Effect of neutral salt spray (NSS) exposure on the lap-shear strength of adhesive-bonded 5052 aluminum alloy (AA5052) joints

This work explores the mechanisms for the non-linear degradation of the lap-shear strength of adhesive-bonded 5052 aluminum alloy (AA5052) joints exposed to neutral salt spray (NSS) environment up to 1200?hours. The lap-shear testing results show that a mixed failure dominated by adhesive failure occurred in both unexposed and exposed adhesive-bonded AA5052 joints. The lap-shear strength of adhesive-bonded AA5052 joints declined sharply in the preliminary stage of NSS exposure (e.g. shorter than 240?hours), then it decreased moderately as the NSS exposure time increased. Differential scanning calorimetry (DSC), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and electrochemical noise measurement were applied to exploring the degradation mechanisms of the lap-shear strength of adhesive-bonded AA5052 joints. The adhesive properties remained nearly unchanged after exposure in the NSS environment. The decreased hydrogen bond at the AA5052/adhesive interface was responsible for the sharp degradation of the lap-shear strength of adhesive-bonded AA5052 joints in the preliminary stage of NSS exposure. In the later stage of NSS exposure (e.g. more than 240?hours), the surface oxidation of AA5052 substrates dominated the lap-shear strength degradation of adhesive-bonded AA5052 joints.     

电化学阻抗谱在电沉积研究中的应用(一)

介绍了电化学阻抗谱在各种金属及合金的电沉积研究中的应用。文章分3期连载。第一部分介绍了电化学阻抗谱的基础知识,包括复数、复阻抗的概念,以及在各种常见条件下电解池的等效电路图。     

Investigation of electrochemical degradation and application of e-paper dyes in organic solvents

To avoid environmental pollution due to organic dye solutions, the electrophoresis and degradation of dye in organic solvents such as alcohol were investigated. Many dyes were tested in the Indium tin oxide (ITO) electrode driving cell, and about 15 dyes moved under voltage driving. Both the curves of ultraviolet-visible (UV-Vis) and infrared (IR) spectra of the electrophoresis samples showed that the metal complexes Red 04 and Acid Black 1 were degradable in alcohol solution by electrochemical reaction. The cyclic volt-ampere curves of the samples from the electrochemical working station proved that electrochemical reactions took place. Based on the analysis of UV-Vis and IR spectra, the electrochemical degradation products of azo and metal complex azo dyes at lower voltage driving (1-5 V) in organic solvents are oxidized azobenzene, not hydrazine, which was found in the electrochemical degradation of dye water solutions. When the ITOelectrode is modified by a polyimide (PI) film to a thickness less than 4 μm, the electrochemical degradation of the dye in alcohol solution will not appear in the cyclic volt-ampere curves. A dye electrophoresis in organic solution flexible prototype e-paper display was formed and the display picture is shown.     

Chemical reactivity of thermo-hardenable steel weld joints investigated by electrochemical impedance spectroscopy

The chemical reactivity of oxide-free weld joints made of thermo-hardened carbon steel in different electrolytes was investigated by chronopotentiometry, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The objective was to identify the role of different electrolyte constituents on the electrochemical behaviour of the different materials constituting the weld joint, namely the weld material, the heat affected zone (HAZ) and the base carbon steel. Hardness measurements by Vickers and nano-indentation techniques indicated that the weld material is harder than the heat affected zone and the base carbon steel due to a Widmanstätten ferrite-type structure of the weld. Electrochemical measurements were performed on polished cross-sections on these weld joints in four electrolytes containing different additives. The weld joints are active in all tested electrolytes and the composition of the electrolytes dictates the dissolution even though the main chemical reactivity mechanism remains unaffected. A balanced presence of oxidative agent, inhibitor and HF in the electrolyte is necessary to obtain a homogeneous chemical attack on weld joint and Si-rich inclusion removal in weld material, while avoiding excessive attack roughening and/or pitting of the carbon steel.     

Performance degradation study of a direct methanol fuel cell by electrochemical impedance spectroscopy

A stability test of a direct methanol fuel cell (DMFC) was carried out by keeping at a constant current density of 150 mA cm⁻² for 435 h. After the stability test, maximum power density decreased from 68 mW cm⁻² of the fresh membrane-electrode-assembly (MEA) to 34 mW cm⁻² (50%). Quantitative analysis on the performance decay was carried out by electrochemical impedance spectroscopy (EIS). EIS measurement of the anode electrode showed that the increase in the anode reaction resistance was 0.003 Ω cm². From the EIS measurement results of the single cell, it was found that the increase in the total reaction resistance and IR resistance were 0.02 and 0.05 Ω cm², respectively. Summarizing the EIS measurement results, contribution of each component on the performance degradation was determined as follows: IR resistance (71%) > cathode reaction resistance (24%) > anode reaction resistance (5%). Transmission electron microscopy (TEM) results showed that the average particle size of the Pt catalysts increased by 30% after the stability test, while that of the PtRu catalysts increased by 10%.     

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     

电化学测试技术在集成电路制程化学机械抛光中的应用现状

简述了包括开路电位法、极化曲线法、恒电位法、电化学阻抗谱在内的常规电化学测试技术的原理.总结了近几年内这几种电化学测试技术在化学机械抛光领域研究中的应用现状,展望了未来的发展方向.     

Acceleration and quantitative evaluation of degradation for corrosion protective coatings on buried pipeline: Part I. Development of electrochemical test methods

The electrochemical degradation of polyethylene coated onto SS400 was examined in synthetic groundwater. Electrochemical techniques (electrochemical impedance spectroscopy, potentiodynamic and potentiostatic polarization tests) and surface analysis (scanning electron microscopy) were used to accelerate and evaluate the coating degradation. The pulsed potentiostatic polarization test accelerating both the cathodic reduction and anodic oxidation reactions was applied to reproduce the coating degradation mechanisms of cathodic disbondment and oxide lifting. The applied potentials were determined to be ±300 mV_SCE versus open-circuit potential from the analysis of the anodic and cathodic polarization data. Results from the EIS confirmed that coating degradation is accelerated effectively by the pulsed potentiostatic polarization testing.     

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.     

Subadhesive hydration of aluminum adherends and its detection by electrochemical impedance spectroscopy

Hydration of an aluminum oxide surface under an adhesive film was shown to occur when the specimen was immersed for extended periods in hot water. The absence of a crack and lack of access of the water to the specimen edges forced the moisture to reach the interface by migrating through the adhesive. The increased volume of the hydration product forced it to erupt through the adhesive. This subadhesive hydration is conclusive proof that hydration can proceed in advance of a crack to promote its propagation. Electrochemical impedance spectroscopy (EIS) measurements on the specimen during exposure readily detected both the ingress of moisture through the adhesive and the hydration of the substrate.     

Preliminary evaluation of the anticorrosive properties of aircraft coatings by electrochemical methods

Strict regulations concerning the content of volatile organic compounds (VOCs) and heavy metals (Cr⁶⁺) in aircraft coating systems have increased the economic burden of the United States Air Force (USAF) in the area of coating maintenance. To this end, it is critical to have methods to characterize new coating systems in such a manner that the data can be used to predict accurately and reliably the expected lifetime of the coatings in service. Electrochemical noise method (ENM) and electrochemical impedance spectroscopy (EIS) are two techniques used to monitor extent and rate of corrosion. The USAF is currently employing these methods in order to supplement data acquired from traditional salt-spray methods. ENM and EIS are used to evaluate each component of the coating system and its contribution to corrosion prevention. Preliminary evaluations of an aircraft coating system on aluminum substrate (Al 2024-T3) produces resistance noise values of 10⁶ to 10⁷ Ω/cm². It is hoped that these results will form the basis of coatings that give increased USAF fleet service life and reduction in maintenance manpower and materials costs.     

LY12铝合金表面硅烷杂化膜的电化学性能研究

以γ-缩水甘油醚基丙基三甲氧基硅烷(GPTMS)和甲基三乙氧基硅烷(MTES)为前驱体,制备了正硅酸乙酯(TEOS)改性溶胶,并在LY12铝合金表面制得了2种有机硅烷杂化薄膜.对裸铝合金、钝化膜和硅烷杂化膜合金电极进行了动电位极化曲线和电化学阻抗谱(EIS)测试,评价了各化学转化膜的防腐蚀性能.结果表明:有机硅烷杂化膜可有效提高铝合金的耐蚀性,其耐蚀效果与传统铝合金表面钝化膜相当,其中GPTMS/TEOS膜的性能更优于钝化膜.     

Corrosion of 7A04 aluminum alloy under defected epoxy coating studied by localized electrochemical impedance spectroscopy

In this work, corrosion of the coated 7A04 aluminum alloy with and without ultraviolet (UV) aging was studied by salt spray test, surface observation and localized electrochemical impedance spectroscopy measurements. Results demonstrated that, in the absence of UV aging, the impedance at coating defect increases with time, indicating the formation and accumulation of corrosion product, while the impedance in the adjacent coating decreases, which is attributed to the permeation of corrosive solution from defect and the resultant disbondment of coating. Upon UV aging, the impedance values at both defected area and the coating decrease. The coating contains a significant number of wrinkles. The wrinkles provide micro-pathways where the corrosive species, such as chloride ions, could permeate and reach the aluminum alloy surface for corrosion reaction. Different from the coating without UV aging where corrosion is limited to the defected area, a layer of corrosion product would not be formed to cover the defected area when coating experiences UV aging. Therefore, corrosion occurs continuously with time.     

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。     

Evaluation of thick organic coatings degradation in seawater using cathodic protection and thermally accelerated tests

Organic coatings are often associated with cathodic protection to fight against the corrosion of metallic structures when immersed in seawater. However, cathodic protection leads to the generation of a strong alkalinity at the metal/coating interface, which causes the degradation of the coating. It is then necessary to develop a reliable method to evaluate the compatibility between organic coatings and the application of cathodic protection.

On one hand, cathodic disbonding tests (ASTM G-8 and G-80) can be driven with an artificial defect but this defect is mainly responsible for the electrochemical response. In addition, calcareous deposit rapidly forms onto the defect zone when cathodic protection is applied which can make difficult the evaluation of coating delamination. On the other hand, immersion of defect-free specimens requires very long testing periods (several months or even years) in order to detect the coating degradation.

In this work, an attempt to accelerate the coatings degradation by imposing a high temperature and thermal cycles were made in order to decrease the test-time duration. The influence of the applied cathodic potential was also investigated. The coating degradation was evaluated by EIS, considering the defect-free zone of coatings. It was shown that the coating degradation is faster in the presence of a defect and for high temperature (45 °C). Moreover, thermal cycles allow to greatly accelerate the degradation of defect-free coatings and then to compare the compatibility of both coatings with cathodic protection.     

等离子喷涂TiO2涂层的海水环境失效机制

运用电化学阻抗测试技术对不同腐蚀时间的涂层进行测试,参照等离子喷涂制备的TiO₂涂层的形貌结构特点,分析TiO₂涂层在海水介质中的腐蚀失效过程.研究表明：涂层的极化电阻在浸泡初期降低较快,后因腐蚀产物和污损物阻塞腐蚀通道,极化电阻又有所上升,趋于稳定.建立合适的等效电路分析涂层腐蚀的阻抗谱,考察各元件参数的变化,进一步分析涂层腐蚀的规律.     

Effect of CNT dispersion methods on the strength and fracture mechanism of interface in epoxy adhesive/Al joints

The tensile and shear strengths of adhesively bonded aluminum (Al) joints were inspected in the presence of amino functionalized multi-wall carbon nanotubes (MWCNTs). Tensile and shear tests were carried out using butt and lap-shear joints. The main goal was to compare the effects of dispersion methods of functionalized-CNT into epoxy on the mechanical performances and failure mechanisms of Al joints. Two different types of dispersion procedures, distributing CNT in the hardener (HH method) and distributing CNT in the resin (RR method), were applied. To identify the failure mechanisms, the morphology of fracture surfaces were analyzed using scanning electron microscopy (SEM). Comparing two dispersion methods against one another ascertained that following the RR method for dispersing CNTs in the adhesive displayed larger shear strength, while applying HH method offered fairly greater tensile strength. Moreover, dispersing CNTs in the resin induced more uniform dispersion of CNTs as compared to distributing nanofillers in the hardener. Following RR method, CNTs good dispersion as well as the presence of effective crack growth dissipating mechanisms, increased the shear strength of CNT reinforced adhesive joint. Incorporating CNTs using HH approach encouraged the plastic void formation of epoxy around the agglomerated CNTs, and as a consequence, promoted the plastic deformation under tension.     

The use of electrochemical noise methods (ENM) to study thick, high impedance coatings

Thick, high impedance organic coatings are those class of coatings used to provide corrosion protection to naval vessels, pipelines, gasoline storage tanks, and other large structures such as bridges and plant structures. These coatings, especially the newest generations now being used in practice, can provide exceptional protection and lifetime of performance such that properly and accurately assessing and differentiating among competing coatings is a very difficult task. The standard protocol of salt fog testing (ASTM B117), immersion testing, and outdoor exposure in a corrosive environment with subjective evaluation of a coating's performance durings and after testing, does not adequatcly rank and predict coating lifetimes for new coating systems, especially for the environmentally compliant coating systems such as powder coatings (especially the thick, fusion bonded epoxy (FBE) coatings used for pipelines), two component epoxy and urethane coatings and waterborne coatings. New, objective test methods are desperately needed by users and manufacturers of coatings. A relatively new electrochemical test procedure, electrochemical noise methods (ENM), as developed by Skerry and Eden, has been shown in our laboratory to be very successful in the ranking and prediction of relative coating performance. We have used the method successfully on naval ship coatings, several pipeline coatings and other related systems, and Skerry has used them successfully on industrial maintenance coatings. We have used these methods in conjunction with electrochemical impedance spectroscopy, d.c. resistance measurements and cyclic salt fog testing of the Prohesion^TM type. In our studies of pipeline coatings, we needed to investigate thermal effects because of their extended range of use temperature. In these studies, we have discovered that electrochemical methods can be used for an in situ measurement of the T_g of coatings in electrolyte immersion. Further, the ‘plasticizing’ effect of aqueous electrolyte absorption as well as its relative irreversibility has been shown. For all coatings studied, ENM provided useful, objective, numerical data which rapidly ranks coatings and provides useful information on the relative lifetime prediction of coatings which may provide up to 30 years of service.     

Decolorization and aromatic ring degradation of colored textile wastewater using indirect electrochemical oxidation method

In this research, decolorization and aromatic ring degradation of colored textile wastewater was investigated by indirect electrochemical process in a batch reactor. The graphite and sodium chloride were used as electrode and supporting electrolyte, respectively. Reactive Yellow 3 (RY3) was used as model compound. The effects of influential variables governing the efficiency of the process such as initial dye concentration, pH, current density, and electrolyte concentration were studied. The decrease of absorbance at UV region in UV-Vis spectra was indicative of the aromatic ring degradation. Kinetic analysis indicates that the electrochemical decolorization rates might be obeyed as a first order model. The UV-Vis data supported the decolorization and degradation of aromatic intermediates of RY3.     

Application of the dynamic EIS to investigation of transport within organic coatings

The paper presents results of an investigation on rapid degradation of organic coating using a novel method called dynamic electrochemical impedance spectroscopy (DEIS). For 60 s, polyvinyl coating has been subjected to the impact of 0.01 M solution of tetraethylammonium tetrafluoroborate in methylene chloride. During that time instantaneous impedance spectra have been determined allowing tracing the dynamics of a degradation process. Usefulness of the DEIS technique in the investigation of non-stationary phenomena has been proved in the field of coating research.