Cyclic Polarization Curves Research Articles

Electrochemical Studies of Structural Materials in Acidic Peroxide Media

Corrosion in paper industries is responsible not only for weakening of metal structures but also for pollution of process liquors and contamination of products. The bleaching sections in pulp and paper industry are among the worst affected by the ravages of corrosion. In bleach plants the materials are exposed to highly corrosive bleaching liquors. Now day’s new norms of safety of environment are forcing paper industries to use peroxide as a bleaching agent instead of chlorine. So in the present study an effort has been done to propose an appropriate material for the construction of future bleach plants keeping in mind their mechanical factors and cost of the material. Accordingly electrochemical polarization tests, E vs. time curve, potentiodynamic polarization curve and cyclic polarization curve were performed on stainless steels samples of 316L, 317L, 2205 and 254SMO in peroxide containing solutions having H2O2, 500 and 1000 parts per million (ppm). The pH of these solutions was kept 4. The Chloride content varied from 0 to 1000 ppm. These tests was performed at room temperature. These tests showed increased resistance against corrosion in order of: 316L<317L<2205<254SMO. Thus 254SMO shows highest resistance for attack of corrosion but keeping in mind fabrication and cost aspects optimal material for treating these peroxide media is recommended to be SS 2205.

ELECTROCHEMICAL SYNTHESIS OF IRON MONOSELENIDE THIN FILMS

In the presented research work, the kinetics and mechanism of the deposition process of thin iron, selenium and Fe-Se films have been studied by recording a cyclic and linear polarization curves by potentiodynamic method using Pt and Ni electrodes. Individual and co-deposition potential areas of the components of the electrolyte on the Pt electrode were determined. In order to determine the optimal electrolysis mode and electrolyte composition, the effect of various factors (concentration of initial components, temperature, etc.) on the co-electrodeposition process of Fe-Se was studied. In addition, Fe-Se samples deposited on the surface of Ni electrodes were thermally treated at 4500C and studied by SEM and X-ray phase analysis methods. Elemental analysis of the films shows that they contain 42.2% Fe and 57.8% Se.

Effect of hexamethylenetetramine on surface smoothness of electroplated copper coating

In this paper, hexamethyltetramine is introduced into the electroplating bath to improve the surface morphology of electrodeposited copper. The cyclic voltammetry (CV) and dynamic polarization curves are used to study the effect of Cu(Ⅰ) and hexamethyltetramine on the electrochemical behaviors of electroplating solution. After implementing the electrodeposited copper experiment, scanning electron microscope (SEM) and X-ray diffraction (XRD) are used to explore the influence of Cu(Ⅰ) and hexamethyltetramine on the Surface morphology and crystal plane orientation of the electrodeposited copper. The results show that 5ppm hexamethyltetramine and 7.5ppm hexamethyltetramine can solve the problem of the loose and uneven surface of the electroplated copper layer caused by Cu(Ⅰ).

Study of electrochemical deposition of Ni-Mo thin films from alkaline electrolytes

The process of co-deposition of Ni with Mo from alkaline electrolytes was studied by taking linear and cyclic polarization curves of Pt electrode at various concentrations of initial components and potential scan rates. Solutions of Na2MoO4∙2H2O and NiSO4∙7H2O were used as sources of ions of the main components in NH4OH electrolyte. It was found that co-deposition of nickel with molybdenum goes through the oxide formation stage, and a solid solution of these two metals is deposited on the cathode surface. The film obtained at constant current on Ni electrode under optimal conditions was found amorphous, but additional thermal treatment at 500 °C for one hour made it polycrystalline. This was confirmed by peaks in X-ray diffraction patterns, corresponding to NiMoO4, Ni, and MoO3. The proposed electrolyte and electrolysis conditions allow to obtain thin films with molybdenum content ranging from 17.1 to 50.9 at.%. The co-deposition of Ni with Mo is limited by diffusion of these ions to the cathode surface. The knowledge of the mechanism of co-deposition of Ni and Mo will make possible a selection of optimal conditions for deposition of alloys of the required composition with satisfactory electrocatalytic properties.

ELECTROCHEMICAL REDUCTION OF SELENIUM IONS FROM ORGANIC SOLUTION

Due to the unique properties of metal dichalcogenides, they are wide used in various fields of nano- and optoelectronics. Bi2Se3 is one of the promising n-type semiconductor materials belonging to the Av – Bvı group, with a band gap of 0.3 eV. To obtain these compounds by co-electrodeposition, we study the electroreduction of the initial components separately. Therefore, the study is devoted to the electrochemical reduction of selenite ions from the ethylene glycol solution. By drawing cyclic and linear polarization curves on Pt electrodes, the kinetics, the mechanism of the process, and the influence of various factors on the electroreduction of selenite ions are studied. Using the obtained data on the influence of temperature, the effective activation energy was calculated by the Gorbachov method. The calculation results show that the electroreduction of selenite ions from ethylene glycol is accompanied by electrochemical kinetics closer to diffusion

Modifying Carbon Felt Electrodes Using High-Temperature Ammonia Treatment to Improve the Performance of All-Vanadium Redox Flow Batteries

High temperature ammonia treatments were performed on carbon felt electrodes in this study. Their physical and electrochemical properties were investigated.Carbon felt electrodes are often used in vanadium redox flow batteries (VRFBs). Without intervention, carbon felt has poor wettability which frustrates electrochemical activity. This material must be modified to make it more effective, which has been historically accomplished with thermal treatments to promote oxygen functional groups. [1] Many attempts have been made to improve performance of carbon felt in VRFBs, but some of the more successful modifications have resulted in an increase in the specific surface area. [2-4] Preliminary experiments on carbon felt performed by this lab with ammonia at high temperatures have shown promising results. [5]For our experiments, commercially available carbon felts (SIGRACELL® GFD3 by SGL Carbon, Meitingen, Germany) were modified by exposure to flowing ammonia gas through a furnace at 900°C for varying lengths of time. The samples were tested in a single-cell flow battery using cyclic voltammetry (CV), polarization curves, and electrochemical impedance spectroscopy (EIS). This treatment results in a significant increase in electrochemical surface area and performance.The physical properties were characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and Raman spectroscopy. A pitting effect was observed in SEM images, preceded by surface blistering at shorter lengths of exposure.Greatly increased active surface area, along with a substantial increase in cell performance, was achieved with the ammonia-modified carbon felts described in this work. Sun, B. and M. Skyllas-Kazacos, Modification of graphite electrode materials for vanadium redox flow battery application—I. Thermal treatment. Electrochimica Acta, 1992. 37(7): p. 1253-1260.Lu, W., et al., High-performance porous uncharged membranes for vanadium flow battery applications created by tuning cohesive and swelling forces. Energy & Environmental Science, 2016. 9(7): p. 2319-2325.Zhou, X.L., et al., A high-performance dual-scale porous electrode for vanadium redox flow batteries. Journal of Power Sources, 2016. 325: p. 329-336.Wei, L., et al., Highly catalytic hollow Ti3C2Tx MXene spheres decorated graphite felt electrode for vanadium redox flow batteries. Energy Storage Materials, 2020. 25: p. 885-892.Pezeshki, A.M., "Impedance-Resolved Performance and Durability in Redox Flow Batteries. " PhD diss., University of Tennessee, 2016. Figure 1

Corrosion resistance improvement of additive manufactured scaffolds by anodizing

Ti–6Al–4V ELI scaffolds produced by additive manufacturing and functionalized by anodizing technique in two different conditions have been evaluated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, optical confocal microscopy, cyclic potentiodynamic polarization curves (CPP), and electrochemical impedance spectroscopy (EIS). Despite the differences in composition and morphological features between the anodic layers grown, the results revealed an improvement of the corrosion resistance in both anodized conditions regarding non-anodized samples. The non-anodized scaffolds presented pitting corrosion in phosphate-buffered saline solution at 37 °C. Conversely, the anodized samples prevented pitting corrosion and enhanced barrier properties by decreasing the passive current density in two orders of magnitude. EIS data show, anodized scaffolds presented good stability after 168 h of immersion time and better protective properties than non-anodized samples.

Silicate Ions as Corrosion Inhibitors for Carbon Steel in Chloride-Contaminated Concrete Pore Simulating Solutions

Silicate ions were tested as corrosion inhibitors for construction steel using concrete pore simulating solutions contaminated with chloride ions. The results were compared to those from solutions with no silicate and with no silicate and no chloride ions. The evaluation included typical electrochemical techniques such as cyclic voltammetry, polarization curves, and weight loss evaluation after a 60 day immersion. Surface analysis was undertaken using micro-Raman spectroscopy and x-ray photoelectron spectroscopy (XPS). Polarization curves showed no sign of pitting and low corrosion current densities if silicate ions were present, even when chloride ions were also in the system. In parallel, no localized attack was observed after 60 days of immersion in solutions containing an inhibitor/chloride = 1 ratio. Cyclic voltammograms and XPS spectra indicated that the presence of silicate ions affects the composition and thickness of the passive film: the film becomes thinner and contains more Fe(II) species. All of the results showed that silicate ions act as promising inhibiting agents.

Study of Microbially Influenced Corrosion in the Presence of Iron-Oxidizing Bacteria (Strain DASEWM2)

The present study deals with the investigation of microbially influenced corrosion of mild steel by the iron-oxidizing bacterium (IOB), Pseudomonas sp. strain DASEWM2, using electrochemical tests, immersion tests, and surface analysis. The corrosion rate obtained by Tafel plots was higher after exposure of ~ 24 h to 72 h when the concentration of sessile cells and constituents of extracellular polymeric substances were high. In inoculated media, cyclic polarization curves show lower pitting potential, repassivation potential, and large area under the hysteresis loop, indicating higher susceptibility of steel to localized corrosion. Immersion tests show higher corrosion rate (0.252 ± 0.05 mpy) and large deep pits in the open area (maximum pit depth 140 ± 8 µm) and under crevice (maximum pit depth 95 ± 4 µm) indicating a higher degree of corrosion in inoculated media. Corrosion products formed on corroded steel samples were analyzed using EDAX, XRD, and FTIR techniques. Goethite and lepidocrocite are the main corrosion products in the case of inoculated media. In contrast, lepidocrocite and iron hydrogen phosphate are the main corrosion products in the case of control media. The absence of iron hydrogen phosphate, a protective type of corrosion product, on steel exposed to inoculated media may be responsible for observing a higher degree of corrosion due to bacteria.

Fabrication of NbN-Coated Porous Titanium Sheets for PEM Electrolyzers

Porous titanium sheets are attractive for application as the porous transport layer (PTL) for polymer electrolyte membrane (PEM) water electrolyzers. However, the titanium passivation increases its surface contact resistance, deteriorating the electrolyzer performance. A solution for long-term operation has been to coat titanium-based PTLs with platinum or gold, which considerably increases PEM electrolyzer costs. To overcome this limitation, a NbN coating is proposed as an alternative to decrease materials costs while avoiding titanium surface oxidation. Therefore, porous titanium sheets of ca. 250 μm were powder metallurgically produced by tape casting and then sputter-coated with a NbN thin film. A systematic investigation of NbN film deposition on porous titanium sheets by reactive magnetron sputtering was undertaken. Coating microstructure and constitution were evaluated before and after electrochemical characterization. First electrochemical characterizations throughout cyclic voltammetry and potentiodynamic polarization curves demonstrate that the addition of NbN coatings decreases titanium surface oxidation and improves electrochemical performance of the porous titanium sheets. These results indicated that NbN-coated PTLs are promising candidates for PEM electrolyzer application.

Effect of cerium on microstructure, mechanical properties and corrosion properties of Al-Zn-Mg alloy

The effects of trace Ce on the microstructure, mechanical properties and corrosion resistance of Al-Zn-Mg alloy were studied by means of metallographic analysis, scanning electron microscopy (SEM), mechanical tensile test, slow strain rate tensile test, cyclic polarization curve test, electrochemical impedance spectroscopy test and anodic oxidation test. The results show that the addition of trace Ce has little effect on the strength of Al-Zn-Mg alloy, but can significantly improve the corrosion resistance of the alloy; The mechanical properties and corrosion resistance of the alloys decrease significantly with the addition of excessive Ce; the addition of 0.04 wt% Ce can reduce significantly the self-corrosive current density of Al-Zn-Mg alloy and increase obviously passivation film resistance of the alloy. The stress corrosion sensitivity index decreases from 0.612 to 0.219, which improves the corrosion resistance properties significantly.

Potential Difference of Cyclic Polarization Curve of an Aircraft Al Alloy: ΔE (Esec,corr – Ecorr)

Potential Difference of Cyclic Polarization Curve of an Aircraft Al Alloy: ΔE (Esec,corr – Ecorr)

Effect of Low-Temperature Plasma Nitriding on Corrosion and Surface Properties of Duplex Stainless Steel UNS S32205

The duplex stainless steel UNS S32205 was plasma nitrided at 380 °C for 10 h using a gas mixture of 25% N2-75% H2. The thickness of the nitrided layer was 4.5 ± 0.5 μm, composed mainly of nitrogen-expanded austenite and iron nitrides precipitates. There was an increase in surface hardness around 2.6 and 3.8 times in the nitrided layer formed on the austenite and the ferrite phases, respectively, in relation to the untreated samples. The surface texture parameters skewness (Ssk), maximum peak height (Sp) and texture aspect ratio (Str) were the most appropriate parameters for studying the topography changes after treatment. An improvement in the localized corrosion properties after the nitriding treatment was revealed by the cyclic polarization curves. The nitrided samples showed higher pitting corrosion and repassivation potentials compared to the untreated material. The ferritic phases and grain boundaries were more susceptible to corrosion in the nitrided samples. The potentiodynamic curves of the nitrided samples exhibited a hillside on the passive-to-transpassive transition. This feature was already observed by other researchers, but it has not been well investigated. Potentiostatic studies demonstrated that metastable pitting took place on this transition.

Effect of DC stray current on electrochemical behavior of low-carbon steel and 10%Cr steel in saturated Ca(OH)2 solution

The effect of direct current (DC) stray current on passivation behavior of low-carbon (LC) reinforcing steel and a 10 %Cr reinforcing steel in saturated Ca(OH)2 solution was investigated by means of EIS, AFM and XPS measurements. In addition, cyclic potentiodynamic polarization curves were employed to evaluate the influence of stray current on chloride-induced pitting corrosion behavior of steels. The results indicate that stray current leads to reduced passivation capability of LC steel, whereas stray current induced degradation of passive film is less pronounced for 10 %Cr steel. Moreover, pitting corrosion resistance of both steels decreases significantly in the presence of stray current.

Study on electrochemical properties of gelled electrolytes using nano fumed silica in the presence of some organic additives

A gelled electrolyte is made on the basis of liquid glass and sulphuric acid using nano fumed silica (NFS) in the presence of some other organic additives such as polyacrylamide (PAM) and polypropylene glycol (PPG). Lead-antimony alloy electrodes are prepared to examine the electrochemical properties of manufactured gelled electrolytes through cyclic voltammetric behaviour, electrochemical impedance and polarisation curves. The results from cyclic voltammetric diagrams show that the peak of lead solubility increases while the peak of oxygen evolution decreases due to using nano NFS for gelled electrolytes. Obtained Nyquist diagrams all show that the adsorption process occurs, in which the electrochemical impedance measured in the gelled electrolyte containing NFS increases in comparison with that without NFS. Observing the bigger slope of the outlet branch of oxygen in comparison with that of hydrogen on polarisation curves indicates that the rate of oxygen escape is stronger than that of hydrogen. The results also show that the oxygen overpotential increases while the hydrogen overpotential decreases slightly when NFS is present in gelled electrolytes.

Исследование коррозии нержавеющей стали 10Х17Н13М2Т в хлорной кислоте

The authors study the corrosion of AISI 316 stainless steel in 1M perchloric acid at 90 °C, including in the presence of the benzotriazole corrosion inhibitor. Electrochemical experiments were carried out in a three-electrode glass cell with a platinum counter electrode and a saturated silver chloride electrode as a reference electrode. The authors carried out the potentiodynamic measurements at the temperature of (90±2) °C and the potential sweep speed of 1 mV/s; the impedance measurements within the frequency range from 20 kHz to 0.1 Hz at the voltage amplitude of ±10 mV. Cyclic polarization curves show that the cathode direction currents are always lower than the anode direction currents of the potential sweep. Consequently, the curves of anode and cathode directions of the potential sweep are analyzed separately. When analyzing, the authors use the modified Tafel equation, which is linear at any overload that allow determining the corrosion currents more accurately. The study shows that with an increase in the inhibitor concentration, the potentiodynamic curves shift to the cathode side, and the cathode currents decrease more strongly than the anode currents. Therefore, benzotriazole in perchloric acid is an inhibitor of cathodic action, i.e. slows down the cathodic reaction of the perchloric acid anion reduction to chloride ions. The authors identified that benzotriazole inhibits corrosion at concentrations of more than 10 -4 mol/L. At the concentration of 1×10 -3 mol/L, the inhibition efficiency is 33±10 %, and at the concentration of 1×10 -2 mol/L, it is 36±13 %. The inhibiting effect of a benzotriazole molecule in the acidic medium is caused by the possibility of its protonated form to be adsorbed on the metal surface. The protonated form of benzotriazole in acidic medium allows explaining the slow-down of the cathode depolarization reaction as the inhibitor is adsorbed predominantly on metal surface areas charged more negatively. The impedance measurements showed that the corrosion process is modeled by the element parallel circuit with the constant phase shift and corrosion resistance.

Applications of cathodic Co100-XNiX (x = 0, 30, 70, and 100) electrocatalysts chemically coated with Pt for PEM fuel cells

The present work comprises a study about the synthesis, characterization, and performance evaluation of four Co100-X-NiX (x = 0, 30, 70, and 100) electrocatalysts coated with Pt with potential catalytic activity towards ORR. Electrocatalysts were prepared through a two-stage process combining the versatile high-energy ball milling synthesis and the galvanic displacement method. On a first stage, high-energy ball milling was used to produce nanoparticles of non-noble transition metals, (M = Co100 and Ni100) and (BM = Co30Ni70and Co70Ni30). On a second stage, galvanic displacement reactions via chemical reflux treatment were employed to promote a Pt coating over the milled nanoparticles. The four electrocatalysts were dispersed on Vulcan carbon maintaining a metal:carbon (wt.%) ratio of 50:50 each one. The result was two type of systems: (M-Pt/C = Co100–Pt/C and Ni100–Pt/C) and (BM-Pt/C = Co30Ni70–Pt/C and Co70Ni30–Pt/C). All the electrocatalysts presented a final composition: ~10 wt%. of Pt, ~40 wt% of Co100-xNix, and ~50 wt% of Vulcan carbon. Physical characterization of the synthesized electrocatalysts involved XRD, STEM, AAS-ICP-MS and EDS-SEM studies confirming the formation of homogeneously-distributed metallic nanoparticles on the carbon. The electrochemical evaluation, through cyclic voltammetry and steady-state polarization curves using rotating disk electrode technique, was performed for the four synthesized electrocatalysts and for a commercial platinum-loaded carbon black (Pt Etek 20 wt%) catalysts. All four synthesized electrocatalysts were electroactive for ORR. Moreover, the Ni100–Pt/C electrocatalyst presented the highest mass activity whereas Co30Ni70–Pt/C electrocatalyst showed the major stability after 3000 cycles of accelerated degradation test than the others. Two membrane electrode assemblies (MEAs) for PEM fuel cell were fabricated with the synthesized Ni100–Pt/C and Co30Ni70–Pt/C electrocatalysts used as cathodes. Results under single-fuel cell operation showed the same performance trend for those materials that observed under electrochemical glass cell conditions.

The Mixture of Nanoparticles of RuO2 and Pt Supported on Ti as an Efficient Catalyst for Direct Formic Acid Fuel Cell

An active coating, composed of a mixture of nanocrystals of RuO2 with the rutile structure and nanocrystals of metal Pt, was thermally synthetized on a titanium substrate. Cyclic voltammograms and polarization curves showed that the catalytic activity of the coating for the formic acid oxidation in an acidic solution increased with an increase in the RuO2 content, reaching the maximum value at 50 mol % RuO2. Additionally, further increase in the RuO2 content resulted in a decline of the catalytic activity. The catalytic effect was attributed to a bifunctional mechanism and an electronic effect. The bifunctional mechanism had a dominant role and was based on the fact that Ru–OH species were formed on Ru atoms of RuO2 at more negative potentials than on Pt. Those species oxidized the adsorbed COad and HCOOad—species on adjacent Pt atoms of clusters of metal Pt and thus discharge them to oxidize new HCOOH molecules.

Corrosion Resistance of Alloy 2024 Anodized on Sulfuric-Citric Acid

Aluminium alloys are used on aerospace and automotive industry due to excellences mechanical properties. Unfortunately, aluminium alloys are susceptible to corrosion and that limit them in some corrosive environments. The aim of this work is researching the characteristics of anodized film generated with sulfuric-citric acid through to electrochemical techniques. For matrix material, an Aluminium (Al) 2024 alloy was used applying a mixt of sulfuric and citric acid with a current of 0.01 and 1 A at 25°C each one while 30 minutes. Electrochemical evaluation used was cyclic potentiodynamic polarization curves (CPPC) and Electrochemical Impedance Spectroscopy (EIS) in NaCl at 3.5% wt. Scanning Electron Microscopy (SEM) was used to determinate morphology and thickness of coating. Results shows that aluminium anodized with mixt of sulfuric-citric acid presented less pitting corrosion resistance with out present a significative difference in surface morphology.

Structure and Electrochemical Properties of Laser Cladding Al2CoCrCuFeNiTix High-Entropy Alloy Coatings

Al2CoxCrCuFeNiTi high-entropy alloy coatings were prepared on Q235 steel by laser cladding. The structure was tested by scanning electron microscopy; the corrosion resistances of the alloys were tested by electrochemical workstation. The results show that the microstructures of Ti2.0 high entropy alloy are mainly equiaxed grains, spherical particles, white particles and "plum blossom" particles are distributed on it, columnar grains are located near the bonding zone. The corrosion resistance of Al2CoCrCuFeNiTix high-entropy alloy coatings in 1 mol/L NaOH and 0.5 mol/L HCl solutions are excellent. In 1 mol/L NaOH solution, compared with Q235 steel, the corrosion current density of the coating decrease by 5 orders of magnitude, the corrosion potential increased by 0.03–0.34 V. In 0.5 mol/L HCl solution, compared with Q235 steel, the corrosion current density of the coating decreases, the corrosion potential increased by 0.06–0.14 V. With the increase of Ti content, the corrosion resistance of Al2CoCrCuFeNiTix high-entropy alloy coating in 0.5 mol/L HCl solution is enhanced, while, in 1 mol/L NaOH solution, the corrosion resistance of the coatings decreased. Cyclic polarization curves showed that negative hysteresis loops appeared in Ti0.5 high-entropy alloy coating in 1 mol/L NaOH solution and Ti2.0 high-entropy alloy coating in 0.5 mol/L HCl solution, which indicated that the coatings has excellent pitting corrosion resistance.