Delamination of organic coating on carbon steel studied by scanning Kelvin probe force microscopy

Corrosion‐induced delamination of an epoxy coating on the AISI/SAE 1045 carbon steel was studied under a humid atmospheric condition (temperature of 25 °C, 1 standard atmospheric pressure, relative humidity of 90%) by the technique of scanning Kelvin probe force microscopy (SKPFM). Surface‐polished 1045 samples were first cold‐coated with the epoxy and then subject to the atmospheric corrosion under the specified condition. At predetermined time intervals, surface Volta potential differences of the samples were measured using the SKPFM over the dry surface of epoxy coating. The map of Volta potential differences demonstrated high contrasts among three characteristic zones: intact steel‐epoxy interface, delaminated interface, and interface with active corrosion, which was then linked to the actual corrosion potential of the steel (measured using a potentiostat with respect to a saturated calomel electrode) based on a rigorous calibration procedure. It was found that the SKPFM was able to provide direct and nondestructive detection of early active corrosion and coating delamination on steels at a submicroscopic resolution, which outperformed the conventional electrochemical techniques for the same purposes. Copyright © 2012 John Wiley & Sons, Ltd.     

Investigation of coating delamination on steels by surface topography and Volta potential difference

Corrosion-induced delamination of an epoxy coating on the AISI/SAE 1045 carbon steel was studied under a humid atmospheric condition (temperature of 25 °C, one standard atmospheric pressure, and relative humidity of 90 %) by the technique of scanning Kelvin probe force microscopy (SKPFM). Surface-polished 1045 samples were first cold coated with the epoxy and then subject to the atmospheric corrosion under the humid atmospheric condition. At specified time intervals, surface Volta potential of the samples was measured using the SKPFM over the dry surface of epoxy coating. The map of Volta potentials demonstrated high contrasts among three characteristic zones: intact steel-epoxy interface, delaminated interface, and interface with active corrosion, which based on a rigorous calibration procedure were then linked to the actual corrosion potential of the steel (measured using a potentiostat w.r.t. a saturated calomel electrode). The SKPFM was found to be able to provide a mean of direct and nondestructive detection of early active corrosion and coating delamination of steels at a submicroscopic resolution, which outperformed the conventional electrochemical techniques for such purposes.     

Effect of mechanical stress on the kinetics of heterogeneous electron transfer

The scanning electrochemical microscope (SECM) combined with a computerized tensile stage was employed to measure the kinetics of electron transfer (ET) reactions at stainless steel electrodes as a function of the applied mechanical stress. Reproducible current versus distance curves were obtained for different values of the tensile stress applied to a stainless steel (T-316) sample by using hexaammineruthenium as a redox mediator. The dependences of the extracted rate constant on substrate potential (i.e., Tafel plots, ln k versus E) were linear, in agreement with classical electrochemical theory. Possible origins of the stress effect on the ET rate and its implications for studies of stress corrosion cracking are discussed.     

A combined TEM and SKPFM investigation of the surface layers on rolled AA5050 aluminium alloy using ultra‐microtomy

This article studies the evolution of near‐surface morphology as a function of various thermo‐mechanical treatments along the fabrication line of rolled AA5050 aluminium alloy. Ultra‐microtomy has been used to prepare cross‐sectional thin foils for transmission electron microscopy (TEM) and proper surfaces for scanning Kelvin probe force microscopy (SKPFM) analysis. A slight increase in the Volta potential difference (between the inter‐metallics and the matrix) between the as‐cast surface and the surface obtained after the first hot‐mill pass, emphasized that the changes in surface micro‐structure, which in turn affect the corrosion and electrochemical properties of the finished product, had already occurred at that stage. The Volta potential difference during the subsequent hot‐mill pass remained relatively constant. As far as the near‐surface morphology was concerned, hot‐rolling resulted in the formation of a heavily deformed surface layer. Annealing of the hot‐rolled aluminium sheet resulted in partial re‐crystallization of the surface layer. Subsequent cold‐rolling re‐introduced deformation in the near‐surface region. Copyright © 2008 John Wiley & Sons, Ltd.     

Dynamic electrochemical impedance spectroscopy measurements of passive layer cracking under static tensile stresses

Electrochemical impedance spectroscopy allows the examination of corrosion susceptibility and resistance for different construction materials, in particular the determination of the properties of their passive films. This technique makes possible the analysis of electrochemical processes in time domain, including rapid phenomena such as changes in the properties of passive films, but it has never been used for passive layer cracking examination. In many cases, fracture of the passive film under tensile stresses leads to stress corrosion cracking. Therefore, investigations of passive layer cracking on austenitic stainless steels under tensile stresses facilitate the understanding of the mechanism of stress corrosion cracking in these common engineering materials. The effect of static tensile stresses on the passive film cracking behaviour of type 304L stainless steel immersed in 0.5 M NaCl solution at room temperature has been investigated. This paper presents the impedance spectra obtained for 304L stainless steel samples at different potential values.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003)     

Development of pitting corrosion of stainless steel 403 in sodium chloride solutions

Pitting corrosion of stainless steel 403 in the NaCl solutions is studied. It is shown that the experimental results obtained under the potentiostatic conditions do not provide sufficient information on the behavior of steel under the conditions of free corrosion. The corrosion experiments take long time, their results exhibit poor reproducibility; however, they are necessary for obtaining reliable data on the corrosion behavior of steel. The development of corrosion process is reflected in the variation of corrosion potential with time. The effect of concentration and temperature of NaCl solutions on the development of pitting corrosion is studied. The peculiarities of the distribution of pits over the test specimen surface are revealed. In 1 M NaCl solution at 20°C, few pits arise. Some of them repassivate; some pits grow, initially, in diameter and depth and, then, almost only in depth. The examples of through pit formation on the specimens 4 mm thick are presented.     

Microstructural and in-depth electrochemical characterization of Zn diffusion layers on aluminum 3xxx alloy

AA 3XXX alloys are widely used in heating, ventilation, and air conditioning (HVAC) field. Diffusion joining using a filler metal together with flux is employed in some applications as for heat exchangers. In this work, the effect of diffusion of a Zn-based flux on both microstructure and electrochemical behavior has been investigated. In particular, an AA3xxx was coated with a Zn-rich flux and subjected to controlled atmosphere brazing (CAB). Glow discharge optical emission spectroscopy (GDOES) composition profiles were acquired in order to determine the Zn distribution in the diffusion layer. The GDOES was also employed to produce a controlled erosion of the surface in order to obtain craters with defined depths in the Zn diffusion layer, in which electrochemical analyses could be performed. The Volta potential maps at different depths in the Zn diffusion layer were obtained by scanning Kelvin probe force microscope (SKPFM). The Zn diffusion layer was also investigated by means of Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy (SEM-EDXS) and the chemical composition of the phases present in the regions was investigated by SKPFM. Finally, the electrochemical microcell was used in the produced craters in order to determine the electrochemical behavior along the Zn diffusion profile. SKPFM and microcell results showed a correlation between the Zn content and the electrochemical properties. In particular, a higher Zn content in the diffusion layer leads to an increase of the Volta potential difference between the intermetallic particles and the matrix. The electrochemical measurements also showed that the Zn diffusion layer provides galvanic protection to the underlaying aluminum alloy.     

Effect of cyclic oxidation on electrochemical corrosion of type 409 stainless steel in the simulated muffler condensates

The electrochemical corrosion behavior of 409 stainless steel after cyclic oxidation below 400 °C was investigated in the simulated muffler condensates by using surface analysis and electrochemical measurement techniques. In the cyclic processes of condensate-dipping and oxidation, specimens may form defective oxide films and weak Cr depletion underlying the oxide films. Sulfate from the condensate-dipping will give rise to sulfidation during the cyclic oxidation, being detrimental to both the oxidation and corrosion properties of stainless steel. The oxidation above 300 °C deteriorates the corrosion resistance, even leading to active corrosion in the acidic condensate solutions. Comparatively, specimens oxidized cyclically without condensate-dipping show much higher condensate corrosion resistance. It is suggested that the acidic condensate corrosion is accelerated by the synergetic effect of oxidation and condensation in the mufflers, and then may result in perforation through the defects such as cracks and nodules in oxide films on the stainless steel surface.     

有机涂层失效过程的电化学阻抗和电位分布响应特征

结合使用电化学阻抗谱(EIS)和扫描Kelvin探针(SKP)技术研究了在质量分数为3.5%的NaCl溶液中的铁基有机涂层劣化过程特征. 结果表明, 根据EIS和SKP的响应特征, 可将涂层劣化过程分为3个主要阶段: (Ⅰ) 涂层渗水阶段. 此时, 涂层渗水阶段的EIS阻抗持续减小, 但保持单容抗弧特征, SKP特征是电位持续降低, 但分布保持均匀; (Ⅱ) 基底金属腐蚀发生阶段. 此时, EIS阻抗快速下降, 并产生第二时间常数; SKP特征为表面电位差增大; (Ⅲ) 基底金属腐蚀发展与涂层失效阶段. 此时, EIS出现扩散尾, SKP电位差保持较大数值. 实验结果表明, 在研究有机涂层劣化过程中, EIS和SKP的结合使用能够互相补充完善, 获得涂层劣化过程中更为准确\, 可靠的变化信息.     

18／8型不锈钢在受力形变条件下腐蚀电化学行为的研究

应用电化学稳态技术、电化交流阻、抗微区电化学技术及扫描电等方法，研究１８／８型不锈钢在Ｎａ２Ｓ２Ｏ３稀溶液中，受外力形变条件下，的腐蚀电化学行为，结果表明，力学因素可使表面腐蚀电化学活性增加，表面微裂纹的发生、消失和再钝化的动态过程，同时受电位和拉应力的影响；点腐蚀可优先发生在应力集中位置，点蚀的发展可能诱导不锈钢的应力腐蚀开裂。     

高温高压喷射湍流区中X70管线钢CO2腐蚀电化学特征

采用高温高压环路喷射装置并结合腐蚀微电极技术, 开展了湍流区中X70 管线钢CO₂腐蚀实验. 利用扫描电镜对不同实验时间的试样表面腐蚀产物微观形貌进行了观察和分析, 并进行了湍流区原位电化学测试和分析. 结果表明, 湍流区中X70 钢的CO₂腐蚀电化学特征与其表面所覆盖腐蚀产物膜层变化密切相关. 实验12 h内, 湍流区中X70钢表面从最初的基体与腐蚀产物共存, 转变为由疏松且不完整的膜层覆盖的特征. 实验12 h 后, 试样表面出现内外两层腐蚀产物膜, 内层膜堆垛致密, 外层膜疏松多孔, 同时湍流区中高切应力导致外层腐蚀产物脱落, 材料表面逐渐被完整致密的内层膜覆盖, 这是腐蚀速率持续下降的主要原因. 电化学结果表明, 实验12 h 内, 湍流区中X70 钢的腐蚀电位E_corr和线性极化电阻R_p不断下降; 电化学阻抗谱由高频容抗弧、中频容抗弧和低频感抗弧组成, 膜层电阻R_f缓慢增加, 电荷传递电阻R_t不断下降, 双电层电容C_dl和膜层电容C_f迅速下降; 12 h后, 腐蚀产物膜层对基体材料保护性随喷射时间延长逐渐增强, E_corr和R_p逐渐增大, 电化学阻抗谱中低频感抗弧逐渐收缩并在48 h 时消失, 最后转变为双容抗特征, R_f、R_t和C_dl随时间迅速增大, C_f趋于稳定.     

磁场对316L不锈钢微生物腐蚀行为的影响

采用循环极化、微生物分析法、扫描电镜及表面能谱分析等方法,研究了磁场对316L不锈钢在含硫酸盐还原菌(SRB)的土壤模拟溶液中的腐蚀行为。结果表明,磁场可以抑制SRB的生长;未外加磁场时316L不锈钢表面膜层以局部堆积为主,加有磁场时,局部堆积明显减小,膜层均匀致密的排列于基体表面;无论有或没有外加磁场,316L不锈钢表面均发生钝化膜破裂型点蚀,未外加磁场时的点蚀电位低于加有磁场时的。在相同的浸泡时间,未外加磁场时循环极化滞后环面积明显比加有磁场时的大,说明磁场可以有效抑制316L不锈钢点蚀的形成与发展,降低316L不锈钢的点蚀诱发能力。     

Study on the Corrosion Resistance of 304L Stainless Steel

304L is an austenitic stainless steel with very low carbon content, and is served as the application to the oxidizing media, however, its corrosion resistance is not satisfactory in reducing media. For example, the pitting corrosion occurred on 304L stainless steel tube, which had been mounted for one year, somewhere at the power station in die seashore of China. For this reason we have studied the corrosion behavior of 304L in some media and invented a novel surface treatment technique of stainless steel for extremely improving the corrosion resistance of 304L. The characteristics of the modified passive film on the steel were examined in this paper, and the corrosion resistance of treated 304L stainless steel was tested in our laboratory and the testing ground. The results are satisfactory.     

Corrosion inhibition of 302 stainless steel with schiff base compounds

The effects of 2,2′-[bis-N(4-cholorobenzaldimin)]-1,1′-dithio (BCBD) and bis-(2-aminophenyl) disulphide (BAPD) on the corrosion behavior of 302 stainless steel in 0.5 M sulfuric acid solution as corrosive medium were investigated using weight loss and potentiostatic polarization techniques. Some corrosion parameters such as anodic and cathodic Tafel slopes, corrosion potential, corrosion current density, surface coverage degrees and inhibition efficiencies were calculated. The polarization measurements indicated that the inhibitors were of mixed type which inhibited corrosion by parallel adsorption on the surface of stainless steel due to the presence of more than one active centre in the inhibitor molecule. The adsorption followed Langmuir adsorption isotherm. The activation energy and thermodynamic parameters were calculated at different temperatures. Results showed that BCBD had a higher inhibition efficiency compared with BAPD.     

Interfacial Behavior of beta-Lactoglobulin at a Stainless Steel Surface: An Electrochemical Impedance Spectroscopy Study

The electrochemical impedance spectroscopy technique was used to investigate the interfacial behavior of beta-lactoglobulin at an austenitic stainless steel surface over the temperature range 299 to 343 K at an open circuit potential. The electrode/electrolyte interface and corresponding surface processes were successfully modeled by applying an equivalent-electrical-circuit approach. A charge-transfer resistance value was found to be very sensitive to the amount of adsorbed protein (surface concentration), thus indicating that the adsorption of the protein (i) was accompanied by the transfer of the charge, via chemisorption, and (ii) influenced the mechanism and kinetics of the corrosion reaction. This was also apparent from the large decrease in the corrosion activation energy (16 kJ mol(-1)) caused by the adsorption of the protein. Adsorption of beta-lactoglobulin onto the stainless steel surface at an open circuit potential resulted in a unimodal isotherm at all the temperatures studied and the adsorption process was described with a Langmuir adsorption isotherm. From the calculated Gibbs free energies of adsorption it was confirmed that beta-lactoglobulin molecules adsorb strongly onto the stainless steel surface. The enthalpy and entropy values indicated that the molecule partially unfolds at the surface upon adsorption. The adsorption process was found to be entirely governed by the change in entropy. Copyright 2000 Academic Press.     

Corrosion behavior of 316 stainless steel for advanced high-temperature water-cooled nuclear plant

Corrosion occurs widely in the supercritical water system materials under high temperature and pressure. To select reliable candidate materials, corrosion behavior of many alloys was investigated. This study focused on investigating the corrosion behavior of 316 stainless steel (316 SS) in supercritical water (798 K/24 MPa). After exposed to SCW for 200 h, the oxidation kinetics, surface morphology, and diffusion of elements were investigated by weight measurement, scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The surface of 316 SS showed isolated and discontinued oxide scales. The oxide scale was determined to be a monolayer layer, and the main composition was determined to be Fe–Cr-rich spinel with a few amounts of magnetite attached to the surface. A few pores due to pitting corrosion were found on the surface, and the oxidation mechanism was also investigated.     

Corrosion and biological behavior of nanostructured 316L stainless steel processed by severe plastic deformation

Nanostructured metals have different mechanical, chemical, and physical behaviors in comparison with the microstructured ones. Numerous research studies demonstrated that the biological behavior of nanostructured metallic implants was improved significantly. Concerning the nanostructured metals, decreasing the corrosion rate and the releasing of hazardous ions from metallic implants, and thus increasing the biocompatibility of implants are due to improving the native oxide layer. In the present study, nanostructured 316L stainless steel (biomedical grade) was manufactured via equal channel angular pressing (ECAP) method. To do so, the 316L stainless steel (SS) was exposed to the ECAP operation for eight passes. The impact of the ECAP process on corrosion behavior of SS samples was evaluated through performing the electrochemical polarization corrosion tests in Ringer's solution. Scanning electron microscopy was employed to study the surface morphology of common SS and ECAPed SS sample after the electrochemical polarization tests. Moreover, the biological behavior of the samples was evaluated via cell culture using fibroblast cells. The corrosion test results revealed a substantial decrease of corrosion rate from 3.12 (coarse‐grained sample) to 0.42 μA cm^?2 (for nanostructured). Furthermore, the cell proliferation in the interface of nanostructured sample and cell culture medium enhanced dramatically compared with the coarse‐grained one. The much better biological behavior of nanostructured SS sample in comparison with the coarse‐grained one is mostly due to the significant decrease of corrosion rate on the surface of SS samples, and the presence of much more chrome oxide on the surface of SS sample. Copyright © 2015 John Wiley & Sons, Ltd.     

聚吡咯/聚苯胺复合型导电聚合物防腐蚀性能

采用循环伏安法,在含吡咯和苯胺的0.3 mol/L草酸水溶液中制备了聚吡咯/聚苯胺(PPy/Pani)的复合型导电聚合膜。采用红外光谱、极化曲线、自腐蚀电位-时间曲线、扫描电子显微镜和电化学阻抗谱研究了共聚膜的防腐蚀性能。结果表明,在1 mol/L H2SO4中,PPy、Pani与不锈钢基体发生氧化还原反应,促进不锈钢表面发生钝化;当苯胺与吡咯浓度比为1∶3时,制备得到的复合型导电聚合膜所保护的不锈钢自腐蚀电流最小,自腐蚀电位最高,保护时间最长。PPy、Pani及其共聚膜在3.5%NaCl溶液中电化学阻抗谱表明,所制备的PPy、Pani及其共聚物膜与不锈钢基体发生氧化还原反应,使其表面钝化;当Cl-到达不锈钢表面时,破坏钝化膜导致不锈钢腐蚀。     

Misorientation mapping for visualization of plastic deformation via electron back-scattered diffraction.

The ability to map plastic deformation around high strain gradient microstructural features is central in studying phenomena such as fatigue and stress corrosion cracking. A method for the visualization of plastic deformation in electron back-scattered diffraction (EBSD) data has been developed and is described in this article. This technique is based on mapping the intragrain misorientation in polycrystalline metals. The algorithm maps the scalar misorientation between a local minimum misorientation reference pixel and every other pixel within an individual grain. A map around the corner of a Vickers indentation in 304 stainless steel was used as a test case. Several algorithms for EBSD mapping were then applied to the deformation distributions around air fatigue and stress corrosion cracks in 304 stainless steel. Using this technique, clear visualization of a deformation zone around high strain gradient microstructural features (crack tips, indentations, etc.) is possible with standard EBSD data.     

Magnetic field effect on stainless steel corrosion in FeCl3 solution

Corrosion of AISI 303 stainless steel in FeCl₃ solution was studied in the magnetic field, whose direction was perpendicular to the corroding surface. The magnetic field inhibited corrosion in both quiet and stirred solutions. This was evident from the increased repassivation potential, the reduced number of pits and the decreased mass loss. By contrast, an accelerating effect of the magnetic field was observed on the single cathodic reaction of the corrosion process, viz. Fe(III) reduction to Fe(II). This was confirmed by voltammetric measurements on both platinum and stainless steel electrodes. The corrosion magnetoinhibition was explained in terms of field-assisted development of a passive layer, whose passivation capacity was higher than that under the field-free conditions.