应用电化学方法原位研究薄液膜下青铜的大气腐蚀行为(英文)

采用阴极极化曲线、开路电位和电化学阻抗谱,监测青铜在不同薄液膜厚度下的大气腐蚀行为。阴极极化曲线结果表明,阴极极限电流密度随着液膜的减薄而增大。电化学阻抗谱结果表明,在腐蚀初期,腐蚀速率随着液膜的减薄而增加,这主要是由于腐蚀速率是由阴极过程控制的;随着时间的延长,腐蚀程度随着液膜厚度的变化从强到弱的趋势为:150μm,310μm,100μm,本体溶液,57μm。开路电位和电化学阻抗谱实验较好地再现了原位电化学腐蚀信息,且电化学结果与物理表征具有良好的一致性。     

Kelvin探头振动电容法技术在大气腐蚀中的应用

介绍了Kelvin探头振动电容法在腐蚀中的应用原理及试验装置,Kelvin探头(也称为振动电容法)技术应用到金属腐蚀的研究中,可以在不需与被测试样表面相接触的条件下,用Kelvin探针作参比电极,测量液膜下金属的腐蚀速率,电极电位及极化曲线.     

利用Kelvin探针进行金属薄液层下电化学测量

利用线性回归法测Kelvin电位装置对铜,锌及碳钢进行了阴极极化曲线测试和腐蚀电位随相对湿度变化的监测结果表明阴极极限电流密度随液膜厚度的减小而增大金属腐蚀电位随相对湿度增加而下降.     

Effect of microcrystallization on pitting corrosion of pure aluminium

A microcrystalline aluminium film with grain size of about 400 nm was prepared by magnetron sputtering technique. Its corrosion behaviour was investigated in NaCl containing acidic solution by means of potentiodynamic polarization curves and electrochemical noise (EN). The polarization results indicated that the corrosion potential of the sample shifted towards more positive direction, while its corrosion current density decreased compared with that of pure coarse-grain Al. The EN analysis based on stochastic model demonstrated that there existed two kinds of effect of microcrystallization on the pitting behaviour of pure aluminium: (1) the rate of pit initiation is accelerated, (2) the pit growth process was impeded. This leads to the enhancement of pitting resistance for the microcrystallized aluminium.     

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.     

Characterization of corrosion of X65 pipeline steel under disbonded coating by scanning Kelvin probe

Corrosion of X65 pipeline steel under a disbonded coating was studied by scanning Kelvin probe measurements. Three types of specimen were designed and prepared to investigate the effects of immersion time, oxygen concentration and wet-dry cycle on Kelvin potential profile and thus corrosion behavior of the steel. Kelvin potential measured on “intact” area is shifted negatively with time, indicating an increasing water uptake under the “intact” coating. With the increase of the amount of solution, it is expected that the electrolyte concentration and electrochemical reaction rate change, resulting in a significant decrease of interfacial potential. Moreover, there is a more negative Kelvin potential on disbonded area than that on “intact” area. The negative shift of Kelvin potential is attributed to corrosion reaction of steel occurring under the disbonded coating. Due to the narrow geometry of coating disbondment, an oxygen concentration difference exists along the depth of the disbondment. The corrosion behavior under disbonded coating strongly depends on the oxygen partial pressure and local geometry. With continuous purging of nitrogen and removing of oxygen, Kelvin potential tends to be identical throughout the disbonded area. During wet-dry cycle, the thickness of solution layer trapped under disbonded coating decreases due to evaporation of water. With the decrease of solution layer thickness, the measured Kelvin potential decreases, indicating that the effect associated with the reduction of oxygen solubility in the concentrated solution during drying of electrolyte is favored over that related to the enhanced oxygen diffusion and reduction. There exists a critical thickness of solution layer, below which the oxygen solubility is sufficiently low to support the electrochemical corrosion reaction of steel.     

A study of the corrosion of aluminum alloy 2024-T3 under thin electrolyte layers

The corrosion of aluminum alloy 2024-T3 (AA2024-T3) under thin electrolyte layers was studied in 3.0 wt% sodium chloride solutions by cathodic polarization and electrochemical impedance spectroscopy (EIS) method. The cathodic polarization measurements show that, when the electrolyte layer is thicker than 200 μm, the oxygen reduction current is close to that of the bulk solution. But in the range of 200-100 μm, the oxygen reduction current is inversely proportional to the layer thickness, which shows that the oxygen diffusion through the electrolyte layer is the rate-determining step for the oxygen reduction process. In the range of 100 μm to about 58 μm, the oxygen reduction current is slightly decreased probably due to the formation of aluminum hydroxide or the change of the diffusion pattern from 2-dimensional diffusion to one-dimensional diffusion. The further decrease in electrolyte layer thickness increase the oxygen reduction current to some extent again, because the diffusion of oxygen plays more important role in thin electrolyte layers.The EIS measurements show that the corrosion is controlled by the cathodic oxygen reduction at the initial stage, showing the largest corrosion rate at the electrolyte layer thickness of 105 μm. But at the later stage of corrosion, the anodic process begin to affect the corrosion rates and the corrosion rates show a maximum at 170 μm, which may be the thickness where the corrosion changes from cathodic control to anodic control. The corrosion rate under the very thin electrolyte layer (62 μm in this study) is even smaller than that in bulk solution, this is due to that the anodic process is strongly inhibited.     

南海大气环境下304不锈钢的点蚀特性研究

目的 研究南海大气环境中服役的304不锈钢的点蚀原因与机理。方法 以不同暴露周期的304不锈钢试样为研究对象,采用动电位极化、电化学交流阻抗谱、扫描电镜和Kelvin 探针技术对其进行分析研究。结果 随着暴露时间的延长,304不锈钢表面的点蚀坑数量和深度均逐渐增加,其极化曲线中,钝化区间缩短,点蚀电位负移,阳极极化曲线斜率明显减小,并出现反复再钝化现象,钝化曲线逐渐消失,同时阻抗测试中的膜层电阻越来越小。SEM分析表明,304不锈钢暴露初期出现不连续的点蚀,点蚀坑向纵深发展,暴露后期出现点蚀群,局部有多个点蚀坑连成一片形成溃疡状的腐蚀表面,同时随暴露时间的延长,扫描试样微区的Kelvin表面电位不均匀性逐渐增强。结论 304不锈钢试样的耐蚀能力随暴露时间的增加而不断下降,点蚀现象不断增加。暴露初期,点蚀坑主要向纵深发展;暴露后期,点蚀坑的宽度达到一定程度后,本体溶液向坑内迁移,稀释了坑内溶液的酸度,点蚀坑向纵深和横向同时发展。     

The effects of Cl ion concentration and relative humidity on atmospheric corrosion behaviour of PCB-Cu under adsorbed thin electrolyte layer

The effects of Cl⁻ ion concentration and relative humidity on atmospheric corrosion behaviour of PCB-Cu under adsorbed thin electrolyte layer were investigated by cathodic polarization curves and electrochemical impedance spectroscopy. Results indicated that the cathodic process of PCB-Cu corrosion was dominated by the reduction of oxygen and corrosion products. The cathodic current density increased with increasing relative humidity and Cl⁻ ion concentration. The corrosion rate was initially dominated by oxygen reduction, but at the later stage of corrosion, the anodic process began to affect the corrosion rate due to the accumulation of corrosion products.     

电化学合成聚吡咯及其腐蚀防护性能研究

    采用循环伏安法在304不锈钢(304SS)基体上电化学合成聚吡咯(PPy)膜层,并通过Tafel极化曲线、电化学交流阻抗谱法(EIS)研究聚吡咯膜层的腐蚀防护性能.结果表明,聚吡咯膜层使304不锈钢基体的自腐蚀电位正移60 mV,腐蚀电流密度由10^-6 A/cm² 变化到 10^-7 A/cm²;覆有聚吡咯膜层的304不锈钢在腐蚀液中浸泡的过程中,由于聚吡咯的氧化还原能力,在金属表面加速钝化层的形成及修复破坏的钝化层,进一步提高了金属的抗腐蚀性能;聚吡咯膜层的防腐机制归结为物理屏蔽作用和钝化机制.     

Pitting corrosion of 304ss nanocrystalline thin film

Pitting corrosion behavior of coarse crystalline (CC) 304ss and its nanocrystalline (NC) thin film have been investigated by electrochemical measurement and in situ AFM observation in 3.5% NaCl solution. Results show two effects of nanocrystallization on pitting corrosion behavior: (1) more frequent occurrence of metastable pits, but with lower probability of transition to stable pits, which is attributable to differences in morphologies of sulfur and manganese as well as outstanding repassivation ability of NC thin film; (2) nanocrystallization decreases stable pit generation rate and its propensity to form larger pit cavities, and modifies the morphology of stable pit cavity.     

Corrosion behaviour of copper under chloride-containing thin electrolyte layer

The corrosion behaviour of copper under chloride-containing thin electrolyte layers (TEL) was investigated using electrochemical impedance spectroscopy (EIS), cathodic polarization, linear polarization, SEM/EDS and XRD. The results indicate that the copper corrosion rate increases as TEL thickness decreases during the initial stages. After 192 h of immersion, the corrosion rate of copper under TEL in this order: 300 > 402 > 199 > bulk solution > 101 μm. The corrosion behaviour is uniform under TEL, and pitting is the primary corrosion type in the bulk solution. A corrosion model of the behaviour of copper under chloride-containing TEL is proposed.     

Kelvin探头参比电极技术在大气腐蚀研究中的应用

Kelvin探头参比电极技术是近年来大气腐蚀领域中最为活跃的研究方向之一．它能够不接触、无破坏的检测薄液膜甚至涂层下金属表面的腐蚀电位分布，文中介绍了该技术的发展历史、技术要点，着重讨论了该技术在研究金属表面有机涂层的剥离和薄液层下金属的腐蚀两方面的应用。     

Pitting corrosion mechanism of Type 304 stainless steel under a droplet of chloride solutions

Pitting corrosion of Type 304 stainless steel under drops of MgCl₂ solution has been investigated to clarify the rusting mechanism in marine atmospheres. A pitting corrosion test was performed under the droplets with various combinations of the diameter and thickness (height) by exposure to a constant relative humidity. Probability of occurrence of pitting corrosion decreased with decreasing the diameter and thickness. Pitting corrosion progressed only when the [Cl⁻] exceeded 6 M (RH < 65%). In almost cases, there was a small hole (∼10 μm diameter) in the center of a single pit, which may be the trace of an inclusion particle like MnS dissolved out. The pitting corrosion mechanism of Type 304 under droplets containing chloride ions has been proposed.     

大气中SO_2对金属银的电化学腐蚀行为

利用三电极电化学电池研究了大气环境中的SO2对金属银的腐蚀行为。通过电化学阻抗谱和极化曲线分析了金属银在不同厚度液膜、不同湿度、不同SO2气体浓度及不同暴露时间下的初期腐蚀行为。结果显示:电极表面液膜越薄,金属银的腐蚀电流密度越大;采用镜头纸控制银电极表面液膜厚度,随着大气环境湿度的增加,银的腐蚀速度减小;在自然大气环境中,随着大气中SO2浓度的增加,暴露时间的延长,银电极的阻抗值增大,这可能是由于银电极表面Ag2O、AgOH和亚硫酸银等反应产物膜的形成的原因。     

Influence of ultrasound on pitting corrosion and crevice corrosion of SUS304 stainless steel in chloride sodium aqueous solution

The change of polarization curves and surface morphologies of SUS304 stainless steel was investigated in 3.5 mass% NaCl solution with or without the application of ultrasound (US). As the result, both the pitting corrosion and the crevice corrosion were largely suppressed by the application of US. The reason is attributed to the decrease in the concentration of hydrogen and chloride ions in pits or in the crevice by removing the corrosion product and stirring the liquid there.     

金属在薄层液膜下电化学腐蚀电池的设计

设计了用于研究金属材料在薄层液膜下腐蚀行为的参比电极后置式三电极电化学测量电池,并用此研究了铜在薄层液膜下的阳极极化行为,用双电极电解池研究了铜在薄层液膜下的交流阻抗行为。结果表明：薄层液膜（0.5mol/LHCl 0.25mol/LNa2SO4电解质）厚度的减小,影响了Cu腐蚀的阳极过程,使Cu的阳极溶解由Tafel区转向极限扩散电流区,腐蚀机制发生了变化,增大了Cu的自腐蚀电位。     

On the first breakdown in AA7075-T6

The first breakdown in AA7075-T6 was studied by an in situ observation system in which a combination of a magnified image of the surface and the instantaneous polarization curve allowed determination of the corrosion process as a function of potential. As-polished (to 1 μm) AA7075-T6 clearly exhibited dissolution of a thin surface layer corresponding to a sharp increase of current just above the first breakdown potential. No surface layer dissolution was observed for samples that were either ion milled or chemically etched to remove the effects of polishing. This susceptible surface layer was apparently the result of the mechanical polishing process. The surface microstructure of an as-polished sample was analyzed by TEM and several distinct features were found: (1) a unique thin layer with thickness of 100 nm on average; (2) many fewer fine hardening particles in the thin surface layer than in the bulk matrix, which suggests that the fine particles were destroyed and eliminated by polishing; (3) high aspect ratio nano-grains elongated along the final polishing direction; (4) a high concentration of Zn and Mg at the nano-grain boundaries. The attack of the surface layer might initiate at the active nano-grain boundary followed by nano-grain dissolution.     

Influence of temperature and applied potential on the electrochemical behaviour of nickel in LiBr solutions by means of electrochemical impedance spectroscopy

The effects of temperature, applied potential and hydrogen generation on the passive behaviour of nickel were investigated in lithium bromide aqueous solution using different electrochemical techniques: open circuit potential (OCP), potentiodynamic and potentiostatic measurements, and electrochemical impedance spectroscopy (EIS). From the polarization curves, it is observed that localised corrosion resistance decreases with temperature, the repassivation of nickel is more difficult at 75 °C and the hydrogen evolution reaction is favoured with an increase in temperature. Impedance results showed that the most suitable corrosion mechanism of nickel in LiBr solutions includes the double layer and the passive film formed on the nickel surface. The passive film of nickel partially disappears when a low cathodic potential is applied.     

Modeling bimetallic corrosion under thin electrolyte films

A finite element model (FEM) was developed to calculate the potential distribution in the electrolyte in the case of bimetallic corrosion between iron and zinc electrodes, taking into account mass transport of oxygen in the solution. This model was first compared with experimental results obtained by scanning vibrating electrode technique (SVET) on a galvanized steel cut-edge in immersion conditions in a 0.03 M NaCl electrolyte. A good agreement was obtained between the calculated and experimental current densities. The model predicted the evolution of the galvanic coupling as function of the electrolyte thickness and for various iron–zinc surface area ratios. Different coupling regimes were highlighted when the electrolyte thickness was decreased: from a kinetic (cathodic) control in full immersion conditions, to an ohmic control for very thin electrolyte films, leading to a decrease of the protection efficiency. The evolution of the critical electrolyte thickness limiting these different regimes as function of the conductivity and geometrical conditions was also studied.