Interpretation of electrochemical impedance spectroscopy(EIS) circuit model for soils

Based on three different kinds of conductive paths in microstructure of soil and theory of electrochemical impedance spectroscopy(EIS), an integrated equivalent circuit model and impedance formula for soils were proposed, which contain 6 meaningful resistance and reactance parameters. Considering the conductive properties of soils and dispersion effects, mathematical equations for impedance under various circuit models were deduced and studied. The mathematical expression presents two semicircles for theoretical EIS Nyquist spectrum, in which the center of one semicircle is degraded to simply the equivalent model. Based on the measured parameters of EIS Nyquist spectrum, meaningful soil parameters can easily be determined. Additionally, EIS was used to investigate the soil properties with different water contents along with the mathematical relationships and mechanism between the physical parameters and water content. Magnitude of the impedance decreases with the increase of testing frequency and water content for Bode graphs. The proposed model would help us to better understand the soil microstructure and properties and offer more reasonable explanations for EIS spectra.

Electrochemical impedance spectra of V_2O_5 xerogel films with intercalation of lithium ion

Vanadium pentoxide xerogel films used for lithium rechargeable batteries were prepared from crystalline c-V2O5 by melt quenching method,then the electrochemical process of lithium intercalation into vanadium pentoxide xerogel films was simulated with an equivalent circuit model, which was derived from the mechanism of electrode reactions. Measured electrochemical impedance spectra at various electrode potentials were analyzed by using the complex non-linear least-squares fitting method. The results show that impedance spectra consist of 2 high-to- medium frequency depressed arcs and a low frequency straight line. The high frequency arc is attributed to the absorption reaction of lithium ions into the oxide film, the medium frequency arc is attributed to the charge transfer reaction at the vanadium oxide/electrolyte interface and the low frequency is characterized by a straight line with a phase angle of 45° corresponding to the diffusion of lithium ion through vanadium oxide phase. The experimental and calculated results are compared and discussed focusing on the electrochemical performance and the state of charge of the electrode. Moreover, the high consistence of the fitted values of the model to the experimental data indicates that this mathematical model does give a satisfying description of the intercalation process of vanadium pentoxide xerogel films.

Anticorrosion performance of the coating/metal system by electrochemical impedance spectra

In order to investigate the anticorrosion performance of the organic coating/metal system, electrochemical impedance spectra （EIS） were measured in the 3.5wt% NaCl solution, the chemical component and the formation of corrosion products scale were analyzed by laser Raman microspectroscopy, and the pattern of the organic coating/metal system was observed by scanning electron microscopy （SEM）. The characteristics and the delamination process of the organic coating/metal system were investigated systematically, and the emphases were on the transportation of the corrosive medium and the changes of the coating/metal interface. The results show that the impedance decreases at the initial immersion, then increases at the middle-immersion, and again decreases at last, which is related to the corrosion products scale. The concentration of Cl in the coating, which destroys the corrosion products scale, increases with the immersion time.

ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY STUDY OF CORROSION INHIBITION OF MODIFIED LIGNOSULPHONATE FOR CARBON STEEL

The corrosion inhibition for carbon steel in circulating cooling water by modified lignosulphonate has been investigated using electrochemical impedance spectroscopy technique. Results show that the inhibition efficiency of modified lignosulphonate GCL2 is a great improvement on that of lignosulphonate. The maximum inhibition efficiency of GCL2 reaches 99.21% at the concentration of 400mg·L^-1 at 303K. The corrosion inhibition of GCL2 is attributed to forming adsorption film on the metal surface for the electrochemical impedance spectroscopy in GCL2 solution shows more than one time-constant.Moreover,results also indicate that it is more efficient in stirring solution than in still solution for GCL2 because the constant of adsorption in stirring solution is much larger than that in still solution. The adsorption of inhibitor GCL2 follows Langmuir＇s adsorption isotherm.

Evaluation of electrochemical impedance and biocorrosion characteristics of as-cast and T4 heat treated AZ91 Mg-alloys in Ringer’s solution

The present study aims at understanding the electrochemical impedance and biocorrosion characteristics of AZ91 Mg-alloy in Ringer’s solution.As-cast AZ91 Mg-alloy was subjected to T4 heat treatment in a way to homogenize its microstructure by dissolving most of theβ-Mg 17 Al 12 phase at the vicinity of grain boundaries.The electrochemical impedance and biocorrosion performances of these two different microstructures(as-cast and T4 heat treated AZ91 Mg-alloys)in Ringer solution were evaluated by electrochemical impendence spectroscopy,potentiodynamic polarization and weight loss method.EIS spectra showed that both microstructures exhibit similar dynamic response as a function of the immersion time;however,the value of impedance and maximum phase angle are about 50%higher in as-cast AZ91 Mg-alloy as compared to that of homogenized AZ91 Mg-alloy.Weight loss measurement indicated that corrosion resistance of as-cast AZ91 was significantly better than that of homogenized AZ91.Microstructural and XRD analysis revealed that as-cast AZ91 contains a passive film of MgCO_(3)and CaCO_(3)precipitates with near spherical morphologies,whereas homogenized AZ91 comprised mainly unstable Mg(OH)_(2)film featured by irregular plate-like morphologies.

Effect of sulphate-reducing bacteria on the electrochemical impedance spectroscopy characteristics of 1Cr18Ni9Ti

The electrochemical characteristics of 1Cr18Ni9Ti in sulphate-reducing bacteria （SRB） solutions and the biofilm of SRB on the surface of the 1Cr18Ni9Ti electrode were studied by electrochemical, microbiological, and surface analysis methods. Electrochemical impedance spectroscopy （EIS） of 1Cr18Ni9Ti was measured in the solutions with and without SRB at the culture time of 2, 4, 8 d, respectively. The measurement used two test methods, the nonimmersion electrode method and the immersion electrode method. It was found that the polarization resistance （Rp） of 1Cr18Ni9Ti in the solutions without SRB is the greatest for each test method. When using the nonimmersion electrode method, Rp shifts negatively at first and then positively, and the time constant is only one. Although using the immersion electrode method, the Rp shifts positively at first and then negatively, and the time constant also changes when the biofilm forms. The biofilm observed through SEM is with pores. It was demonstrated that SRB has accelerated corrosion action on 1Cr18Ni9Ti. The protection effect of the biofilm on the electrode depends on the compact degree of the film.

ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY DURING CORROSION PROCESS OF 8090 Al-Li ALLOY IN EXCO SOLUTION

The corrosion behavior and electrochemical impedance spectroscopy (EIS) features of 8090 Al-Li alloys in EXCO solution were investigated, and the EIS was simulated using an equivalent circuit. At the beginning of immersion in EXCO solution, the EIS is comprised by a depressed capacitive arc at high-mediate frequency and an inductive arc at low frequency, and the inductive component decreases and disappears with im- mersion time. Once exfoliation or severe pitting corrosion is produced, two capacitive arcs appear in the EIS. These two capacitive arcs are originated from the two parts of the corroded alloy surface, the original flat alloy surface and the new inter-face exposed to the aggressive EXCO solution due to the exfoliation or pitting corrosion. Some corrosion development features of 8090 Al-Li alloys in EXCO solution can be obtained through simulated EIS information.

Exfoliation corrosion susceptibility of 8090 Al-Li alloy examined by electrochemical impedance spectroscopy

The exfoliation corrosion susceptibility and electrochemical impedance spectrosc opy(EIS) of rolled and peak-aged 8090 Al-Li alloys in EXCO solution were studi ed,and the EIS after exfoliation was simulated. Once exfoliation occurs,two ca pacitive arcs appear in the EIS at high-mediate frequency and mediate-low freq uency respectively. The exfoliation-attacked alloy surface consists of two part s,an original flat alloy surface and a new inter-face exposed to EXCO solution due to the exfoliation. The capacitance corresponding to the new exfoliation in ter-face increases approximately linearly with time at early exfoliation stage,due to the enlargement of the new inter-face. Then it maintains stable,due to the corrosion product covering on the new inter-face. The exfoliation suscepti bility can be judged through the average slope of the capacitance vs time curve of the early exfoliation stage. This average slope of the rolled 8090 alloy is m uch higher than that of the peak-aged 8090 alloy,accordingly the rolled 8090 a lloy is more susceptible to exfoliation than the peak-aged 8090 alloy.

Investigation of exfoliation corrosion of rolled AA8090 Al-Li alloy using electrochemical impedance spectroscopy

The exfoliation morphologies and electrochemical impedance spectroscopy (EIS) features of as received rolled AA8090 Al Li alloy in EXCO solution were studied. The EIS was simulated using an equivalent circuit. The results show that once the exfoliation occurs, the EIS is composed of two capacitive arcs at high frequency and mediate low frequency; among them, the capacitance corresponding to high frequency ( C 1) is originated from original flat alloy surface, while the capacitance corresponding to mediate low frequency ( C 2) from new interface exposed to EXCO solution due to the exfoliation and the ratio of C 2 to C 1 increases with exfoliation degree. It is advanced that the exfoliation degree can be quantitatively judged through this ratio.

Electrochemical Performance and EIS Analysis of Commercial Lithium-Ion Battery

Degradation behavior is the main technical problem in the field of commercial application of lithiumion batteries. According to the characteristics of voltage, discharge capacity and inner resistance during the charge/discharge process of commercial lithium-ion batteries of mobile telephone, degradation analysis and related mechanisms are put forward and discussed in the paper. The impedance spectra of prismatic commercial lithium-ion batteries are measured at various state of charge after different charge/discharge cycles. The incastared impedance spectra are discussed with a proposed equivalent circuit. Results indicated that the structure change of electrode materials or swell and shrink of crystal lattice, decompose of electrolyte, dissolution of active materials and solid electrolyte interphase film formation are the main reasons leading to the capacity degradation.

氯离子侵蚀下钢筋在混凝土中腐蚀行为的EIS研究

应用电化学阻抗谱(EIS)和氯离子探针技术,研究在氯化物侵蚀作用下混凝土中钢筋的腐蚀行为.结果表明,钢筋混凝土体系的阻抗谱中包含两个时间常数,分别对应于界面的双电层和钢筋表面的混凝土保护层.自行研制的氯离子探针可连续、无损地测量钢筋/混凝土界面的氯离子浓度.根据腐蚀反应电阻Rct、Warburg阻抗等元件参数和界面氯离子浓度的变化,讨论了混凝土中钢筋腐蚀发生、发展各阶段界面化学环境及钢筋腐蚀参数的变化规律.

Electrochemical behaviors of tantalum in anhydrous ethanol containing hydrogen sulfate ions

The electrochemical behaviors of Ta in tetrabutylammonium hydrogen sulfate（TBAHS） ethanol solutions were studied using potentiodynamic polarization,cyclic voltammetry,potentiostatic current time transient and impedance techniques.The results revealed that no active-passive transition is presented in the cyclic voltammogram,and the anodic current density increases with the increase of solution temperature,TBAHS concentration,potential scan rate and water content.The apparent activation energy is about 43.389 kJ/mol and the dissolution process is diffusion-controlled.Potentiostatic measurements showed that the current density gradually decays to a steady value when the potential is low;however,when the potential is higher than a certain value,the current density initially declines to a minimum value and then increases gradually.The resistance of passive film decreases with increasing potential,and inductive loops are presented when the potential is higher than 2.0 V.

用电化学阻抗谱(EIS)研究环氧树脂涂层的防腐蚀性能

测试了环氧树脂/钢体系在3.5%NaCl溶液中的电化学阻抗谱,并结合激光拉曼光谱测量和扫描电镜观察,系统地研究了有机涂层/金属体系性能与失效过程。重点在于涂层内部腐蚀性介质的传输以及涂层/金属界面发生的变化。结果表明:浸泡初期阻抗减小,中期阻抗增大,后期阻抗又减小,这与界面处生成的腐蚀产物膜有关。随着涂层在电解质溶液中浸泡时间的延长,涂层中Cl-浓度增加,破坏了界面处的腐蚀产物膜。

防锈颜料三聚磷酸铝作用机理的EIS研究

利用电化学阻抗技术研究了含有活性防锈颜料三聚磷酸铝的环氧涂层的耐蚀性。当涂层中加入20％的三聚磷酸铝时,涂层的耐蚀性能最好,并以此为代表探讨了含有活性防锈颜料的有机涂层的作用机理。

采用PITT与EIS技术测定锂离子电池正极材料LiFePO_4中锂离子扩散系数

采用恒电位间歇滴定法(PITT)和电化学阻抗谱技术(EIS)测定锂离子电池正极材料LiFePO4中Li+扩散系数。结果表明:随着嵌锂量的变化,锂离子的扩散系数(D Li+)先出现一个极大值,然后出现一个极小值,随后随嵌锂量的增加而增大;扩散系数在10-13 cm2/s^10-16 cm2/s数量级范围内变化;2种方法计算得到的扩散系数在数量级上相符合。

N80钢CO_2腐蚀过程的EIS研究

应用电化学阻抗谱研究了N80钢在饱和CO2的模拟地层水中CO2腐蚀过程的电化学行为。结果表明:在饱和CO2的模拟地层水中阻抗谱出现三个时间常数,分别对应高频的容抗弧,中低频的感抗弧和低频的容抗弧。阳极极化条件下的阻抗谱与自腐蚀电位下的阻抗谱形状相同,表明腐蚀机理未发生改变。但极化条件下反应电阻下降,反应速率加快。阴极极化条件下,阻抗谱未出现感抗弧,表明阴极过程不存在吸附中间产物。

灰土电化学阻抗谱(EIS)与力学性能的试验研究

在电化学体系研究和分析中,电化学阻抗谱的拓扑结构是一项十分重要的内容。把灰土的的电化学阻抗谱性质和其抗剪强度指标联系起来,可以得出一定关系,这为灰土的力学性能测试提供一个新的方式和途径。通过对不同龄期的灰土电化学测试,得出Nyquist图和Bode图,用相应的等效电路模拟其电化学阻抗谱并得出其参数;结合灰土的内部反应机理,分析参数变化过程,以及与相应龄期灰土抗剪强度指标的关系。试验结果表明:灰土的硬化过程可以分为前期和相对稳定期;其阻抗谱在前期呈现准Randles模型,相对稳定期呈现非Randles模型;通过等效电路模拟,得出其电路的参数:灰土溶液电阻Rs、灰土内部双电层CPE、电荷转移电阻Rt以及扩散阻抗ZW。随着龄期的增长,Rs、Rt、ZW在不断增大,CPE不断减小;通过灰土内部反应机理与等效电路参数的分析,灰土的黏聚力c、内摩擦角φ可以用参数α,β表示出增长的关系。

金属在流动氯化物体系中流动腐蚀的EIS研究

流动氯化物体系中碳钢、双相钢电极的电化学阻抗谱(EIS)明显不同.随着流速增大,电极表面受到的切应力增大,反应阻抗减小,电化学腐蚀加速,协同效应增强,结果使电极流动腐蚀速度增加.与碳钢相比,双相钢电极在较高流速下其电化学阻抗谱才在低频区发生特征变化.证明了曹楚南提出的不可逆电极阻抗谱理沦同样适用于流动腐蚀过程中电极过程的研究,揭示了在流动体系中,当电极表面受到足够大的切应力作用时,在低频区电极电化学阻抗谱会发生特征改变.其中,电化学阻抗谱的低频感抗弧特征预示着在流动腐蚀过程中,受到强力流体力学作用的电极表面会改变其常规的溶解速度和溶解机制,同时表面伴随有坑、点局部腐蚀的发生.在此情况下,钝态金属电极的电化学阻抗谱进一步反映了电极表面受到固体颗粒摩擦或撞击的阻抗谱特征.

Electrochemical and corrosion behaviors of pure Mg in neutral 1.0% NaCl solution

The corrosion behaviors and corresponding electrochemical impedance spectroscopy（EIS） and polarization curves of pure Mg in neutral 1.0% NaCl solution were investigated.The fractal dimension of EIS at different time was studied.The corrosion process and EIS evolution are divided into three stages.In the initial stage,EIS is composed of two overlapped capacitive arcs,the polarization resistance and charge transfer resistance increase rapidly with immersion time,and the corrosion rate decreases.Then,two well-defined capacitive arcs appear,and the charge transfer resistance and corrosion rate remain stable.After a long immersion time,inductive component appears in a low frequency range,the charge transfer resistance decreases and the corrosion rate increases with the immersion time.The fractal dimension obtained from the time records of EIS seems to be a promising tool for the analysis of corrosion morphology because of its direct relationship with the metal surface.

用时域法EIS技术研究LY12CZ铝合金的局部腐蚀

通过周期浸泡腐蚀实验和时域法电化学阻抗谱 (EIS)技术研究了LY1 2CZ铝合金的腐蚀损伤 ,用金相法测量最大腐蚀深度 ,用统计分析方法处理实验数据 .结果表明 ,LY1 2铝合金经周期浸泡腐蚀试验后 ,低频阻抗倒数 1 Rd 符合Gum bel分布 ,1 Rd 随腐蚀时间变化的动力学曲线呈S形 ,该曲线分成点蚀和剥蚀两个阶段 ,点蚀阶段符合Sigmoidal曲线关系 ,剥蚀阶段符合线性关系 .1 Rd 与最大腐蚀深度在空间统计分布和腐蚀动力学规律两个方面都有一致性 ,因此可以用 1 Rd 表征腐蚀损伤程度 .由此可见 ,时域法EIS技术可作为一种快速、无损、定量的腐蚀评估手段 .