电化学阻抗谱在电沉积研究中的应用(二)

文章的第二部分介绍了电化学阻抗谱在金属(包括锌、铜、镍、铅、铬)及合金(锌–铁、钴–镍、镍–钼)电沉积研究中的应用。     

电化学阻抗谱在电沉积研究中的应用(三)

文章的第三部分介绍了电化学阻抗谱在Ni–SiC复合镀、化学镀镍和镀层性能(耐蚀性、电化学行为和腐蚀行为)研究中的应用。     

电化学阻抗谱在缓蚀剂研究中的应用进展

概括了电化学交流阻抗谱的基本原理,介绍了电化学阻抗谱在缓蚀剂研究中的应用进展,并对电化学阻抗谱在腐蚀科学领域其他方面的应用进行了展望。     

用交流阻抗谱研究活性砂浆胶结材料的电化学行为

海水环境潮差浪溅区钢筋混凝土结构易腐蚀破损,可采用锌网阳极与活性砂浆组成的牺牲阳极阴极保护系统进行修复保护.用交流阻抗谱方法对活性砂浆胶结材料的电化学性能进行了研究,并采用等效电路对阻抗谱进行拟合解析.结果表明:砂浆中掺入活性组分后,砂浆电阻显著降低,极化电阻与扩散阻抗系数也随活性组分的掺入大幅度降低;活性砂浆中阳极表面膜层不再是致密钝化的状态,表面易于进行阴极反应;活性组分同等掺量条件下,溴化锂更利于提高砂浆的电化学活性.     

用电化学阻抗谱(EIS)最大相角频率(f_(θmax))法快速评价风电涂料

应用电化学阻抗谱Bode图,求出最大相位角处频率fθmax,应用fθmax与涂层电阻Rc的线性关系,现场快速评价有机涂层性能。用该法对几种风电涂料进行了评估,对聚氨酯类风电涂料的防腐机理进行了讨论。分析表明,本法既可作为快速定性比较评价涂层性能的方法,也可作为涂料生产企业质量控制的一种快速有效的方法。     

不同腐蚀试验的电化学阻抗谱评价

采用电化学阻抗谱分析了环氧涂层的介质浸泡、ASTM-B117盐雾试验、PROHESION循环试验的性能变化。实验结果表明:介质浸泡更侧重考察涂层的屏蔽作用,对环氧-聚酰胺体系酸性电解质更容易导致涂层失效;而盐雾试验更容易导致涂层吸收水分,干湿交替增加了有机涂层吸水能力;划痕试验表明样板在ASTM-B117和PRO-HESION遵循不同的腐蚀机理。     

钛纳米聚合物涂料在NaCl溶液中的电化学阻抗谱

采用电化学阻抗谱方法对钛纳米聚合物涂料的防腐性能进行了研究,并通过与环氧树脂清漆、环氧玻璃鳞片涂料的对比,说明钛纳米聚合物涂料的防腐性能显著优于上述两种涂料的防腐性能。     

水泥混凝土电化学进展—交流阻抗谱理论

水泥混凝土材料体系的电化学研究最近取得了若干重要进展，本文涉及交流阻抗谱应用于水泥混凝土材料科学的若干理论问题，包括交流阻抗谱各个参数与硬化水泥浆体结构相关的理论关系式，及其在若干水泥水化体系中的验证，表明了在复平上出现的交流阻抗半圆的位置和大小取决于材料固－液界面特性，即与孔隙率、孔分布和孔溶液中电解质浓度有关，用交流阻抗谱研究水泥浆体结构可望成为一种快速，非破坏性的测试方法。     

磁场辅助射流电沉积Ni-SiC纳米复合镀层耐蚀性的研究

采用磁场辅助射流电沉积方法在45^#钢表面制备了Ni-SiC纳米复合镀层,并研究了镀层的表面形貌、耐蚀性及物相组成。结果表明:当电流密度为4 A/dm²时,镀层的腐蚀失重最小为3.2 mg/cm²;当磁场强度超过0.8 T后,镀层的腐蚀失重基本保持不变;当喷射速率达到3 m/s时,镀层的腐蚀失重最小为3.5 mg/cm²。经SEM分析可知,当磁场强度达到0.8 T时,腐蚀产物最少,晶间腐蚀较轻。由极化曲线及电化学阻抗谱分析可知,当磁场强度达到0.8 T时,镀层的耐蚀性最好。由XRD分析证实了Ni、SiC两相的存在,并且随着磁场强度的增加,衍射峰变矮、变宽,说明镀层晶粒细化,改善了镀层的耐蚀性。     

电沉积镍基和铜基纳米复合镀层耐蚀性的研究

通过腐蚀浸泡实验、阳极极化曲线和电化学阻抗谱等测定,探讨了Ni-W-(Si3N4,Al2O3)和Cu-(Al2O3,SiO2)纳米复合镀层的耐蚀性能;通过综合分析,对比添加不同柱子所得镀层的性能,直观地得到添加不同粒子的镍基和铜基纳米复合镀层耐蚀性能的差异.结果表明:Ni-W-Si3N4、Ni-W-Al2O3纳米复合镀层致密度较高,耐蚀性能较好,Cu-Al2O3、Cu-SiO2纳米复合镀层耐蚀性能较差.     

Characterization of boron-doped diamond electrodes by electrochemical impedance spectroscopy

Charge transfer on boron doped diamond (BDD) electrodes was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The diamond films of 5 μm thickness and boron content between 200 ppm and 3000 ppm were prepared by the hot filament CVD technique on niobium substrate and mounted in a Teflon holder as rotating disk electrodes. The electrochemical measurements were carried out in aqueous electrolyte solutions of 0.5 M Na₂ SO ₄ + 5 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆]. Significant deviation in the redox behaviour of BDD and active Pt electrodes was indicated by a shift of the peak potentials in the cyclic voltammograms with increasing sweep rate and lower limiting diffusion current densities under rotating disk conditions. In the impedance spectra an additional capacitive element appeared at high frequencies. The potential and rotation dependence of the impedance spectra can be described quantitatively in terms of a model based on diffusion controlled charge transfer on partially blocked electrode surfaces. Direct evidence for the non-homogeneous current distribution on the diamond surface was obtained by SECM measurements.     

Evaluation of nickel deposition by electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy was used to characterize the deposition of nickel from unbuffered acid sulfate electrolytes, from which a wide range of deposit morphologies and current efficiencies are possible. The operating parameters were in the range of 40 to 60 g L^–1 Ni²⁺, 40 to 60 °C, and the pH from 2.0 to 3.5. The resulting impedance spectra for nickel deposition at 20 mA cm^–2 consisted of one or two characteristic loops whose frequency and capacitance were dependent upon the electrowinning conditions and indicative of the resultant deposit morphology. A single high frequency capacitive loop, on the order of 1 kHz, correlated to good quality deposits which were flat, smooth and ductile. The presence of a low frequency loop, on the order of a few hertz, indicated a degraded deposit morphology which showed localized dark, glassy areas and were cracked, curled and brittle. The second loop may be associated with a diffusion controlled component in the reaction mechanism. Deposits of intermediate quality had impedance spectra consisting of both type loops. No apparent trend between the impedance spectra and the deposit current efficiency was determined, but a correlation with deposit quality was clearly established.     

Adhesion characterization of protective organic coatings by electrochemical impedance spectroscopy

Adhesion is considered in many situations to be a very important property of organic coatings for corrosion protection and much scientific work is devoted both to the study of the mechanism involved in polymer-metal adhesion and to the ways of measuring this property. The large number of experimental methods in existence to obtain information on coating adhesion is an indication of both the scientific and the technological interests in this material science and engineering area, but it is also a consequence of the difficulty in measuring adhesion in a general sense. As a partial alternative to the traditional adhesion measurement approaches for organic coatings, the evaluation of adhesion by electrochemical techniques such as electrochemical impedance spectroscopy (EIS) is discussed for different examples. The influences on adhesion of different pretreatments or organic coatings are discussed, considering aluminium, galvanized steel, and stainless steel substrates, and we have shown that the information obtained by using an electrochemical approach can be used for adhesion evaluation, with particular attention to the monitoring of adhesion in an aqueous environment, which is the most detrimental for protective organic coatings.     

Investigation of strength degradation of adhesive-bonded aluminum joints exposed to corrosive environment using electrochemical methods

Interfacial corrosion is responsible for the strength degradation of adhesive-bonded aluminum joints (ABJs) exposed to corrosive environment. In this study, electrochemical noise and electrochemical impedance spectroscopy (EIS) measurements were performed on the aluminum alloy X610-T4PD covered with adhesive (ACA) to understand the interfacial corrosion. And environmental simulation tests (i.e. neutral salt spray (NSS) and hot humidity environment) for ABJ were carried out to investigate the joint strength degradation. Test results indicated that the variations of current and potential in the EN measurement were closely related to the initiation of corrosion in the samples. The Nyquist plots in the EIS measurement for various immersion times showed that the corrosion of ACA accelerated after about 140 h. Furthermore, a linear relationship between the residual strength of ABJ exposed to NSS and the reciprocal of interfacial corrosion resistance (R_t) of ACA was found, which was verified by ABJ exposed to hot humidity environment.     

Defect dimension evaluation in organic coated galvanized steel by electrochemical impedance spectroscopy

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.     

Study of electrical properties of polymeric materials using electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) has been used to determine the water absorption characteristics of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyaromatic amide (Aramid), and amine–quinone polyurethane (AQ) free-standing polymer films. A method for calculating percent moisture uptake is presented based on capacitance measurements via EIS, which requires initial or “dry” capacitance values, C₀. Three different methods for obtaining C₀ values were described and employed, but the most reliable values were obtained via EIS measurement using Hg contacts. C₀ values obtained by this method resulted in calculated water uptake values nearly identical to those obtained by measured weight gain. Lower capacitance values were observed for films immersed in distilled water compared to 0.1M NaCl, which indicates that water uptake is greater in NaCl than in pure water. The four polymers examined in this study can be listed in order of decreasing resistance to moisture absorption as AQ > PET > PEN > Aramid. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 553–560, 1998     

Evaluation of thin defect-free epoxy coatings using electrochemical impedance spectroscopy

The water sorption of thin defect free epoxy films and coatings on aluminium electrodes was studied using the gravimetric method and electrochemical impedance spectroscopy. The results show that the double layer capacitance of the wetted surface of the aluminium electrode under the epoxy film is considerably smaller than that of a bare aluminium electrode, except in the early period of immersion. The resistivity of the solution absorbed in the epoxy coating is much higher than that of the bulk solution. A method for approximately determining the equilibrium water sorption of the epoxy coatings on the metal surface from the double layer capacitance is reported.     

Local electrochemical impedance spectroscopy: Considerations about the cell geometry

Local electrochemical impedance spectroscopy provides a powerful tool for the investigation of surface heterogeneities on electrode surfaces. However, measurements are greatly influenced by geometry-induced frequency dispersion. In order to account for this frequency dispersion, both simulations and experiments were performed to explore the influence of a recessed electrode on the local and global impedance response. The calculations presented here demonstrated that the depth of the recessed electrode required to achieve a uniform primary current distribution was twice the electrode radius. The calculations provide guidelines for design of LEIS measurements, and were in good agreement with results obtained for a stainless steel disk electrode in a Na₂SO₄ electrolyte.     

Corrosion of steel under the defected coating studied by localized electrochemical impedance spectroscopy

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.