Factors affecting the anodic behaviour of zinc electrode in borate solutions

The anodic behaviour of Zn electrode in 1 × 10⁻² M Na₂B₄O₇ solutions in the absence and presence of various concentrations of Na₂SO₄, Na₂S₂O₃ or Na₂S as aggressive agent was studied by galvanostatic polarization technique. In the absence of sulphur-containing anions in solution, the polarization curves are characterized by one distinct arrest corresponding to Zn(OH)₂ and/or ZnO, after which the potential increases linearly with time due to the formation of barrier oxide film before reaching the oxygen evolution reaction. The duration time of the arrest decreases with increasing current density while the rate of oxide film formation increases. On the other hand, the duration time of the arrest increases with the number of anodic cyclization while the rate of oxide film formation decreases. Additions of low concentration of the aggressive anions have no effect on the passive film formed on the metal surface. The potential starts to oscillate within the oxygen evolution region with increases in the concentration of these aggressive anions. Further increases in the concentration of these aggressive anions are associated with impaired Zn passivity that might indicate pitting attack. The aggressiveness of the sulphur species decreases in the order: . The effect of raising pH of the solution on the anodic behaviour of Zn electrode in the presence of anions was also investigated. It was found that the raising the pH of the solution affecting on the rate of oxide film formation and the breakdown potential value.     

Electrochemical behaviour of the Mg alloy AZ91D in borate solutions

Corrosion and passivation behaviour of Mg-based alloy AZ91D was investigated in aqueous sodium borate solutions (pH 9.2) in relation to some test parameters, using electrochemical techniques. Increasing borate concentration (0.01–0.10 M) or temperature up to 298 K leads to increase the corrosion rate of the alloy. However, at temperatures higher than 298 K borate anions have stronger propensity to passivate the alloy, thereby decreases its corrosion rate. For a fixed borate concentration increasing Cl⁻ addition is correlated with a more negative corrosion potential and a higher corrosion rate, as well as increase the vulnerability of the anodic passive film for breakdown. The influence of oxidizing potentials over the range −1.5 V to 2.75 V (SCE) on the performance of the alloy in the most aggressive borate solution (0.10 M) reveals that higher potentials, induces better passivation due to formation of a rather thick and more protective n-type semiconducting film. A modified Randles circuit including Warburg impedance to account for the diffusion of reactants or products through the surface film was adopted to analyse the EIS data, that gave impedance parameters in good agreement with the results of open circuit potential and dc polarization measurements.     

A Contribution to the Study of the Critical Pitting Potential of Oxide Covered Aluminum in aqueous chloride solutions

The critical pitting potential of oxide covered aluminum electrodes in aqueous chloride solutions has been investigated as a function of chloride ion concentration, temperature, solution pH and oxide film thickness. The steady state critical pitting potential decreases with chloride ion concentration and increasing solution temperature. Solution pH in the range 5 to 9 has no effect on the breakdown potential. The role of the oxide film thickness is to slightly increase the critical potential for passivity breakdown and intiation of pitting. It is postulated that at the critical pitting potential, passivity breakdown occurs by a process of field assisted Cl adsorption on the hydrated oxide surface and formation of a soluble basic chloride salt with a lattice cation which readily goes in solution. This process of localized dissolution of the hydrated oxide film via formation of a soluble basic aluminum chloride salt, once initiated, is likely to continue in an “autocatalytic” fashion until the oxide is locally “penetrated” and dissolution of the substrate metal begins.     

Auger analysis of the anodic oxide film on iron in neutral solution

The composition depth-profile of anodic oxide films on iron at various potentials in a boric acid-sodium borate solution of pH 8.4 was measured by the sequential use of Auger electron spectroscopy (AES) and sputter-etching. It was found that the anodic oxide film consisted mainly of oxygen and iron with minor impurities such as boron, sulphur and carbon. The composition ratio of boron or sulphur to oxygen exhibited a maximum value at a certain depth in the outer layer of the film and the maximum value of ($\text{B}\text{O}$) increased with increasing potential up to 500 mV (SCE). The film formation mechanism is discussed from the observed dependence of boron content in the film.     

Anodic oxidation and kinetics of titanium in 1 M chloride solutions

The anodic behaviour of titanium was investigated in 1 M chloride solutions of pH ranging from 0.0 to 12.0 by using electrochemical techniques combined with chemical analysis. No active region appears in solutions of pH above 2.0. In the passive region, the amount of titanium dissolved into the solution during 1 h oxidation decreases with increasing pH, and no dissolution occurs at pH 10.5. The thickness of passive films estimated from the electric charge accumulated on the surface increases linearly with the potential. The kinetic analysis between the anodic current and the film charge indicates that the growth of the passive film obeys the inverse logarithmic rate law, and the kinetic parameters are calculated.     

硼酸-硼砂介质中硫离子对不锈钢钝化膜的侵蚀性

 Mott-Schottky图、Nyquist图及阳极极化曲线测定研究了硼酸-硼砂缓冲溶液中硫离子对不锈钢钝化膜耐蚀性能的影响，结果表明：随浸泡时间增加不锈钢电极阻抗值增大，但硫离子加入后阻抗值快速降低；阳极极化曲线测定显示硫离子使不锈钢钝态电流增大；硫离子浓度的增加使不锈钢电极的Mott-Schottky图中体现p-型半导体(铬氧化物)性质的直线段发生较大变化，说明硫离子影响了钝化膜中铬氧化物的性质，使其耐蚀性能降低. 钝化膜      

Photoacoustic study on cathodic reduction of anodic oxide films formed on copper in borate solution

An in-situ photoacoustic (PAS) technique, using a piezoelectric detector with high sensitivity was applied to the study on duplex oxide films anodically formed on copper in pH 8.4 borate solution. The PAS signals from the copper electrode were produced by an irradiation of light beam with a wavelength of 514.5 nm. The PAS amplitude during cathodic reduction of the outer oxide layer to Cu₂O changed in the opposite direction, depending on the anodic potential of film formation and oxidation time. Assuming that the change in PAS amplitude is proportional to both optical absorption coefficient and film thickness, it was deduced from comparison of the estimated absorption coefficients for Cu (OH)₂, CuO and CuO_0.67 films that dehydration of the outer layer having an average composition of CuO_x (OH)_2?2x proceeded with increasing anodic potential of film formation and oxidation time during growth of the duplex oxide film. Moreover, it was found that the change in PAS amplitude during cathodic reduction of the total Cu₂O film involving the inner layer to metallic copper was proportional to the electric charge required for cathodic reduction, i.e., the film thickness, irrespective of anodic potential of film formation and oxidation time, which proved the validity of the above assumption.     

Wachstum und Auflösung anodisch erzeugter Oxidschichten auf Titan

Growth and dissolution of anodically obtained oxide layers on titanium Oxide films were grown by anodic polarization of titanium in various aqueous electrolytes. The field strength derived from film thickness and voltage is linearly related to the logarithm of the total current density. The current efficiency for film formation depends upon current density, pH-value, and film thickness. The dielectric constant of the film decreases with field strength from ε = 110 to ε = 7, but rises again at high field strengths and thick films. The dissolution rate of anodic oxide films on titanium was investigated as a function of pH-value, concentration of chloride, and temperature, respectively. Aging of the films in distilled water causes the dissolution rate to decrease by up to 3 order of magnitude.     

In-depth profiles of anodic oxide films on FeNi alloy in boric acid-sodium borate solutions

The in-depth profiling of anodic oxide films formed for 1 h on a 55Fe-45Ni alloy in boric acid-sodium borate solutions was made by the simultaneous use of AES (Auger Electron Spectroscopy) and sputter-etching with Ar⁺ ion to determine the thickness and composition of anodic oxide films and to elucidate the experimental variables which affect them. The anodic oxide film was thicker and richer in the Fe component in pH 6.48 solution than in pH 8.45 solution. It was estimated from the in-depth profile of the anodic oxide film that a significant part of the Fe component in the anodic oxide film was in the di-valent state. Enrichment of the Ni component at the oxide/substrate interface and depletion of Ni component in the film were measured as a function of pH and anodic potential. These results are explained in terms of the combination of the following factors: (i) preferential dissolution of the Fe component, (ii) preferential oxidation of the Fe component, and (iii) preferential anodic deposition of the Fe or Ni component.     

Corrosion behavior of titanium-clad carbon steel in weakly alkaline solutions

The electrochemical polarization curves and corrosion potentials during long-term immersion of Ti, carbon steel, carbon steel tightened-Ti and Ti-clad carbon steel specimens were investigated in bentonite-contacting solution (mixture of sodium sulfate and sodium carbonate solutions), sodium sulfate solution and borate solution adjusted to pH=9.0-9.84. Ti and carbon steel were passivated during immersion in borate solution, while carbon steel was corroded in the solutions containing SO₄²⁻ ions. The immersion potentials of Ti-clad steel and steel-tightened Ti specimens were controlled by the corrosion potential of carbon steel (about 0 V vs. RHE at 298 K). The Ti side of the clad specimen was, therefore, polarized cathodically at this immersion potential, and this caused hydration of and/or hydrogen penetration into the oxide film, resulting in degradation of its barrier property. Furthermore, the cathodic current on the Ti side was partially coupled with the anodic current in the corrosion reaction on the carbon steel side, resulting in acceleration of the overall corrosion rate.     

Temperature dependence of the anodic oxidation of titanium below the oxygen evolution potential

The growth of thin anodic oxide films on Ti in the temperature range between 20 and 70° C can be expressed in purely coulometric terms. In diluted and aerated borate solutions the potential increases linearly with time; the slope of the curves increases with increasing current intensity; after 10 to 20 min all the curves show a transition to a flattened shape. Temperature changes have but an insignificant influence on the general character of the curves; the transition to the flatter portion occurs after about 20 min, too, but potentials are the lower, the higher the temperature. The values of the activation energy calculated from the results show, that the layer formation is not only controlled by the bound are face reactions, but also by certain factors coming from the bulk of the solution.     

镁合金阳极氧化膜在NaCl溶液中的腐蚀行为

利用盐水浸泡实验研究了AZ91D镁合金阳极氧化膜层在3．5％NaCl溶液中的腐蚀行为。结果表明：AZ91D镁合金阳极氧化膜层不论封闭与否,在中性NaCl溶液中浸泡出现第一个腐蚀点后,膜层表面均很少再出现新的腐蚀点,而是原有的腐蚀点向纵、横两个方向扩展形成腐蚀坑,表面呈“树枝”状腐蚀形貌;浸泡溶液的pH值对阳极氧化膜层的耐蚀性影响很大,酸性溶液中的腐蚀速率明显大于中、碱性溶液的;随浸泡溶液温度的升高阳极氧化膜层的腐蚀速率加快。据此,提出了AZ91D镁合金阳极氧化膜层在NaCl溶液中腐蚀过程的模型。     

Role of ClO4 in breakdown of tin passivity in NaOH solutions

The anodic behaviour of a tin electrode in NaOH solutions containing different concentrations of NaClO₄ was studied by employing potentiodynamic, potential transient under constant current density methods and complemented with scanning electron microscopy (SEM). In perchlorate-free NaOH solutions, the E/i response exhibits active/passive transition. The active region involves two anodic peaks corresponding to the formation of Sn(II) and Sn(IV) species respectively. The permanent passive layer is duplex and consists of SnO and SnO₂. Additions of NaClO₄ to the alkali solution, accelerates the active dissolution of tin and tends to breakdown the duplex passive layer at a certain breakdown potential. SEM examination confirms the occurrence of film breakdown. The breakdown potential decreases with an increase in ClO₄⁻ concentration, but increases with increasing both OH⁻ concentration and scan rate. The potential-time transients display that the incubation time for pit initiation decreases with increasing both ClO₄⁻ concentration and anodic current density.     

高pH值完井液中钛合金管材的腐蚀行为研究

基于高温高压腐蚀速率和原位电化学测试,并结合分子动力学模拟和第一性原理计算,探讨了钛合金(TC4)管材在高pH值完井液中的腐蚀行为,以及钝化膜的热力学稳定性。结果表明:TC4钛合金在180℃的高pH值磷酸盐完井液中的腐蚀极为严重,其均匀腐蚀速率高达0.4429mm/a;在高pH值磷酸盐完井液中,TC4钛合金的腐蚀为阳极反应过程控制,随着温度的升高,其腐蚀电位、腐蚀产物膜的膜阻和极化电阻显著降低,腐蚀反应的热力学驱动力增大、动力学阻力降低,腐蚀电流密度显著升高;在碱性溶液中,TiO_2钝化膜的钛氧键发生不同程度断裂,并且随着温度升高、碱性增强,TiO_2与溶液的界面结合能逐渐增大,钝化膜的热力学稳定性明显降低;在碱性焦磷酸钾溶液中,TiO_2钝化膜均可与K_2HPO_4、K_3PO_4反应生成疏松多孔的KTiOPO_4腐蚀产物膜,但TiO_2与K_3PO_4反应的热力学倾向更大。     

镍阳极氧化膜形成和破坏过程的光电化学响应

测定了镍表面阳极氧化膜在ｐＨ＝８．４硼砂－硼酸缓冲溶液中不同电位下的光电流响应。基于阻抗测量结果的计算表明，钝化膜的平带电位和载流子密度分别为－０．６８Ｖ和１．３×１０（２０）ｃｍ（－３）。对钝化膜和高价氧化膜在形成、生长和破坏过程中的光电流变化进行了现场监测。     

以新型硼源制备硼掺杂金刚石膜的性能研究

采用微波等离子体化学气相沉积技术,以氧化硼-乙醇溶液作为硼源,制备不同掺硼浓度的金刚石膜。利用扫描电子显微镜、X射线衍射仪、激光拉曼光谱仪、电化学工作站等研究其表面形貌、晶体结构、薄膜质量和电化学性能。结果表明:随硼元素含量升高,金刚石膜的晶体颗粒尺寸先减小后增大,电势窗口由3.1V降至2.6V,阳极电流密度由0.022 7mA·cm-2降至0.011 9mA·cm-2,但对背景电流及电化学可逆性几乎不影响。      

Electrochemical corrosion of X65 pipe steel in oil/water emulsion

The electrochemical corrosion behavior of X65 pipeline steel in the simulated oil/water emulsion was investigated under controlled hydrodynamic and electrochemical conditions by rotating disk electrode technique. Results demonstrated that mass-transfer of oxygen plays a significant role in the cathodic process of steel in both oil-free and oil-containing solutions. Electrode rotation accelerates the oxygen diffusion and thus the cathodic reduction. The higher limiting diffusive current density measured in oil-containing solution is due to the elevated solubility of oxygen in oil/water emulsion. The anodic current density decreases with the increase of electrode rotating speed, which is attributed to the accelerated oxygen diffusion and reduction, enhancing the steel oxidation. Addition of oil decreases the anodic dissolution of steel due to the formation of a layer of oily phase on steel surface, increasing the reaction activation energy. The steel electrode becomes more active at the elevated temperature, indicating that the enhanced formation of oxide scale is not sufficiently enough to offset the effect resulting from the enhanced anodic dissolution reaction kinetics. The corrosion reaction mechanism is changed upon oil addition, and the interfacial reaction is activation-controlled, rather than mass-transfer controlled. When sand particles are added in oil/water emulsion, there is a significant increase of corrosion of the steel. The presence of sands in the flowing slurry would impact and damage the oxide film and oily film formed on the steel surface, exposing the bare steel to the corrosive solution.     

Semiconductive properties of titanium anodic oxide films in McIlvaine buffer solution

The semiconductive properties of anodic oxide films grown on titanium surface at different formation potentials: 1.0, 2.0, 3.0 and 4.0 V were investigated by means of electrochemical impedance spectroscopy and cyclic voltammetry in McIlvaine buffers at pH 2, 4 and 5. The passive films show a Mott-Schottky behavior typical for an n-type semiconductor at the studied potential range with a high concentration of donors. On increasing the film formation potential, the flat band potential and the donor density decrease. Further, lower flat band potentials were obtained for higher pH buffer. These experimental results were related to the film thickness and composition. The influence of film thickness on the oxidation reactions taking place at the titanium electrodes covered by oxide film was evaluated.     

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.     

铬酸钠对铀钛合金在氯化钠溶液中的缓蚀作用

采用失重法和电化学方法研究了铬酸钠对铀钛合金在200 mg/L氯化钠溶液中的缓蚀作用,并用X射线光电子能谱(XPS)和激光共聚焦显微镜分析铀钛合金表面氧化物成分和形貌。结果表明,铬酸钠属于阳极型钝化剂,缓蚀效率随浓度的增加而增大。但溶液温度对铬酸钠的缓蚀效率影响较大,溶液温度高于45℃时,加入100 mg/L的铬酸钠对铀钛合金具有加速腐蚀作用。XPS分析表明,铀钛合金表面形成的钝化膜中铀的氧化物存在两种形式,最外层为UO2+x,内层为UO2;加入铬酸钠后,钝化膜最外层含有UO2+x和多种铬化合物,厚度小于3 nm。