Free Corrosion Research Articles

Examining the Relationship Between Post-Build Microstructure and the Corrosion Resistance of Additively Manufactured 17-4PH Stainless Steel

The performance of wrought and post-build heat treated, additively manufactured SS17-4PH stainless steel was evaluated to determine whether additive processing can produce material with a similar corrosion resistance to the alloy in wrought form, and to establish whether the additive manufacturing (AM) processing conditions alter the electrochemical conditions required for corrosion attack. Samples built by laser powder bed fusion (LPBF) from nitrogen-atomized and argon-atomized powder were heat treated to achieve a homogenized, solutionized martensitic microstructure. A wrought sample was also solutionized to minimize the influence of Cu precipitates. Multicomponent E-pH diagrams were constructed for the three compositions in a chloride containing environment using equilibrium thermodynamic data to elucidate the chemical reactions that can occur in the SS17-4PH alloy and to indicate the regions where variations in passivity would occur. Electrochemical measurements compared the behaviors under free corrosion conditions and the pitting resistances of the three compositions in chloride environments with differing solution pH levels. The results revealed that the nitrogen retained from atomization does enhance the corrosion resistance of additively-processed SS17-4PH and that the benefit was strongest in a neutral pH environment. The results also revealed that the dissolution of the nitrogen containing matrix suppressed the activity of CuCl3−2 in the solution and enhanced the activity of NH+4 ions at electrode potentials near Epit. This signifies that the ionic phases at the surface of the electrode are influenced by both the alloy composition and the processing conditions.

Reliability assessment of subsea pipelines under the effect of spanning load and corrosion degradation

Subsea pipelines are delicate infrastructures with high importance to the oil and gas industry. These structures are surrounded by an extreme environment, in which free spanning is a major issue that can lead to several unwanted events such as local buckling or vortex-induced vibration. Moreover, corrosion is inevitable problem to these structures. All these problems highly reduce the safety levels of subsea pipelines. Hence, this paper proposes a new framework for the probabilistic analysis of subsea pipelines subjected to both free spanning and corrosion degradation. For the subsea pipeline, new limit state functions are developed that include failure modes due to corrosion degradation and spanning loads caused by the maximum bending stress. In addition, new probabilistic burst pressure models for corroded pipelines have been included, taking into consideration pipeline steel grade strength as well as the surrounding uncertainty. The importance sampling method is proposed to estimate the reliability analysis results in terms of failure probability and reliability index. The proposed framework is applied on a real case study of API 5 L X65 subsea pipeline. The impact of several parameters on the reliability analysis outcome are investigated and discussed through several scenarios. Results indicate the importance of early-inspection data for planning the suitable operating regime of the pipeline in terms of internal pressure, which can be used to estimate the allowable critical spanning lengths and corrosion defect geometries to alert the appropriate actions to avoid failures.

Accumulated fatigue damage assessment of side structural details in a double hull tanker based on spectral fatigue analysis approach

The fatigue life of structural details in the double side of a tanker ship was investigated, employing the spectral fatigue analysis approach. The stochastic environmental loads were derived by seakeeping software based on the 3D diffraction theory, in the frequency domain, and then mapped on a structural finite element model for the ship hull. The stress response at the considered details was extracted from the finite element analysis and the accumulated damage was estimated by Palmgren-Miner's rule. The reduction of the hull girder section modulus and the deterioration of fatigue strength due to corrosion were taken into account. The influences of different wave scatter diagrams, reduction of hull girder section modulus, stress concentration factor, free corrosion S–N curve, wave direction, wave spectrum and operational profile on the accumulated fatigue damage were investigated.

Corrosion behaviour of hard coatings on Mg substrates

Abstract TiN and CrN coatings were deposited with magnetron sputtering on magnesium alloy AZ 31 hp. Magnesium oxide and metallic interlayers were used to improve the corrosion resistance of the compound. The magnesium oxide was produced by plasma chemical oxidation process. Polarization curves were recorded and the free corrosion potential was measured to test the corrosion resistance of all samples. The results were compared with uncoated Mg AZ31 alloy. The investigations showed that the corrosion resistance can be improved by the PVD coatings. Thick CrN coatings with Cr interlayer exhibited the best results. The protection with the magnesium oxide layer was insufficient up to now. Here, the etching before plasma chemical oxidation process should be improved.

Effect of high temperature oxidation on dealloying mechanism of Ag-Cu alloy

Nanoporous silver (NPS) with a three-dimensional (3D) bicontinuous ligament/pore structure can be fabricated in different ways and with different treatments. Thermal treatments before or after dealloying can have a considerable impact on the dealloying process. High-temperature oxidation (HTO) has been researched as a method to tune the process of NPS fabrication. In this work, X-ray diffraction and X-ray photoelectron spectroscopy characterizations were used to identify the phase after HTO and dealloying. Copper oxide was found in the precursor alloy after HTO, which could be the key factor that would influence the mechanism of NPS fabrication. Scanning electron microscopy and transmission electron microscopy were executed to characterize the pathway of forming NPS and research the difference between HTO specimens and the as-cast sample. This demonstrated that, compared to the free corrosion pathway, the diffusion method of Ag atoms was different under HTO pretreatment, which was the predominant factor causing a larger 3D bicontinuous ligament/pore structure. Finally, the microstructure of the final NPS pretreated with HTO for 3 min was much more homogeneous than that of the others, and when the pretreatment time of HTO reached 5 min, the ligament/pore structure almost collapsed.

The Corrosion of Mg-Sn-Ca Tertiary Alloys in NaCl Solutions and Their Performance for the Sacrificial Cathodic Protection of Mg Alloy AZ31B-H24

The high specific strength of Mg makes it a desirable material for use in light-weight transport applications, and its high theoretical energy density has driven interest in its use as a battery for primary and secondary systems. As such, Mg alloys have been the subject of much recent attention and the issues pertaining to its poor corrosion performance are well known. Cathodic activation, specifically, is a major problem. Previous publications have investigated the efficacy of alloying with Sn [1,2] and shown a reduction in the extent of cathodic activation [1] and demonstrated the galvanic protection of AZ31B-H24 by Mg-1Sn with 95% efficiency [3]. There are two key requirements for a viable and sustainable sacrificial anode, (1) A galvanic couple potential must be maintained at a value consistently lower than that of the lowest open circuit potential (OCP) of the protected metal in order to dissolve preferentially and to avoid detrimental polarity reversal; (2) Low self-corrosion in order to provide long-term corrosion protection such that cathodic polarization on the protected metal is maximized and the residual anodic reaction rate on the sacrificial anode at OCP, is minimized. Previous findings suggest that an optimum Sn content would be 1 % > Sn < 5% [3] such that self-corrosion is minimize whilst retaining a low galvanic couple potential. However, the latter has continued to pose a problem. Small additions of Ca are thought to suppress the corrosion potential of the alloy such that a consistently negative galvanic couple potential (when coupled to AZ31B-H24) can be achieved. As such, the current work investigates the corrosion behavior of Mg-xSn-0.1Ca (x = 2.5, 5, 7.5 wt%) tertiary alloys as a function of Sn content in chloride-containing conditions and the ability of these alloys to galvanically protect AZ31B-H24 over a 24-hour immersion period in chloride conditions. Data obtained from a suite of in situ electrochemical techniques and an in situ scanning vibrating electrode technique (SVET) to assess free corrosion rates and the extent of cathodic activation with and without coupling to AZ31B-H24 will be presented.

Peculiarities in the Structure Formation and Corrosion of Quasicrystalline Al65Co20Cu15 Alloy in Neutral and Acidic Media

In the present study, the structure and corrosion properties of quasicrystalline conventionally solidified Al65Co20Cu15 alloy cooled at 5 К/s were investigated. Structure was characterized by metallography, X-Ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Corrosion properties were determined by gravimetric and potentiodynamic methods at room temperature. The investigations performed confirm the peritectic formation of stable quasicrystalline decagonal D-phase that coexists with crystalline Al4(Co,Cu)3 and Al3(Cu,Co)2 phases in the structure of Al65Co20Cu15 alloy. According to energy dispersive spectroscopy, the stoichiometric composition of D-phase is Al63Co24Cu13. The susceptibility of the Al65Co20Cu15 alloy to corrosion significantly decreases with increasing pH from 1.0 (acidic media) to 7.0 (neutral medium). A corrosion rate of the Al65Co20Cu15 alloy in the aqueous acidic solutions (pH=1.0) increases in the order HNO3®HCl®H2SO4®H3PO4. The mass of the specimens decreases in the solutions of H2SO4 or H3PO4 and increases in the solutions of HNO3 or HCl which relates to different rate ratios of accumulation and dissolution of corrosion products. The Al65Co20Cu15 alloy exhibits the highest corrosion resistance in the NaCl solution (pH=7.0) in which it corrodes under electrochemical mechanism with oxygen depolarization. The better corrosion resistance in sodium chloride solution is achieved due to the formation of passive chemical compounds blocking the surface. Free corrosion potential of the Al65Co20Cu15 alloy has value –0.43 V, the electrochemical passivity region extends from –1.0 V to –0.4 V, and a corrosion current density amounts to 0.18 mА/сm2. Depending on media, two typical surface morphologies are revealed after corrosion of quasicrystalline specimens of the Al65Co20Cu15 alloy. In the H2SO4 and H3PO4 acidic solutions, clean specimens’ surface due to its homogeneous dissolution is observed except for the more defective areas, such as boundaries of crystalline Al3(Cu,Co)2 phase containing less Co, which dissolve at a higher rate. In the HNO3, HCl or NaCl solutions, a porous layer on the surface is formed which is visually revealed as surface darkening. After staying in the NaCl solution, on the surface of the Al65Co20Cu15 alloy, the pits are also found due to preferential dissolution of components where the boundaries of Al3(Cu,Co)2 phase and flaws are located.

Corrosion Resistance of a Plasma-Oxidized Ti6Al4V Alloy for Dental Applications

A Ti6Al4V alloy was plasma-oxidized at 600 °C during 1, 2, 3, 5 and 8 h and corroded in an artificial saliva solution. Electrochemical evaluation was performed by using potentiodynamic polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) measurements during 100 h. Corroded specimens were characterized by using Raman spectroscopy and scanning electronic microscopy (SEM). All tests indicated that the highest corrosion resistance was obtained for specimen oxidized during 3 h since the noblest free corrosion potential, lowest passive and corrosion current density values, as well as the highest polarization resistance values were obtained under these circumstances. EIS measurements indicated that the highest impedance and phase angle values obtained for this specimen exhibited a high capacitive behavior typical of a very compact passive film.

Improved electrochemical corrosion resistance of hot-press sintered WC–Al2O3 composites with added TiC in alkaline solutions

(85-x)WC–15 wt%Al2O3–xTiC (x = 0, 1.5, 2.5, 5, 10, and 20 wt%) composites were prepared by vacuum hot-press sintering. The influence of TiC addition on the corrosion behaviour of WC–Al2O3 composites in 0.1 M NaOH solution was revealed. The results suggest that all the samples containing added TiC had the TiC phase and (W, Ti) C solid-solution phase, while the base composite had neither phase. With increasing added TiC content, the average grain size of WC decreased, and the relative density first increased and then decreased. Furthermore, the results suggest that the addition of TiC could noticeably increase the free corrosion potential and impedance and reduce the corrosion current density. However, the composite containing 20 wt% added TiC showed the opposite trend. Therefore, it can be concluded that the corrosion performance of the composites in an alkaline medium can be improved by adding an appropriate amount of TiC. The change in corrosion properties was caused by changes in the solid-solution phase, relative density, and TiO2 oxide film.

Formation and Structure of Sulfide Deposits on Carbon Steel Under Free Corrosion Potential

The corrosion of alloy materials in the H2S environment has considerably limited the growth of oilfield manufacturing. The sour corrosion of iron has frequently been studied, and steel corrosion under the H2S scheme has been investigated. Many parameters affect the corrosion of carbon steel (CS) in the H2S natural environment, including a concentration of H2S, pH, and the temperature, which has significant impacts on the electrochemical responses of the bare metal surface, the formation, and the nature of the created sulfide scale. The latter could be either protective or nonprotective, depending on the formation conditions. This work presents a full experimental investigation for the initial corrosion events of iron/steel at the free corrosion potential for different periods of time in H2S-saturated solutions of different temperatures where H2S/N2 gas was purged into the solutions. The structure, morphology, composition, depth, and ion-concentration of the sulfide film that is established on the pipeline CS (mild carbon steel) in an acidic sour solution was examined using different bulk and surface techniques, e.g., an optical microscope, scanning electron microscopy, and Raman spectroscopy.

A Study of Natural Rosmarinus Corrosion Inhibitor for Zinc In HCl Solution

In this study, the effect of important variables on the corrosion rate of Zinc metal was studied with free corrosion, weight loss, and polarization techniques. The test system was designed to measure corrosion potential, corrosion rate, limited current density, and the polarization technique. The experiment used a 0.1M HCl solution as its medium. Temperatures (20,30, 40, 50, and 60) C and rosemary inhibitor concentrations (1 and 5) g/L were used to study the efficacy of the zinc corrosion process. The results showed that the corrosion rate increased with increasing temperature but decreased with increasing inhibitor concentration in acid solution. The maximum inhibition efficiency in Weight Loss Experiments observed at 5g/L of rosemary and 20 °C is 49.07%. The corrosion potential became more negative with increasing temperature and became nobler (less negative) with increasing inhibitor concentration. It has been shown that rosemary is good as a green inhibitor in acid solution.

Structure, Corrosion Resistance, Mechanical and Tribological Properties of ZrB2 and Zr-B-N Coatings

The coatings ZrB2 and Zr-B-N were deposited by magnetron sputtering of ZrB2 target in Ar and Ar–15%N2 atmospheres. The structure and properties of the coatings were investigated via scanning and transmission electron microscopy, energy dispersion analysis, optical profilometry, glowing discharge optical emission spectroscopy and X-ray diffraction analysis. Mechanical and tribological properties of the coatings were investigated using nanoindentation, “pin-on-disc” tribological testing and “ball-on-plate” impact testing. Free corrosion potential and corrosion current density were measured by electrochemical testing in 1 N H2SO4 and 3.5%NaCl solutions. The oxidation resistance of the coatings was investigated in the 600–800 °C temperature interval. The coatings deposited in Ar contained 4–11 nm grains of the h-ZrB2 phase along with free boron. Nitrogen-containing coatings consisted of finer crystals (1–4 nm) of h-ZrB2, separated by interlayers of amorphous a-BN. Both types of coatings featured hardness of 22–23 GPa; however, the introduction of nitrogen decreased the coating’s elastic modulus from 342 to 266 GPa and increased the elastic recovery from 62 to 72%, which enhanced the wear resistance of the coatings. N-doped coatings demonstrated a relatively low friction coefficient of 0.4 and a specific wear rate of ~1.3 × 10−6 mm3N−1m−1. Electrochemical investigations revealed that the introduction of nitrogen into the coatings resulted in the decrease of corrosion current density in 3.5% NaCl and 1 N H2SO4 solution up to 3.5 and 5 times, correspondingly. The superior corrosion resistance of Zr-B-N coatings was related to the finer grains size and increased volume of the BN phase. The samples ZrB2 and Zr-B-N resisted oxidation at 600 °C. N-free coatings resisted oxidation (up to 800 °C) and the diffusion of metallic elements from the substrate better. In contrast, Zr-B-N coatings experienced total oxidation and formed loose oxide layers, which could be easily removed from the substrate.

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

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

Effect of cerium-based conversion coating on corrosion behavior of squeeze cast Mg-4 wt% Y alloy in 0.1 M NaCl solution

Cerium-based conversion coating (CeCC) has been utilized to improve the corrosion resistance of squeeze cast Mg-4wt%Y alloy in 0.1 M NaCl solution. The morphology and composition of the coating analyzed using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), glancing angle X-ray diffraction (GIXRD), and X-ray photoelectron spectroscopy (XPS) demonstrate the formation of few microns thick pseudo-crystalline phase(s) composed of mainly Mg, O, C and Y species, assigned to hydrated Y(III) (Y(OH)3/Y2O3) CeO2, Mg(OH)2, and lower amount of PO43− ions with mud-crack morphology. The duration of the treatment in cerium nitrate salt bath has a pronounced effect on the evolution of the coating with 30 s treatment demonstrated the formation of uniform coating with dehydrated cracks that becomes loose and porous with nodular CeO2 precipitates for longer duration (1800 s). Potentiodynamic polarization (PDP) and mass loss test reveals that CeCC effectively reduces the corrosion rate by ~50–70% compared to base alloy, with the pitting corrosion around the second phase being the dominant mechanism due to the formation of the micro-galvanic couple between α-Mg phase and Mg24Y5 precipitates. The deep pit formation was severe around Y-rich cathodic sites due to the formation of Y(OH)3/Y2O3 as the corrosion products confirmed by EDX and elemental mapping. Electrochemical impedance spectroscopy revealed that corrosion protection was provided mainly by the barrier layer at the coating/Mg interface with a progressive increase in diameter of the capacitive loop up to 24 h commensurate with the surge in double-layer film resistance (RP) and free corrosion potential (Ecorr) shift towards noble value. Overall, cerium nitrate salt bath treatment in the presence of hydrogen peroxide for short duration is effective to retard the severe corrosion of Mg-4wt%Y alloy in 0.1 M NaCl solution.

Tribocorrosion Mechanisms of Martensitic Stainless Steels

AbstractIn the present study, the influence of the electrochemical potential on the tribocorrosion behavior of X20Cr13 in 0.15 molar NaCl-solution was investigated with the aid of a universal-tribometer under potentiostatic control. The resulting material loss was determined through laser confocal microscopy, while the morphology of the wear tracks and the deformation of the material structure near the surface were observed using light and scanning electron microscopy. The results showed a clear dependence of the material loss and the wear mechanisms from the applied potential. Within the cathodic region, a small amount of the material degradation could be attributed to a strong adhesion and resulting strain hardening as a consequence of an electrochemical weakening and mechanical destruction of the passive layer. The maximum of wear during polarization at the free corrosion potential under friction was explained by galvanic coupling between the wear track and the passive surface near the stability threshold between Fe2+-Ion and Fe2O3development. Through increasing Polarization onto the free corrosion potential in the absence of friction and into the passive region, a decrease in material loss could be observed which is presumably attributed to the stable passive layer that inhibits electrochemical degradation and favors the formation of a grain refinement zone that slows down mechanical destruction.

The key role of contact time in elucidating the mechanisms of enhanced decontamination by Fe0/MnO2/sand systems

Metallic iron (Fe0) has shown outstanding performances for water decontamination and its efficiency has been improved by the presence of sand (Fe0/sand) and manganese oxide (Fe0/MnOx). In this study, a ternary Fe0/MnOx/sand system is characterized for its discoloration efficiency of methylene blue (MB) in quiescent batch studies for 7, 18, 25 and 47 days. The objective was to understand the fundamental mechanisms of water treatment in Fe0/H2O systems using MB as an operational tracer of reactivity. The premise was that, in the short term, both MnO2 and sand delay MB discoloration by avoiding the availability of free iron corrosion products (FeCPs). Results clearly demonstrate no monotonous increase in MB discoloration with increasing contact time. As a rule, the extent of MB discoloration is influenced by the diffusive transport of MB from the solution to the aggregates at the bottom of the vessels (test-tubes). The presence of MnOx and sand enabled the long-term generation of iron hydroxides for MB discoloration by adsorption and co-precipitation. Results clearly reveal the complexity of the Fe0/MnOx/sand system, while establishing that both MnOx and sand improve the efficiency of Fe0/H2O systems in the long-term. This study establishes the mechanisms of the promotion of water decontamination by amending Fe0-based systems with reactive MnOx.

Study on the ZrN/Ag2O Micro–Nano Gradient Composite Structure Constructed on Pure Ti for Biomaterials

Titanium and titanium alloys have been extensively utilized in biomedical implants due to their excellent comprehensive mechanical properties and biocompatibility. In this study, a ZrN/Ag2O micro–nano gradient composite structure was prepared on the surface of pure Ti by multi-arc ion plating (MAIP) technique and metal vapor vacuum arc (MEVVA) ion implantation technology. This study indicated that a dramatic improvement in performance in the surface hardness (~1800 HV0.1) was attributed to the presence of the ceramic phase (ZrN) with high hardness included in composite structure. The relatively low wear rate of gradient composite structure confirmed its excellent performance in abrasion resistance and the abrasion mechanism of gradient composite structure was mainly abrasive wear. After the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests, because of the synergy effect of ZrN micron coating and Ag2O nanoparticles, the ZrN/Ag2O gradient coatings indicated the highest free corrosion potential (Ecorr) and lowest corrosion current density (icorr) in Ringer’s solution, and the polarization resistances of multilayer coatings were greater than that of the substrate, exhibiting positive effects on retarding localized corrosion tendency. Additionally, the suitable dose of ZrN/Ag2O gradient composite coating can obtain antibacterial ability, which exerts no significant cytotoxicity and even excellent cytocompatibility over a longer service process. Furthermore, this study is conducive to design and develop for multifunctional coatings of implant materials.

Nanostructured Molybdenum Oxides from Aluminium-Based Intermetallic Compound: Synthesis and Application in Hydrogen Evolution Reaction.

Characterized by a large surface area to volume ratio, nanostructured metal oxides possess unique chemical and physical properties with applications in electronics, catalysis, sensors, etc. In this study, Mo3Al8, an intermetallic compound, has been used as a precursor to obtain nanostructured molybdenum oxides. It was prepared into ribbons by arc-melting and melt-spinning techniques. Single and double-step free corrosion of the as-quenched material have been studied in 1 M KOH, 1 M HF and 1.25 M FeCl3 at room temperature. In both cases, nanostructured molybdenum oxides were obtained on a surface layer a few microns thick. Two of the as-prepared samples were tested for their electrocatalytic capability for hydrogen evolution reaction (HER) in 0.5 M H2SO4 giving low onset potential (−50 mV, −45 mV), small Tafel slopes (92 mV dec−1, 9 mV dec−1) and high exchange current densities (0.08 mA cm−2, 0.35 mA cm−2 respectively). The proposed nanostructured molybdenum oxides are cost-effective and sustainable due to the cheap and abundant starting material used and the simple synthetic route, paving the way for their possible application as HER electrocatalysts.

Chelation-mediated synthesis of nanoporous gold at near-neutral pH and room temperature by free corrosion dealloying of gold-copper alloy driven by oxygen reduction

Dealloyed nanoporous gold (NP-Au) is commonly created with hazardous chemicals including strong oxidizing acids. This work presents a green alternative to the common methods for making NP-Au. In this work, we create NP-Au by free corrosion dealloying of a Au-Cu parent alloy at room temperature in a near-neutral pH aqueous solution of ethylenediaminetetraacetic acid (EDTA), a non-toxic chelating ligand. The oxygen reduction reaction (ORR), catalyzed by activated carbon cloth (ACC), is employed to drive selective oxidation of Cu into Cu2+ ions, and EDTA is used to sequester the Cu2+ ions, preventing passivating copper oxide (CuOx)-forming reactions. We call this methodology chelation-mediated dealloying. Using small-angle x-ray scattering (SAXS), x-ray diffraction (XRD), and scanning electron microscopy (SEM), we observe that the NP-Au produced under mild conditions is similar to that produced by free corrosion dealloying in nitric acid (HNO3), a highly hazardous and strong oxidizing acid.

Study on the free corrosion potential at an interface between an Al electrode and an acidic aqueous NaCl solution through density functional theory combined with the reference interaction site model

We investigated the free corrosion potential at an interface between an Al electrode and an aqueous NaCl solution (NaCl(aq)) under acidic conditions via density functional theory combined with the effective screening medium and reference interaction site model (ESM-RISM). Firstly, the electrode potentials for the anodic and cathodic corrosion reactions were obtained from the grand potential profile as a function of the electron chemical potential at the interface. Thereafter, we determined the free corrosion potential using the Tafel extrapolation method. The results of the free corrosion potential were consistent with previous experimental data. By controlling the pH of the NaCl(aq), we determined the pH dependence of the free corrosion potential, and the results reasonably reproduce the previous experimental results. Our results indicated that the ESM-RISM method duly described the environmental effect of an acidic solution and precisely determined the free corrosion potential. Therefore, the application of this method presents an efficient approach toward calculating the free corrosion potential for various reactions.