Anodization Conditions Research Articles

Understanding the effect of galvanic corrosion on the sulfide stress corrosion cracking of X80/Inconel 625 weld overlay

Purpose This study aims to investigate the effect of galvanic corrosion on the sulfide stress corrosion cracking (SSCC) of X80/Inconel 625 weld overlay by altering the cathode/anode area ratios, Na2S2O3 concentrations and temperatures. Design/methodology/approach The effects of galvanic corrosion on X80/Inconel 625 weld overlay SSCC were investigated by immersion test, galvanic corrosion current test, electrochemical measurement, four-point bending experiment, hydrogen permeation experiment and scanning electron microscopy. Findings The anodic dissolution of the fusion boundary was enhanced as the cathode/anode area ratio increased, which is necessary for the SSCC of the X80/Inconel 625 weld overlay. However, severe galvanic corrosion reduced the SSCC susceptibility. The SSCC susceptibility showed a linear increase with Na2S2O3 concentration in the range of 10−4 ∼ 10−2 mol/L. However, further increasing the Na2S2O3 concentration to 10−1 mol/L resulted in the disappearance of SSCC. This is likely because sufficient hydrogen was required for SSCC initiation even under severe anodic dissolution conditions, which was further supported by the reduced SSCC susceptivity at elevated temperatures. Originality/value Limited studies aim to establish the relationship between the galvanic corrosion and SSCC of welded joints through altering the cathode/anode area ratios, Na2S2O3 concentrations and temperatures. This work will pave the way for understanding the effect of galvanic corrosion on the SSCC of dissimilar weld joints.

Design and synthesis of autogenous growth NiFe bimetallic phosphide catalysts on a nickel iron foam-like substrate for efficient overall water splitting.

The design of low-cost, highly active, and stable electrocatalysts is pivotal for advancing water electrolysis technologies. In this study, carbonyl iron powder (CIP) was anchored within the pores of nickel foam (NF) by electroplating nickel, creating nickel iron foam-like (NFF-L) substrates. Subsequently, nickel-iron hydroxide (NiFe-OH) was synthesized on the NFF-L substrate employing an autogenous growth strategy, followed by a phosphating treatment that produced a nanoflower-like NiFe bimetallic phosphide heterostructure catalyst (Fe2P-Ni2P@NFF-L). This novel method of substrate filling enhanced space utilization, while the presence of micropores and mesopores on the nanosheet surfaces facilitated electrolyte infiltration and ion diffusion, thereby significantly increasing the specific surface area. The formation of a two-phase heterointerface accelerated electron transmission and transfer, enhancing water dissociation and the adsorption of hydrogen adatoms (Had). In addition, under anodic oxidation conditions, the dynamic surface reconstruction facilitated a synergistic interaction between the highly active β-NiOOH and α-FeOOH phases, which significantly contributed to the catalyst's exceptional intrinsic activity for the oxygen evolution reaction (OER).

Oscillatory Transcranial ElectricalStimulation and the Amplitude-Modulated Frequency Dictate the Quantitative Features of Phosphenes.

Previous research demonstrated that transcranial alternating current stimulation (tACS) can induce phosphene perception. However, tACS involves rhythmic changes in the electric field and alternating polarity (excitatory vs. inhibitory phases), leaving the precise mechanism behind phosphene perception unclear. To disentangle the effects of rhythmic changes from those of alternating polarity, this study employs oscillatory transcranial direct current stimulation (otDCS), in which the current oscillation remains confined to either a positive or negative polarity, thereby eliminating the influence of polarity switching. We applied scalp electrical stimulations using both polarity-switching (tACS) and non-polarity-switching (otDCS) methods, with anodal or cathodal polarities, targeting the occipital lobe. All stimulations were performed using sinusoidal or amplitude modulation (AM)waveforms at threshold or suprathreshold intensities. Our results show that tACS results in faster response times compared to cathodal otDCS, but not anodal otDCS, while anodal otDCS elicits greater brightness perception than both cathodal otDCS and tACS. Additionally, AM frequency induced a higher threshold than the sinusoidal frequency, and response times were slower in the AM condition across all positive, negative, and polarity-switching stimulations. However, stimulation intensity in the anodal AM condition could influence speed ratings, unlike in cathodal or tACS conditions. Our findings reveal that both tACS and otDCS induce phosphenes, with significant differences between polarities and current oscillation types, indicating that both mechanisms are critical in phosphene induction. This study provides evidence linking phosphene occurrence to oscillatory current activity and highlights the robustness and impact of AM coding in visual perception.

Design Criteria for Active and Selective Catalysts in the Nitrogen Oxidation Reaction.

The direct conversion of dinitrogen to nitrate is a dream reaction to combine the Haber-Bosch and Ostwald processes as well as steam reforming using electrochemistry in a single process. Regrettably, the corresponding nitrogen oxidation (NOR) reaction is hampered by a selectivity problem, since the oxygen evolution reaction (OER) is both thermodynamically and kinetically favored in the same potential range. This opens the search for the identification of active and selective NOR catalysts to enable nitrate production under anodic reaction conditions. While theoretical considerations using the computational hydrogen electrode approach have helped in identifying potential material motifs for electrocatalytic reactions over the last decades, the inherent complexity of the NOR, which consists of ten proton-coupled electron transfer steps and thus at least nine intermediate states, poses a challenge for electronic structure theory calculations in the realm of materials screening. To this end, we present a different strategy to capture the competing NOR and OER at the atomic scale. Using a data-driven method, we provide a framework to derive generalized design criteria for materials with selectivity toward NOR. This leads to a significant reduction of the computational costs, since only two free-energy changes need to be evaluated to draw a first conclusion on NOR selectivity.

MXenes Spontaneously Form Active and Selective Single-Atom Centers under Anodic Polarization Conditions.

Single-atom catalysts (SACs) have emerged as a new class of materials for the development of active and selective catalysts. These materials are commonly based on anchoring a noble transition metal to some kind of carrier. In the present work, we demonstrate that MXenes─two-dimensional materials with application in energy storage and conversion─spontaneously form SAC-like sites under anodic polarization conditions, using the applied electrode potential as a probe to form catalytically active surface sites reminiscent of a SAC-like structure. Combining ab initio molecular dynamics simulations and electronic structure calculations in the density functional theory framework, we demonstrate that only the SAC-like sites rather than the basal planes of MXenes are highly active and selective for the oxygen evolution or chlorine evolution reactions, respectively. Our findings may simplify synthetic routes toward the formation of active and selective SAC-like sites and could pave the way for the development of smart materials by incorporating fundamental principles from nature into material discovery: while the pristine form of the material is inactive, the application of an electrode potential activates the material by the formation of active and selective single-atom centers.

(Invited) Fabrication of Anodic Porous Alumina via Anodizing Aluminum in Novel Electrolyte Solutions

Anodizing aluminum in several appropriate acidic electrolyte solutions, such as sulfuric, dicarboxylic, phosphoric, and chromic acids, causes the formation of anodic porous alumina. The porous alumina film possesses vertical nanoscale pores in its structure, and is typically used for corrosion protection and nanostructure fabrication. Particularly, since the self-ordering behavior of nanoscale pores in the porous alumina film under the appropriate anodizing conditions was reported by Masuda et al. in 1995, the ordered porous alumina film is widely used for the fabrication of various nanomaterials, such as plasmonic devices, antireflection structures, filters, memory devices, and sensors. The nanostructure and property of the porous alumina film strongly depends on the electrolyte used during anodizing. The discovery of additional electrolytes for anodizing aluminum would cause the novel nanostructures and properties of anodic oxide, thus expand their applicability. In this lecture, we describe various electrolytes for the formation of novel anodic oxide films on the aluminum surface. In addition, many interesting nanostructures and properties exhibited by these anodic oxide films will be presented. The interpore distance of porous alumina, D int, increases with the applied voltage, U, during anodizing. We studied anodizing aluminum in various acidic electrolyte solutions for the formation of porous alumina, and the self-ordering behaviors with new applied voltages and interpore distance regions are found via anodizing in selenic acid at U = 42-48 V for D int = 95-112 nm, phosphonic acid at 150-180 V for 370-440 nm, and etidronic acid at 210-270 V for 530-670 nm. The interpore distance of these and typical porous alumina films was proportional to the applied voltage with a proportionality constant of k = 2.5 nmV-1. Recently, we reported a novel anodizing method in several alkaline electrolyte solutions. For example, anodizing in sodium tetraborate (Na2B4O7) solution causes the self-ordering behavior at 90-190 V for 260-590 nm. Interestingly, the interpore distance obtained in this alkaline solution also had a linear relationship with the voltage, but the proportionality constant obviously increased by 1.2 times, with k = 3.0 nmV-1 under the new regime. A wide interpore distance range for the self-ordering of porous alumina can be obtained by anodizing in these novel electrolyte solutions. Pyrophosphoric acid is a unique electrolyte that produces anodic alumina nanofibers and provides higher controllability of their nanomorphologies. As the aluminum specimen is anodized in pyrophosphoric acid, the anodic alumina without anions at the apices of the honeycomb structure remains during anodizing due to their slow dissolution rate, thus numerous alumina nanofibers measuring less than 10 nm in diameter are formed on the extremely thin, porous alumina film. As a result, sub-10 nm alumina nanofibers completely cover the aluminum surface. The nanofiber-covered aluminum surface exhibits superhydrophilic behaviors with the rapid spreading of a water droplet. In addition, superhydrophobic surfaces can be fabricated by modification with hydrophobic self-assembled monolayers (SAMs) on the surface of alumina nanofibers. Moreover, opposite water slipping properties such as slippery and sticky states can be obtained by controlling the nanomorphology of alumina nanofibers. As described above, the nanostructure of the anodic oxide changes significantly depending on the type of electrolyte used, thus we can obtain interesting nanomorphologies and properties by anodizing in various electrolyte solutions. However, even now there are many unknown behaviors during anodizing. Therefore, anodizing science and technology will continue to evolve in the future. Figure 1

Microporous Layer-Supported Catalyst-Coated Membrane for PEM Water Electrolysis

Innovative approaches are necessary for thrifting iridium (in the form of IrO2) from PEM water electrolysis (PEMWE) anodes without compromising catalyst utilization. Adding a microporous layer (MPL) to the anode can realize high performance with low IrO2 loadings (<0.1 mg cm-2) by facilitating the efficient conduction of electrons from catalyst particles to the current collector.As an alternative to fabricating a monolithic, sintered MPL on the porous transport layer (PTL), we demonstrate how a loose-particle microporous layer (MPL) can be fabricated directly on the CCM via decal transfer with a single added step of particle ink deposition on a PTFE decal. Benchmarking tests confirm that when low-loaded IrO2 catalyst layers (0.05-0.2 mg cm-2) are supported with 0.4 mg cm-2 platinum black (PtB) in a bilayer configuration, kinetic and mass transport performance at parity or better than unsupported 1.0 mg cm-2 IrO2 anodes can be achieved for PEMWE.First, an idealized in-plane catalyst utilization model is developed to estimate the requisite sheet conductivity for the MPL to minimize electronic conduction losses assuming in-plane electronic resistance is dominant. Then, several materials were screened for sufficient conductivity as loose-particle MPLs on a fluorinated ethylene propylene sheet under realistic confinement conditions using the Van der Pauw method using a gasket with conductive edges. Due to non-ideal airbrushing and agglomerates, the actual amount of PtB required to achieve requisite conductivity is roughly four times higher than that expected assuming sheet conductivity is proportional to the areal mass loading.An initial formulation for the MPL particle ink using an ionomer binder was then reformulated to use an insulating polymer binder (PVDF) to avoid a reversible >1 Ω cm2 contact resistance present under anodic conditions at current densities as low as 0.01 A cm-2. Since tests used pure water and the contact resistance vanishes under cathodic conditions, it is likely that the loose PtB MPL reversibly oxidizes near the onset of the oxygen evolution reaction due to the ionically conductive binder.Then, MPL-supported CCMs (0.4 mg cm-2 PtB, PVDF binder) were benchmarked against bare CCMs operating as a PEMWE cell at 80C with pure water fed to the anode. A five-electrode method was utilized to extract informative anode electrodynamics such as catalyst layer resistance, charge transfer resistance, and conduction resistance via impedance spectroscopy to enhance the data quality of the benchmark tests. Finally, the stability and reusability of the MPL-supported CCM was checked by cycling between a galvanostatic hold at 4 A cm-2 and a short series of impedance measurements at 0.1 A cm-2. Break-in effects were observed for the membrane and cathode (directly measured) while anode-specific hardware and MPL issues such as the passivation of the titanium endplate and MPL delamination were observed.The results of these experiments for the flexible MPL-supported CCM for PEMWE along with the generalizability of the Van der Pauw method, and five-electrode method for other membrane-based cells will be discussed. Figure 1

(Invited) Direct Observation of Nanoscale Heterogeneity in Ruthenium Oxide Rutile Nanocrystals for the Oxygen Evolution Reaction via Liquid Phase Transmission Electron Microscopy

Oxygen-evolving electrocatalysts in acid undergo structural changes that result in a loss of activity, which necessitates high catalyst loadings of precious noble metal oxides. A fundamental understanding of the structural dynamics at the electrode/electrolyte interface that occur during oxygen evolution is necessary to design the next generation of electrocatalyst materials with improved performance. The Moreno-Hernandez Laboratory utilizes liquid phase transmission electron microscopy to directly observe the stability of single-nanocrystalline and highly faceted metal oxide nanocrystals under anodic conditions in acidic electrolytes. Our studies reveal the distribution of stability relationships between different crystallographic facets for nanocrystalline materials, and enable the direct determination of nanoscale heterogeneity at the single nanocrystal level. Substantial stability differences are observed across multiple nanocrystals, which are correlated to variability in the nanoscale strain present in individual nanocrystals. These studies suggest that nanoscale heterogeneity occluded in conventional bulk-scale analysis techniques substantially influences stability under relevant operation conditions, and provide crucial information for the design of resilient electrocatalyst materials.

(Invited) Engineering Anodic Porous Alumina-Based Photonic Structures and Prospective Applications

Nanoporous anodic alumina (NAA) has become a popular material because of cost-competitive fabrication processes and fully scalable process compatible with conventional micro- and nanofabrication approaches. NAA is a nanostructured material that under specific conditions, their porous structure presents a self-ordering defined by a close-packed hexagonal array of well-defined cylindrical nanopores. The outstanding set of properties of NAA such as self-organized nanoporous structure, straight cylindrical nanopores of high aspect ratio, optical properties, chemical resistance and thermal stability and intrinsic photoluminescence demonstrate its versatility and potential [1]NAA is produced by electrochemical etching of aluminum, and their geometric characteristics such as pore diameter and length and separation distance between pores can be precisely tuned by the anodization conditions (voltage and time of anodization, temperature, and electrolyte) and by post-anodization treatments (etching and annealing). The highly effective surface area (hundreds of m2/cm3) makes of NAA an interesting platform for sensing and loading and releasing of active agents. Recently, different anodization approaches have been proposed to create new structures and pore geometries such as cone-like, funnel-like, modulated, tip-like, etc. [2-4].NAA has been used to fabricate photonic structures with the aim to control, enhance or inhibit the propagation of light. Photonic properties can be obtained by engineering the pore shape. For instance, the application of periodic variations of current or voltage during the anodization is transferred to the material as the periodic variation of the pore diameter and consequently, it is possible design, 3D structures and photonic structures with stop bands tunable within the UV-VIS-NIR range [5]. The fabrication of new photonic structures with single or multiple narrow photonic stopbands at different spectral positions, remains a challenge. These photonic structures can be obtained by using non-conventional pulse anodization for example, averaging the sum of multiple sinusoidal waves, Gaussian-like pulse or combining a gold coating layer on top of a NAA−photonic structure to create a hybrid metal−dielectric structure (Tamm plasmon resonance) [6-8]In this work, will show recent advances in the design and fabrication of nanoporous anodic alumina and their photonic and optic applications such as optical encoding tags, optical sensing, photonics and photovoltaics. We will analyze different technological parameters and its effect on the structure and future applications. Acknowledgements This work was supported by the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN/FEDER) PDI2021-128342OB-I00, by the Agency for Management of University and Research Grants (AGAUR) 2021-SGR-00739 and by the Catalan Institution for Research and Advanced Studies (ICREA) under the ICREA Academia Award 2021.

Highly Active Raney-Nickel Electrodes Based on 3D Pin Structures for Use in High Temperature Alkaline Electrolysis

The efficiency of alkaline electrolysers can be improved in a multitude of ways from overall system design to optimal operation conditions. One possibility is to increase the operating temperature which usually is 80 °C for industrial electrolysers. Increasing the temperature is a straightforward way to increase system efficiency significantly but leads to escalating corrosion problems due to the high concentration of KOH and the presence of oxygen (dissolved and gas phase) in the anolyte.In this work we have developed highly active electrodes for the use at 120 °C. The electrodes are based on engineered 3D pin structures that were coated with Raney-Nickel. Since the interplay between electrode structure and catalyst layer are crucial for electrode performance in alkaline electrolysis a selection of nickel pin structures based on nickel mesh with differences in pillar as well as hole shape and size were investigated to find a optimal configuration. The aluminum for the formation of leachable NiAl-phases was applied by rolling Aluminum foil of varying thickness onto the pin structures. A following heat treatment and leaching resulted in a layer of Raney-Nickel on the substrates. The general performance at standard operating conditions was investigated as well as the behavior at 120 °C in 40 wt% KOH. The obtained electrodes showed excellent performance at a current density of 500 mA/cm² with overvoltages below 110 mV as cathodes and below 300 mV as anodes. During these tests and an additional testing campaign, the corrosion resistance of the Ni substrate and specially developed alloys under anodic conditions were evaluated. Figure 1

(Invited) Predicting Surface Phase Diagrams of Complex Oxides Under Functionally Relevant Conditions

Understanding deduced from multiscale simulations have benefited the advancement of materials for solid oxide fuel and electrolysis cells (SOCs) over the past decades. This in particular includes ion transport and defect properties of materials. A remaining key gap is predicting the atomic structure and chemistry of the complex oxides, that is the surface phase diagrams under functional conditions of SOCs. In particular, perovskite oxides that serve as cathode and anode form complex surfaces at elevated temperatures and under varying oxygen chemical potentials. I will share perspectives and progress from the field, including our work, that integrate first principles, machine learning, thermodynamic and grand canonical Monte Carlo calculations to predict surface phases under relevant anodic and cathodic conditions. Being able to predict surface phases will allow us to also interpret and predict the performance of the material, as key reactions in SOCs (oxygen reduction/evolution, water splitting) take place at these surfaces.

Corrosion-Related Degradation Phenomena in PEM Water Electrolysis - an Industrial Perspective

One of the most reliable ways to produce green hydrogen is to use electrolysis systems from renewable energy sources. Proton exchange membrane water electrolysis (PEMWE) is one of the most promising electrolyzer technologies. To reach the goal of 1 Dollar per 1 kilogram of hydrogen in 1 decade – launched by the Department of Energy on June 7, 2021 [1] a long lifetime of electrolysis systems is key. The research focus is therefore to achieve low degradation rates for PEMWE-systems, measured in µV/h.Within this presentation two different aspects of degradation related to metallic parts within the stack and within the process technology will be presented briefly. From this, open research questions concerning these aspects will be derived and their evaluation discussed. This industrial view reveals the needs and possible future development-trends of large-scale PEM water electrolyzer manufacturers.First, corrosion of metallic parts, and thereby ion release into the process water, should be avoided as much as possible. It is well known that metal cations can lower the cell performance or even accelerate membrane degradation. The influence of stainless steel parts on PEMWE degradation has been studied by performing electrolysis tests on two different test-stands. One is made of commonly used stainless steel pipes and a stainless steel heat exchanger and the other is made of plastic piping and a titanium heat exchanger to exclude contamination from the Balance of Plant. In following electrolysis experiments on the plastic test-stand, titanium cell components have been subsequently replaced by stainless steel cell components. Resulting contamination (determined with ICP-MS) will be presented, and future work will be addressed as starting point for academic research.Next, ohmic resistances in the PEMWE cells should be low to achieve low cell voltages. High anodic potentials within the electrolyzer cell can lead to growing oxide layers with poor electrical conductivity. The resulting additional ohmic resistance increases cell voltage over time and therefore promotes cell degradation. Especially for titanium, the commonly applied metal under anodic PEMWE conditions, it is known that growing Ti-oxide layers can result in increased cell voltages. Consequently, the impact of conductive coatings on different cell components on the degradation rate has been studied. Bipolar plates, coarse gas diffusion layers and porous transport layers have been coated with noble metals. The influence of these coatings on cell performance will be presented, and open questions will be addressed.Finally, for the evaluation of the above-mentioned aspects, ex-situ experiments should be performed prior to electrolysis experiments. They are much easier to perform, reduce cost and time and allow a more separate look on certain material properties than in an electrolysis cell where the interaction of many parts needs to be considered. When compared to PEM fuel cells, no comparably clear guidance exists for the study of metallic parts for PEMWE [2]. We will provide insights on “how to perform ex-situ corrosion experiments” for PEMWE applications as a guidance for future testing based on the experience from researchers from both, academia and industry [3].In conclusion, several sources for metal contamination exist in PEMWE-systems which can have a significant influence on degradation rates. Unfortunately, only limited research is available on the criticality of different contamination types. Furthermore, long-term stability information and degradation mechanisms on coating are of great importance as the currently used materials are rare. In addition, it is a challenge to generate a common understanding of suitable test conditions to simulate PEMWE-environment in ex-situ testing which would simplify improving components.[1] Department of Energy, Hydrogen and Fuel Cell technologies Officehttps://www.energy.gov/eere/fuelcells/hydrogen-shot [latest access: 15.03.2024][2] Department of Energy, Hydrogen and Fuel Cell technologies Office: DOE Technical Targets for Polymer Electrolyte Membrane Fuel Cell Componentshttps://www.energy.gov/eere/fuelcells/doe-technical-targets-polymer-electrolyte-membrane-fuel-cell-components [latest access: 15.03.2024][3] L. H. Prado et al., to be submitted Figure 1

Influence of Annealing Parameters on the Photoelectrochemical Performance of Spaced TiO2 Nanotubes

Fossil fuels, currently comprising 80% of global energy consumption, are major contributors to environmental pollution due to their substantial carbon emissions. In contrast, hydrogen energy, characterized by its high energy density and zero carbon emissions, is increasingly recognized as a promising alternative energy source. Among the various hydrogen production technologies, photoelectrochemical (PEC) water splitting stands out as a leading method for generating clean hydrogen. Titanium dioxide (TiO2) is the most widely studied material for PEC hydrogen production, as it forms electron-hole pairs upon absorbing light with wavelengths shorter than 400 nm (3.0 to 3.2 eV), thereby enabling water splitting.Crystalline TiO2 exists in three phases: anatase, rutile, and brookite, with anatase being recognized for its superior PEC properties. However, some studies have reported that mixed-phase anatase-rutile TiO2 exhibits higher PEC activity than pure anatase. Anodization is a general method for forming nanostructures to enhance the PEC efficiency of TiO2. Anodizing a titanium metal substrate in a fluoride ion-containing electrolyte produces one-dimensional nanotube structures. The length, inner diameter, and spacing of these tubes can be precisely controlled by adjusting the anodization conditions. In this study, spaced TiO2 nanotubes (SPNTs) with wide inter-tube spacing were fabricated via anodization, and their structural, physical, and PEC properties were analyzed based on annealing temperature and atmosphere. Under optimized annealing conditions, the SPNTs exhibited a mixed anatase-rutile phase, a photocurrent of 0.34 mA/cm² at 1.23 V vs RHE, and a charge transfer resistance of 556 Ω at open circuit potential.

Formation of Ordered Nanostructures By Anodization of Ag Substrates with Depression Patterns

The anodization of metals is an effective technique for preparing metal oxide nanohole arrays on substrate surfaces. It has been reported that nanohole arrays can be formed by anodizing various metals, not only Al and Ti. The variety of metals that can be anodized has increased, and the range of applications for the resulting nanohole arrays has expanded. In various applications using nanohole arrays obtained by the anodization of metals, control of the geometrical structure of the nanohole arrays is essential because its geometrical structure affects the performance of the device. However, structural control of nanohole arrays has not been achieved in the anodization of many metals. We previously reported that nanohole arrays with regularly arranged pores can be obtained by anodizing metal substrates with ordered depression patterns [1–3]. This is because the depressions formed on the metal surface served as the starting point for pore generation. We have previously reported that this method is applicable to various metals such as W, Fe, Cu, and SUS. In this report, we describe the preparation of ordered nanostructures of Ag oxide by the anodization of an Ag substrate with ordered depression patterns. A depression pattern was formed on the Ag substrate surface by Ar ion milling using an ordered anodic porous alumina mask. An anodic porous alumina mask with an ordered pore arrangement was prepared by a previously reported two-step anodization process. The resulting alumina mask was placed on an Ag substrate, with the barrier layer facing upward and the pore-forming surface facing downward. Ar ion milling was performed for 60 min at 5 kV to penetrate the alumina mask and form depression patterns on the Ag substrate surface. The alumina mask remaining on the Ag substrate surface was dissolved using a mixture of 0.17 M chromic acid and 0.07 M hydrofluoric acid at 20℃, which can dissolve only alumina without dissolving Ag. Ag sheets with the depression pattern were anodized in 0.05–0.13 M NH4F ethylene glycol electrolyte containing 0-0.13 M KOH or 0.1 M CH3COONa at 10℃ under a constant voltage of 2 V. For anodization of the Ag sheet, a two-electrode cell was used with a Pt plate as the counter electrode, and the distance between the electrodes was adjusted to 5 mm. The surface structures of the obtained samples were observed using field-emission scanning electron microscopy (SEM). The compositions and crystallinities of the obtained samples were evaluated using X-ray photoelectron spectroscopy and X-ray diffraction. Anodization of the Ag substrate with a depression pattern in an ethylene glycol solution containing NH4F and KOH induced pore generation from depressions, resulting in ordered nanohole array structures [4]. In addition, ordered nanopillar array structures were obtained by the anodization of an Ag substrate with depression patterns in an ethylene glycol solution containing NH4F and CH3COONa. This is the first report on the formation of ordered nanohole array structures of Ag oxide by the anodization of an Ag substrate. This is also the first report of the successful fabrication of ordered nanohole and nanopillar array structures from the same metal substrate by changing anodization conditions. The ordered nanostructures of Ag oxides obtained by this method are expected to be applicable in various functional devices, such as sensors, catalysts, and batteries.

(Invited) Mild Anodization of Aluminum: From Fundamentals to Industrial Applications

Considering the recent energy crisis and global environmental pollution, the weight reduction of vehicles through the modification of several parts (e.g., engines and wheels) is emerging as an important research area. One strategy for achieving this is the use of aluminum. Aluminum, a lightweight material with excellent recyclability, is widely used in various industrial fields. There are various surface treatment methods for aluminum, depending on the purpose of use in each operating environment. Corrosion resistance and hardness of native oxides are not enough under some environment.To improve the surface properties of aluminum, anodic oxidation of aluminum (so-called anodizing or anodization), is generally applied. The surface treatment has a history of nearly 100 years. In Japan, anodization using oxalic acid was first patented in 1923. A porous-type oxide film formed on aluminum by anodization, or a product covered with the porous alumina film, is industrially called alumite in Japan. The structure of a porous-type oxide film (alumite) determines the various surface properties of aluminum. For instance, to increase the hardness of anodic films on aluminum, the anodization is industrially carried out at low temperature to avoid chemical dissolution of the formed oxide film during anodization.Here, I present an overview of the progress of anodization in common acidic electrolytes (e.g., sulfuric acid, oxalic acid, or phosphoric acid) containing alcohol as an additive [1-6]. Anodization was mainly conducted using various alcohols with different physical properties under mild anodization conditions with a constant current of 100 A·m−2 at 20 °C. The effects of alcohol addition in electrolytes on the anodization behavior of aluminum, the coating ratio, the porosity, the maximum attainable film thickness, and the hardness of anodic films will be discussed in terms of both basic research and commercial applications. H. Asoh, M. Matsumoto, H. Hashimoto, Surf. Coat. Technol., 378, 124947 (2019).M. Matsumoto, H. Hashimoto, H. Asoh, J. Electrochem. Soc., 167, 041504 (2020).H. Asoh, T. Sano, J. Electrochem. Soc., 168, 103506 (2021).H. Asoh, H. Kadokura, R. Murohashi, M. Matsumoto, J. Electrochem. Soc., 169, 073510 (2022).T. Sano, Y. Wakabayashi, H. Asoh, Surf. Coat. Technol., 459, 129399 (2023).H. Asoh, S. Ota, K. Hagiwara, J. Electrochem. Soc., 171, 033502 (2024).

Electrochemical Methods to Optimize Anodic Aluminum Oxide and Incorporation of Molybdenum Disulfide for Enhanced Wear Performance

Anodized aluminum oxide (AAO) has many beneficial properties leading to its wide use across industries as a surface treatment for many aluminum components, but the wear properties of the coating could be improved significantly. Here, we used an electrochemical method to incorporate molybdenum disulfide (MoS2), a nanomaterial used as a dry lubricant, to modify alloys of aluminum during AAO preparation. Using Raman spectroscopy and tribological scratch measurements, we thoroughly characterized the structure and wear behavior of the films. The MoS2 deposition procedure was optimal on aluminum 5052 anodized in higher acid concentrations, with friction coefficients around 0.05 (~10x better than unmodified AAO). Changing anodization conditions to produce harder films with smaller pores led to worsened wear properties, likely because of lower MoS2 content. Studying a commercial MoS2/AAO film of a different Al alloy (7075) showed that a heat treatment step intended to fully convert all deposited MoSx species to MoS2 can adversely affect wear in some alloys. While Al 6061 and 1100 produced films with worse wear performance compared to Al 5052 or 7075, our results show evidence that acid cleaning after initial anodization likely removes residual alloying elements, affecting MoS2 incorporation. This study demonstrates a nanomaterial modified AAO film with superior wear characteristics to unmodified AAO and relates fabrication procedure, film structure, and practical performance. Methods for production of this enhanced wear coating for several aluminum alloys along with associated wear and scratch performance will be presented.

The Effects of Transcranial Direct Current Stimulation over the Ventromedial Prefrontal Cortex on Reactive Aggression in Intoxicated and Sober Individuals

Alcohol-related aggression is a widely observed phenomenon that has detrimental effects on both individuals and society, putatively caused by dysfunction in the prefrontal cortex. The ventromedial prefrontal cortex (vmPFC) plays a critical role in representing the reward value of future actions. Emerging research has suggested that transcranial direct current stimulation (tDCS) over the vmPFC can reduce aggression. However, no study has examined whether tDCS can mitigate intoxicated aggression. In this study, 153 healthy participants consumed alcohol or not and completed the anger-infused Ultimatum Game with simultaneous double-blind anodal tDCS or sham over the bilateral vmPFC. For participants in the anodal tDCS condition, intoxicated participants were less aggressive than sober participants when insulted. However, among sober participants, anodal tDCS increased aggression. For participants in the alcohol condition, we observed no differences in aggression between the anodal tDCS and the sham tDCS conditions. These findings provide mixed support for tDCS as a means to attenuate intoxicated aggression.

Characterization of thin oxide layers formed by Ti-Nb Alloy anodization

Ti-Nb alloys are gaining more prominence in the industrial and scientific environment due to their high biocompatibility, mechanical strength/weight ratio, and exceptional corrosion resistance compared to other metallic materials. Metals exhibiting this passivation characteristic are known as metal valves and may exhibit semiconductive or insulating oxides. Controlling the growth of distinct thickness layer films is possible through tunning anodization conditions. In this work, a Ti-Nb binary system is anodized, and the grown oxide layer is comprehensively characterized using ellipsometry based on its optical properties and thickness at different applied potentials. Confocal Microscopy assessed their surface roughness, and SEM/EDS probed the surface material's elemental composition. CF-LIBS successfully confirmed the 70/30 composition of the Ti-Nb alloy. Raman spectra have detected the presence of amorphous TiO2 and Nb2O5 at potentials higher than 80V, 100V, and 120V. Finally, a linear dependence of the oxide thickness with the applied potential was observed.

Improving Bioactivity of Anodic Titanium Oxide (ATO) Layers with Chlorine Ion Addition in Electrolytes

Appending diverse quantities of additional elements to the anodizing solution leads to the formation of a highly corrosion-resistant and biocompatible anodic Ti oxide (ATO) on the titanium surface. This study aims to investigate the synergistic effect of chlorine and sulfate ions in the anodizing solution on the formation mechanism and biocompatibility of anodized layers formed on pure Ti. For this purpose, sulfuric acid-based anodizing solutions with different molar ratios () of 0.25, 0.5, and 0.75, and total molars () of 1, 1.5, and 2 M, were utilized for galvanostatic anodizing conditions at different current densities. The response surface methodology was employed on these three anodizing parameters to optimize the quality of anodic Ti oxide layers. Voltage vs. time behavior, SEM surface morphology, and FE-SEM fractured cross-sectional observations were used to thoroughly discuss the formation mechanism. X-ray diffraction method, micro-Raman spectroscopy, and water contact angle measurements were performed to characterize the coatings. Corrosion properties of ATO layers were evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in simulated body fluid (Hanks’ solution). The total molar () is recognized as the most influential factor on the anodic oxide layer properties, and a three-step formation mechanism, based on the competition between the formation and dissolution of anodic Ti oxide, was proposed in detail. The sample anodized with a molar ratio () of 0.5 at a constant current density of 70 mA.cm-2 and a total molar of 1.5 M achieved maximum corrosion resistance with a corrosion current density of 2.138e-11 A.cm-2 compares to 1.39e-8 A.cm-2 for the substrate. Furthermore, the addition of chloride ions to the anodizing bath resulted in more hydrophilic surfaces, promoting the formation of granular hydroxyapatite (HAp) on the TAO coating with maximum corrosion resistance in the Hank solution.

Influence of anodization conditions on deposition of hydroxyapatite on α/β Ti alloys for osseointegration: Atomic force microscopy analysis

Influence of anodization conditions on deposition of hydroxyapatite on α/β Ti alloys for osseointegration: Atomic force microscopy analysis