Electrochemical Anodic Dissolution Research Articles

Kinetic investigation of sulfur corrosion: First principles calculations

The expressions of two important kinetic parameters (chemical activation energy of electrode reaction and absolute potential of equilibrium state) that determine the reaction rate during the anodic dissolution reaction are derived from the thermodynamic and kinetic relationships of the anodic dissolution reaction, the relationship between absolute potential and current density in the anode dissolution process is constructed. Under the framework of first principles, the calculation model of the electrochemical corrosion anodic dissolution reaction is proposed. Density functional theory study of the process of dissolving Fe atoms from the surface of Fe(111) alloy models in vacuum and explicit water molecules. The addition of water molecules and sulfur atoms promotes charge transfer during dissolution and increases the corrosion rate, while water molecules reduce the work function, while S goes increases the work function. Through the corrosion current density model of activation energy, the role of alloy dissolution kinetics with different alloys added was explored. The analysis shows that the addition of Mn and Cr can greatly reduce the anodic corrosion rate and increase the corrosion resistance of Fe.

Jet Electrochemical Micromilling of Ti-6Al-4V Using NaCl-Ethylene Glycol Electrolyte.

Titanium alloys are widely used in aerospace and biomedicine because of their excellent mechanical characteristics, but these properties also make such alloys difficult to cut. Jet electrochemical micromilling (JEMM) is based on the principle of electrochemical anodic dissolution; it has some inherent advantages for the machining of titanium alloy microstructures. However, titanium oxidizes readily, forming an oxide film that impedes a uniform dissolution during electrochemical machining. Therefore, a high voltage and an aqueous NaCl electrolyte are usually used to break the oxide film, which can lead to severe stray corrosion. To overcome this problem, the present study investigated the JEMM of Ti-6Al-4V using a NaCl-ethylene glycol (NaCl-EG) electrolyte. Electrochemical testing showed that Ti-6Al-4V exhibits a better corrosion resistance in the NaCl-EG electrolyte compared to the aqueous NaCl electrolyte, thereby reducing stray corrosion. The localization and surface quality of the grooves were enhanced significantly when using JEMM with a NaCl-EG electrolyte. A multiple-pass strategy was adopted during JEMM to improve the aspect ratio, and the effects of the feed depth and number of passes on the multiple-pass machining performance were investigated. Ultimately, a square annular microstructure with a high geometric dimensional consistency and a smooth surface was obtained via JEMM with multiple passes using the optimal parameters.

Modeling of the material removal rate in internal cylindrical plunge electrochemical grinding

The material removal rate (MRR) in the internal cylindrical plunge electrochemical grinding (ICPECG) is hard to assess because it involves two feed motions: workpiece circumferential rotation and grinding wheel motion in the radial direction. This study attempts to model the MRR and electrochemical overcut in the stable grinding stage of ICPECG by using an equivalent plane electrochemical grinding model with a single feed motion. The differential equation of the interelectrode gap (IEG) in the machining area in the stable grinding stage of ICPECG is derived. Then, based on Faraday's electrolytic law, MRR models of electrochemical anode dissolution (EAD), abrasive mechanical grinding, and electrochemical overcut depth are established and numerically simulated by a variable replacement under different machining parameters. The numerical results indicate that the grinding wheel's radial feed rate most significantly influences the EAD share in the total MRR. In contrast, the power supply voltage mainly controls the electrochemical overcut depth. The proposed model's feasibility and revealed correlations are experimentally verified.

Material Removal Mechanism in Photocatalytic-Assisted Jet Electrochemical Machining of SiCp/Al.

Silicon carbide particle reinforced aluminum matrix (SiCp/Al) composites are increasingly used in high−end industries because of their superior comprehensive material properties. However, their advanced properties also create severe challenges for traditional processing technologies. A new hybrid machining method named photocatalytic−assisted jet electrochemical machining (PAJECM) is proposed to improve the machining capability by synchronously removing the metal aluminum matrix and the SiC particles. Comparative experiments were carried out on whether photocatalysis was added. The results show that after photocatalytic−assisted jet electrochemical machining, the height of SiC particles’ extrusion on the surface is significantly reduced. Compared with jet electrochemical machining (JECM) without photocatalysis at the same processing voltage, the surface roughness value is reduced, and the processing quality is improved. In PAJECM, the aluminum matrix is removed by electrochemical anodic dissolution, while the SiC particles generate a SiO2 reaction layer through photocatalysis, and the TiO2 abrasive flow’s mechanical action repeatedly removes the reaction layer. The electrochemical polarization curves and energy diffraction spectroscopy elemental analysis confirmed the material removal mechanism of PAJECM. Based on analyzing the phenomenon of material removal in detail, a qualitative model of the PAJECM material removal mechanism is established. This study provides valuable insights into the material removal mechanism in photocatalytic and jet electrochemical machining composite processes.

Electropolishing and the Mass Transfer During the Electrochemical Anodic Dissolution of Metals in Ionic Liquids

Electropolishing and the Mass Transfer During the Electrochemical Anodic Dissolution of Metals in Ionic Liquids

Investigating the mechanism of stress corrosion cracking of controllable rolling pipe steel X70 in near-neutral environment

The results of investigating the mechanism of stress-corrosion cracking of a controllable rolling pipe steel X70 at a cathodic protection in near-neutral pH environment, using slow strain rate tests and polarization curves, are presented. Using the method of polarization curves, a critical range of potentials, namely, from −0.75 VAg/AgCl to −0.97 VAg/AgCl was determined, in which the steel stays in a non-equilibrium electrochemical state and anodic dissolution proceeds simultaneously with hydrogen reducing. It has been shown that in this range, the sensitivity of X70 steel to a stress-corrosion cracking is observed, which correlates with the loss of plastic properties and the appearance of a brittle component in the fracture. At the potential of −2.0 VAg/AgCl, the predominant cathodic reaction is hydrogen reducing at the tip of a crack and its walls. Here, the brittle fracture dominates, which correlates with the character of the fracture.

Experimental Research on Discharge Forming Cutting-Electrochemical Machining of Single-Crystal Silicon

During the wire electrical discharge machining (WEDM) process, a large number of discharge pits and a recast layer are easily generated on the workpiece surface, resulting in high surface roughness. A discharge forming cutting-electrochemical machining method for fabricating single-crystal silicon is proposed in this study to solve this problem. On the same processing equipment, single-crystal silicon is first cut using the discharge forming cutting method. Second, electrochemical anodic reaction technology is used to dissolve the discharge pits and recast layer on the single-crystal silicon surface. The machining mechanism of this process, the surface elements of the processed single-crystal silicon and a comparison of the kerf width are analyzed through experiments. On this basis, the influence of the movement speed of the copper foil electrode during electrochemical anodic dissolution on the final surface roughness is qualitatively analyzed. The experimental results show that discharge forming cutting-electrochemical machining can effectively eliminate the electrical discharge pits and recast layer, which are caused by electric discharge cutting, on the surface of single-crystal silicon, thereby reducing the surface roughness of the workpiece.

Low-Frequency Dielectric Relaxation in Structures Based on Macroporous Silicon with Meso-Macroporous Skin-Layer.

The spectra of dielectric relaxation of macroporous silicon with a mesoporous skin layer in the frequency range 1–106 Hz during cooling (up to 293–173 K) and heating (293–333 K) are presented. Macroporous silicon (pore diameter ≈ 2.2–2.7 μm) with a meso-macroporous skin layer was obtained by the method of electrochemical anodic dissolution of monocrystalline silicon in a Unno-Imai cell. A mesoporous skin layer with a thickness of about 100–200 nm in the form of cone-shaped nanostructures with pore diameters near 13–25 nm and sizes of skeletal part about 35–40 nm by ion-electron microscopy was observed. The temperature dependence of the relaxation of the most probable relaxation time is characterized by two linear sections with different slope values; the change in the slope character is observed at T ≈ 250 K. The features of the distribution of relaxation times in meso-macroporous silicon at temperatures of 223, 273, and 293 K are revealed. The Havriliak-Negami approach was used for approximation of the relaxation curves ε″ = f(ν). The existence of a symmetric distribution of relaxers for all temperatures was found (Cole-Cole model). A discussion of results is provided, taking into account the structure of the studied object.

Micro Electrochemical Milling of Micro Metal Parts with Rotating Ultrasonic Electrode.

With the rapid development of MEMS, the demand for metal microstructure is increasing. Micro electrochemical milling technology (MECM) is capable of manufacturing micro metallic devices or components based on the principle of electrochemical anode dissolution. To improve the capacity of MECM, this paper presents a compound method named ultrasonic vibration-assisted micro electrochemical milling technology (UA-MECM). Firstly, the simulation and mathematical model of UA-MECM process is established to explain the mechanism of ultrasonic vibration on micro electrochemical milling. Then, the effects of ultrasonic parameters, electrical parameters and feedrate on machining localization and surface quality are discussed considering sets of experiments. The surface roughness was effectively reduced from Ra 0.83 to Ra 0.26 µm with the addition of ultrasonic vibration. It turns out that ultrasonic vibration can obviously improve machining precision, efficiency and quality. Finally, two- and three-dimensional microstructures with good surface quality were successful fabricated. It shows that ultrasonic vibration-assisted electrochemical milling technology has excellent machining performance, which has potential and broad industrial application prospects.

Corrosion Behavior of an Equiatomic CoCrFeMnNi High-Entropy Alloy- a Comparison Between Selective Laser Melting and Cast

The corrosion behaviors of equiatomic CoCrFeMnNi high-entropy alloys (HEAs) were comparatively investigated between selective laser melting (SLM) and casting. The casted sample shows better corrosion resistance in 3.5 wt. % NaCl solution than the SLM printed samples due to the higher density of dislocations, pores, and cracks in SLM samples, which significantly reduces their corrosion resistance. Furthermore, it is found that the corrosion resistance is different between the planes parallel and perpendicular to the building direction because of the differences in grain orientation, grain size, and surface morphology. Electrochemical anode dissolution rates of the SLM printed CoCrFeMnNi HEAs on their planes parallel and perpendicular to the building direction are calculated and the results show that the pores and cracks dominate the corrosion resistance rather than the grain boundary and the grain orientation.

Distinction in anodic dissolution behavior on different planes of laser solid formed Ti-6Al-4V alloy

Microstructure, electrochemical impedance, and Tafel and potentiodynamic polarizations were characterized to investigate the electrochemical anodic dissolution behavior of Ti-6Al-4V alloy produced by the laser solid forming (LSF) additive manufacturing process with a specific focus on the distinction on different planes. Electrochemical measurements show that the anodic dissolution characteristic of LSFed Ti-6Al-4V reveals anisotropic behavior on different planes. The horizontal-plane (XOY plane) is more resistant to corrosion than the vertical-plane (XOZ plane) in 15 wt% NaCl solution. Additionally, the vertical-plane shows a lower initial machining potential for the process of electrochemical machining compared to the horizontal-plane. The microstructure of Ti-6Al-4V alloy deposit is composed of dominant α-laths and small amounts of β phase, and its horizontal-plane has higher content of the β phase, lower content of the α phase, slightly finer α-laths, and more uneven α-lath width distribution compared to the vertical-plane. These differences in the microstructural characteristics produce the distinctions observed in the electrochemical anodic dissolution behavior of LSFed Ti-6Al-4V alloy on the vertical- and horizontal-planes.

TiO2‐Graphene Nanocomposites for Effective Photocatalytic Degradation of Rhodamine‐B Dye

AbstractThe hazardous Rhodamine‐B dye is photocatalytically degraded by anatase TiO2 and its graphene nanocomposites. These are prepared by a simple electrochemical anodic dissolution of pure titanium in graphene oxide solution, here particle size is tuned by current variation. The structural, morphological and optical properties of these composites are studied by X‐ ray diffraction, UV‐visible spectroscopy, field emission SEM, high resolution TEM and XPS. The photocatalytic activity of Rhodamine‐B in water is studied with visible and UV light irradiation. A significant degradation is observed with 1 wt% of reduced graphene oxide with TiO2 nanoparticles. The stability and reproducibility are tested by recycling the catalyst for more than five times. The results are interpreted in terms of energy band alignment of TiO2‐ graphene interface with respect to energy levels of Rhodamine‐B molecule through water redox potentials. The present work demonstrates that these composites are novel and cost effective in photocatalytic degradation of Rhodamine‐B and hence are potential materials for environmental remedy.

Experimental Research on Improving ECM Accuracy and Stability for Diamond-hole Grilles

The demand for high-quality diamond-hole grilles, characterized by a voluminous and closely spaced array distribution of holes, has stretched traditional machining to the limit. For this reason, electrochemical machining is considered to be one of the better processing technologies for diamond grid holes. In order to improve the accuracy of electrochemical machining (ECM) for diamond-hole grilles, factors affecting the ECM process based on the electrochemical anodic dissolution theory were investigated in this study. The importance of small-gap processing for achieving higher machining accuracy was highlighted. In small-gap processing of diamond holes, the ECM mode was optimized using cathode side insulation, pulse power supply, passivating electrolyte, and other measures. A test-based comparative analysis of two differing machining modes, i.e., composite-feed ECM mode and precise ECM mode, was performed. The results showed that precise ECM mode, which precisely synchronizes the composite feed vibration with the pulse power supply, offered better machining accuracy and process stability in the ECM process for diamond-hole grilles. Precise ECM mode is envisaged to play a prominent role in the development of ECM technology.

Effects of the electrolyte species on the electrochemical dissolution of polycrystalline ZnO:Al thin films

The electrochemical anodic dissolution of sputter-deposited, aluminum-doped zinc oxide (ZnO:Al) was investigated. The dissolution proceeds mainly via a local oxygen evolution reaction and subsequent dissolution of the zinc oxide lattice. The present work focuses on the influence of the anion species in the used electrolyte. Several electrolytes (KCl, K2SO4, KNO3, KClO4) were applied. The anion species turned out to be a major factor that influenced the kinetics of the etching process. In K2SO4 solutions a strong limitation of the etching process to the close vicinity of the grain boundaries was observed. However, anodic dissolution in KCl, KNO3, and KClO4 showed an unexpected etching behavior, which lead to the formation of cavern-like structures within the ZnO:Al thin films. This was attributed to different local pH values at the ZnO:Al/electrolyte interface.

On the Technologies of Electrochemical Mechanical Finishing

The service properties and lives of mechanical parts and components are closely related to their surface quality and precision, and many of the frictional surfaces are required to be finished thereby improving the surface quality and precision. In electrochemical mechanical finishing (ECMF) processes, the surfaces of metal parts are removed through the electrochemical anodic dissolution to obtain the desirable dimensions and surface finish. ECMF is characterized by the independence of the hardness of workpiece and little wear in tools. As a result, it has received more and more attention in the research area of polishing and finishing for mechanical parts. This article reviews the practical works in ECMF technologies from the aspects of surface quality and precision characteristics. Not only excellent surface quality but also high precision dimensions of parts can be obtained with ECMF. It has wide applications in machining precision mechanical parts and components.

Direct chemical and electrochemical syntheses of coordination compounds of benzazolyl azo ligands

The chelates of 2-hydroxy(aminophenylnaphthyl)-azo-1-alkylbenzimidazoles were obtained from electrochemical (anodic dissolution of zero-valent d-metals) and chemical (from acetates of the same metals) syntheses in methanol. The EXAFS and X-ray single crystal diffraction data revealed the existence of octahedral nickel, zinc, and cadmium complexes containing four five-membered metallocycles with the N4О2 or N6 ligand environments. The formation of five-membered coordination units, non-typical for azo ligands, is explained on the basis of inner-chelate competitive metal binding of ambidentate ligand systems.

Electrochemical anodic dissolution of FeCuNiCoMn alloy in ammonium solutions containing clorine ions

The effect of chlorine ion concentration, temperature and current density on metal distribution among the electrolyte, cathode deposit and mud in the process of electrochemical dissolution of FeCuNiCoMn alloy in an ammonium medium is examined. High iron content (65.90%) compared to that of non-ferrous metals (12.07% Cu, 12.81% Ni, 1.30% Co) and Mn 5.33% is a specific feature of the alloy. The alloy was produced by means of high-temperature reduction smelting of manganese nodules from the Clarion Cliperrton area in the Pacific Ocean. It was found that electrochemical dissolution of the alloy is accompanied by formation of a CuNiCo-cathodic deposit and two types of mud: one tightly clinging to the anode surface, and another, finely suspended in the electrolyte. The highest-purity cathode deposit in mass %: 40.28 Cu, 50.27 Ni, 1.21 Co, 7.63 Fe and 0.61 Mn was obtained at ion ratio in the solution NH4+: Cl− = 2.5: 0.5, temperature 323 K, anodic current density 350 A/m2, separation of the anode and cathode spaces by a shielding screen, continuous removal of the anodic mud and maintaining of a constant pH in the electrolyte (10 ± 0.2). In these conditions, >99% of Fe and Mn, 25% Cu, 54% Ni and 52% of Co is transferred into the mud.

Electrochemical Anodic Dissolution Kinetics of Titanium in Fluoride-Containing Perchloric Acid Solutions at Open-Circuit Potentials

The influence of fluoride on the anodic dissolution kinetics of titanium was studied by several electrochemical techniques at steady-state open-circuit potentials in 1.0 M containing fluoride with various concentrations ranging from 0 to 0.1 M. The promoting effect of fluoride (especially when ) on the anodic dissolution behavior of titanium was characterized and discussed by taking into account the changes in the estimated electrochemical and kinetic parameters. The faradaic impedance for the anodic dissolution of titanium was analyzed both by fitting based on an equivalent electrical circuit model and by theoretical derivation based on a two-step mechanism involving one adsorbed intermediate species. By correlating the faradaic impedance expression derived from the dissolution mechanism with that deduced from the equivalent electrical circuit model, some important kinetic parameters (such as the apparent rate constants and and the surface coverage ) could be estimated from the equivalent circuit elemental parameters (such as , , and ). The charge-transfer reaction was the rate-determining step at lower fluoride concentrations of , leading to a high surface coverage of , while the chemical dissolution reaction is the rate-determining step at higher fluoride concentrations of , leading to a decreased surface coverage of .

Thermal diffusion in nanostructured porous InP

Nanostructured porous InP samples were prepared by electrochemical anodic dissolution of InP for various current densities and etching periods. The samples were characterized by SEM and photoluminescence (PL) where a blue shift was observed in PL. Thermal properties studied by photoacoustic (PA) spectroscopy revealed one order decrease in thermal conductivity of porous InP compared to the bulk. Further it is shown that the thermal conductivity of porous InP decreases with decrease in size of the particles.

Synthesis and thermal diffusion of nanostructured porous GaAs

AbstractNanostructured porous GaAs samples were prepared by electrochemical anodic dissolution of GaAs for various current densities and etching periods. The samples are characterized by SEM and photoluminescence (PL) where a blue shift is observed in PL. Thermal properties of this nanostructured GaAs are then studied by photoacoustic (PA) spectroscopy, where one order decrease in thermal conductivity of porous GaAs compared to bulk is observed. Further it is shown that the thermal conductivity of porous GaAs decreases with decrease in size of the particles. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)