Electrochemical Dissolution Process Research Articles

In Situ Analysis of the Effect of Ultrasonic Cavitation on Electrochemical Polishing of Additively Manufactured Metal Surfaces

Abstract The effects of a hybrid process that combines ultrasonic cavitation and electrochemical polishing on the electrochemical behavior and the resulting surface characteristics of additively manufactured 316-L stainless steel were investigated. In situ potentiodynamic scans and electrochemical impedance spectroscopy (EIS) were conducted to gain a fundamental understanding of the effect of ultrasonic cavitation on the electrochemical processes involved, considering the influence of electrolyte temperature at 60 and 70 °C. The potentiodynamic scans revealed that increasing the ultrasonic excitation amplitude from 20 to 80 µm at 20 µm intervals and temperature from 60 to 70 °C led to reduced polishing resistance, and elevated passivation current density at equivalent applied potentials, thus leading to an increased polishing rate. These findings are attributed to intensified cavitation near the material surface, which promoted anodic dissolution reactions and accelerated the polishing rate. In situ EIS measurements provided valuable information on the charge transfer resistance and double-layer capacitance and their influence on the hybrid process. Specifically, higher ultrasonic amplitudes and elevated temperatures contributed to enhanced electrical double-layer formation and ion adsorption, resulting in a faster rate of polishing, indicating the efficacy of the hybrid process. These findings enhance our understanding of the complex interactions between ultrasonic cavitation and electrochemical dissolution processes that occur during ultrasonic cavitation-assisted electrochemical polishing. The research provides valuable insights for optimizing the process and its potential application in the post-processing of metal additive manufactured parts.

АНАЛИЗ МОРФОЛОГИИ ПРИ ВОЗДЕЙСТВИИ ЭЛЕКТРОЛИТИЧЕСКОЙ СТРУИ НА ПОВЕРХНОСТЬ НЕРЖАВЕЮЩИХ СТАЛЕЙ

The article is devoted to the study of the effect of an electrolytic jet on the surface of a metal anode. The studies were carried out in the electrolysis mode with a study of the transition to the electrolyte-plasma treatment mode. Special attention is paid to the mechanisms of formation of the morphology of the surface of stainless steels 08X18H9T, AISI 301, AISI 304. It is shown that for different steels, the process of electro-chemical dissolution of the anode material is accompanied by different mechanisms of dissolution of the micronerities of the microprofile. The current-voltage characteristics of the process in the voltage range in the range of 20-250 V. The effect of the decrease in the mass of the anode material on the current value is considered. The morphology of steels has been studied under different technological conditions and at different points of contact of the electrolytic jet with the surface. The criteria accompanying the transition to the electrolyte-plasma regime from the electrolysis regime are considered.The effect of an electrolytic jet on the risks formed by mechanical treatment on the anode surface is investigated. The influence of stress on the formed surface roughness parameter Ra is considered. The calculation of the electric field strength for surface nanodefects was performed in the Comsol Multithisics program. The results of this work can be used for the development of turbine blade processing technology, electrochemical cutting and nanoobrabotation of materials.

Elektrokhimicheskaya pererabotka otkhodov tyazhelykh vol'framovykh splavov v rastvorakh karbonata ammoniya

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.

Synergistic effect of transpassive film and gamma double prime phase on the electrochemical dissolution behavior of Inconel 718 manufactured by laser directed energy deposition

This study investigated the synergistic effect of transpassive film and γ″ phase on the electrochemical dissolution behavior of Inconel 718 manufactured by laser directed energy deposition. The investigation was based on samples after homogenization and aging with (γ + γ″) phases and homogenization with γ phase. The compositions of the transpassive films for two kinds of heat-treated samples were similar, mainly comprising porous Ni hydroxides. The incompact transpassive film induced the local preferential dissolution of the γ matrix and generated multiple dispersive pits on the surface. Compared with the sample after homogenization, the spatial distribution of the γ″ phase in the sample after homogenization and aging restricted the expansion of pits in the γ matrix, leading to superior surface quality. The detachment of the γ″ phase during electrochemical dissolution provided extra mass loss and higher current efficiency. A qualitative model was proposed to demonstrate the synergistic effect of the transpassive film and γ″ phase on the dynamic electrochemical dissolution process.

Sustainable electrochemical gold dissolution process based on triboelectric nanogenerator

The development of sustainable, energy-free dissolution methods is crucial for gold recycling. For the first time, we have achieved the dissolution of gold through a triboelectric nanogenerator (TENG). With 1 wt% Au/SiO2 as the research subject in KI solution, the gold dissolution efficiency can reach 100 % in three hours driven by R-TENG. However, by using a direct current (DC) source with 25 mA and 5 V, the gold dissolution efficiency is only 85 % after the same operation time. Meanwhile, to achieve the same 85 % gold dissolution rate, the total charge consumed from TENG is only 1.6 % of that from the DC source, indicating an ultrahigh charge utilization rate. Thus, the side reactions such as water splitting and the formation of the iodine oxide film in KI aqueous solution can be avoided by using TENG, which blocks the adhesion on the anode and facilitates the reaction. The amount of gold extracted from the waste central processing units (CPU) board (4 × 4 cm) by the solution method could reach 6 mg/piece. Hence, TENGs provide a new direction for the recovery of other metals in secondary resources and many other applications in the direction of electrochemistry can be also inspired.

Surface modification of nickel-based superalloy by electrochemical selective dissolution

In order to improve the poor machinability of nickel-based superalloys, a new strategy, the surface modification of nickel-based superalloys to remove the γ' phase in the surface layer, was proposed in this paper. A new electrochemical selective dissolution process using NaCl electrolyte was developed through theoretical analysis combined with testing and applied for surface modification. The results showed that in the NaCl electrolyte, the Cr-rich γ matrix is protected from electrochemical dissolution by a stable Cr-passive film, while the Al-rich γ' phase is exposed to electrolyte and undergoes electrochemical dissolution because the Al-passive film on its surface is eroded into AlCl3 by the Cl- ions. Through the electrochemical selective dissolution, the surface layer of nickel-based superalloy was modified into a low-hardness porous layer composed of the undissolved γ matrix, and its thickness can be well controlled by adjusting electrochemical corrosion time or electrolyte concentration. This study provides an effective pretreatment method for nickel-based superalloys to reduce the machining difficulty.

Towards a circular economy for Pt catalysts. Case study: Pt recovery from electrodes for hydrogen production

This work links two challenges that our society is facing nowadays, the climate change and the scarcity of key raw materials as the platinum group materials are. Hence, Pt from membrane electrode assemblies used in the well-known Westinghouse cycle for hydrogen production has been successfully recovered using the selective electrochemical dissolution process and reaching global efficiencies of 70 wt%. Pt electrocatalysts were synthesized from the Pt recovered from the spent electrodes and characterized. Thus, the scanning electrochemical microscopy technique demonstrated that Pt was well dispersed onto the carbon support. Moreover, electrodes with both, commercial and recovered Pt/C catalysts were prepared and tested. The electrodes with the catalyst prepared from the spent MEAs show a good activity towards the SO2 oxidation, the reaction for H2 production, and above all, a very high stability. In conclusion, the circular economy of Pt based catalyst for a H2 production process has been achieved.

Investigation of electrochemical machining on SS304 using NaCl and NaNo3 as electrolyte

ABSTRACT In electrochemical machining (ECM), the material in the workpiece is removed in a localized electrochemical dissolution process, and metal oxides are formed as by-products. In this study, the electrolyte is present only above the workpiece, and the electrolyte thickness is maintained as 2 mm to limit the variation in radial current flow from the micro-tool. In this research work, experiments were conducted using two electrolytes, namely, NaCl and NaNO3, to machine through holes on a 1-mm-thick SS 304 workpiece, using a hollow tool of outer diameter 261 µm. The pressurized electrolyte was sent through the hollow tool to remove the metal oxides formed in the machining zone. A fixture was designed and used for the identification of through holes. Two sets of L16 orthogonal array (OA) were applied; the factors selected for this experimental study were voltage, electrolyte concentration, electrolyte temperature, and pressure. The output responses considered are radial overcut, taper angle and material removal rate (MRR). Analysis of variance (ANOVA) and Taguchi techniques were utilized in the analysis of results. The results showed voltage and concentration of the electrolyte as the major influencing factors, while the influence of stray current was controlled using NaNO3.

Precision improvements in ECM via tool insert development by 3D printing

This paper reports the tool developments for electrochemical machining (ECM) of precision parts for automotive industry using polymer 3D printed inserts. The role of these inserts is to control the fluid flow in the inter-electrode gap as well as to prevent stray machining by providing insulation. Initial trial and error machining experiments with various tool insert shapes yielded positive outcomes in terms of controlling stray dissolution. It became evident that by 3D printing the entire machining cell structure with integrated, exchangeable tool inserts, all made from polymer, can further enhance the ECM process. This cell-insert assembly enabled better control of the electrochemical dissolution process and allowed for less restrictive flow of the electrolyte, reducing turbulence in the inter-electrode gap. Thus, by improving the electrolyte flow conditions and providing appropriate insulation to prevent stray machining, the 3D printed cell/insert assemblies enabled ECM to achieve a shaped profile of an auto engine component to required tolerances.

Ionic concentration in periradicular medium after dissolution of endodontic file fragments: an in vitro study.

The aim of this study was to obtain ionic quantification in periradicular medium after diffusion tests of the solution used inside root canals during the electrochemical dissolution of endodontic file fragments and the NiTi-containing dissolution product via an apical foramen. Thirty single-rooted extracted human teeth had root canals prepared and were attached to Eppendorf tubes filled with sterile saline. The samples were divided into 3 groups (n = 10) according to the solution used inside the root canal during the diffusion tests: Group 1: [NaF 12 g/L + NaCl 1 g/L]; Group 2: [NaF 12 g/L + NaCl 1 g/L + NiTi 0.50 g/L]; Group 3: [NaF 6 g/L + NaCl 0.5 g/L + NiTi 0.25 g/L]. The sample in each Eppendorf tube was then analyzed to assay the ionic quantification in periradicular medium. The groups were compared in relation to ionic quantifications (Kruskal-Wallis and Dunn's tests, p ≤ 0.05). Group 2 showed significantly higher F-, Ni and Ti quantities than groups 1 and 3 (p < 0.05). Group 3 showed significantly higher Ti and Ni quantities than group 1, where no measurable quantities of Ti and Ni were observed (p < 0.05). The conclusions were that a 50% dilution of the NiTi-containing dissolution product resulted in significantly lower F-, Ni and Ti quantities compared to the undiluted product. The quantifications observed here suggest that irrigation is recommendable during the electrochemical dissolution process to reduce the resultant ion concentrations in both the root canal and the periradicular medium.

РАСТВОРЕНИЕ НЕРЖАВЕЮЩЕЙ СТАЛИ В РАСТВОРЕ ХЛОРИДА НАТРИЯ ПРИ ПОЛЯРИЗАЦИИ НЕСТАЦИОНАРНЫМИ ТОКАМИ

Stainless steel is in great demand due to its mechanical strength, heat resistance, and resistance to corrosive environments. This article presents the result of a study of the electrochemical dissolution behavior of a stainless steel electrode (12X18H10T) at polarization by 50 Hz alternating current in a neutral medium (NaCl). Preliminary experiments have shown that the main processes do not take place when two stainless steel electrodes are polarized with an alternating current. It was observed that by the polarization of the “stainless steel – titanium” pair electrodes with alternating current, the alloy is intensively dissolved with the formation of iron (II) and chromium (III) ions. This is due to the "valve" properties of the oxide layer formed on the surface of the titanium electrode. A change in the value of the current density of the titanium and steel electrodes significantly affects the process of electrochemical dissolution of the alloy. At high current densities, the dissolution rate of the alloy decreases due to the deterioration of the current correcting properties of titanium. With an increase in the electrolyte concentration, the current efficiency is reduced as salt passivation occurs. A maximum value of the current efficiency of dissolution of stainless steel was observed at a current frequency of 50 Hz. High frequencies of the alternating current do not provide an adjustable duration of the anodic half-cycle for the oxidation reaction due to the frequent change of halfcycles of the alternating current. It was observed that increasing the temperature of the electrolyte reduces the current efficiency of the electrochemical dissolution of stainless steel electrodes. The effects of main electrochemical parameters on the electrolysis process have been investigated, and the optimal conditions of the alloy dissolution were established (іТі = 60 kA/m2 , іSS = 800 A/m2 , [NaCl] = 2.0 M, t = 30, ν = 50 Hz.).

Electrochemical Dissolution Behaviors of Scrap Superalloys in Different Electrolytes

Owing to the demand for strategic metals, the dissolution of scrap superalloys is imperative for their recycling. This study investigates the electrochemical dissolution process of superalloys in different electrolytes. The results indicate that the dissolution rate of the samples is significantly emulative in organic electrolyte at current densities greater than 0.7 A cm−2. The dissolution behavior of the sample in aqua regia electrolyte can be classified as dissolution of the oxidation layer, formation of the anode product layer, and formation of the Cr-rich hindered-dissolution layer. While in organic electrolyte, the dissolution behavior can be partitioned as dissolution of the oxidation layer, formation of the porous Cr-rich hindered-dissolution layer, formation of dissolved pores, and detachment of the porous Cr-rich hindered-dissolution layer. Therefore, the formation of dissolved pores and detachment of the porous Cr-rich hindered-dissolution layer can effectively reduce the electrolytic resistance and the diffusion resistance in the electrolyte.

Real-time imaging of nanoscale electrochemical Ni etching under thermal conditions.

The ability to vary the temperature of an electrochemical cell provides opportunities to control reaction rates and pathways and to drive processes that are inaccessible at ambient temperature. Here, we explore the effect of temperature on electrochemical etching of Ni–Pt bimetallic nanoparticles. To observe the process at nanoscale resolution we use liquid cell transmission electron microscopy with a modified liquid cell that enables simultaneous heating and biasing. By controlling the cell temperature, we demonstrate that the reaction rate and dissolution potential of the electrochemical Ni etching process can be changed. The in situ measurements suggest that the destabilization of the native nickel oxide layer is the slow step prior to subsequent fast Ni removal in the electrochemical Ni dissolution process. These experiments highlight the importance of in situ structural characterization under electrochemical and thermal conditions as a strategy to provide deeper insights into nanomaterial transformations as a function of temperature and potential.

Electrochemical dissolution behavior of heat treated laser solid formed Inconel718

Microstructure characteristic and its effects on electrochemical dissolution behavior of horizontal plane (HP) and vertical plane (VP) in the laser solid formed (LSF) Inconel718 alloy after double aging (DA) heat treatment (DA-LSF Inconel718) were investigated. Compared to the as-deposited one, DA-LSF Inconel718 shows more phases and presents electrochemical anisotropy between HP and VP including the polarization curves, current efficiency curves and surface roughness. It is caused by different electrochemical dissolution processes on HP and VP and proved that surface energy has no obvious effect. Three models were proposed to illustrate electrochemical dissolution behavior, surface formation mechanism and electrochemical anisotropy, respectively.

A systematical study on the electrodeposition process of metallic lithium

In this study, commercial copper (Cu) foil and Cu foam are used as the working electrodes to systematically investigate the electrochemical deposition and dissolution processes of metallic lithium (Li) on these electrodes; Li metal deposited on the Cu foil electrode is porous and loose. The surface solid electrolyte interface (SEI) film after dissolution from Li dendrites maintains a dendritic porous structure, resulting in a large volume effect of the electrode during the cycle. The Cu foam electrode provides preferential nucleation and deposition sites near the side surface of the separator; the difference in Li affinity results in a heterogeneous deposition and dendrite growth of metallic Li. Electrodeposition process study of metallic Li has been researched using Cu foil and Cu foam as the working electrodes. The nonuniform electrode surface causes the deposition of particulate Li and dendritic Li, which in turn leads to the formation of dead Li and moss Li during the repeated cycles.

Surface Morphology Analysis of 1Cr11Ni2W2MoV Steel Subjected to Electrochemical Machining in NaNO3 Solution

Electrochemical machining (ECM) is a noncontacting method for machining complex contours that is independent of the hardness and strength of metals. Since the materials are removed in the form of ions via electrochemical dissolution, good surface integrity is a primary advantage of ECM. However, the selective dissolution of the metal phase and the differences in current density have significant effects on the local surface film composition and surface morphology of the machined sample. This paper focused on the morphology and the surface film composition of 1Cr11Ni2W2MoV heat-resistant steel after ECM processing. Herein, experiments were conducted with specialized fixtures. Moreover, the anodic polarization curve and current efficiency curve of 1Cr11Ni2W2MoV steel were obtained. The analysis of the experimental process and the examination of the specimens indicated that the material heterostructure and the current density seriously influenced the stability of the electrochemical dissolution process, and that carbide enrichment led to a poor-quality surface with a dense water ripple texture. Based on the experimental results, a three-layer metal dissolution model in NaNO3 solution was established. A machining current density of 30–40 A cm−2 for ECM of 1Cr11Ni2W2MoV steel was found to obtain good surface quality.

State of the Art on Laser Assisted Electrochemical Machining

Laser Assisted Electrochemical Machining (LAECM) has proven its advantages and applications over almost all the range of conductive materials. It offers its adroitness to generate simple shapes to complex shapes from macro to micro machining. Laser assisted ECM is a hybrid approach of machining which has been manifested to obtain improved results in terms of surface integrity, thermal damage, geometrical tolerance and material removal rate. Laser assisted Electrochemical Machining (LAECM) is a hybrid machining process in which laser enhances the electrochemical dissolution process by increasing the temperature and hence the current density of the electrolyte. Laser helps to remove material from the particular machining zone and stray machining effect is reduced and thus improves the precision and efficiency of LAECM, also productivity. New route of laser assisted hybrid machining processes has been built in the past decade by few of the researchers to reduce the intrinsic problems of ECM. This paper reviews on the investigation into LAECM process. The article also highlights various possibilities and applications of LAECM process. There are various challenges in LAECM process which have been also discussed in this paper.

The Anodic Behaviour of Bulk Copper in Ethaline and 1-Butyl-3-Methylimidazolium Chloride

The anodic dissolution of bulk metallic copper was conducted in ionic liquids (ILs)—a deep eutectic solvent (DES) ((CH3)3NC2H4OH) comprised of a 1:2 molar ratio mixture of choline chloride Cl (ChCl), and ethylene glycol (EG)—and imidazolium-based ILs, such as C4mimCl, using electrochemical techniques, such as cyclic voltammetry, anodic linear sweep voltammetry, and chronopotentiometry.To investigate the electrochemical dissolution mechanism, electrochemical impedance spectroscopy (EIS) was used. In addition to spectroscopic techniques, for instance, UV-visible spectroscopy, microscopic techniques, such as atomic force microscopy (AFM), were used. The significant industrial importance of metallic copper has motivated several research groups to deal with such an invaluable metal. It was confirmed that the speciation of dissolved copper from the bulk phase at the interface region is [CuCl3]− and [CuCl4]2− in such chloride-rich media, and the EG determine the structure of the interfacial region in the electrochemical dissolution process. A super-saturated solution was produced at the electrode/solution interface and CuCl2 was deposited on the metal surface.

High-performance corrosion-resistant fluorine-doped tin oxide as an alternative to carbon support in electrodes for PEM fuel cells

The advent of new technologies and growing demand for fuel cell innovation has led to the development of novel non-carbon material strategies with inherent electrical conductance and corrosion resistance. Problems are often observed with carbon-based support materials, due to their limited electrochemical stability. The emphasis is therefore on fabricating high-performance, stable non-carbon alternatives that exhibit advantageous electrochemical properties compared to conventional carbon black, and are thus regarded as ideal electrocatalyst support materials. In this work, we investigated the influence of dopants, and the morphology of conductive, porous doped tin-based oxides, on corrosion resistance and electrical conductivity for fuel cell electrode applications. Among the various doping elements, fluorine anion doping into tin oxide plays a key role in the formation of such structures as a complexing agent for improving electrical conductivity and suppressing electrochemical dissolution processes. When used in polymer electrolyte membrane fuel cells with platinum electrocatalyst loading, fluorine tin oxide nanotubes exhibit not only cell performance comparable to that of state-of-the-art commercial Pt/C, but also excellent cycling stability. The superior electrochemical performance and stability of this novel non-carbon support material is due to its unique features, i.e., excellent electrical conductivity, electrochemical corrosion resistance, and electronic and compressive strain effects due to strong metal-support interactions.

Kinetics of electrochemical dissolution of metals in porous media.

Metals embedded in porous media interact electrochemically with the liquid phase contained in the pores. A widespread form of this, adversely affecting the integrity of engineered structures, is corrosion of steel in porous media or in natural environments. While it is well documented that the rate of this electrochemical dissolution process can vary over several orders of magnitude, understanding the underlying mechanisms remains a critical challenge hampering the development of reliable predictive models. Here we study the electrochemical dissolution kinetics of steel in meso-to-macro-porous media, using cement-based materials, wood and artificial soil as model systems. Our results reveal the dual role of the pore structure (that is, the influence on the electrochemical behaviour through transport limitations and an area effect, which is ultimately due to microscopic inhomogeneity of the metal/porous material interface). We rationalize the observations with the theory of capillary condensation and propose a material-independent model to predict the corrosion rate.