Bildungsgeschwindigkeit kathodisch erzeugter Hydroxid-Deckschichten

Rate of formation of cathodically produced hydroxide surface layers The cathodic hydrogen evolution shifts the pH values in the vicinity of the electrode to ward higher values. If a metal ion is present in the solution and if the pH shift results in a condition where the solubility product of the metal oxide or hydroxide respectively is attained at the electrode surface a further current density increase may give rise to the precipitation of the metal hydroxide which then forms a suface layer on the electrode. The rate of formation of such layers is assessed whereby it is presumed that the rate controlling step is exclusively the transport of the ions taking part in the reactions. Tracing current density overtension curves and weighing the surface layers formed enables the rate of formation to be measured as a function of current density, pH value, metal ion concentration and diffusion layer thickness. The results obtained for layers of Ni(OH)₂, Cd(OH)₂, Co(OH)₂, Zn(OH)₂, Mg(OH)₂, Ce(OH)₃ and La(OH)₃ are in good agreement with theoretical considerations. In the case of the formation of Al(OH)₃ layers it is necessary to take account of the contribution to charge transport by aluminium ions dissolved in the form of hydroxo-complexes.     

α-Ni(OH)2 electrodeposition from NiCl2 solution

α-Ni(OH)₂ was synthesized from a NiCl₂ solution by electrodeposition method. In order to conduct a systematic study on the effects of experimental parameters, a series of electrolyte initial pH values, current densities, electrodeposition temperatures, and electrodeposition time were used. Cyclic voltammetry results demonstrated a side reaction of Ni²⁺+2e→Ni. The X-ray diffraction analysis, Fourier-transform infrared spectrum, and the color of the product showed that pure α-Ni(OH)₂ could be obtained in the initial pH value range of 2–5.86, current density range of 10–25 mA/cm² electrodeposition temperature range of 25–35 °C, and electrodeposition time range of 1.0–3.0 h. When electrodeposition temperature increased to 45 °C, a mixture of α-Ni(OH)₂ and metallic Ni was obtained. A current density higher than 30 mA/cm² resulted in the sample with features of β-Ni(OH)₂. A small amount of metallic Ni existed in the as-prepared sample when current density decreased to 5 mA/cm². A slight increase of electrolyte pH was observed with increasing initial solution pH and current density. Electrodeposition mass revealed a slight decrease with initial pH decreasing and showed an almost linear increase with current density increasing. The slope of the curve for electrodeposition mass versus electrodeposition time remained stable in the first 2.0 h and then decreased.     

Measurement of the resistivity of the electrode NiOOH/Ni(OH)<Subscript>2</Subscript> solid phase active substance during the discharge process

The quantitative relation between the resistivity of the solid phase active substance NiOOH/Ni(OH)₂ and its bulk resistivity, which can be measured experimentally according to the potential jump when the current is switched on, is established with the simplified mathematical model of a thin porous electrode with a solid phase reagent. The dynamics of the resistivity of the NiOOH/Ni(OH)₂ particles in the course of the discharge is ascertained with the help of the proposed method.     

Electrochemical performance of multiphase nickel hydroxide

The high density nano-crystalline multiphase nickel hydroxide containing at least three doping elements was synthesized and its electrochemical characteristics were studied. The electrochemical behavior of the high density spherical multiphases α-Ni（OH）2 were also investigated. The results show that the structure of the material is a mixed phase of α-Ni（OH）2 and β-Ni（OH）2, which has a the same stabilized structure as α-Ni（OH）2 during long-term charge/discharge process. High density spherical multiphases α-Ni（OH）2 have a much better redox reversibility, a much lower oxidation potential of Ni（ Ⅱ） than the corresponding oxidation state in the case of β-Ni（OH）2, and a much higher reduction potential. They exchange one electron during electrochemical reaction and have a higher proton diffusion coefficient. The mechanism of the electrode reaction is proton diffusion, and the proton diffusion coefficient is 5.67×10^-10 cm^2/s. Moreover, they reveal a higher discharge capacity than β-Ni（OH）2/β-NiOOH because they exchange one electron per nickel atom during charge/discharge process.     

Regeneration and decontamination of a nickel citrate complex in spent electroless nickel plating solutions

The possibility of citrate precipitation by excess metal ions in alkaline solutions suggests the use of Ni(II) together with OH^? to precipitate a Ni(II)-citrate complex from spent electroless plating solutions. After treatment of the precipitate with acid, excess Ni(II) can be removed in the form of insoluble Ni(OH)₂. The solution of the Ni(II)-citrate complex can then be reused for electroless nickel plating. During this procedure the additive adipate is not regenerated. For decontamination of spent electroless nickel plating solutions Fe(III) can be used as Ni(II)-citrate complex precipitant.     

B参杂对NiO/Ni(OH)2电极材料电容性能的影响

通过化学镀再电化学氧化的方法在铜片表面制备出带有微米微坑和微米微球的均一NiO/Ni(OH)₂和B参杂的NiO/Ni(OH)₂(B)两种电极材料,采用扫描电镜(SEM/EDX)、X射线衍射(XRD)、X射线光电子能谱(XPS)和电化学技术对所制备的两种电极材料进行表征和电化学性能测试。SEM、XRD和XPS的测试结果表明, 所制备的两种电极材料由Ni、NiO和Ni(OH)₂组成,并且NiO/Ni(OH)₂(B)中B的参杂量可达14.6wt%。循环伏安测量和恒电流充放电试验表明,两种电极材料均具有较高的电化学活性和可逆性;在1 A/g的充放电电流密度下, 两种NiO/Ni(OH)₂和NiO/Ni(OH)₂(B)电极材料经历10000次充放电循环后分别给出了1380 和1930F/g的比电容, 显示出较高的比电容特性和良好的电化学稳定性;电化学阻抗谱表明NiO/Ni(OH)₂(B)电极材料较NiO/Ni(OH)₂电化学反应电阻降低了约2个数量级;Ragone曲线揭示了所制备的两种电极材料具有较高的功率密度和较低的能量密度。B的参杂使得NiO/Ni(OH)₂(B)电极材料表面氧化物含量增大并且形成微米微球形貌,增大了电极表面积以及与电解液的接触和润湿作用,降低了电极材料表面能带带隙能,从而导致较小的电化学反应电阻和电导率的提高是其显示优异赝电容性能的主要原因。     

Ni（OH）2 particles synthesized by high energy ball milling

1 Introduction Ni(OH)2/NiOOH has been used as positive materials in alkaline secondary batteries for more than 100 years[1- 3]. The performance improvement of Ni(OH)2/NiOOH electrode is crucial for the application of these batteries as they are all positi…     

In-situ hydrothermal synthesis of Ni–MoO2 heterostructure on porous bulk NiMo alloy for efficient hydrogen evolution reaction

The Ni–MoO₂ heterostructure was synthesized in suit on porous bulk NiMo alloy by a facile powder metallurgy and hydrothermal method. The results of field emission scanning electron microscopy (SEM), field emission transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) reveal that the as-prepared electrode possesses the heterostructure and a layer of Ni(OH)₂ nanosheets is formed on the surface of Ni–MoO₂ electrode simultaneously after hydrothermal treatment, which provides abundant interface and much active sites, as well as much active specific surface area. The results of hydrogen evolution reaction indicate that the Ni–MoO₂ heterostructure electrode exhibits excellent catalytic performance, requiring only 41 mV overpotential to reach the current density of 10 mA/cm². It also possesses a small Tafel slope of 52.7 mV/dec and long-term stability of electrolysis in alkaline medium.     

Das Korrosionsverhalten von sauerstoffionenimplantiertem Magnesium in schwach saurem Elektrolyten

The corrosion behaviour of oxygen implanted magnesium in weekly acid solution Under atmospheric conditions magnesium forms oxide layers which consist mainly of magnesium hydroxide. The protective action of Mg(OH)₂ is minor in sulphate‐, carbonate‐ or chloride containing solutions [2, 18]. Additionally, the crystallographic misfit between magnesium and magnesium hydroxide leads to crack formations inside the hydroxide layer and the metallic surface is then exposed. By using the ion implantation of oxygen (1*10¹⁸ O⁺/cm²) a MgO‐layer can be formed and buried within the bulk metal. Pre‐tests of MgO‐layers produced by ion implantation suggest that it is successful as corrosion protection [17]. Crystallographic stresses between metal‐ and oxide phase will be reduced, depending on the gradient of oxygen concentration. The investigation in weekly acid sodium solution shows, that the oxygen ion implantation leads to a significant improvement in the corrosion behaviour of magnesium.     

Entstehung und Aufbau farbiger schichten auf rostfreiem stahl: I. Verfärbungen beim Kochen von Nahrungsmitteln

Formation and structure of coloured layers on stainless steel: I. Discolorations by cooking of food Upon cooking of vegetables and other food coloured layers can be formed on stainless steel. By cooking tests, AES-studies of the formed layers and by electrochemical experiments the formation of these layers was simulated and their structure was elucidated. By the process of oxygen corrosion OH^? ions are formed near the surface of the steel, precipitation of Mg(OH)² is caused which is bound to the surface together with silicates and phosphates. The layer is 100 to 200 Å thick and appears coloured by built-in ions of the alloy metals. The ions needed for formation of the layers, Mg²⁺, SiO₃^2? and PO₄^3?, all are present in tap water, thus the formation of such layers can occur always upon cooking and is only intensified by substances from the food (phosphates). The use of steels which are more corrosion-resistant or the precipitation or complex formation of the above mentioned ions or the exclusion of oxygen during cooking would prohibit the layer formation. However, such measures are hardly feasible and they are even unnecessary since the described process is harmless concerning hygienic aspects.     

Room temperature ferroelectric property of BiMnO<Subscript>3</Subscript> thin film with double SrTiO<Subscript>3</Subscript> buffer layers on Pt/Ti/SiO<Subscript>2</Subscript>/Si substrate

We fabricated high quality BiMnO₃ thin films with double SrTiO₃ buffer layers on Pt/Ti/SiO₂/Si substrates, in which the SrTiO₃ buffer layers were used for the reduction of leakage current in BiMnO₃ thin films. We chose an SrTiO₃ thickness of about 5 nm, which was obtained by the fitting of ellipsometer data. We confirmed a remarkable enhancement in leakage current. BiMnO₃ thin films exhibited a ferromagnetic transition with Curie temperature of about 105 K. The BiMnO₃ thin film also showed a good ferroelectric property with a remnant polarization of about 9 μC/cm².     

Enhanced growth of intermetallic phases in the Ni–Ti system by current effects

The effect of direct current upon interfacial reactions in the Ni–Ti system was investigated. Isothermal diffusion couple experiments were conducted under varying current densities to de-couple Joule heating from intrinsic effects of the current flux. Current densities of up to 2546 A cm⁻² were used in the temperature range of 625–850 °C. All of the intermetallic compounds (NiTi, Ni₃Ti and NiTi₂) present in the equilibrium phase diagram were identified in the product layer. In addition, β-Ti solid solutions formed in samples annealed above the α→β temperature, 765 °C. The growth of all product layers was found to be parabolic and the applied current was found to significantly increase the growth rate of the intermetallic layers. Using Wagner’s analysis the present results were compared to published results on current-free diffusion couples. The intrinsic growth rate constant of the NiTi₂ intermetallic was found to be 43 times higher under the influence of 2546 A cm⁻² than that obtained without a current at 650 °C. The effective activation energy for the formation of all phases was found to decrease with increasing current density. The effect was strong for all phases but the decrease was most marked for Ni₃Ti. In this case, the activation energy decreased from 292 kJ mol⁻¹ under the influence of a current density of 1527 A cm⁻² to 86 kJ mol⁻¹ when the current density was 2036 A cm⁻². The results are explained in terms of current induced changes in the growth mechanism arising from changes in the concentration of point defects or their mobility.     

Wear and corrosion resistance of AZ91 magnesium alloy coated by pulsed current electrodeposited Ni–Al2O3 nanocomposite

In this work, Ni and Ni–Al₂O₃ nanocomposite coatings were applied on AZ91 magnesium alloy using a pulse plating process and the corrosion resistance of coated samples was evaluated by means of the potentiodynamic polarisation method in 3.5?wt-% NaCl solution. Field emission scanning electron microscopy was employed to identify microstructure and morphology of the coatings. Vickers microhardness and pin-on-disc wear tests were also used to investigate mechanical properties of the coatings. The polarisation test revealed that the pure Ni coating on AZ91 along with the presence of nanoparticles were key factors leading to a reduction in the corrosion current density and the improvement of corrosion resistance so that the corrosion current density of 210.45?µA?cm^?2 for the substrate (AZ91) decreases to 31.92 and 1.54?µA?cm^?2 by applying pure Ni and Ni–Al₂O₃ nanocomposite coatings, respectively. Furthermore, Ni–Al₂O₃ nanocomposite coating increased the microhardness and wear resistance compared to the substrate up to 435 and 340%, respectively.     

用于氧还原反应的氮掺杂空心多孔碳球封装的过渡金属氮化物的制备和性能

通过浸渍和热处理方法制备一系列氮掺杂空心多孔碳球(NHPCS)封装的过渡金属氮化物(MxNy,M=Fe,Co,Ni)纳米颗粒复合材料.此纳米复合材料兼具氮化物的高催化活性和氮掺杂多孔碳球的高效传质特性.氧气还原反应结果表明,Fe2N/NHPCS表现出优异的催化性能,其具有较高的起始电位(0.96 V)、电子转移数(～4...     

Characterization of corrosion of X70 pipeline steel in thin electrolyte layer under disbonded coating by scanning Kelvin probe

Scanning Kelvin probe technique was used to characterize the electrochemical corrosion behavior of X70 steel in a thin layer of near-neutral pH and high pH solutions, respectively. Results demonstrate that passivity can be developed on steel in the near-neutral pH solution layer as thin as 60 μm, which is attributed to the fact that Fe²⁺ concentration in aqueous phase could reach saturation in the thin solution layer. The solubility of FeCO₃ is reached to drop out of solution as a precipitate. With the increase of solution layer thickness, it becomes more difficult for Fe²⁺ concentration to reach saturation. Consequently, the passivity cannot be maintained, and the steel shows an active dissolution state. Anodic dissolution rate of steel increases with the immersion time. The electrochemical polarization behavior of X70 steel in high pH solution is approximately independent of the solution layer thickness and immersion time. In thin solution layer, diffusion and reduction of oxygen dominate the cathodic process, as demonstrated by the presence of cathodic limiting diffusive current. In the bulk solution, the absence of limiting diffusive current density in cathodic polarization curve indicates that the main cathodic reaction is reduction of H₂CO₃ and , and the formed film is thus mainly FeCO₃.     

Development and characterization of vacuum plasma sprayed thin film solid oxide fuel cells

The vacuum plasma spraying (VPS) process allows the production of thin solid oxide fuel cells (SOFCs) with low internal resistances. This enables the reduction of the cell operating temperature without a significant decrease in power density. Consequently, the long-term stability of the cells can be improved and low-cost materials can be used. Different material combinations and spray parameter variations were applied to develop thin-film SOFCs, which were plasma sprayed in a consecutive deposition process onto different porous metallic substrates. The use of Laval nozzles, which were developed at the German Aerospace Center (DLR), and the use of conical F4V standard nozzles enable the fabrication of thin gas tight yttria- and scandia-stabilized ZrO₂ (YSZ and ScSZ) electrolyte layers and of porous electrode layers with high material deposition rates. The optimization of the VPS parameters has been supported by laser doppler anemometry (LDA) investigations. The development of the plasma-sprayed cells with a total thickness of approximately 100 μm requires an overall electrical and electrochemical characterization process of the single layers and of the completely plasma-sprayed cell assembly. The plasma-sprayed cell layers reveal high electrical conductivities. The plasma-sprayed cells show very good electrochemical performance and low internal resistances. Power densities of 300 to 400 mW/cm² at low operating temperatures of 750 to 800 °C were achieved. These cells can be assembled to high performance SOFC stacks with active cell areas up to 400 cm², which can be operated at reduced temperatures and good long-term stability.     

Corrosion and layer formation of passive copper in alkaline solutions

Copper forms passivating layers in alkaline solutions. Depending on the electrode potential a Cu₂O or a Cu₂O/CuO, Cu(OH)₂ layer is present. The structure and composition of the film has been examined by different methods like X-ray Photoelectron Spectroscopy (XPS), Ion Scattering Spectroscopy (ISS) and in situ Photoacoustic Spectroscopy (PAS). The thickness and growth of the passive layer has been determined by its electrochemical reduction i. e. the charges of potentiodynamic reduction peaks or the evaluation of the corresponding galvanostatic steps. The results support a high field mechanism for the oxide formation with an inverse logarithmic rate law and a linear increase of the oxide thickness with the electrode potential. The capacity of a Cu₂O-layer refers to the characteristics of a thin semiconducting film. Studies with a rotating Pt split ring Cu disc electrode permit the subdivision of the current density into a part of layer formation and corrosion. The efficiency for the corrosion part is very small during the beginning of oxide formation and achieves ν = 90% after some few minutes. In the potential range of Cu₂O formation only ν = 50% is achieved.     

Thin-layer electrolytic nickel hydroxide Ni(OH)2 in an electrochemical capacitor

Thin-layer electrolytic nickel hydroxide Ni(OH)₂ has been obtained from an aqueous solution of nickel sulfate and nickel nitrate. The capacitor characteristics of Ni(OH)₂ depending on the synthesis and technology parameters, the thermal treatment and storage conditions of the deposits, the KOH concentration, the potential sweep rates, and the relation with the adverse process of oxygen isolation in an electrochemical capacitor were investigated by cyclic voltammetry. It was established that the optimal KOH concentration in the solution of an electrochemical capacitor is 0.1 M, and it allows one to attain an active material discharge capacitance of 427?C457 F/g. The additional anode polarization of cathode deposited Ni(OH)₂ stabilizes the discharge characteristics of the obtained Ni(OH)₂ + NiO mixture in storage processes. It was established that the mass transport process in the solid state phase is the limiting stage of the Ni(OH)₂/NiOOH system??s electrode process in a KOH medium.     

Numerical model of Ca(OH)2 transport in concrete due to electrical currents

A mathematical model is being developed to describe a repair method in concrete, called cathodic protection (CP). The model is in principle also useful to describe electrodeposition in concrete, e.g. the process of re‐precipitation of Ca(OH)₂ invoked by an electrical current. In CP, the current is sent from an external anode to the reinforcement inside the concrete. This model is implemented using the numerical software package Comsol Multiphysics. The model is based on the Nernst–Planck equations and the electroneutrality condition considering the ionic species Na⁺, OH^? and Ca²⁺ and the solid Ca(OH)₂. The mathematical model makes it possible to predict the location where Ca(OH)₂ precipitates when a certain current density is used. This could be of great use for controlled crack repair in concrete and for electrochemical re‐alkalisation. This paper presents the qualitative behaviour of dissolution and re‐precipitation of Ca(OH)₂ in CP. It discusses model calculations and preliminary experimental results. Experiments for a more complete validation of the model are in process.     

Corrosion of Ni in Molten Alkali Sulphates

The corrosion of Ni base alloys under molten ash deposits containing considerable quantities of alkali sulphates can take place as a sulphidation or oxidation. The former is very dangerous with respect to gas turbine operation since it gives rise to a decrease in strength of the materials; this type of corrosion is also predominant under thick layers of molten deposits at higher oxygen pressures, the effect being then increased by the poorer transport properties of the melt respect to oxygen diffusion. When cobalt sulphate is found in the ash the accelerated oxidation of Ni base alloys is due to the stable redox system Co⁺²/Co⁺² in the melt Increasing the acidity of the flue gases (increasing SO₃ content) enhances the corrosion rate and the solubility of corrosion products in the melt.