Rate of metallic anode oxidation in the course of electrolysis of cryolite-alumina melts. Derivation of basic equations

The well known oxidation law is offered as a basis for the new method that allowed predicting the service life of metallic anodes by extrapolation of the experimental results (time dependences of the substrate oxidation depth, oxide layer mass and its chemical composition) to a long-term period (a year). The suggested calculation technique allows predicting the steady state characterized by constant equal rates of metallic anode oxidation and erosion of its oxide layer and also the constant oxide layer thickness in the case when it features an ability to hinder further oxidation.     

Titanium-supported nickel-copper oxide catalysts for oxidation of carbon(II) oxide

Nickel-copper compositions for catalytic oxidation of carbon(II) oxide to carbon(IV) oxide were prepared by impregnation of oxide films on titanium surface, obtained by plasma electrolytic oxidation followed by annealing. Plasma electrolysis oxide coatings with a layer thickness of 5 to 50 μm were generated using different electrolytes. The compositions were studied by X-ray powder diffraction, X-ray spectral analysis, and electron microscopy, and moisture absorption of the initial plasma electrolytic structures was estimated. A linear correlation was found between the overall concentration of nickel and copper (4 to 25 mol %) in the surface layer of ∼2–5-μm compositions and their catalytic activity. The overall concentration of nickel and copper was found to increase in parallel with the moisture absorption of plasma electrolytic oxidation coatings. Nickel-copper compositions based on plasma electrolytic oxidation coatings generated in a silicate electrolyte displayed the best catalytic, mechanical, and adhesion properties.     

Electrochemical oxidation of tertiary phosphines in the presence of camphene

Anodic oxidation of tertiary phosphines (tripropyl-, tributyl-, and triphenylphosphine) in the presence of a bicyclic alkene (camphene) on a platinum and a glassy carbon electrodes was studied. For the first time the voltammetric characteristics of the process of camphene anodic oxidation were obtained. The electrochemical reactions with alkyl and aromatic phosphine were found to be dissimilar. The results of preparative electrooxidation of trialkylphosphines showed that in the course of electrolysis the tertiary phosphine cation-radicals generated on the anode enter into two concurrent reactions: (1) with the parent phosphine to form eventually trialkylphosphonium salts and trialkylphosphine oxides presumably as complex compounds and (2) with camphene to form trialkylcamphenylphosphonium salts and probably phosphonium salts with a monocyclic substituent. Preparative electrochemical oxidation of triphenylphosphine in the presence of camphene affords almost exclusively either triphenylphosphine oxide (in the experiment with platinum anode) or the triphenylphosphine oxide complex with perchloric acid (at the electrolysis on a glassy carbon anode).     

炼铝用碳阳极中碱金属氧化物作用机理的量子化学研究

本文应用CNDO/2法研究了炼铝用碳阳极中添加碱金属氧化物的吸附行为, 通过优化得到了吸附的最佳模型, 考察了吸附结合能随分子间距的变化, 进而给出了碱金属氧化物在碳阳极中作用的机理。量子化学计算结果表明: 碱金属氧化物添加到炼铝用碳阳极中起传输电子的电桥作用, 是碳阳极在空气中氧化反应以及铝电解时生成氧气的氧化反应的催化剂; 理论计算和实验结果二者吻合较好, 可以用来解释若干实验结果。     

Solid-state water electrolysis with an alkaline membrane

We report high-performance, durable alkaline membrane water electrolysis in a solid-state cell. An anion exchange membrane (AEM) and catalyst layer ionomer for hydroxide ion conduction were used without the addition of liquid electrolyte. At 50 °C, an AEM electrolysis cell using iridium oxide as the anode catalyst and Pt black as the cathode catalyst exhibited a current density of 399 mA/cm(2) at 1.80 V. We found that the durability of the AEM-based electrolysis cell could be improved by incorporating a highly durable ionomer in the catalyst layer and optimizing the water feed configuration. We demonstrated an AEM-based electrolysis cell with a lifetime of >535 h. These first-time results of water electrolysis in a solid-state membrane cell are promising for low-cost, scalable hydrogen production.     

Investigation of the synthesis and internal structure of protective oxide layers on high-purity chromium with SIMS scanning techniques

The major problem affecting the application of chromium in high temperature processes is the ongoing spallation of the protective oxide layer formed during hot-gas oxidation. This results in a continuous material erosion. To gain a deeper insight in the spallation and oxidation process, a high-purity powder-metallurgically produced chromium sample was submitted to a two-stage hot gas oxidation process. The formed oxide layers were investigated by 3D SIMS and scanning SIMS. The formation of the protective oxide layer is carried by the diffusion of chromium from the bulk through the already existing oxide layer and the reaction of the diffused chromium with the oxygen from the gaseous phase. In parallel to the growing of the oxide layer, an accumulation of impurities at the interface oxide layer – bulk can be observed. The enrichment of trace elements at the interface level (for the investigated sample Cl and N) can be explained by the low solubility of these elements in chromium oxide and therefore their inability to diffuse through the already formed protective layer. Received: 24 June 1996 / Revised: 22 January 1997 / Accepted: 26 January 1997     

Computer-aided control of electrolysis of solid Nb2O5 in molten CaCl2

Low energy production of Nb powders via computer-aided control (CAC) of two-electrode electrolysis of porous Nb2O5 pellets (ca. 1.0 g) has been successfully demonstrated in molten CaCl2 at 1123 K. It was observed that potentiostatic electrolysis of the oxide in a three-electrode cell led to a cell voltage, i.e. the potential difference between the working (cathode) and counter (anode) electrodes, that decreased to a low and stable value within 1-2 h of the potential application until the end of the electrolysis (up to 12 h in this work). The cell voltage varied closely according to the current change. The stabilised cell voltage was below 2.5 V when the cathode potential was more positive than that for the reduction of Ca2+, leading to much lower energy consumption than that of constant voltage (>3.0 V) two-electrode electrolysis, as previously reported. Using a computer to program the variation of the cell voltage of two-electrode electrolysis according to that observed in the potentiostatic three-electrode electrolysis (0.05 V vs. Ca/Ca2+), a Nb powder with ca. 3900 ppm oxygen was produced in 12 h, with the energy consumption being 37.4% less than that of constant voltage two-electrode electrolysis at 3.0 V. Transmission electron microscopy revealed thin oxide layers (4-6 nm) on individual nodular particles (1-5 microm) of the obtained Nb powder. The oxide layer was likely formed in post-electrolysis processing operations, including washing in water, and contributed largely to the oxygen content in the obtained Nb powder.     

苯酚在热氧化法制备的SnO2/Ti电极上的电氧化研究

以热氧化法制备的ＳｎＯ２／Ｔｉ电极作为阳极用于含苯酚酸性溶液的恒电流电解,测定了苯酚浓度、溶液中化学需氧量（ＣＯＤ）以及瞬时电流效率等随电解时间的变化。结果表明,用ＳｎＯ２／Ｔｉ电极代替铂作为阳极可使相同氧化电量下的ＣＯＤ明显下降,而平均电流效率提高了３倍,讨论了两种电极上苯酚氧化的反应机理。     

ToF‐SIMS studies of the oxidation of Fe by D2O vapour: comparison with XPS

The oxidation of iron (Fe) by water (D₂O) vapour at low pressures and room temperature was investigated using time‐of‐flight (ToF) SIMS. The results supported those found previously using XPS and the QUASES^? program in that a duplex oxide structure was found containing a thin outer surface hydroxide (Fe(OD)₂) layer over an inner oxide (FeO) layer. The extraordinary depth resolution of the ToF‐SIMS profiles assisted in identifying the two phases; this resolution was achieved by compensation for surface roughness. A substantial concentration of deuterium was found in the subsurface oxide layer. This observation confirmed previous assessments that the formation of FeO was from the reaction of Fe(OD)₂ with outward‐diffusing Fe, leaving deuterium as a reaction product. Copyright © 2005 John Wiley & Sons, Ltd.     

Efficient photoelectrochemical water splitting by anodically grown WO3 electrodes

The potentiostatic anodization of metallic tungsten has been investigated in different solvent/electrolyte compositions with the aim of improving the water oxidation ability of the tungsten oxide layer. In the NMF/H(2)O/NH(4)F solvent mixture, the anodization leads to highly efficient WO(3) photoanodes, which, combining spectral sensitivity, an electrochemically active surface, and improved charge-transfer kinetics, outperform, under simulated solar illumination, most of the reported nanocrystalline substrates produced by anodization in aqueous electrolytes and by sol-gel methods. The use of such electrodes results in high water electrolysis yields of between 70 and 90% in 1 M H(2)SO(4) under a potential bias of 1 V versus SCE and close to 100% in the presence of methanol.     

In situ monitoring of the H concentration change near an electrode surface through electrolysis using slab optical waveguide pH sensor

The H⁺ concentration change was monitored near an electrode surface through an electrolysis using a slab optical waveguide technique. Indium tin oxide transparent electrode modified by porous insulating polymer to which methyl red was covalently immobilized was used as a guiding layer, and the absorbance change of the polymer film was monitored. H⁺ generation at the vicinity of the electrode through the oxidation of ascorbic acid could be monitored by this technique.     

A study of aldehyde oxidation at glassy carbon,mercury, copper,silver, gold and nickel anodes

The rate, potential and mechanism of the anodic oxidation of aliphatic aldehydes have been found to be highly dependent on solution conditions and electrode material. Aldehyde oxidations in neutral acetonitrile on glassy carbon occur at very positive potentials (ca. +3 V vs. SCE) and the peak potentials correlate with the ionization potentials of the aldehydes. In aqueous base, aldehyde oxidation is assisted by reversible addition of hydroxide to the carbonyl group to form electroactive gem-diolate (II). Oxidations of aldehydes in aqueous base on Hg, Ni, Ag and Au all yield the corresponding carboxylate via two-electron oxidation plus aldol and Cannizzaro byproducts and the oxidations occur at potentials far negative of the unassisted oxidation in neutral acetonitrile. On Ni, Cu and possibly Hg the oxidation involves the formation of a metal oxide which acts as a chemical oxidizing agent. On Ag and Au the oxidations take place on a surface which is not covered by a phase oxide. A mechanism involving a direct electrochemical process with oxidation of gem-diolate adsorbed on an oxide-free metal surface is proposed. A pulsed electrolysis technique was utilized to circumvent deactivation of Ag and Au electrodes during electrolysis and preparation of an “aurized” gold surface with a much slower deactivation rate is described.     

Effects of anodic oxidation on corrosion properties of Al coating by arc spraying in seawater

A layer of Al coatings was prepared on the S355 steel by arc spraying, which was conducted by anodic oxidation treatment; the morphologies, chemical element compositions and phases of Al coating, and anodic oxide layer were analyzed with field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS) and X‐ray diffraction (XRD), respectively. The corrosion protections of Al coating before and after anodic oxidation were discussed with a seawater immersion test; the corrosion resistance mechanisms of Al coating and anodic oxide layer in the seawater were also investigated. The results show that the thickness of Al coating is about 300 µm by arc spraying, the sample surfaces become loose after seawater immersion corrosion and Cl^? and O^2? penetrate into the substrate from the cracks, destroying the binding properties of coating–substrate, and the coating fails. After anodic oxidation, the oxide layer is formed in the surface of Al coating with the thickness of about 30 µm; the corrosion products are mainly composed of Al(OH)₃, which barraged the holes caused by seawater corrosion. The corrosion cracks are formed during the corrosion, while the number and depth of cracks decrease obviously after anodic oxidation treatment. The corrosion of Al coating becomes the local corrosion after anodic oxidation treatment, and the grains are smaller, which are easily nucleated to form a new corrosion resistance layer. Copyright © 2015 John Wiley & Sons, Ltd.     

GaAs(100)表面氧化的XPS研究

X-ray photoelectron spectroscopy（XPS）was used to study two different oxidation treatments on the GaAs（100）surface———the thermal oxidation in the air,and the ultraviolet-light oxidation in the UV-ozone. A series of properties including the oxide composition,chemical states,the surface Ga/As atomic ratio and the thickness of the oxide layer grown on GaAs surface were compared. The results indicate that the oxide composition,the surface Ga / As atomic ratio and the thickness of the oxide layer oxide on GaAs surface are different for different oxidation methods. The oxides on GaAs surface grown by thermal oxidation in the air are composed of Ga2O3,As2O5,As2O3 and elemental As;and the Ga/As atomic ratio is drifted off the stoichiometry far away. The Ga/As atomic ratio of oxide layer on GaAs surface is increases with the thickness of oxide. However,the oxides on GaAs surface grown by UV-ozone are made up of only Ga2O3 and As2O3,As2O5 and elemental As are not detected,the Ga/As atomic ratio is close to unity. The thickness of oxide layer on GaAs can be controlled by the UV exposing time. The mechanism of oxidation of GaAs is also discussed. The UV-light radiation not only causes the oxygen molecular excited forming atomic oxygen,but also induces the valence electrons of the GaAs excited from the valence band,and then the reactivity of Ga and As atom increase,and they can easily react with the excited atomic oxygen at the same reactive velocity.     

SbOx+SnO2中间层对Ti/MnO2电极性能的影响

采用热分解方法制备了含SbO_x+SnO₂中间层的钛基二氧化锰电极. 在0.5 mol·L^-1 H₂SO₄溶液中对添加和没有添加SbO_x+SnO₂中间层的二氧化锰阳极进行了加速电解试验. 采用极化曲线和循环伏安曲线测量电极的析氯反应. 用循环伏安曲线和电化学阻抗谱来分析电极电解过程中内部结构和表面的变化. 结果表明, 二氧化锰阳极钝化失效的主要原因是绝缘的TiO₂层的生成和变厚. 引入中间层可以降低钛基体和活性涂层间的电阻, 并且在电解过程中, 可以显著延缓接触电阻的升高, 从而可以显著提高其寿命.     

Indirect Electrochemical Oxidation of 4-Amino-dimethyl-aniline Hydrochloride

Introduction4Amino dimethyl anilinehydrochlorideisoneof themaincomponentsofthewastewaterresultedfrom vanillinproduction[1]whichinhibitsthenormalactivity ofthemicroorganismsofmicrobialpopulation,thereby affectingthebiologicaltreatmentprocessofvanillin.Comm…     

Rapid quantitative analysis of fayalite and silica formed during decarburization of electrical steel

Subscales on surfaces are affected by the temperature and oxidation potential during decarburization annealing of electrical steel containing 3 wt% silicon. Knowledge of the structural and chemical properties of the surface oxide layer subscales permits the control of high‐temperature oxidation processes in the electrical steel. In the present work, the oxide layers were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectrometry, and glow discharge optical emission spectrometry (GD‐OES). The main oxide compounds formed within the subscales during decarburization annealing of the electrical steel were fayalite (Fe₂SiO₄) and silica (SiO₂). The fayalite and silica contents were quantitatively determined by wet analysis via the galvanostatic electrolysis method, and these oxide content measurements were compared with the fayalite content determined by FTIR spectrometry and the silica determined by GD‐OES. The results determined by rapid methods and wet analysis showed good agreement. The present findings show that FTIR spectrometry and GD‐OES measurements may be used for the rapid quantitative analysis of fayalite and silica in surface oxide layers during the manufacture of electrical steel. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of oxidation pretreatment temperature on Kovar used as CO_2 reforming catalyst

The effect of oxidation pretreatment temperature(500 ~ 1 000 ℃) on the catalytic activity of Kovar applied on hydrocarbon CO2reforming was examined. Catalytic performance evaluation using tetradecane at 800 ℃ with 70 μmol/s CO2revealed 700 and 1 000 ℃ as the best pre-oxidation temperature in producing CO and H2,respectively. XRD and SEM-EDX analyses showed that a separate metal oxide layer composed of iron oxide(Fe2O3and F3O4),nickel,cobalt,and possibly their respective oxides started to form when oxidation was conducted at 700 ℃ or higher.The presence of iron enhanced the stability of nickel in the structure while the compact structure of Fe3O4resulted into the formation of a thick and rigid metal oxide layer on the surface of the Kovar tube. The strong physical bond between the metal oxide layer and Kovar tube provided the catalyst good mechanical strength and consequently good catalytic activity.     

Isothermal oxidation behavior of a thermal barrier coating prepared using EB‐PVD

A novel two‐layer structural thermal barrier coating (TBC) system with a ~150‐µm‐thick CoCrAlY bond coat (BC) and a ~60‐µm‐thick yttria stabilized zirconia (YSZ) ceramic top coat (TC) was prepared on superalloy K444 matrix using electron beam physical vapor deposition (EB‐PVD). This deposited coating was characterized using isothermal oxidation tests (1000 °C × 200 h). The results indicated that the deposited coating had a dense structure and close bonding between the layers. The thermally grown oxide (TGO) layer (predominantly alumina) that formed at the interface between the TC and the BC as a consequence of the oxidation process was effective in preventing the further oxidation of the BC. In the later stages of the oxidation process, embedded oxides of chromium/cobalt were observed among the TC's columnar grains, and the TGO underwent densification thinning. Through observations of the growth behavior of the TGO, the element diffusion, displacement reaction, and volatilization of the oxides were found to be related to the weight loss in the coating and the densification thinning of the TGO. These coatings displayed superior high‐temperature oxidation resistance properties. Copyright © 2014 John Wiley & Sons, Ltd.     

Electrochemical oxidation of 2-thiouracil at pyrolytic graphite electrode

2-Thiouracil has been studied in phosphate buffers of pH 1.95-11.08 using linear and cyclic sweep voltammetry, coulometry, controlled potential electrolysis and spectral studies. One well-defined oxidation peak I(a) in the pH range 1.95-11.08 was noticed. The number of electrons involved in peak I(a) was found to be four in a thin layer cell whereas under exhaustive electrolysis condition oxidation was found to involve six electrons. A reduction peak II(c) (2e, 2H(+)) is noticed in the reverse sweep. Spectral studies during oxidation were carried out at different pH. Kinetic studies indicated that the decay of the UV-absorbing intermediate is a first order reaction. The products of the electrooxidation have been characterized and a tentative EC mechanism has been suggested for the oxidation of 2-thiouracil.