A computer analysis of electrochemical impedance data

CIRFIT, a computer analysis of electrochemical impedance data, minimizes the sum of squares of the radial difference between observed and calculated impedance data presented in either the complex impedance or admittance plane. CIRFIT requires no assumptions of ideal capacitive frequency response for the double layer in order to extract the values of solution resistance and polarization resistance that are important to corrosion rate analysis. Examples are presented of the use of CIRFIT for the analysis of corroding iron in tapwater and for model pit electrodes that have two time constants in 0.5 M NaCl.     

用随机单纯形法分析交流阻抗教据

本文提出了一种可以应用于由交流阻抗数据计算等效电路元件数值的数据拟合方法-随机单纯形法。这一方法能一次同时求解多个电路元件,对复杂的等效电路尤为有效,因此十分适合于有弥散效应时的数据处理。利用按随机单纯形法编制的软件,给出了计算实例,还分析了阻抗测量误差对拟合计算结果的影响。     

Fe-Cr合金在650℃共晶(Li,K)2CO3熔盐中的腐蚀电化学阻抗谱研究

应用电化学阻抗技术并结合物相分析技术研究了合金元素Cr对Fe在 650℃ (Li,K) 2 CO3 共晶熔盐中的腐蚀行为的影响 .结果表明 ,加入 5 %和 1 0 %Cr不能改善Fe的耐腐蚀性能 ,而加入 2 0 %和 2 5 %Cr则能显著提高其耐腐蚀性能 ;Fe及Fe Cr合金腐蚀电化学阻抗谱呈双容抗弧特征 ,合金腐蚀受荷电粒子在氧化膜中的迁移控制 .提出将合金表面形成的氧化膜理想化为一电容器 ,并建立了氧化物电容与双电层电容相串联的等效电路来描述合金腐蚀的阻抗特征 .此外 ,根据所提等效电路对合金腐蚀电化学阻抗谱进行了解析 .     

Separating iterative solution model of generalized nonlinear dynamic least squares for data processing in building of digital earth

1　INTRODUCTIONDataincludingspatialdataandattributiondata ,geometricaldataandphysicaldata ,arebasesforbuildingofthedigitalearth .Toaccuratelyandvisuallyexpresstheearthwiththesedata ,theyshouldfirstlybeprocessed .Atpresent ,theclassicalcommonleastsquaresmethodisusedtoprocessthesedata ,butthesedatacomingfromdifferentsourceshavedifferentcharacteristics ,temporalstatesandaccuracies.Relationsbetweendataarealmostnonlinear .Soparameterestimationmodelsinthedataprocessingarealmostcomplexnonlinearf…     

Electrochemical noise analysis: detection of electrode asymmetry

One major application of electrochemical noise (EN) analysis for corrosion studies is the estimation of corrosion rate via impedance measurement. The measurement involves coupling two electrodes, whereupon the associated EN is measured and the noise resistance and the spectral noise impedance are computed. However, the two electrodes are required to be “nominally identical” (i.e. symmetrical) for the noise resistance and spectral impedance techniques to be valid. This paper proposes that the correlation between the measured potential and the current noise can be used to detect an asymmetric electrode pair and thus provides a necessary but not sufficient test for electrode symmetry. The potential/current coefficient of correlation is derived based on an equivalent circuit to demonstrate the concept and experimental data is presented to support the theory.     

A review of impedance plot methods used for corrosion performance analysis of painted metals

Modern impedance measuring instrumentation has made testing and data acquisition of the corrosion degradation behaviour of painted metal systems a relatively simple matter, compared to methods used in past decades. However, the analysis of such data is not so simple and requires considerable future work input. This paper reviews some of the various methods available for impedance analysis and discusses their applicability to painted metals. A small library of Bode and Nyquist plot shapes is presented, based on increasingly more complex equivalent electrical circuit models, along with methods for obtaining equivalent circuit component values. Other plotting methods are also reviewed, as well as limitations of impedance plot methods for painted metals.     

Variation of a.c. electrical properties of emeraldine base of polyaniline during its drying from suspension in m-cresol

The variation of electrical properties of the emeraldine base form of polyaniline during its transformation from a suspension in m-cresol to the dry state was studied in situ, employing electrical impedance measurements at 30 °C in a wide range of frequencies (10⁻²–10⁵ Hz). The obtained results were fitted using the equivalent electrical circuit with the elements corresponding to different physical processes in the polymer/solution system. The PANI-EB suspension was approximated by a Randles-type equivalent circuit containing an additional element responsible for the a.c. conductivity in the bulk polymer. During the drying of PANI-EB the configuration of the equivalent circuit was consistently changed from the electrochemical one to that corresponding to the dry polymer. The assumption is put forward that a double layer presented at the polymer/electrolyte interface is transformed into surface states in a dry polymer.     

Fe—Cr合金在650℃共晶（Li,K）2CO3熔盐中的腐蚀电化学阻抗谱研究

应用电化学阻技术并结合物相分析技术研究了合金元素Ｃｒ对Ｆｅ在６５０℃（Ｌｉ,Ｋ）２ＣＯ３共晶熔盐中的腐蚀行为的影响。结果表明,加入５％和１０％Ｃｒ不能改善Ｆｅ的耐腐蚀性能,而加入２０％和２５％Ｃｒ则能显著提高其耐腐蚀性能;Ｆｅ及Ｆｅ－Ｃｒ合金腐蚀电化学阻抗谱呈双容抗弧特征,合金腐蚀受荷电粒子在氧化膜中的迁移控制。提出将合金表面形成的氧化膜理想化为一电容器,并建立了氧化物电容与双电层电容相串联的等效电路来描述合金腐蚀的阻抗特征.此外,根据所提供等效电路对合金腐蚀电化学阻抗谱进行了解析.     

Estimating the barrier layer thickness of porous aluminium oxide films with A.C. impedance measurements

The a.c. impedance behaviour of porous aluminium oxide films has been investigated. According to the characteristics of the equivalent circuit, the capacitance corresponding to the porous film layer can be obtained for the frequency ω → ∞. As the capacitance is related to the thickness of the layer, it provides a method for the evaluation of the thickness of the porous aluminium oxide film. Measurements were performed in the range from 2 mHz to 100 kHz.Results showed that the capacitance measured does not correspond to that of the porous film. Since the capacitance attained at high frequencies is closely related to the anodization voltage, and since it is independent of the anodization time, it can be ascribed to the thin barrier layer.     

Correlation between the oxide impedance and corrosion behavior of Zr−Nb−Sn−Fe−Cu alloys

The correlation between the oxide impedance and corrosion behavior of two series of Zr−Nb−Sn−Fe−Cu alloys was evaluated. Corrosion tests were performed in a 70 ppm LiOH aqueous solution at 360°C for 300 days. The results of the corrosion tests revealed that the corrosion behavior of the alloys depended on the Nb and Sn content. The impedance characteristics for the pre- and post-transition oxide layers formed on the surface of the alloys were investigated in sulfuric acid at room temperature. From the results, a pertinent equivalent circuit model was preferably established, explaining the properties of double oxide layers. The impedance of the oxide layers correlated with the corrosion behavior; better corrosion resistance always showed higher electric resistance for the inner layers. It is thus concluded that a pertinent equivalent circuit model would be useful for evaluating the long-term corrosion behavior of Zr−Nb−Sn−Fe−Cu alloys.     

Determination of impedance parameters for mild steel/HCl interface using integration method

Impedance measurements for the interface between mild steel/hydrochloric acid as a function of cysteine (Cys) concentration were carried out for a wide enough frequency range. The validity of the impedance data was checked using the Kramers–Kronig (K–K) transforms. Despite the deviations at low frequencies for both transforms, imaginary-to-real and real-to-imaginary, a successful fit for the high frequencies was reached. The impedance parameters were determined from imaginary component of experimental impedance vs. logf diagrams using integration method and from complex plane plots fitting experimental results to an appropriate equivalent circuit. A compromise of parameters from two different plot methods was seen.     

Electrochemical characterisation of electrodeposited organic coatings

The electrochemical impedance spectroscopy and the potentiostatic polarization techniques have been used to characterize the organic coatings electrodeposited on carbon steel. The coatings were formed during the cathodic and anodic electrodeposition of the modified epoxy resins on carbon steel samples previously polished and degreased (no primer was used). The experiments were conducted in stagnant, natural aerated 3% NaCl solution under ambient conditions. Analysis of the impedance spectra has established that an electrical equivalent circuit with two time constants fits to describe the electrodeposited epoxy coating/carbon steel system in the electrolyte solution. For the characterisation of the electrodeposited epoxy coatings the physical properties obtained from the principal elements of the equivalent electrical circuit and the electrochemical parameters obtained from the anodic polarization curves were used. It was established that these coatings present good performances characterized by low porosity, low water uptake and few conductive pathways and therefore a high efficiency. The coatings present a good adhesion to the carbon steels substrate; during the exposure period (60 days), no degradation or delamination process could be observed.     

LiFePO4基正极材料容量的温度敏感特性及交流阻抗谱研究

采用原位碳包覆法制备了锂离子二次电池用LiFePO4／C复合正极材料。考察了环境温度对LiFePO4/C电池容量的影响，得到容量与绝对温度之间符合Arrhenius关系。运用交流阻抗谱分析了温度与电池电化学特性的关系，并对电极基于电荷和质量传递控制过程给出了一种新的模拟等效电路，通过Zview拟合软件得到了各个模拟元件的数值及变化趋势，从而定量地解释LiFePO4／C复合电极容量与温度的关系。     

恒电量瞬态响应的频谱分析Ⅰ.原理与测试方法

在用时频变换测量电极阻抗的技术中,介绍了用恒电量作为激励信号的时域法阻抗测量技术,分别用等效电路和实际腐蚀体系验证了恒电量测量的精确性,同时体现快速测量的特点．提出用拉普拉斯频谱分析恒电量瞬态响应的方法。不仅能够简化恒电量激励条件下电路模型的解析,而且对于包含多个时间常数的腐蚀体系,有助于判断腐蚀反应的子过程和解析电极阻抗．     

Exfoliation corrosion of Al–Zn–Mg–Cu–Zr alloy containing Sc examined by electrochemical impedance spectroscopy

The exfoliation corrosion behavior of an Al–Zn–Mg–Cu–Zr alloy containing Sc artificially aged at 120 °C for 24 h is studied by macroscopic observation techniques and electrochemical impedance spectroscopy (EIS) measurements. After 48 h immersion, the blisters start bursting and delamination initiates, along with the appearance of two time constants in the impedance diagrams. According to the simulation by equivalent circuit, the corrosion rate decreases sharply and then reaches a steady state, which is due to the change of the solution pH and oxide layer thickness, as well as the accumulation of corrosion products.     

Electrochemical evaluation of Ti‐13Nb‐13Zr,Ti‐6Al‐4V and Ti‐6Al‐7Nb alloys for biomedical application by long‐term immersion tests

In this investigation the electrochemical behaviour of the Ti‐13Nb‐13Zr, Ti‐6Al‐4V and Ti‐6Al‐7Nb alloys, for application as implant materials was evaluated in Hanks' solution by electrochemical techniques. The alloys were immersed in this solution for 410 days and periodically they were tested by electrochemical impedance spectroscopy. At the end of this period, polarization curves of the three titanium alloys were obtained. The electrochemical impedance experimental results were interpreted using an equivalent electrical circuit that simulates a duplex structure oxide composed of an inner compact layer, here called barrier layer, and an outer and porous layer. The results indicated that all the alloys present a very high corrosion resistance in the electrolyte used, typical of passive alloys, and that the corrosion resistance is mainly due to the barrier layer. The passive like behaviour was maintained during the whole period of test.     

细菌对碳钢腐蚀的电化学研究

采用开路电位测量、极化曲线和电化学交流阻抗法（EIS）研究了小球菌对45＃碳钢的腐蚀行为。结果表明：（1）小球菌存在时试样表面上所形成的疏松、不均匀的生物膜加速了碳钢的腐蚀过程；（2）有菌存在时暴露2d、4d的Rpo值和Cc值非常接近，表明细菌的生长代谢过程已趋于稳定，两种暴露条件下所形成的生物膜趋向于成熟一致；（3）分别提出了不同暴露条件下EIS的等效电路，并计算了相应的等效元件参数；（4）小球菌影响下腐蚀反应的阻抗行为存在弥散效应。     

Interpretation of A.C. impedance response of chromated electrogalvanized steel

A need exists for the development of a fast and accurate testing technique which plating shops could use to evaluate the corrosion resistance of chromated galvanized steel. A.c. impedance techniques were explored as a method to evaluate the corrosion protection properties of chromated electrogalvanized steel. Experimental impedance data were analyzed with respect to a non-linear model. Parameters from the model have been given physical interpretations which provide insight into the possible formation and protection mechanisms of a chromate coating on electrogalvanized steel. The measurement of these parameters may prove useful for predicting the corrosion protection properties of chromated electrogalvanized steel.     

Corrosion Inhibition of Zn-Al-Cu Alloy by 2-Aminothiazole

The inhibitive effect of 2-aminothiazole on corrosion of Zn-Al-Cu alloy was investigated in acid, neutral and alkaline media by impedance and polarization techniques. The impedance data were fitted to a simple equivalent circuit model and indicated control by a diffusion process. Satisfactory inhibition was obtained in alkaline and neutral media. On the other hand, quite low inhibition efficiency was observed in acid medium. Increase in concentration of the inhibitor increased the inhibitive effect, whereas the reverse was observed when the temperature was increased. Different adsorption isotherms were tested in neutral and alkaline media, the best fit was obtained for the Freundlich isotherm. The highest value for the free energy change was recorded in alkaline medium in accordance with the high inhibition efficiency observed in this medium.     

富锌涂层的电化学阻抗谱特性

根据在不同浸泡时间测得的富锌涂层的电化学阻抗谱特征,提出了两种等效电路作为其物理模型。讨论了阻抗谱特征变化与富锌涂层结构及性能变化的关系,并根据阻抗谱的解析结果对两种富锌涂层的防护性能进行了评价。