Anodic Dissolution Research Articles

Electropolishing of gold and gold alloys in HCl-glycerol-ethanol electrolytes

Electropolishing or electrochemical polishing (EP) is an ultrafinishing process that improves esthetic, technical and functional properties of metallic surfaces by reducing their roughness. This process is based on anodic dissolution of the workpiece through an oxidation reaction. For many years, cyanide-based electrolytes were used to electropolish precious metals like gold and its alloys. The need for safer working conditions encouraged the replacement of cyanide by other complexing agents, mainly thiourea. However, the latter is also harmful. Therefore, the aim of this work is to electropolish pure gold and 18k jewelry gold alloys (yellow, rose, red and gray) in a cyanide-free electrolyte, to evaluate the electrochemical behavior and the influence of different parameters. For this purpose, a previously reported solution based on hydrochloric acid and glycerol was used. In the first part of the study, the influence of chloride concentration on pure gold EP was determined by electrochemical techniques and surface properties analysis. The effects of adding ethanol to electrolyte composition and of variating rotation speed were also evaluated. The best results were obtained for a HCl 50% vol. - Glycerol 25 % vol. - Ethanol 25 % vol. electrolyte at a rotation speed of 1000 rpm. In the second part of the study, this solution was used to electropolish 18 K gold alloys. Silver-containing alloys were not uniformly polished due to the formation of an AgCl film on the surface that partially masks the substrates.

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.

The effects of σ phase on localized corrosion of 2205 duplex stainless steel in the presence of Pseudomonas aeruginosa

Pitting and galvanic corrosion of 2205 DSS with σ phase were investigated in the presence of Pseudomonas aeruginosa. Pitting corrosion was accelerated by σ phase, and further promoted by P. aeruginosa. The σ phase changed the distribution of pitting sites from being concentrated on phase boundaries and α phase in the solution treated coupons to being around σ phase in the biotic medium. The galvanic corrosion between α and γ phases was enhanced by the bacterium, and σ phase led to anodic dissolution of γ phase instead of α phase in DSS with solution treatment.

Chrysophyllum Albidum extract as a new and green protective agent for metal

ABSTRACT Gravimetric measurements and potentiodynamic polarization techniques were employed to investigate the protective performance of the metal in 1 M HCl and 0.5 M H2SO4 solutions by the C. albidum leaf extract at different concentrations (400-1600 mg/L) and time periods (1-4 days). The results showed the highest protection ability of over 96-97%, with inhibition increasing with higher extract concentrations. Polarization studies indicated a mixed inhibition mechanism, reducing both anodic dissolution and cathodic hydrogen evolution rates. Gas chromatography–mass spectrometry (GC–MS) analysis identified major organic constituents in the extract. Thermodynamic data fit the Langmuir isotherm model, suggesting chemisorptive adsorption of inhibitor molecules on the mild steel surface. Computational methods, including density functional theory (DFT), molecular dynamics simulations, and quantum chemical calculations, provided insight into inhibitor-metal interactions and adsorption behaviour at the molecular level. Overall, the study establishes C. albidum leaf extract as an effective, sustainable alternative to commonly used toxic chromate and phosphate inhibitors. It performs competitively even at low concentrations and in environments. The promising green inhibition properties, combined with the extract's nontoxicity and abundance from a natural source, suggest its potential as a cost-effective corrosion protection solution, especially for applications in developing economies.

Electrochemistry of Uranium on Liquid Cadmium Electrode in LiCl-KCl Eutectic

This work presents the electrochemical study of LiCl-KCl-UCl3 solutions at the temperature range 673–823 K on inert and reactive electrodes, i.e. W and Cd, respectively. On inert electrode, U(III) ions were reduced to metallic uranium through one step and the mechanism of the cathode reaction was irreversible. The diffusion coefficients of U(III) ions in molten chloride eutectic and liquid cadmium were calculated. On reactive electrode, U(III) ions were reduced with depolarization and were accompanied by the formation of intermetallic compound UCd11. The reactions of the cathodic deposition and anodic dissolution of the U-Cd alloy were studied and the conditions of the alloy formation via galvanostatic electrolysis were found. The solubility and the activity of uranium in liquid cadmium were determined.

Inhibition of anodic dissolution and corrosion of copper and its alloy in aqueous solutions by fuchsin

Inhibition of anodic dissolution and corrosion of copper and its alloy in aqueous solutions by fuchsin

Electric field simulation in the electrochemical machining of a thin-walled part cavity

The article is aimed at simulating an electric field in the interelectrode gap during the electrochemical machining of a thin-walled part cavity for aerospace equipment. The study involved simulating the process of electrochemical cavity machining at a constant voltage in a steady-state mode in the COMSOL Multiphysics environment. The simulation was carried out for the scheme of electrochemical machining with a movable cathode and vertical and horizontal feeding to the workpiece surface undergoing machining while maintaining a constant interelectrode gap. The following simulation conditions were adopted: 12Cr18Ni10Ti stainless steel as the material of the cathode tube; AlMg6 aluminum alloy as the material of the thin-walled part; NaNO3 solution as the electrolyte. When simulating the electric field in the interelectrode gap, the heat exchange process was taken into account. The simulation of the electric field in the electrochemical cavity machining of a thin-walled part yielded a macro that allows the process simulation to be adapted to different input process conditions. As a result of the simulation, the following distribution patterns were obtained: current density in the cathode, potentials, electric field in the interelectrode gap and adjacent area, and process temperature of electrochemical machining. The simulation results show that the electric field lines are directed toward the cathode from the workpiece periphery. This means that anodic dissolution of material occurs in a given region, which characterizes the law concerning the distribution of potentials in an electrochemical cell. The temperature distribution pattern obtained in the simulation revealed that a temperature increase in the machining zone is insignificant. An increase in electrolyte temperature is shown to result in a proportional increase in wall temperature. Thus, the conducted study provides a theoretical insight into the examined process.

Failure mechanism of Al-Zn-In sacrificial anode under the synergic action of water pressure and fluid in the extreme deep-sea environment

Corrosion failure of sacrificial anodes in extreme deep-sea environment is a key problem in metal protection technology. This study investigated the failure mechanism of the Al-Zn-In sacrificial anode under the synergic action of water pressure and fluid flow, by microstructure characterization and finite element analysis. The results exhibit that water pressure promotes the dissolution of Al-Zn-In alloy near the precipitates that are enriched at the grain boundaries. The flow amplifies the promoting effect of the pressure on anodic dissolution by inhibiting the formation of corrosion layers, and it accelerates the mass loss by mechanically aggressing the aluminum matrix. The synergic effect of water pressure and fluid flow results in a rapid degradation in the extreme deep-sea environment.

Study of the effect of static stresses on the hydrogen content and electrochemical characteristics of steels of different types

When cathodic protection is applied in places where paint films are damaged, an intense release of hydrogen occurs, which is removed both through diffusion and by transition from the adsorbed state on the metal surface to the subsurface layers thus leading to static hydrogen fatigue of steels, i.e., a brittle fracture occurs suddenly under static loading conditions at stress values significantly lower than the strength limit and even below the plasticity limit. We present the results of studying the impact of static tensile stresses on the hydrogen absorption by a metal during its cathodic polarization and the distribution of hydrogen over the cross-section of the metal surface. Three types of metal samples were used: wire samples made of U8A steel, plate samples made of 10KhSND steel, and semicircular samples made of Kh18N9T stainless steel with a stress concentrator. Tests of wire and semi-ring samples were carried out under a constant load and plate samples were tested under constant deformation. Polarization of wire and plate samples was carried out at different current densities for 4 days and semi-ring samples for 1 hour. At the end of polarization, the layer-by-layer distribution of hydrogen absorbed by the metal was determined by the anodic dissolution method. It is shown that with increasing deformation, the hydrogen content of the surface layers of the metal increases. Moreover, application of tensile loads and deformation of the metal by bending contribute to an increase in the amount of absorbed hydrogen and affect hydrogen distribution over the metal cross section. The thickness of the layer containing the maximum amount of hydrogen differs in steels of different compositions and structures. The results obtained can be used to protect structural steels against corrosion in sea water.

Towards understanding stress corrosion cracking of austenitic stainless steels exposed to realistic sea salt brines

Stress corrosion cracking behavior of stainless steel 304 L was investigated in full immersion, evaporated artificial sea salt brines (ASW) at 55 °C. It was observed that brines representative of thermodynamically stable brines at lower relative humidity (40% RH, MgCl2-dominant) had a faster crack growth rate than high relative humidity brines (76% RH, NaCl-dominant). Observed crack growth rates (da/dt) under constant stress intensity (K) conditions were determined to be independent of transitioning procedure (rising K or decreasing frequency) regardless of solutions investigated for the orientation presented. Further, positive strain rates had little to no impact on the observed da/dt. The observed behavior suggests an anodic dissolution enhanced hydrogen embrittlement mechanism for SS304L in concentrated ASW environments at 55 °C. Additional explorations further examined environmental influences on da/dt. Nitrate additions to 40% ASW at 55 °C solutions were shown to decrease measured da/dt and further additions stopped measurable crack growth. After sufficient nitrate had been added to fully stifle crack growth, a temperature increase to 75 °C induced cracking again, and a subsequent decrease to 55 °C once again stopped da/dt. These tests demonstrate the importance of ascertaining both brine-specific chemical and dynamic environmental influences on da/dt.

Effect of Mo on intergranular corrosion behavior in super-austenitic stainless steel

The effect of the Mo element on the intergranular corrosion behavior was investigated on super-austenitic stainless steels. The σ-phase structure and compositional changes of stainless steels with different Mo contents during aging at 800–900°C were investigated by TEM, combined with electrochemical tests, and two different intergranular corrosion mechanisms were revealed. The low-Mo 904 L stainless steel induces severe intergranular electrochemical corrosion due to selective anodic dissolution at grain boundaries caused by decreased passivation ability and σ-phase composition changes. The σ-phase precipitation of 254SMo and AL-6XN with high-Mo leads to Cr and Mo depletion reduces passivation film continuity, and causes intergranular corrosion.

Interfacial bonding and corrosion inhibition of 2-mercaptobenzimidazole organic films formed on copper surfaces under electrochemical control in acidic chloride solution

The interfacial bonding and the layered structure of 2-mercaptobenzimidazole (2-MBI) organic films adsorbed on electrochemically controlled copper surfaces and their corrosion inhibition effects in acidic chloride aqueous solution were investigated using an integrated approach of electrochemical methods and advanced surface analyses by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. It is shown that organic films formed on the copper surfaces are bi-layered with a chemisorbed inner layer and a physisorbed outer layer. In the chemisorbed inner layer, 2-MBI is bonded primarily by its nitrogen atoms with metallic and oxidized copper surfaces. Sulphur atoms are also involved in the bonding mechanism when metallic copper is directly accessible to the 2-MBI molecules. The initial presence of native copper oxides at the interface promotes the formation of Cu(I)-2-MBI metal-organic complexes in the chemisorbed inner layer using cathodic reduction to dissociate the oxide. Metal-organic complexes also form upon anodic polarisation due to Cu(I) ions generated by oxidation of the copper metal. 2-MBI effectively inhibits copper anodic dissolution in varying degrees, between 84% and 93%, depending on the pre-treatment used for the formation of the organic bi-layers. An enhanced protection of the substrate is obtained by adsorbing the 2-MBI inhibitor on an initially oxide-free surface, which is achieved by cathodic pre-treatment in absence of the inhibitor followed by 1 hour exposure to the inhibitor.

Specifics and Methods of Inhibiting the Underfilm Corrosion of Carbon Steel.

The process of metal dissolution under a delaminated insulating polymer coating (underfilm dissolution) has been studied. For this purpose, we used an experimental setup that simulates the process of corrosion of underground metal structures in the presence of through defects in the polymer coating and/or extended areas of peeling of the polymer coating from the metal (loss of adhesion)-subfilm cavities partially or completely filled with electrolyte. In particular, the distribution of the protective current under a peeled polymer coating was studied, and a sharp decrease in the value of the protective current was shown at a distance of 1-3 cm from the edge of the defect with a gap between the metal and the coating of 1-6 mm. The localized nature of metal corrosion under the exfoliated polymeric coating has been demonstrated. The ratio of the areas with accelerated corrosion to the total area of the metal can be 1 to 100. It has been established that there are areas of anodic dissolution of the metal during cathodic polarization of the entire sample with a peeled coating. The activating effect of carbon dioxide and hydrogen sulfide on the corrosion and anodic dissolution of steel under the coating was shown. So, it has been established that the dissolution current flowing from the anodic sections on a surface can increase approximately 10 times in the presence of carbon dioxide and hydrogen sulfide. A synergistic effect of these compounds on the process of localized underfilm corrosion of steel was detected. It has been developed a mechanism for the formation of localized corrosion damage to steel under a delaminated polymeric coating, which can be the nuclei of corrosion cracks upon reaching a certain level of mechanical loads, i.e., stress corrosion cracking (SCC) of carbon steel. Possible manners of inhibiting underfilm dissolution of metals are considered, and a method for pre-treatment of the surface with solutions of organosilanes, which ensures the formation of surface self-assembled polymeric siloxane nanolayers responsible for inhibiting underfilm corrosion of steel, is proposed.

Microfabricating Mirror-like Surface Precision Micro-Sized Amorphous Alloy Structures Using Jet-ECM Process.

Amorphous alloy (AA) is a high-performance metal material generally with significantly excellent mechanical and corrosion resistance properties and thus is considered as a desirable material selection for micro-scale articles. However, the microfabrication of AA still faces a variety of technical challenges mainly because the materials are too hard to process and easily lose their original properties, although at moderately high temperatures. In this study, jet-electrolyte electrochemical machining (Jet-ECM) was proposed to microfabricate the Zr-based AA because it is a low-temperature material-removal process based on the anode dissolution mechanism. The electrochemical dissolution characteristics and material removal mechanism of AA were investigated, and then the optimal process parameters were achieved based on the evaluation of the surface morphologies, surface roughness, geometrical profile, and machining accuracy of the machined micro-dimples. Finally, the feasibility was further studied by using Jet-ECM to fabricate arrayed micro-dimples using the optimized parameters. It was found that Jet-ECM can successfully microfabricate mirror-like surface AA arrayed precision micro-dimples with significantly high dimensional accuracy and geometrical consistency. Jet-ECM is a promisingly advantageous microfabrication process for the hard-to-machine AA.

Stress corrosion cracking behavior and mechanism of 2205 duplex stainless steel under applied polarization potentials

In this work, a non-steady electrochemical model for assessing stress corrosion cracking (SCC) of 2205 duplex stainless steel (DSS) under applied polarization potentials was proposed, and the SCC mechanism was revealed. With the negative shift of potentials, hydrogen enhances SCC susceptibility by deteriorating passive film, inhibiting repassivation and causing serious damage. In particular, at −850 mV (vs. SCE), the synergetic effect of anodic dissolution (AD) and hydrogen embrittlement (HE) causes severe pitting and SCC. The negative shift of applied potentials changes the preferential pit/SCC initiation site due to high hydrogen concentration in austenite.

Simulation-Assisted Tool Design for Pulsed Electrochemical Machining of Magnetic Shape-Memory Alloys

Shape-memory alloys set high demands on the production technologies being used. During cutting, continuous heat input and mechanical stress have an undesirable influence on the shape-memory effect. Pulsed electrochemical machining (PECM), which is based on anodic dissolution, enables force-free machining without thermomechanical influence on the edge-zone properties of the workpiece. Depending on the desired geometry, the development of a customized PECM fixture is necessary. The design of the fixtures is often based on the experiences of the designers and manufacturers, which often results in an estimation of the functionally critical dimensions. For this reason, the study focuses on a methodical approach for evaluating crucial fixture dimensions using knowledge of the specific material dissolution behavior linked with a numerical simulation model. It has been shown that the shape-memory alloy NiMnGa has a non-linear dissolution behavior in sodium nitrate. A reduction of stray currents up to 20% resulting from a lateral gap between the cathode and electrical insulation was demonstrated using numerical simulation. The study shows that a low cathode shaping height has the strongest influence on precise processing. Varying the process parameters allowed for the lateral gap to be adjusted between 0.15 and 0.25 mm.

Repassivation-oriented pitting corrosion analysis in a cause-effect relationship with microstructure, precipitation, and mechanical behavior of low-carbon medium-chromium ferritic stainless steel

Ferritic stainless steels (FSS), which are potentially ferromagnetic, play a vital role in electromagnetic applications, including solenoid valves, owing to their ferromagnetic properties. This study delves into the microstructure's impact on the localized pitting corrosion behaviour of cold-drawn (CD) low-carbon medium-chromium ferritic/ferromagnetic EN1.4106. Employing potentiostatic-based corrosion analysis, mechanical assessments, and microstructural evaluations on 44 designated specimens subjected to varied annealing conditions, we unveil a nuanced correlation between corrosion resistance and microstructure. Lower reduction rate of 15% versus 45%, extended-enough annealing conditions, and meticulous microstructural control with average grain size of around 45–46 μm, particularly in minimizing dislocation density alongside the local misorientaion of 15° up to at most 35°, significantly enhance corrosion resistance. Overall, this FSS grade demonstrates commendable non-hardenable characteristics with moderate resistance to pitting corrosion in the two of the most corrosive (acidic and chlorinated) environments. The grade notably passivates in sulfuric acid electrolyte solution (SAES) but undergoes active anodic dissolution in sodium chloride electrolyte solution (SCES), ultimately forming a sort of passive-like oxide layer.

Crevice Corrosion Behavior of 201 Stainless Steel in NaCl Solutions with Different pH Values by In Situ Monitoring.

Crevice corrosion (CC) behavior of 201 stainless steel (SS) in 1 M NaCl + x M HCl/y M NaOH solutions with various pH was investigated using SECM and optical microscopic observations. Results show that the CC was initiated by the decrease in pH value within the crevice. The pH value near the crevice mouth falls rapidly to 1.38 in the first 2 h in the strongly acidic solution, while the pH value was observed to rise firstly and then decrease in the neutral and alkaline solutions. It indicates there is no incubation phase in the CC evolution of 201-SS in a pH = 2.00 solution, while an incubation phase was observed in pH = 7.00 and 11.00 solutions. Additionally, there appeared to be a radial pH variation within the gap over time. The pH value is the lowest at the gap mouth, which is in line with the in situ optical observation result that the severely corroded region is at the mouth of the gap. The decrease in pH value inside results in the negative shift of open circuit potential (OCP) and the initiation of CC of 201-SS. The increased anodic dissolution rate in the acidic solution accelerates the breakdown of passive film inside, reducing the initiation time and stimulating the spread of CC.

INFLUENCE OF THE ELECTROLYTE FLOW AND CLEANING AIR PRESSURE ON THE OVERCUT IN BIPOLAR PULSED ELECTROCHEMICAL MICRO-MACHINING PROCESSES

This paper presents an experimental investigation on the reduction of overcutting in the bipolar pulsed electrochemical pulsed machining process. It is described how this unconventional manufacturing method, which involves the anodic dissolution of a metal part immersed in an electrolytic medium, can be improved by incorporating compressed air as a residue-cleaning medium and modifying the electrolyte flow rate to reduce overcutting. These results can be helpful for the inclusion of these variables in process control systems and generate significant improvements in the fabrication of components at micrometer scales. Keywords: micromachining, electrochemical machining, overcut, electrolyte, automatic processes.

Investigation of Iron Dissolution Mechanism in Acidic Solutions with and without Dissolved CO2—Part II: Time of Flight-Secondary Ion Mass Spectrometry 3D Mapping

Time-of-flight-secondary ion mass spectrometry (ToF-SIMS) 3D mapping and depth profiling were used to study the anodic iron dissolution mechanisms of mild steel in chloride-containing aqueous CO2 environments. The technique detected adsorbed hydroxide and chloride intermediates formed during the corrosion process, consistent with the proposed multipath reaction mechanism for anodic iron dissolution reaction. Despite the presence of aqueous carbonic species and their observed effect on the kinetics of iron dissolution, no additional adsorbed intermediates have been detected in aqueous CO2 environments, indicating that carbonic species do not directly participate in the iron dissolution reaction. ToF-SIMS 3D mapping results on characterization of the specimens immersed in a chloride-containing solution with and without CO2 suggest that one role of aqueous carbonic species CO2 could be to accelerate the adsorption of chloride ions and the formation of chloride intermediates.