Die Inhibition der Sauerstoffreduktion durch dünne Ni(OH)2-Filme

Inhibition of oxygen reduction by thin Ni(OH)₂ films During the cathodic reduction of oxygen in Ni²⁺-contending solutions thin Ni(OH)₂-layers can be precipitated. These layers inhibit the electrode reaction. During stationary measurements the current density is equal to the limiting diffusion current density of the hydronium ions, which is necessary for the stabilization of the layer in the non-saturated electrolyte. The thickness of the layers can be calculated with Faraday's law.     

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。     

Influence of flow on the corrosion inhibition of St52-3 type steel by potassium hydrogen-phosphate

Influence of hydrodynamic conditions on the corrosion of St52-3 type steel rotating disc electrode, RDE, in 3.5% NaCl and its corrosion inhibition using K₂HPO₄ have been studied. Results showed that by rotating the electrode in blank and inhibited solutions, corrosion current density, i_corr, increased, corrosion potential, E_corr, shifted toward more positive values and charge transfer resistance, R_ct, decreased. The inhibition efficiencies increased with electrode rotation rate. This increase was attributed to the enhanced mass transport of inhibitor molecules toward the metal surface and formation of more protective films. Little decrease of efficiencies at higher rotation speeds was probably because of the separation of protective films due to high shear stresses.     

Electrochemical fabrication of a porous nanostructured nickel hydroxide film electrode with superior pseudocapacitive performance

A porous nickel film is prepared by selectively anodic dissolution of copper from an electrodeposited Ni-Cu alloy film. A porous nanostructured nickel hydroxide film electrode is further fabricated by the cathodic electrodeposition of Ni(OH)₂ film on the obtained porous nickel film. The specific capacitances of the as-prepared porous nanostructured Ni(OH)₂ film electrode at current densities of 2, 5 and 10 A/g are 1634, 1563 and 1512 F/g, respectively. The nanoporous Ni substrate significantly improves the electrochemically cyclic stability of the electrodeposited nickel hydroxide film in 1.0 M KOH solution. The superior pseudocapacitive properties such as large specific capacitance, excellent rate capability and improved electrochemically cyclic stability of the as-prepared nickel hydroxide electrode suggest its potential application in electrochemical capacitors.     

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.     

Effects of copper on the corrosion properties of low-alloy steel in an acid-chloride environment

The influence of Cu addition on the corrosion resistance of low-alloy steel in an acid-chloride solution was investigated by electrochemical methods, such as potentiodynamic polarization tests and an electrochemical impedance spectroscopy (EIS). The XPS analysis of the corroded surfaces indicated the formation of protective Cu₂O and Cu(OH)₂ layers on the surface. The formation of Cu products on the surface reduced the uniform corrosion rate of the steel, but promoted localized corrosion due to the galvanic interaction between the covered areas of copper oxide/hydroxide and the uncovered areas on the surface of steel.     

The corrosion and passivity of aluminum exposed to dilute sodium sulfate solutions

The composition and thickness of the oxide/hydroxide film that forms on pure aluminum surfaces that are polarized in 0.05 M Na₂SO₄ in acidic, near-neutral, and alkaline solutions have been characterized using XPS. The results of this effort have been plotted on surface behavior diagrams to follow the evolution of the surface film during polarization. Although a thin layer of gibbsite [Al(OH)₃] is often indicated to be the film that forms and protects aluminum from corroding in near-neutral pH solutions after 10–20 h of exposure, the composition of the film that initially forms on Al after a short period of time (1 h) was actually closer to boehmite (AlOOH), the oxyhydroxide phase. This film generally grows thicker during either anodic or cathodic polarization in both the pH 7 and pH 10 solutions. For the solution at pH 2, the air-formed film dissolves to a very thin oxyhydroxide film that is replaced by an oxide film, Al₂O₃, during anodic polarization. The growth of the oxyhydroxide film at each pH during cathodic polarization is attributed to the local buildup of hydroxyl ions at the surface of the working electrode.     

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.     

Use of the scratching electrode technique to interpret the stress corrosion cracking behaviour of α-brass in ammoniacal copper sulphate solutions

Stress corrosion cracking (s.c.c.) of α-brass in Mattsson solutions [1 M (NH₃ + NH₄⁺); 0.05 M CuSO₄] at a given strain-rate intensifies in pH order: 4.75 < 7.35 < 11.35. There is no cracking at pH 8.9 or when tarnishing at pH 7.35 is prevented by reducing [NH₃ + NH₄⁺] to 0.25 M. A technique of continously scratching a shallow circular track on a rotating electrode has been used to investigate the electrochemical behaviour of bared metal surfaces in these environments with the object of examining the relative contributions of slip-dissolution and tarnish-rupture in the crack propagation mechanism. It is shown that the observed s.c.c. propensity correlates well with: (i) the physico-chemical nature of the reaction products, (ii) the bare surface current density at the applied potential and (ii) oxide growth kinetics on the bare surface. Thus, in non-tarnishing solutions s.c.c. does not occur if either the rate of protective oxide formation is sufficiently rapid [pH 7.35 (0.25 M NH₃)] or the whole surface is dissolving uniformly (pH 8.9); in the intermediate case (pH 4.75) cracking is observed. In tarnishing solutions [pH 7.35 (1 M NH₃) and pH 11.35] the crack propagation rate increases with the tarnishing rate. Qualitative agreement between s.c.c. behaviour and bare surface oxide growth rate, as determined by the scratching electrode method, supports a slip-dissolution model of propagation.     

Electrodissolution of 304 stainless steel in neutral electrolytes for surface decontamination applications

Brightening of 304 stainless steel in concentrated electrolytes of Na₂SO₄, Li₂SO₄, NaNO₃, LiNO₃, NH₄NO₃, and Ca(NO₃)₂ was studied. It is observed that the current efficiency and quality of the surface depend on the electrolyte concentration, ions present in the electrolyte and the operating current density. While sulfate electrolytes etch the electrodes, oxidizing electrolytes generally yield brightened surfaces. Surface brightening is achieved at the lowest current density in LiNO₃/Na₂Cr₂O₇ composite electrolyte at a pH of 5.2. The results are explained on the basis of salt film formation near the specimen surface.     

Effect of heat treatment on corrosion properties of CuAlNi shape memory alloy

The effect of heat treatment on corrosion properties of CuAlNi shape memory alloy was investigated in 0.9% NaCl solution at pH 7.4 and 37 °C by open circuit potential measurements, polarisation techniques, and electrochemical impedance spectroscopy. Investigations were performed on CuAlNi alloy samples in as-cast state and after heat treatment procedure containing annealing at 850, 885 and 920 °C followed by water quenching. Electrochemical impedance measurement results indicate that heat treatment of CuAlNi alloy leads to the increase in charge transfer resistance and surface layer resistance and the decrease in values of capacitance of the double and surface layers, indicating higher corrosion resistance compared with the as-cast CuAlNi alloy. The increase in polarisation resistance and the decrease in corrosion current density of heat-treated CuAlNi alloy also suggest beneficial influence of heat treatment on corrosion resistance of CuAlNi alloy. Optical microscopy, SEM/EDX and XRD analysis of samples surface after polarisation measurements show the occurrence of pitting corrosion on the electrode surfaces, with the existence of CuCl₂, AlCl₃ and Cu₂Cl(OH)₃ compounds as the surface corrosion products.     

Kinetics of anodic behaviour of Pb in HCl solutions

The galvanostatic polarization technique was used to study the electrochemical behaviour of lead electrode in HCl solutions. The general shape of the resulting anodic potential-time curves is found to depend on magnitude of the imposed current density, the acid concentration and the temperature of the solution. The data of the curves were characterized by the presence of various regions due to different electrochemical processes. (i) A rapid and almost linear change of potential due to the decay of hydrogen overpotential and the subsequent charging of the electrical double layer at the metal/solution interface, (ii) a potential arrest corresponding to anodic dissolution of the lead to Pb²⁺ ions, (iii) a linear rise in the electrode potential indicating the onset of passivity due to the formation of PbCl₂, (iv) a second potential arrest due to the chemical dissolution of the passive PbCl₂ layer, and (v) finally, a continuous rise in the Pb electrode potential with time. The electrode potentials corresponding to the different arrests were found to depend on the magnitude of the imposed current density, the acid concentration and the temperature of the solution. The duration time, τ, of the dissolution process was found to increase with the decease of the solution acidity and the current density and also with the increase of solution temperature.     

Studies on the anodic polarization of amalgams. The behaviour of manganese amalgams in alkaline solutions

Manganese amalgams of varying concentrations were anodically oxidized galvanostatically in 0·1, 1·0, 2·0 and 4·0N NaOH solutions at 25°C. For each amalgam and solution composition a number of constant polarizing currents were used. The anodic polarization curves in 1·0 and 2·0N NaOH solutions showed potential arrests corresponding to discharge of sodium amalgam formed during the pre-cathodization treatment, dissolution of Mn as Mn²⁺ followed by precipitation of Mn(OH)₃, formation of MnO₂ and oxidation of mercury before oxygen evolution. In 4·0N NaOH, the development of a new step or steps at potentials intermediate between those for the formation of MnO₂ and the oxidation of mercury is noticed.The correlation between polarizing current, i, and time of passivation, τ, was found to follow the following relation: log T = A – n log i where A and n are constants. The results indicate that the passivation of manganese amalgams in alkaline solutions is governed by the rate of diffusion of metal atoms (or ions) at the electrode solution interface and by the physical and chemical properties of surface oxide film.     

Determination of the zero-charge ph value of a passive iron surface in aqueous solution

Two techniques of measurement of pH₀, which represents the pH of solution at which the total charge of passive metal electrode surface is zero have been developed. The procedures are based on the use of acid-base equilibria between oxide on electrode surface and solution. In the former technique, the pH of the drop of solution that is applied onto the electrode surface is measured. At pH₀, the pH of the drop does not change in time. In the latter procedure, the potential of a passive electrode that is immersed into solutions with various pH values is measured. pH₀ has been measured on a passive iron electrode. The pH₀ values measured by the two procedures are similar. Comparison of pH₀ of passive electrode and various oxides one to determine the composition of a passive film. The introduction of surface-active ions Ba²⁺ and Cl^? to the solution leads to a shift of pH₀ values and electrode potential in opposite directions.     

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.     

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.     

First-principle investigation on mechanism of Ca ion activating flotation of spodumene

Different hypotheses of the activation mechanisms of metallic ions for silicate minerals flotation were stated in this work. Spodumene and Ca ion were taken to illustrate this issue. Flotation test results and diagram of Ca ion species distribution vs pH show that the dominant hydrolyzed species are Ca（OH）？and Ca（OH）2, which is in correspondence with the maximum flotation recovery of spodumene. Density functional theory（DFT） calculation results reveal further that the precipitation of calcium hydroxide on spodumene surface is the effective process to activate the flotation of spodumene.     

Anodic behaviour of tin in maleic acid solution and the effect of some inorganic inhibitors

The anodic behaviour of a tin electrode in maleic acid solutions was investigated by potentiodynamic and chronopotentiometric methods. Measurements were conducted under different experimental conditions. The results demonstrated that the polarization curves exhibit active/passive transition. In active regions, tin dissolves as Sn²⁺ which is subsequently oxidized to Sn⁴⁺ and the dissolution process is controlled partly by diffusion of the solution species. The passivity is due to the presence of thin film of SnO₂ on the anode surface formed by dehydration of precipitated Sn(OH)₄. The active dissolution of tin increases with increasing acid concentration, temperature and scan rate. The potential transients showed that the passivation time decreases with increasing applied current density. The effect of adding increasing concentrations of CrO₄²⁻, MoO₄²⁻ and NO₂⁻ ions on the anodic behaviour of tin in maleic acid was studied. These ions inhibit the active dissolution of tin and promote the attainment of passivity. The extent of these changes depends upon the type and concentration of the inhibitor.     

花球状Mg(OH)2的制备及其对重金属离子的快速高效去除(英文)

由MgSO₄废液制备球形花状Mg(OH)₂,并评估其对重金属离子的吸附性能。合适的制备条件为Mg²⁺浓度2 mol/L、Mg²⁺/NH₄OH摩尔比1:0.5、温度120℃和时间1h。由超薄片组成的球形花状Mg(OH)2对重金属离子具有良好的吸附能力,6min即可达到吸附平衡。20℃时Mg(OH)₂对Ni²⁺、Cu²⁺、Zn²⁺、Pb²⁺、Fe³⁺和Co²⁺的最大吸附量分别为58.55、85.84、44.94、485.44、625.00和27.86 mg/g。吸附过程符合Langmuir模型,为单分子层吸附。吸附动力学符合准二级动力学模型,化学吸附是其作用机制。球形花状Mg(OH)₂是合格的重金属离子吸附材料。