Cathode Region Research Articles

Design and Development of Dual‐Function Nano‐CeO2‐Integrated PUF/Epoxy Microcapsule Systems for Self‐Healing and Corrosion‐Resistant Epoxy Coatings

ABSTRACTA dual‐function microcapsule system was developed to overcome the limitations of single‐mechanism self‐healing coatings. Nano‐CeO2 particles were embedded in a polyurea formaldehyde (PUF) shell, with epoxy resin encapsulated inside. SEM, FTIR, and XRD characterization confirmed the successful integration of CeO2 and epoxy within the microcapsules. These microcapsules were incorporated into an epoxy resin‐based coating at varying weight percentages to assess their impact on coating performance. EIS was employed to evaluate the self‐healing properties of coatings with artificial scratches in simulated seawater. When the coating is damaged, CeO2 is released and deposited on the metal surface, rapidly forming a passivation film that protects the substrate in advance. CeO2 also releases cerium ions. A cerium hydroxide precipitate is formed by reacting with OH− produced in the cathode region. Prevents penetration of corrosive ions. Meanwhile, the microcapsules rupture, releasing epoxy resin to heal the cracks. Electrochemical Impedance Spectroscopy (EIS) results demonstrated that the optimal self‐repair performance was achieved with 10 wt% microcapsules, while higher concentrations negatively affected the coating's adhesion. This dual‐function microcapsule approach significantly improves both protective and self‐healing capabilities, offering potential for advanced corrosion‐resistant coatings.

Effects of cation types on physicochemical parameters and micro-structure of soft clay for electrochemical treatment

To investigate the influence of cations on the microstructural characteristics of electrochemical reinforcement in soft clay, a study was conducted using three different cationic salt solutions—NaCl, CaCl₂, and FeCl₃—for grouting treatment. Four sets of indoor experiments were performed to examine the reinforcement mechanism of the electrochemical method. The findings indicate that increasing the valence of injected cations significantly affects the electrochemical reinforcement effect and the soil’s microstructural properties. Higher-valence cations notably enhanced the soil’s electrical permeability coefficient and conductivity, leading to a substantial improvement in shear strength. Furthermore, the pore volume of the soil increased following electrochemical treatment compared to soil treated solely by electro-osmosis, due to the flocculation effect induced by cation injection. Nevertheless, the pore size distribution became more uniform, especially in the cathode region, as a result of pore redistribution. The chemical cementation reactions triggered by Ca2+ and Fe3+ injections mitigated the impact of flocculation on the microstructure, resulting in a more favorable pore volume and size distribution compared to Na+ treatment.

Analysis of Technologies for Applying High-Entropy Coatings by Physical Deposition Method

Introduction. Modern tribology solves the problems of increasing the reliability of friction units through applying vacuum wear-resistant coatings by the physical vapor deposition (PVD) method. More than five thousand scientific papers are devoted to high-entropy alloys (HEA). However, an urgent question about the possibility of obtaining wear-resistant and antifriction high-entropy coatings (HEC) using the PVD method remains unsolved. Its solution opens up the possibility of using HEC in mechanical engineering. The presented article is intended to fill this gap. Research objectives are as follows: to identify the key results on the creation of HEC by such PVD methods as vacuum arc evaporation and magnetron sputtering, to establish tribological characteristics of PVD coatings.Materials and Methods. From November 2023 to February 2024, the authors analyzed materials published in the Web of Science, Elibrary, Scopus, Medline, CINAHL databases in the Russian and English languages.Results. At the first stage, the literature on the vacuum arc coating method was considered. The issues of creating a vacuum arc discharge, its technological features, disadvantages, as well as processes in the cathode region of the arc were studied. The conditions of existence of cathode spots, the influence of temperature on the erosion coefficient, and processes on the anode and substrate were noted. The dependence of the deposition rate on the value of the potential on the substrate was shown. Nitride and combined coatings obtained by vacuum-arc method were analyzed: TiN, TiCN, TiAlN, TiMoS, TiSiN, TiN/VN, TiAlN/DLC-Ti. At the second stage, the history of the magnetron sputtering method was presented; technological features, types of magnetrons and nitride coatings obtained in this way were described. The third stage was devoted to the five-stage process of forming the coating structure. Island, layer-by-layer, and mixed growth modes of coating were considered. A schematic representation of the fundamental processes of structure formation was given. Defects in vacuum coatings were noted. At the fourth stage, the HEC based on the HEA were presented. Parameters predicting the formation of a HEA solid solution were indicated. Six families of high-entropy alloys were considered. Modern high-entropy coatings obtained by vacuum arc and magnetron methods were evaluated. The results of studies of structural-phase and physico-mechanical properties were summarized in the form of a table. The data of tribological studies of high-entropy coatings were presented.Discussion and Conclusion. The literature on HEC describes the coating structure, physical and mechanical properties, and thermal stability. The authors of the presented article found a gap in the research of tribology of high-entropy coatings. From the known results, it can be concluded that these coatings are frictional. However, due to their high hardness and ductility, they exhibit high wear resistance. In addition, it is difficult to talk about their tribological purpose. To solve the issue of the possibility of using PVD coatings in mechanical engineering, attention should be paid to the development of compositions with high hardness, wear resistance, and low coefficient of friction. They can be operated in tribo-loaded nodes.

Kinetics of electroreduction of fluorozirconates in fluoride melts

At present, the demand for aluminum alloys, including those with zirconium additives, is growing significantly. One of the methods for producing such alloys is the reduction of alkali and alkaline earth metal fluorozirconates in molten salts; this method is characterized by a high degree of extraction and process intensity. According to scientific and technical literature, the use of electrolysis can contribute to increasing the efficiency of such processes, in connection with which, it is relevant to study the electrochemical behavior of fluorozirconates in molten media. Using the cyclic chronovoltammetry method, some patterns of electroreduction of zirconium and aluminum from a low-melting melt of KF–AlF3–Al2O3–ZrO2 at a temperature of 750°C were studied, depending on the composition of the additive and the substrate material. A series of polarization curves were obtained, both in a pure melt and with additives of potassium fluorozirconate, at potential sweep rates from 0.01 to 2 V. It was shown that cathode currents of aluminum electrolysis appear at potentials of –1.6…–1.7 V, relative to the potential of the CO/CO2 electrode, and a further shift of the potential to the cathode region leads to the joint release of aluminum and potassium. When K2ZrF6 is introduced into the KF-AlF3-Al2O3 melt, a discharge area of zirconium ions appears on the cathode branch of the voltammograms at potentials of –1.4 and –1.6 V. When comparing the voltammograms obtained with the addition of zirconium oxide and potassium fluorozirconate under otherwise equal conditions, it was found that when the oxide is added, two inflections are observed on the cathode branch of the voltammograms at potentials of –1.4 and –1.7 V, while only one inflection is observed at a potential of –1.3 V upon reduction of fluorozirconate. The presence of two responses when introducing the oxide can be caused by both the electrolysis of elemental zirconium in two electrochemical stages and the discharge of zirconium-containing ions of different composition. Analysis of the diffraction patterns of the melts shows that, regardless of the composition of the additive, both potassium fluorozirconate and zirconium oxide can be present in the melt. Based on the data obtained, it can be concluded that zirconium can either discharge in several stages or form a number of intermediate compounds when interacting with the components of the melt.

Unravelling the Mechanism of Filiform Corrosion on Painted Carbon Steel

Filiform corrosion (FFC) is recognized as a special case of an oxygen-concentration cell that forms on a metal beneath a paint layer, exhibiting a distinctive thread-like appearance. Under the paint, it is possible to distinguish the leading head from the growing tail thanks to the marked colour gradient. In fact, the front part of the head appears green coloured (in correspondence of the so called “green rust”) and tail brown coloured (in correspondence of the corrosion product containing Fe2O3, FeOOH, Fe (OH)3). FFC occurs on low carbon steel more frequently than expected, requiring only a relative humidity between 65% - 95% and mild chloride contamination to be triggered.This study introduces a novel methodology for investigating the mechanism of filiform corrosion in organic coated steel. The approach leverages the scanning vibrating electrode technique (SVET) and potentiometric scanning electrochemical microscope (SECM), also known as micropotentiometry. By creating artificial defects in specific locations of the filaments under the coating, the electrochemical activity beneath the coating is evaluated by mapping ionic current densities. In addition, antimony tips are utilized to probe the metal-paint interface, enabling the assessment of local pH changes associated with various corrosion reactions.Through in-situ measurements of electrochemical activity governing FFC on organic coated steel, this study precisely identifies the anodic and cathodic regions and determines the pH values at the metal-paint interface along the filament. Consequently, a more comprehensive depiction of the FFC mechanism emerges, addressing gaps in existing literature and validating hypotheses proposed over decades of research. Beyond insights into FFC, this investigation serves as a pioneering application of established techniques to explore corrosion mechanisms in coated metals.

(Digital Presentation) Experimental Analysis of Pit Initiation at MnS Inclusion in Low-Alloy Steel Using in-Situ Raman Spectroscopy

Low-alloy steel is an indispensable material for industry and infrastructure and is widely used in many fields because it can save cost and elemental resources. However, one of the disadvantages of low-alloy steel is its limited corrosion resistance compared to that of high alloys. Specifically, a major weakness is its high susceptibility to pitting in an environment containing Cl- ions. MnS inclusions are well known as preferential pitting sites because of its poor stability against chemical dissolution and ease of deformation by rolling. A lot of studies have investigated the mechanisms of pit initiation at MnS so far. Some detail analyses revealed that S species such as S2O3 2-, HS- and elemental S were generated due to dissolution of MnS, and they were harmful to pit initiation and active dissolution. However, these studies did not focus on ‘when’ those S species were generated. In addition, most of these previous studies focused on pitting in high alloys such as stainless steel and Ni-based alloy, so the mechanism of pit initiation in low-alloy steel is not yet fully understood.This study aims to clarify the chronology between MnS dissolution, S species generation and pit initiation in low-alloy steel. The microscopic potentiodynamic polarization test was carried out in 20 mM NaCl added boric-borate buffer solution at pH 8.0. To analysis S species dissolved from MnS inclusions during the electrochemical test, in-situ observation using an optical microscope with high magnification and Raman spectroscopy were employed.The polarization curve started at cathodic region, and then the corrosion potential was observed. In the anodic region, active dissolution and passive regions appeared in the curve as the potential increased. Finally, surges in the current density, attributed to pit initiation, was observed. In-situ observation ascertained that pit initiated at MnS inclusion whose longer diameter was 20 µm. Interval analysis of Raman spectroscopy during the test detected elemental S about 0.1 V below the pitting potential.Analysis of the test solution after the polarization test also detected elemental S, although other S species such as S2O3 2- and HS- were not detected.To confirm the morphology of the pit, cross-sectional observation was carried out using FIB/SEM. The pit was found to grow hemispherically, and corrosion product composed by Fe, Mn, O, and S was formed on the inner wall of the pit.This study clarified that, MnS started to dissolve 0.1 V below the pitting potential. Then, elemental S was formed and concentrated in the vicinity of MnS inclusion. After elemental S concentrated enough to accelerate pit initiation, the active dissolution at the interface between MnS inclusion and steel matrix occurs rapidly to form pit. A part of elemental S deposited on the inner surface of the pit and form oxysulfide of Fe and Mn as corrosion product.

Effect of Bentonite Properties on Corrosion Behavior of Carbon Steel

Geological disposal is being considered as a disposal method for liquid waste resulting from nuclear power generation. In geological disposal, liquid waste and glass materials are melted together and solidified in an overpack (metal container), and a buffer material is compacted between the overpack and the bedrock. Carbon steel is as a candidate for overpack material and bentonite as a buffer materialin Japan. Overpack materials are required to be safe and reliable over a very long period, and their corrosion behavior and long-term corrosion resistance have been investigated before. However, most of these researches have been conducted in environments where oxygen is fully consumed, and the corrosion behavior and resistance during transient periods have not been fully clarified. In this study, the effects of bentonite properties on the corrosion behavior of carbon steel in compacted bentonite were investigated by electrochemical methods in order to clarify the corrosion behavior of carbon steel during the transient period. An iron wire grinded with sandpapers was used as the sample. The amount of bentonite was weighed to achieve the specified compacted density, and firstly approximately one-half of the amount was filled into a titanium compacted vessel. The iron wire was then set on the bentonite and the remaining bentonite was filled into the vessel using a hydraulic press. The properties of the bentonite were adjusted from 0.9 Mg/m3 to 1.8 Mg/m3 with the compaction density when packed. The titanium vessel was then immersed in a 0.1 mol/L NaCl solution and depressurized at room temperature. The solution was supplied to the cell through a filter on the side of the cell. Polarization and electrochemical impedance measurements were performed in a three-electrode system under open air. The test solution was 0.1 mol/L NaCl solution, a saturated KCl/Ag/AgCl electrode (SSE) was used as the reference electrode, and a platinum wire as the counter electrode. Polarization measurements were conducted by polarizing in the anodic and cathodic directions from the immersion potential at a scanning rate of 0.5 mV/sec. The polarization measurements of an iron wire were also performed in the same solution for comparison. Electrochemical impedance was measured at 24 and 48 hours after immersing the titanium vessel in the test solution. Polarization curve of iron wire in bentonite with a compressibility density of 1.5 Mg/m3 were compared with that in the solution. A clear diffusion-limiting current of oxygen was observed in the polarization curve of iron wire in the solution, whereas it was unclear for iron wire in bentonite. This result is attributed to the influence of water reduction reaction in a cathodic region. On the other hand, in the anodic region, the anodic current of iron in bentonite was about two orders of magnitude lower than that in the solution. This indicates that electrochemical measurements are possible in bentonite as well as in solution, but the influence of compacted bentonite is not small. Electrochemical impedance characteristic of the iron wire in bentonite with a compressive density of 1.6 Mg/m3 showed one time constant after 25 hours of immersion and two time constants after 48 hours, respectively.The diameter of the capacitive semicircles decreased with immersion time. The titanium vessel immersed for 48 hours was opened and the surface of the iron wire was visually observed. As a result, corrosion products were observed. These results suggest that the test solution penetrated into the compacted bentonite after at least 25 hours, and that corrosion progressed to form corrosion products on the electrode surface by 48 hours. Curve fitting was performed on the obtained impedance spectra, assuming the two equivalent circuits. As a result, it was confirmed that the polarization resistance at the electrode surface decreases with time.

Application of Scanning Probe Microscopy Towards Clarifying the Mechanism of Localized Corrosion

Aluminum alloys are applied to transportation equipment due to their lightweight and excellent mechanical properties, making a significant contribution to reducing CO2 emissions. In the material structure, intermetallic compounds, such as μm-order or nm-order precipitates, are formed by unavidable impurities or components added for the purpose of improving mechanical properties. On the other hand, these precipitates cause localized corrosion around themselves, which lead to the formation of large pits. Localized corrosion is well known to be caused through a mechanism where potential difference generated between the compounds and the matrix drives the formation of local battery, and intensive electrochemical reactions occur with the noble region becoming cathode and the less noble region becoming anode. However, localized corrosion behavior varies depending on potential difference changes caused by the material structure or the environment. Therefore, it is important to understand the localized corrosion mechanism in detail from the viewpoint of potential difference and environment to improve alloy's corrosion resistance.One of the useful tools for clarifying the localized corrosion mechanism is Scanning Probe Microscopy (SPM). SPM enables us to measure not only the shape of the material surface but also its physical values in various environment such as vacuum, atmosphere and liquid. For example, Kelvin probe Force Microscopy (KFM) is a technique that measures the contact potential difference between the probe and the sample surface, allowing us to measure the distribution of the potential difference on the sample surface. Open-Loop Electric Potential Microscopy (OL-EPM) is also capable of measuring the nanoscale distribution of ion concentrations in liquids and can visualize the anodic and cathodic regions during corrosion reactions, because the potential in the liquids is dependent on the cation/anion concentration occurring at the reaction interface. Thus, SPM can be used to obtain information on the potential difference of material structure and the electrochemical reaction field in a small area, which cannot be obtained by macroscopic electrochemical tests such as polarization tests.In this study, we use these SPM techniques to clarify the localized corrosion mechanism of aluminum alloys based on their material structure.

A yarn-ball-shaped graphene microsphere-coated separator design for enhanced electrochemical performance in Li-S batteries

Lithium-sulfur batteries (LSBs) present a promising alternative to conventional lithium-ion (Li-ion) batteries due to their high energy density and theoretical capacity. However, their practical application is hindered by issues such as poor sulfur utilization, highly soluble lithium polysulfides (LiPSs), and rapid capacity decay. This study introduces an innovative cell configuration using a separator coated with reduced graphene oxide/carbon nanotube (rGO/CNT) microspheres. The rGO/CNT-coated separator aims to enhance electron transfer, confine LiPSs within the cathode region, and mitigate their migration to the anode. In particular, the LSB cell with an rGO/CNT-modified separator delivers an impressive initial capacity of 1482 mAh g−1 and demonstrates a low capacity decay rate of 0.09% per cycle. The highly conductive rGO/CNT-coated separator enhances active material utilization even at high rates, resulting in a significant capacity of 824 mAh g−1 at 4C. Furthermore, the rGO/CNT-modified separator shows an impressive capacity of 895 mAh g−1 under high sulfur loading of 4.8 mg cm−2 with long-term cycling performance. The results demonstrate that the rGO/CNT-coated separator significantly enhances sulfur reutilization, reduces capacity decay, and improves the electrochemical stability of LSBs. This configuration simplifies the manufacturing process and offers a viable solution for the practical application of LSBs.

An Analysis of the Conceptual and Functional Factors Affecting the Effectiveness of Proton-Exchange Membrane Water Electrolysis

Hydrogen has the potential to decarbonize the energy and industrial sectors in the future, mainly if it is generated by water electrolysis. The proton-exchange membrane water electrolysis (PEMWE) system is regarded as a propitious technology to produce green hydrogen from water using power supplied by renewable energy sources. It offers many benefits, such as high performance, high proton conductibility, quick response, compact size, and low working temperature. Many conceptual and functional parameters influence the effectiveness of PEM, including temperature, pressure of anode and cathode regions, water content and wideness of the layer, and cathode and anode exchange current density. In addition, the anodic half-reaction (known as the oxygen evolution reaction (OER)) and cathodic half-reaction (known as the hydrogen evolution reaction (HER)) perform an important function in the development of PEMWE. The current study aims to present these parameters and discuss their impacts on the performance of PEM. Also, the PEM efficiency is presented. The different methods used to enhance the scattering of OER electrocatalysts and minimize catalyst loading to minimize the price of PEMWE are also highlighted. Moreover, the alternative noble metals that could be used as electrocatalysts in HER and OER to minimize the cost of PEM are reviewed and presented.

Experimental and zero-dimensional simulation study of an embedded bismuth LaB6 hollow cathode

Experiments and zero-dimensional simulation were conducted to evaluate the discharge performance of an embedded bismuth LaB6 hollow cathode. The experimental results demonstrate that the embedded bismuth hollow cathode can operate in diode mode without any external heating, with a mass flow rate of approximately 0.21 mg/s. In Keeper-cathode mode, the discharge voltage for bismuth was slightly lower than that of xenon and exhibited strong stability, with a maximum discharge variation of less than 0.5 V at a discharge current of 2 A. The simulation results showed that at the same mass flow rate, the electron and ion densities in the insert region of the bismuth hollow cathode were higher than those of xenon, whereas the opposite was true for the orifice region. Notably, at discharge currents below 4 A, the power deposition of bismuth in both the insert and orifice regions was lower than that of xenon, indicating reduced erosion.

Functionalization of two-dimensional vermiculite composite materials for improved adsorption and catalytic conversion reaction of soluble polysulfides in lithium-sulfur batteries

In lithium-sulfur batteries (LSBs), the limited utilization of sulfur and the sluggish kinetics of redox reaction significantly hinder their electrochemical performance, especially under high rates and high sulfur loadings. Here, we propose a novel separator structure with an interlayer composed of a vermiculite nanosheet combined with Ketjen Black (VMT@KB) for LSBs, facilitating efficient adsorption and rapid catalytic conversion toward lithium polysulfides (LiPSs). The VMT@KB nanosheets with an electrical double-layer structure and electronic conductivity are obtained through a high-temperature peeling process and Li+ exchange treatment in LiCl solution, followed by a mechanical combination process with KB. The results demonstrate that incorporating VMT@KB as an interlayer on a conventional separator enhances the conductivity and limits the LiPSs in the cathode region. The Li-S cell with VMT@KB interlayer shows satisfactory cycle and rate performance, especially in high sulfur loading. It exhibits a remarkable initial discharge capacity of 1225 mAh g−1 at 0.5 C and maintains a capacity of 816 mAh g−1 after 500 cycles. Besides, the discharge capacity remains 462 mAh g−1 even at 6 C. Moreover, the cell with high sulfur loading (8.2 mg cm−2) enables stable cycling for 100 cycles at 0.1 C with a discharge capacity of over 1000 mAh g−1.

Thermal fluctuations on the corrosion behaviour of 17-4PH stainless steel alloys fabricated via material extrusion additive manufacturing technique

Herein, the influence of fluctuating thermal conditions on the corrosion behaviour of 17-4PH stainless steel alloys manufactured via fused filament fabrication is reported. The printed samples were sintered and then exposed to different temperature-fluctuating conditions to simulate the application environment of such alloys. The first set of samples (A) was studied as-sintered, the second set of samples (B) was aged at 480°C for 3 h followed by quenching in water, the third set (C) was exposed to conditions of B followed by aging at 360°C for 3 h and quenching in water and the final set of samples (D) was exposed to conditions of C followed by aging at 200°C for 3 h, quenching in water, aging at 400°C for 3 h, and finally quenching in water. The surface roughness evolved with the temperature conditions. The optical microscopy revealed that sample B had a fine and homogenous distribution of precipitates. Sample B had the highest microhardness values followed by C, D, and A in that order. XRD analysis revealed the presence of retained FCC austenitic phases within the microstructure whose peaks became stronger with the increased thermal fluctuations. The potentiodynamic polarisation studies revealed a distinct linear Tafel region on the cathodic region and a dual-slope inflection point on the anodic region of the polarisation curves. Sample D exhibited the highest corrosion rate whereas sample B revealed the lowest. As such, exposing fused filament fabricated 17-4 PH SS to fluctuating temperature conditions leads to degradation of mechanical strength and corrosion resistance.

Local ionic transport enables selective PGM-free bipolar membrane electrode assembly

Bipolar membranes in electrochemical CO2 conversion cells enable different reaction environments in the CO2-reduction and O2-evolution compartments. Under ideal conditions, water-splitting in the bipolar membrane allows for platinum-group-metal-free anode materials and high CO2 utilizations. In practice, however, even minor unwanted ion crossover limits stability to short time periods. Here we report the vital role of managing ionic species to improve CO2 conversion efficiency while preventing acidification of the anodic compartment. Through transport modelling, we identify that an anion-exchange ionomer in the catalyst layer improves local bicarbonate availability and increasing the proton transference number in the bipolar membranes increases CO2 regeneration and limits K+ concentration in the cathode region. Through experiments, we show that a uniform local distribution of bicarbonate ions increases the accessibility of reverted CO2 to the catalyst surface, improving Faradaic efficiency and limiting current densities by twofold. Using these insights, we demonstrate a fully platinum-group-metal-free bipolar membrane electrode assembly CO2 conversion system exhibiting <1% CO2/cation crossover rates and 80-90% CO2-to-CO utilization efficiency over 150 h operation at 100 mA cm−2 without anolyte replenishment.

Effects of electrokinetic stabilization combined with addition of calcium ions on soil shear strength characteristics in the hilly granitic region of southern China

Enhancing soil shear strength is of great importance in preventing soil collapse and erosion in the hilly granitic region of southern China. However, limited studies have been conducted on improving soil shear strength in collapsing gullies. Electrokinetic stabilization (EKS) involves applying an electrical current through a soil mass to promote the migration of chemicals from injection points, thereby altering the chemical composition of the treated soil to improve its physical properties. In this study, the effects of calcium chloride (CaCl 2 ) addition and EKS techniques on the soil shear characteristics (shear strength, and its two components: cohesion and internal friction angle) of three different soil layers in collapsing gullies were investigated. The results showed that the EKS techniques significantly increased the migration of calcium ions from the anode to the cathode region of the power supply device used in the soils. Using EKS process alone did not increase or even decrease the soil shear strength, but combining EKS with CaCl 2 injection (Ca-EKS) increased the soil shear strength, and this increase was mainly due to the increasing the soil cohesion. The soil cohesion after Ca-EKS treatment increased on average by 49.84%, 83.11%, and 100.36% compared with the soil without treatments (CK) for the red soil, sandy soil, and detritus, respectively. However, soil amended by sole CaCl 2 addition, Water-EKS or Ca-EKS all can not increase soil internal friction angles compared with the CK. These results demonstrated that the application of Ca-EKS can be applied to improve the soil shear strength and stability of gully walls in hilly granitic regions.

Numerical investigations of spatiotemporal dynamics of space-charge limited collisional sheaths

Electrostatic particle-in-cell (PIC) and direct simulation Monte Carlo (DSMC) methods are used to compare the plasma dynamics of collisionless with collisional emissive sheaths in partially ionized environments. Space-charge limited emissive sheaths submersed in a plasma with a density of ∼1017 m−3 are examined using a PIC-DSMC solver, CHAOS. Collisionless emissive sheaths with plasma domains sufficiently long (30 and 60 Debye lengths, λD) are subject to strong oscillations due to two-stream electron instability, whereas emissive sheaths in weakly collisional conditions with a short domain (15 λD) exhibit self-spike (sawtooth) oscillations in the plasma field due to the trapped charge-exchange (CEX) ion population within the virtual cathode (VC) region. The two-stream electron instability leads to strong temporal fluctuations in the total emission current, with maximum deviations of 60% and 100% from the time-averaged current for the long plasma domains, whereas CEX collisions cause strong spikes in the emission current if the domain size is short. Our PIC-DSMC simulations show for the first time that the interaction of the two types of instabilities causes the strength of the self-spike to be weakened due to the strong fluctuations caused by the two-stream instability when a sufficiently long computational domain with ion-neutral collisions is employed. By conducting a two-dimensional Fast Fourier Transform (FFT) on the collisional and collisionless sheaths with long domains, we show that the transient evolution of CEX entrapment in the VC increases frequency of sheath oscillations up to two times the ion-acoustic frequencies observed in the collisionless sheath. CEX collisions weaken the VC region and result in a total emission current more than that obtained from the collisionless case for the same domain length. With a more rarefied neutral environment of 1019 m−3 in the plasma sheath, the total emission current increases only 4% in comparison with 14% for one order of magnitude denser environment, within 20 μs. In addition, the spike period is tested with different neutral temperatures and densities. While we do not observe any self-spike in the more rarefied environment, the spike period increased from 5 to 7.5 μs when the neutral temperature is increased from 300 to 2000 K in the denser environment with the simulation time of 20 μs.

Dual-mode iodine sensing: Colorimetric and electrochemical detection methods using functionalized gold nanoparticles

Iodine in natural and treated waters exists mainly as iodide, iodate, and molecular iodine (I2). I2 is a highly volatile and reactive species impacting biological and chemical systems. Iodine, a vital micronutrient, is essential for human and animal growth and metabolism. It also plays a crucial role in synthesising artificial adrenaline within the metabolic processes of humans and animals. It is also widely used as an antiseptic, disinfectant, and for emergency water disinfection. Moreover, iodine deficiency can result in various diseases, especially hypothyroidism and goitre. Given its critical functions, it is imperative to have a straightforward, dependable, and efficient method for monitoring iodine levels. This study introduces a simple and innovative I2 detection system based on its reactivity, toxicity, and role as an indicator of oxidative conditions in water. It operates in terms of based on optical and electrochemical signal changes, utilising the anti-aggregation mechanism of gold nanoparticles (AuNPs) and 6-mercaptohexanol (MHA) for sensitive and selective detection under mild conditions. I2 determination is achieved by observing the colour change in AuNPs, which is influenced by competitive interactions between MHA, I2, and AuNPs. The optical detection system, with its low detection limit (LOD=260 nM), is based on the straightforward observation of colour changes. On the other hand, the electrochemical detection method utilises changing redox peaks observed in anodic region, providing selective and sensitive I2 detection (LOD=100 nM). The probe effectively detects the presence of I2 in real water samples as a practical application. Moreover, the proposed method revolutionises I2 detection by incorporating a smartphone for signal reading, eliminating the need for specialised equipment and significantly reducing the detection cost. This cost-effective approach carries the potential to expedite on-site and naked-eye I2 detection, opening up new possibilities for research and application.

Self-powered multifunctional platform based on dual-photoelectrode for dual-mode detection and inactivation of Salmonella enteritidis

Self-powered photoelectrochemical (PEC) sensing is a novel sensing modality. The introduction of dual-mode sensing and photoelectrocatalysis in a self-powered system enables both detection and sterilization purposes. To this end, herein, a self-powered multifunctional platform for the photoelectrochemical-fluorescence (PEC-FL) detection and in-situ inactivation of Salmonella enteritidis (SE) was constructed. The platform utilized Bi4NbO8Cl/V2CTx/FTO as a photoanode and CuInS2/FTO as a photocathode and incubated quantum dot (QDs) signaling probes on the surface of the photocathode. During detection, the system drives the transfer of photogenerated electrons between the dual photoelectrodes through the Fermi energy level difference. The photoanode amplifies the photoelectric signal, while the photocathode is solely dedicated to the immune recognition process. QDs provide an additional fluorescence signal to the system. Under optimal experimental conditions, the multifunctional platform achieves detection limits of 3.2 and 5.3 CFU/mL in PEC and FL modes respectively, with a detection range of 2.91 × 102 to 2.91 × 108 CFU/mL. With the application of an external bias voltage, it further promotes electron transfer between the dual photoelectrodes, inhibits the recombination of photogenerated electrons and holes. It generates a significant amount of superoxide radicals (·O2−) in the cathodic region, resulting in strong sterilization efficiency (99%). The constructed self-powered multifunctional platform exhibits high sensitivity and sterilization efficiency, it provides a feasible and effective strategy to enhance the comprehensive capability of self-powered sensors.

Study on separation and purification of titanium alloys (TC4-6Al-4V) by molten salt electrolysis

With the widespread expansion of titanium applications and its significant increase in usage, the issue of recycling titanium resources after consumption has emerged. Focusing on titanium alloys with high usage, such as TC4 (Ti-6Al-4V), this article proposes a titanium separation and recovery method based on molten salt electrolysis. This method thoroughly analyzes the characteristics of elements in TC4 and electrochemical principles, ensuring that vanadium in the TC4 alloy does not undergo electrochemical dissolution when the electrolysis potential is below 0.3 V vs Pt. Subsequently, through electrochemical analysis, it was discovered that the precipitation of aluminum ions is influenced by concentration. Therefore, by controlling the concentration of aluminum in the eutectic molten salt, such as increasing the electrolyte concentration and shortening the electrolysis time, the precipitation of aluminum can be effectively avoided. Under the experimental conditions mentioned above, vanadium elements deposit at the bottom of the crucible in the form of anode slime, while aluminum dissolves and remains in the electrolyte. Meanwhile, titanium ions in the cathode region undergo electron reduction and deposit in the cathode area in the form of titanium, thus achieving precise separation of alloy elements. Experimental verification shows that the purity of the obtained titanium reaches 99.17 atomic percent. Therefore, this molten salt electrolysis method, which combines the physical properties of alloy elements with electrochemical principles, not only provides a new perspective for the separation and recovery of titanium and other critical metals, but also offers new research directions for the recovery technology of other alloy elements.

Recovering metallic lead from spent lead paste by slurry electrolysis

Spent lead paste, the most challenging component of discarded lead-acid batteries, contains approximately 70 % Pb. Improper handling of lead-acid battery waste poses severe risks to both the environment and human health. Here, we present a novel and short process for directly recycling metallic Pb from spent lead paste by chlorine slurry electrolysis and investigate the parameters that affect Pb recovery rate and cathodic current efficiency. Our experiments showed that under optimal conditions (250 g/L NaCl, 0.8 mol/L HCl, 10 g/L Pb2+, 30 A/m2, 40 g/L pulp concentration, 65 °C, and 12 h), the Pb recovery rate and cathodic current efficiency were, respectively, 90.54 and 85.25 %. During slurry electrolysis. Cl- combined with Pb in spent lead paste in the anode chamber, converting lead oxides and insoluble PbSO4 into soluble lead chloride complexes ([PbCl3]-, [PbCl4]2-). Driven by the electric field and concentration gradient, the lead chloride complex ions then migrated to the cathode region, where they were reduced to metallic Pb with a purity higher than 99 %. The application of this cost-effective and efficient novel method can contribute to the sustainable reuse of waste lead-acid batteries and other Pb-bearing scrap.