Cyclic Polarization Curves Research Articles

ELECTRO RECOVERY OF TELLURUM IONS FROM NON-AQUEOUS N-N DIMETHYLFORMAMIDE ELECTROLYTE

The work presents studies of the mechanism of recovery of tellurium ions from non-aqueous N-N dimethylformamide. For this, linear and cyclic current-voltage polarization curves have been recorded. The influence on the process of the concentration of tellurium ions, change of potential sweep rate and temperature has been investigated. By recording linear polarization curves, it has been established that the reducing process of tellurium ions is controlled by their diffusion to the cathode surface. The influence of the concentration of its ions in the electrolyte, the rate of change of the potential and the temperature on the tellurium deposition process was studied. By recording the cyclic polarization curve, the potential area where tellurium ions precipitate and its anodic dissolution occurs is determined. It was determined that the increase in the concentration of tellurium ions and the temperature increases the speed of the reduction process of tellurium, and the reduction process itself is controlled by the diffusion of tellurium ions on the cathode surface. To confirm the obtained data, polarization curves have been recorded on a rotating platinum disk electrode. Data received, exactly the linear dependence of ip on the electrode rotation speed (ω) to the power of 0.5, confirms that, that the process of reduction of tellurium electrodes in non-aqueous N-N dimethylformamide is controlled by diffusion polarization

The Mechanical and Electrochemical Stability of Trimethysilane Plasma Nanocoatings Deposited onto Cobalt Chromium Cardiovascular Stents.

The objective of this study was to evaluate the coating integrity performance and corrosion protection property of trimethylsilane (TMS) plasma nanocoatings that were directly deposited onto cobalt chromium (CoCr) L605 cardiovascular stents. Hydrophilic surfaces were achieved for the TMS plasma nanocoatings that were deposited onto the coronary stents through NH3/O2 (2:1 molar ratio) plasma post-treatment. With a coating thickness of approximately 20-25 nm, the TMS plasma nanocoatings were highly durable and able to resist delamination and cracking from crimping and expansion by a Model CX with a J-Crimp Station. The stent surface that was evaluated by Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) showed no indications of pitting, corrosion, or adsorption products on either the luminal or abluminal surfaces of the stents, in contrast to the uncoated stent surface. The TMS plasma nanocoatings significantly enhanced the stent's corrosion resistance in immersion experiments that followed the ASTM F2129-15 corrosion protocol, evident in the increase of the open circuit potential (OCP) from 0.01 V for the uncoated L605 stent to 0.18 V for the plasma-nanocoated L605 stent, reducing potential cytotoxic metal ion release. Cyclic polarization (CP) curves show that the corrosion rate (density level) observed in plasma-nanocoated L605 stents was approximately half an order of magnitude lower than that of the uncoated stents, indicating improved corrosion protection of the stents. CP curves of the TMS plasma-nanocoated stents with different coating thicknesses show that, in the range of 20-65 nm, the coating thickness does not result in any difference in the corrosion resistance of the stents.

A Novel Approach of Electrocatalytic Deamination From Aromatic Amide to Diarylimide on Ni-PTFE Modified Electrode.

A hydrophobic Ni-PTFE modified electrode has been prepared by constant current and cathodic electroplating with a nickel sheet as substrate in a PTFE suspension. Then the Ni-PTFE modified electrode was used for electroreduction from aromatic amide to diarylimide. The electrochemical characterizations such as cyclic voltammogram, EIS, polarization curves, and electrode stability have been carried out by electrochemical workstation. The structure of the electroreduction product diarylimide was characterized by 1HNMR, FT-IR, MS(Mass Spectrum), and EA(Elemental Analyzer). Based on the hydrophobicity of the electrode, an approach suggested that the phenyl ketone radical may be formed by electroreductive deamination at the cathode. With the construction of C-N bond by the radical coupling, the electrocatalytic reduction may be comprised of a one-electron process including an ECC (Electrochemical-Chemical-Chemical) process. The electroreduction of aromatic amide to diarylimide may be controlled by both charge migration and concentration polarization. Electrocatalytic reduction of aromatic amides on Ni-PTFE modified electrodes is all well conversion ratio.

Electrochemical Evaluation of Penta‐Coordinated Fe Phthalocyanine During the Oxygen Reduction Reaction in Various Acidic Solutions

AbstractIron phthalocyanine (FePc) was penta‐coordinated with pyridine ligand (Py) grafted on carbon nanotube (CNT), to form (FePc‐Py‐CNT). The complex was studied as a catalyst for the oxygen reduction reaction ORR in seven different supporting electrolytes: OH− (0.1 M), OH− (1 M), NO3− (1 M), HSO4− (1 M), ClO4− (1 M), Br− (1 M), Cl− (1 M), to unveil anion‐poisoning effects and mechanism. Through cyclic voltammetry and polarization curves in N2 and O2 saturated atmospheres, thermodynamic and kinetic data were acquired. In acid media, the formal potential Fe(III)/(II) (E0’Fe(III)/(II)) of the complex is biased to more negative potentials by the anion presence. Similar effects were observed for the onset potential (Eonset) during polarization curves for the ORR. When the ORR was performed in the presence of either ClO4−, or HSO4−, anions, Tafel analysis showed different values depending if were derived from the low or from the high overpotential regions, revealing an inner‐sphere electron transfer mechanism (ISET). The Tafel values derived from measurements in the presence of Cl− and Br− anions do not change when extracted at low or at high overpotentials evidencing an outer‐sphere reaction mechanism (OSET). Gibbs free energies were derived from poisoning tests confirming the ISET and OSET mechanisms. The poisoning effect is responsible for the immediate loss of performance for these catalysts during the ORR in acidic media.

Anodizing of AA2024 Aluminum–Copper Alloy in Citric-Sulfuric Acid Solution: Effect of Current Density on Corrosion Resistance

Al–Cu alloys are widely used as a structural material in the manufacture of commercial aircraft due to their high mechanical properties such as hardness, strength, low density, and tolerance to fatigue damage and corrosion. One of the main problems of these Al–Cu alloy systems is their low corrosion resistance. The purpose of this study is to analyze the influence of anodizing parameters on aluminum–copper alloy (AA 2024) using a bath of citric-sulfuric acid with different anodizing current densities on the thickness, microhardness, and corrosion resistance of the anodized layer. Hard anodizing is performed on AA 2024 Al–Cu alloy in mixtures of solutions composed of citric and sulfuric acid at different concentrations for 60 min and using current densities (i) of 0.03, 0.045, and 0.06 A/cm2. Scanning electron microscopy (SEM) was used to analyze the surface morphology and thickness of the anodized layer. The mechanical properties of the hard anodized material are evaluated using the Vickers hardness test. The electrochemical techniques use cyclic potentiodynamic polarization curves (CPPC) according to ASTM-G6 and electrochemical impedance spectroscopy (EIS) according to ASTM-G61 and ASTM-G106, respectively, in the electrolyte of NaCl at 3.5 wt. % as a simulation of the marine atmosphere. The results indicate that corrosion resistance anodizing in citric-sulfuric acid solutions with a current density of 0.06 A/cm2 is the best with a corrosion current density (jcorr) of 1.29 × 10−8 A/cm2. It is possible to produce hard anodizing with citric and sulfuric acid solutions that exhibit mechanical properties and corrosion resistance similar or superior to conventional sulfuric acid anodizing.

Influence of tin additions on the corrosion passivation of TiZrTa alloy in sodium chloride solutions

Abstract In this study, the fabrication of Ti-12%Zr-4%Ta-2%Sn alloy, Ti-12%Zr-4%Ta-4%Sn alloy, and Ti-12%Zr-4%Ta-6%Sn alloy using powder metallurgy fabrication technique has been carried out. The influence of Sn addition on the corrosion of these alloys after 30 min and 3 days in 3.5% NaCl solution using various techniques has been reported. The Nyquist spectra revealed that boosting Sn content from 2 to 4% and further to 6% increases the corrosion resistance of the alloy through increasing the diameter of the obtained semicircle. Bode spectra also elucidated that the increased percentage of Sn increases the values of the impedance of the interface |Z| and the maximum degree of the phase angle (Φ). It was indicated from the cyclic polarization curves that the increased Sn content increases the passivation of the alloy through decreasing its rate of corrosion and increasing its corrosion resistance. The measured current over time at −0.10 V showed that the alloy with low Sn content, 2%, records the highest currents, which pronouncedly decreases when Sn content increases to 4% and further to 6%. Prolonging the time of exposure from 30 min to 3 days greatly enhances the passivation of the TiZrTaSn alloys due to the formation of mixed oxides of TiO2, ZrO2, TaO2, and SnO2. The results of these electrochemical measurements were confirmed by the surface investigations carried out by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results collectively proved that the uniform corrosion remarkably decreases with the increase in the Sn% and that the pitting corrosion is not likely to take place.

ELECTROCHEMICAL REDUCTION OF ELEMENTAL SULFUR IN ETHYLENE GLYCOL ELECTROLYTE

The work is devoted to the study of the mechanism of reduction of elemental sulfur from ethylene glycol. For this purpose, linear and cyclic voltampere polarization curves were recorded. The influence of sulfur concentration in ethylene glycol electrolyte, potential unfolding rate and temperature on the sulfur reduction process was investigated. By recording the cyclic polarization curve, the range of potentials at which the reduction of elemental sulfur and its anodic oxidation occur was determined. It has been established that an increase in the concentration of sulfur in the electrolyte and temperature raises the speed of its reduction, and the process itself is controlled by the diffusion of sulfur ions to the cathode surface. In addition, the polarization curves on the platinum rotating disc electrode were recorded. The obtained data, namely the rectilinear dependence of ip on the rotation speed of the electrode (ω) to the power of 0.5, confirm the proposal that the process of reduction of elemental sulfur is accompanied by diffusion polarization. The dependence of the current density on the rotation speed of the electrode to the power of 0.5 at different potentials showed that the process of reduction of elemental sulfur in non-aqueous ethylene glycol at potentials of (0.25÷0.4 V) is accompanied by diffusion polarization, whereas at potentials above 0.4 V, it is accompanied by electrochemical polarization. Keywords : Sulfur ions, electroreduction, polarization, scanrate.

Electrochemical characteristics and damage mechanism in scrubber washing water of UNS N08367 with plasma ion nitriding and electropolishing

In this investigation, electropolishing and plasma ion nitriding are applied to super austenitic stainless steel for the purpose of improving its corrosion and pitting resistance. Electrochemical experiments are conducted with washing water collected directly from the ship’s scrubber. After electropolishing, the surface roughness is improved by about 73.6% compared to mechanical polishing. After plasma ion nitriding, CrN (precipitate), Fe4N (compound), and γN (solid solution) are observed on the surface. The thickness of the layer formed on the surface is measured to be about 10 μm. A hysteresis loop is observed in the cyclic potentiodynamic polarization curves of mechanical polishing and electropolishing, and the areas are calculated as 23.33 mW cm−2 and 0.17 mW cm−2, respectively. The polarization curve of plasma ion nitriding presents perfect passivation characteristics. Accordingly, mechanical polishing and electropolishing reveal local corrosion, whereas plasma ion nitriding presents a tendency towards general corrosion. In the mechanical polishing, electropolishing, and plasma ion nitriding, the corrosion current densities are 0.665 μA cm−2, 0.093 μA cm−2, and 16.47 μA cm−2, respectively, and the maximum damage depth is observed to grow progressively smaller from plasma ion nitriding to electropolishing and then mechanical polishing.

Effect of hydrochar-doping on the performance of carbon felt as anodic electrode in microbial fuel cells.

In this study, the feasibility of using hydrochars as anodic doping materials in microbial fuel cells (MFCs) was investigated. The feedstock used for hydrochar synthesis was metal-polluted plant biomass from an abandoned mining site. The hydrochar obtained was activated by pyrolysis at 500 °C in N2 atmosphere. Under steady state conditions, the current exerted by the MFCs, as well as the cyclic voltammetry and polarization curves, showed that the activated hydrochar-doped anodes exhibited the best performance in terms of power and current density generation, 0.055 mW/cm2 and 0.15mA/cm2, respectively. These values were approximately 30% higher than those achieved with non-doped or doped with non-activated hydrochar anodes which can be explained by the highly graphitic carbonaceous structures obtained during the hydrochar activation that reduced the internal resistance of the system. These results suggest that the activated hydrochar materials could significantly enhance the electrochemical performance of bioelectrochemical systems. Moreover, this integration will not only enhance the energy generated by MFCs, but also valorize metal polluted plant biomass within the frame of the circular economy.

Мырыш электродын өндірістік айнымалы токпен натрий хлориді ерітіндісінде поляризациялау арқылы мырыш оксидін алу

The purpose of the work is to dissolve the zinc electrode during polarization with an alternating current with a frequency of 50 Hz and to obtain zinc oxide. It is shown that the pre-recorded anode-cathode cyclic potentiodynamic polarization curves allow to predict to a certain extent the processes occuriing on the zinc electrode during alternating current polarization. It has been established that when two zinc electrodes are polarized in sodium chloride with an alternating current with a frequency of 50 Hz, they do not dissolve, but when one electrode is replaced with a titanium one, zinc dissolves intensively with the production of zinc hydroxide. It is shown that the rate of zinc dissolution directly depends on the current density at the titanium electrode. When the values of the current density on the titanium electrode change in the range of 5-10 kA/m2, the zinc dissolution current efficiency exceeds 100%. Based on the results of the research, it was established that zinc (II) hydroxide is produced during electrolysis, and zinc oxide can be obtained by dehydration. The composition of the resulting compound was identified by X-ray phase and elemental analyses

An electrochemical method for the regeneration of trivalent iron to increase the efficiency of in-situ leaching of uranium

Due to the increasing demand for electricity with the development of production and general infrastructure, increasing the production of uranium as an economically and environmentally efficient source of energy is an urgent problem. The purpose of this study is to develop an electrochemical method for the regeneration of iron (III) ions used as a uranium oxidizer in the process of in-situ leaching of uranium minerals with sulfuric acid solutions. Methods. The mechanism of reactions in the iron (II)-iron (III) redox system was studied by recording potentiodynamic polarization curves and conducting electrolysis of the oxidation of divalent iron ions under galvanostatic conditions. Results and discussion. Cathode-anodic and anodic-cathode cyclic polarization curves taken on platinum electrodes showed that the redox reactions of iron ions are reversible and these reactions occur at a slight overvoltage. The influence of the main electrochemical parameters (current density, concentrations of iron (II) ions and sulfuric acid) on the oxidation of divalent iron ions was studied for the first time using granular anode electrodes, the electrode spaces of which are separated by an anionite membrane. It has been found that the use of granular graphite electrodes in the oxidation divalent iron ions increases the current output by more than 2 times compared to a plate graphite electrode. Conclusion. According to the results of the study, it was noted that under optimal conditions, the current output of the oxidation of divalent iron ions exceeds 90%. Extensive research has shown that trivalent iron ions, widely used in the in-situ leaching process for uranium production, can be regenerated by electrochemical methods.

Electrochemical behavior and degradation mechanism of lithium disilicate glass ceramics in acidic environment

AbstractIPS e.max Press, a lithium disilicate‐based glass ceramic, is renowned in dental restorations for its mechanical strength and aesthetic appeal. This study delves into its behavior within oral environments, employing electrochemical and surface analysis techniques. By utilizing cyclic polarization curves and impedance spectroscopy, we evaluated its degradation resistance. Surface morphology, composition, and crystal stability were explored through scanning electron microscopy (SEM)/energy‐dispersive X‐ray spectroscopy (EDX) and X‐ray powder diffraction (XRD) analysis. The glass ceramic exhibited robust resistance to localized degradation across all tested electrolytes. The degradation potential (Ecorr) varied with time and pH, indicating electrolyte influence. SEM/EDX affirmed oxide layer formation, while XRD confirmed a stable structure. While showcasing favorable resistance in saliva, citric acid, and lactic acid, IPS e.max Press demonstrated susceptibility to acetic acid. This comprehensive analysis enhances our understanding, providing valuable insights for the development of durable dental materials through a combination of electrochemical analysis and surface characterization.

Effect of Sulfide and Chloride Ions on Pitting Corrosion of Type 316 Austenitic Stainless Steel in Groundwater Conditions Using Response Surface Methodology.

This study investigates the corrosion resistance of Type 316 stainless steel as a candidate material for radioactive waste disposal canisters. The viability of stainless steel is examined under groundwater conditions with variations in pH, bisulfide ions (HS-), and chloride ions (Cl-) concentrations. Utilizing response surface methodology, correlations between corrosion factors and two crucial response variables, passive film breakdown potential and protection potential, are established. Cyclic potentiodynamic polarization tests and advanced analytical techniques provide detailed insights into the material's behavior. This research goes beyond, deriving an equation through response surface methodology that elucidates the relationship between the factors and breakdown potential. HS- weakens the passive film and reduces the pitting corrosion resistance of the stainless steel. However, this study highlights the inhibitory effect of HS- on pitting corrosion when Cl- concentrations are below 0.001 M and at equivalent concentrations of HS-. Under these conditions, immediate re-passivation occurs from the destroyed passive film to metal sulfides such as FeS2, MoS2, and MoS3. As a result, no hysteresis loop occurs in the cyclic polarization curve in these conditions. This research contributes to the understanding of Type 316 stainless-steel corrosion behavior, offering implications for the disposal of radioactive waste in geological repositories.

Electrochemical Evaluation of Manganese Electrolytes for Redox Flow Batteries

Redox flow batteries (RFBs) are promising candidates for long-duration energy storage mainly due to the lower cost of improving the energy density compared to lithium-ion batteries. However, the full sustainability of RFBs has not been achieved yet, and there is a lot of room for further improvement. One of the main parameters showing a strong influence on the sustainability of RFBs is redox active materials. In this work, manganese was selected for electrochemical evaluation as it fulfills the sustainability requirements. Manganese is a non-toxic, low-cost and abundant material with sufficient aqueous solubility[1]. Moreover, the standard potential of manganese (1.51 V) is higher than that of vanadium (1.26 V).For electrochemical parameters, we have, through cyclic voltammetry (CVs) and polarization curves, estimated the diffusion coefficient (D0 ) and heterogeneous standard electron transfer rate (k 0) of manganese in an acidic electrolyte in the presence of titanium as an additive. In order to investigate the performance of an RFB system using a manganese electrolyte, a hybrid system was designed that uses hydrogen gas on the negative side and an acidic manganese electrolyte the positive side. We have studied the resistance behavior of the hybrid RFB through electrochemical impedance spectroscopy at different states of charge. From EIS data, cell ohmic resistance, and a general idea of the different processes taking place at different state of charge were obtained. Moreover, we studied the performance of the hybrid RFB during 70 cycles, obtaining an average coulombic efficiency of 98.1%, voltage efficiency of 77.8% and capacity retention of 97.7%. Carney, J.R., B.R. Dillon, and S.P. Thomas, Recent Advances of Manganese Catalysis for Organic Synthesis. European Journal of Organic Chemistry, 2016. 2016(23): p. 3912-3929.

ELECTROCHEMICAL BEHAVIOR OF BISMUTH IONS IN CITRATE SOLUTIONS

The scientific paper is devoted to the electrochemical reduction of bismuth ions from citrate electrolytes. The kinetics and mechanism of the process and the influence of various factors on the electroreduction process of bismuth ions were studied by recording cyclic and linear polarization curves on Pt, Ni and Ni/Bi electrodes. The effective activation energy and diffusion coefficient were calculated according to the obtained data. The results of the calculation show that the electroreduction process of the bismuth ions from citrate solutions is accompanied by diffusion polarization

Corrosion Behavior and Mechanisms of Co-Cr-Mo Alloy Fabricated by Powder Metallurgy Route in Ringer's Solution

The current research is aimed to study the corrosion behavior and mechanism of Co-Cr-Mo alloy fabricated by powder metallurgy route in Ringer's solution with 7.4 and 37oC for pH and temperature values, respectively.The research was done by using a potentiostat to obtain the potentiodynamic and cyclic polarization to measure and calculate some significant parameters of the alloy corrosion. The cyclic polarization curve is indicated the resistance of the fabricated samples to the pitting and crevice corrosions. Optical, SEM and SEM-Mapping observations were revealed that the corrosion of the tested alloy was due to inter-particle and inter granular corrosion

ELECTROCHEMICAL REDUCTION OF CADMIUM IONS FROM ETHYLENE GLYCOL ELECTROLYTE

The work is devoted to the study of the process of cathodic reduction of Cd ions from anhydrous ethylene glycol electrolyte. The mechanism of the process of cadmium reduction was studied by taking linear and cyclic potentiodynamic polarization curves. The influence of cadmium chloride concentration, potential sweep rate and temperature on the process of electrochemical deposition of cadmium ions was studied. With an increase in the concentration of cadmium in the electrolyte, the rate of its release at the cathode increases. Precipitates of good quality are obtained at current densities of 25 mA/sm2. It has been established that the cadmium deposition potential almost does not change with increasing potential sweep rate. The dependence of cadmium electrodeposition from ethylene glycol electrolyte on temperature was studied, which made it possible to establish the optimal deposition temperature, which was 363–373 K, and to conclude that the deposition process is controlled by electrochemical polarization. The diffusion coefficient of cadmium ions to the cathode surface has been calculated

Optimal corrosion resistance of cobalt-based dual-phase entropic alloys via compositional modulation of aluminum

A new category of Al-doped cobalt-based dual phase entropic alloys with high corrosion resistance properties was designed in the present work. CALPHAD (CALculation of PHAse Diagram) aided prediction was performed to facilitate the alloy design. Two groups of alloys have been extensively investigated by various techniques. One group was quenched in water from the homogenization temperature (i.e. 1200 °C) to room temperature. The other group was subsequently quenched in liquid nitrogen from room temperature. The microstructure of the proposed alloys was characterized by X-ray diffraction (XRD). Several kinds of electrochemical tests were performed to study the corrosion behaviors of the designed alloys in NaCl solution, including open circuit potential (OCP), polarization and cyclic polarization curves, electrochemical impedance spectroscopy (EIS), electrochemical noise (ECN), linear voltammetry curves and staircase voltammetry scan, and Mott–Schottky method. The obtained results show that Al has a minor influence on the corrosion property of this series alloy with a 0 to 2 at.% Al addition. All the designed alloys hold quite acceptable corrosion resistance. In addition, a mechanical property, i.e. micro-hardness, is also provided as a supplement information. This work sheds light on the correlation between computational thermodynamics and corrosion behaviors in cobalt-based dual-phase entropic alloys, as well as to provide a feasibility study on the important role of CALPHAD method for a rapid development of a new category of high performance alloys.

Localized and stress corrosion cracking of sensitized Al-Mg-Sc-Zr alloy manufactured by laser powder bed fusion

The effect of thermal ageing at 150 ºC on the corrosion behaviour of Scalmalloy® (Al-Mg-Sc-Zr) alloy additively manufactured by laser powder bed fusion (LPBF) is reported for the first time. Samples before and after the thermal treatment exhibit similar results on cyclic polarisation curves, electrochemical impedance measurements in 3.5 wt% NaCl, and tensile and hardness tests. However, electron microscopy characterisation reveals that the application of this temperature for sufficient time causes most of the grain limits to be decorated by Al3Mg2 particles which in turn provokes the sensitization of the alloy to intergranular corrosion processes due to microgalvanic coupling.

Synthesis and Characterisation of CeO2 Coatings on the AZ31 Alloy for Corrosion Protection and In Vitro Biocompatibility of MC3T3-E1 Pre-Osteoblasts

The use of bioabsorbable metals as temporary medical implants has attracted considerable research interest as they do not require a second surgical operation for removal after the healing process is completed. However, magnesium (Mg) and its alloys have a degradation rate that is too high in biological environments. Therefore, it must be controlled using various strategies. In this study, an AZ31-Mg-based alloy coated with CeO2 is investigated to analyse the effect of the coating on its corrosion protection and biocompatibility. The AZ31 alloy is anodised with NaOH solution, before coating to stabilise the alloy surface. The CeO2 coating is deposited on anodised AZ31 by chemical conversion treatment. The electrochemical properties of samples are evaluated using electrochemical impedance spectroscopy and cyclic polarisation curves using Hank’s solution. Structural and morphological characterisation of the samples are performed using X-ray diffraction and scanning electron microscopy–energy dispersive X-ray spectroscopy. Additionally, biocompatibility is determined by live/dead assay using MC3T3-E1 pre-osteoblasts. The preliminary results indicate that CeO2 coatings exhibit higher electrochemical properties. Additionally, an increase in the ratio of live/dead cells of the AZ31OH-CeO2 surface is detected, in contrast with AZ31, thus indicating improvement in biocompatibility upon CeO2 coating.