共查询到6条相似文献,搜索用时 4 毫秒
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Hui Cheng Yu Bai Zhen Chen Xi Chang Shi Hai Ying Wu Bin Li 《Journal of Applied Electrochemistry》2009,39(2):303-309
The influence of five variables (i.e. deposition temperature, time, bath pH, and concentrations of Cr3+ compound (KCr(SO4)2) and H3PO4) on the preparation of Cr3+ coating on Al 6063 alloy was investigated using AC impedance spectroscopy (EIS) in 3.5 wt% NaCl. The optimal conditions were
determined by AC impedance spectroscopy. The results indicated that the formation and quality of the coating were very sensitive
to the deposition bath pH. A mechanism was proposed to explain the results. A simple model was derived and experimentally
tested in terms of an equivalent circuit. Good agreement was found between the model predictions and the experimental results.
The morphologies of the coated and uncoated electrodes were examined by scanning electron microscopy (SEM), and the results
also support the proposed surface model. 相似文献
2.
KeunWoo Cho 《Electrochimica acta》2007,52(13):4449-4456
A trivalent chromium based conversion coating (CCC), based on chromium nitrate solution with Co(II) ions, was developed on Zn substrate. The corrosion resistance of the trivalent CCC, measured in deaerated pH 8.0 borate buffer + 0.01 M NaCl solution using anodic polarization and electrochemical impedance spectroscopy (EIS), was very sensitive to both immersion time and bath pH. Micro-cracks were found on the surface of the CCC. Besides, the density of micro-crack and the coating thickness also depended on immersion time and bath pH. With increasing the coating thickness its pitting potential increased and passive current density decreased. The trivalent CCC formed on Zn for 40 s in pH 1.7 bath showed the best corrosion resistance, and the pitting potential increased significantly from −355 mVSCE for Zn to 975 mVSCE for the trivalent CCC on Zn. To explain the corrosion behavior of the trivalent CCC using EIS analysis, a modified equivalent circuit, which considered the micro-cracks in the coating and chromium corrosion product (CCP) deposited in the micro-cracks, was designed and the variation of each electrical parameter was examined. Especially, its corrosion behavior was well described by the variation of the resistance of CCP (Rccp). 相似文献
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功能梯度Ni-P合金镀层在酸性和碱性介质中的电化学腐蚀行为 总被引:4,自引:1,他引:3
通过电镀法制备了功能梯度N i-P合金镀层。SEM形貌照片显示,梯度层截面致密、无明显的宏观界面;400℃热处理前后梯度层中P含量分布曲线表明,从界面到镀层表面,P含量逐渐降低,呈现明显的梯度变化。在质量分数分别为10%的盐酸和氢氧化钠介质中的动电位极化曲线和电化学交流阻抗谱分析、含氯酸性介质中的腐蚀前后的表面形貌照片表明,与硬铬镀层相比,经过400℃热处理后的梯度N i-P合金镀层的腐蚀电位提高了600 mV以上,腐蚀电流分别降低了2个和1个数量级,阻抗值亦明显提高,而且,其腐蚀前无裂纹,腐蚀后仅发生轻微的点蚀现象。梯度N i-P合金镀层较硬铬镀层表现出更优异的耐蚀性能。 相似文献
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Zinc dust and manganese powder as pigments were incorporated in epoxy-polyamide and butyl titanate medium, with different pigment volume concentration (PVC) ranging from 20 to 74. These protective coatings were coated on sand blasted mild steel substrates and immersed in 3 wt.% sodium chloride solution and the corrosion current was measured by the Tafel extrapolation method. From the corrosion current produced by these primers, the optimum level of the pigments in these binders was identified. Thus the protective performance of optimised primers was evaluated on a sand blasted mild steel surface by the Tafel polarisation method in 3 wt.% sodium chloride solution, over different periods of time. The results were found to be comparable with the salt spray test and galvanic current measurements. The manganese powder used for this investigation showed that it could be used as an alternative to zinc powder for metal rich primers. 相似文献
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Ni + Mo + Si coatings were obtained by nickel deposition from a bath containing suspension of molybdenum and silicon powders. These coatings were obtained in galvanostatic conditions, at the current density of jdep = −0.100 A cm−2. For determination of the influence of phase composition and surface morphology of obtained coatings on changes of corrosion resistance, these coatings were modified in argon atmosphere by thermal treatment at the temperature of 1100 °C during 1 h. A scanning electron microscope was used for surface morphology characterization of the coatings. Chemical composition of obtained coatings was determined by X-ray fluorescence spectroscopy method. Phase composition investigations were conducted by X-ray diffraction method. It was found that the obtained coatings are composed of three phase structures, i.e., nickel, molybdenum and silicon. Phase composition for the Ni + Mo + Si coatings after thermal treatment is markedly different. The main peaks corresponding to the Ni and Mo coexist with the new ones corresponding to new phases: Mo5Si3, NiSi, Mo2Ni3Si and Ni6Mo6C1.06.Electrochemical corrosion resistance investigations were carried out in the 5 M KOH, using potentiodynamic and electrochemical impedance spectroscopy methods. On the basis of these investigations it was found that Ni + Mo + Si coatings after thermal treatment are more resistant in alkaline solution than Ni + Mo + Si as-deposited coatings. The reason of this is presence of silicides in the coatings. 相似文献