Open Circuit Potential Curves Research Articles

Interrogation of Oxidative Pulsed Methods for the Stabilization of Copper Electrodes for CO2 Electrolysis.

Using copper (Cu) as an electrocatalyst uniquely produces multicarbon products (C2+-products) during the CO2 reduction reaction (CO2RR). However, the CO2RR stability of Cu is presently 3 orders of magnitude shorter than required for commercial operation. One means of substantially increasing Cu catalyst lifetimes is through periodic oxidative processes, such as cathodic-anodic pulsing. Despite 100-fold improvements, these oxidative methods only delay, but do not circumvent, degradation. Here, we provide an interrogation of chemical and electrochemical Cu oxidative processes to identify the mechanistic processes leading to stable CO2RR through electrochemical and in situ Raman spectroscopy measurements. We first examine chemical oxidation using an open-circuit potential (OCP), identifying that copper oxidation is regulated by the transient behavior of the OCP curve and limited by the rate of the oxygen reduction reaction (ORR). Increasing O2 flux to the cathode subsequently increased ORR rates, both extending lifetimes and reducing "off" times by 3-fold. In a separate approach, the formation of Cu2O is achieved through electrochemical oxidation. Here, we establish the minimum electrode potentials required for fast Cu oxidation (-0.28 V vs Ag/AgCl, 1 M KHCO3) by accounting for transient local pH changes and tracking oxidation charge transfer. Lastly, we performed a stability test resulting in a 20-fold increase in stable ethylene production versus the continuous case, finding that spatial copper migration is slowed but not mitigated by oxidative pulsing approaches alone.

Degradation study for 18650 NMC batteries at low temperature

This research focuses on the identification and quantification of lithium-ion battery degradation indicators at low temperatures. We studied the cycling aging of 18,650 commercial NMC lithium-ion batteries at 10 °C. For this purpose, we carried out life cycle tests and performed Galvanostatic Intermittent Titration Technique (GITT) tests in the voltage range for the charge and discharge processes for different States of Health (SoH). The diffusion time constant and the ohmic overpotential were determined from GITT for different SoH. As the batteries degrade both parameters increase. A degradation mechanism associated with faradaic effects (increase in ohmic drop overpotential) and a thermodynamic effect associated with changes in the active material (diffusional time constant) is observed. Furthermore, we performed Electrochemical Voltage Spectroscopy studies through Incremental Capacity (IC) curves. IC curves peaks and valleys are associated with battery phase transformations due to aging phenomena. Each peak has a unique peak height, area, and position associated with a degradation mode. This research focuses on the IC curves derived from the discharge capacities at 3A and OCP (Open Circuit Potential) to study the thermodynamic and faradaic effects separately. The peak at 3.6 V and 3.4 V for the 3A and OCP studies, respectively, is the main feature for the detection of the degradation mechanism. The valley in the OCP curves intensifies with the decrease in SoH and is shifted to lower potentials, an effect that is not observed in the 3A curves. So, we could associate this with thermodynamic effects, Loss of Lithium Inventory (LLI) and Loss of Active Material (LAM) of both the positive electrode and the negative electrode.

Lithium-ion battery degradation diagnosis and state-of-health estimation with half cell electrode potential

Lithium-ion batteries (LiBs) have been widely used in electric vehicles and portable electronics. However, the performance and safety of these applications are highly dependent on degradation of LiBs. In this paper, three contributions have been made to achieve reliable degradation diagnosis and State-of-Health (SOH) estimation: (1) Open-circuit voltage is reconstructed to diagnose degradation modes of LiBs by performing scaling and translation transformations on open-circuit potential curves. (2) A degradation diagnosis model is developed to quantify aging characteristics of LiBs. In this model, a segment of charging data is taken to estimate SOH and the degradation modes in a degradation path. (3) An appropriate voltage range of the charging data is selected to improve model estimation accuracy. Experimental results show that the proposed method can achieve reliable degradation diagnosis and accurate SOH estimation with the maximum error of 1.44%.

Effects of Current Density and Deposition Time on Corrosion Behaviour of Nickel-based Alloy Coatings

Corrosion of fasteners is an on-going issue and stainless steel 304 (SS304) is prone to this destructive process. One method to mitigate corrosion is electrodeposition of Co-Ni-Fe nanoparticles. This paper studied the effects of deposition time and current density on corrosion behaviour of Co-Ni-Fe coated SS304 bolt. Co-Ni-Fe ternary alloys were electrodeposited onto SS304 bolt in 15, 30, or 45 minutes by using current density of 28, 35, 42 mA/cm2. Combinations of these parameters produced 9 samples. These samples were electrochemically tested by a potentiostat using open circuit potential (OCP) and potentiodynamic polarization (PDP). The samples were also characterised in terms of surface roughness and thickness of the coatings by using 3D surface metrology system. The OCP value decreased when deposition time was increased. All sample synthesised in 30 minutes had a more stable OCP curve. PDP curves exhibited active behaviour without passivation region. The corrosion potential (Ecorr) of T15 samples was more anodic than T30 and T45 samples. The corrosion current density (Icorr) of all samples fluctuated. Sample synthesised in 30 minutes using 42 mA/cm2 had the lowest corrosion rate. It was found that the surface roughness influences the corrosion behaviour in which a lower surface roughness tends to produce coating with better corrosion performance. Current density had small effect on the thickness of coating, whereas the tendency of a thickness to increase was obvious for deposition time.

Influence of twin wire arc spraying and machine hammer peening on the corrosion fatigue of ZnAl4 coatings on S355 J2C + C substrate

ZnAl-based coatings are used as corrosion protection for offshore application, e.g., offshore wind turbines. These applications are subjected to superimposed mechanical and corrosive stresses, e.g., wind, tide, seawater and mist. Thermally sprayed coatings processed by twin wire arc spray process and the mechanical post-treatment process machine hammer peening (MHP) were investigated. The coating consisting of ZnAl4 was deposited on a S355 J2C + C substrate. In addition to two conditions produced with different process parameters during MHP post-treatment, uncoated and as-sprayed conditions were evaluated as reference. The aim was to determine the effect of the coating and its properties, such as hardness, porosity and roughness, on the corrosion and corrosion fatigue behavior. In this study, potentiodynamic polarization tests and instrumented corrosion fatigue tests using a self-designed corrosion cell were performed in 3.5% NaCl solution. Mechanical and electrochemical measurement techniques in combination with fractographic and microstructural analyses were used to characterize corrosion fatigue damage mechanisms.MHP resulted in a uniform coating thickness with lower roughness and porosity in comparison to the as-sprayed coatings, which were further reduced by adjusting the process parameters of MHP. The electrochemical potential of the ZnAl coating provides passive corrosion protection for the substrate. The coating system improved corrosion fatigue resistance at high cycle fatigue regime. While as-sprayed and MHP post-treated specimens run out at 280 MPa, uncoated specimens run out at 240 MPa. The open circuit potential (OCP) curves plotted during the corrosion fatigue tests can be correlated with the damage mechanisms. Crack initiation and propagation in the coating and crack propagation in the substrate can be identified from the OCP curves.

Drop cast coating of leather dye on copper and investigation of its corrosion behavior in sodium chloride solutions

The copper (Cu) is used in many heat exchange, electrical and electronics applications for its good thermal and electrical conductivity. In addition, copper have other attractive properties like corrosion resistant and antibacterial properties. However, these properties of copper can be vanished upon its corrosion in aggressive chloride environments. The present work report corrosion behavior of black leather dye (LBD) coated copper substrates in 0.5 M NaCl. The coating of copper has been done by drop casting. The investigation is carried out through UV–visible spectroscopy (UVS), Fourier transform infrared spectroscopy (FTIR), open circuit potential curves (OCP), electrochemical impedance spectroscopy (EIS), Tafel polarization curves (TPC) and optical microscopy (OM). EIS and TPC propose that LBD coated Cu perform better than bare copper substrates in NaCl solutions. The OM results are in accordance with the fact that coating has been successfully formed on copper substrates and protective in nature. In the view of obtained results, LBD is recommended for corrosion prevention of Cu in NaCl.

Non-Destructive Degradation Diagnostics of Lithium-Ion Cells Considering Aging-Related Changes in the Shape of the Half-Cell Open Circuit Potential Curve of Silicon-Graphite

Analyzing changes in the quasi-stationary open circuit potential (OCP) curve during aging is a well-established method for the non-destructive diagnosis of degradation occurring in lithium-ion cells during calendar and cycle aging. It allows detecting and quantifying different degradation modes, especially loss of lithium inventory and loss of active material at a specific electrode, without the need of opening up the cells and performing post-mortem analysis. In order to obtain information on the degradation, the quasi-stationary OCP curve measured from an aged cell is reconstructed based on the half-cell OCP curves of the electrode materials. For this purpose, both half-cell OCP curves are linearly scaled and relatively shifted against each other until the difference between cathode and anode OCP fits the measured full-cell OCP. The parameters for the scaling and shifting of the half-cell OCP curves obtained during this optimization procedure are quantitative indicators of the degradation modes that have occurred in the full-cell. Usually, half-cell OCP curves obtained from pristine electrode material are used in this process and the shape of the half-cell OCP curves is assumed invariant during aging.While this assumption is probably justified for graphite and most established cathode materials, there are a number of recent publications describing a change in the shape of the OCP curve of blended silicon-graphite electrodes during cycle aging. This change is probably mainly caused by a decrease in the relative contribution of the silicon to the overall electrode capacity because of its faster degradation in comparison with the graphite. In this study, we investigate the influence of aging-induced changes in the shape of the OCP of silicon-graphite on the applicability of the method for non-destructive degradation analysis described above for cells containing silicon-graphite as anode material. We also present possible extensions of this method to consider changes on the half-cell level.In the scope of this study, we cycle commercial lithium-ion cells containing nickel-rich nickel manganese cobalt oxide (NMC-811) as cathode material and silicon-graphite as anode material until different degradation stages are reached. We then measure the quasi-stationary OCP of the full-cell and subsequently open the cells to extract samples from both electrodes. Afterwards, we measure the quasi-stationary OCP curve of the electrode samples by building coin-cells containing an electrode sample as cathode and lithium metal as anode.We reconstruct the full-cell OCP curves at different degradation stages by linear scaling and shifting of half-cell OCP curves both obtained from pristine electrodes and from the electrodes extracted from aged cells as shown in figure 1. This allows us to analyze whether the accuracy of the full-cell OCP reconstruction can be improved by using half-cell OCP curves of aged electrodes. We also present the changes in the quantitative results concerning the occurrence of different aging modes depending on whether pristine or aged half-cell OCP curves are used to reconstruct the full-cell OCP.In addition to this, we present an extended method for non-destructive degradation diagnostics that contains silicon-specific active material degradation as an additional aging mode. We analyze to which degree this method is capable of determining the loss of silicon-related capacity in the anode from full-cell OCP measurements.These results are relevant for both science and application as lithium-ion cells containing blended silicon-graphite as anode material are increasingly used due to their high specific capacity. Adapting the methods for aging diagnosis to this anode material is necessary to obtain valid results from experiments investigating the degradation of full-cells containing silicon-graphite anodes. Furthermore, expanding the existing models describing the aging-related change in full-cell OCP curves by considering changes in the shape of the half-cell OCP curves is a first step for the development of reliable algorithms for electrode-specific state of health estimation for cells containing silicon-graphite. Such algorithms could then be used on-board as part of the functionality of battery management systems.Figure 1: Reconstruction of the open circuit potential curve of a cycle aged full-cell based on both half-cell open circuit potential curves obtained from pristine and cycle aged electrodes Figure 1

Comparison of Electrochemical Behavior in a 3 % NaCl of Cast or Elaborated Electrochemically CuZn α and Αβ'

Brass is frequently use in connector applications due to its good formability, electrical and thermal conductivities, but it’s also exposed to aggressive environments with a high chloride contents [1]. Indeed, degradation of brass due to pitting corrosion in a solution containing chloride leads to structural failures and significant economic losses. While a great attention is paid to the determination of the corrosion parameters and the finding of different efficient inhibitors, only few studies have examined the relationship between crystal structures of brass substrates (alpha/alpha beta) and the related corrosion mechanisms, and consequently passive films evolutions. Moreover, it is only in recent studies that CuZn electroplating is reported to be possible, in efficient manner, in a range of 1 to 99 % of zinc content [1].In this context, the present work is devoted to investigating the behavior of α and αβ’ brasses, originated from foundry and obtained by electrodeposition, in a 3% NaCl solution [2]. This allow the comparison between both elaboration modes at different levels i.e. corrosion mechanisms and evolution of the protective layers. The same set of characterization was systematically applied. Firstly, anodic potentiometric and open circuit potential curves were recorded on the different samples to evaluate the electrochemical behavior of both alloys, and to determine characteristic potentials. Partial anodic oxidations were performed to allow precise detection of the evolution of crystallographic changes on the studied surfaces, comparatively to XRD diffractograms. The evolution of the morphology and of the surface conductivity was evaluated by AFM, at different anodization stages. Finally, microstructural evolution of different anodized samples was evaluated by SEM, and EDS analyzes. For both elaboration modes, microstructure organization in α or αβ’ induces the same kind of behavior irrespectively of the elaboration mode, and the presence of “plug in” in the case of cast alloys and the evolution of passive layers composition constitute the main differentiating factor.

Change in the half-cell open-circuit potential curves of silicon–graphite and nickel-rich lithium nickel manganese cobalt oxide during cycle aging

The relationship between the degree of lithiation and open-circuit potential (OCP) of the half-cells of lithium-ion batteries is mostly regarded to be invariant during battery aging. In electrical cell modeling, the OCP curve of aged half-cells is therefore usually obtained by linear scaling of OCP curves measured for pristine electrodes. In this study, the aging invariance of the shape of both half-cell OCP curves of a commercial NMC-811/silicon–graphite cell is investigated experimentally. Full-cells are cycled until different degradation levels are reached. Subsequently, several electrode samples are extracted and the OCP of both electrodes is measured using coin-cells containing electrode samples as working electrode and lithium metal foil as counter electrode. Changes in half-cell OCP are analyzed using differential voltage analysis and incremental capacity analysis. The OCP of the NMC-811 does not change with aging, while the OCP of silicon–graphite exhibits changes which are mainly due to a decrease in the relative capacity contribution of the silicon. The main consequence of our findings is, that changes in the shape of the OCP curve of silicon–graphite during cycle aging should be considered in electrical battery models which are used for full-cell aging diagnostics and state estimation algorithms in battery management systems.

Tribo-corrosion response of additively manufactured high-entropy alloy

High-entropy alloys (HEAs) with multiple principal elements represent a paradigm shift in structural alloy design and show excellent surface degradation resistance in corrosive environment. Here, the tribo-corrosion response of laser-engineered net-shaped CoCrFeMnNi HEA was evaluated in 3.5 wt% NaCl solution at room temperature. The additively manufactured (AM-ed) CoCrFeMnNi showed five times lower wear rate, regenerative passivation, and nobler corrosion potential during tribo-corrosion test compared to its arc-melted counterpart. A significant anisotropy was seen in the tribo-corrosion response with 45° to the build direction showing better performance compared to tests along the build direction and perpendicular to it. The open circuit potential curves were characterized by a sharp drop to more negative values as wear began, followed by continuous change for the active tribo-corrosion duration and finally a jump to nobler value at the end of the test indicating excellent surface re-passivation for the AM-ed alloy. The superior tribo-corrosion resistance of AM-ed CoCrFeMnNi was attributed to the refined microstructure and highly protective surface passivation layer promoted by the sub-grain cellular structure formed during additive manufacturing. These results highlight the potential of utilizing additive manufacturing of HEAs for use in extreme environments that require a combination of tribo-corrosion resistance, mechanical durability, extended service life, and net shaping with low dimensional tolerance.

Corrosion characterization of the experimental alloy Ti-35Nb-7Zr-5Ta by electrochemical techniques

The objective of the present study was to evaluate the corrosion resistance of the experimental alloy Ti-35Nb-7Zr-5Ta, modified by laser beam, in a physiological solution of 0.9% NaCl. This evaluation was carried out by open circuit potential analysis (EOCP), potentiodynamic polarization curves and cyclic polarization curves. The open circuit potential curves show the specimen irradiated by laser beam at 35 Hz presented a more stable and corrosion resistant surface. It was observed in the polarization curves, low current densities in the order of nA /cm2, for all specimen indicating an expected passive behavior for the investigated alloy. The cyclic polarization curves show that for specimen treated with laser, the potential for repassivation (Er) is greater in relation to the potential for corrosion (Ecorr), which indicates greater resistance to corrosion of metal alloys when treated with laser.

Predicting the Open Circuit Potential Curve for a Class of Ni-Rich Cathode Materials

Ni-rich cathodes are a class of materials for lithium-ion batteries (LIBs), which are currently gaining popularity in applications requiring high energy density, such as electric vehicles (EVs). Successful integration of these materials into EVs necessitates a fundamental understanding of their electrochemical properties, including the open circuit potential (OCP) curve. This study investigates the relationship between Ni stoichiometry and the OCP curve of two cathode families: Ni-rich NCAs and Ni-rich NCMs with a constant Mn content of 20%. First, it demonstrates how to predict the OCP curves of the materials within these two cathode families. Then, it applies the same methodology to determine the Ni content in a Ni-rich NCA cathode with an unknown chemical formula with similar accuracy as the inductively coupled plasma (ICP) technique. Our results suggest that the presented methodology can be further extended to additional cathode families and aid both in the prediction of their OCP curves and in validating the stoichiometry of newly synthesized materials.

New Method for Characterization of the Open Circuit Potential Curve for Battery Cathode Materials

Battery management system (BMS) is a key component of the battery for electric vehicles and portable electronics, as it guaranties reliable and safe operation of the battery, while ensuring its longevity and optimal performance. State-of-the-art BMS relies on an equivalent circuit model, while an important research topic is the development of BMS, which is based on an electrochemical model.[1] The main task of BMS is to accurately estimate the available energy and power of the battery by tracking its current state of charge (SOC). The open circuit voltage (OCV) of a cell is often used for estimation of the SOC of a battery. It depends on the open circuit potential (OCP) of the anode and the cathode materials, which give the potential associated with a certain amount of lithium stored in each structure. The accuracy of the OCP curves of each electrode material is critical for use with BMS based on electrochemical models, as in addition to tracking the bulk SOC of a battery, it also tracks the surface SOC.[1] As a result, BMS based on electrochemical models can offer improved prediction for both instantaneous and pulse power relative to systems based on an equivalent circuit model.In this contribution, we propose a novel method for characterization of the open circuit potential vs. state of lithiation (OCP) curves for active materials commonly used in lithium-ion batteries. Our method offers increased accuracy over existing electrochemical procedures [1-3]by providing a standardized mapping process from the measured gravimetric capacity to state of lithiation and improving characterization in the region of the curve that is close to the lithium content of 1. We demonstrate the strengths of the method on two different cathode materials: LiCoO2 and LiNi1/3Mn1/3Co1/3O2, which are widely used in commercial cells for portable electronics and electric vehicles. [2-3] 1. Chaturvedi, N. A., Klein, R., Christensen, J., Ahmed, J. & Kojic, A. Algorithms for Advanced battery-Management Systems. IEEE Control Syst. Mag. 49–68 (2010).2. Daniel, C., Mohanty, D., Li, J. & Wood, D. L. Cathode materials review. AIP Conf. Proc. 1597, 26–43 (2014).3. Cairns, E. J. & Albertus, P. Batteries for Electric and Hybrid-Electric Vehicles. Annu. Rev. Chem. Biomol. Eng. 1, 299–320 (2010).

Effect of porosity on mechanical and electrochemical properties of Ti–6Al–4V alloy

In this work, the effect of porosity on Ti–6Al–4V alloy was studied by using the Archimedes method, BET analysis, ultrasound method, micro-hardness, surface analysis, such as scanning electron microscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy, and electrochemical measurements, such as open circuit potential curves, electrochemical impedance spectroscopy and linear swept voltammetry. Apparent porosity of porous electrodes was close to 31% and 42%, which decreased significantly the elastic modulus. BET analysis revealed that the primary porosity for the porous electrodes was macro-porosity and that the micro- and meso-porosity was increased slightly by exposure. Surface analysis revealed the presence of α-phase and β-phase prior to exposure for bulk and porous electrodes. The impedance response for bulk and porous electrodes were completely different. For bulk electrodes, two time-constants were observed in high and low frequencies ranges, being associated with the formation of an oxide layer and the oxygen reduction reaction taking place at the electrolyte/oxide interface. Whereas the porous electrodes showed a De Levie behavior that was not influenced by porosity and exposure time. Anodic current was not modified by exposure.

Interrelationship Between the Open Circuit Potential Curves in a Class of Ni-Rich Cathode Materials

Ni-rich cathodes, such as nickel cobalt aluminum oxides (NCAs, LixNi0.80+0.15εCo0.15(1−ε)Al0.05O2, 0 ≤ ε ≤ 1), are a class of cathode materials for lithium-ion batteries (LIBs), which are among the leading candidates for battery electric vehicle (BEV) applications. In this study we focus on an important, fundamental electrochemical property, the open-circuit potential function (OCP, U vs x), and investigate its relationship with the Ni stoichiometry. First, we demonstrate that published differential capacity curves (dQ/dU vs U) for Ni-rich NCA materials can be derived as a stoichiometric linear combination of differential capacities of the two end members, LixNi0.8Co0.15Al0.05O2 and LixNi0.95Al0.05O2. Subsequently, the OCP curves are obtained by taking the inverse of the integrated dQ/dU vs U curves, which match literature OCP curves. Then, we apply the same method to determine the composition of an unknown cathode extracted from a commercially available LIB. Lastly, we show that the identified relationship also holds true for the LixNi0.60+0.20εCo0.20(1−ε)Mn0.20O2 family by demonstrating that the OCP curve of LixNi0.70Co0.10Mn0.20O2 can be predicted from a fractional combination of LixNi0.60Co0.20Mn0.20O2 and LixNi0.80Mn0.20O2. We anticipate that this methodology can be adapted to predict OCP curves for additional cathode families and used to validate the chemical composition of newly synthesized materials.

Effects of harmonic structure on the electrochemical behavior of biomedical Ti6Al4V

Metallic implants with Harmonic Structure has been reported to perform better mechanical properties compared to traditional microstructure on several biomedical alloys. Researchers have shown mechanic improvement when obtaining this microstructure but, there is a literature gap about the electrochemical behavior of these alloys related to harmonic microstructure obtainment. Thus, in this paper, the HS Ti6Al4V was obtained by Spark Plasma Sintering in order to be compared on its electrochemical behavior to commercial α + β Ti6Al4V ELI (Extra Low Interstitial), which is one of the most studied alloys for implants due to its biocompatibility and because of its good relation of the mechanical and electrochemical properties. Optical microscopy was conducted to verify the morphology and microstructure of the alloys, X-ray diffraction analyses to crystalline phase determination. For the electrochemical stability analysis, Open Circuit Potential curves were obtained in chloride media followed by voltammetry profile analysis on simulated blood solution, finally, the electrical parameters of the corrosion process were obtained using Electrochemical Impedance Spectroscopy. The results indicated that the materials presented a very similar electrochemical behavior with high polarization resistance, with almost no difference in the values of the curves, indicating there is no inference on the electrochemical behavior or corrosion resistance from the Ti6Al4V alloy with the harmonic structure.

Formation of Corrosion Resistant Hard Coating of Litao3 by Anodizing in Molten Lino3

Background: Lithium tantalate (LiTaO3) thin film was synthesized and in situ coated on tantalum substrate via anodic oxidation. Methods: The effects of temperature, voltage and time on composition, morphology and hardness of film were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Vickers hardness, respectively. Results: Our results showed that surface hardness of all coated samples has been increased compared with that of pure tantalum. The value of hardness was found to gradually increase with temperature, voltage and reaction time of the coating process. Selected specimens, after coating, were immersed into 10 wt% NaOH solution at 50oC for 96h to explore their anti-corrosion performance. Immersing results indicated that LiTaO3 coated samples have a smaller mass loss and corrosion rate compared to those of pure Ta substrate. Pure tantalum sample and those coated by LiTaO3 thin film were further examined by electrochemical methods including open-circuit potential (OCP), potentiodynamic polarization curves and electrochemical impedance spectra (EIS). Conclusion: We have found that samples coated with LiTaO3 thin film exhibit higher potentials and lower corrosion current densities than those of pure tantalum substrate, according to the results and analysis of OCP curves and potentiodynamic polarization curves. Upon anodic oxidation, samples display higher polarization resistance with higher resistance to corrosion.

Impedance Analysis of Ti-Based Porous Alloy

Ti-based alloys as porous materials with low elastic modulus has been recently developed due to the evident need to avoid the stress shielding problems related to stiffness mismatch related to human bone. In this work, Ti-30Nb-13Ta-2Mn alloy as porous material was obtained by powder metallurgy using (NH4)2(CO3) as space-holder. Powders and space-holder were mixed together and compacted with 400 MPa stress. (NH4)2(CO3) particles were removed from the compacts during sintering at 1250 °C for 3 h in Ar atmosphere. The porosity and active area of the porous electrode were estimated by using Archimedes methods and BET analysis. In addition, the surface analysis was carried out by SEM and XRD. Finally, electrochemical measurements such as open circuit potential curves, polarization curves and electrochemical impedance spectroscopy were carried out in a simulated blood plasma fluid called Ringer’s solution at 37 ºC. Results revealed foams with heterogeneous pore distribution in diameter as well as length. The electrochemical results showed that the corrosion potential was shifted to more negative values and the anodic and cathodic current were increased as a function of exposure time. On the other hand, impedance analysis displayed an impedance of the de Levie associated to the anodic response in parallel with an interfacial impedance attributed to cathodic response. Additionally, an evolution of the passive oxide layer as a function of exposure time was observed, which was mainly formed at the pore walls and, the cathodic reaction related to the oxygen reduction reaction took place mainly outside the pore. Reference E. Orazem and B. Tribollet, Electrochemical Impedance Spectroscopy, 2nd Edition, John Wiley & Sons, Inc. Hoboken, New Jersey (2017) 322-332.O.E. Barcia, E. D’Elia, I. Frateur, O.R. Mattos, N. Pébère, B. Tribollet, Application of the impedance model of de Levie for the characterization of porous electrodes, Electrochimica Acta 47 (2002) 2109-2126.

Corrosion behavior and mechanism of Mg-Y-Zn-Zr alloys with various Y/Zn mole ratios

Abstract The effect of Y/Zn mole ratio on microstructure, corrosion behavior, corrosion product and electrochemical behavior of MgY1.72Zn2.81Zr0.17, MgY3.83Zn3.03Zr0.17 and MgY2.58Zn1.27Zr0.15 alloys (at.%) are investigated. The weight loss and electrochemical tests all reveal that MgY2.58Zn1.27Zr0.15 alloy (at.%) has the best corrosion resistance among the three investigated alloys. The second phases in the three alloys transform from eutectic W-phase to continuous wide plate-like X-phase and further to compact plate-like X-phase with the increase of Y/Zn mole ratio. The type and distribution pattern of second phase play the key roles in determining the corrosion mechanism and rate. Eutectic W-phase leads to serious transgranular corrosion by forming many micro-pores. Compact plate-like X-phase acts as corrosion barrier and effectively protects the substrate from further corrosion. The porous, petal-like Mg(OH)2 corrosion product layer is hardly able to provide any protection to the substrate. Additionally, this hydroxide layer is unstable and easily to detach from the substrate due to the mechanical stress and hydrogen evolution. The open-circuit potential curves and the polarization curves are acquired through electrochemical test and the results have been discussed.

Effect of Nickel Content on the Corrosion Resistance of Iron-Nickel Alloys in Concentrated Hydrochloric Acid Pickling Solutions

The effect of Ni content on the resistance against corrosion of Fe-36% Ni and Fe-45% Ni alloys in 1 M hydrochloric acid pickling solution was reported. Various electrochemical and spectroscopic techniques such as potentiodynamic cyclic polarization (CPP), open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiostatic current-time (PCT), and scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) have been employed. CPP measurements indicated that the corrosion current and corrosion rate recorded lower values for the alloy that had higher nickel content. OCP curves proved that the presence of high Ni content shifts the absolute potential to the positive potential direction. EIS results revealed that the surface and polarization resistances were much higher for the alloy with higher Ni content. PCT curves also showed that the absolute currents were lower for Fe-45% Ni alloy. All results were in good agreement with others and confirmed clearly that the corrosion resistance in HCl solutions for Fe-45% Ni alloy was higher than that obtained for Fe-45% Ni alloy.