Добірка наукової літератури з теми "Local electrochemical analysis"

The aim of the present work was to study the surface chemistry, microstructure, and local corrosion processes at the decarburized layer of the SAE 9254 automotive spring steel. The samples were austenitized at 850°C and 900°C, and oil quenched. The microstructure was investigated using confocal laser scanning microscopy and scanning electron microscopy. The surface chemistry was analyzed by x-ray photoelectron spectroscopy. Electrochemical impedance spectroscopy and potentiodynamic polarization were used to assess the global corrosion behavior of the decarburized samples. Scanning electrochemical microscopy was used to evaluate the influence of decarburization on the local corrosion activity. Microstructural characterization and x-ray photoelectron spectroscopy analysis indicate a dependence of the local electrochemical processes with the steel microconstituents and Si oxides in the decarburized layer.

Stochastic fluctuations of the corrosion potential and the current generated by corrosion reactions are known as electrochemical noise. These fluctuations can be measured in freely corroding systems, therefore the characteristics of electrochemical noise are influenced only by the type and rate of corrosion. The classical spectral analysis of electrochemical noise in the frequency domain achieve good correlation to corrosion rate and type; however, the chaotic nature of corrosion processes requires different mathematical treatment. In this paper self-similarity and fractal dimensions of electrochemical noise are examined in order to explain its mechanism and improve the corrosion monitoring system. Capacity and correlation fractal dimensions of voltage and current-noise, measured on various metals, are calculated and compared to the results of the classical spectral analysis. Relations between different rates and types of corrosion (passivation, local, uniform) and the fractal characteristics of electrochemical noise are established. The analysis of spontaneous electrochemical voltage and current fluctuations is confirmed as a rich source of information in corrosion processes.

Au cours des 30 dernières années, les techniques de microscopie à sonde électrochimique à balayage (SEPM) ont été développée comme outils puissants pour des études électrochimiques à l’échelle micro/nano. Les techniques les plus développées et commercialisées sont la microscopie électrochimique à balayage (SECM) et la microscopie de conductance ionique à balayage (SICM). Cependant, les mesures impliquent l’immersion totale de l’échantillon au sein de la solution d’électrolyte, qui peut produire des modifications incontrôlées de la surface en raison du long temps de balayage. A défaut de localiser l’électrode elle-même, l’électrolyte peut également être localisé, ce qui est connu sous le nom de microscopie de cellules à balayage de gouttelettes (SDC) ou de microscopie à balayage de cellule électrochimique (SECCM). Ceci permet de réaliser les expériences dans des conditions ambiantes. Toutefois, l’étalement des gouttelettes sur la surface de l’échantillon peut être affecté par l’hydrophilie et la rugosité de l’échantillon, ce qui pose des problèmes pour l’analyse quantitative. Récemment, la microscopie électrochimique à balayage à sonde à gel (SGECM) a été proposée comme nouvelle technique de SEPM. Elle est principalement basée sur une sonde à gel qui immobilise l’électrolyte sur une électrode de type micro-disque. Par conséquent, l'analyse peut être réalisée dans un environnement ambiant avec un étalement d'électrolyte contrôlable. Cette thèse est consacrée aux développements ultérieurs de la SGECM. Avant tout, le contexte des développements de SGECM est présenté dans le chapitre I. Différentes techniques SEPM, électrolytes polymères gel, réalisations de SGECM sont systématiquement présentées, respectivement. Au chapitre II, la résolution physique latérale de la SGECM est étudiée de manière approfondie et quantitativement en marquant des pixels uniques et en balayant périodiquement les échantillons. Dans le chapitre III, le mode potentiométrique de la SGECM est développé à partir d’une nouvelle électrode de micro-référence Ag/AgCl-gel. Comme la sonde à gel subit des milliers de cycles d’étirement et de compression au cours d’une mesure de cartographie, il est très important d’améliorer sa résistance mécanique. Le chapitre IV décrit une approche préliminaire basée sur la réticulation chimique du gel de chitosane par le glutaraldéhyde. Le chapitre V pousse plus loin le développement des sondes à gel ainsi que l’intégration des électrodes de travail et de référence
In the past 30 years, scanning electrochemical probe microscopy (SEPM) techniques have been developed as powerful tools for studying electrochemistry at micro/nano scale. The most developed and commercialized techniques are Scanning Electrochemical Microscopy (SECM) and Scanning Ion Conductance Microscopy (SICM). However, the entire sample is immersed in the electrolyte solution during the measurements, which may yield uncontrolled change of the surface due to the long scanning time. Instead of localizing electrode, the electrolyte can also be localized, which is known as Scanning Droplet Cell (SDC) or Scanning Electrochemical Cell Microscopy (SECCM). The experiments are carried out under ambient conditions. However, the spreading of droplet over sample surface may be affected by the hydrophilicity and roughness of sample, which brings challenges in quantitative analysis. Recently, Scanning Gel Electrochemical Microscopy (SGECM) was reported by our group as a novel SEPM technique. It is mainly based on a gel probe that immobilizes the electrolyte on a micro-disk electrode. Thus, the analysis can be achieved in ambient environment with controllable electrolyte spreading. This thesis is devoted to the further developments of SGECM. Foremost, the background of developments of SGECM is introduced in Chapter I. Different SEPM techniques, gel polymer electrolytes, achievements of SGECM are systematically presented, respectively. In Chapter II, the lateral physical resolution of SGECM is thoroughly and quantitatively studied by both marking single pixels and scanning over periodic samples. In chapter III, the potentiometric mode of SGECM is developed based on a novel Ag/AgCl-gel micro-reference electrode. As the gel probe undergoes thousands of pressing-stretching cycles in a mapping measurement, it is highly important to improve its mechanical strength. Chapter IV describes the preliminary effort of chemically cross-linking chitosan gel by glutaraldehyde. Chapter V further pushes forward the development of integrated gel probes with both working and reference electrode

AbstractOnly 10–15% of Nairobi’s informal settlements are sewered, and these sewer pipes are often broken or clogged. In addition to posing a threat to human health, human waste contains high concentrations of nitrogen and phosphorus, which can wreak ecological harm when improperly discharged. However, nitrogen and phosphorus are also key ingredients for fertilizers used in agricultural food production. This case study follows the development of ElectroSan, a pre-revenue process engineering spinoff that focuses on novel processes for converting urine into valuable products. The two primary technologies ElectroSan uses to extract nitrogen from urine are ion exchange and electrochemical stripping. The efficacy of these technologies (primarily ion exchange) was investigated through field trials enabled by a partnership with Sanergy in Nairobi, Kenya. Through experimentation and market analyses, Dowex Mac 3 was identified as the most suitable resin for nitrogen recovery. Additionally, this process could produce ammonium sulfate fertilizer at a lower cost to competing products and also had the advantages of providing a steady, local supply of fertilizer that could be applied by fertigation. This approach thus avoided local ecosystem damage from improper disposal, created local economic opportunities, and partially closed the nutrient cycle locally. Life cycle and techno-economic assessments (in the context of San Francisco, CA) found that the sulfuric acid used for regeneration of the resin represented 70% of greenhouse gas emissions and energy input (embedded energy from the manufacturing process). Providing insights into the importance of partnerships, being adaptive with assumptions, and the realities of conducting fieldwork, the ElectroSan research project continues to explore the valorization of urine and has expanded to new contexts, including other parts of Kenya (with Sanivation) and Dakar, Senegal (with Delvic Sanitation Initiatives).

The German chemist Richard Wilhelm Heinrich Abegg (Fig. 13.1), was born on 9 January 1869 in Danzig (now Gdansk, Poland) (1). He received his PhD in 1891 from the University of Berlin for work in the field of organic chemistry done under the direction of August Hofmann. He switched to the new and rising field of physical chemistry immediately upon graduation, doing postdoctoral work in the laboratories of Wilhelm Ostwald at Leipzig and Svante Arrhenius at Stockholm, as well as serving as personal assistant to Walther Nernst at Göttingen. In 1897 Abegg was appointed professor of chemistry at the University of Breslau (now Wroclaw, Poland). In 1909 he moved to the local Technischen Hochschule, where he remained until his untimely death on 3 April 1910 at age 41 in a ballooning accident near Koszalin in what is now modern-day Poland. As might be inferred from his association with Ostwald, Arrhenius, and Nernst, Abegg’s research interests quickly focused on the newly formulated theories of ionic dissociation and chemical equilibrium, where he is credited with contributing to an understanding of the theory of freezing point depression and with writing two popular introductory textbooks on the use of the ionic theory and equilibrium in reinterpreting various traditional areas of chemical synthesis and analysis (2, 3). With the discovery of the electron in 1897 Abegg soon became interested in its use to rationalize various electrochemical phenomena and in its possible implications for both the periodic table and chemical bonding. That year he published, in collaboration with Guido Bodländer, his theory of electroaffinity in which he postulated that electrochemical half-cell oxidation potentials could be used as a measure of an atom’s attraction for electrons and that this, in turn, could be qualitatively correlated with periodic trends (Fig. 13.2) in such properties as molecular polarity, solubility, and the tendency to form complex ions (4, 5).

Surface enhanced Raman scattering (SERS) is, potentially, a very powerful technique for in situ surface analysis, particularly in an electrochemical environment. Unfortunately, few studies to date have taken advantage of the technique for the purpose of analysis. The present study, however, utilizes SERS to probe analyte molecules in the electrochemical double layer in order to obtain information about the behavior of the double layer as the electrode potential is altered.

A solid oxide fuel cell (SOFC) is expected to be applied to the distributed energy systems because of its high thermal efficiency and exhaust gas utilization. The exhaust heat from the SOFC can be transferred to the electric power by a gas turbine, and the high efficiency power generation can be achieved by constructing the SOFC and gas turbine hybrid system. In this study, the local processes in the electrodes and electrolyte of unit SOFC are analyzed taking into account the heat conduction, mass diffusion, electrode reactions and the transport of electron and oxygen ion. The temperature and concentration distributions perpendicular to the electrolyte membrane are shown. The effects of the operating conditions on the cell performance are also shown. Furthermore, the entropy generation and exergy loss of each process in the electrodes and electrolyte are analyzed and the reason for generating the exergy loss in the SOFC is clarified. It is noted that two electrode reactions are responsible for the major exergy loss.

A three-dimensional heat/fluid flow analysis procedure to predict the planar SOFC performance has been developed. The continuity, Navier-Stokes, energy and species equations, coupled with the electro-chemical relation models, are solved for the single periodic module of a unit cell which is composed of the anode/cathode channels, the porous electrodes, the electrolyte, and the interconnect. Using the FVM method of SIMPLE type, the local current density, which is proportional to the rate of chemical reaction, is determined iteratively by forcing the local current density and the mass-transfer rate at the reacting surface match. The Butler-Volmer equation is used to estimate the activation overpotential while the diffusion in the porous electrodes is simulated to accurately predict the concentration overpotential. Upon validation of the procedure, the average current density and voltage relation has been successfully obtained for the given structure. The cell characteristics, which include the local current density, temperature, and concentration distributions, are presented and discussed. The effects of various parameters, namely, the inlet temperature, the electrode thickness, and the channel/rib width, on the cell performance are carefully examined for different electric loads.

Abstract. Sintered permanent magnets, consisting of the neodymium-iron-boron (Nd-Fe-B) alloy, are installed as rotor magnets in small and precision electric drives due to their high magnetic forces in small volumes. When permanent magnets are brought into their final shape by electrical discharge machining (EDM), the thermal influence of this manufacturing process has negative effects on the magnetic properties of the workpieces. In consequence, re-magnetization of the workpieces is necessary after the finishing process. As an alternative manufacturing technology, electrochemical precision machining with an oscillating electrode and pulsed direct current (PECM) has the potential to eliminate this subsequent processing step. Based on Faraday's law of induction, an electrical induction current is expected to be generated by the cathode oscillation during the manufacturing process. In this study, the effect of the magnetic field of the workpiece on the process current and on the ablation-effective local electrical current density of the PECM process is analyzed based on multiphysics simulation.

A three-dimensional numerical procedure to predict the performance of a molten carbonate fuel cell has been developed. The Navier-Stokes, energy, and species equations are solved to obtain the velocity, temperature, pressure, and concentration distributions in the cathode/ anode channel. The channel with the trapezoidal supports is approximated by an anisotropic porous medium, of which the effective permeability and conductivity are obtained by separate 3D FVM calculations. For a given average current density, the local current density, which is directly related to the rate of chemical reaction and heat generation on the reaction surface, and the cell voltage are determined to satisfy the electrochemical relations at the electrode surface. The process is iterative and the solution is assumed to have converged when the cell voltage and the local current density fall within the specified convergence limits. The unit cell characteristics, such as current-density distribution, and average current density vs. cell voltage are presented and discussed. Once the relation between the flow rate and the pressure loss in a unit cell are known, the mass flow to each cell of a MCFC stack is estimated by coupling the manifold flow and the flow within the unit cell. The stack performance is then calculated by integrating the individual cell performance using this information.

ABSTRACT The casing is one of the main barriers to ensuring the well integrity. Casing integrity damage due to eccentricity and corrosion is a severe failure mode. This study aims to evaluate the time-variant burst strength of casing with geometric eccentricity in a corrosion environment. Based on a complex stress function in bipolar coordinates, the analytical solution of casing stress distribution is obtained. The prediction model of burst strength is established, in which the mechano-electrochemical (M-E) interaction is considered. Next, the accuracy of this model is validated by comparing the results with numerical simulations. Finally, the effects of eccentricity, initial corrosion rate, and internal pressure on the casing burst strength are investigated. Results indicate that the casing eccentricity is critical for casing burst strength. The casing eccentricity results in a local stress concentration at the thinnest wall thickness and enhances the M-E interaction. The enhanced M-E interaction accelerates the corrosion rate, resulting in the rapid strength degradation of the casing. The service time of the casing decreases with the increase of internal pressure and initial corrosion rate, and the eccentricity aggravates this trend. The work provides guidelines for casing integrity evaluation in a corrosive environment. INTRODUCTION In the process of oil and gas well development, the casing is often corroded because of acid gas. Corrosion will lead to the thinning of casing wall thickness and the degradation of casing burst strength. (Lin et al., 2016). On the other hand, casing internal eccentricity is typical in manufacturing and difficult to avoid altogether (Tan et al., 2018). Therefore, it is important to predict the burst strength of corroded casing with internal eccentricity in the casing integrity assessment; burst strength is the minimum internal pressure that can cause casing burst failure. The types of casing corrosion include uniform corrosion, pitting corrosion, and stress corrosion, which not only cause the wall thickness of the casing to be thinned but also cause local corrosion perforation and cracking. So far, the influence of different types of corrosion behavior on casing strength has been widely studied. Sun et al. (2004) studied the influence of different corrosion pit shapes on the stress concentration degree of the casing and established a calculation model to predict the strength degradation of the casing. The results show that the corrosion depth is the most sensitive parameter affecting the stress concentration factor. Xu et al. (2014) used ANSYS finite element software to study the influence of different shapes of corrosion defects on the strength of casing and obtained the strength change law of corroded casing. Zhang et al. (2018) used a high-temperature and high-pressure reactor to simulate downhole production conditions, predicted the corrosion rate of the casing, and then calculated the residual strength of the corroded casing according to the API specification 5CT. The above research mainly starts from the electrochemical theory of casing corrosion, which fully considers the influence of different types of corrosion defects on the strength degradation of the casing, but ignores the influence of mechanical factors on the casing corrosion process. Many studies have shown that stress can accelerate the corrosion evolution process, resulting in the early failure of engineering structures. Gutman (1994) proposed the original mechanical-electrochemical model to study the corrosion process of metals under stress. According to this theory, the applied stress will cause the equilibrium potential to move in the negative direction. The local current density will increase, eventually leading to the aggravation of the anodic metal corrosion dissolution process (Xu et al., 2012). Cheng et al. (2009; 2010;2016) based on the theoretical relationship between corrosion current density and mechanical stress, a large number of numerical and experimental analyses of metal corrosion were carried out. The results show that the synergistic effect of the stress field and electrochemical field at adjacent corrosion defects is significant. Specifically, M-E interaction leads to higher stress concentration, larger current density, and faster corrosion growth. Gao et al. (2008) combined with the theory of chemical mechanical effect, established the calculation model of the influence of external stress on casing corrosion rate and concluded that the greater the stress of the corroded casing, the more the service life of the casing is reduced. Yang et al. (2016) analyzed the effect of load on the corrosion behavior of steel in an acid solution by electrochemical experiments and verified the synergistic effect of elastic stress and corrosion. Then, a finite element analysis (FEA) simulation program considering the coupling process of corrosion and stress is proposed to analyze the fatigue damage of the joint. Based on the mechanical-electrochemical interaction mechanism, Zhang et al. (2017) established an analytical formula for the influence of stress on the life attenuation of the casing. Sun et al. (2020) used finite element software to analyze the mechanochemical interaction at the overlapping corrosion defects on the steel pipe. The results show that the presence of corrosion defects will cause local stress concentration in the pipeline and enhance the influence of M-E interaction on pipeline corrosion. Yan et al. (2014) established a string strength attenuation model under uniform corrosion conditions. The results show that the life of the casing is prolonged by 46.7% without considering the promoting effect of stress on corrosion. The above results show that coupling corrosion and stress will lead to accelerated corrosion and mass loss, resulting in material strength degradation. However, the casing integrity defects due to eccentricity and corrosion should be studied more systematically.

Surface forces arising in AFM imaging of a deformable, negatively charged biological membrane in an electrolyte solution are investigated in the limit of continuous electrohydrodynamics. Specifically, we extend our previous analysis [1] of purely hydrodynamic interactions between an AFM tip and the elastic cell membrane by accounting for electric double-layer forces under the assumption of a dilute electrolyte solution and local electrochemical equilibrium. The solution of the problem is obtained by integrating the quasisteady, electrically-forced Stokes equation for the electrohydrodynamic field, the linearized Poisson-Boltzmann equation for the electrostatic field in the electrolyte inside and outside of the cell, and the Laplace equation for the electrostatic field within a dielectric AFM tip. The Helfrich and Zhongcan’s equation for an equilibrium shape of the cell membrane is employed as a quasi-steady, nonlinear boundary condition linking the stress fields on both sides of the cell membrane augmented by the local membrane incompressibility condition in order to find the local tension/compression force acting on the membrane. For the first time, an integrated framework for the dynamic coupling of the membrane double-layer effects and the AFM tip-electrolyte-membrane motion is established that allows for characterizing of the local electrolyte flow field, the electrostatic field, the elastic deformation of the membrane, and the electrohydrodynamic surface force acting on the AFM tip in great detail. The results of the analysis provide information on the motion of the membrane and the surface forces induced by both an electrolyte motion and the Maxwell stresses resulting from the charge double-layer screening effect for a full cycle motion of the AFM tip in a non-contact mode imaging of the cell membrane.