Open Circuit Potential Values Research Articles

Electron Transport Between an Electrode and Red Blood Cells

It is well known that red blood cell (RBC) membranes are charged negatively and surrounded by an electric double layer (EDL). The electrochemical nature of blood cell interaction with foreign materials that are electrical conductors is due to the interaction of blood cell EDL with the foreign material. Numerous investigations of the above systems have led to a hypothesis of charge transfer occurring between the cell and the electrode [1]; however, there has been no experimental corroboration of this phenomenon to date. The present work attempted to bridge this gap by investigating the electrochemical behavior in the Pt/RBC system in isotonic (physiologic) saline solution (aqueous 0.15 M NaCl), where the above solution served as the background electrolyte. Erythrocyte suspension for experiments was prepared from donor whole blood by centrifugation using a CR 3.12 (Jouan, France) centrifuge at 4-6 °C and 1500 g. The erythrocytes were subsequently washed with isotonic physiologic saline to remove residual blood plasma. Erythrocyte counts in suspensions were measured using a Beckman Coulter AcT Diff 2 hematology analyzer. Erythrocyte counts in suspensions used in the electrochemical cell were 4.0×1012 L–1. Polarization and microcoulometric measurements were performed with an IPC Pro L potentiostat (ZAO «Kronas») in a three-electrode electrochemical cell, with the cathodic and anodic chambers separated by a polypropylene porous membrane. A platinum microelectrode and platinum wire mesh were used as the working and counter electrode, respectively. Potentials were measured against a saturated silver/silver chloride reference electrode. For microcoulometric measurements, the electrochemical cell was filled with the above background electrolyte, and the platinum electrode was polarized to a set potential for 30 min; subsequently, the erythrocyte suspension was added to the background electrolyte, and microcoulometric data were recorded for 30 min. Oxygen was removed from the background electrolyte by the addition of Na2SO3 to a final sulfite concentration of 0.02 M in the electrochemical cell. The residual quantity of Na2SO3 was monitored in the cell via the sulfite/sulfate anode oxidation peak. A considerable difference in the charge Q was found to be required to maintain the same cathode potential of Pt electrode in the background electrolyte and in the background electrolyte containing the RBC suspension, with the difference between those measured values (ΔQ= Q saline – Q saline+RBC) varying depending on the working electrode potential (Fig. 1(a)). It turned out that a similar phenomenon occurs in the anodic range (Fig. 1(a)). Thus, electrochemical activity of erythrocytes in isotonic saline was shown at the platinum electrode for cathode potentials more negative than E = –150 mV, and for anode potentials more positive than E= +200 mV. This observation is very important because it provides the first experimental corroboration of electron transport between the electrode and erythrocytes. It should also be emphasized that electrochemical processes were not observed between –150 mV and +200 mV (no changes of charge Q), which indicates relative indifference of the electrode material with respect to the erythrocytes. Additionally, electron transport without polarization was observed on the Pt electrode. It was observed that open-circuit potential (OCP) values of Pt in isotonic saline changed with the addition of RBC suspension to saline. These data for the Pt electrode are shown in Fig. 1(b). Negative shifts of OCP for Pt electrode were observed after a addition of RBC suspension to saline with ∆E= 106 mV. This phenomenon can be rationalized by the leveling of charge densities of erythrocyte membranes and electrode surface in the electrostatic field of the [electrode/erythrocyte] system. Thus, electron transport occurred from the erythrocyte membrane to the electrode. Reference [1] Sawyer P. N. et al. Electrochemical Aspects of Thrombogenesis-Bioelectrochemistry Old and New // Journal of The Electrochemical Society. – 1974. – V. 121. – №. 7. – P. 221C-234C. Figure 1

Passive Film Properties and Electrochemical Behavior of Co-Cr-Mo Stainless Steel in Chloride Solution

The electrochemical behavior and passive film properties of Co-Cr-Mo ultrahigh-strength stainless steel in neutral and acidic chloride solution were evaluated by potentiodynamic polarization curves, electrochemical impedance spectroscopy and x-ray photoelectron spectroscopy. The results indicate that the steel exhibited good passivation behavior in neutral NaCl solution. Both the film formation potential and the applied potential time showed great effects on the open-circuit potential value and stability of the passive film. Furthermore, the oxides and hydroxides of Fe, Co, Mo and Cr were the primary components of the passive film, and the composition of the passive film was changed with a change of pH environment.

Corrosion protection of AISI 1018 steel using Co-doped TiO2/polypyrrole nanocomposites in 3.5% NaCl solution

A polypyrrole nanocomposites (PPy NTCs) have been effectively synthesized in the presence of TiO2 and Co-doped TiO2 nanoparticles (NPs) by an in situ chemical oxidative polymerization. Field Emission Scanning Electron Microscopy and Transmission Electron Microscopy revealed a tube shape structure of the PPy. The TEM results confirmed that the nanocomposite size of Co-doped TiO2/PPy NTCs was smaller than TiO2/PPy NTCs thereby increasing the interaction between the PPy nanotube and the AISI steel surface. The corrosion performance of the coatings was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements in 3.5% NaCl solution. The EIS results show that the log |Z| of AISI 1018 coated with Co-doped TiO2/PPy NTCs and TiO2/PPy NTCs reached about 8.2 and 6.0 respectively after 30 days of exposure in 3.5% NaCl solution. This is likely due to the increased surface area of the PPy synthesized in the presence of Co-doped TiO2 NPs. The EIS results are confirmed by the potentiodynamic polarization and open circuit potential values of the Co-doped TiO2/PPy which indicated little changes between 1 and 30 days of exposure which confirms the protection ability of this coating. . It is evident that the presence of Co-doped TiO2 NPs can enhance the resistance against corrosion at the steel/electrolyte interface.

Effects of Hydrogen on Corrosion Products Formed on Iron in Chloride Solutions

The effects of charged-hydrogen on the properties of the surface films formed on iron after 21 h immersion in pure water and 10-4 to 0.5 mol/L NaCl solutions at 25 °C are investigated by open circuit potential (OCP) measurements, optical microscope, Raman spectroscopy and X-ray diffraction (XRD). Hydrogen-charging favors the formation of with dark film with yellow corrosion sites on iron. After immersion in 10-4 mol/L NaCl solution, the non-charged iron is partly covered by surface film, while the hydrogen-charged iron is fully covered by surface film. After immersion in 0.5 mol/L NaCl solution, the surface of the non-charged iron is partly dark and partly covered with yellow rusts, and the surface of the hydrogen-charged iron has a larger area covered with yellow rusts than that on the non-charged iron. OCP values for hydrogen-charged iron in pure water, 10-3 and 10-4 mol/L NaCl solutions are lower than those for non-charged iron. In 0.5 mol/L NaCl solution, the OCP difference between non-charged iron and hydrogen-charged iron is at first large and gradually becomes smaller with increasing immersion time. Raman spectra and XRD patterns show the presence of magnetite in the film on hydrogen-charged iron after immersion in 10-4 mol/L NaCl solution. In solutions with a high chloride concentration, hydrogen in iron can promote the formation of high valence iron oxide layer by precipitation.

Microstructural and electrochemical characterization of Ni-based bi-layer coatings produced by the HVAF process

Bi-layer coating systems comprising a Cr3C2-NiCr coating with different underlying coatings of Ni, NiCr, NiCoCrAlY, and CoNiCrAlY were deposited on 304L stainless steel substrates using the high-velocity air fuel (HVAF) process. The corrosion behavior of the coating systems was studied using electrochemical and immersion tests in 3.5 wt% NaCl at 25 °C. The higher open-circuit potential (OCP) value of the NiCoCrAlY coating (− 120 mV/SCE) compared to the value of the Cr3C2-NiCr coating (− 230 mV/SCE) revealed that the underlying NiCoCrAlY coating was sacrificially protected by Cr3C2-NiCr coating. The polarization resistance (Rp) of the bi-layer coatings with the different underlying coatings of Ni, NiCr, NiCoCrAlY and CoNiCrAlY was approximately 77, 189, 487, and 74 kΩ·cm2 respectively, while the value was 101 kΩ·cm2 for the single-layer Cr3C2-NiCr coating and 30 kΩ·cm2 for the 304L substrate, which confirmed a higher corrosion protection of the NiCoCrAlY coating. The electrochemical impedance spectroscopy (EIS) results showed that the corrosion resistance of the 304L substrate was significantly improved by adding an intermediate layer of NiCoCrAlY to the Cr3C2-NiCr coating. Results of the immersion tests confirmed that the underlying coatings in the different bi-layer coating systems acted as protective barriers. Moreover, the NiCoCrAlY coating showed the best corrosion protection among the investigated underlying coatings.

Laser fabrication of W-reinforced Cu layers: I. Corrosion behavior in 3.5% NaCl solution and synthetic acid rain

Surface modification of commercially pure copper (cp Cu) with W powder was achieved by using a high power diode laser (HPDL) resulting in a microstructure of micron-sized W particles in a Cu matrix. In both 3.5 wt% NaCl solution and synthetic acid rain (SAR), the laser-fabricated specimens possess lower corrosion current density (Icorr) than that of cp Cu despite the active shift in open-circuit potential (OCP). Although Cu is cathodic to W in 3.5 wt% NaCl solution, the Cu phase in the laser-fabricated specimens dominantly dissolves during the immersion test. This anomalous observation is possible because the OCP values of the laser-fabricated specimens, cp Cu and cp W are quite near to each other, while the anodic and cathodic current densities are all not negligible for the Cu and W phases at OCP. As the anodic current density of the Cu phase is greater than anodic current density of the W phase, the Cu phase corrodes more quickly than the W phase. For the laser-fabricated specimens immersed in SAR, the Cu phase is anodic and is selectively attacked while the W phase is passive due to the formation of WO3.

Analysis of Li Dendrite Formation on Graphite Anode Based on Realistic Electrode Microstructure Using Numerical Simulation

Li dendrite formation on graphite anode electrode of Li ion batteries (LIBs) during fast charging processes is one of the significant safety concerns in the application of electric vehicles. Catastrophic failures due to thermal runaway could be triggered by the short circuit due to Li dendrite. In order to understand the mechanism and suppress the dendrite formation, lots of research has been focused on the experimental analysis [1, 2] and nucleation and growth of Li electrodeposit [3]. In addition to the electrode and electrolyte materials, the microstructure inside anode electrode also plays a critical role in determining the dendrite formation because the anode microstructure forms the boundary condition for the Li dendrite formation reaction and other physical and electrochemical processes. Therefore, it is necessary to study the effect of heterogeneous microstructure on the Li dendrite formation during charging process. This study is to investigate Li dendrite formation according to the electrochemical reaction potential at the interface between the anode active material and electrolyte based on realistic 3D anode electrode microstructures. An Xradia microXCT-400 system (Xradia, Pleasanton, CA) was employed to obtain the computed tomography (CT) images of the anode electrodes. A total of 729 projection images were captured over 182 degrees scan angle. The spatial resolution of the CT had been set as 0.56 μm. A C++ code was developed to rebuild and mesh the realistic microstructure of anode electrode through Micro-CT scanned images. The half-cell LIB model was composed of electrolyte, anode active materials and current collector. By employing 3D finite volume method, another C++ code was developed to simulate the charge processes by solving coupled model equations of charge conservation, mass conservation and electrochemical reaction. The simulation revealed the distribution of physical and electrochemical variables in the electrode such as concentration, voltage, current density, electrochemical reaction rate, overpotential, open circuit potential (OCP) et al. The value of overpotential plus OCP is critical for Li dendrite formation. If the value is lower than zero, Li deposits and then dendrite starts to form. The simulation results revealed that Li dendrite formation doesn’t take place simultaneously and uniformly at the surface of anode active material particles during fast charging processes. The knowledge from the study will help to understand the mechanism of Li dendrite formation in a realistic anode electrode and suppress it in LIBs, which could be useful to improve LIB design and manufacturing. Acknowledgments: This work was supported by US National Science Foundation under Grant No. 1335850.

Electrochemical Investigation of the Effects of Acid Concentration and Dissolved Oxygen on the Corrosion Behavior of Austenitic Low-Nickel Stainless Steels in Citric Acid

All materials which are intended to have in contact with food and other commodities produced or processed for human consumption are called food contact materials (FCM’s). Stainless steel (SS) – a widely known metallic FCM is used mainly in processing equipment, containers and household utensils. It is known for having numerous industrial and domestic applications worldwide due to its special characteristics of having notable corrosion resistance. However, this corrosion resistance is not all-encompassing since SS may still undergo degradation when subjected to a specific corrosion-inducing environment. SS may be classified according to its microstructure. If the atoms which make up the SS can be viewed as having a face-centered cubic structure, then the alloy is said to be austenitic. This SS grades include the conventional 300-series and the newly-developed 200-series. The former has superior corrosion resistance while the latter is far cheaper. In this study, the corrosion behavior of AISI 202 SS in two different levels of dissolved oxygen (O2) and three acid concentrations was investigated using electrochemical techniques, namely, open-circuit potential (OCP) measurements and electrochemical impedance spectroscopy (EIS). As the concentration of citric acid is increased, the measured OCP values of the alloy decreased and the polarization resistance (Rp) decreased, indicating decrease in alloy stability and decline in the corrosion resistance, respectively. With regards to effects of dissolved O2, results revealed that increasing the level of dissolved O2 has consequently increased the polarization resistance and shifted the OCP to more positive values. All the generated Nyquist plots exhibited a depressed capacitive loops indicating that corrosion in the designated solution occurred with charge transfer as the rate-determining step.

Comparative Study of the Corrosion Behavior of Low-Nickel AISI 202 and Conventional AISI 304 Stainless Steels in Citric Acid Using Electrochemical Techniques

Stainless steel (SS) is one of the most commonly used metallic food contact materials. It may be classified based on its microstructure whether ferritic, austenitic, martensitic, duplex or precipitation hardened. Austenitic SS, among mentioned grades, has the largest contribution to market due to its numerous industrial and domestic applications. In this study, the corrosion behavior of AISI 202 SS – a cheaper grade of stainless steel, in three different solution temperatures of citric acid was investigated using different electrochemical techniques such as open-circuit potential (OCP) measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results were compared to that obtained from conventional AISI 304 SS. OCP, polarization and impedance measurements agreed that AISI 202 SS has comparable resistance to that of AISI 304 SS in citric acid at ambient temperature and at 50 °C. At 70 °C, results of OCP measurements suggest that AISI 304 SS exhibited greater performance as indicated by more positive OCP values in the designated solution. EIS results indicate that the two alloys have identical corrosion resistance even at 70 °C as indicated by their comparable polarization resistance (Rp). The corrosion mechanism in both alloys is charge-transfer controlled as indicated by depressed semi-circular appearance of the generated Nyquist plots. The values of corrosion current densities (icorr) extracted from polarization curves indicate that the initial corrosion rates were higher in AISI 304 than AISI 202 SS suggesting that formation of more protective film may have occurred on the former alloy.

Electrochemical Behaviors of Various Alloys in Ferric Sulfate Solution

A508III low alloy steels (LAS) are often used as reactor pressure vessel materials in nuclear power plants. LAS could be exposed to primary water of nuclear power plants when stainless steel or Ni-based alloy corrosion resistant layers failed or as a result of small leaks in flanged joints valves, fittings, etc. Primary water contains boric acid and lithium hydroxide. Under leaking conditions, the primary water could be concentrated due to evaporation and become aerated as the results of contacting with the environment, producing varying degrees of external corrosion. There could be corrosion product such as rust or ferric ions at the leaking sites. Previous work has conformed that the corrosion rates of A508III steel increased dramatically when ferric sulfate was added in boric acid solution. While in the ferric sulfate solution, adding boric acid had no significant effect on the electrochemical behavior and corrosion rates, suggesting that ferric ions promoted the subsequent corrosion process. A508III LAS contains about ~97 wt.% Fe, with Cr, Ni, Mn and other elements added to improve the corrosion resistance, mechanical properties and processing performance, etc. The present work investigated the electrochemical behavior of various alloys and their main alloying elements in 0.05 mol/L Fe2(SO4)3 solution at 25 oC. Pure iron, Cr, Ni, A508III LAS, 430 steel, 316L steel, and Alloy 690 were used as working electrodes. Open circuit potential (OCP), electrochemical impedance spectroscopy and anodic polarization curve were measured. OCP values of A508III steel and iron in 0.05 mol/L Fe2(SO4)3 solution were lower than -0.52 V(SCE). The OCP of A508III steel is a little higher than that of iron. OCP values of the other materials were stable at relatively higher values that range from 0.37 V(SCE) to 0.56 V(SCE), and the ascending order was that 316L steel, 430 steel, Cr, Alloy 690, and Ni. The anodic polarization curves for various materials in 0.05 mol/L Fe2(SO4)3 solution are shown in Figure 1. Anodic polarization curves for A508III and iron were nearly the same, and neither current peak nor dissolution/passivation transition could be observed. Active-passivation transition appeared and single current peak were observed on the curves for 316L and 430 steel. The anodic polarization curves for Cr, 690 alloy and Ni showed different trends at different potential ranges. The EIS Nyquist plots of various materials in 0.05 mol/L Fe2(SO4)3 solution are shown in Figure 2. The Nyquist plots of A508III steel and iron exhibited two capacitive loops at higher and intermediate frequencies, and one inductive loop at low frequencies. The second capacitive loop was smaller than the first which suggest that the protectiveness of surface film is not good. The second capacitive loop of iron was a little larger than that of A508III steel and this suggest that protectiveness of iron was slightly better. The Nyquist plots of Cr, 316L steel, 430 steel and Alloy 690 exhibited two capacitive loops. The second capacitive loop was far greater than the first one, suggesting that the high protectiveness of the surface films. The size of second capacitive loop decreased in the order as 316L steel, Alloy 690, 430 steel, and Cr. This suggests that when immersed in 0.05 mol/L Fe2(SO4)3 solution, the surface film protectiveness of Cr was good. The Nyquist plots of Ni exhibited two capacitive loops at high and intermediate frequencies, and Warburg characteristics at low frequencies. The first capacitive loops were nearly the same for all materials in this context. The second capacitive loop of Ni was significantly greater than those of A508III steel and iron, but far smaller than those of 316L steel, Alloy 690, 430 steel and Cr. The amounts of Cr and Ni in A508III LAS were not enough to significantly affect the electrochemical behavior in the Fe2(SO4)3 solution. The electrochemical behaviors of A508III steel and iron were nearly the same. Protective films could form on the electrode surfaces at OCPs in 0.05 mol/L Fe2(SO4)3 solution if there was a certain Cr content in alloys. The reactivity of materials with certain Cr element was higher than that with certain nickel element under anodic polarization. Figure 1

The Effects of Hydrogen on Corrosion Products Formed on Iron in Chloride Solutions

The effects of charged hydrogen on the properties of the surface films formed on iron in pure water and 10-4 to 0.5 mol/L NaCl solutions at 25°Cwere investigated by open circuit potential (OCP) measurements, optical microscope, scanning electron microscope and X-ray diffraction (XRD). After 21h immersion in pure water, the surface of non-charged iron did not significantly and showed only local corrosion sites, while the surface of hydrogen-charged iron was covered with dark film with many yellow corrosion sites on it. After 21h immersion in 10-4 mol/L NaCl solution, the non-charged iron was partly covered by surface film, while the hydrogen-charged iron was fully covered by surface film, as shown in Fig. 1. After 21h immersion in 0.5 mol/L NaCl solution, the surface of the non-charged iron was partly dark and partly covered with yellow rusts, and the surface of the hydrogen-charged iron had a larger area covered with more yellow rusts than that on the non-charged iron, as shown in Fig. 2. Results of OCP monitoring showed that OCP values for hydrogen-charged iron in pure water, 10-3 and 10-4 mol/L NaCl solutions were lower than those for non-charged iron, as partly shown in Fig. 3a. In 0.5 mol/L NaCl solution, the OCP differences between non-charged iron and hydrogen-charged iron was at first big but gradually became smaller with increasing immersion time, as shown in Fig. 3b. Raman spectra showed the presence of magnetite in the film on hydrogen-charged iron after immersion in 10-4 mol/L NaCl solution, as shown in Fig. 4a, which was supported by XRD results. Yellow rust and the XRD peak for hematite in the films on non-charged and hydrogen iron specimens (Fig. 4) indicated that the mechanism for the effect of hydrogen on the corrosion products of iron in dilute NaCl solutions could be different from that in concentrated NaCl solutions. In solutions with a high chloride concentration, hydrogen in iron might be able to promote the formation of high valence iron oxide, while in many other cases it was found that the formation of magnetite was promoted by hydrogen in iron. Figure 1

Behavior of Passive Film on New Ti-Zr-Ta-Ag Alloy Surface in Simulated Biofluid

We elaborated a new Ti-20Zr-5Ta-2Ag alloy with innovative composition and properties to fulfil the necessities of corrosion resistance, biocompatibility and antibacterial protection; this alloy was complete and complex characterized: its microstructure by scanning electron microscopy (SEM); its native passive film by X-ray photoelectron spectroscopy (XPS); the surface wettability by contact angle measurements; the electrochemical behaviour in simulated human biofluid (Ringer solution of different pH values) by cyclic and linear polarization, electrochemical impedance spectroscopy (EIS) and monitoring of the open circuit potentials for 1000 exposure hours; the quantity of ions released in time by inductively coupled plasma-mass spectroscopy (ICP-MS). The new alloy has bi-phase, α + β, acicular microstructure, homogeneous and fine; also, lamellas of α and β phases, separated by distances of few microns can be observed (SEM images). Both survey and high resolution XPS spectra showed that the native passive film on Ti-20Zr-5Ta-2Ag alloy surface consists from the protective TiO2, ZrO2, Ta2O5 oxides, Ti and Ta suboxides and metallic Ag, which compact, reinforce and thicken the alloy passive film in comparison with that of Ti. The new alloy native passive film has a thickness of about 12 nm that is well above of that for Ti (1.3 – 3.7 nm). The contact angle for the new Ti-20Zr-5Ta-2Ag alloy has value of 64.54 0; it is a surface with high hydrophilic properties; its surface energy is 29.4 mJ/m2, representing a good value that promotes the interactions with biological fluids, cells and tissue and leads to a better biocompatibility. The corrosion and passivation potentials of the new alloy have more electropositive values than those of Ti, as result of the beneficial effect of Zr and Ta elements (which take part to the formation of the new alloy passive film, as XPS data showed) and of Ag that has a higher mixed potential. The passive current densities for Ti-20Zr-5Ta-2Ag alloy have lower values (of about 6 times) than those of Ti; corrosion current densities and rates are about 25-28 times lower and the polarisation resistances are about 21-28 times higher than those of Ti; this behaviour is due to the more protective passive layer existing on the new alloy surface. Nyquist spectra displayed capacitive loops associated with passive film like an insulator. Bode impedance spectra presented higher impedance values for the new alloy suggesting a more protective passive film than that on Ti surface. The new Ti-20Zr-5Ta-2Ag alloy exhibited higher phase angles than those for Ti, fact that demonstrates a nobler behaviour, a more capacitive film, a more resistant layer as result of its more compact, thicker, more complex composition. The impedance results were modelled with an electric equivalent circuit with two time constants corresponding to those two phase angles; the high phase angle represents a very capacitive, very resistant, barrier layer; the lower phase angle reflects the defective, less resistant, porous layer. The electrical parameters evinced slightly more unfavourable values for Ti, indicating that the passive film on its surface has lower insulating properties than the passive film on Ti-20Zr-5Ta-2Ag alloy surface; this fact is normal because the passive film on the new alloy surface is more compact, thicker, and, in addition, contains very protective ZrO2, Ta2O5 oxides, Ta suboxide and metallic Ag (as results from XPS data). The new Ti-20Zr-5Ta-2Ag alloy releases into Ringer solution low quantities of metallic ions, order of parts per million (ppm) beginning after 120 immersion hours; the quantity of the released ions increased over time. Silver ions were released in very low amount that enhanced in time, assuring long term antibacterial activity of the new alloy (ICP-MS data). The values of the open circuit potentials for the new Ti-20Zr-5Ta-2Ag alloy have more electropositive values than those of Ti, due to the alloy thicker, more compact (XPS results), more resistant (electrochemical and corrosion parameters) passive film. After about 500 immersion hours, all open circuit potential values tended to constant levels and maintained very constantly till 1000 hours, proving the alloy good stability. Open circuit potential differences had very low values situated under limits of 500 mV ÷ 600 mV necessary to form galvanic cells. Therefore, both Ti and new Ti-20Zr-5Ta-2Ag alloy are not susceptible to galvanic corrosion. The coupling of Ti with noble metals (Pt, Au, Ag) conducts to a higher mixed potential, because the noble metals are catalyst for the reducing both of the oxygen and water reactions. Thus, a quantity of 2% Ag is capable to increase the corrosion potentials of the new alloy.

Antibacterial Ag/a-C nanocomposite coatings: The influence of nano-galvanic a-C and Ag couples on Ag ionization rates

Biofilm formation has been pointed as a major concern in different industrial applications, namely on biomedical implants and surgical instruments, which has prompted the development of new strategies for production of efficient antimicrobial surfaces. In this work, nano-galvanic couples were created to enhance the antibacterial properties of silver, by embedding it into amorphous carbon (a-C) matrix. The developed Ag/a-C nanocomposite coatings, deposited by magnetron sputtering, revealed an outstanding antibacterial activity against Staphylococcus epidermidis, promoting a total reduction in biofilm formation with no bacteria counts in all dilution.The open circuit potential (OCP) tests in 0.9% NaCl confirmed that a-C shows a positive OCP value, in contrast to Ag coating, thus enhancing the ionization of biocidal Ag+ due to the nano-galvanic couple activation. This result was confirmed by the inductively coupled plasma-optical emission spectroscopy (ICP-OES), which revealed a higher Ag ionization rate in the nanocomposite coating in comparison with the Ag coating. The surface of Ag/a-C and Ag coatings immersed in 0.9% NaCl were monitored by scanning electron microscopy (SEM) over a period of 24h, being found that the Ag ionization determined by ICP-OES was accompanied by an Ag nanoparticles coalescence and agglomeration in Ag/a-C coating.

Electrochemical behavior of titanium modified with TiO2 nanotubes

Event Abstract Back to Event Electrochemical behavior of titanium modified with TiO2 nanotubes Nilson Oliveira1 and Claudemiro Bolfarini1 1 Federal University of São Carlos – UFSCar, Department of Materials Engineering – DEMa, Brazil Introduction: It is know that the physicochemical properties of the biomaterial surface influence the biological response of an implant, and as Ti is considered a bioinert metal, it is necessary to use surface modification methods in order to improve its osseointegration [1]-[3]. It is important to develop materials and surfaces with adequate corrosion resistance, which is a necessary condition for the biocompatibility [4],[5]. Considering that nanotubes layers on the Ti surface can enhance the osseointegration [6],[7], the aim of the present work was to obtain nanotubes on the Ti surface and to study its electrochemical behavior in a simulated physiological media. Materials and Methods: Nanotubes were obtained on Ti (grade II) surface by anodic oxidation, using a two electrode system [8],[9]. The electrochemical anodization was performed applying 10V/1h, 20V/1h or 20V/2h, using as working electrolyte Glycerol / H2O / NaF [8]. The electrochemical analyses were carried out using a standard three-electrode cell, a saturated Ag/AgCl electrode as reference, and Ringer Physiological solution [8]-[10]. The open circuit potential values, Eoc, were monitored until 144h of immersion, and the polarization measurements were performed from -0.100 mV up to 1.5V (vs Eoc) at 1mV/s. Results and Discussion: After anodization, it was obtained well-defined nanotubes on the entire surface of all samples, with average diameter of 45nm for 10V and 90nm for 20V, and length of 1µm for 1h and 2 µm for 2h, consistent with previous work[8]. Exemplifing, in the Fig.1 are presented SEM micrographs for 10V and 20V for 1 h. Figure 1 - SEM micrographs of nanotubes layer formed at (a) 10V / 1h and (b) 20V / 1h. The Eoc profiles were similar (Fig.2a), indicating that the nanotubes films formed are not suffering spontaneous dissolution and also that the different diameters and lengths are not influencing their electrochemical properties. These values are higher than the values found by Oliveira & Guastaldi[5] for cp Ti polished after 360h immersion in Ringer's solution: -200mV (vs SCE). The voltammetric profiles are similar for all surfaces (Fig. 2b), with low current values​​, on the order of µA, without the occurrence of transpassivation in the potential range studied, indicating the presence of a barrier-type oxide film[5], that is probably related to the oxide layer at the bottom of the nanotubes. The shift of the corrosion potential from -600 mV (as polished surface) to -300mV (nanotubes surfaces) indicates that the presence of the nanotubes is improving the Ti corrosion resistance. The variation in diameter and length of the nanotubes did not influence their electrochemical behavior, confirming the results obtained in the Eoc measurements. Figure 2 – (a) Open-circuit potential measurements and (b) potentiodynamic polarization for Ti with nanotubes layer formed at 10V / 1h, 20V / 1h, and 20V / 2h. Conclusion: The nanostructured layers formed on pure Ti with different diameters and length of the nanotubes improved the electrochemical stability and corrosion resistance of the Ti. The authors are grateful to FAPESP for scholarships (proc. 2012/11350-0) and grants (2012/01652-9).

Local electrochemistry of reinforcement steel – Distribution of open circuit and pitting potentials on steels with different surface condition

Local electrochemical measurements (open circuit potential (OCP), cathodic and anodic polarization curves, pitting potentials) were performed at random locations on 1m long ribbed steel bars with different surface conditions. The results show that the local OCP values are statistically distributed. The standard deviation was found to be 45mV for “as received” surface condition, decreasing to 10mV only after prolonged immersion in sat. Ca(OH)2. A model based on local variations of the reduction current density could explain the variations in local OCP and allowed predicting the overall global OCP of the long bars when completely immersed in solution.

High PEC conversion efficiencies from CuSe film electrodes modified with metalloporphyrin/polyethylene matrices

Electrodeposited CuSe film electrodes have been prepared onto FTO/glass by a facile method based on earlier methods described for other systems. The films were characterized, modified by annealing and further characterized. The films were then modified by coating with tetra(-4-pyridyl) pophyrinato-manganese (MnTPyP) complexes embedded inside commercial polyethylene (PE) matrices. The effects of modifications on different film properties, such as X-ray diffraction (XRD) patterns, surface morphology, photoluminescence (PL) spectra and electronic absorption spectra were investigated. Compared with other thin film electrode systems, very high photoelectrochemical (PEC) conversion efficiency values have been observed here. Pre-annealing the CuSe films at 150°C for 2h, followed by attaching the MnTPyP/PE matrices remarkably enhanced their PEC characteristics. The conversion efficiency was significantly enhanced, from less than 1.0% to more than 15%. Fill factor (FF) was also enhanced from ∼30% to ∼80%. Values of open-circuit potential (VOC) and short-circuit current (JSC) were significantly enhanced. While annealing affects uniformity, particle inter-connection and surface texture of the CuSe films, the MnTPyP complex species behaves as an additional charge-transfer mediator across the film/electrolyte junction. Optimization of PEC characteristics, using different deposition times, different annealing temperatures, different annealing times and different redox couples, was also investigated.

Surface characteristics and electrochemical behaviour of sputter-deposited NiTi thin film

Thin nanocrystalline amorphous NiTi film was deposited on Si substrate using DC magnetron sputtering. The as-deposited NiTi thin film was crystallized by heat treatment at 500 °C for 1 h. The crystal structure, surface morphology, microstructure and surface chemistry of the deposited films were studied using X-ray diffraction, atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy (XPS), respectively. Corrosion behaviour was assessed in Ringer’s solution at 37 °C by open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy as a function of exposure time. OCP values indicate that the tendency for the formation of a spontaneous oxide film is greater for the NiTi thin films than the bulk NiTi. Long time exposure to Ringer’s solution was found to have a great effect on the corrosion behaviour of the samples. Significantly low corrosion current density was obtained for the annealed NiTi film from the potentiodynamic polarization curves indicating a typical passive behaviour, but as-deposited film and bulk NiTi alloy exhibited breakdown of passivity at potentials approximately +1.4 V (vs. SCE). XPS showed that the oxide film formed on the annealed NiTi thin film mainly composed of Ti oxides, and no evidence of Ni was found up to 8.2 nm beneath the top surface, suggesting the excellent corrosion resistance of this sample in Ringer’s solution.

Corrosion Evolution of Low Alloy Steel in Deaerated Bicarbonate Solutions

Corrosion evolution during immersion tests (up to 43 days) of NiCu steel in deaerated 0.1 mol/L bicarbonate solutions was investigated by electrochemical measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results show that NiCu steel transformed from the anodic dissolution in the early stage of immersion to a metastable passive state in the final stage as the open-circuit potential value shifted positively, which was aroused by the precipitation of corrosion products. This process was mainly promoted by the trace amount of oxygen. Simultaneously, dominant cathodic reaction transformed from the hydrogen evolution in early stage to reduction processes of corrosion products in later stages. Possible corrosion processes were discussed with the assistance of a corresponding Pourbaix diagram.

Real Time Measurement of Biosorption Efficiency of Chemically Modified Coconut Powder for Pb(II) and Cd(II) Using Open Circuit Potential

The present communication reports a new method for the potentiometric determination of adsorbent efficiency of coconut shell powder for removal of lead and cadmium from water. A three-electrode system containing metal-coated copper wire electrode was used as a working electrode. At equilibrium Open Circuit Potential (OCP) values represents metal ion concentration in solution. With the addition of coconut powder an appreciable decrease in the OCP was observed, which is associated with the reduction of the metal ion concentration due to the uptake of metal ions by the coconut powder. Chemical modification of coconut biomass was carried out by graft co-polymerization of acrylic acid. Modified biopolymer has been characterized using FTIR technique. An increase in the adsorbent efficiency of the biomass was observed by graft-copolymerized biopolymer i.e. from 54.4 mg/g to 122.1 mg/g and 58.8 mg/g to 141 mg/g respectively for Pb (II) and Cd (II) ions. The OCP based method provides an easy and simple approach for real time measurement of adsorption efficiency, which is a low cost and less time consuming process.

Development of Prognostic Criteria of Kidney Transplantation Complications Based on Open-Circuit Potential Moniroting Using Probit Analysis

At the present time, early posttransplant complications in patients are diagnosed and evaluated based on the analysis of a complex of clinical observations and laboratory tests reflecting the status of various bodily systems. One important diagnostic parameter for transplant patients is the status of the prooxidant/antioxidant balance in bodily fluids (such as whole blood or blood plasma), which reflects the position of redox equilibrium of the organism. The organ transplant may be subject to various types of injury that would affect the prooxidant/antioxidant homeostasis. It has been previously shown that an electrochemical measurement of open-circuit potential (OCP) at the platinum electrode in blood plasma or blood serum is a reflection of the redox state of these biological media [1], and the final OCP value after 15 min of measurement, corresponding to near-equilibrium conditions, was used as the characteristic OCP value for further analysis, termed “redox potential” (RP) in relevant medical literature. Moreover, changes in the time dependence of the measured RP correlate with clinically diagnosed transplant dysfunction, with RP changes often preceding clinical symptoms by one or more days [2]. Thus, in order to develop prognostic criteria to predict the probability of posttransplant complications, the above method of RP measurement was used, and statistical analysis of RP values was performed. RP measurements were performed in blood plasma against a silver/silver chloride reference electrode using an IPC-Compact potentiostat (NPO “Volta”). The electrode was pre-treated prior to each measurement according to the previously developed method [1]. A total of 59 kidney transplant patients took part in the study (42 male and 17 female) in the early postoperative recovery period (20-35 days). Statistical analysis was performed using the STATISTICA 6.0 (StatSoft), EViews 8.0 (IHS Global Inc.) and IDE Microsoft Visual Basic 6.0 software. Patients who took part in the study can be categorized into two groups, according to their recovery dynamics: 35 patients had unremarkable recoveries, without any complications, while 24 patients experienced complications. A total of 967 analyses was performed. Statistical analysis performed on the RP values and clinical/laboratory data has yielded average values of complication probability depending on RP, shown in Fig. 1: an RP more positive than +20 mV corresponds to a 50 percent probability of posttransplant complications, while an RP of +50 mV or higher, to a 75% probability. Subsequently, an evaluation of the probability of postoperative complications depending on the time elapsed since transplantation was performed. Since the presence or absence of complications is a qualitative characteristic, the method of probit analysis [3] was used for the evaluation of complication probability. This method is based on the interpretation of the standard normal distribution function (Ф) as the conditional probability of the event at the given value of its argument; the latter is derived from a linear transformation of the observed value (RP in this case). Then the probability (P) of incidence of a complication can be evaluated from the following equation: P = Ф(α + β∙E) where α, β are coefficients determined by the maximum-likelihood estimation (MLE) method and E is the RP value. The correlation of the probit function curve with a sampling of data points was evaluated using the χ2 test. The use of probit analysis allows for the evaluation of transplant complication probability depending on the measured RP for a specific day of patient postoperative recovery during the hospital stay (Fig. 2).