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Corrosion of steel under the defected coating in near-neutral pH solution was investigated by localized electrochemical impedance spectroscopy (LEIS) measurements. The LEIS response is dependent on the size of the defect. For small defects, e.g., less than 200 μm in diameter, localized corrosion process and mechanism of steel, as indicated by the measured LEIS plots, change with time. The diffusion process dominates the interfacial corrosion reaction, which is due to the block effect of the deposited corrosion product combined with the geometrical factor of a large coating thickness/defect width ratio. In the presence of a big defect, e.g., up to 1000 μm, the LEIS responses measured at the defect are always featured by a coating impedance in the high-frequency range and an interfacial corrosion reaction in the low-frequency range. The block effect of corrosion product does not apply due to the relatively open geometry. Conventional EIS measurements on a macroscopic-coated electrode reflect the “averaged” impedance results from both coating and defect. The information of the localized electrochemical corrosion processes and mechanisms at the small defect is lost, and the coating impedance information is “averaged” out when a big defect is contained. LEIS measurement provides an essential technique to characterize microscopically the local electrochemical corrosion reaction of steel under the defected coating. 相似文献
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F. Deflorian L. Fedrizzi S. Rossi P.L. Bonora 《Journal of Applied Electrochemistry》2002,32(8):921-927
The protective effectiveness of organic coatings, in controlling corrosion processes by the barrier effect, is dominated by the absence of defects passing through the coating and reaching the substrate. It is, however, difficult in general to identify and quantify the presence of defects. This work is an effort to reach a more precise quantification of the size of defect in organic coatings by means of electrochemical impedance spectroscopy (EIS) measurements. Artificial defects with controlled dimensions between 60 and 200 m were produced on organic coated galvanized steel (coil coating). After optimization of the experimental procedure for EIS data acquisition, the parameters obtained, according to a classical electrical model, were correlated with the defect dimensions. The results show that the double layer capacitance (C
dl) values depend in linearly on the defects area, while this is not true for the pore resistance (R
p) values, as the electrolyte resistivity inside the defects is a function of the defect size. Further work is necessary to extend the results to smaller defects and different systems, that is, different organic coatings and substrates. 相似文献
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X-ray photoelectron spectroscopy (XPS) is used to analyse variations during exposure to humidity and UV radiation (UVCON test) in the chemical composition of the outer surface of organic coatings (lacquers) containing phosphating or chromating reagents applied on galvanised steel, galvanneal and galfan substrates. By means of electrochemical impedance spectroscopy (EIS) measurements the protective character of the coatings analysed by XPS is studied and an attempt is made to establish possible relationships between the chemical composition of the surface of the lacquered substrates after exposure to the UVCON test and their electrochemical characterisation in immersion in a 3% NaCl solution. In general, the formation of defects or the loss of adhesion of the lacquer film leads to a significant reduction in charge transfer resistance values and, at the same time, an increase in interfacial capacitance values. The special behaviour of the galfan/lacquer “with chromating reagents” system is associated with the presence of a thin insulating film of chromium and aluminium oxides at the base of the pores in the lacquer. Interfacial capacitance values tend to evolve in close correspondence with the content of some elements on the surface of the materials. 相似文献
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Xiankang Zhong Junying Hu Shiyan Zhang Bo Chen Shuqiang Xu Fei Luo 《Electrochimica acta》2010,55(7):2424-3798
Sol-gel-based coatings exhibit high potentiality to be as an alternative to toxic chromate coatings for surface pre-treatment of metals and alloys. However, as soon as even small defects appear in the coating, the coating cannot stop the development of corrosion process. Present work demonstrates the possibility to use zinc nitrate as healing agent to repair the organic silane coatings in NaCl solution. The zinc nitrate was added to the 0.005 M NaCl solution where AZ91D magnesium alloy coated with organic silane coating was immersed. The healing process and the healing mechanism were investigated by electrochemical measurements and scanning electron microcopy coupled with energy dispersive spectroscopy. The results demonstrated the introduction of zinc nitrate to the electrolyte could stop the development of corrosion process of the coating system and a remarkable recovery on corrosion resistance could be obtained. This effect may be attributed to the formation of zinc oxide/hydroxide on the defective areas, hindering the corrosion activities. 相似文献
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In situ electrochemical Scanning Kelvin Probe Blister-Test studies of the de-adhesion kinetics at polymer/zinc oxide/zinc interfaces 总被引:1,自引:0,他引:1
Fundamental investigations of the polymer/zinc oxide/zinc interface corrosion stability were performed in situ by means of the electrochemical Height Regulated Scanning Kelvin Probe Blister-Test (HR-SKP-BT) under controlled atmospheric conditions. A hole under an adhesive layer film served as electrolyte reservoir to initiate cathodic de-adhesion processes. Then a combinatorial approach was undertaken to simultaneously study the influence of electrolyte pressure at constant defect polarisation and of relative atmospheric humidity on the de-adhesion rate. The time resolved blister growth and the propagation of the three phase boundary polymer/oxide covered zinc/interfacial electrolyte layer could be detected. It could be proven that the oxygen reduction induced electrochemical damage of the interface precedes the subsequent mechanical de-adhesion process. By variation of the relative atmospheric humidity the water concentration within the bulk adhesive and its interphase adjacent to the metal substrate could be adjusted. These processes were further analysed by peel-tests and in situ Attenuated-Total-Reflection Infrared Spectroscopy (ATR-IR) studies of water diffusion. A decrease of the interphasial water concentration led to a deceleration of the de-adhesion kinetics for constant defect conditions and to smaller interfacial ion transport rates. This could be assigned to an inhibition of the electron transfer reactions at the front of de-adhesion and an increased adhesion force between polymer film and oxide covered metal preventing the formation of an extended interfacial electrolyte layer. 相似文献
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Maria Luisa Foresti Andrea Pozzi Giovanni Pezzatini Emanuele Salvietti Fabio D’Anca Francesco Borgatti 《Electrochimica acta》2006,51(25):5532-5539
An innovative setup to combine electrochemical and in situ surface X-ray diffraction (SXRD) measurements is described. This electrochemical cell has a different design from the other ones commonly used for X-ray diffraction studies. It allows the sample surface to stay always completely immersed into the solution under controlled potential conditions even during the SXRD measurements. The X-ray beam crosses the liquid (about 1 cm) and the cell walls. Because of the high X-ray energy, the beam attenuation is negligible and by an appropriate positioning of the detector arm slits it is possible to minimize the diffuse scattering induced by the liquid and cell walls in order to still detect the minima of the crystal truncation rods (CTRs). The liquid solution in the cell is managed by a special device, which allows the controlled exchange of the electrolyte solutions necessary in the electrochemical atomic layer epitaxy (ECALE) growth. The whole setup can be remotely controlled from outside the experimental hutch by a dedicated computer. As an example we report measurements on S layers deposited at underpotential on the Ag(1 1 1) surface, and on CdS films of increasing thickness. 相似文献
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The corrosion behavior of mild steel in CO2-saturated 5% NaCl solution with N-[2-[(2-aminoethyl) amino] ethyl]-9-octadecenamide corrosion inhibitor at 25 °C has been studied by using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) measurements. Both potentiodynamic polarization and EIS measurements reveal that this amido-amine precursor inhibits the carbon steel corrosion and the inhibition efficiency increases with increasing the inhibitor concentration. The corrosion inhibitor exhibits high corrosion efficiencies as a mixed-type inhibitor, with a predominant influence on the anode process. The organic inhibitor acts blocking surface sites at low concentrations and by modifying the adsorption mechanism forming a protective barrier against corrosive ions at high concentrations. EIS results show that the mechanism of its corrosion inhibition at concentrations higher than 0.82 × 10−5 M is by forming a protective bilayer with small pore sizes that hinders the passage of the reactive species. PM-IRRAS measurements demonstrate that the inhibitor is chemisorbed to surface steel. Therefore, its spectrum reveals that the inhibitor monolayer has an amorphous structure. 相似文献
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低温高效钢铁磷化及其成膜机理的研究 总被引:4,自引:0,他引:4
由于常温磷化存在沉渣多 ,耐磨、耐蚀性差等缺点 ,低温磷化的研究正日益受到人们的重视。本文研制了一种低温、高效锌系钢铁磷化液。探讨了磷化膜的成膜机理 ,沉渣的形成条件及抑制沉渣生成的方法。该磷化液具有处理温度低、成膜快、沉渣少、耐磨、耐蚀性好等特点。 相似文献
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锌钙系磷化的最新应用研究 总被引:6,自引:2,他引:6
研究了3种新的锌钙系磷化工艺和配方,中温高耐蚀黑色磷化,磷化膜细致,耐蚀性优异,可用于钢铁的防锈磷化;钙改良的低温低锌磷化,钙的加入有利于镀锌板,铝板,钢板的复合件的磷化,可用于电泳涂装,中温耐热锌钙系磷化可用于需高温烘烤涂料涂装前的磷化处理,锌钙系磷化是磷化技术发展的一个方向。 相似文献
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Kerry N. Allahar Vinod UpadhyayGordon P. Bierwagen Victoria Johnston Gelling 《Progress in Organic Coatings》2009
Two-layered organic coatings protect metallic structures against corrosion by reducing the transport of water, ions, and oxygen from the environment to the substrate and storing species that provide corrosion inhibition. The topcoat and the primer provide the former and latter, respectively, with the primer also providing adhesion between the topcoat and the substrate. A standard testing method for coatings is the ASTM G85 Prohesion® test. This test involves alternating between a wet exposure of 1-h salt spray at 25 °C and a dry exposure of 1-h air at 35 °C. Apart from visual inspection, conventional monitoring of coating properties is achieved by ex situ electrochemical tests under immersion in a suitable electrolyte. In situ monitoring during a Prohesion® test was performed for a military vehicle coating system using embedded sensors located between the topcoat and primer. In situ results associated with the dry and wet exposures are presented from electrochemical impedance spectroscopy and electrochemical noise measurements. In situ single-frequency impedance measurements were used to monitor the water uptake/loss associated with the exposures of the test conditions. Ex situ monitoring was also performed for comparison with the in situ embedded sensor monitoring. 相似文献
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G. Klimow 《Electrochimica acta》2007,53(3):1290-1299
Scanning Kelvin Probe (SKP) measurements of thin amorphous conversion film coated galvanised steel in combination with current density-potential curves and electrochemical impedance spectroscopy (EIS) were performed with the aim to improve the understanding of electrode potentials at the coating/metal interface and their influence on corrosive de-adhesion. The thin hybrid conversion films contained Zn-phosphates, titanates and also complexing organic compounds and led to an inhibition of the cathodic oxygen reduction and anodic zinc dissolution. In the polymer coated area the conversion film leads to a cathodic shift of the potential as measured by means of the SKP. This cathodic potential shift is explained by the substitution of the n-semiconducting Zn-oxide with an insulating inorganic layer. When the SKP detects the potential of freely corroding iron at a defect, where no protective coating layer is, the interfacial potential for the conversion film coated zinc layer is more negative than the defect potential. This leads to a diminished driving force for an oxygen reduction induced delamination process which is of relevance for the understanding of cut-edge corrosion. 相似文献
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