Potentiodynamic Mode Research Articles

Influence of alkaline earth metals on the corrosion-electrochemical behavior of lead babbit BKa, BSt, BBa (PbSb15Sn10) in NaCl electrolyte medium

The article presents the results of study of the effect of additions of calcium, strontium and barium (0.01–1.0 wt %) as a structure modifier on the anodic behavior of lead babbits BKa, BSt, BBa (PbSb15Sn10) in NaCl electrolyte medium. The studies were carried out by the potentiostatic method in a potentiodynamic mode with a potential sweep rate of 2 mV/s.Studies show that with time the free corrosion potential of alloys shifts to the positive side, and with an increase in the concentration of the modifier (calcium, strontium and barium) in lead babbits, acquires a positive value. The addition of calcium to lead babbit BKa (PbSb15Sn10Ca) increases its corrosion resistance by 10 – 15%, strontium BST (PbSb15Sn10Sr) by 15–20%, and barium BBa (PbSb15Sn10Ba) by 20–25%. An increase in the corrosion rate of alloys was noted, regardless of t heir composition from the NaCl concentration in the solution. It has been shown that an increase in the chloride ion concentration in the NaCl electrolyte leads to a decrease in the potentials of free corrosion, repassivation, and pitting formation of alloys.

Effect of lithium on the anodic behavior of AlTi0.1 aluminum conducting alloy in NaCl electrolyte environment

Aluminum ranks as the fourth most conductive metal, trailing behind silver, copper, and gold in electrical conductivity. Annealed aluminum demonstrates an approximate 62 % conductivity of the International IACS compared to annealed standard copper, which registers 100 % IACS at t = 20 °C. Because to its low specific gravity, aluminum exhibits twice the conductivity per unit mass compared to copper, showcasing its potential economic advantage as a material for conducting electricity. For equal conductivity (in terms of length), an aluminum conductor exhibits a cross-sectional area 60 % larger than that of copper, while weighing only 48 % of copper's mass. However, the widespread use of aluminum as a conductor in electrical engineering is often challenging and sometimes unfeasible due to its inherent low mechanical strength. Enhancing this crucial property is achievable through the addition of dopants. However, this approach tends to elevate mechanical strength at the cost of noticeable reductions in electrical conductivity. This study investigates the impact of lithium addition on the anodic behavior of an A5 aluminum conductor alloy, specifically modified with 0.1 wt.% Ti (AlTi0.1 alloy), within a NaCl electrolyte environment. The experiments were conducted utilizing the potentiostatic method in potentiodynamic mode at a potential sweep rate of 2 mV/s. Results indicate that the introduction of lithium to the AlTi0.1 alloy leads to a shift in the potentials of free corrosion, pitting, and repassivation towards positive values. Additionally, the corrosion rate decreases by 10–20 % with the incorporation of 0.01–0.50 wt.% Li. Moreover, varying concentrations of chloride ions in the NaCl electrolyte prompt fluctuations in the corrosion rate of the alloys and a shift in electrochemical potentials towards the negative range.

A novelty in local electrochemical analysis with a pressing sensor cell (a review)

Local electrochemical analysis (LEA) with a pressure cell-sensor (CSC) is based on electrodecrystallization of the material studied (metal, alloy, powder composition, semiconductor structures, etc.) in an area limited by the size of the hole in the graphite CSC filled with the appropriate electrolyte, and recording the dissolution current strength. The selected surface of the analyzed material or product is the working electrode, and the graphite body of the cell or a special electrode inserted into the inert body of the cell is the counter electrode. Choice of the electrolyte and dissolution mode determines the possibility of using LEA with CSC for studying thickness of the layer, surface composition or the distribution of the composition over the thickness of the material layer in the controlled area, with a diameter of 1–2 mm. Design of the CSC and methods of its application were developed in the 60s of the last century by a team of authors from Kuibyshev Polytechnical Institute (now SamSTU) for coulometric control of monolayer metal coatings on watch cases, which resulted in the corresponding requirements to the size of the cell body and its contact hole. Subsequent studies showed possibility of using LEA with CSC for controlling thickness of multilayer metal coatings with individual metals on various products, composition of binary alloy coatings by selective dissolution of their components in a potentiodynamic mode, as well as powders and powder compositions pressed into a pellet electrode, control of the distribution profile of the alloying impurity in silicon epitaxial structures, thickness of oxide films, phase composition of metal alloy samples and a number of other application parameters. The present work provides an overview of advances in the development of theory, methodology, tools and practical applications of local electrochemical analysis over the last decade.

Анодное поведение свинцового баббита БСт (PbSb15Sn10Sr), модифицированного стронцием, в среде электролита NaCl

The article presents the results of a study of the effect of strontium additives (0.01 – 1.0 wt. %) as a structure modifier on the anodic behavior of lead babbit (PbSb15Sn10Sr) in the NaCl electrolyte medium. The studies were carried out by the potentiostatic method in the potentiodynamic mode with a potential sweep rate of 2 mV/s. Studies have shown that over time, the free corrosion potential of alloys shifts to the positive side and with an increase in the concentration of the modifier (strontium) in lead babbit, it acquires a positive value. The addition of strontium to lead babbitt (PbSb15Sn10Sr) increases its corrosion resistance by 10 – 15 %. An increase in the corrosion rate of alloys was noted, regardless of their composition from the NaCl concentration in the solution. Studies have shown that an increase in the concentration of the chloride ion in the NaCl electrolyte leads to a decrease in the potentials of free corrosion, repassivation, and pitting of alloys.

Электрохимическая переработка отходов ренийсодержащих сплавов на основе вольфрама в аммиачно-карбонатных растворах

The electrochemical behavior of rhenium-containing tungsten alloys waste of the type WRe (wt. %: W — 80–95, Re — 5–20) in a solution of (NH4)2CO3 1,0 M was studied using the method of linear voltammetry in potentiodynamic mode and potentiostatic electrolysis. Separation of tungsten and rhenium from the resulting electrolyte was carried out by crystallization of ammonium paratungstate and concentration of rhenium in the mother liquor. A basic technological scheme for the processing of rhenium-containing tungsten alloys is proposed.

Effect of Barium on the Corrosion and Electrochemical Behavior of Lead Babbit BBa (PbSb15Sn10Ba) in a NaCl Electrolyte Medium

Results are presented from studying the effect barium additives (0.01–1.0 wt %) as a structure modifier have on the anodic behavior of lead babbit BBa (PbSb15Sn10Ba) in a NaCl electrolyte medium. The studies are performed using the potentiostatic technique in the potentiodynamic mode with a potential sweep rate of 2 mV/s. It is shown that the free corrosion potential of alloys shifts to the positive side over time and acquires a positive value upon an increase in the concentration of the modifier (barium) in the lead babbit. Adding barium to lead babbit BBa (PbSb15Sn10Ba) raises its corrosion resistance by 20–25%. An increase in the rate of the corrosion of alloys is noted, regardless of their composition and the concentration of NaCl in a solution. It is shown that raising the concentration of chloride ions in a NaCl electrolyte lowers the potentials of the free corrosion, repassivation, and pitting of alloys.

Electrodeposition and Properties of Composite Ni Coatings Modified with Multilayer Graphene Oxide.

Within the framework of this study, Ni-based composite electrochemical coatings (CECs) modified with multilayer graphene oxide (GO) processed using microwave radiation have been deposited. The process of these coatings' electrodeposition in the potentiodynamic mode has been studied. The structure of Ni-GO and Ni-GO (MW) CECs has been studied using X-ray phase analysis (XPA) and scanning electron microscopy (SEM).It has been shown that the addition of GO into a nickel deposit contributes to the formation of uniform fine-grained coatings. As a result, the microhardness of the Ni-GO (MW) CECs increases by 1.40 times compared to Ni without GO. The corrosion-electrochemical behavior of nickel CECs in 0.5 M H2SO4 solution was researched. It was established that the corrosion rate of the nickel-GO (MW) CEC in 3.5% NaCl decreases by about 1.70 times in contrast to unmodified nickel coatings. This effect is due to the absence of agglomeration of the graphene oxide in the volume of the nickel matrix and the impermeability of GO particles to the corrosive environment.

ELECTROCHEMICAL PROCESSING OF HEAVY TUNGSTEN ALLOY WASTE IN AMMONIUM CARBONATE SOLUTIONS

The electrochemical behavior of tungsten and the VNZHK alloy (wt. %: W 90; Ni 7.2; Fe 1.8; Co 1) in solutions of (0.5—1.5 M) ammonium carbonate was investigated by linear voltammetry in a potentiodynamic mode. An increase in the maximum anodic density of the oxidation current of tungsten and the VNZHK alloy was revealed with an increase in the ammonium carbonate concentration. The process of electrochemical dissolution of the VNZHK alloy waste in a 1.0 M solution of ammonium carbonate was investigated by galvanostatic electrolysis, as well as electrolysis under the action of a sinusoidal alternating current of industrial frequency. The advantage of alternating use of direct and alternating currents is justified. It has been established that during the processing of the VNZHK alloy waste under the alternating action of direct and alternating currents, the transition of tungsten from the alloy to an ammonium carbonate solution is accompanied by the concentration of the iron subgroupmetals in the microdisperse sludge of electrolysis. A basic technological scheme for the tungsten extraction from the heavy tungsten alloys waste with the production of ammonium paravolframate as the final product is proposed.

АНОДНОЕ ПОВЕДЕНИЕ АЛЮМИНИЕВОГО СПЛАВА АlМg5.5Li2.1Zr0.15 ЛЕГИРОВАННОГО КАЛЬЦИЕМ В СРЕДЕ ЭЛЕКТРОЛИТА NaCl

Duralumin alloy is widely used in the aircraft industry, in the production of high-speed trains (for example, Shinkansen trains) and in many other branches of mechanical engineering (since it is significantly more durable than pure aluminum). Along with high operational properties, the diverse use of duralumin is due to its high technological efficiency, which creates prerequisites for obtaining products by all known methods of casting and plastic processing. Duralumin belongs to the category of structural alloys, which are characterized by increased strength. They are based on aluminum. Copper, manganese, and magnesium are used as additives in different percentages. The properties of duralumin depend on the heat treatment and the amount of alloying elements added. The article presents the results of a study of the effect of calcium on the anodic behavior of aluminum alloy АlМg5.5Li2.1Zr0.15 of the duralumin type in the medium of the NaCl electrolyte. The study of the corrosion−electrochemical behavior of alloys was carried out by a potentiostatic method in a potentiodynamic mode with a potential sweep rate of 2 mV ⋅ s ^(-1). It is shown that calcium additives reduce the rate of anodic corrosion of the initial alloy АlМg5.5Li2.1Zr0.15 by 8-10%. It was found that an increase in the concentration of chloride ions contributes to an increase in the rate of anodic corrosion regardless of the calcium content in the alloy АlМg5.5Li2.1Zr0.15.

Электрохимическая переработка отходов тяжелых вольфрамовых сплавов в аммиачно-карбонатных растворах под действием постоянного и переменного тока

The method of linear voltammetry in the potentiodynamic mode was used to study the anodic behavior of the W, Ni, Fe, Co alloy waste (wt. %: W 90, Ni 7, Fe 2, Co 1) in a 1 M ammonium carbonate solution. The process of the W, Ni, Fe, Co alloy dissolution under the action of direct and sinusoidal alternating current, was also studied. It was found that the use of alternating current makes it possible to achieve the maximum rate of alloy oxidation, the effect of direct current ensures the process proceeds with the maximum current efficiency.

Fabrication and Development of Binder-Free Mn-Fe-S Mixed Metal Sulfide Loaded Ni-Foam as Electrode for the Asymmetric Coin Cell Supercapacitor Device.

Currently, the fast growth and advancement in technologies demands promising supercapacitors, which urgently require a distinctive electrode material with unique structures and excellent electrochemical properties. Herein, binder-free manganese iron sulfide (Mn–Fe–S) nanostructures were deposited directly onto Ni-foam through a facile one-step electrodeposition route in potentiodynamic mode. The deposition cycles were varied to investigate the effect of surface morphologies on Mn–Fe–S. The optimized deposition cycles result in a fragmented porous nanofibrous structure, which was confirmed using Field Emission Scanning Electron Microscopy (FE−SEM). X-ray photoelectron spectroscopy (XPS) confirmed the presence of Mn, Fe, and S elements. The energy dispersive X-ray spectroscopy and elemental mapping revealed a good distribution of Mn, Fe, and S elements across the Ni-foam. The electrochemical performance confirms a high areal capacitance of 795.7 mF cm−2 with a 24 μWh cm−2 energy density calculated at a 2 mA cm−2 current density for porous fragmented nanofiber Mn–Fe–S electrodes. The enhancement in capacitance is due to diffusive-controlled behavior dominating the capacitator, as shown by the charge–storage kinetics. Moreover, the assembled asymmetric coin cell device exhibited superior electrochemical performance with an acceptable cyclic performance of 78.7% for up to 95,000 consecutive cycles.

Anodic Composite Nanostructure: Formation, Morphology, Optical and Photoluminescent Properties

Two-layer Al/Nb (1000/200 nm) was deposited by sputtering using a DC magnetron method on Si wafers. The anodizing was in 0.2 M oxalic solution at 53 V, re-anodized in the 0.5 M boric acid in potentiodynamic mode at increase of potential until 400 V. For forming anodic composite nanostructure, the porous anodic aluminum oxide was partially removed in 50 % aqueous solution of phosphoric acid at 50°C for 1200 s. The morphology, photoluminescence, and optical reflection of an anodic composite nanostructure were investigated. The anodic composite nanostructure showed effective optical reflection in the wavelength range from 540 to 1000 nm, and the maximum reflective efficiency was observed at a wavelength of 850 nm, 52 % reflectance occurs. The photoluminescence maximum was observed at a wavelength of 453 nm.

Anodic behaviour of indium doped zinc alloy TsAMSv4-1-2,5 in NaCl Electrolyte

Zinc-aluminium alloys find a wide application in different industries. Approximately half of the produced zinc is used as corrosion protection coatings for steel structures. Corrosion resistance is one of the essential properties of zinc alloys as well. Zinc alloys are highly resistant to atmospheric and marine corrosion, as well as basic and acidic solutions. They have low density and are easily workable by cutting. As is well-known, lead serves as the main concomitant metal for metallic zinc, and its concentration may reach 2.5 wt. % (for TsZ grade of zinc). This research is aimed at designing a new alloy on the basis of zinc alloy TsAM 4-1, which is obtained from a low zinc grade TsZ labelled as TsAMSv4-1-2,5. The alloys were analyzed following potentiostatic technique in a potentiodynamic mode at the potential sweep rate of 2 mV/s in NaCl electrolyte on the pulse potentiostat PI-50-1.1. The TsAMSv4-1-2,5 alloy was doped with 0.05–1.0 wt. % of metallic indium. It was found that as the chloride ion concentration in NaCl electrolyte rises, the free corrosion, pitting and repassivation potentials tend to shift in the negative region while the corrosion rate increases by 28%. It is shown that indium additions cause a 10% drop in the corrosion rate while the alloys’ electrochemical potentials tend to shift in the positive region. Due to increased corrosion resistance of the zinc alloy TsAMSv4-1-2,5 doped with indium, one can save 10% of metal and thus achieve a more cost-effective production of zinc alloy items.

Полипорфириновые покрытия на основе металлокомплексов 5,10,15,20-тетракис(3-аминофенил)порфирина в реакции электрокаталитического восстановления кислорода

Carbon-based materials are widespread and promising in areas such as electrochemical and electrocatalytic power generation and can be excellent choices for use as electrode substrates. To increase the efficiency of using carbonaceous materials, the surface of the electrodes is modified with metal complexes of phthalocyanines and porphyrins with electrocatalytic properties. In this work polyporphyrin coatings were obtained on a glassy carbon electrode based on individual metal complexes of 5,10,15,20-tetrakis(3-aminophenyl)porphyrin and a composite based on two metal complexes Fe and Mn. Polymerization was carried out by the electrochemical method in the region of positive values of the potential in the potentiodynamic mode. Electrodeposited polyporphyrin coatings have a developed surface and exhibit catalytic activity in the reaction of oxygen electroreduction. The results of evaluating the catalytic activity of polyporphyrins obtained by various methods are in good agreement with each other and indicate a higher catalytic activity of a composite based on two metal complexes compared to films of individual porphyrins, which suggests the presence of a synergistic effect. Based on the results of our research, we propose potential directions for the creation of electrodes based on glassy carbon modified with polyporphyrins for electrocatalytic oxygen reduction.

Mathematical modeling of the influence of non-catalytic dissociation / recombination of water molecules in the desalination channel on electric convection

The article formulates a two-dimensional mathematical model of non-stationary transport of 1: 1 electrolyte in a potentiodynamic mode, taking into account electroconvection and non-catalytic dissociation / recombination reaction of water molecules in electromembrane systems, which are considered as the desalting channel of an electrodialysis device. The model is described by a system of coupled Navier-Stokes and Nernst-Planck-Poisson equations taking into account the electric force and physically justified boundary conditions. The article establishes the basic laws of mass transport, taking into account the dissociation / recombination of water molecules. It was shown for the first time that a double electric layer of hydrogen and hydroxyl ions arises in the recombination region. It is shown that between the region of recombination and quasi-equilibrium regions of space charge there are regions of electroneutrality and equilibrium with an almost linear distribution of concentrations. It was found that even under prelimiting, but close enough to the limiting current, modes, non-catalytic dissociation of water molecules in the quasi-equilibrium region of space charge occurs so intensely that the concentration of hydrogen and hydroxyl ions becomes comparable to the concentration of potassium and chlorine ions. At overlimiting current densities, due to the appearance of an extended space charge region and intense dissociation of water molecules in this region, as well as an increase in the electric double layer in the recombination region, the space charge and the dissociation / recombination reaction of water molecules significantly affect each other. In turn, this has a decisive effect on electroconvection and, accordingly, on the transport of salt ions.

Some new aspects of the study of dependence of properties of PEO coatings on the parameters of current in potentiodynamic mode

The method of plasma electrolytic oxidation (PEO) for modifying surface of magnesium alloys is increasingly being used in many areas of industry and medicine. In this paper, the influence of the parameters of PEO process on the formation of coatings in potentiodynamic modes was investigated. The morphology and corrosion properties of PEO coatings were studied by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffractometry, and electrochemical techniques. It was shown that in the potentiodynamic mode, properties of coatings can be controlled by the maximum formation current density. The influence of a surface area of treated sample on the PEO process and coatings' properties was studied.It was shown that an increase in voltage limit increases the formation current density of PEO process, which leads to an increase in the thickness and porosity of the coatings. It was found that the rate of voltage's change did not affect the change in the formation current densities; however, it significantly affected the thickness of the formed layer. It was established that a large coating's thickness and a small number of pores are not an indicator of high corrosion resistance, the pores size is more significant. The results of this study allow to adjust various surface properties by modifying coating formation mode.

In Situ Measurement of the Conductance of Regioregular Poly-3′,4′-didodecyl-2,2′:5′,2′′-terthiophene during Potentiodynamic Growth

This work reports a study of regioregular poly-3′,4′-didodecyl-2,2′:5′,2′′-terthiophene (poly-3′4′-DDTT) deposited electrochemically onto a double-band electrode for the in situ measurement of the electrical conductance. The electrodeposition of poly-3′4′-DDTT was conducted in the potentiodynamic mode within the applied potential interval 0 ≤ E appl ≤ 0.9 V vs Ag/Ag+ employing an electrolyte that contained the terthiophenic monomer 3′4′-DDTT (the starting redox species). These electrochemical conditions warrant the oxidation of 3′4′-DDTT (initiation step) and prevent the oxidative degradation of the polymerization product(s). Through the adoption of conformal mapping we could calculate the electrical conductivity of the electrodeposited polymer thanks to the observation of a linear variation of conductance with the consumed charge of polymerization. The use of conformal mapping has allowed also the determination of the volume yield for the poly-3′4′-DDTT under consideration. The electrical conductivity of poly-3′4′-DDTT depended nonlinearly on the scan rate of electrodeposition and varied in the broad range 12 − 34 S cm−1. The variability of poly-3′4′-DDTT conductivity depended on the nature of the electrodeposit which, in turn, depended on the rate of oxidative coupling (determined by the electrical current) and on the rate of precipitation (determined by the conditions of saturation in proximity of the double-band electrode).

Anodic behaviour of Zn0.5Al doped with molybdenum in acidic, neutral and alkaline media

The paper presents the results of a potentiodynamic study of the anodic behaviour of Zn0.5Al doped with molybdenum in the acidic (0.1 M, pH = 1; 0.01 M, pH = 2; 0.001 M, pH = 3), neutral (0.03, 0.3, 3%, pH = 7) and alkaline (0.001 M, pH = 10; 0.01 M, pH = 11; 0.1 M, pH = 12) media of HCl, NaCl and NaOH electrolytes. In the potentiodynamic mode with an electrode potential sweep rate of 2 mV/s, all Zn0.5Al-Mo samples containing from 0.01 to 1.0 wt% of molybdenum demonstrated a shift in the potentials of corrosion, pitting formation and repassivation. These potentials shift towards negative values in acidic and alkaline media, while shifting to positive values in a neutral medium. It was established that an increase in the concentration of electrolytes led to a shift of all the considered potentials towards negative values in all media - acidic, neutral and alkaline. This dependence is associated with the specific features of the process of anodic dissolution of alloys during the formation of an oxide film on their surface. The significance of the dependence of the stationary potential of free corrosion of alloys on time for establishing the passivity of surfaces in acidic, neutral and alkaline media was shown. It was determined that zinc alloys doped with molybdenum are resistant to pitting corrosion in all the investigated media. This resistivity is particularly high in acidic (0.001 M), neutral (0.03%) and alkaline (0.001 M) media of HCl, NaCl and NaOH electrolytes. The favourable effect of molybdenum on both the anodic behaviour of Zn0.5Al and the overall increase in the corrosion resistance of alloys was demonstrated. In comparison with undoped Zn0.5Al alloys, the corrosion rate of alloys doped with molybdenum (0.01-1.0 wt%) is 2-2.5 times lower. The proposed compositions of Zn0.5Al-Mo alloys can be used as noncorrosive coatings for steel products.

Optical Properties of Porous Alumina Assisted Niobia Nanostructured Films-Designing 2-D Photonic Crystals Based on Hexagonally Arranged Nanocolumns.

Three types of niobia nanostructured films (so-called native, planarized, and column-like) were formed on glass substrates by porous alumina assisted anodizing in a 0.2 M aqueous solution of oxalic acid in a potentiostatic mode at a 53 V and then reanodizing in an electrolyte containing 0.5 M boric acid and 0.05 M sodium tetraborate in a potentiodynamic mode by raising the voltage to 230 V, and chemical post-processing. Anodic behaviors, morphology, and optical properties of the films have been investigated. The interference pattern of native film served as the basis for calculating the effective refractive index which varies within 1.75–1.54 in the wavelength range 190–1100 nm. Refractive index spectral characteristics made it possible to distinguish a number of absorbance bands of the native film. Based on the analysis of literature data, the identified oxide absorbance bands were assigned. The effective refractive index of native film was also calculated using the effective-medium models, and was in the range of 1.63–1.68. The reflectance spectra of all films show peaks in short- and long-wave regions. The presence of these peaks is due to the periodically varying refractive index in the layers of films in two dimensions. FDTD simulation was carried out and the morphology of a potential 2-D photonic crystal with 92% (wavelength 462 nm) reflectance, based on the third type of films, was proposed.

Electrodeposition of Graphene Oxide Modified Composite Coatings Based on Nickel-Chromium Alloy

Composite electrochemical coatings (CECs) based on nickel-chromium alloy and modified with multilayer graphene oxide (GO) were obtained. The electrodeposition process of these coatings was studied in the potentiodynamic mode. The structure and the composition of nickel–chromium–GO CECs were studied by scanning electron microscopy and laser microspectral analysis. Nickel–chromium–GO CECs are dense and uniform. The carbon content in them increases when moving from the substrate to the surface. It was established that the addition of GO particles into the composition of electrolytic coatings with a nickel-chromium alloy results in the increase in their microhardness from 4423–5480 MPa to 6120–7320 MPa depending on the cathodic current density.