Change Of Open Circuit Potential Research Articles

In Situ Observation of Pitting Corrosion on AA1050 Under Open Circuit Conditions

Commercial purity aluminum alloys show high formability and high strength, and its application is expanded to infrastructure and battery materials. The aluminum alloys contain various types of intermetallic particles, and it is well known that the intermetallic particles have an important role in improving the mechanical properties. However, some of the particles can be a pit initiation site under corrosion environments. The intermetallic particles, such as Al5Fe2 and Al8Fe2Si, show higher electrode potential than that of the Al matrix. Therefore, these intermetallic particles work as a preferential cathodic reaction site. Due to the generation of the hydroxide ions by O2-reduction reaction, the pH around the intermetallic particles increases. The Al matrix is dissolved by the pH increase, and a trench is formed around the particles. Inside the trench, pH decreases due to the hydrolysis reactions of Al ions, and it triggers the initiation of a crystallographic pit.1) Although the role of the solution chemistry in pitting corrosion has been widely studied, the correlation between the initiation and propagation of pitting and the change in open circuit potential (OCP) is not well known. Because the pitting occurs at the small intermetallic particles, it requires specific technique to measure the OCP and observe the initiation of pitting at the same time. In this research, the pitting behavior under open circuit conditions was analyzed by in situ microscopic observation technique, and the correlation between the dissolution behavior and change in the OCP was elucidated.AA1050 was used as specimens. The intermetallic particles were characterized by an optical microscope and a field emission scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS). Two types of the intermetallic particles, Al-Fe and Al-Fe-Si, were confirmed to exist.Before the measurements, the specimen surface was mechanically ground with SiC paper to 4000-grid and polished with a diamond paste (15, 6, 1, and 0.25 µm). Ethanol was used as a lubricant to minimize any water exposure. After the polishing, the specimens were cleaned ultrasonically with ethanol and dried by N2 gas. To evaluate the macroscopic electrochemical behavior of the specimens, the electrode area of 1 mm × 1 mm was fabricated, and the OCP was measured in naturally aerated 0.1 M NaCl (pH 6.0) at 298 K. In this research, all potentials refer to the Ag/AgCl (3.33 M KCl) electrode. To analyze the correlation between the pitting corrosion behavior and the change in OCP, the electrode area of 500 µm × 500 µm, 300 µm × 300 µm, and 100 µm × 100 µm was fabricated and the OCP measurements were conducted. During the OCP measurements, whole electrode area was observed in situ using water immersion objective lens. After the measurements, the specimen surface was observed using an optical microscope and SEM-EDS.To analyze the corrosion behavior of AA1050, the OCP of the specimen with the electrode area of 1 mm × 1 mm was measured in 0.1 M NaCl for 1 ks. During the measurements, potential oscillations were observed. The initiation of pitting corrosion was confirmed, and the pit initiation site was found to be Al-Fe-Si particle. Neither trenching nor pitting was initiated around the Al-Fe particles. To confirm the smallest size of the electrode area containing a pit initiation site, the OCP measurements were conducted using the electrode areas of 500 µm × 500 µm, 300 µm × 300 µm, and 100 µm × 100 µm. During the measurements with 100 µm × 100 µm, no pitting was confirmed by in situ observation, and almost no oscillation of the OCP was generated. In the case of the measurements with the electrode area of 300 µm × 300 µm, one large pit and some small pits were initiated, suggesting that the distribution density of the initiation sites for pitting is ca. one site per 300 µm × 300 µm. During the measurements with the electrode area of 500 µm × 500 µm, many large pits were initiated. The size of the pits was larger than that observed in the electrode area of 300 µm × 300 µm. The OCP dropped at the moment of pit initiation. During the growth of pitting, the OCP remained at lower potentials. Finally, the stop of the pit growth and the increase in OCP were observed simultaneously. In this research, the microscopic measurements were conducted four times to confirm the reproducibility of the results.

Single-Entity Approach to Investigate Surface Charge Enhancement in Magnetoelectric Nanoparticles Induced by AC Magnetic Field Stimulation.

Magneto-electric nanoparticles (MENPs), composed of a piezoelectric shell and a ferromagnetic core, exhibited enhanced cell uptake and controlled drug release due to the enhanced localized electric field (surface charge/potential) and the generation of acoustics, respectively, upon applying alternating current (AC) magnetic (B)-field stimulation. This research, for the first time, implements an electrochemical single-entity approach to probe AC B-field induced strain mediated surface potential enhancement on MENP surface. The surface potential changes at the single-NP level can be probed by the open circuit potential changes of the floating carbon nanoelectrode (CNE) during the MENP-CNE collision events. The results confirmed that the AC B-field (60 Oe) stimulation caused localized surface potential enhancement of MENP. This observation is associated with the presence of a piezoelectric shell, whereas magnetic nanoparticles were found unaffected under identical stimulation.

Additively Manufactured Ti6Al4V-Si-Hydroxyapatite composites for articulating surfaces of load-bearing implants

Directed-energy deposition (DED)-based additive manufacturing (AM) was explored for composite development using silicon (Si) and hydroxyapatite (HA) in Ti-6Al-4 V (Ti64) matrix for articulating surfaces of load-bearing implants. Specifically, laser engineered net shaping (LENSTM) – a commercially available DED-based AM technique – was used to fabricate composites from premixed-feedstock powders. The AM’d composites proved to not only improve upon Ti64’s mechanical properties but also produced an in-situ Si-based tribofilm during tribological testing that minimized wear induced damage. Additionally, it was found that with the introduction of Si, titanium silicides and vanadium silicides were formed; allowing for 114% increased hardness, decreased coefficient of friction (COF) and a reduction of wear rate of 38.1% and 70.8%, respectively, for a 10 wt.% Si presence. The produced composites also displayed a positive shift in open-circuit potential (OCP) during linear wear, along with a reduction in the change of OCP from idle to linear wear conditions. Additionally, contact resistance (CR) values increased with a maximum value of 1500 ohms due to the formation of Si-based tribofilm on the wear surface. Such composite development approach using DED-based AM can open up the possibilities of innovating next-generation implants that are designed and manufactured via multi-material AM.

Permeability and Equivalent Circuit Model of Ionically Conductive Mortar Using Electrochemical Workstation.

Ionically conductive mortar is a new Portland cement-based construction material prepared by permeating electrolyte solution into porous mortar specimen. The conductive mechanism of ionically conductive mortar is the directional movement of internal free ions under external electric field. Because of the strong electrochemical properties of ionically conductive mortar, electrochemical workstation was used to test the performance of ionically conductive mortar. The open-circuit potential during the permeation process of ionically conductive mortar was tested. The results show that the change of open-circuit potential can effectively reflect the permeability rate of the samples with different porosity and electrolyte mass fraction. Besides the permeation of specimen, electrochemical workstation was also used to test the EIS (electrochemical impedance spectroscopy) of permeated specimens with different porosity, concentration of electrolyte solution, and different kinds of electrolyte solution. The quasi-Randles circuit model was then used to establish an equivalent circuit of ionically conductive mortar. Finally, the relation between parameter of circuit and the porosity or electrolyte solution was established. The test results show that solution resistance of the equivalent circuit and real resistivity of specimens is linearly correlated. This shows the equivalent circuit can effectively reflect the real resistivity of ionically conductive mortar, and the variation of electronic component parameters of equivalent circuit conforms to the conductive mechanism of ionically conductive mortar.

Nanoimpact Based Single-Entity Detection of Proteins using a Nanopore-Nanoelectrode Nanopipette

Nanopores and nanoelectrodes are two promising electrochemical methods for single entities analysis. Combining these two methods in one nanopipette apex allows us to simultaneously monitor the signal changes at nanopore and nanoelectrode when a biomolecule enters the nanopore or collides at the nanoelectrode. Here, I present a facile electrical method of detecting proteins at the single-molecule level in the solution based on the nanoimpact events at the nanoelectrode. Proteins such as Horse Spleen Ferritin, Bovine Hemoglobin, and Lysozyme are used to test the method. Open circuit potential (OCP) changes are detected from the nanoimpact events due to the collision of individual proteins at or near the vicinity of the floating nanoelectrode. Compared to the commonly used amperometric method, the detected OCP changes are more sensitive showing a bigger detection range and a higher time resolution. The new nanopipette based potentiometric method provides new opportunities to study various biological entities at a single-entity level with close to physiological conditions.

Differentiation of metallic and dielectric nanoparticles in solution by single-nanoparticle collision events at the nanoelectrode

In this work, we demonstrate a highly effective method to generate and detect single-nanoparticle (NP) collision events on a nanoelectrode in aqueous solutions. The nanoelectrode of a nanopore–nanoelectrode nanopipette is first employed to accumulate NPs in solution by dielectrophoresis (DEP). Instead of using amperometric methods, the continuous individual NP collision events on the nanoelectrode are sensitively detected by monitoring the open-circuit potential changes of the nanoelectrode. Metallic gold NPs (GNPs) and insulating polystyrene (PS) NPs with various sizes are used as the model NPs. Due to the higher conductivity and polarizability of GNPs, the collision motion of a GNP is different from that of a PS NP. The difference is distinct in the shape of the transient potential change and its first time derivative detected by the nanoelectrode. Therefore, the collision events by metallic and insulating NPs on a nanoelectrode can be differentiated based on their polarizability. DEP induced NP separation and cluster formation can also be probed in detail in the concentrated mixture of PS NPs and GNPs.

Natural organic antioxidants from green tea inhibit corrosion of steel reinforcing bars embedded in mortar

Natural antioxidants with multiple polar atoms and electron-rich bonds are potential mixed-type corrosion inhibitors and ‘green’ alternatives to commercial inorganic corrosion inhibitors. Green tea is one of the richest sources of natural antioxidants. Therefore, this paper compares the corrosion inhibition efficiency (IE) of green tea extract (GT) against commercial calcium nitrite corrosion inhibitor (CI), on steel reinforcing bars (rebars) embedded in mortar. Rebar corrosion was accelerated with impressed current and cyclic wetting-drying, and corrosion development was measured with linear polarization resistance. Selected CI dosages encompassed four chloride-to-nitrite ratios, and the IE of CI and GT were compared at: 1) similar concentration and 2) equal volume. At similar concentration, CI and GT demonstrated a similar IE (51–70%). However, at equal volume, GT exhibited a higher IE than CI (75–80% vs. 14–24%), due to a significant increase in rebar polarization resistance and reduction in iron oxidation rate (anodic slope). Meanwhile, oxygen reduction rate (cathodic slope) and open circuit potential did not change significantly. The changes in anodic and cathodic slope without a significant open circuit potential change suggested that GT was a mixed-type corrosion inhibitor as hypothesized, which formed a protective layer on rebar surface and increased the polarization resistance of the rebars. Based on liquid chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry analyses, it is hypothesized that (-)-epigallocatechin gallate, (-)-epicatechin gallate, and catechin or (-)-epicatechin are responsible for the anti-corrosion activity of GT as a mixed-type corrosion inhibitor.

Effect of sodium molybdate and sodium tungstate in concrete rebar corrosion

PurposeThis paper aims to identify an inhibitor to protect rebar corrosion in concrete.Design/methodology/approachThe authors use the simple method of polarization and calculate the change in open-circuit potential and corrosion current density.FindingsSodium molybdate is an efficient inhibitor compared with sodium tungstate for rebar corrosion in concrete.Research limitations/implicationsThis paper has limitation of 0.0001 M concentration of inhibitors for 400 days of exposure in 3.5 per cent sodium chloride solution.Originality/valueThe research focused on the concentration of both inhibitors in the range from 0.1 to 0.0001 M, which resulted in greater structural protection from corrosion in adverse conditions, such as coastal areas.

A 3rd generation Biosensor Towards the Continuous Long-Term Glucose Monitoring without Ag/AgCl Reference Electrode

Continuous glucose monitoring (CGM) is highly important, especially, for the diagnostics and control of Type I diabetes. [1] In recent years, automatic insulin pumps (artificial pancreas) are being applied and CGM is necessary for their operation. The insulin pump should deliver a correct dose of insulin based on real-time data about glucose levels in blood. Therefore, CGM sensors should be very selective and accurate, as well as reliable and stable. For this reason, CGM sensors are developed using selective enzymes – glucose oxidase or and FAD-dependent glucose dehydrogenase. [2] They usually operate by measuring either glucose oxidation current (amperometric biosensors) or potential (potentiometric biosensors). Historically, those biosensors are divided into three generations according to the electron acceptor: O2 dependent (1st), mediator depended (2nd) and direct electron transfer (3rd). The 3rd generation biosensors are the most attractive since they are most accurate, sensitive, operate at low potential and their response does not depend on the concentration of external mediator (either O2 or synthetic). However, to this date there are multiple unresolved problems which still hold the development of 3rd generation glucose biosensors for the CGM. Some of those problems include low stability (typically from a few hours to a few days) and miniaturization difficulties due to the usage of bulk reference electrodes for the control of the potential (Ag/AgCl, Hg/Hg2Cl2, etc.). Moreover, typical reference electrodes are poorly suited for long-time operation because they leak electrolyte and ions to the media. [3] A prolonged leakage of electrolyte solution changes the potential of reference electrode and may cause health risk if CGM biosensor in directly implanted in the patient. In this work, we present an open circuit potential (OCP) type 3rd generation glucose biosensor, which addresses the mentioned issues and operates in an electrolyte solution (pH 7.4) which mimics the composition of human serum. Our biosensor is composed of two electrodes: gold nanoparticle-glucose dehydrogenase (AuNPs-GDH) based bioanode and gold nanoparticles-laccase (AuNPs-LAC) based biocathode (Figure A). We have used AuNPs-LAC biocathode, which we have reported earlier [4], as a counter/reference electrode since its potential depends on oxygen reduction reaction. In the majority of solutions, O2 concentration is constant, thus it has a very stable OCP which is independent on glucose concentration and holds a constant value of 0.48 V vs.Ag/AgCl (Sat.) in an electrolyte solution. We have used AuNPs-GDH electrode as a working electrode since its OCP is dependent on glucose concentration raging from 10-6 M to 0.05 M. The OCP difference between two electrodes was -0.374 V and decreased depending on the concentration of glucose (10-6 M – 0.05 M) according to Nernst model (Figure B and C). The biosensor was calibrated in glucose range of 0.001 M to 0.01 M (typical glucose concentrations present in human blood) and a high correlation calibration curve was obtained (Figure D). Moreover, biosensor had showed an excellent stability and was able to operate at least for two weeks without a significant change in OCP. In conclusion, we have developed a promising biosensor for a constant long-term glucose monitoring which operates in an electrolyte solution, mimicking human serum conditions. A future challenge is to apply and optimize our biosensor to operate in serum and blood.

Interconnection of Open Circuit Potential in Blood Plasma with Oxidative Stress Parameters in Patients with Acute Poisoning

The problem of acute poisoning of chemical etiology is relevant due to the fact that their prevalence does not decrease and continues to lead in the statistics of morbidity and mortality [1]. The most prevalent are acute poisoning with drugs, narcotic substances, varied chemical organic and inorganic substances. A dangerous group is cauterizing agents, because this group is characterized by severe course of illness and frequent development of complications. It is important that the hospital lethality of this group of acute poisonings can reach up to 30%. Acute poisoning by cauterizing agents, as a rule, is accompanied by severe disturbances of the lipid peroxidation processes (LPO) and the antioxidant system (AOS), caused by damage of the digestive and respiratory tracts. The imbalance of the LPO/AOS system can also lead to the development of oxidative stress [2]. From the electrochemical point of view, the platinum electrode open circuit potential (OCP) in biological media is the integral indicator of the balance of the oxidation-reduction system of the organism. Therefore, the study of the diagnostic capabilities of this technique for assessing the condition of patients with acute poisoning by cauterizing agents seemed perspective. In addition, this study could help establish the relationship between the magnitude of the platinum electrode OCP and the oxidative stress coefficient. It was investigated 30 patients (25 male and 5 female) with acute poisoning by cauterizing agents. OCP measurements were performed in blood plasma according to the method [3]. The oxidative stress coefficient was determined as ratio of the level of malondialdehyde (MDA) in serum to the total antioxidant activity of serum (TAS). A comparative analysis of monitoring data on the magnitude of the platinum electrode OCP and the oxidative stress coefficient showed that the direction of the changes in these values was coincided (Fig. 1). On average, the changes of OCP value was about 26 mV, in some cases reaching extremely high values, for example, in the patient A the shift in the value of the OCP was 63 mV (Fig. 1a). Moreover, a sharp shift in the values OCP to positive potentials and beyond the region for apparently healthy people (-60÷-20 mV) is the evidence of the development of complications. This phenomenon make it possible to use the OCP changes during daily monitoring for diagnostics of the patient's condition and correction of its treatment. Thus, a relationship between the value of the platinum electrode OCP in blood plasma and the oxidative stress coefficient was established. OCP values in blood plasma in patients with acute poisoning by cauterizing agents can serve as an additional diagnostic criterion for assessing the severity of oxidative stress. Public health impact of chemicals: knowns and unknowns. World Health Organization: Geneva, 2016. Belova M.V., Ilyashenko K.K., Luzhnikov Y.A. // General Reanimatology. 2009; 5 (6): 40-4. Khubutiya M.Sh., Evseev A.K., Kolesnikov V.A. et al. // Russ. J. Electrochem. 2010; 46 (5): 537-41. Figure 1

Corrosion inhibition of green tea extract on steel reinforcing bar embedded in mortar

Polar atoms and π–electron bonds in molecular structures of natural antioxidants make the antioxidants potential mixed-type corrosion inhibitors and ‘green’ alternatives to commercial inorganic corrosion inhibitors. In this paper, the corrosion inhibition efficiency (IE) of green tea extract (GT), being one of the richest sources of natural antioxidants, was compared against commercial calcium nitrite corrosion inhibitor (CI) on steel reinforcing bars (rebars) embedded in mortar. Rebar corrosion was accelerated with impressed current and cyclic wetting-drying, and corrosion development was measured with linear polarization resistance. The IE of CI and GT were compared at same inhibitor volume. Results show that GT had a significantly higher IE than CI (75-80% vs. 14-24%), due to a reduction in iron oxidation rate (βa) and an increase in rebar resistance to polarization potential/current (Rp). Meanwhile, oxygen reduction rate (βc) and rebar open circuit potential (OCP) did not change significantly. The changes in βa and βc with an insignificant change in OCP suggest that GT was a mixed-type corrosion inhibitor, which formed a protective layer on rebar surface and increased Rp of the rebars.

Artificial lipid membrane: surface modification and effect in taste sensing

In this work, an artificial lipid membrane was synthesized using tetra-dodecyl ammonium bromide (TDAB) and doped with gold nanoparticles (AuNP). The taste sensor designed using artificial lipid membrane is composed of tetradodecylammonium bromide (TDAB) as a lipid, dioctylphenyl phosphonate (DOPP) as a plasticizer, and polyvinyl chloride (PVC) as a supporting polymer in the ratio of 1:3:2. The lipid/polymer membrane acts as the recognition element which transforms the taste information generated by the chemical substances into an electric potential change. The fundamental taste analytes (like fructose for sweetness, HCl for sourness, NaCl for saltiness, MgCl2 for bitterness and MSG for umami) were used to study the effect of doping on taste sensing at different concentrations (10μM to 10mM). The study was based on the open circuit potential (OCP) change of the membrane with the analytes. The observations implicate that the doping increases the specificity of the artificially synthesized lipid membrane taste sensor for the sweet analytes, particularly for fructose.

A single particle model with chemical/mechanical degradation physics for lithium ion battery State of Health (SOH) estimation

State of Health (SOH) estimation of lithium ion batteries is critical for Battery Management Systems (BMSs) in Electric Vehicles (EVs). Many estimation techniques utilize a battery model; however, the model must have high accuracy and high computational efficiency. Conventional electrochemical full-order models can accurately capture battery states, but they are too complex and computationally expensive to be used in a BMS. A Single Particle (SP) model is a good alternative that addresses this issue; however, existing SP models do not consider degradation physics. In this work, an SP-based degradation model is developed by including Solid Electrolyte Interface (SEI) layer formation, coupled with crack propagation due to the stress generated by the volume expansion of the particles in the active materials. A model of lithium ion loss from SEI layer formation is integrated with an advanced SP model that includes electrolytic physics. This low-order model quickly predicts capacity fade and voltage profile changes as a function of cycle number and temperature with high accuracy, allowing for the use of online estimation techniques. Lithium ion loss due to SEI layer formation, increase in battery resistance, and changes in the electrodes' open circuit potential operating windows are examined to account for capacity fade and power loss. In addition to the low-order implementation to facilitate on-line estimation, the model proposed in this paper provides quantitative information regarding SEI layer formation and crack propagation, as well as the resulting battery capacity fade and power dissipation, which are essential for SOH estimation in a BMS.

Corrosion Fatigue Studies on a Bulk Glassy Zr-Based Alloy under Three-Point Bending

Corrosion fatigue (CF) tests were carried out on bulk glassy Zr52.5Cu17.9Al10Ni14.6Ti5 (Vitreloy 105) samples under load-controlled three-point bending conditions with a load ratio of R = 0.1 in 0.01 M Na2SO4 + 0.01 M NaCl electrolyte. During cyclic testing, the bar-shaped specimens were polarized in situ at constant potentials and the current was monitored. Three different anodic potentials within the interval between the pitting potential EP and the repassivation potential ER, and three different load amplitudes were applied. In some cases, in situ microscopic observations revealed the formation of black corrosion products in the vicinity of the crack tip during anodic polarization. Fractographic analysis revealed a clear distinction between two modes of crack growth characterized by smooth dissolution induced regions on the one hand and slim fast fracture areas on the other hand. Both alternating features contributed to a broad striated corrosion fatigue fracture surface. Moreover, further fatigue tests were carried out under free corrosion conditions yielding additional information on crack initiation and crack propagation period by means of the open circuit potential (OCP) changes. Thereby, a slight increase in OCP was detected after rupture of the passive layer due to bare metal exposed to the electrolyte. The electrochemical response increased continuously according to stable crack propagation until fracture occurred. Finally, the fracture surfaces of the corrosion fatigue samples were investigated by energy dispersive X-ray with the objective of analyzing the elemental distribution after anodic dissolution. Interestingly, anodic polarization at a near repassivation potential of -50 mV vs. SCE (Saturated Calomel Electrode, E = 0.241 V vs. SHE, Standard Hydrogen Electrode) led to favorable effects on the fatigue lifetime. In conclusion, all results are conflated to a corrosion fatigue model for bulk glassy Vitreloy 105 under anodic polarization in chloride-containing electrolyte and compared to the previously proposed stress corrosion mechanisms under similar conditions.

Corrosion Resistance of Zinc-Rich Metallic Coatings on Aluminum

Thin walled aluminum heat exchanger tubes, with solid-solution Zn-rich surface are widely used by the automotive industry and considered by the HVAC&R (Heat, Ventilation, Air Conditioning and Refrigeration) market for improved corrosion resistance against pitting. It is well known that alloying Al with Zn causes decrease in the corrosion potential in chloride solution.1 Thus, Zn-rich coating can provide cathodic protection to the aluminum substrate, in particular prevent pitting corrosion. However, corrosion rate of Zn itself is quite high in chloride solution.2 This work investigates the extent to which the self-corrosion of the Zn-rich layer can be a limiting factor in determining the service life time of the heat exchanger tubes. Zinc was applied on AlMn alloy extruded tubes by thermal arc spraying immediately after extrusion. Typical Zn load on the surface was 0.8 ± 0.2 mg/cm2. The tubes were subsequently subjected to heat treatment at various temperatures (350 - 430°C) and durations to obtain solid-state AlZn alloy diffusion layer with varying thickness and Zn-concentration profiles at the surface of the AlMn substrate. The Zn depth profiles were characterized by glow discharge optical emission spectroscopy (GD-OES). Corrosion rate was determined by weight loss resulting from immersion for predetermined times in acidified artificial sea water solution of pH 3 at 25°C for slight acceleration of the corrosion rate, during which the open circuit potential change was recorded with respect to time. The morphology and composition of the Zn-rich layer before and after corrosion were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).The Zn concentration distribution in the layer could be modeled by the solution to Fick's 2nd law with appropriate boundary conditions, giving an effective diffusion coefficient for Zn in the Al substrate of order 10-10 cm2/s in the temperature range of interest, varying according to the Arrhenius law with respect to temperature. Zn-rich layer thickness obtained on the samples heat treated at selected conditions varied approximately in the range 35 to 80 µm with increasing heat treatment temperature and time, corresponding to Zn surface concentrations of 28 to 7 wt%, respectively. Reduction in thickness due to corrosion, calculated from the weight loss measurements by taking into consideration the density depth-profile of Zn, which was obtained from the GD-OES data, increased with increasing thickness of the Zn-rich layer. Unexpectedly, decreasing Zn concentration level in the layer did not have a significant effect on the corrosion rate, unless it was lower than a threshold of a few wt%, which appeared to be sufficient to give the necessary protection. The results confirmed also that Zn gave satisfactory protection against pitting corrosion. Corrosion potential of samples as coated with Zn (no heat treatment) reached the pitting potential of the AlMn substrate in about 4 days. After 11 days of immersion, corrosion potential of the samples heat treated at 350°C for 2 hours increased up to about 30 mV below the pitting potential of the substrate, while the corrosion potential of the samples heat treated at 430°C for 4 hours remained about 120 mV lower than the pitting potential of the substrate. The reduction in thickness after 11 days of immersion for those heat treatment conditions was 23 µm and 54 µm, respectively. These results indicate that optimal Zn concentration and Zn-rich layer thickness, in terms of service life and loss of thickness, lie at levels much lower than those used in this study. The optimal concentration needs to maintain the corrosion potential at a level lower than the critical pitting potential. At the same time, the Zn concentration level in the layer has to be low enough to restrict the rate of self-corrosion, such that the layer thickness can also be reduced to give sufficiently long service life time. The well-known relationship between the corrosion potential of AlZn alloys and Zn concentration1 was extended over a wide concentration range and related further to the corrosion rate in acidified synthetic seawater. The database thus developed is useful for optimizing the Zn-rich layer thickness and Zn concentration profile in the layer to minimize uniform corrosion, and therefore maximize service lifetime, without reducing the protection against pitting.

Open Circuit Potential Changes upon Protonation/Deprotonation of ω‐Functionalized Alkanethiols on Au: Determination of Surface pK1/2 in Aqueous and Non‐Aqueous System

Open Circuit Potential Changes upon Protonation/Deprotonation of ω‐Functionalized Alkanethiols on Au: Determination of Surface p<i>K</i>_1/2 in Aqueous and Non‐Aqueous System

Sinusoidal current and stress evolutions in lithium-ion batteries

Abstract Mechanical breakdown of graphite materials due to diffusion-induced stress (DIS) is a key aging mechanism of lithium-ion batteries. In this work, electrochemical-thermal coupled model along with a DIS model is developed to study the DIS distribution across the anode thickness. Special attention is paid to the evolution behavior of surface tangential stress (STS) in the discharge process for graphite at different locations of the anode. For the first time, we report that the evolution of STS, as well as local current, at all locations of the anode, evolve like sinusoidal waves in the discharge process with several crests and troughs. The staging behavior of graphite active material, in particular the sharp change of open-circuit potential (OCP) of graphite in the region between two plateaus, is found to be the root cause for the sinusoidal patterns of current and stress evolution. Furthermore, the effects of various parameters, such as starting state of charge, discharge C-rate and electrode thickness on the current and stress evolutions are investigated.

Application of Polytyramine Nanoparticles to the Corrosion Protection of Copper

AbstractElectrochemical polymerization of tyramine was achieved on copper electrode surface from tyramine in 0.3 M oxalic acid (pH=1.2) solution by using cyclic voltammetry technique. The formation of polytyramine nanoparicles (PTN) were characterized by cyclic voltammetry (CV), fourier transform infrared‐attenuated total reflectance (FTIR‐ATR) spectroscopy and scanning electron microscopy (SEM). The corrosion behavior of PTN coated copper was investigated by means of the change of open circuit potential with exposure time (Eocpt), electrochemical impedance spectroscopy (EIS) and anodic polarization curves in 3.5 % NaCl solutions at room temperature. The obtained results showed the shift of corrosion potential toward positive values for electropolymerized copper and a significant decrease in corrosion current and corrosion rate in comparison with bare copper, so that the PTNs coating could be used as an important protection against corrosion of copper.

Thin Oxide Film Reduction Via the Polyol Method: An Electrochemical Study of a Polyol Reduction Process

Polyols are non-aqueous hydrogen bonded liquids, analogous to alcohols, which have the ability to dissolve both organic and inorganic solids. Polyol synthesis [1] has been widely employed for the preparation of metallic nanoparticles using the temperature-dependent reducing ability of polyols in the presence/absence of capping agents, such as polyvinylpyrrolidone (PVP). In a typical polyol synthesis process, ethylene glycol (EG) is used as a solvent to dissolve metal precursors and as a mild reducing agent. By heating the mixture, the reducing power of the EG increases and ultimately reduces the metal precursors, forming metal nanoparticles with narrow-size distribution. In a modified-polyol method [2], an external reducing agent that is stronger than EG is used. This is usually practiced when the metal precursor can’t be reduced by the ethylene glycol alone. In a polyol or a modified polyol method, the metal precursor can be oxides, hydroxides, nitrates, and acetates that are either dissolved or suspended in the solvent. In case of oxide or hydroxide precursors, they have to be at least slightly soluble in EG at high temperature, otherwise, the addition of an acid is needed. In the work we are presenting here, we are investigating the possibility of using a (modified-)polyol method to reduce thin oxide films of solid surfaces and surface oxide of bulk oxide materials. We investigated the reduction of Sn oxide thin film [3] on a Sn metal substrate as well as the surface reduction of Sn oxide particles to produce meta-stable SnO2@Sn particles that spontaneously form stable SnO2@SnO particles once in contact with air. The reduction of the Sn oxide thin film on a Sn metal substrate was indicated by the sudden change in the Sn electrode potential when measured vs. a reference electrode (Ag/AgCl). Fig. 1 shows a typical OCP (open circuit potential) measured during heating and cooling cycles of hydrazine-containing ethylene glycol. The sudden change of the OCP at ~110°C is attributed to the reduction of the Sn oxide film as the interface changes from SnO2/EG to Sn/EG. More details about the origin of this OCP change will be provided in the presentation with the help of information obtained from quartz crystal microbalance (QCM) and/or impedance spectroscopy (EIS). The surface reduction of bulk Sn oxide in the form of SnO2 particles (50-100 nm) was also investigated. It was found that NaBH4 can reduce the surface oxide resulting in surface SnO. Raman spectroscopy showed that a very small amount of SnO was formed, which is reasonable if it was a surface oxide. Auger and XPS analyses did not show any SnO formation on the surface. The two pieces of information together suggest that SnO has formed on top of the SnO2, but due to the exposure to the atmosphere, the SnO on the top surface oxidized to SnO2 and therefore protected the remaining SnO underneath it and so it was detectable by the Raman and only SnO2 was found on the outermost surface. Further details and supporting results about the oxide reduction in both cases will be provided in the presentation. Acknowledgements The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2013-2016) for the Fuel Cell and Hydrogen Joint Technology Initiative under grant agreement CATAPULT n°.325268. Special thanks to Sebastian Schwaminger for the assistance with XPS and Raman analyses, Katia Rodewald for the superb SEM pictures and analyses and Marianne Hanzlik for the TEM analysis.

Tungsten oxide electrode for measurement of ultralow liquid flow velocity

This study demonstrated the application of a tungsten oxide electrode to the measurement of ultralow liquid flow velocity based on streaming potential, using a pH glass electrode and temperature sensor to compensate for changes in open circuit potential induced by pH and temperature, respectively. A change in flow velocity on the surface of the tungsten oxide electrode caused the expected shift in its open circuit potential. Experimental results showed that the open circuit potential was linear relative to the logarithmic flow velocity, and the flow sensor exhibited excellent reproducibility and a large dynamic range, with the ratio between measurable maximum and minimum flow velocity surpassing 60:1. Moreover, a higher sensitivity was observed in the alkaline solution relative to the acidic solution, indicating that the alkaline solution is more suitable for this type of measurement. In conclusion, the tungsten oxide flow sensor provides a cheap, simple, adaptable, and energy-saving solution for the measurement of ultralow liquid flow velocity.