Impedance measurements of corroding mild steel in an automotive fuel ethanol with and without inhibitor in a two and three electrode cell

The impedance measurements in a highly resistive electrolyte medium are difficult. The use of two identical electrode cells having a large surface area may overcome this difficulty, but measurements have to be restricted to the corrosion potential. The advantages of each type of cell are discussed. The electrochemical system tested in this work was the corrosion of mild steel in an automotive fuel ethanol with or without ethanolamines as corrosion inhibitors. It was found that in a three electrode cell, the use of a special electronic circuit increasing the input impedance of reference electrode was necessary to perform correct measurements. No particular care was needed in the impedance measurements in a two electrode cell. If the two electrode plates were set too close, the measured impedance was significantly great, thus leading to an erroneous prediction of the corrosion behaviour. A tentative explanation to this phenomenon is given.     

使用Kelvin探头参比电极技术进行薄液层下电化学测量

研究了Ｋｅｌｖｉｎ探头参比电极技术测定薄液层下金属电化学行为的方法。为改善Ｋｅｌｖｉｎ探头装置的测试性能，采取和若干提高信噪比的措施，如采用压陶瓷振动驱动器和测量交流信号的电压成分等。实验结果表明，改进的这套装置可用于测试极薄液层下的金属电极电位，电位随时间的变化，腐蚀电位分布及极化曲线等稳态电化学行为，是研究大气腐蚀过程的有效工具之一。     

采用丝束电极研究防锈油膜的防护性能

将１０１根金属丝聚集成束，制成一种检测防锈油膜防护性能的新型测试电极，测定了涂油丝束电极的腐蚀电位和油膜电阻的分布。结果表明，腐蚀电位分布服从非连续二基分布。油膜极化电阻分布服从对数正态分布。     

Polarisierte Elektroden für Korrosionsmessungen im Boden

Polarized electrodes for corrosion measurements in the ground Lead electrodes enable redox potentials in the soil to be measured within 20 hrs and can therefore be used to advantage instead of Cu/CuSO₄-half cells for monitoring potential conditions around underground structures. Areas in danger of being corroded are always indicated by a negative potential. The polarized lead vertical structural elements in the soil, either as individual electrode or as an electrodes can be used on horizontal or electrode chain.     

Suspended electrode kinetics of mechanically activated pyrite

1　ＩＮＴＲＯＤＵＣＴＩＯＮＭｅｃｈａｎｉｃａｌａｃｔｉｖａｔｉｏｎｉｓｗｉｄｅｌｙａｐｐｌｉｅｄｉｎｅｎ ｈａｎｃｉｎｇｍｅｔａｌｌｕｒｇｉｃａｌｐｒｏｃｅｓｓ[1～ 3] ａｎｄｃｈｅｍｉｃａｌｓｙｎ ｔｈｅｓｉｓ[4 ,5] .Ｓｏｆａｒｉｔｉｓｄｉｆｆｉｃｕｌｔｔ     

Factors influencing electrode potential of steel in concrete

Abstract

An investigation of the rusting of steel wire in concrete and mortar is reported. Steel corrosion was monitored using electrode potential measurements, and five experimental parameters were controlled: cement type, mortar porosity, mortar cover thickness, mortar cracking, and carbonation thickness. Measurements were made by connecting the reference electrode to three locations on each face of every reinforced mortar parallelepiped sample. The results showed that the mean value of the electrode potential for a sample is correlated with the degree of rusting of the steel, although the location of the measurement does have some effect on the recorded electrode potential. Cracking of the mortar has also been shown to influence the electrode potential.     

Ag/AgCl固体参比电极的研究

研制了结构简单、性能稳定、温度系数较小的Ag/AgCl固体参比电极,并制备了固体三电极体系探头,在5％NaCl溶液中及气相环境中考核该探头。结果表明,该固体参比电极完全能适用于高阻及低阻介质。     

Strom‐Potential‐korrelierte Rauschmessung (CorrElNoise) – Ein neues Verfahren zur elektrochemischen Rauschanalyse

Current‐potential correlated noise measurement (CorrElNoise) – a new technique for the evaluation of electrochemical noise analysis A new method for electrochemical noise measurements is presented. In contrast to most conventional noise measurement techniques which require an electrode arrangement of three “identical” electrodes, the new method is able to work with a two electrode set‐up. As a consequence, the recorded noise response of current and potential in this two electrode system is strongly correlated. This method is denoted as correlated noise measurement technique (CorrElNoise), therefore. It is shown by examples using aluminum as well as stainless steel electrode systems in corrosive environment that the CorrElNoise technique is more sensitive than the conventional method. This was checked by variation of particular experimental parameters during the noise measurements. Compared with the conventional set‐up, the resulting changes in the noise spectra become more clearly recognisable using CorrElNoise.     

Electrochemical characterization and CFD simulation of flow-assisted corrosion of aluminum alloy in ethylene glycol-water solution

An impingement jet system was used to study flow-assisted corrosion (FAC) of 3003 aluminum (Al) alloy in ethylene glycol-water solutions that simulates the automotive coolant by corrosion potential and electrochemical impedance spectroscopy (EIS) measurements as well as computational fluid dynamics (CFD) simulation. The effects of solution pH and fluid impact angle on Al FAC were determined. An increase of solution pH enhances the activity of Al due to dissolution of Al oxide film in alkaline environment. Moreover, Al activity decreases with the increasing fluid impact angle to the specimen. A CFD simulation shows that, with the increase of impact angle, the electrode area under high-velocity flow field decreases and that under low-velocity flow field increases. Consequently, the shear stress generated on electrode surface and the resultant mechanical effect on electrode activity decreases. Therefore, the electrode is more stable than that impacted at a smaller impact angle. There is an essential role of fluid hydrodynamics in corrosion of Al electrode, which is confirmed by corrosion potential and EIS measurements as well as CFD analysis.     

Anodic behavior of cobalt silicides in potassium hydroxide solutions

Anodic behavior of a CoSi₂ electrode in 0.1–4 M KOH solutions and a Co₂Si electrode in 1 M KOH was studied in a range from the corrosion potential (E _cor) to the oxygen evolution potentials with the use of polarization and impedance measurements. A number of results indicate enrichment of electrode surface layers in cobalt. At potentials from E _cor to E _tp transpassivation potential, impedance spectra correspond to the passive state of the silicides. At potentials from E _tp to the onset potential of oxygen evolution, impedance spectra can be described taking into account the inclusion of hydroxide ions in the passivating film. Equivalent electric circuits are proposed for different electrode potential ranges.     

局部腐蚀电池中阴极和“闭塞”阳极之间电位差及其组份的研究

从理论上分析了分别插在局部腐蚀电池阳极液和本底溶液中的两个饱和甘汞电极之间,以及局部腐蚀电池阴、阳极之间的电位差及其组份的性质,导出了一组定量关系式。采用铁与10~(-8)NNaCl溶液构成的模拟电池,实验证明了这些定量关系。结果表明,前一种电位差主要是由阳极液和本底溶液之间的扩散电位差和欧姆电位降两部份组成。在两种溶液之间一旦建立起稳定的扩散区以后,其间的扩散电位差就趋于一个定值;而欧姆电位降则主要随阴极电位的变化而变化。其最终的稳定值将不因同一局部腐蚀电池的内电阻而异,接近于模拟电池在阴、阳极处于断路状态时其间电位差的绝对值。而后一种电位差,还包含有第三个组份,即它们电极电位的差值。     

The corrosion behavior of carbon steel in CO2‐saturated NaCl crevice solution containing acetic acid

The corrosion behavior of X52 carbon steel electrodes in CO₂‐saturated NaCl crevice solution containing HAc was investigated by electrochemical measurements. Chemical environment measurements by Cl^? and pH microprobes show an enrichment of Cl^? ions and an increase of pH values inside the crevice. Moreover, both increments could accelerate with the decreasing dimension of the crevice mouth due to the high diffusive resistance. When the electrode in the crevice solution is coupled with the electrode in bulk solution, the alkalization and the enrichment of Cl^? ions in the crevice solution can result in a negative shift of potential of the electrode in crevice solution, while the potential of the electrode in bulk solution shifts positively during the corrosion process. Thus, a galvanic corrosion is established with the electrode in the crevice solution acting as anode while another in the bulk solution as cathode, i.e., the corrosion in the crevice solution was enhanced while the corrosion in the bulk solution was retarded. The anodic dissolution and the cathodic reduction processes dominate in the crevice solution and in the bulk solution, respectively.     

Complex Formation and Corrosion Rate for Tin in Fruit Acids

Abstract

Estimates have been made from electrode potential measurements of the composition and stability constants of the complexes formed by tin with citric, malic, oxalic and tartaric acids in solutions of the concentration range appropriate to canned fruits. The stability constants suggested are highest for oxalic acid, smular to one another for citric and malic acids and a little lower for tartaric acid. Corrosion rates of tin in oxygen-free solutions of the acids fall in the same order as the stability constants, reflecting the influence on the potential of the tin electrode of changes in Sn²⁺ concentration.     

Linear polarisation resistance measurements using a potentiostatically controlled guard ring

The use of a sensor controlled guard ring has been developed in recent years to enhance the accuracy of linear polarisation corrosion rate measurements on reinforced concrete structures. The established method of measurement uses a galvanostatically controlled guard ring device. In the method reported in this article the reinforcing steel is polarised potentiostatically by an inner auxiliary electrode and the real time plot of the current response is displayed on a laptop computer which controls the guard ring device. The area of steel polarised is confined by a current applied from an outer guard ring electrode which is controlled by two sensor electrodes positioned between the inner auxiliary and outer guard ring electrode. The potential between the two sensor electrodes is continually monitored, and the current output from the guard ring electrode varied to maintain a constant potential difference between the two sensor electrodes. The method has been validated on an electrical test circuit simulating active and passive reinforcement corrosion. Further testing has been conducted on a reinforced concrete specimen and the results compared with those of commercially available galvanostatically controlled equipment and those of standard unconfined linear polarisation resistance measurements.     

Kelvin Probe electrode for contactless potential measurement on concrete – Properties and corrosion profiling application

The practical feasibility of Kelvin Probe measurement of potential of the concrete surface was demonstrated. The measurements require no contact between the reference element and the concrete. Potential readings when placing the probe on dry concrete were nearly instantaneous and highly stable, in contrast with considerable potential drift with a conventional wet-tip electrode. The probe output was only modestly sensitive to the reference element working distance. The shape and range of potential profiles measured with the probe on concrete with locally corroding reinforcement were consistent with those using a conventional wet-tip reference electrode, both identifying the anode location.     

On the Determination of Pitting Potentials by galvanostatic polarization techniques

Various characteristic pitting potentials are defined which may be observed in a system simultaneously. Following these definitions, galvanostatic polarization techniques are expected to result in potential oszillations whenever the pit nucleation potential, U_np, differs from the critical potential for pit repassivation, U_cp, of a system. With nickel polarized in neutral, chloride containing sulphate solution the electrode potential oscillates periodically. The lower limit responds to the critical potential, U_cp, determined by potentiostatic measurements.     

Corrosion and impressed current cathodic protection of copper-based materials using a bimetallic rotating cylinder electrode (BRCE)

A bimetallic rotating cylinder electrode (having individual electrode areas of 10 cm² and rotating at 200-1400 rpm) has been used to examine the corrosion and protection characteristics of copper/nickel aluminium bronze and 90-10 copper-nickel/nickel aluminium bronze galvanic couples in filtered seawater at 25 °C. The flow-influenced electrochemistry of the systems was determined using zero resistance ammetry, corrosion potential measurements and a potential step current transient technique. In each case, the galvanic corrosion potential and corrosion rate displayed a Reynolds number dependency where mass transport control of the anodic dissolution reaction partially controlled the reaction rate. Bimetallic impressed current cathodic protection (ICCP) has also been demonstrated for a range of applied protection potentials and Reynolds numbers. A comparison has been made between the directly measured bimetallic ICCP current demand and that determined from independent, single-metal rotating cylinder electrode measurements. In this case, the mixed charge and mass transport controlled rate of oxygen reduction was examined.     

Effects of Pd substitution for Ni on corrosion performances of Mg_(0.9)Ti_(0.1)Ni_(1-x)Pd_x hydrogen storage alloys

1 Introduction MgNi-based amorphous hydrogen storage alloys have drawn much attention in the last ten years. Compared with AB5 or AB2 type electrode alloys, the alloy candidates for the negative electrode of Ni-MH batteries possess several advantages, su…     

Electrochemical potentials measured at the tip of a growing fatigue crack in demineralized water 93°C: The effect of frequency,wave form and oxygen content

Electrochemical potential measurements have been made during fatigue crack growth tests on pressure vessel A533B steel. The measurements were made inside the growing crack, with a method which follows the crack tip position as the crack grows; another electrode was positioned in the notch, close to the specimen surface. Measurements have been made during loading cycles at different frequencies and wave forms; the environment was demineralized water at 93°C and an over pressure of about 0.015 MPa, at two different oxygen contents (10 ppb and 5–6 ppm). The present paper describes the electrode assembly used, which proved to give reproducible results. The behavior of potential in the two positions is discussed as a function of crack depth, frequency and wave form, and oxygen content.