Anodic Dissolution Mechanism Research Articles

Resistance of the welded joint of X70 steel for main gas pipelines against corrosion-mechanical cracking under cathodic polarization in near-neutral pH solutions

ABSTRACT Resistance of welded joint of X70 steel welded using Sv-08G1NMA and OK 10-74 flux wire against stress-corrosion cracking in near-neutral pH solution NS4 was investigated by slow-strain rate method, voltammetry, optical and scanning electron microscopy, electrolytic permeation of hydrogen. It was established that the stress-corrosion cracking of welded joint occurs through the base metal in the range of potentials more positive than −0.921 V by the anodic dissolution mechanism, more negative than −1.050 V is consistent with a hydrogen embrittlement mechanism, and in the potentials' range from −0.921 V to −1.050 V – both by the anodic dissolution and hydrogen embrittlement mechanism. The susceptibility to stress-corrosion cracking coefficient KS increases with the polarization potential shift −0.750 V → −0.950 V → −1.050 V as follows: for the welded joint – 1.1 → 1.16 → 1.35, for X70 steel as 1.0 → 1.12 → 1.0.

Mechanism of Anodic Dissolution of Tungsten in Sulfate–Fluoride Solutions

Thin passive films on tungsten play an important role during the surface levelling of the metal for various applications and during the initial stages of electrochemical synthesis of thick, nanoporous layers that perform well as photo-absorbers and photo-catalysts for light-assisted water splitting. In the present work, the passivation of tungsten featuring metal dissolution and thin oxide film formation is studied by a combination of in situ electrochemical (voltammetry and impedance spectroscopy) and spectro-electrochemical methods coupled with ex situ surface oxide characterization by XPS. Voltametric and impedance data are successfully reproduced by a kinetic model featuring oxide growth and dissolution coupled with the recombination of point defects, as well as a multistep tungsten dissolution reaction at the oxide/electrolyte interface. The model is in good agreement with the spectro-electrochemical data on soluble oxidation products and the surface chemical composition of the passive oxide.

Improving intergranular cracking and stress corrosion cracking resistance of highly sensitized AA5083 Al-Mg alloy via reversion heat treatment

This study systematically examines the impact of reversion heat treatments (220–280 ℃ for 1 h) on the microstructure evolution, electrochemical corrosion, intergranular cracking (IGC) and stress corrosion cracking (SCC) of a severely sensitized (175 ℃/100 h) AA5083 alloy. Increasing the reversion temperature gradually enhances the corrosion resistance by dissolving the β′-Al3Mg2 phase, with the optimal treatment identified as 280 ℃/1 h. The βˊ phase maintains its planar film shape and continuously covers the grain boundaries after reversion treatment below 240 °C, but spheroidizes at the triple junctions at 260 °C. The morphology of the βˊ phase is dictated by grain boundary diffusion and interface diffusion. Reversion treatments improve SCC resistance by dissolving the β′ phase and reducing yield strength, attributed to anodic dissolution and hydrogen embrittlement mechanisms. This research offers valuable insights into the practical benefits of reversion treatments for Al-Mg alloy marine applications, addressing safety concerns related to sensitization.

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.

Effect of Coating on Stress Corrosion Performance of Bridge Cable Steel Wire

Hot galvanization on steel surfaces can isolate the steel from corrosive environments and alleviate the stress corrosion cracking caused by the anodic dissolution mechanism. However, the cathodic protection potential of the coating is excessively negative, which may aggravate the hydrogen embrittlement problem. The effect of a coating on the stress corrosion performance of bridge cable wire was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), a thermal desorption analysis (TDA), an electrochemical workstation, and an FIP test. The results show that hot-dip ZnAl and ZnAlMg alloy coatings can significantly prolong the stress corrosion fracture time of steel wire substrates. From a macroscopic perspective, the stress corrosion cracking fracture is a brittle fracture caused by hydrogen embrittlement. Moreover, the coating type has little effect on the fracture morphology of bridge cable wire. In NH4SCN solution (50 °C, 20 wt.%), a corrosion product layer composed of ZnS and Al2O3 was formed on the surface of the coated steel wire. The electrochemical analysis showed that the corrosion resistance of the ZnAlMg coating was better than that of the ZnAl coating, which was the main reason for the improvement of the stress corrosion performance.

Modeling electrochemical oxide film growth—passive and transpassive behavior of iron electrodes in halide-free solution

The phenomenon of passivity is crucial for many areas of our technological and metal-based civilization. Nevertheless, the mechanisms leading to passivity are still under investigation and not fully understood. Modeling passive film growth can bring insights into these processes, which are experimentally hard or impossible to access. Therefore, this paper presents a comprehensive model which can describe oxide film growth and dissolution under an external potential for various metal oxides. The simulation gives insights into the defect concentrations and electric field during passive film growth and film dissolution and delivers an anodic transpassive dissolution mechanism. The simulation is compared to experiments derived from the oxidation of iron electrodes and shows very good agreement. The addition of a transpassive dissolution mechanism to oxide film models is the next step toward model-based corrosion prediction.

Research on the Flow Field of Electrolytic Processing for Shaped Holes with Large Depth-to-diameter Ratio

For parts with large deep-diameter ratio shaped hole features, the complex structure of the profile and large deep-diameter ratio led to poor profile machining accuracy. The shaped hole processing requires high efficiency, high precision and low cost. Therefore, it is difficult to use the traditional processing method, and the electrolysis method based on the anodic dissolution mechanism is adopted, which has no shear stress and accurate profile forming. The 3D model is established based on the part, and the cathode and tooling structure is designed. Based on COMSOL software, we designed the flow channel uniformity of electrolytic processing of shaped holes and analyzed the arrangement of cathode outlet holes in electrolytic processing, which affects the uniformity of the processed surface and flow field. The arrangement of cathode exits holes to meet the uniform distribution of electrolyte at the surface boundary and high-speed flow at the surface was obtained by simulation analysis. By analyzing the flow field of different inlets, the flow rate magnitude of the shaped boundary and surface of the surface shaped hole is positively correlated with the inlet pressure of the electrode liquid.

Effect of cathodic protection potential on stress corrosion susceptibility of X80 steel

By simulating the different electrochemical characteristics of the crack tip and crack wall in the stress corrosion process of X80 steel through the dynamic potential polarization test with different scanning rates, it is reasonable to predict that the crack tip of tensile sample might still be in anodic dissolution state even under cathodic protection, and meanwhile, the hydrogen atoms generated by the cathodic reaction would have a facilitating effect on the anodic dissolution of crack tip. Thus, with the cathodic potential being negatively shifted, the hydrogen-promoted anodic dissolution and the cathodic protection effect may compete at the crack tip of steel, simultaneously. Combined with the results of electrochemical hydrogen permeation and SSRT (Slow strain rate tensile test), the authors quantitatively analyzed the effect of cathodic polarization potential on the kinetics of anodic dissolution at the crack tip, and the results showed that the cathodic protection effect on the specimen at the critical potential (about −950 mV) for stress corrosion of X80 steel is sufficient to offset the hydrogen-promoted anodic dissolution effect caused by the enrichment of hydrogen atoms at the crack tip, compared to that of the free-corrosion condition. Therefore, the dominant factor that caused a significant increase in stress corrosion cracking (SCC) susceptibility, which was indicated by the comprehensive loss rate IΣ>20% of X80 steel and brittle fracture morphology obtained through SEM, was the hydrogen embrittlement mechanism rather than the anodic dissolution mechanism.

Corrosion and Mechanical Behavior of the As-Cast and Solid-Solution-Treated AM50 Magnesium Alloy in Different Media

Hydrogen embrittlement and the anodic dissolution mechanism are two important aspects of the corrosion behavior of magnesium alloys. Here, to evaluate the effects of these two aspects on the corrosion failure of magnesium alloys under stress, the stress and corrosion behaviors of the AM50 magnesium alloy in air, deionized water, and NaCl solution after solid-solution (T4) treatment were investigated by X-ray diffraction, scanning electron microscopy, slow strain rate tensile testing, and vacuum dehydrogenation. The as-cast AM50 magnesium alloy was mainly composed of the α-Mg and β-Mg17Al12 phases. After T4 treatment, the amount of the β-Mg17Al12 phase was significantly reduced, and only a small amount existed at the grain boundaries. After T4 treatment, the stress corrosion resistance in deionized water improved, but it decreased in an NaCl environment. Dehydrogenation experiments showed that the effect of hydrogen on the corrosion process was weakened owing to the decrease of the β-Mg17Al12 phase after solution treatment. The effects of hydrogen embrittlement and the anodic dissolution mechanism on the corrosion behavior of the AM50 magnesium alloy under stress were different. In deionized water, the hydrogen embrittlement mechanism played the major role, while the anodic dissolution mechanism played the major role in the presence of Cl- ions.

The anodically polarized Mg surface products and accelerated hydrogen evolution

To clarify the anodic dissolution mechanism of Mg, the hydrogen evolution from pure Mg in acidic solutions under galvanostatic conditions were systematically measured. With increasing anodic current density, the cathodic hydrogen evolution rate decreased, and the anodic hydrogen evolution became faster while some surface area on the Mg was becoming dark under anodic polarization. Based on the surface analysis results and the generally accepted basic electrochemical equations, the evolution kinetics of hydrogen from Mg was deduced, and the most possible surface intermediate active species that could facilitate the anodic Mg dissolution and anodic hydrogen evolution were proposed. This paper further develops the model of incomplete film Mg + dissolution, explains many reported experimental phenomena, and clarifies misunderstandings of current mechanism.

Direct electrochemical dissolution of metallic uranium into deep eutectic solvent

Deep eutectic solvents (DESs) could make uranium recycling processes greener than using conventional solvents, owing to their inherent advantages such as being biodegradable and non-toxic. However, the chemistry of uranium ions in DES systems, particularly the mechanism of direct anodic dissolution of uranium metal, remains unclear. The anodic dissolution of uranium metal in choline chloride (ChCl)–ethylene glycol (EG) DES was conducted by applying a constant current. The oxidation state of uranium in ChCl-EG DES was uranium(IV) when compared to concentration and applied charge. Absorption spectra showed 8 coordinated U(IV) centered complexes formed in the ChCl-EG DES, regardless of the uranium source (i.e. uranium chloride or metallic uranium anodic dissolution). The in situ spectroelectrochemistry during potentiostatic electrolysis, cyclic voltammograms, and absorption spectra of different times of potentiostatic electrolysis showed U(IV) oxidized to U(V), and then the U(V) disproportionated into U(IV) and U(VI) species. Understanding fundamental uranium speciation in DES systems and electrochemical properties could facilitate the development of an eco-friendly nuclear fuel cycle and nuclear uranium recycling process using green DESs.

Vibration anode-abrasive polishing of channels of small cross section

The mechanism of anodic dissolution of microroughnesses in the combined method of anodic-abrasive vibratory polishing with magnetic-abrasive electrically polarized charged grains of channels of pipes of small cross section made of non-magnetic materials is presented. Materials that can be used as magnetic-abrasive composite grains such as Fe3C, FeB, FeB2, etc. or magnetic NbC-Fe modified with graphene, carbon nanotubes, or a combination thereof have been selected. A passivating electrolyte used in this combined method of vibration anode-abrasive polishing, for example, 3% NaNO3 + (3-6)% Fe3C, is proposed. The article shows the developed scheme of the process of combined magnetic-abrasive polishing and describes the process itself. The value of the allowance to be removed can be estimated from the proposed formula for calculating the removed layer of microroughness in the joint electrochemical process of polishing the channel surface with stationary and pulsed currents flowing in the electrolyte flow.

The effect of bird droppings on the corrosion of steel and aluminum used in offshore applications

AbstractEngineering materials in service are frequently exposed to bird droppings (BDs). In this study, the interaction has been studied of BDs from chicken with a carbon steel, AISI 316, 22% Cr duplex stainless steel (DSS), 25% Cr super duplex stainless steel (SDSS), carbon steel with a thermally sprayed aluminum (TSA) coating, and aluminum alloy EN AW 6082. Samples with and without BDs are exposed to a cyclic salt spray test for up to 692 h (29 days). Electrochemical experiments in the presence of BDs were conducted in a syringe‐based droplet cell. Characterization of the corrosion products by infrared (IR) and Raman spectroscopy shows no build‐in of organic components into the corrosion products in the samples exposed to BDs. In general, BDs affect the anodic dissolution mechanism of metals and increase the critical pitting potential. For carbon steel, a component of the BDs acts as an anodic inhibitor, leading to passivation of the surface and decreasing corrosion rates by 1–2 orders of magnitude. For 316, BDs increase the critical pitting potential but may facilitate crevice‐like initiation of localized corrosion. There are negligible effects of BDs on the corrosion of SDSS, and no evidence either for adverse effects on DSS. TSA shows an increased corrosion rate by half to one order of magnitude with BDs, but its ability to galvanically protect a steel base material is not compromised. AW 6082 shows decreased corrosion rate, no difference in mass loss, but increased pitting in the presence of BDs. Overall, these model experiments may only be seen as the start of a more systematic understanding of the interaction of BDs with engineering materials.

Sress-corrosion cracking under cathodic protection of low alloy steel joints with high frequency weld and arc weld

According to the results of complex electrochemical, corrosion-mechanical and fractographic studies, the existence of three potential regions, in which the stress-corrosion cracking (SCC) of 17G1S (17G1S-U) steel in the NS4 model soil electrolyte occurs by different mechanisms was established and experimentally confirmed: at potentials positively than -0.8 V – by the mechanism of local anodic dissolution, at potentials region from -0.8 V to -0.98 V – by the mixed mechanism, at potentials less than -0.98 V by hydrogen breaking mechanism. The susceptibility to SCC of high-frequency weld joints, estimated by the coefficient of KS, in the potential range from the corrosion potential to -1.2 V increases (KS increases from 1.1 to 1.8), which is less intense than for steel 17G1S/17G1S-U (KS increases from 1.1 to 2.8), for arc weld joints – does not change much enough (KS increases from 1.1 to 1.3). The validity of KS coefficient introduced for the base metal for comparative assessment of the susceptibility to SCC of welded joints, is provided in case that there are no defects in the welds and SCC occurs on base metal.

Effect of Corrosive Medium and Surface Defect-Energy on Corrosion Behavior of Rolled ZK61M Alloy.

Magnesium alloys have been widely used as lightweight engineering structural materials, but their service performances are severely restricted by corrosion failure. In this paper, the influence of corrosive medium and surface defect energy on the corrosion behavior of rolled ZK61M alloy was investigated. The corrosion tests were conducted in different concentrations of sodium chloride solution for different durations, and the polarization curves and electrochemical impedance spectroscopy were reported. The surface morphology of rolled ZK61M alloy before and after corrosion tests were analyzed. The results showed that the corrosion tendency became stronger with the increase of the concentration of corrosive medium and the number of surface defects of ZK61M alloy. Moreover, the initial corrosion pattern was the pitting caused by micro galvanic corrosion at the surface defect, which gradually developed into uniform corrosion. Furthermore, the main damage occurred at the grain boundary, resulting in the destruction of grain bonding force and the removal of material along the rheological layer. The oxidation corrosion mechanism was mainly the anodic dissolution mechanism.

A generalised, multi-phase-field theory for dissolution-driven stress corrosion cracking and hydrogen embrittlement

We present a phase field-based electro-chemo-mechanical formulation for modelling mechanics-enhanced corrosion and hydrogen-assisted cracking in elastic–plastic solids. A multi-phase-field approach is used to present, for the first time, a general framework for stress corrosion cracking, incorporating both anodic dissolution and hydrogen embrittlement mechanisms. We numerically implement our theory using the finite element method and defining as primary fields the displacement components, the phase field corrosion order parameter, the metal ion concentration, the phase field fracture order parameter and the hydrogen concentration. Representative case studies are addressed to showcase the predictive capabilities of the model in various materials and environments, attaining a promising agreement with benchmark tests and experimental observations. We show that the generalised formulation presented can capture, as a function of the environment, the interplay between anodic dissolution- and hydrogen-driven failure mechanisms; including the transition from one to the other, their synergistic action and their individual occurrence. Such a generalised framework can bring new insight into environment–material interactions and the understanding of stress corrosion cracking, as demonstrated here by providing the first simulation results for Gruhl’s seminal experiments.

Corrosion Inhibition and Electro-ballistic properties of Green Inhibitor for Mild Steel in Mineral Acid

Implementation of Amaranthus extract as corrosion inhibitor for mild steel in pickling containing hydrochloricacid has been investigated. The electrochemical experiments were conducted to bring forth results regardingvarious parameters, viz., Corrosion Current, Anodic Polarization and Cathodic Polarization. Alongside,experiments for assessing the inhibitor efficiency and concentration of acid were also conducted. Therewas observed a gradual decrease in corrosion current with time for both uninhibited and inhibited systems.The experiments for plotting polarization curves for mild steel at various concentrations of Amaranthusextract in aerated solutions were conducted. These experiments, which are conducted Galvano-statically,depicted the polarization effect of inhibitor on different electrodes. The values, thus obtained, indicatedthat adsorption of Amaranthus extract tends to modify the mechanism of anodic dissolution as well ascathodic hydrogen evolution. The results clearly show that both the cathodic and anodic reactions areinhibited and there was found an increase in inhibition as the inhibitor concentration increases in acidmedia, but the cathode was more polarized than anode. This indicated that Amaranthus extract may beclassified as cathodic inhibitor in 4N hydrochloric acid solution. The aim of conducting these experimentsis to use inhibited acid for pickling so that large structures as well as small tools can be pickled/ cleaned. Asa contribution to the current interest on environment friendly, green, corrosion inhibitors, the present studyinvestigates the inhibiting effect of Amaranthus extract, a green inhibitor which is commonly known asPigweed.

Anodic dissolution mechanism of TA15 titanium alloy during counter-rotating electrochemical machining

Anodic dissolution mechanism of TA15 titanium alloy during counter-rotating electrochemical machining

Influence of chloride ion concentration on initial corrosion of AZ63 magnesium alloy

The initial corrosion behavior of AZ63 magnesium alloy was investigated in 1, 3, 5 and 7 wt.% NaCl solutions by means of corrosion potential, linear polarization, electrochemical impedance spectroscopy, and polarization measurements, during exposure in the corrosion media. Results show that the increase in chloride concentration provokes an increase in the corrosion rate. Based on the obtained kinetics parameters the mechanisms of anodic dissolution and hydrogen evolution reactions were discussed, and kinetic models were proposed. It is concluded that anodic dissolution proceeds under Temkin conditions and hydrogen evolution reaction depends on the surface coverage of Mg(OH)2 species.

A preliminary account of electro-chemical machining of Ti-48Al-2Nb-2Cr produced by electron beam melting

Electron beam melting (EBM) made feasible γ-titanium aluminide (TiAl) alloys. However, the surface roughness resulting from EBM is poor, and the high mechanical properties make γ-TiAl difficult to be machined. Electro-Chemical Machining (ECM) is gaining interest as a finishing process to achieve low surface roughness. Based on the anodic dissolution mechanism, ECM realises a contactless material removal and results particularly suitable for difficult-to-cut materials. The paper investigates the use of ECM for the finishing of Ti-48Al-2Nb-2Cr, a γ-TiAl alloy made by EBM. The effects of current, voltage, feed rate and duty ratio have been accounted for under pulsed machining conditions.