Potentiostatic Polarization Measurements Research Articles

Microbiological corrosion acceleration of N80 steel in shale gas field produced water containing Citrobacter amalonaticus at 60 °C

Microbiologically influenced corrosion (MIC) is one of typical reasons leading to a lot of damage of pipeline steels in the shale gas environments. MIC behavior and mechanism studies are important towards to steel protection. In this work, Citrobacter amalonaticus, a corrosive bacterium, was isolated from a shale gas well of China. And the corrosion behavior of N80 steel caused by C. amalonaticus was studied in simulated shale gas produced water at 60 °C making use of weight loss, surface analysis, electrochemical impedance spectroscopy (EIS), anodic potentiostatic polarization measurements, and potentiodynamic polarization curves. Results demonstrate that C. amalonaticus could accelerate the uniform and localized corrosion rates of N80 steel at 60 °C with values of (0.221 ± 0.016) and (0.557 ± 0.062) mm/y, respectively. Experimental results suggested that the adsorption of an organic inhibitor film on steel surface caused the corrosion rates of abiotic specimens going down. However, the existence of C. amalonaticus inhibited the adsorption of organic inhibitor film. The adhesion and biofilm formation of C. amalonaticus contributed to steel corrosion acceleration. The nucleation and growth of metastable pitting were enhanced by C. amalonaticus, thus causing a severe localized corrosion.

Corrosion of Linear-Friction-Welded AZ91 and AZX912 Mg-Al Alloys

The corrosion performance of the AZ91 and AZ91 + 2%Ca (AZX912) magnesium alloys joined using linear friction welding was investigated. For similar and dissimilar metal combinations—namely AZ91/AZ91, AZX912/AZX912, and AZ91/AZX912, the performance was evaluated by mass loss analysis and the scanning vibrating electrode technique in 1 wt% NaCl solution. Galvanic behavior between AZ91 and AZX912 was examined by potentiostatic polarization and galvanic current measurements. Approximately 0.3–0.6 mm thick seamless weld zones were generated in all of the welds, which did not show any appreciable changes in the surface profiles acquired after the corrosion test. The corrosion-induced mass loss rate of the AZ91/AZX912 dissimilar weld was 10% higher than those of the AZ91/AZ91 and AZX912/AZX912 similar welds. The galvanic test indicated that AZ91 and AZX912 were the anodic and cathodic regions, respectively, with a difference in the corrosion potential of 20–30 mV. The corrosion of the AZ91/AZX912 weld was presumed to proceed via a macro-galvanic cell between the base alloys, whereas the weld acted as a bridge and did not influence the corrosion.

Electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V controlled by elements segregation and phases distribution

The electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V were investigated through Tafel polarization, potentiostatic polarization and AC impedance measurements. The results show that the solution treatment−aging (STA) process aggravates the element micro-segregation compared to the annealing process, leading to varied Al and V contents of the phases from different samples. It is proven that either Al-rich or V-rich condition can highly affect the electrochemical dissolution behaviors due to thermodynamical instability caused by element segregation. The dissolution rate in the metastable passivation process is controlled by the stability of the produced film that is affected by phases distribution, especially the difficult-to-dissolve phase. And then, the dissolution rate of the phases in the transpassivation region is consistent with the rank in the activation process because the dense film is not capable of being produced. Compared to the annealed sample, the higher dissolution rate of the STA sample is beneficial to the electrochemical machining (ECM) of Ti6Al4V.

Novel combination of indicators to compare the corrosion behaviors of Al, Al–Li alloy 2A97, and other Al alloys

AbstractAl–Li alloys have higher mechanical properties and are more lightweight than pure aluminum and other aluminum alloys. The element lithium is highly active; therefore, it is necessary to evaluate corrosion behaviors of Al–Li alloys. However, the existed methods and indicators that compare their corrosion properties are hard to characterize the continuous variations of corrosion performances with time. The potentiostatic polarization measurement is first proposed to compare corrosion resistances of Al, Al–Li alloy 2A97, and Al alloys 2024, 6061, 7050 in this study. Polarization current densities of these materials are measured. Then, equivalent resistances and charges amounts are respectively derived by Ohm's law and integration. Mass losses of these materials are calculated with Faraday's law. Measured current densities and three derived indicators above are applied to compare corrosion behaviors of these materials. Comparative results indicate that alloy 2A97 possesses the best corrosion property at the initial corrosion stage. During steady corrosion processes, the corrosion resistance of alloy 2A97 is better than those of alloys 2024, 6061, and Al except alloy 7050.

Corrosion and interfacial contact resistance of nanocrystalline β-Nb2N coating on 430 FSS bipolar plates in the simulated PEMFC anode environment

The corrosion of metallic bipolar plates in the proton exchange membrane fuel cells (PEMFCs) anode environment would degrade the performance and shorten the lifespan of the fuel cell. Hence, it is essential to develop a conductive coating with good corrosion resistance. Herein we demonstrate a dense, defect-free, and well-adhered nanocrystalline β-Nb2N coating prepared on 430 ferritic stainless steel (430 FSS) via disproportionation of Nb(Ⅳ) species in molten salts. The corrosion mechanism of bare and β-Nb2N coated 430 FSS in the simulated PEMFC anode environment is also studied by electrochemical techniques including potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy. Results show that β-Nb2N coating can significantly improve the corrosion resistance of the steel alloy with acceptable contact resistance. In addition, no obvious degradation is observed for the β-Nb2N coating after potentiostatic polarization measurement for 500 h. This work offers a promising strategy to develop the corrosion protective coating on metallic bipolar plates for PEMFCs.

Ionic and electronic transport in the fast Ag+ conductor α*-Ag3SI

Understanding the manifold origins that lead to fast ion transport in crystalline and amorphous solids is a vital topic in materials science. To advance in this field, the study of ion dynamics in model substances, partly inspired by applications, is a suitable route to identify the most important cause of ultrafast ion exchange processes in selected classes of materials. The ternary compound Ag3SI, which crystallizes with different space groups, represents such a model substance; its complex Ag-sublattice offers many, only partly occupied and adjoining Ag+ sites that guarantee a very high Ag+ ion conductivity. Here, we used broadband impedance spectroscopy and studied the temperature stability of the ionic conductivity of the α* phase of Ag3SI at a given temperature. β-Ag3SI, synthesized by a mechanochemical approach combined with a subsequent annealing step, transforms into the α form at high temperatures. Quenching this phase leads to (metastable) α*-Ag3SI that is characterized, at 20 °C, by a conductivity σ of 38 mS cm−1. The corresponding activation energy turned out to be 200 meV. Storing α*-Ag3SI at 30 °C for 140 h causes σ to drop to ca. 15 mS cm−1 (30 °C). A more drastic decrease is seen for the sample when annealed in situ at 60 °C resulting in 9 mS cm−1 (60 °C). For comparison, the thermodynamically stable β form is characterized by 3 mS cm−1 (20 °C). This high Ag+ ion dynamics is confirmed by 109Ag NMR which yields a single, sharp line at room temperature. Importantly, we also measured electronic conductivities σeon to corroborate that σ is predominantly governed by ionic contributions. As an example, for the α* form room-temperature potentiostatic polarisation measurements yield σeon = 2.7 × 10−8 S cm−1, which is by a factor of 106 lower than its total conductivity of 38 mS cm−1. For β-Ag3SI the maximum electronic conductivity turned out to be ≈ 2.0 × 10−7 S cm−1.

NICOTINAMIDE-BASED IONIC LIQUID AS A POTENTIAL COPPER CORROSION INHIBITOR

In this paper, the possibility of using newly synthesized ionic liquid based on nicotinamide as a potential inhibitor of copper corrosion in an acidic sulfate medium was investigated. Inhibition efficiency of butyl-nicotinamide, [C4Nic]Br on copper corrosion in acidic (pH=3) 0.1 mol/dm3 sodium sulphate solution was analyzed using potentiostatic polarization measurements and electrochemical impedance spectroscopy (EIS). It was found that the investigated ionic liquid had inhibitory properties of the corrosion of copper in acidic media. The inhibitory effect of the test compound is manifested by rapid and spontaneous adsorption of [C4Nic]Br molecules on the copper surface following Langmuir’s adsorption isotherm. As a result, the cathodic corrosion current decreases, as well as the polarization resistance of the system, increases compared with the basic solution. The inhibition efficiency of the investigated compound largely depends on the applied concentration.

Influences of formation potential on oxide film of TC4 in 0.5 M sulfuric acid

The correlation between film formation potential and the thickness, valence state, and corrosion resistance of the oxide film on TC4 (Ti-6Al-4V) in 0.5 M sulfuric acid is investigated. Potentiostatic polarization and electrochemical impedance spectra measurements reveal the passivation process and electrochemical properties of TC4 alloy. Relative quantitative X-ray photoelectron spectroscopy and Auger electron spectrum analyses illustrate that the formation of thicker and higher valence state film is promoted by the increase in applied potential. Those passive films formed at the potentials in passive region show good protections, and the corrosion resistance of the passive film becomes larger with the increase in passivation potentials. The TiO2 form in oxide films generated under the above conditions transforms from anatase to rutile with the increase in applied potentials and this transformation is found through comparing with the X-ray absorption spectroscopy of reference oxides.

The Effect of CuCl2 on Pitting Corrosion of the Extra High Purity Type 316 Stainless Steel

The effects of Cu addition on corrosion behavior of stainless steels are known to be controversy1,2, which depends on the corrosion environment or the amount of alloying Cu. In chloride environment, alloying Cu is known to prohibit the growth of pitting corrosion. The dissolved Cu2+ acted as an inhibiter inside the pits3. On the other hand, there are few studies about the effect of Cu2+ ions in the solution on the pitting corrosion of the stainless steels. Since the commercially made stainless steels commonly contains more than 0.1 mass% Cu, the Cu2+ ions which was dissolved from stainless steels made it difficult to evaluate the effect of Cu2+ ions on the pitting behavior of the stainless steels. Although the amount of dissolved Cu2+ was quite few, the Cu2+ concentration inside the pits was expected to be much higher than the solution bulk because the pitting corrosion was very localized phenomenon. Therefore, Cu2+ in the solution and dissolved Cu2+ should be analyzed separately. To clarify the effect of Cu2+ in the solution on the pitting corrosion of the stainless steels, the amount of alloying Cu is needed to be low enough not to affect the corrosion morphology. In this study, extra high purity Type 316 stainless steel (316EHP) was used as specimen. The Cu content of the specimen was 6.8 × 10-4 mass %. The specimens were heat-treated at 1373 K for 3.6 ks and then quenched in water. The surfaces of the specimens were polished down to 1 µm with a diamond paste. After that, specimens were ultrasonically cleaned in ethanol. Electrochemical measurements were conducted in deaerated 0.1 M NaCl or 0.098 M NaCl-1 mM CuCl2. Except the electrode area (ca. 10 × 10 mm), the surfaces of the specimens were insulated by an epoxy resin. The potential scan rate was 3.33 × 10-4 V s-1 (20 mV min-1). The reference electrode was an Ag/AgCl (Sat. KCl) electrode. All the potentials cited in this work refer to the Ag/AgCl (Sat. KCl) electrode. After the electrochemical measurements, the surfaces were analyzed by SEM/EDS and XPS. The inclusions of the specimen were characterized by SEM/EDS. The inclusions were identified as a Cr-oxide. The anodic polarization curves were measured in deaerated 0.1 M NaCl or 0.098 M NaCl-1 mM CuCl2. Although no pitting was observed in 0.1 M NaCl, pitting was occurred in 0.098 M NaCl-1 mM CuCl2. In both solutions, the dissolution of inclusions was not confirmed. Therefore, the inclusions were not thought to be the initiation site of pitting. This indicates that the pitting potential of 316EHP was decreased by Cu2+ in the solution. Cu2+ ions were thought to act as an accelerator of pitting corrosion. To analyze the effect of Cu2+ ions on the forming passivation film, potentiostatic polarization measurements at 0.4 V were carried out in 0.098 M NaCl-1 mM CuCl2. As a result, existence of a Cu signal on the surface was confirmed by XPS although it was not detected by SEM/EDS. This result indicatets that the few amounts of Cu compound was deposited on the surface in passive region of the 316 EHP.

Effects of Solid-Solute V on the Phosphatability of Hot-Rolled Steel Sheets

The phosphatability of hot-rolled steel sheets has become increasingly important with application of higher strength and thinner steel sheets to automotive parts. Although vanadium (V) is an alloying element which is often added to high strength hot-rolled steel sheets, the effect of V on phosphatability was still unclear. This study investigated the phosphatability of V-added hot-rolled steel sheets by using V-free, 0.20% V, and 0.47% V steel sheets as test specimens. After phosphate treatment, phosphate crystals covered the whole surface of the V-free and 0.20% V steel sheets, but no phosphate crystals were observed on the surface of the 0.47% V steel sheets. In order to clarify this difference, potentiostatic polarization measurement was carried out in the phosphate treatment solution. Phosphate crystals were found on the surface of the V-free steel sheet after both cathodic and anodic polarization. In contrast, no phosphate crystals were found on the surface of the 0.47% V steel sheet after anodic polarization, but similarly to the V-free steel sheet, phosphate crystals had formed after cathodic polarization. A surface analysis by XPS revealed that V oxides had precipitated on the surface of the 0.47% V steel sheet after anodic polarization. V oxidation reaction involves the generation of hydrogen ions and prevent the steel/solution interfacial pH from rising. This reaction identified as the deterioration mechanism of the phosphatability of V-added hot-rolled steel sheets.

Comparative investigations on the electrochemical behaviors among Al and aluminum alloys

Al and aluminum alloys are widely used in the transportation industry and aerospace field owing to their low density. They are always utilized as the sheathing materials, whose corrosion resistances need special attention. In the study, the electrochemical impedance spectroscopy (EIS) measurements and potentiodynamic polarization tests are performed on pure Al, aluminum alloys 2A97, 6061, 7050 and 2024. The corrosion behaviors of the five materials are respectively characterized by the resultant indicators, such as the corrosion potential E c , the corrosion current density I c , the corroded surface morphology and the frequency characteristics. The materials sequences that determined respectively by these indicators are compared with each other. The conflicts among these sequences are found. Then potentiostatic polarization measurements are carried out on the five materials. The instantaneous characteristic of the corrosion potential and polarization current density of each material during its corrosion process is revealed. Because of the characteristic, it is concluded that the potentiostatic polarization measurement and resultant polarization current density are more suitable to characterize the corrosion behaviors of Al and aluminum alloys. The investigation could provide help in the exploitation of new aluminum alloys with the better corrosion property.

Effects of the α/γ-Phase Ratio on the Corrosion Behavior of Cast Duplex Stainless Steel

The effects of the α/γ-phase ratio on pitting corrosion initiation and growth in cast duplex stainless steel were studied, including the preferential dissolution of the two phases inside the pits, using pitting potential measurement and potentiostatic polarization measurement with a high concentration of chloride ions and a low pH. The initiation of pitting was not dependent on the α-phase ratio. The γ phase preferentially dissolves when a high potential in the active dissolution region is applied, and the α phase preferentially dissolves when a low potential is applied. In addition, with an increase in α-phase ratio, the potential range where the α phase preferentially dissolves enlarged toward the higher potential side. The growth rate of stable pitting increased with the α-phase ratio. Dissolution of the α phase increased with an increase in the α-phase ratio. This phenomenon is presumably caused by the decreased amount of Cr in the α phase, resulting from the increased α-phase ratio, as well as by Cr depletion around Cr nitrides.

Promotion of anhydrous proton conduction by polyvinyl alcohol in liquid crystalline composite membranes containing 1-tetradecyl-3-methylimidazolium hydrogen sulfate

Composite membranes composed of liquid crystalline 1-tetradecyl-3-methylimidazolium hydrogen sulfate and polyvinyl alcohol are prepared for anhydrous proton conduction. The composite membranes exhibit smectic A liquid crystal phase in which polyvinyl alcohol chains aggregate into lamellas between the bilayers formed by the alkyl imidazolium hydrogen sulfate. Smectic order of hydrogen sulfate anions ensures formation of hydrogen-bonded chains for proton conduction via a hopping mechanism. Electrochemical measurements reveal that temperature-dependent ionic conductivity of the composite membranes approximately follows an Arrhenius-type law and reaches 20.5 mS cm−1 at 140 °C, which is twice that of the pure ionic liquid crystal. Potentiostatic polarization measurements show that proton transfer number of the composite membrane is also promoted. Polyvinyl alcohol promotes anhydrous proton conduction by constructing additional hybrid hydrogen-bonded chains consisting of hydroxyl groups of PVA and hydrogen sulfate anions. The ionic liquid crystalline composite membranes possess the potential application in intermediate temperature fuel cells.

Synergistic effect of cold work and hydrogen charging on the pitting susceptibility of 2205 duplex stainless steel

Solution-treated 2205 duplex stainless steel (DSS) was cold-worked to different degrees and then charged with hydrogen. The pitting susceptibility and passivation of cold-worked 2205 DSS samples in neutral chloride solutions were investigated by chemical immersion, potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy measurements. The dislocation densities in austenite and ferrite inside 2205 DSS samples both increased as the degree of cold work increased from 0% to 80%. After hydrogen charging, the hydrogen content in 2205 DSS samples increased from 13.52 ppm to 41.49 ppm as the degree of cold work increased from 0% to 80%, accompanied by an increased tendency to form hydrogen blisters. Deformation alone had little effect on the corrosion performance of 2205 DSS samples, but the deterioration effect of hydrogen charging on pitting resistance has been promoted by cold work, which could be ascribed to the increased hydrogen content as the degree of cold work increased. The change in pitting potential before and after hydrogen charging was linearly dependent on the hydrogen content in 2205 DSS samples. Pits preferably nucleated within austenite or at the austenite/ferrite boundaries for the hydrogen-charged 2205 samples regardless of the degree of cold work.

Influence of sintering aid on the microstructure and conductivity of the garnet-type W-doped Li7La3Zr2O12 ceramic electrolyte

Li6.4La3Zr1.7W0.3O12 (LLZWO) garnet-type structure was prepared with SiO2 as sintering aid via solid-state reaction method. The prepared ceramic samples were characterized by X-ray diffraction and Raman spectra to judge the structure. Microstructure, lithium-ion conductivity and electronic conductivity of all components were investigated by means of scanning electron microscopy, electrochemical impedance spectroscopy and potentiostatic polarization measurement, respectively. These investigations show that SiO2 was found to be a better additive to reduce the porosity and improve conductivity. The relative density and ionic conductivity increase first and then decrease with increasing SiO2 content. The relative density of 93.8% and ionic conductivity of 9.11 × 10−4 S cm−1 in the sample with 0.2 wt% SiO2 were obtained. In contrast, the activation energy reaches a minimum value of 0.38 eV.

Reprint of “Effect of target composition on the microstructural, mechanical, and corrosion properties of TiAlN thin films deposited by high-power impulse magnetron sputtering”

Ti1−xAlxN thin films were deposited using reactive high-power impulse magnetron sputtering on silicon Si (100), tungsten carbide (WC-Co), and SUS304 substrates using three metallurgical TixAly alloy targets with Al/(Al + Ti) atomic ratios of 0.19, 0.36, and 0.57. A fixed duty cycle of 1% and a N2/Ar ratio of 15.8% was used. The current–voltage characteristics of the TixAly alloy targets were first investigated. Then, the microstructural evolution and the mechanical and corrosion properties of the as-deposited Ti1−xAlxN thin films were analysed by scanning electron microscopy, grazing incident X-ray diffractometry, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, and anodic potentiodynamic polarisation tests. The power density of 1.86 kW/cm2 achieved with the square-like power output wave obtained in the constant current mode was higher than the 1.37 kW/cm2 power density obtained with the triangular-like power output wave. The deposition rates of the Ti1−xAlxN thin films increased from 13.4 to 28.6 nm/min with an increasing alloy target Al/(Al + Ti) atomic ratio due to the higher sputter yield of Al than Ti. The Al/(Al + Ti) atomic ratio of the alloy target determines the structure, which changed from a highly preferred TiN (111) orientation (Al/(Al + Ti) ratio = 0.19) to a nanocomposite structure (Al/(Al + Ti) ratio = 0.57). The nanoindentation results indicated that the highest hardness and elastic modulus values of the Ti1−xAlxN thin films were 33.3 GPa and 405.9 GPa, respectively, obtained using the Al/(Al + Ti) = 0.19 alloy target. In addition, the friction coefficients of the Ti1−xAlxN thin films were between 0.68 and 0.77. However, the potentiostatic polarisation measurements showed that the amorphous TiAlN films exhibited the highest corrosion resistance in 3.5% NaCl solution, as the corrosion resistance of the Ti1−xAlxN coatings increased as the Al/(Al + Ti) atomic ratio increased.

Electrochemical properties of niobium and niobium compounds modified AISI430 stainless steel as bipolar plates for DFAFC

ABSTRACTThe highly conductive and corrosion resistant diffusion layers of niobium, niobium nitrides and niobium carbides have been successfully fabricated on AISI430 stainless steel (430 SS) via a plasma surface diffusion alloying (PSDA) method as bipolar plates for direct formic acid fuel cells (DFAFCs). The surface of niobium carbides modified 430 SS (NbC 430 SS) is relative densification and uniformity without other surface flaw and micropore. Potentiodynamic and potentiostatic polarisation measurements indicate that NbC 430 SS enhances the corrosion resistance more effectively than other modified samples and its corrosion current density is maintained approximately 2.5 μA cm–2 in the simulated anodic environment of DFAFC. Moreover, NbC 430 SS presents a superior hydrophobicity with a contact angle of 105.5° and a lower interfacial contact resistance (ICR) before and after potentiostatic polarisation tests than other specimens. Therefore, NbC 430 SS developed in this work has a great potential to be bipolar plates for DFAFCs.

Magnetic Field Effect on Anodic Dissolution of Axle Steel in Bicarbonate Solution with Chlorides

The vehicle axle in the railway locomotive is a very important component. Localized corrosion is a cause of its degradation. Localized corrosion is usually caused by corrosive environments especially in media containing chloride ions. Harmonic currents in the power supply loops (contact nets and guide rails) of the train during train travel can produce stray current that produces stray magnetic fields. Some studies have shown that magnetic fields can accelerate or inhibit localized corrosion of metals. In this study, optical microscopy (OM) and electrochemical measurements were used to study the effects of magnetic field on the electrochemical behavior and corrosion morphology of axle steel in sodium bicarbonate solutions with and without chloride ions. Different scan rates were used in the measurements of anodic polarization curves. Potentiostatic polarization measurements were performed with applying or removing a 0.4 T magnetic field. The surface morphologies of the electrodes were observed after potentiostatic polarization. Figure 1 show that, for axle steel in 0.05 mol/L NaHCO3 with or without 0.001 mol/L NaCl, the magnetic field increased the peak current, positively shifted the potential for the onset of passivation, and narrowed the passivation range. Chlorides increased the anodic current in the transpassivation region. The synergistic effect of magnetic field and chlorides on breakdown of passivation was more significant at high potential scan rate for the anodic polarization curve measurements. Obvious corrosion pits could be found after polarization, according to the morphology of the axle steel after polarization at a scan rate of 50 mV/min. It is found that the magnetic field significantly accelerated the corrosion. For axle steel in 0.05 mol/L NaHCO3 system, the potentiostatic polarization was carried out at -0.3 V(SCE). The current density decreased with increasing the polarization time. The current decreasing rate was mitigated by applying a 0.4T magnetic field, i.e., the anodic current density tended to be more stable under applied magnetic field, showing a significant magnetic field effect on anodic dissolution and pitting behavior of axle steel in this environments. Figure 1

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

Magnetic Field Effect on Anodic Dissolution Behavior of Iron in Sodium Perchlorate Solution

It has been reported that magnetic field affects the anodic dissolution and passivation behavior of iron in acidic, neutral, slightly alkaline solutions. Perchlorate solution has been used in the mechanistic study of anodic dissolution mechanism of iron. In this study, the effects of 0.4T magnetic field on the electrochemical behavior and corrosion morphologies of iron in sodium perchlorate solution were studied by optical microscope (OM), scanning electron microscope (SEM) and several electrochemical methods such as potentiodynamic polarization curve and potentiostatic polarization. Magnetic field was placed horizontally and parallel to the working electrode. The anodic polarization curves show that magnetic field did not have strong effect on anodic current at the potential before the transpassivation potential. In the transpassivation range, magnetic field increased the anodic current, increased the slope of the i/E curve. After the potentiodynamic polarization curve measurements up to 2.0V(SCE), severe electrode thinning was observed under both 0T and 0.4T. Macroscopically uniform dissolution was observed on the electrode after measurements under 0T, while locally accelerated thinning was found on the iron electrode after the measurements under 0.4T, showing the accelerating effect of magnetic field on the anodic dissolution at the edges of the electrode along the horizontal direction, as the result of uneven distribution of the actual magnetic field flux density. Potentiostatic polarization measurements show that magnetic field decreased the anodic current density in the passive range, where the electrode was not significantly affected by magnetic field due to low current density. The accelerating or inhibiting effect of magnetic field can be interpreted based on the magnetohydynamic driving force and the magnetic field gradient driving force theory. Figure 1