Dissolution Reaction Research Articles

Thermodynamic Data of Copiapite-Group Minerals

Abstract Copiapite-group minerals are common products of weathering of sulfides, especially pyrite and pyrrhotite. They have a general formula AFe3+4(SO4)6(OH)2·20H2O and all crystallize in the triclinic crystal system (space group P). In this work, we have determined the thermodynamic properties of copiapite (A = Fe2+), ferricopiapite (A = 2/3Fe3+), magnesiocopiapite (A = Mg), and aluminocopiapite (A = 2/3Al). Enthalpies of formation were calculated from enthalpies of dissolution in 5 mol/dm3 HCl (measured by acid-solution calorimetry) and entropies from low-temperature heat capacity data (measured by relaxation calorimetry). Differential scanning calorimetry was used in a restricted temperature range to verify the accuracy of the heat capacity measurements. We also present calculated molar volumes and densities for the copiapite-group phases. The calculated Gibbs free energies of formation are (all values in kJ/mol) −10,322.6 ± 11.8 (A = Mg), −9862.7 ± 12.4 (A = 2/3Fe3+), −10,177.4 ± 10.9 (A = 2/3Al), and −9949.0 ± 12.1 (A = Fe2+). They correspond to solubility products (log Ksp) of −21.24 (A = Mg), −18.55 (A = 2/3Fe3+), −18.17 (A = 2/3Al), and −19.66 (A = Fe2+). They all relate to the dissolution reaction AxFe3+4(SO4)6(OH)2·20H2O + 2H+ → xA + 4Fe3+ + 6SO42− + 22H2O. Using an extended Pitzer model for highly concentrated ferric iron-sulfate solutions, positions of solubility curves for several ferric sulfates were calculated. The shape of the solubility envelope was reproduced, but the position of the curves was not matched. It seems that there is a considerable way to go before a satisfactory thermodynamic model can be constructed for this particular system.

Kinetics and dynamics of atomic-layer dissolution on low-defect Ag.

Electrochemical metal dissolution reaction is a fundamental process in various critical technologies, including metal anode batteries and nanofabrication. However, experimentally revealing the kinetics and dynamics of active sites of metal dissolution reactions is challenging. Herein, we investigate metal dissolution on near-perfect single-crystal surfaces of Ag within regions of a few hundred nanometers isolated by scanning electrochemical cell microscopy (SECCM). Potential oscillation is observed under constant current conditions for dissolution. The one-to-one correspondence between the dissolution charge and the geometry of the dissolution pit from colocalized imaging allows ambiguous correlation, which suggests that each oscillation cycle corresponds to the dissolution of one atomic layer. The oscillation behavior is further explained in a kinetic model, which reveals that the oscillation comes from the dynamic evolution of the number of different active sites as the dissolution progresses on each atomic layer. In addition to the fundamental interest, the ability to observe layer-by-layer dissolution in electrochemical measurements suggests a potential pathway for developing electrochemical atomic layer etching for fabricating structures and devices with atomic precision.

Priority Recovery of Lithium From Spent Lithium Iron Phosphate Batteries via H2O‐Based Deep Eutectic Solvents

ABSTRACTThe growing use of lithium iron phosphate (LFP) batteries has raised concerns about their environmental impact and recycling challenges, particularly the recovery of Li. Here, we propose a new strategy for the priority recovery of Li and precise separation of Fe and P from spent LFP cathode materials via H2O‐based deep eutectic solvents (DESs). Through adjusting the form of the metal complexes and precipitation mode, above 99.95% Li and Fe can be dissolved in choline chloride‐anhydrous oxalic acid‐water (ChCl‐OA‐H2O) DES, and the high recovery efficiency of Li and Fe about 93.41% and 97.40% accordingly are obtained. The effects of the main parameters are comprehensively investigated during the leaching and recovery processes. The recovery mechanism of the pretreated LFP is clarified and the rate‐controlling step of the heterogeneous dissolution reactions is also identified. Results show that soluble phases of Li3Fe2(PO4)3 and Fe2O3 are formed after roasting pretreatment, and Li(I) ions tend to form Li2C2O4 precipitates with C2O42− during the leaching process so that Li can be recovered preferentially in purity of 99.82%. After UV‐visible light irradiation, Fe(III) ions are converted into Fe(II) ions, which can react with C2O42− to form FeC2O4 precipitates by adjusting the H2O content, and P is recovered as Na3PO4∙12H2O (99.98% purity). Additionally, a plan for the recycling of used DES is proposed and the leaching and recovery performances still maintain stable after three recycling circles. The method offers an approach with a simple process, high efficiency, and waste‐free recycling for priority recovery Li and precise separation of Fe and P from spent LFP batteries in DESs.

Amount and Composition of NOx Generated by Metal (Cu, Ni, and Fe) Dissolution Reaction with Nitric Acid

Amount and Composition of NOx Generated by Metal (Cu, Ni, and Fe) Dissolution Reaction with Nitric Acid

Unveiling the Corrosion Mechanism of the NixSey Intermetallic Compound in Water-Based Solution.

In this study, Ni-Se intermetallic compound coatings were fabricated using electrodeposition at various process temperatures (40-70 °C). The results show that increasing the process temperature promotes the deposition of Se, which leads to a transition in the crystal phase of the samples from the Ni0.85Se phase, prepared under low-temperature conditions, to a NiSe2 phase. The dissolution rate of Se in pure water from Ni-Se coatings is inversely related to the incorporated Se content, which indicates that the Ni0.85Se phase has a higher natural corrosion rate compared to the NiSe2 phase. Under the influence of an electric field, the corrosion behavior of Ni-Se coatings is dominated by a two-stage reaction involving Se transformation and dissolution. Coatings with a predominant Ni0.85Se phase exhibit more severe corrosion behavior compared to those with a predominant NiSe2 phase, which suggests that the corrosion reaction is enhanced by the electric field. However, because coatings with a predominant NiSe2 phase contain a higher proportion of Se22- ions, the dissolution reaction of SeOx, generated during the electrochemical reaction, is retarded, thereby inhibiting the progression of the corrosion reaction. Consequently, coatings with a predominant NiSe2 phase exhibit relatively better corrosion resistance in a water-based electrolyte.

(Invited) Plasmonic Fabrication of Chiral and Magneto-Chiral Nanostructures

Chiral and magneto-chiral plasmonic nanostructures attract attention because they have various potential applications including catalysts, chemical sensors, and optical and optoelectronic materials and devices. In many cases, those nanostructures are fabricated by lithographic techniques. However, those top down methods are generally time-consuming and expensive. Therefore, we have developed photoelectrochemical methods in which site-selective deposition or dissolution reactions are driven by optical near field generated around anisotropic metal nanoparticles under right- or left-circularly polarized light (CPL).We have used gold or silver nanocuboids,1 nanorods,2 nanocubes,3 triangular nanoplates,4 and intricate nanoporous films5 on semiconducting or dielectric substrates as anisotropic metal precursors for preparation of chiral plasmonic nanostructures. If an anisotropic metal nanoparticle is irradiated with CPL, chiral electric field is generated around the nanoparticle, and energetic electron-hole pairs generate at the resonance sites, where electric field is localized. As a result, reductive deposition of silver or oxidative deposition of lead oxide proceeds preferentially at the resonance sites, resulting in formation of chiral plasmonic nanostructures, which exhibit circular dichroism (CD).Chiral metal nanoparticles were also prepared from less anisotropic, circular metal nanodisks. In this case, initial nucleation of metal at an arbitrary site of the nanodisk edge breaks its symmetry and gives rise to chiral electric field distributions under CPL. As a result, the nanodisk is grown into chiral plasmonic nanostructure.We also prepared magneto-chiral nanostructures by employing superparamagnetic magnetite nanocubes as precursors. The magnetite nanocubes on a glass substrate exhibit magnetic circular dichroism (MCD) but not CD. Magnetite is also reported to be conducting enough for its nanoparticles to show LSPR. Therefore, chiral electric field generates at around a magnetite nanocube under CPL and plasmonic photoelectrochemical reactions can proceed at those localized resonance sites. In addition, magnetite also has valence band and conduction band, and an electron in the valence band can be excited to the conduction band by a photon with energy higher than the band-gap energy. This photoexcitation can also occur at the localized resonance sites.6 As a result of those localized photoelectrochemical reactions induced by CPL, chiral magnetite-silver nanocomposite structures were obtained, and those nanocomposites not only MCD but also CD based on the chiral morphologies. Thus, the nanocomposites break both inversion and time-reversal symmetries. As a result, they exhibit nonreciprocal transmission of visible light, which is recognized also as magneto-chiral dichroism (MChD). K. Saito and T. Tatsuma, Nano Lett. 18, 3209-3212 (2018).K. Morisawa, T. Ishida, and T. Tatsuma, ACS Nano 14, 3603-3609 (2020). K. Shimomura, Y. Nakane, T. Ishida, and T. Tatsuma, Appl. Phys. Lett. 122, 151109 (2023).T. Ishida, A. Isawa, S. Kuroki, Y. Kameoka, and T. Tatsuma, Appl. Phys. Lett. 123, 061111 (2023).H. Nishi, T. Tojo, and T. Tatsuma, Electrochemistry in press (doi: 10.5796/electrochemistry.24-00027).Y. Oba, S. H. Lee, and T. Tatsuma, J. Phys. Chem. C 128, 827-831 (2024). Figure 1

(Invited) Plasmonic Photocatalysis and Near-Field Photocatalysis

It is well known that finding of Honda-Fujishima effect1 opened up the way to semiconductor photocatalysis. The semiconductor photocatalysts, typically TiO2, are often modified with noble metal nanoparticles such as platinum as co-catalysts, for improvement of the photocatalytic activity. We modified TiO2 photocatalysts with plasmonic silver2 or gold3 nanoparticles and found that plasmon-induced charge separation (PICS) occurs at the metal-TiO2 interface.3,4 If a metal nanoparticle such as silver or gold is irradiated with light of the resonant wavelength, energetic electrons and holes are generated in the course of relaxation of the photoexcited plasmons. The electron can be injected into the conduction band of the TiO2 in contact with the resonant metal nanoparticle, and PICS is achieved (Figure 1a).3,4 We have applied PICS to visible-light-driven and NIR-light-driven photovoltaics and optoelectronic devices,3,4 photocatalysts,3,4 plasmonic chemical sensors,4 multicolor photochromic materials,2,4 and photo-morphing gels.4 For PICS, we can employ not only silver and gold nanoparticles, but also other plasmonic metal nanoparticles such as copper and plasmonic and electroconducting compound nanoparticles such as ITO. We have developed photovoltaic devices responsive to NIR light by coupling TiO2 with plasmonic ITO nanoparticles.5 If the plasmonic nanoparticles are morphologically or optically anisotropic, plasmonic electron oscillation is localized at certain resonance sites. In other words, optical near field is confined at the resonance sites. We can take advantage of the localization for nanoscale photo-fabrication beyond the diffraction limit, on the basis of deposition and dissolution reactions.6 We have fabricated variety of nanostructures, for instance anisotropic composite nanostructures and chiral plasmonic nanostructures (Figure 1b).7 ,8 Optical near field is generated by various processes other than plasmon resonance, for instance Mie resonance. Mie resonance occurs not only at metal nanoparticles but also at dielectric and semiconducting nanomaterials. We employed hexagonal ZnO nanoplates to achieve near-field photocatalysis based on Mie resonance.9 The ZnO nanoplates were adsorbed onto a glass plate, and irradiated with linearly polarized UV light for reductive deposition of silver. The optical near field was localized at sites corresponding to the polarization direction of the irradiated light. Namely, silver deposition site can be controlled by the polarization angle (Figure 1c). Self-oxidative etching of the ZnO nanoplates themselves and oxidative deposition of cobalt oxide onto the ZnO nanoplates can also be conducted in the site-selective manner.Thus, near-field photocatalysis has been achieved via plasmon resonance and Mie resonance. The technique enables photonic nanofabrication beyond the diffraction limit and design of nanomaterials and nanodevices including sophisticated photocatalysts and metamaterials. A. Fujishima and K. Honda, Nature 238, 37-38 (1972).Y. Ohko, T. Tatsuma, T. Fujii, K. Naoi, C. Niwa, Y. Kubota, and A. Fujishima, Nature Mater. 2, 29-31 (2003).Y. Tian and T. Tatsuma, J. Am. Chem. Soc. 127, 7632-7637 (2005).T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci. 8, 3325-3337 (2017) [review].S. H. Lee, H. Nishi, and T. Tatsuma, Phys. Chem. Chem. Phys. 21, 5674-5678 (2019).K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett. 7, 4363-4368 (2016).K. Saito and T. Tatsuma, Nano Lett. 18, 3209-3212 (2018).T. Tatsuma and H. Nishi, Nanoscale Horiz. 5, 597-606 (2020) [review].Y. Oba, S. H. Lee, and T. Tatsuma, J. Phys. Chem. C 128, 827-831 (2024). Figure 1

Electrochemical Properties of Indium CMP for Quantum Applications

Indium is emerging as a promising material in the semiconductor and quantum device integration technology, particularly as an interconnect material. Its application is extensively studied for fabricating microbumps and for filling into Through-Silicon Vias, thereby facilitating hybrid bonding connections crucial for quantum computing advancements. Achieving such connections, especially hybrid bonding, demands precision at the submicron level. Chemical Mechanical Planarization is a critical process in this context, which plays an important role in achieving the desired flatness and required surface quality. It achieves this through a combination of mechanical abrasion and electrochemical dissolution of the metal. Despite its importance, research on Indium CMP is relatively nascent, indicating a significant opportunity for exploration in this area. This study aims to delve into the specifics of Indium CMP, particularly focusing on understanding the electrochemical characteristics during the polishing process. By examining the impact of slurry composition and various influencing factors on the polishing efficacy, we aim to offer a comprehensive insight into the Indium CMP process.We investigate Indium films electroplated onto Cu substrates with a thickness of approximately 1 µm. The films' electrochemical behaviors were evaluated in both acidic (pH 3) and alkaline (pH 10) slurry, utilizing dynamic electrochemical evaluation equipment. The abrasive type for both slurries is a Silica base with less than 50 nm diameter. To explore the effects of oxidants, varying concentrations of Hydrogen Peroxide were introduced. The experimental parameters included an applied force of 1 psi and a testing area of 1.3 cm².Figures 1a and 1b show in situ open-circuit potential (OCP) measurements of Indium over time with and without polishing. In both acidic and alkaline slurries, OCP values for Indium experienced a sharp decrease during polishing, followed by a rapid increase upon stopping polishing, indicating the quick formation and subsequent removal of a passivation layer. With the addition of H2O2, the passivation layer's removal, growth, and subsequent removal continue under dynamic and static conditions in the pH 3 slurry. However, in the pH 10 slurry, the potential jump was minimal, and the passivation layer was only partially removed upon restarting polishing. The rate of passivation layer removal roughly corresponded to its formation rate, suggesting the presence of a thin oxide film throughout polishing. This phenomenon may be due to the excessive thickness of the passivation layer at a 0.4% H2O2 concentration, forming too thick layer to remove by CMP.Figures 1c and 1d illustrate the corrosion current and potential of Indium at various concentrations of H2O2. With increasing H2O2 concentration, the corrosion potential increases in both slurries. In acidic slurry without H2O2, the corrosion potential of Indium was -0.54 V corresponding to its presence as Indium metal in the Pourbaix diagram. When H2O2 was added, the corrosion potential increased, indicating the formation of Indium (III) ions in an acidic environment and the strong oxidizing agent H2O2. In the pH 3 slurry, despite the addition of an oxidant, the passivation layer exits, attributed to the presence of a corrosion inhibitor within the slurry. This phenomenon contributes to the reduction in the corrosion current of the Indium film with increasing H2O2 concentration, as corrosion inhibitor mitigates active corrosion by blocking it. Inhibitors enhance the resistance area between the metal surface and the electrolyte, thus impeding or stopping galvanic reactions and the loss of electrons from the metal surface.In alkaline solutions, Indium metal remains stable in the absence of oxidants. However, upon the addition of H2O2, the corrosion potential value shifted from -0.714 V without H2O2 to -0.38 V for 0.2% H2O2. This alteration aligns with the emergence of the In2O3 passive layer, as indicated by the Pourbaix diagram. The rise in corrosion potential with H2O2 stemmed from the restricted anodic reaction due to the concurrent growth of the cathodic reaction, leading to the formation of a thick passivation layer. This layer impedes ion transport, so necessitating energy (potential) for the polishing process to proceed. Simultaneously, the corrosion current of Indium increased in the alkaline slurry, signifying active dissolution. According to Haedo Jeong et al., the active zone corresponds to the oxidation reaction's dissolution area, indicating the ongoing oxidation of the metal.The investigation into Indium CMP revealed a notable dependence on the composition of the abrasive slurry. Indium metal demonstrates stability in both acidic and alkaline slurry in the absence of oxidants. Notably, the introduction of H2O2 to the slurry distinctly induces a phase transition from Indium ions in acidic slurry to In2O3 in alkaline environments, suggesting a potential study to elucidate the mechanism of Indium CMP. Figure 1

Reaction Transport Analysis and Parameter Identification for Designing Lithium–Sulfur Battery Electrodes

Electrical energy storage systems for renewable energy sources and the popularization of next-generation vehicles with low CO2 emissions and high energy efficiencies are required to realize a sustainable society. However, current cathode materials such as lithium–containing oxides used in lithium-ion batteries (LiBs) have limited storage capacities, and their energy density peaks at approximately 150–250 Wh/kg. To improve this, lithium–sulfur batteries (LiSBs) with high theoretical energy densities are currently being developed and expected to be deployed as the next-generation battery technology. In LiSBs, the complex dissolution and precipitation reactions of sulfur are the driving forces. However, the complex operating mechanisms of LiSBs are yet to be investigated. Ren et al. (1) modeled the precipitation mechanism of lithium sulfide by focusing on the characteristics of a two-step discharge reaction to clarify the relationship between the complex reaction mechanism and the battery characteristics of LiSBs. In addition to considering multistep polysulfide dissolution and reduction, they describe the rate-dependent Li2S precipitation phenomenon using electro-crystallization kinetics based on nucleation and growth theory. Thus far, research has been actively conducted on clarifying the complicated reaction mechanisms of LiSBs. These studies only simplify the reaction mechanisms and calculations using estimates of many dynamic parameters of intermediate products that are otherwise difficult to measure. However, if such a numerical analysis is applied to a new electrode system, it can lead to incorrect conclusions regarding the reaction mechanisms. In our previous study, we established a technique to identify parameters that are difficult to measure after cell assembly by fitting the measured and calculated values of the fully discharged characteristics of LiBs using a complex nonlinear optimization method (2). For LiSBs, combining actual measurements and calculations is useful to estimate the unknown parameters of a new electrode system. In LiSBs, the volume change of sulfur during charging and discharging is problematic. During discharge, the volume expands by approximately 1.8 times when sulfur combines with lithium and changes to lithium sulfide (3). Although the microstructure of the electrode is expected to be destroyed by volume expansion, which affects the battery performance, only a few studies have verified the volume change by numerical analysis with complicated mechanisms. In contrast, in our study, reaction transport analysis models that consider volume changes were established for LiBs (4). Therefore, we aimed to construct a lithium–sulfur battery design support system that combines a numerical analysis method for lithium–sulfur batteries considering volume changes with an optimization method.In this study, we examined the effect of sulfur-filled microporous activated carbon. Recently, it was reported that this microporous carbon with sulfur can be repeatedly cycled as a sulfur cathode exhibiting a high coulombic efficiency of almost 100% (5). Firstly, by using numerical simulation and optimization method, we evaluated mass transport and reaction properties with various parameters of pore structure. Next, we simulated the discharge performance with or without this activated pore. From this data, it was found that pore size strongly affects effective surface area and Li+ conduction and diffusion performance. As described above, it was suggested that an optimum pore structure exists from the viewpoint of the balance of reaction and mass transport, and the effect of different structures on transport properties was qualitatively evaluated. In the future, it is necessary to confirm the validity of the optimal structure through experiments and to quantitatively evaluate the effect of different CB.AcknowledgmentThis study was supported by JST GteX, Development of lithium-sulfur batteries with low environmental impact and high performance, Grant JPMJGX23S0, Japan.(1) M. Hagen et al., Adv. Energy Mater., 5(16), 1401986 (2015).(2) G. Inoue et al., J. Chem. Eng. JAPAN, 54(5), 207–212 (2021).(3) M. M. Islam et al., Phys. Chem. Chem. Phys., 17(5), 3383–3393 (2015).(4) G. Inoue et al., ECS Trans., 80(10), 275-282, (2017).(5) T. Tonoya et al., Electrochemistry Communications, 140, 107333 (2022).

Simulation for Elucidating a Formation Mechanism of 6-Coordinated Si in Phosphate Glass

Phosphate glasses are materials that are expected to have a wide range of applications, including highly ion-conductive materials in fuel cells and biomaterials that supply therapeutic ions. Diffusion of ions in glasses plays an important role in designing glasses for these applications. The diffusion of protons is one of the most important properties of fuel cells, and the diffusion of network-modified cations such as Na+ and Ca2+ ions is closely related to glass dissolution and hydration reactions. In general, these diffusion properties are strongly dependent on the atomic-scale glass structure. We found that the difference in the morphology of PO4 tetrahedra (P-Qn : number of bridging oxygen) greatly affects the diffusion of protons and Na+ ions in phosphate glass, where these ions can diffuse much more easily near P-Q2 than near P-Q3 , and suggested that ionic conductivity and glass solubility can be designed by controlling the P-Qn distribution of phosphate glasses [1]. We also suggested that the P-Qn distribution can be controlled using 6-coordinated Si (6cSi), which is formed in phosphate glasses containing more than 40 mol% P2O5 [2]. However, the formation mechanism of 6cSi is not clear. In this study, we aim to elucidate the formation mechanism of 6cSi in phosphate glasses based on first-principles molecular dynamics (MD) simulations.The glass models for 55.0P2O5-21.3SiO2-23.7Na2O (mol%) were generated by quenching from the melt using classical MD simulations with the DL POLY [3] program. Subsequently, first-principles MD simulations using the SIESTA code [4] were performed to observe the reaction process from 4cSi to 5/6cSi. Atomic energies were calculated using orbital decomposition of the total energy by the OpenMX code [5]. For these electronic structure calculations, a localized basis with the GGA-PBE functional was used.In obtained models, atomic energies for non-bridging oxygen (NBO) are higher than those for bridging oxygen (BO). In the first-principles MD simulation, the formation of chemical reaction from "4cSi + P-Q2 " to " 5/6cSi + P-Q3 " was observed as shown in Fig. 1. The energy decreases by the change from a NBO in P-Q2 to a BO in P-Q3 is larger than the energy increase by the change for 4cSi to 5c/6cSi.It will be possible to design highly functional glasses by applying the 6cSi formation mechanism and controlling the amount of 6cSi formed.Reference:[1] K. Takada, T. Tamura, H. Maeda, and T. Kasuga, Phys. Chem. Chem. Phys. 23, 14580 (2021). [2] K. Takada, T. Tamura ,and T. Kasuga, RSC Adv. 12, 35043 (2022). [3]T. Todorov et al., J. Chem. 16, 1911 (2006). [4] J. Solar et al., J. Phys. Cond. Matt. 14, 2745 (2000). [5] T. Ozaki, Phys. Rev. B 67, 155108 (2003). Figure 1

Galvanic and Local Corrosion of Aluminum Alloy 6061-T6 Coupled to Non-Passivating and Passivating Alloys

Marine and aerospace structures sometimes combine lightweight aluminum alloys with dissimilar metals to optimize mechanical performance and reduce costs. Unfortunately, the exposure of such dissimilar couples in a harsh environment can cause severe corrosion damage to the aluminum structure due to its position in the galvanic series. Corrosion of Aluminum Alloy (AA) 6061-T6 coupled to non-passivating and passivating alloys was studied to elucidate galvanic effects on local corrosion. In this work, local and galvanic corrosion were quantified, the effects of cathode material on local electrolyte pH were explored, and a relationship between pH and local-corrosion of AA6061-T6 was established.Experimental studies quantified local and galvanic corrosion of AA6061-T6 coupled to 316 stainless steel, copper, titanium alloy Ti6Al4V, and 316 stainless steel coated with titanium nitride, chromium nitride, and a sol-gel nano-coating. Galvanic couples were misted with 3.15 wt.% sodium chloride solution and exposed in a controlled temperature-humidity chamber. Galvanic currents were measured during exposure, and the total mass loss of the aluminum alloy was determined to quantify the corrosion damage. Exposure tests showed that galvanic corrosion decreases over time and accounts for less than 15% of the total corrosion of AA6061-T6. Therefore, most aluminum corrosion damage was caused by local corrosion. In addition, immersion experiments of AA6061-T6 galvanic couples in gelled 3.15 wt.% NaCl solutions showed that galvanic coupling influences the evolution of electrolyte pH leading to severe acidification at the aluminum anode surface and alkalization around the cathode. The solution pH at the aluminum surface was decreased by galvanic action and severity of pH decrease depends on galvanic couple materials and design. To quantify the effect of acidity on local corrosion of AA6061-T6, potentiodynamic polarization tests were performed in aerated and deaerated 3.15 wt.% NaCl solution adjusted to different pH values. Anodic dissolution reactions and cathodic oxygen reduction reactions show significantly higher anodic and cathodic currents for more acidic solutions due to the instability of the passive oxide film of aluminum. This film is stable in near-neutral solutions and unstable in highly acidic solutions. As a result, the breakdown of the passive film increases the effective area contributing to anodic or cathodic currents resulting in enhanced local corrosion.The series of experimental results show that galvanic interaction leads to a decrease of pH at the aluminum anode, and therefore increasing local corrosion of the aluminum surface. The increase of local corrosion induced in a galvanic couple depends on the cathode material and underlines the importance of accounting for local corrosion and pH-dependent corrosion kinetics when predicting the galvanic compatibility of aluminum alloys.

Online ICP-OES for Studying the Alloying Effect of Zn and Cu on Corrosion of Al-10 Mass% Si Alloy

Introduction Alloying elements in Al alloy have important effects on corrosion properties as well as strength, formability, brazinability, and other properties. This is mainly due to the low solubility of the alloying elements in Al, which leads to the formation of precipitates along with various structures [1]. Al-Si is one of the major Al alloys, particularly applied in automotive industry due to high castability and machinability despite being lightweight. However, various studies have highlighted their poor corrosion resistance, which shortens the lifetime of alloy products. Previous studies have extensively investigated the effect of Si particle size and morphology on corrosion, suggesting that Si particles act as a cathode and selectively dissolve the surrounding Al matrix [2]. On the other hand, the actual dissolved mass and the effects of other alloying elements on corrosion have not been sufficiently discussed because of the difficulty of detecting the mass of corrosion for each element.Recently, online inductively coupled plasma-optical emission spectroscopy (ICP-OES), which combines electrochemical measurements with solution analysis, has attracted attention as an innovative method for analyzing the dissolution reaction of alloys [3,4]. Elements dissolved into the electrolyte solution through electrochemical reactions are carried away by flow and introduced to ICP-OES, enabling simultaneous qualitative and quantitative analysis of dissolved elements. In this study, we apply it to measure the reaction rate of Al-Si alloy corrosion and elucidate the effect of additive elements on the corrosion. Experimental Alloys of Al-10 mass% Si, Al-10 mass% Si-3 mass% Zn, and Al-10 mass% Si-3 mass% Zn-0.5 mass% Cu were employed as specimens. Potentio-dynamic polarizations of specimens in a 0.1 mol dm-3 KCl aqueous solution and solution analyses using a SPECTRO ICP-OES apparatus (ARCOS) were conducted at a solution flowing rate of 1 cm3 min-1. In the OES, the dissolution rates of Al, Si, Zn, and Cu were detected at wavelength of 176, 288, 206, and 219 nm, respectively. Results and discussion Specimen alloys exhibited hypoeutectic, which is composed of a primary α-Al phase and a eutectic structure consisting of α-Al and Si particles. Added Zn and Cu in the alloy were melted in α-Al phase, especially eutectic α-Al phase. In the simple immersion test in KCl solution, the formation of a pit was observed on Al-10 mass% Si surface after several hundred seconds. In the polarization experiment in anodic direction, anodic current density increased with increasing electrode potential, a detection rate of Al (vAl ) and Si (vSi) was also increased with increasing the current density. At anodic potential, a ratio of vSi to vAl was significantly larger than a solid-solubility limit of 1.6%. This suggests natural oxide film on eutectic α-Al phase initiates breakdown easier than those on other phases and allows to dissolve eutectic α-Al more than primary α-Al. In the polarization in cathodic direction, the dissolution of Al, which was above the detection limit of ICP-OES, was detected. The detection rate of Al was strongly depended on pH or buffering effect of solution, indicating that alloy surface dissolves Al species in local alkaline environment. In the presentation, we discuss the alloying effects of Zn and Cu on corrosion of Al-Si alloy as well.

(Invited) Coherent X-ray Studies of Electrode Nanoparticles and Surfaces

Coherent X-rays provide a unique structural and dynamical viewpoint of electrode surfaces and nanoparticles. Using the coherent X-ray techniques, we have been studying several electrochemical phenomena such as electrochemical dissolution reactions of silver surfaces and nanoparticles, oxygen reduction/evolution reactions of platinum and platinum alloy nanoparticles, and the surface reconstruction dynamics of gold surfaces and nanoparticles. The coherent X-ray techniques are typically developed for real-space images and real-time dynamics. For imaging techniques, X-ray imaging such as Bragg Coherent Diffraction Imaging (BCDI) is used to image nanoparticles, and X-ray Ptychography is used to image electrode surfaces, and X-ray photon correlation spectroscopy (XPCS) is used to monitor the electrode surface dynamics.In this talk, we will present a broad overview of the examples based on our previous studies and provide each example with an emphasis on the uniqueness of the coherent X-ray techniques and the structural and dynamical aspects of the electrodes, unavailable in traditional X-ray techniques. We will also provide a perspective of the coherent X-ray techniques using the more powerful and brilliant coherent X-rays becoming available in the newest generation X-ray photon sources such as upgraded Advanced Photon Source (APS-U).

(Invited) Analysis of Electrochemical Reaction in Polysulfide-Insoluble Lithium Sulfur Battery with in-Situ Electrochemical Impedance Spectroscopic Method

Lithium-Sulfur battery (LiSB) has attracted attention as a new generation secondary battery. However, one of the major problems is dissolution of discharge products of lithium polysulfides (Li2S n ) that cause the self-discharge. Ionic liquids and super-concentrated electrolyte solution (SCES) have been attracting attention as a LiSB electrolyte due to its low solubility of the polysulfides. SCESs are electrolyte solutions which consist of only two or three times as much solvent as lithium salt. Watanabe and Dokko et al. [1] proposed polysulfides insoluble LiSBs using lithium-glyme based solvate ionic liquid (Li-Gn SIL) and sulfolane (SL)-based SCES. Various battery materials have been proposed for LiSBs; on the other hand, the discharge behavior strongly depends on the battery materials. Both the Li-Gn SIL and SL-based SCES are polysulfide-insoluble electrolytes, whereas the LiSB with the SL-based SCES has better battery performance than that with the Li-Gn SIL, implying that the discharge behavior is different between the LiSB with the SCES and LiSB with the SIL [1]. In this contribution, we carried out in situ electrochemical impedance spectroscopic measurement (EIS) [2,3] to reveal influence of different electrolytes on electrode reactions.A positive electrode slurry was obtained by mixing a sulfur S8, a Ketjen black (KB, EC600JD, Lion Corporation) and a carboxymethyl cellulose (CMC2200, Daicel) at a weight ratio of 60 : 30 : 10. The Slurry was spread on an Al foil to obtain a KB-S composite electrode. A negative electrode and a separator were used a lithium metal foil (Honjo Metal) and a glass separator (GA-55, Advantec), respectively. SL-based SCES and Li-Gn SIL are used as electrolyte solutions. The cells were assembled using three-electrode typed cell in an Ar-filled glove box. In situ EIS measurements were conducted at 0.025~0.1C-rate using an electrochemical measurement system (SP-150e, BioLogic). The DC current was superimposed with a small AC current adjusted so that the response voltage amplitude did not exceed 5~10 mV. The measurements were carried out in the frequency range from 500 kHz to 10 mHz. The measured impedance spectra during discharging/charging include the contribution of changes over time. Accordingly, the instantaneous impedance spectra at an arbitrary time were determined using the method to compensate for the changes over time [2,3].In discharge curves of the LiSB with Li-Gn SIL, a voltage drop was observed at DOD = 20−35% during discharge at a high C-rate (0.1C). This voltage drop did not appear in the discharge curve at a low C-rate (0.025C). The capacitive semicircle at 457 Hz appeared in the instantaneous impedance spectra of the LiSB during discharging. The diameter of this semicircle increased as the voltage dropped and the semicircle could be assigned to the charge transfer resistance of the lithium negative electrode. The charge transfer resistance of the negative electrode is related to the resistance of the Li+ ion dissolution/deposition reaction. During discharging at a high C-rate, the Li+ ion dissolution reaction could be suppressed.In the instantaneous impedance spectra of positive electrode in LiSB with SL-based SCES exhibited three capacitive semicircles and an inductive loop at DOD = 5%. Upon further discharging, the inductive loop changed into a capacitive semicircle. The Warburg impedance appeared at the end of the discharge period. This low-frequency impedance behavior was attributed to the Faradaic impedance due to elementary reactions on the electrode, such as intermediate reactions and redox species adsorption/desorption processes. This suggests that multi-step reactions occur in each DOD for the LiSB battery using SL based SCES.References1) A. Nakanishi et al., J. Phys. Chem. C, 123, 14229-14238 (2019).2) Z. B. Stoynov et al., J. Electroanal. Chem., 183, 133-144 (1985).3) M. Itagaki et al., J. Power Sources, 135, 255-261 (2004).

Oxidative Dissolution Behavior of Synthetic Chalcopyrite with Non-Stoichiometric Compositions

Chalcopyrite (CuFeS2) is the most important Cu mineral, accounting for 70% of copper reserves in the world. Cu metal is primarily produced from chalcopyrite-containing ores by an extraction process involving flotation, pyrometallurgy, and electrorefining. Owing to the ongoing depletion of high-grade ores, hydrometallurgical processes involving copper leaching from chalcopyrite-containing ores using acidic ferric sulfate solutions have been intensively studied. However, efficient copper leaching remains a challenge, and the details of the dissolution mechanism of chalcopyrite in natural resources remain unclear.Investigation using synthetic minerals with controlled compositions and morphologies is an effective approach for understanding the dissolution mechanism. In this study, we prepared dense pellets of synthetic chalcopyrite with stoichiometric and non-stoichiometric compositions and compared their oxidative dissolution behaviors in an acidic ferric sulfate solution.The nominal compositions of the prepared samples are Cu0.250Fe0.250S0.500 (stoichiometric composition), Cu0.240Fe0.260S0.500, Cu0.245Fe0.260S0.495, and Cu0.265Fe0.245S0.490. The powder samples were synthesized via a high-temperature reaction using Cu wire, Fe wire, and S powder as raw materials. The dense pellets (diameter 10 mm and thickness of approximately 3 mm) were obtained by pulse current pressure sintering and subsequent annealing at 500 ℃. Density measurements and scanning electron microscopy observations revealed that the morphologies such as grain size and density of the obtained pellets were almost constant, regardless of the nominal composition. In X-ray diffraction analyses, the diffraction peaks of the obtained pellets were consistent with the chalcopyrite phase (CuFeS2, PDF #00-037-0471). The scanning electron microscopy with energy dispersive spectrometry analysis confirmed that no other phase was detected in the Cu0.250Fe0.250S0.500, Cu0.240Fe0.260S0.500, and Cu0.265Fe0.245S0.490 pellets.To enable electrochemical measurements, dense pellets were cut and embedded in resin after connecting the copper leads. Obtained electrode samples were immersed in 0.1 M Fe(SO4)1.5 – 10−4 M FeSO4 – 0.18 M H2SO4 at 70 ℃ for 24 h. The concentration of Cu ions in the solution was determined by inductivity coupled plasma atomic emission spectrometry and the dissolution rates of the samples were evaluated. The corrosion potentials of the synthesized chalcopyrite samples were also measured. shows the measured dissolution rates and corrosion potentials. The Cu dissolution rates for the chalcopyrite samples with non-stoichiometric compositions (Cu0.240Fe0.260S0.500, Cu0.245Fe0.260S0.495, and Cu0.265Fe0.245S0.490) were over one order of magnitude than those for the samples with stoichiometric composition (Cu0.250Fe0.250S0.500). This result demonstrates that a small difference in composition significantly affects the dissolution rate in the ferric sulfate solution. The corrosion potentials of the electrodes with non-stoichiometric compositions were less noble than those of the stoichiometric composition sample. At the corrosion potential, the rate of anodic dissolution of the chalcopyrite phase was equal to that of the cathodic reaction of the oxidant in the solution (mainly the reduction rate of the Fe(III) species). Considering the shift in the corrosion potential, increasing the dissolution rate is attributed to the enhancement of the anodic dissolution reaction of the chalcopyrite phase by the change in its composition from stoichiometry. Figure 1

Combined EIS/Tof/SIMS Investigation of Iron Dissolution Mechanisms in CO2 Saturated Chloride Solutions

Aqueous corrosion of mild steel is one of the major problems in the oil and gas industry. The current understanding of corrosion mechanisms, mainly focused to the cathodic reaction, was used to build electrochemical models to predict the corrosion rate of mild steel. However, the effect of aqueous CO2 on the anodic iron dissolution reaction was less studied. In contrast, the mechanism of iron dissolution in strong acidic environments has been thoroughly investigated over many decades. Among the proposed mechanisms in the literature, a broadly applicable multi-path mechanism was identified that could explain the behavior of anodic dissolution of iron in strong acidic sulfate solution; both in terms of steady state polarization sweeps and impedance data at various pH values and current densities. However, the role of aqueous CO2 in solutions containing chlorides on the mechanism of anodic reaction had remained an open question.The present study used EIS measurements and ToF-SIMS in-depth profiling and 3D imaging, as the main techniques, to study the mechanism of iron dissolution in strong acid chloride solution with and without the presence of . EIS results showed that the presence of chloride ions (0.5 M) decreases the rate of the anodic iron dissolution and results in the formation of an additional adsorbed intermediate species which participates in the anodic reaction multi-path mechanism in parallel with the other oxide/hydroxide intermediates. The presence of increases the anodic current density mainly in transition and pre-passivation regions, however, EIS investigation of this mechanism showed that aqueous and other carbonic species do not react directly on the bare metal surface and do not form an additional adsorbed intermediate species that is involved in the anodic reaction. Based on EIS results, it is suggested that the presence of aqueous might effect a change of the chemical composition of the adsorbed species (including hydroxide and chloride intermediates), value of kinetic constants and extent of surface coverage by different adsorbed intermediates and ions, leading to the change in the kinetics of the underlying reactions.ToF-SIMS 3D mapping was used to provide supporting evidence for the anodic iron dissolution mechanisms of mild steel in chloride containing aqueous CO2 environments. The technique detected adsorbed hydroxide and chloride intermediates formed during corrosion process, which is consistent with the proposed multi-path 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 environments, indicating that carbonic species do not directly participate in the iron dissolution reaction. ToF-SIMS 3D mapping results further suggest that one role of aqueous carbonic species could be to accelerate the adsorption of chloride ions and formation of chloride intermediates.

Purification of Li2CO3 Obtained through Pyrometallurgical Treatment of NMC Black Mass from Electric Vehicle Batteries.

The recycling of lithium batteries is essential for a sustainable energy transition. However, impurities in the products obtained from the black mass can lower their market value. In this work, lithium carbonate, which has the highest market share among lithium-based products, is purified using distilled water at controlled temperature, time and stirring speed. The purification process involves dissolving lithium carbonate in distilled water at low temperatures (between 0 and 10 °C), followed by crystallization through water evaporation. Optimal conditions yielded lithium carbonate with a purity of 99.66 % after two stages of purification. The dependence of the variables on the final purity was deeply analyzed and the thermodynamics of the reaction was studied, confirming the exothermic nature of the dissolution reaction.

Condensable Particulate Matter Removal and Its Mechanism by Phase Change Technology During Wet Desulfurization Process

Limestone-gypsum wet flue gas desulfurization (WFGD) played a key role in SOx removal and clean emissions. However, it would also affect the condensable particulate matter (CPM) removal and compositions. The effects of the WFGD system on the removal of CPM and the contents of soluble ions in CPM were investigated in a spray desulfurization tower at varied conditions. The results indicate that the emission concentration of CPM decreased from 7.5 mg/Nm3 to 3.7 mg/Nm3 following the introduction of cold water spray and hot alkali droplet spray systems. This resulted in a CPM reduction rate of approximately 51%, reducing the percentage of CPM in total particulate matter and solving the problem of substandard particulate matter emission concentrations in some coal-fired power plants. The concentrations of NO3−, SO42−, and Cl− among the soluble ions decreased by 41–66.6%. As the liquid-to-gas ratio of the cold water spray and hot alkali droplet spray increased, CPM came into contact with more spray, which accelerated dissolution and chemical reactions. Consequently, the CPM emission concentration decreased by 17.4–19%. The liquid-to-gas ratio has a great effect on the ion concentrations of NO3−, SO42−, Cl− and NH4+, with a decrease of 28–66%. The temperatures of the cold water spray and the hot alkali droplet spray primarily affect the ionic concentrations of SO42− and Ca2+, leading to a decrease of 32.3–51%. When the SO2 concentration increased from 0 mg/Nm3 to 1500 mg/Nm3, large amounts of SO2 reacted with the desulfurization slurry to form new CPM and its precursors, the CPM emission concentration increased by 57–68.4%. This study addresses the issue of high Concentration of CPM emissions from coal-fired power plants in a straightforward and efficient manner, which is significant for enhancing the air quality and reducing hazy weather conditions. Also, it provides a theoretical basis and technical foundation for the efficient removal of CPM from actual coal-fired flue gas.

Kinetics of the Dissolution Reaction of the U3O8 Powder in Nitric Acid after Oxidation Volatilization at 850 °C.

Due to a series of factors such as variations in powder preparation methods, the kinetic parameter data for its dissolution in nitric acid solution exhibit dispersion. This study investigates the U3O8 powder which underwent oxidation and volatilization at 850 °C. The particle size of the U3O8 powder prior to dissolution was measured, and the surface area during dissolution was calculated under certain assumptions. By comparison of unit area dissolution rates at different temperatures and acidities, apparent kinetic parameters were derived. Results indicate an escalation in the dissolution rate of the U3O8 powder with increasing temperature and acidity. The initial stage of the reaction period reaction order was raised to n 1 = 2.12, while the rapid reaction period exhibited a reaction order of n 2 = 1.40, and the reaction end period showed a reaction order of n 3 = 1.50. The apparent activation energy during the initial stage of the reaction period, rapid reaction period, and the reaction end period was measured as 98.93, 99.39, and 99.13 kJ/mol, respectively.

Investigation of the Dissolution Behavior of AlN in CaO–Al2O3–MgO Refining Slag and CaO–Al2O3–F–Li2O–BaO Mold Flux

Low‐density steels have garnered widespread attention as novel lightweight materials. Owing to its high Mn and Al content, brittle AlN inclusions, detrimental to both steelmaking and steel properties, can precipitate directly from the molten steel. Employing slag absorption effectively removes these floating AlN inclusions from the molten steel. Herein, a series of analytical methods are utilized to investigate the dissolution behavior of AlN in CaO–Al2O3–MgO refining slag and CaO–Al2O3–F–Li2O–BaO mold flux. The results indicate that the initial dissolution temperatures of AlN in the slag and mold flux are 1361 and 1080 °C, respectively. The dissolution in the refining slag is attributed to the high‐temperature self‐decomposition of AlN, producing N2(g). In the mold flux, the dissolution reaction involves both the high‐temperature self‐decomposition of AlN and its reaction with Li2O in mold flux, generating N2(g) and Li(g). No reaction interface is observed at the AlN‐slag/mold flux boundary. As the dissolution mass of AlN in the slag/mold flux increases, the Al2O3 content in the slag/mold flux rises. The main phases in slag transition from Ca9(Al6O18) to Ca12Al14O33 and Ca3Al2O6. In the mold flux, the LiBaF3 phase disappears, and the 11CaO·7Al2O3·CaF2 phase, which can degrade the flux's physicochemical properties, becomes the dominant phase.