Cathodic Polarization Curves Research Articles

Production and New Green Activation of Conductive 3D-Printed Cu/PLA Electrode: Its Performance in Hydrogen Evolution Reactions in Alkaline Media

In this study, Cu-polylactic acid (PLA) composite filaments were produced with an extruder and three-dimensional (3D) Cu/PLA electrodes were 3D printed with Fused Deposition Modelling (FDM) method. To improve the electrochemical performance of the 3D-Cu/PLA electrode, a novel electrochemical activation method, which differentiates from complex activation methods in the literature, was applied in 1 M KOH solution without using any solvent. Field emission scanning electron microscopy (FE-SEM), Energy-Dispersive X-ray Spectroscopy (EDX), Fourier Transform Infrared Spectroscopy (FT-IR), and RAMAN techniques were used to characterize the 3D-Cu/PLA electrode before and after activation. The results showed that Cu particles were released after the degradation of PLA after activation. In addition, the thermal stability of the 3D electrode was demonstrated by the TGA technique. The performance of the 3D Cu/PLA electrode before and after activation in the hydrogen evolution reaction (HER) in 1M solution was measured using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and cathodic polarization curves methods. The EIS results showed that the charge transfers resistance values of the 3D-Cu/PLA electrode in 1 M KOH decreased significantly after activation. Post-activation hydrogen content measurements of the 3D-Cu/PLA electrode after electrolysis at different potentials and energy efficiency tests at different current densities were also carried out. The results indicate that the electrocatalytic properties of 3D-Cu electrodes were improved for HER through the activation process.

Electrochemical Synthesis and Performance of AgCl/Ag/Sliver Mesh Collector Composite Electrode for Seawater Batteries

High-energy-density and easy-to-implement battery storage technologies are essential for the exploitation of marine resources. AgCl is a promising cathode material for seawater batteries due to its environmental friendliness and high capacities density, but its inherent low conductivity limits its application in specific scenarios. In this paper, AgCl was electrochemically grown on a sparsely conductive Ag/Sliver mesh collector (SMC) substrate, and an excellent performance AgCl/Ag/SMC composite electrode is obtained. The cathodic polarization curves indicate that the current density of the AgCl/Ag/SMC electrode was 208.2 mA cm−2 at 0.4 V (vs RHE) potential, which is significantly higher than that of the conventional AgCl cathode material. The AgCl/Ag/SMC electrode demonstrated a very high discharge capacity of 181.7 mAh g−1 at 30 mA cm−2, and the assembled cell was found to be in good condition at 100 mA cm−2 with a power density of up to 154.7 mW cm−2, showing very excellent performance. Furthermore, investigation of the mechanism and depth of discharge experiment reveal the kinetic and microscopic reasons for the high performance of AgCl/Ag/SMC composite electrodes. Therefore, this study provides an efficient and feasible solution for the electrochemical preparation of highly active cathode materials for Mg-AgCl seawater batteries.

Analysis of the influence of local electrodeposition conditions on the accuracy of electrochemical 3D-printing

Problem. Additive manufacturing of metal parts by local electrodeposition is a new promising area with several unique features. The use of electrolysis makes it possible to manufacture metal parts at room temperature with high accuracy and low energy consumption. The accuracy and speed of electrochemical 3D printing are inversely related, and therefore it is important to find optimal electrodeposition conditions at maximum speed without degrading accuracy. The aim of the study. The purpose of this work was to analyse the influence of electrodeposition parameters (electrode distance, electrical conductivity and electrolyte polarization) on the accuracy of metal deposit formation in a computer model and to conduct experimental verification of optimal conditions for electroforming a real object from copper sulphate electrolyte. Methodology of implementation. To achieve the goals of the study, computer simulation of the electrochemical deposition process in the COMSOL Multiphysics software and electrochemical measurements of the characteristics of copper sulphate electrolytes were used. Research results. Computer simulation established optimal conditions: the distance between the edge of the capillary and the surface on which deposition occurs is not more than 0.5 mm, the electrolyte in which the inverse slope of the cathode polarization curve is not lower than 2000 mA/(V×cm2) and the electrical conductivity is not higher than 0.02 S/сm. The influence of the electrolyte composition on the inverse polarization of the cathode process and its electrical conductivity was investigated. The optimal composition of the electrolyte was selected, containing 200 g/L CuSO4, 60 g/L H2SO4, 0.2 g/L KCl and RUBIN T-200 additive. In the selected electrolyte, the value of the inverse slope of the cathode polarization curve is 2120 mA/(V×cm2). Verification of the process of local electrodeposition in the selected electrolyte during the electroformation of a cylindrical object with a diameter of 4 mm and a height of 100 μm was carried out. It was determined that no more than 5 % of metal was deposited outside the capillary of the working electrode. Conclusions. The results of the work can be used to create an electrochemical 3D printing system. Further research should be aimed at approbation of the obtained parameters of local electrodeposition in an installation that simulates the operation of a 3D printer and establish the accuracy and speed of printing of a three-dimensional object. Key words: additive manufacturing, electrical conductivity, electrolyte composition, polarization, local electrodeposition.

Electrochemical behavior of aluminum in 1-ethyl-3-methylimidazolium chloroaluminate ionic liquids

The mechanism of electrochemical oxidation and reduction of aluminum in 1-ethyl-3-methylimidazolium-based (EMImCl) chloroaluminate ionic liquids is studied across the concentration range of N = 1.1–2.0 (N the molar ratio of AlCl3 to EMImCl) at temperatures between 303 K and 418 К. Anodic stationary polarization curves (SPCs) indicate that the process of anodic dissolution of aluminum is complicated by passivation. The current density in the passive region and the passivation potential decrease with a higher concentration of Al2Cl7– ion in the melt. To elucidate the processes taking place at the aluminum electrode, the relationship between the concentration of the ions in the vicinity of the electrode and the potential applied in the cathodic and anodic region was analyzed by in-situ Raman spectroscopy for the concentrations of N = 1.1 and 2.0. The resulting dependences of relative peak intensity vs. potential correlate with the cathodic and anodic polarization curves. In the anodic region the content of Al2Cl7– grows with the potential, while the concentration of AlCl4– ion decreases. In the cathodic region the opposite process is observed: the concentration of Al2Cl7– decreases and that of AlCl4–increases with growing potential. It is shown that a precipitate of AlCl3 forms on the electrode surface in the region of passive aluminum dissolution, which is responsible for the electrode passivation. Based on the results obtained, we propose a model for the process of aluminum oxidation/reduction preceded and followed by a chemical reaction of aluminum chloride formation for the cathodic and anodic process, respectively. Temperature dependences of diffusion coefficients are studied by chronopotentiometry. The results indicate that diffusion coefficients are not affected by the concentration across the temperature range studied. The activation energy for diffusion was found to be 13.65 kJ∙mol−1. Impedance spectroscopy was used to investigate the concentration and temperature dependences of exchange current density. The exchange currents increase with increasing aluminum chloride content in the melt. The transfer coefficient and electrochemical reaction rate constant were found to be α = 0.17 ± 0.04, ks = (1.7 ± 0.4)∙10−6 cm∙s−1, respectively. The activation energy for the electrochemical reaction rate constant does not depend on the concentration and was found to be 33.5 kJ∙mol−1.

SURFACE TREATMENT EFFECTS ON THE CORROSION OFREINFORCED STEEL IN CONCRETE EXPOSED TO DRYCONDITION

The destroying of Tafel region in many cases is not due to complication u'ith mass transfer , butdue to IR - drop effsct specially in dilute solutions ( i.e., of high resistivity) . Accordingly, thecorrosion behavior of reinforcement in reinforced concrete was investigated using electro -chemical measurements. The work was carried out with small steel rods: cleaned and previouslyoxidized embedded in resistance Portland cement concrete cylinders exposed to dry conditions' Inthis investigation a theoretical model equation has been adopted including IR- drop term:AE =AEA +RAi = -bclogicorr.+ bclog/Ai/+R /Ai/In order to determine corrosion paiameters of iystem investigated (i.e., icorr., bc, and Rc. A)equation above was based on the analysis of cathodic Polarization curve free from mass transf'ereffect .It has been found that the corrosion curent of pre- oxidized steel is higher than the cleanedone , and this corrosion rate is concrete contaminant & time of exposure dependant. because of theimportance of electrical resistance of concrete & its relationship to the corrosion rate of reinforcingsteel. An attempt was made to find this resistance from the IR-drop term in the above mentionedequation.

Unveiling the potent corrosion-inhibiting power of Ammophila arenaria aqueous extract for mild steel in acidic environments: An integrated experimental and computational study

Plant extracts have emerged as potent inhibiting compounds for metallic corrosion, offering numerous advantages including simple accessibility, low toxicity, eco-friendliness, biocompatibility, effectiveness, and renewability. In this study, the potential of Ammophila arenaria extract as a green corrosion inhibitor for mild steel in 1.0 M HCl over the concentration range of 25–700 ppm was evaluated, using various electrochemical analyses such as Open circuit potential (OCP), potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). Results revealed a notable reduction in the corrosion rate of steel, particularly at 700 ppm, where Ammophila arenaria extract demonstrated its highest inhibition efficiency, reaching 83.67% for polarization and 84.32% for EIS. The cathodic and anodic polarization curves indicated that the aqueous extract of Ammophila arenaria functions as a mixed-type inhibitor. The thermodynamic analysis revealed a negative Gibbs free energy value (∆Gads°), suggesting spontaneous physisorption as the predominant adsorption mechanism. To delve into the inhibition mechanism at the molecular level, the surface morphology of mild steel exposed to 1.0 M HCl solutions, both in the absence and presence of Ammophila arenaria aqueous extract, was scrutinized through Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Theoretical techniques, including Quantum Calculation Theory, Non-Covalent Interaction (NCI), and Atom In Molecule (QTAIM), were concurrently employed, providing valuable insights into molecular-level interactions. Remarkably, the computational studies complemented and corroborated the experimental data. These comprehensive results significantly contribute to the understanding of Ammophila arenaria extract's corrosion inhibiting properties, endorsing its potential as a sustainable and environmentally friendly corrosion inhibitor suitable for diverse industrial applications. The synergistic integration of experimental and computational approaches establishes a robust foundation for future endeavors in the field of green corrosion inhibitors.

KINETICS OF CATHODIC HYDROGEN EVOLUTION ON MOLYBDENUM DISILICIDE IN ACID SULPHATE MEDIA

The kinetics and mechanism of hydrogen evolution on the MoSi2 electrode in x M H2SO4 + (0.5 - x) M Na2SO4 (x = 0.50; 0.35; 0.20) solutions have been studied. The cathodic polarization curves of MoSi2 in the studied solutions are characterized by Tafel region with a slope of (-0.070)±0.002 V. The reaction order of the cathodic process with respect to hydrogen ions at the potentials of Tafel region is ~1.0; the derivative of the electrode potential with a change in electrolyte acidity is ~0.072 V. The impedance spectra of the MoSi2 electrode in the studied potential range have the shape of a semicircle located in the capacitive half-plane, with the centre in the region of positive values of the imaginary impedance component; in the region of the highest frequencies, a short straight section is recorded on the impedance plots, indicating the presence of pores in the surface layer of the electrode. To describe the hydrogen evolution reaction on MoSi2, we used an equivalent electrical circuit, the Faraday impedance of which consists of series-connected charge transfer resistance (R1) and a parallel R2C2Zd-chain responsible for the adsorption of atomic hydrogen on the surface and its diffusion into the depth of the electrode material. The equivalent circuit also includes the solution resistance (Rs) and the double layer capacitance impedance, which is modeled by the constant phase element CPE1. It is shown that the hydrogen evolution reaction on molybdenum disilicide in a sulphuric acid electrolyte proceeds along the discharge - recombination route with a quasi-equilibrium discharge stage when the Temkin logarithmic isotherm for adsorbed atomic hydrogen is fulfilled. The hydrogen evolution reaction is complicated by hydrogen absorption proceeding in the mode of solid-phase diffusion kinetics.

ЭЛЕКТРОХИМИЧЕСКОЕ ЛЕГИРОВАНИЕ ЦИНКОВЫХ ПОКРЫТИЙ ХРОМОМ И НИКЕЛЕМ ИЗ ГЛИЦИНАТНЫХ РАСТВОРОВ

The purpose of this work is the electrochemical alloying of zinc coatings with chromium and nickel from electrolytes containing heteronuclear complexes. Zinc coatings are widely used to protect steel products from corrosion in the atmosphere of various climatic zones. To increase corrosion resistance, zinc coatings are chromated or phosphated. An effective way to increase the corrosion resistance of the coatings under study is their alloying with other metals. Obtaining such coatings makes it possible to reduce their thickness and increase their service life, solve environmental problems when replacing cadmium. The kinetics of the process on zinc and steel electrodes has been studied by removing cathode polarization curves. It is suggested that the absence of characteristic current peaks on the polarization curves is due to the convergence of the electrode potentials of individual metal ions recovering from heteronuclear compounds, as well as the concomitant discharge reaction of proton donors. X-ray fluorescence analysis has shown that in the studied range of current densities 1-5 A/dm2, the content of alloying metals in the coating reaches 1.4% for chromium and 9.8% for nickel. The obtained data on the elemental composition of zinc coatings indicate an abnormal co-deposition of zinc with nickel. Chromium in coatings is observed at higher current densities of 4-5 A/dm2.The data obtained in this work can be used in electroplating in the development of processes for alloying zinc coatings with chromium and nickel in order to replace cadmium coatings.

EFFECT OF SURFACE TREATMENT ON THE ELECTROCHEMICAL ACTIVITY OF Ti3SiC2/TiC/TiSi COMPOSITE MATERIAL IN THE HYDROGEN EVOLUTION REACTION

The effect of treatment of the surface layer of the Ti3SiC2/TiC/TiSi composite material on its electrochemical activity in the of hydrogen evolution reaction in 0.5M H2SO4 has been studied. Surface treatment has been carried out by chemical etching in solutions of 15, 30, 45% HF for 15, 30, 45 min at 25 and 60 °C. It has been established that the cathodic polarization curves of the Ti3SiC2/TiC/TiSi-electrode without and with surface treatment have a Tafel section with a slope of 0.060–0.076 V and they are characterized by an overvoltage value of 0.20–0.26 V at i = 1 mA/cm2. The rate of the cathodic reaction as a result of treatment increases by ~1.6-9.8 times. The greatest increase is caused by high-temperature etching in a solution of 30% HF for 30 min while stirring the solution. The impedance spectra of the Ti3SiC2/TiC/TiSi-electrode at Tafel region potentials consist of a capacitive semicircle with a displaced center. On the impedance graphs of the treated electrode, a straight section with a slope above 45º was registered in the region of the highest frequencies, indicating the presence of pores in the surface layer of the electrode. To describe the hydrogen evolution reaction on Ti3SiC2/TiC/TiSi, we used an equivalent electrical circuit, the Faraday impedance of which consists of charge transfer resistances R1 connected in series and a parallel R2C2-chain corresponding to the adsorption of atomic hydrogen on the electrode surface. The equivalent circuit also includes the electrolyte resistance Rs and the double layer capacitance impedance, which is modeled by the constant phase element CPE1. It has been shown that the results of polarization and impedance measurements agree satisfactorily with the discharge–electrochemical desorption mechanism with a quasi-equilibrium discharge stage when the logarithmic Temkin adsorption isotherm for adsorbed atomic hydrogen is fulfilled. It has been concluded that the composite material Ti3SiC2/TiC/TiSi in sulfuric acid electrolyte is a promising electrode material for the electrochemical production of hydrogen.

Corrosion Inhibition Performance of Euphorbia pulcherrima Bark Extract in 1M H2SO4 on Mild Steel

The bark of the attractive flower Euphorbia pulcherrima (Lalupate), which is widely accessible in Nepal, can be used to extract an alkaloid that acts as a corrosion inhibitor. The methanolic extract of Euphorbia pulcherrima (EP) in 1M H2SO4 was employed to study corrosion inhibition of mild steel (MS) by weight loss and potentiodynamic technique. The immersion time and EP extract concentration consequences on corrosion inhibition were explored. The weight loss of MS is significantly reduced in the presence of EP inhibitors caused by the adsorption of inhibitor molecules. The findings exhibited that the increasing immersion time and EP concentration resulted in an increment in inhibition efficiency (IE). The maximal IE from the weight loss method was determined to be 90.38% for 1000 ppm extract immersed for 6 hours at room temperature and 86.36% IE was obtained for 1000 ppm concentration of the EP extract after 1hr of immersion by potentiodynamic polarization. The open circuit potential (OCP) of the MS in the inhibitor solution confirmed the EP extract behaving as a mixed inhibitor. The current density decreased with the addition of the EP, which reflected the inhibitive nature of inhibitor molecules. Similarly, the corrosion current density decreased as the EP extract concentration increased. Hence, it implied that the bark extract of EP is a potent inhibitor of MS corrosion, even after just one hour of immersion. Because of the reduction of hydrogen ions and the adsorption of inhibitor molecules on the MS surface, EP extract is effective in inhibiting corrosion current on the cathodic and anodic polarization curves, forming a barrier that stops the evolution of hydrogen gas and metal dissolution. Fourier Transform Infrared (FTIR) spectroscopic analysis showed the presence of N-H and C=O functional groups in the EP attributed to the adsorption on MS and consequently reducing the dissolution of MS.

High temperature electrochemical reaction parameters affecting electrochemical corrosion potential of stainless steels in hydrogen peroxide environment

ABSTRACT High-temperature electrochemical reaction parameters for stainless steels have been determined based on data measured in pure water at high temperatures to realize an analytical model that can predict electrochemical corrosion potential (ECP) of stainless steels in a hydrogen peroxide (H2O2) environment without using any adjustment parameters based on ECP data. Behaviors of measured cathodic polarization curves for H2O2 were explained well with the determined parameters. Calculated ECPs of stainless steels agreed with measured values in the cases that it was acceptable for the model to have an error range of ±0.1 V in a range from the deaerated condition to 1000 ppb (= μ g kg−1) H2O2 concentration. It is expected that the ECP model in the H2O2 environment with the determined electrochemical reaction parameters will have greater validity for, and better interpretability of, the ECPs of stainless steels determined in a boiling water reactor environment than previous models.

Cathodic Polarization Behavior of Steel in Aqueous MgCl2 Solutions Containing Zn2+

So far, we have revealed that the dissolution rate of zinc is accelerated in relative high concentrations of MgCl2 in the corrosion process of galvanic couples consisting of zinc and steel. In this study, we investigated the cathodic polarization behavior of steel in MgCl2 solution containing Zn2+ and the effect of Zn2+ dissolved in the solution on the oxygen reduction reaction and hydrogen evolution reaction.The specimens used in the experiments were carbon steel SS400 (Fe-0.12C-0.60Mn-0.011P-0.019S) machined into a 1.5×1.5×0.3 cm3. One side of the specimen was polished with SiC abrasive paper up to #2000 grit and degreased in acetone before being used for the experiment. The test solution was mixtures of 0.25 M MgCl2 + x mM ZnCl2 (x = 2.5, 5 mM, Mg/Zn molar ratio: 100, 50) at room temperature under a naturally aerated condition. As a comparison solution, 0.5 M NaCl + y mM ZnCl2 (x = 5, 10 mM, molar ratio of Na/Zn: 100, 50) with the same chloride ion concentrations were used. Cathodic polarization curves of steel were measured using a three-electrode method with a platinum wire as the counter electrode and an Ag/AgCl electrode (saturated KCl, SSE) as the reference electrode. The potential sweep rate was 0.5 mV/s. After the polarization test, the specimen surfaces were observed with a scanning electron microscope and analyzed for corrosion products formed during cathodic polarization with XRD and laser Raman spectroscopy.The cathodic polarization behavior of steel in MgCl2 solution without Zn2+ was investigated and compared with that of NaCl solution without Zn2+. Diffusion-limited currents of dissolved oxygen reduction (ORR) were observed at -0.6 V to -0.8 V in MgCl2 and NaCl solutions. Furthermore, cathodic polarization in MgCl2 and NaCl solutions showed an increase in current due to hydrogen evolution reaction (HER), and the cathodic current due to HER on steel was larger in the MgCl2 solution than in the NaCl solution. To investigate the difference in HER in both solutions, the steel surface was observed after constant polarization at -1.0 V for 20 min. Mg(OH)2 deposition was observed on the steel surface in the MgCl2 solution, but not in the NaCl solution. This indicates that the increase in pH due to ORR and HER is mitigated by the formation of Mg(OH)2 during cathodic polarization. Therefore, due to the pH buffering action of Mg2+ associated with the formation of Mg(OH)2, it can be considered that a larger HER current flowed in the MgCl2 solution than in the NaCl solution when compared at the same potential.On the other hand, cathodic polarization curves for steel in MgCl2 and NaCl solution containing Zn2+ were investigated. As a result, ORR and HER were observed at potentials down to -1 V in the MgCl2 and NaCl solutions containing Zn2+; the cathodic current due to ORR and HER in the MgCl2 and NaCl solutions containing Zn2+ was reduced compared to the solutions without Zn2+. The inhibition of ORR and HER can be attributed to the precipitation of Zn corrosion products.These results suggest that in solution environments containing Mg2+ and Zn2+, the promotion of HER by the effect of Mg2+ and the inhibition of HER and ORR by Zn corrosion products occur simultaneously.

Study on the electrodeposition of Bi2Te3 thin film thermoelectric material in dimethyl sulfoxide

In this paper, the electrochemical behaviors of Bi3+ and Te4+ ions in dimethyl sulfoxide (DMSO) organic solvent were studied by testing the cyclic voltammetry curves and cathodic polarization curves. The diffusion coefficients of Bi3+ and Te4+ ions were investigated and calculated, and reduction difficulty of them was compared. Then, bismuth telluride thermoelectric thin films were prepared using potentiostatic electrodeposition mode in the electrolytes with different compositions at different potentials. The structure, morphology and compositions of the prepared thermoelectric materials were characterized and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (EDS). The results show that the redox processes of Bi, Te and bismuth telluride on Au electrode are all completely irreversible processes. The diffusion coefficient of Bi3+ ion has an order of magnitude of approximately 10−7 while that of Te4+ ion is about 10−5. The reduction of Bi3+ ion is more difficult than that of Te4+ ion in dimethyl sulfoxide organic solvent. The prepared thin film thermoelectric materials are bismuth telluride alloy, and the electrolyte composition and deposition potential have great influence on the structure, morphology and composition of the films. Increasing the concentration of Bi3+ ions in the electrolyte can greatly increase the content of element Bi in the deposits. In the electrolyte containing 20 mol·L−1 Bi(NO3)3·5H2O and 10 mol L−1 TeCl4, the bismuth telluride film electrodeposited at − 1.2 V has uniform grain size and compact structure, shows good surface morphology, and the atomic fraction ratio of Bi/Te element in the film is 1:1.80.

CATHODIC EVOLUTION OF HYDROGEN ON IRON DISILICIDE IN ALKALINE ELECTROLYTE

The kinetics and mechanism of hydrogen evolution on the FeSi2 electrode in 0.25-1.0 M NaOH solutions have been studied by polarisation and impedance measurements. The cathodic polarisation curves of iron disilicide in the studied solutions are characterized by a Tafel region with constants α and β equal to (-0.78)-(-0.72) and (-0.133)-(-0.128) V, respectively. The impedance spectra of FeSi2 at the potentials of the Tafel region represent a capacitive semicircle with a displaced centre, which corresponds to an asymmetric maximum in the graph of phase angle dependence on the logarithm of the alternating current frequency; the magnitude of the electrode impedance in all solutions changes in accordance with the course of the polarization curves. To describe the hydrogen evolution reaction on iron disilicide, an equivalent electrical circuit was used, the Faraday impedance of which consists of series-connected charge-transfer resistances and a parallel circuit responsible for the adsorption of atomic hydrogen on the surface and its diffusion into the depth of the electrode material; the circuit also includes the electrolyte resistance and the double-layer capacitance impedance, which is modelled by a constant phase element. It is shown that the results of polarization and impedance measurements for the FeSi2 electrode are in satisfactory agreement with the discharge-electrochemical desorption mechanism, in which both stages are irreversible and have unequal transfer coefficients; for adsorbed atomic hydrogen, the Langmuir adsorption isotherm is satisfied; simultaneously with the reaction of hydrogen evolution, the reaction of hydrogen absorption by the electrode material proceeds with diffusion control. It has been found that iron disilicide in an alkaline electrolyte is characterised by the low overvoltage of hydrogen evolution, and it is a promising electrode material for the electrolytic production of hydrogen.

Influence of polarization curve slope on the accuracy of local copper electrodeposition from sulphate electrolyte

Local electrochemical deposition is an emerging technique, used in the field of additive manufacturing. The advantage of electrochemical additive manufacturing lies in the utilization of room temperature electrolyte and permits to manufacture microscale objects with high precision. The increase in deposition current increases the deposition area, so measures are to be taken to focus the electric field. This work describes the influence of polarization curve slope on the accuracy of local deposition, both experimentally and by computer modelling. The copper was deposited using rotating anode on the surface of stainless steel from sulphate electrolyte. The influence of electrolyte composition on the accuracy of deposition was investigated. The profile of deposited parts was analyzed by profilometry and microscopy. The increased amount of sulfuric acid and presence of the additive in the electrolyte was shown to increase the accuracy of deposition by changing the slope of cathodic polarization curve from 320 to 1100 mA V–1cm–2).

Kinetics of corrosion reactions on press hardened steel in atmospheric conditions under thin electrolyte films

Steels with high mechanical performance are prone to hydrogen embrittlement and environmental assisted cracking. Under atmospheric corrosion conditions, the source of hydrogen can be the steel corrosion process itself or galvanic coupling with a metallic coating. Electrochemical behaviour of Press Hardened Steel (PHS) under electrolyte films of different thicknesses using local electrochemical techniques was studied on a fundamental level. Scanning Vibrated Electrode Technique (SVET) was applied to study the evolution and localization of the corrosion process during PHS immersion in NaCl electrolyte. Kelvin Probe (KP) was used as a reference electrode to obtain cathodic and anodic polarization curves on PHS surfaces which were covered by thin electrolyte films (60 to 500 µm) of 0.1 M NaOH and 0.6 M NaCl. For both electrolytes, a strong increase in the oxygen reduction rate due to the decreasing of electrolyte thickness has been clearly demonstrated. Data are correlated well with a theoretical plot determined by Nernst-Fick equation. The influence of the rust layers on the kinetics of corrosion reactions under thin electrolyte films was investigated using KP.

Modeling and Predicting Reduction Reaction Kinetics for a Stainless-Steel in NaCl Solutions

A method for analyzing cathodic polarization curves on stainless steels is described and a framework for predicting the cathodic polarization response for UNS S13800 is developed, including a model for the diffusivity of dissolved oxygen as a function of chloride concentration and temperature. The cathodic polarization behavior of UNS S13800 in NaCl solutions, ranging from dilute to saturated, and across a range of temperature values was studied using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). Analysis of the data indicated that the concentration of the solutions affected the ability of the oxide to catalyze reduction reactions. Dilute-to-low concentration solutions exhibited different Tafel slopes in the ORR-activation region while middle-to-high concentration solutions exhibited a single Tafel slope. The XPS and EIS results show a slightly thicker oxide formed in the low chloride concentration solutions over the course of the 18 hour open circuit duration along with a higher concentration of Fe3+ species.. The EIS data also showed the oxide formed in the low chloride solution had a higher charge-transfer resistance while the oxide formed in the high chloride solution had a higher oxide resistance.

Influence Mechanism of (NH4)2SO4 on the Composition and Structure of Fe-Co Alloys

Fe-Co alloys have the advantages of high saturation magnetization and high magnetic elongation. They are used in electromagnet pole heads, earphone vibration films, magnetostriction transducers, and so on. At present, few papers have been published on the co-deposition process of Fe-Co alloys. In the present work, smooth dense Fe-Co films of 10 μm were successfully prepared in an economical, green, sulfate solution system via electrodeposition. The cathodic polarization curves were measured separately under different conditions, and the electrochemical analyses showed that the increase in the main salt concentration is beneficial for obtaining higher deposition rates. An increase in temperature can increase the current density of electrochemical reduction of Fe2+, and 50 °C is a suitable temperature at which to prepare the Fe-deposited layer with a flat surface. The increase in Co2+ concentration can favor the co-electrodeposition process of Fe-Co alloys. Secondly, the EDS results showed that the mass fraction of Co in the films increased linearly with the increase in Co2+ concentration in the solution. The mass fraction of Co in the films gradually increased with the increase in current density. The mass fraction of Co in the films gradually decreased with the increase in (NH4)2SO4 concentration. In addition, the XRD showed that the grain size of the Fe-Co alloy films was closely related to the concentration of (NH4)2SO4 in the electrolyte, and the smallest crystallite size of the Fe-Co alloy film was 17 nm. SEM showed that (NH4)2SO4 can significantly affect the surface morphology of the films, in which the cracks are obviously removed.

Corrosion of Synthetic Intermetallic Compounds and AA7075-T6 in Dilute Harrison’s Solution and Inhibition by Cerium(III) Salts

This study addresses the behavior of an aluminum alloy and its components in conditions simulating the presence of atmospheric salts. The corrosion of synthetic intermetallic compounds (IMCs) Al2Cu, Al2CuMg, Al7Cu2Fe, MgZn2, and bulk aluminum alloy 7075-T6 was studied in dilute Harrison’s solution (DHS, 0.35 wt% (NH4)2SO4 + 0.05 wt% NaCl). For IMCs, electrochemical measurements were performed using a microcell, and a standard electrochemical cell was used to study the bulk alloy. Separately measured cathodic and anodic potentiodynamic polarization curves were recorded, and prolonged immersion was characterized using electrochemical impedance spectroscopy. Samples were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Bulk AA7075-T6 was less susceptible to corrosion in DHS than in chloride solution stemming from the beneficial presence of sulfate ions and lower chloride concentration. The susceptibility of IMCs to corrosion in DHS increased in the order Al2Cu < Al7Cu2Fe < Al2CuMg < MgZn2 due to the increased dissolution of Mg in the presence of ammonium ions. The relative nobility of IMCs was determined based on the galvanic current density. Further, the possibility of using cerium chloride, nitrate and acetate salts as corrosion inhibitors in DHS was evaluated. Ce salts acted as inhibitors for the alloy during 14 d testing, forming a Ce hydroxide layer. The degree of protection depended on the type of anion, with acetate Ce salt giving the most efficient protection. For the IMC, however, inhibition by Ce salts did not occur during short measurements in the microcell, indicating the importance of galvanic interaction with the alloy matrix in the inhibition mechanism, which was confirmed by long-term measurements of the alloy.

CORROSION OF CARBON STEEL IN THE WATER BASINS OF SHEMKIR AND YENIKEND HYDROELECTRIC POWER PLANTS

Using gravimetric and electrochemical research methods, the corrosion-electrochemical behavior of carbon steel grade St3 in Kura river water has been. Gravimetric measurements were carried out under operating conditions of the Shemkir and Yenikend hydroelectric power stations for one year. Along with this, the ionic and bacteriological composition, as well as some physicochemical parameters of these waters were established. It revealed that St3 in the Kura water corrodes at a rate of (0.04÷0.05) g/m2•hour, which is characteristic of steel corrosion in fresh waters. In the atmosphere of hydraulic structures, steel corrodes at rather a low rate, i.e. (5÷6)10-3 g/m2 hour. As a result of biochemical analysis, sulfate-reducing bacteria (SRB) were discovered in these waters, which are a dangerous organism that releases the corrosive substance of H2S. By taking the anodic and cathodic polarization curves, a quasi-stationary steel corrosion rate was established to be 0.06g/m2 h.