Zincite (ZnO) and Simonkolleite (Zn5(OH)8Cl2·H2O). After 126 cycles of the exposure, the corrosion products were turned to a double-layer structure of which the inner layer was dense and outer layer was porous. The compact inner layer must have offered the high corrosion resistance under the extended term of the aggressive environment. However, such a structure and long state of protection was not observed under NaCl salt films [2]. Alkaline metal chlorides are less aggressive to corrosion of the galvanized steel than NaCl and could promote the formation of homogenous corrosion product layer. Reference [1] Yumiko Tsurumaki, Eiji Tada, Azusa Ooi and Atsushi Nishikata, Anodic Polarization Behavior of Zn in Aqueous MgCl2 Solutions, 2018, ECS Meeting s, No. 1056 [2] Y. Liu, A. Ooi, E. Tada, A. Nishikata. Electrochemical Monitoring of Degradation Process of Galvanized Steels in Atmospheric Environments, 2018, ECS Meeting s, No. 1058 Figure 1

Anodic Polarization Behavior of X80 Steel in Na₂SO₄ Solution under High Potential and Current Density Conditions.

X80 steel has great risk of corrosion in high voltage direct current (HVDC) interference cases. In this study, the anodic polarization behavior of X80 steel under high potential and current density in Na2SO4 solution was investigated. The I × R drop was eliminated using current interrupt technique during the potentiodynamic measurement. Therefore, the real polarization curve was obtained. The corrosion behavior was investigated by galvanostatic polarization, scanning electron microscopy, and X-ray photoelectron spectroscopy. The results show a new form of passivation route. The steel dissolved actively below −0.388 VSCE, then became partly passivated from −0.388 to 1.448 VSCE, and fully passivated above 1.448 VSCE. The passive film was formed containing Fe2O3 and FeOOH, and resistant to SO42− ions. It not only blocked the direct dissolution of steel, but also facilitated oxygen evolution. The corrosion rates of steel samples decreased after the passivation.

A New Narrative for CO2 Corrosion of Mild Steel

The conventionally accepted mechanism of CO2 corrosion considers the direct reduction of carbonic acid as the main process that results in the higher corrosion rates as compared to that observed in strong acid solutions with the same pH. The present study is an attempt to further elucidate the underlying electrochemical mechanisms of CO2 corrosion. In this regard, the mechanism of CO2 corrosion was investigated based on the cathodic and anodic polarization behavior of mild steel in CO2-saturated solutions at elevated pressures. The examination of charge transfer controlled cathodic currents showed that the direct reduction of carbonic acid is insignificant at the condition of the present study. Additionally, the iron dissolution reaction was found to be significantly affected by the presence of CO2, particularly over the transition and pre-passivation ranges. A comprehensive mathematical model based on the presented mechanistic understanding of the system was developed and used for further quantitative examinations. The present mechanistic model was shown to be able to represent the main mechanistic features of polarization curves and predict the corrosion rates with reasonable accuracy.

Anodic Polarization Characteristics and Electrochemical Properties of Fe3C in Chloride Solutions

The anodic polarization behavior of cementite (Fe3C), which was prepared by gas carburizing, was investigated in 10 mM NaCl-containing boric-borate buffers with pH values of 6.0, 7.0 and 8.0. The active dissolution current of the Fe3C was found to be lower than that of the ferrite. This suggests that the corrosion resistance of the Fe3C was clearly higher than that of the ferrite. From the potential-pH diagrams, carbon was predicted to be generated on the Fe3C at lower potentials during the anodic polarization, and the existence of carbon was confirmed by XPS. The carbon layer seems to act as a protective film and suppress the active dissolution of the Fe3C at lower potentials. AES depth profiles clarified that iron oxide layers existed not only on the ferrite but also on the Fe3C. The Volta potential of the Fe3C was approximately 40 mV higher than that of the ferrite. The higher Volta potential of the Fe3C layer seemed to be associated with the nature of the oxide film formed on the Fe3C, and there is a possibility that the passivation of the Fe3C at higher potentials is achieved by an oxide film.