Mechanism Of Anodic Oxidation Research Articles

Effects of sealing and prior shot peening treatments on fatigue behavior of sulphuric acid anodic oxidation coated 6082-T6 aluminium alloy

In this study, the effects of sealing and prior shot peening treatments on the fatigue behavior of the sulphuric acid anodic oxidation coated 6082-T6 aluminium alloy were investigated. Experimental results indicate that the preferential fracture of anodic oxidation coatings due to its higher brittleness and lower fracture toughness as well as the stress concentration of near-interface substrate caused by the interface cyclic dislocation accumulation could cause the fatigue failure of anodic oxidation coated specimens. Consequently, the fatigue property of anodic oxidation coated specimens notably decreases compared to as-machined specimens, with a decrease of 26.7 % in the fatigue limit corresponding to 2 × 107 fatigue cycles. Additionally, the sealing treatment introduces numerous cracks that penetrate the coating entirely, diminishing the coating's resistance to cracking under fatigue loading; this alteration changes the fatigue failure mechanism of anodic oxidation coated specimens, ultimately resulting in a decrease of 15.5 % in the fatigue limit of anodic oxidation coated specimens. Despite exacerbating the surface integrity and increasing the surface roughness of anodic oxidation coated specimens, the prior shot peening treatment increases the fatigue limit of anodic oxidation coated specimens by 82.8 % since the affecting layer beneath the interface plays a crucial role in inhibiting the further propagation of coating cracks into the substrate as well as the crack propagation in the substrate beneath the interface.

Electrolyte pH and operating potential: critical factors regulating the anodic oxidation and zinc storage mechanisms in aqueous zinc ion battery

The complicated multi-electron reactions and electrochemical/chemical evolution of vanadium oxides in zinc ion batteries make the detailed reaction mechanism difficult to understand. Here, we show that these reactions can be easily interpreted from the reliable potential–V-species (electrochemical) and pH–V-species (chemical) relationships. A systematic investigation of several low-valence vanadium oxides (V6O13, VO2, and V2O3) is conducted to study the detailed reaction mechanisms upon the anodic oxidation and routine zinc storage process. Vanadium oxides are thermodynamically converted to layered zinc pyrovanadate Zn3V2O7(OH)2·2H2O (ZVOH) in a certain range of pH (4.0–8.5) and operating potential following the VOx oxidation →V-species dissolution →ZVOH precipitation processes. The establishment of pH–V-species and potential–V-species relationships can well explain the reaction mechanisms not only in anodic oxidation but also in routine zinc insertion/extraction processes with the combination of electrochemical and chemical reactions. Moreover, due to the favorable open and stable crystal framework and unique Zn2+ storage mechanism, the obtained ZVOH exhibits a highly improved capacity of 492.7 mAh/g within the voltage window of 0.3–1.4 V. Our work highlights the critical roles of operating potential and electrolyte pH in zinc ion battery and offers new knowledge and practices for its commercialization.

17β-estradiol (E2) removal in anode-electrodialysis (anode-ED) during nutrient recovery from pig manure digestate

Nutrient recovery from anaerobic digestate through electrodialysis technology (ED) has been investigated and shown high promise, but the removal of 17β-estradiol (E2), which is a natural estrogen and widely found in manure digestate, is not clear. This study examined the mechanism of membrane adsorption and anodic oxidation of E2 during recovering nutrient from manure digestate, and further investigated the performance of Anode-ED in E2 removal. The results showed that the removal of E2 in conventional ED was primarily attributed to membrane adsorption, resulting in no detectable E2 in the product solution. The adsorption capacity of the anion exchange membrane for E2 was significantly higher compared to that of the cation exchange membrane. During Anode-ED operation, E2 was efficiently removed by electrochemical oxidation, in which the chlorination played a primary role. Moreover, the oxidation intermediates of E2 were further removed after 40 min. Even though the carbonate, volatile fatty acid (VFA), and humic acid in the real wastewater have a negative impact on E2 oxidation, the E2 was completely removed from digestate during nutrient recovery in the anode-ED. This study indicates that anode-ED is a promising technology for the removal of E2 during nutrient recovery from digestate.

Metal‐Free Electrocatalytic Diacetoxylation of Alkenes

Abstract1,2‐Dioxygenation of alkenes leads to a structural motif ubiquitous in organic synthons, natural products and active pharmaceutical ingredients. Straightforward and green synthesis protocols starting from abundant raw materials are required for facile and sustainable access to these crucial moieties. Especially industrially abundant aliphatic alkenes have proven to be arduous substrates in sustainable 1,2‐dioxygenation methods. Here, we report a highly efficient electrocatalytic diacetoxylation of alkenes under ambient conditions using a simple iodobenzene mediator and acetic acid as both the solvent and an atom‐efficient reactant. This transition metal‐free method is applicable to a wide range of alkenes, even challenging feedstock alkenes such as ethylene and propylene, with a broad functional group tolerance and excellent faradaic efficiencies up to 87 %. In addition, this protocol can be extrapolated to alkenoic acids, resulting in cyclization of the starting materials to valuable lactone derivatives. With aromatic alkenes, a competing mechanism of direct anodic oxidation exists which enables reaction under catalyst‐free conditions. The synthetic method is extensively investigated with cyclic voltammetry.

Metal-Free Electrocatalytic Diacetoxylation of Alkenes.

1,2-Dioxygenation of alkenes leads to a structural motif ubiquitous in organic synthons, natural products and active pharmaceutical ingredients. Straightforward and green synthesis protocols starting from abundant raw materials are required for facile and sustainable access to these crucial moieties. Especially industrially abundant aliphatic alkenes have proven to be arduous substrates in sustainable 1,2-dioxygenation methods. Here, we report a highly efficient electrocatalytic diacetoxylation of alkenes under ambient conditions using a simple iodobenzene mediator and acetic acid as both the solvent and an atom-efficient reactant. This transition metal-free method is applicable to a wide range of alkenes, even challenging feedstock alkenes such as ethylene and propylene, with a broad functional group tolerance and excellent faradaic efficiencies up to 87 %. In addition, this protocol can be extrapolated to alkenoic acids, resulting in cyclization of the starting materials to valuable lactone derivatives. With aromatic alkenes, a competing mechanism of direct anodic oxidation exists which enables reaction under catalyst-free conditions. The synthetic method is extensively investigated with cyclic voltammetry.

Slurryless electrochemical mechanical polishing of 4-inch 4H–SiC (0001) and (000–1) surfaces

Silicon carbide (SiC) is a very promising next-generation semiconductor material for power device applications, and polishing technology plays an important role in improving the performance of electronics. In this regard, slurryless electrochemical mechanical polishing (ECMP) is a promising polishing technology for SiC wafer in obtaining high efficiency and high precision. In this study, slurryless ECMP of 4-inch 4H–SiC (0001) and (000–1) surfaces (Si and C faces) were investigated aiming to the industrial application. Anodic oxidation property, polishing characteristics, and mechanism of the Si and C faces in slurryless ECMP were compared and clarified. Based on the obtained results, two-step slurryless ECMP (i.e., ECMP with diamond polishing plate and then with ceria polishing plate) was conducted on 4-inch as-sliced Si and C faces. Additionally, 4-inch Si and C faces with peak-to-valley (PV) value less than 2 μm and overall surface roughness in nanometer order were obtained.

Efficient ammonia removal promoted in a bifunctional system constructed with NiCu–S/DSA electrodes

Currently, the treatment of ammonia in wastewater, one of the main causes of eutrophication in water bodies, has received widespread attention. In this work, a novel electrocatalytic bifunctional system was constructed to achieve efficient degradation of ammonia. It consists of Ni1Cu0.25-S/DSA electrodes with both anode and cathode, which is prepared by a combination of electrodeposition and electrochemical tuning strategies. The crystalline phases and oxidation states of the nano-textured particulate metal oxides were determined by using a series of physical characterizations. The Ni1Cu0.25-S/DSA electrode with the best electrocatalytic performance was screened by electrochemical analysis, which has good stability and reliability when processing ammonia nitrogen. The efficiency of electrodes for ammonia removal was verified by running denitrification of synthetic and real wastewater. The results showed that the NH4+-N removal efficiency could approach up to 99%. Kinetically, compared with the monofunctional system, the bifunctional system obtained a higher NH4+-N degradation rate of 45.5 mg L−1 h−1, increased the rate of N2 generation by more than 10 times, and reduced the rate of NO3−-N and NO2−-N generation by one-third on average. The possible reaction mechanism of anodic ammonia oxidation and cathodic nitrate reduction in the bifunctional system was proposed.

Nanotubular TiO x N y -Supported Ir Single Atoms and Clusters as Thin-Film Electrocatalysts for Oxygen Evolution in Acid Media.

A versatile approach to the production of cluster- and single atom-based thin-film electrode composites is presented. The developed TiO x N y -Ir catalyst was prepared from sputtered Ti-Ir alloy constituted of 0.8 ± 0.2 at % Ir in α-Ti solid solution. The Ti-Ir solid solution on the Ti metal foil substrate was anodically oxidized to form amorphous TiO2-Ir and later subjected to heat treatment in air and in ammonia to prepare the final catalyst. Detailed morphological, structural, compositional, and electrochemical characterization revealed a nanoporous film with Ir single atoms and clusters that are present throughout the entire film thickness and concentrated at the Ti/TiO x N y -Ir interface as a result of the anodic oxidation mechanism. The developed TiO x N y -Ir catalyst exhibits very high oxygen evolution reaction activity in 0.1 M HClO4, reaching 1460 A g-1 Ir at 1.6 V vs reference hydrogen electrode. The new preparation concept of single atom- and cluster-based thin-film catalysts has wide potential applications in electrocatalysis and beyond. In the present paper, a detailed description of the new and unique method and a high-performance thin film catalyst are provided along with directions for the future development of high-performance cluster and single-atom catalysts prepared from solid solutions.

Anodic behaviour of manganese germanide Mn5Ge3 in a sodium sulphate aqueous solution

Germanides are an interesting class of two-component systems which consist of metal and germanium. They are similar in their structure with silicides but have the specific properties. The target of the investigation was finding the main anodic electrochemical behaviour mechanisms for magnesium germanide Mn5Ge3 in an Na2SO4 aqueous solution.Electrochemical behaviour of manganese germanide obtained by Czochralski method was investigated by polarization curves and electrochemical impedance spectroscopy methods and accomplished by microscopy data. Individual manganese and germanium were investigated in the same way for comparison. It was established that in the anodic oxidation process germanium is the potential-determining component. The passivation process associated with the formation of surface oxide films was accomplished by the current density oscillations appearing due to the bad adhesion of oxide film to the surface of the sample, its imperfection and discontinuity. The nature of oxide film formed in the polarization process waspartially established. The dependence of the anodic behaviour of the sample on the sulphate concentration was established: in the diluted solutions the passivation occurs at more positive potentials than in the concentrated. This phenomenon can be explained by the different mechanisms of anodic oxidation in the solutions of different concentrations.

Corrosion Resistance and Formation Mechanism of Anodic Oxidation–Organic Structure Super‐Hydrophobic Self‐Assembled Film

AbstractIn this article, the perfluorooctyltriethoxysilane (POTS) is used as a low surface energy substance to self‐assemble in Al2O3 surface to prepare a corrosion‐resistant composite film by anodization and self‐assembly technology. The morphology, structure, wettability, and chemical composition of the composite film are characterized by scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, water contact angle, and X‐ray photoelectron spectroscopy. The corrosion resistance of the composite film is tested through electrochemical test and the neutral salt spray test, and various pollution simulations are performed to test the self‐cleaning performance of the film. The formation mechanism of the film is discussed by quantum chemical calculations. The results show that compared with Al alloy, the AC impedance of the composite film is increased by five orders of magnitude, the corrosion current density is reduced by three orders of magnitude, and the neutral salt spray corrosion test reaches 31 days. Meanwhile, theoretical studies of quantum chemical calculations show that Al2O3/POTS film is adsorbed on the surface of Al alloys through SiOAl chemical bonds. This work puts forward scientific viewpoints and novel design concepts to create effective anti‐corrosion coatings to protect Al alloys, and then expand its potential applications in other fields.

Dominant factors and their action mechanisms on material removal rate in electrochemical mechanical polishing of 4H-SiC (0001) surface

Slurryless electrochemical mechanical polishing (ECMP) has been confirmed as a highly efficient damage-free polishing technique for SiC wafers. To increase the material removal rate of ECMP, it is essential to have a better understanding of the anodic oxidation mechanism of SiC to obtain a much higher anodic oxidation rate. In this study, we investigated the effects of electrolyte temperature, surface damage, doping concentration, and strain on the anodic oxidation rate of SiC. All these factors were found have a promotional effect on the anodic oxidation of SiC. The promotional effects of processing-induced damage and doping on SiC anodic oxidation were attributed to the processing-induced residual strain and doping-induced strain on the SiC surface, which were observed by Raman spectroscopy. The relationship between anodic oxidation rate and strain on the SiC surface was quantitatively investigated by applying a strain-controllable anodic oxidation device. Both compressive and tensile strains were found to increase the anodic oxidation rate of SiC. The promotion mechanism of the strain on the anodic oxidation of SiC was studied by conductive atomic force microscopy observations. This study is expected to be an important guide for improving the efficiency of ECMP and will contribute to the practical application of ECMP.

Anodic oxidation for the degradation of organic pollutants: Anode materials, operating conditions and mechanisms. A mini review

Organic pollutants in domestic sewage, agricultural runoff, industrial wastewater, and contaminated land pose a serious threat to human beings as well as to ecosystems. Anodic oxidation is one of the technologies most commonly used for the degradation of organic pollutants. In this review, we present the current status of promising anodic oxidation technologies for the degradation of organic pollutants, with fundamental insights into anode materials, operating conditions and mechanisms. Firstly, anodes based on metallic Pt, metal oxides (RuO2, IrO2, PbO2 and SnO2), and carbon (BDD and others) are critically reviewed. Secondly, strategies for the effective removal of organic pollutants in wastewater under appropriate operating conditions are systematically investigated. Thirdly, the anodic oxidation mechanism is comprehensively summarized with illustrations of how the organic pollutants can be broken down into small molecules of low or zero toxicity. Finally, we conclude with some future perspectives for application of anodic oxidation.

Similarity in the Kinetics and Mechanisms of Galvanostatic Anodic Oxidation of Silicon, Silicon Carbide, and Nitride

It is shown that the formation of anodic oxides in the galvanostatic mode of electrolytic anodizing of Si, SiC, and Si3N4 proceeds with the activation control of the process. It is suggested that the limiting stage of the oxidation process of these materials is the anodic reaction of the formation of intermediate monoxide SiO.

Degradation of methylisothiazolinone biocide using a carbon fiber felt-based flow-through electrode system (FES) via anodic oxidation

Methylisothiazolinone (MIT) is one of the most widely used non-oxidizing biocides, however its toxicity may pose a threat to ecosystems. A carbon fiber felt-based flow-through electrode system was used for MIT degradation in an aqueous solution. An excellent degradation rate (~90%) was achieved at a low applied cell voltage (2.5 V) and a high feed water flux (3 m3 h−1 m−2) that corresponds to a short resistance time of ~11 s. In-situ sampling experiments and electrochemical characterization indicated that MIT was degraded via a direct anodic oxidation mechanism. In terms of electrode sequence, anode–cathode system (by placing the anode upstream from the cathode) exhibited an improved MIT degradation performance and energy efficiency compared with a reversed cathode–anode system (by placing the anode downstream from the cathode), because the former arrangement prevented parasitic reactions and provided a higher anode potential. Effluent analysis by time-of-flight mass spectrometry and luminescent bacteria acute toxicity showed that the organic sulfur atom was oxidized to the sulfoxide or sulfone structure and then hydrolyzed to release from the MIT molecule, which led to a significant toxicity reduction. No obvious performance loss was observed over 5 h of continuous operation with a total treated MIT solution up to 1400 times the cell volume and an energy requirement of 0.03 kWh m−3. These promising data make the carbon fiber felt-based flow-through electrode system attractive for effective and low-cost water purification.

Anodic Processes at Smooth Platinum Electrode in Concentrated Solution of Methanesulfonic Acid

Some features of processes occurring during the polarization of smooth platinum electrode in 10.0 M methanesulfonic acid (CH3SO3H) solution at high anodic potentials are studied by the cyclic voltammetry method. On cyclic voltammograms of smooth platinum electrode in concentrated methanesulfonic acid solution, well-pronounced oxidation waves are observed at potentials E = 2.0–2.5 V and E = 2.9–3.7 V. The electrochemical processes occurring in 10 M CH3SO3H solution within the E = 2.0–2.5 V potential range are shown to be associated with discharge of water molecules; the broad oxidation wave within the potential range of E = 2.9–3.7 V is related to the formation of peroxide compounds. Based on the electrochemical measurements and analysis of products of preparative electrooxidative electrolysis, the formation of a complex organosulfur peroxide compound, bis(methanesulfonyl) peroxide CH3S(O)2OOS(O)2CH3 (other names: dimethyl disulfoperoxide, or dimethanesulfonyl peroxide, or dimesylate peroxide) is established. Anodic oxidation mechanism in concentrated CH3SO3H solutions is proposed. It is supposed that the formation of the peroxide compound is associated with the participation of mesylate-radicals that dimerize at the smooth platinum anode and then are desorbed into the solution bulk.

The complex fingerprint of vancomycin using electrochemical methods and mass spectrometry

Vancomycin (VAN) is a glycopeptide antibiotic, active against Gram-positive bacteria resistant to other antibiotics. VAN therefore needs to be monitored for maximum efficacy and minimum toxicity. Electrochemical sensors can be used for this purpose, using the direct electrochemical signal of VAN. Due to its molecular complexity and the need for analysis from complex matrices, the electrochemical detection of VAN requires the development of a complex electrochemical fingerprint (CEF), which covers a large variety of possible combinations of samples and interferents at concentrations of interest.The objective of this study was to develop a CEF for VAN, involving a battery of tests and the elucidation of the mechanism of anodic oxidation of VAN, using high-performance liquid chromatography coupled with mass-spectrometric analysis of the products obtained after small-scale electrolysis.A CEF for VAN was obtained, describing the electrochemical behavior of VAN at different commercially available screen-printed electrodes, with several electrolytes, considering successive analyses, after simple pretreatments, and examining both anodic and cathodic peaks. The concept was successfully applied to analysis of VAN in real samples and in the presence of some common interferents. Furthermore, a two-step combined electrochemical–chemical mechanism was proposed for the electrooxidation of VAN.

Commonality of Kinetics and Mechanisms of Galvanostatic Anodic Oxidation of Silicon, Carbide, and Silicon Nitride

Commonality of Kinetics and Mechanisms of Galvanostatic Anodic Oxidation of Silicon, Carbide, and Silicon Nitride

Removal of Methylene Blue by Direct Electrochemical Oxidation Method Using a Graphite Anode

The present work is to degrade methylene blue dye from aqueous solution by direct electrochemical oxidation technique. For this purpose an electrochemical cell was used comprising of two electrodes made from graphite as anode and stainless steel 316 grade as cathode. Different operating parameters that affected the treatment process such as current density, electrolyte temperature and initial dye concentration had also been studied. The reaction mechanism of direct anodic oxidation of M.B. is undertaken and the kinetic follows a pseudo first order reaction. Results revealed that at 20ºC electrolyte temperature, 10 mA/cm2 current density, 0.5 g/l Na2SO4 as supporting electrolyte and 60 min electrolysis time, the decolorization percents for initial concentrations of M.B. 50 and 400 mg/L were 72.51% and 77.94% respectively while at 60ºC the decolorization percent 99.75% and 99.60% respectively for the same others operating conditions. The power consumption increased from 2.055 to 11.714 Kw.h/m3 at applied voltage 14.6 V and 28.5 V respectively.

Investigation of anodic oxidation mechanism of 4H-SiC (0001) for electrochemical mechanical polishing

In an attempt to realize the high-quality and highly efficient polishing of SiC, the anodic oxidation mechanism of SiC was studied to enable the application of electrochemical mechanical polishing (ECMP). Through linear scanning voltammetry (LSV) and anodic oxidation experiments, the etch pits on the processed surface were found to be generated by oxidation on the sites where breakdown occurs in the anodic oxidation process. The origin of the etch pits was investigated through observing the same area on a SiC substrate during the oxidation process using atomic force microscopy (AFM), and they were confirmed to be atomic-scale pits mechanically introduced in the chemical mechanical polishing (CMP) process. The Deal-Grove model was used to model the growth process of the etch pits. It was found that their growth is controlled by a charge transfer process in the initial growth stage, which changes to a diffusion process in the late growth stage. The results of this research provide a reference for obtaining atomically smooth SiC surfaces by applying ECMP.

Heterojunction between anodic TiO2/g-C3N4 and cathodic WO3/W nano-catalysts for coupled pollutant removal in a self-biased system

An anodic TiO2/g-C3N4 hetero-junction and cathodic WO3/W were used to build a self-sustained catalytic fuel cell system for oxidizing rhodamine B or triclosan and reducing NO3−-N to N2 simultaneously. The WO3 nano-catalyst was formed in situ by heating and oxidizing a tungsten wire in air. Cyclic voltammetry and current-time curves were used to characterize the electrochemical properties of the electrodes and system. Aeration and activation of molecular oxygen by self-biased TiO2/g-C3N4 led to the formation of reactive oxidizing species in the fuel cell. The mechanism of simultaneous anodic oxidation of pollutants and cathodic reduction of nitrate was proposed. The spontaneously formed circuit and tiny current were used simultaneously in treating two kinds of wastewater in the reactor chambers, even without light illumination or an external applied voltage. This new catalytic pollution control route can lower energy consumption and degrade many other kinds of pollutants.