Electrochemical noise refers to the spontaneous fluctuations in potential and current that can be observed on a corroding metal. The use of electrochemical noise for obtaining information on the corrosion process generates much interest in research fields. One important application is the measurement of corrosion rate. This can be achieved using the electrochemical noise of a pair of electrically coupled corroding metals to obtain an estimate of electrochemical impedance - an abstract quantity that reflects various aspects of the corrosion process.There are a number of problems associated with estimation of impedance information from the electrochemical noise data, particularly regarding data pre-treatment, accuracy and precision. In addition, the present methods are incomplete: current literature does not offer information regarding the phase of the impedance; and assumptions regarding symmetry of an electrode pair cannot be tested without additional measurements.The thesis addresses the above mentioned problems. Specifically,analysis of the impedance estimation process is given to determine how precision can be affected by various factors;a novel signal processing technique is described that is shown to yield a local optimum precision;the application of the proposed signal processing to time varying systems is demonstrated by use of a time varying, frequency dependent impedance estimate;a technique for recovering phase information, given certain conditions, is suggested so that Nyquist impedance diagrams can be constructed; anda technique for testing the symmetry of a coupled pair of corroding metals is described.An integral part of electrochemical noise analysis is the software used for numerical computation. The Matlab package from MathWorks inc. provides an extensible platform for electrochemical noise analysis. Matlab code is provided in Appendix A to implement ++ / much of the theory discussed in the thesis.Impedance analysis and many other electrochemical corrosion monitoring techniques are primarily used for uniform corrosion, where the corrosion patterns occur uniformly over the exposed surface. In order to map localised corrosion, where the corrosion is typically concentrated within a small area, a wire beam electrode can be used. A wire beam electrode is a surface that is divided into a matrix of mini-electrodes so that the corrosion rate at different points can be monitored. However, manual connection of each mini-electrode to the measurement device can prove cumbersome. The final chapter of this thesis describes the design and testing of specialised multiplexing hardware to automate the process.In general, the thesis shows that by careful conditioning of the electrochemical noise prior to analysis, many of the problems with the technique of impedance estimation from the electrochemical noise data can be overcome. It is shown that the electrochemical noise impedance estimation can be extended to encompass a time varying, frequency dependent quantity for studying dynamic systems; that phase information can be recovered from electrochemical noise for the purpose of constructing Nyquist impedance diagrams; and that asymmetric electrodes can be detected without requiring additional measurements.

It is known that, in addition to corrosion processes, the electrochemical noise (EN) can be generated by some other disturbances such as mass transfer and flow turbulence. In this study the influence of both laminar and turbulent flow on the characteristics of electrochemical noise (EN) has been studied using a carbon steel rotating cylinder electrode (RCE) in aerated neutral (pH=7) 0.1 M NaCl and 0.1 M NaCl+0.1 M NaNO2 solutions. The RCE has a set of four graphite brushes for electrical connection. The supplied cathodic current was applied through the top two graphite brushes and measured the specimen potential through the bottom two to eliminate any expected cyclic variations in the measured potential.Prior to the measurement of EN, calibration of the mass transport properties of the electrode was performed by measuring the limiting current density for oxygen reduction as a function of rotation speed in order to estimate the transition from laminar to turbulent flow regime. EN experiments have been performed in free corrosion conditions (uninhibited and inhibited solutions), and with applied cathodic polarisation in the regions of hydrogen evolution and oxygen reduction processes. In the case of oxygen reduction and hydrogen evolution cathodic reactions it has been found that laminar flow had a negligible effect on the noise produced but a significant increase in the amplitude of the noise was observed in turbulent flow. On the other hand in free corrosion conditions in uninhibited solution the influence of flow was relatively insignificant and that was attributed to the low impedance of the corroding electrode. It is claimed that flow has a negligible effect in inhibited solutions due to the passivity of the system, which is responsible for the low rate of both anodic and cathodic reactions. Finally spectral analysis showed that the noise produced by turbulent flow had power at significantly higher frequencies than is normal for corrosion-related noise.

While it has long been known that water flow can influence non-uniform corrosion of copper pipe (Rushing 2002, Marshall 2004), it has never previously been considered a primary contributor to the problem. This work is the first to describe a fundamentally important phenomenon in aqueous non-uniform corrosion: flow electrification. A conceptual framework for flow electrification was developed from prior work on non-aqueous fluid flow in pipes, where the primary concern was prevention of electrical explosions. Thereafter, a series of experiments was aimed at monitoring flow electrification, quantifying its practical effects, and examining aspects of non-uniform copper corrosion in real situations. Under conditions with little or no flow, in a high pH and high chlorine water known to cause pinholes in copper pipes, while water chemistry influenced corrosion, non-uniform corrosion was not sustained. But when flowrates were higher, flow electrification contributed to severe and sustained non-uniform corrosion, with the most serious attack manifested in the first section of pipe that encountered the flowing water. The magnitude of flow electrification increased with chlorine concentration, pH and flowrate. Containers dosed with inhibitors such as zinc or phosphate experienced lower electrification, current, voltage, scale resistance, and corrosion potential measurements when compared to a control without an inhibitor. Additionally, systems dosed with inhibitors had reduced rate of chlorine decay, weight loss, pit density and/or maximum depth. Zinc orthophosphate had the largest positive impact on electrochemical measures of pitting. However, experimental studies suggested that if zinc orthophosphate was dosed to a system for a period of time, and dosing was then stopped, very serious pitting could occur. A practical case study seemed to strongly confirm this hypothesis in one system. The presence of sulfides caused the separation of anode and cathode along a pipe section, from electrification, to reverse relative to what was observed in the system with high chlorine and high pH. Below a certain level of sulfides, electrification ceased. It seems likely, based on measurement of electrochemical potential (Ecorr) in waters of this type as a function of sulfide concentration, that the onset of pitting would be associated with decreasing Ecorr with time. If so, the fundamental basis of tracking Ecorr rise with time to predict pitting propensity would be invalidated. Electrochemical noise programs were applied to try to differentiate between systems of low and high pitting propensity. Amplitudes of potential noise and current noise measurements drastically increased with the presence of sulfides or chlorine, confirming that tracking electrochemical noise may indicate the presence of a pitting agent. However, the electrochemical noise measurements are at best, an indirect indicator of copper pitting, and their interpretation is complicated by the co-occurrence of flow electrification. Attempts were made to apply these insights to a case study examining pitting in two real waters in Maryland and to examine the effects of orthophosphate, chlorination, chloramination and enhanced coagulation on copper pitting propensity. Tracking of Ecorr suggested that the control water (without phosphate) had the greatest pitting propensity. The free chlorine system with orthophosphate maintained Ecorr values below the control signifying that the presence of phosphate lowered the corrosion propensity. Waters with chloramine and phosphate had the lowest Ecorr values and also had the least variability in Ecorr due to the stability of the disinfectant. There is considerable ambiguity in the results, since the copper pipes exposed to the waters in question did not develop serious pitting over the several months of the study. / Master of Science

The thesis aims to develop an ISFET chip compatible miniaturized planar reference. Such planar reference electrode will be constructed by: silica / silica oxide / titanium / palladium / silver / silver chloride / saturated KCl agar / silica nitride / silica. For the size of the reference electrode is only 10mm (length), 5mm (width) and 1mm (height), which is diminished of hundred-fold to the traditional reference electrode. In addition to develop the fabrication techniques of the electrodes, this thesis will be devoted to systematic measuring and analyzing their stability, AC impedence, cyclic voltammery and electrochemical noise characteristics. The results show that the stability is inside 1mV, offset voltage is about -9 mV and the resistance of AC impedence is 400

In this research, corrosion behaviour of A36 carbon steel under engineered disbonded coating was investigated in sulphuric acid solutions containing sodium chloride and iron (III) sulphate. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) analyses were carried out to study the morphology and phase composition of corrosion products formed on the carbon steel surface. The results of the SEM analysis showed that only general and pitting corrosion occurred on the carbon steel surface with the engineered crevice. The size of the pits increased as the sulphuric acid and sodium chloride concentrations increased. Moreover, the corrosion products had an open, irregular and loose structure at the pits mouth. The loose and open structure of the corrosion products facilitates diffusion of chloride ions, oxygen, water and contaminants into the carbon steel surface. In contrast, the corrosion products had a very compact and continuous structure outside the pits which provided a good protection against further corrosion. The x-ray diffraction analysis showed that the corrosion products layer mainly consisted of lepidocrocite (γ-FeOOH), goethite (α-FeOOH) and iron sulphide (FeS) on the crevice edges. The Pourbaix diagram of iron in sulphuric acid solution at room temperature indicates that iron sulphide is formed on the metal surface at different pH values. The akaganeite (β-FeOOH) diffraction peak was not identified in any spectrum which could be due to the low concentration of chloride ions in the solutions. Furthermore, the number of lepidocrocite peaks decreased as the sulphuric acid concentration increased from 10 g l-1 to 50 g l-1. The lepidocrocite is dissolved in the presence of sulphuric acid, and the dissolved ion acts as an oxidant to the metal and hence lower lepidocrocite peaks are identified. Electrochemical noise measurement (ECN) testing was also performed to investigate the corrosion process occurring on the carbon steel surface with the engineered crevice. The results of the ECN measurements showed that current increased during first few minutes and then decreased slightly. Also, the coupled potential did not change after an initial shift in negative direction. The low current flowing through the carbon steel electrodes and the constant potential showed that the crevice corrosion did not develop. These results imply that the crevice corrosion may not occur on the carbon steel surface in acidic solutions containing chloride ions.

L'objectif de ce travail est d’utiliser le bruit électrochimique comme technique alternative pour détecter et caractériser des particules (gouttelettes, bulles, cellules biologiques, …) circulant dans un système microfluidique. La présence ou le passage de particules entre deux électrodes immergées dans un milieu conducteur entraîne une variation de la résistance de la solution entre les deux électrodes. Cette variation de la résistance d'électrolyte, Re, qui est l’impédance en haute fréquence, s'explique par le fait que la présence des particules modifie le champ primaire de potentiel entre les deux électrodes. Elle dépend de la taille, de la forme, de la position et du nombre de particules. Pour étudier l’influence de ces différents paramètres, un modèle théorique appuyé par des simulations numériques a été réalisé pour deux configurations d'électrodes, l'une à une échelle millimétrique avec deux électrodes à disque de diamètre 5 mm positionnées face à face, l'autre avec deux électrodes carrées de côté 100 m positionnées côte à côte dans un canal microfluidique. Pour confirmer ces résultats, les variations temporelles de Re dues au passage de billes, de gouttelettes d'huile et de bulles d'air ont été mesurées en utilisant la technique du bruit électrochimique développée au LISE et étendue dans ce travail aux électrodes micrométriques. Le bon accord entre les résultats théoriques et expérimentaux permet de valider la technique de mesure employée pour caractériser ces entités de taille allant de plusieurs millimètres à des dizaines de micromètres. Cette étude a permis d'identifier la taille des particules détectables pour une configuration et dimension d'électrodes données. Le travail se poursuit pour diminuer la taille du canal microfluidique et des électrodes afin de pouvoir caractériser des objets de taille allant de quelques centaines de nanomètres à quelques micromètres comme les substances biologiques telles que des cellules ou des bactéries. / This work is aimed at assessing the possibility to use the electrochemical noise technique in miniaturized systems as an alternative technique to detect and characterize particles (droplets, bubbles, biological cells…). The presence or the passage of a particle between two electrodes immerged in a conductive solution, leads to a change in the electrolyte resistance, Re, measured between these electrodes, which represents the impedance of the system at high frequency. This variation is explained by the fact that the presence of the particle modifies the potential and current fields between the electrodes. It depends on the size, form, position and number of particles between the electrodes. Numerical simulations have been developed in this work to study the influence of these different parameters on the Re value in two different geometries, one with electrodes of millimetric size, the other with microelectrodes inserted in a microfluidic channel. The variations of Re in time due to the passages of spheres of millimetric size as well as oil droplets and air bubbles of micrometric size between the electrodes have been measured using a specific home-made electronic device. An excellent agreement was obtained between the experimental and calculated Re values at both scales. The future work will consist in the characterization of smaller objects (from 100 nm to 10 m) as biological substances or bacteria in smaller microfluidic devices.

No description available.

Electrochemical techniques have potential for use in conservation, both to evaluate the protectiveness of existing coatings on metal artefacts and to evaluate potential new conservation coatings. Three electrochemical methods have been examined in this study for their applicability to conservation problems. Corrosion Potential Measurement is simple but provides only minimal information on the corrosion processes occurring in an electrochemical system. Electrochemical Impedance Spectroscopy provides both mechanistic and predictive information on coating performance, but the data are complex to interpret and measurements require equipment that is at present too bulky for effective on-site use and beyond the budget of most conservation laboratories. Electrochemical Noise Measurement can be performed using cheap, portable instrumentation and theoretically requires relatively simple statistical processing and interpretation, making it attractive for conservation applications. This project looks at the development of a simple, low cost electrochemical noise measurement system for conservation needs, and uses it to compare Electrochemical Noise Measurement with the other two techniques.

This thesis devotes to develop a wafer-level packaging technique of the planar AgCl-based micro reference electrode and to investigate its various electrochemical characteristics (including the potential stability and offset voltage, AC impedance, cyclic-voltammetry analysis, electrochemical noise and reproducibility). The miniaturized all-solid-state reference electrode can integrated with many biomedical or biochemical sensors for substantially reduce the dimension of the whole sensing system and improve the commercial capability of portable detecting products. This study reports firstly a smallest module of the micro reference electrode with dimension only about 9 mm (L) ¡Ñ 6 mm (W) ¡Ñ 1 mm (H) in the worldwide using the silicon bulk-micromachining technology, thin film deposition and chloridation techniques. The packaged reference electrode module is constructed by two bonded wafers with different functions. One wafer of this module is defined as ¡§electrode chip¡¨ and it has a Ti/Pd/Ag/AgCl planar quasi-reference electrode deposited on its surface. Another wafer is called as ¡§packaging chip¡¨ and it has two bulk-micromachined silicon cavities for the filling/sealing of 1.33 ~ 6.40 £gL KCl-gel (as the salt-bridge of electrode) and electrical connection. Many electrochemical characteristics of the encapsulated solid-state micro reference electrode are tested and improved for the commercial applications. Including a very stable cell potential (<4 mV in 30000 sec.), an approximately zero offset-voltage, a low AC impedance (1~20 K£[), and high reproducibility (drift less than 3~8 mV in 30000 sec. and the range of offset voltage is -6 ~ 3 mV) of the packaged micro reference electrode are demonstrated. Furthermore, stable CV curve of the packaged Ti/Pd/Ag/AgCl/KCl-gel reference electrode were proved by cyclic-voltammetry analysis and its low electrochemical noise spectrum was investigated and discussed in this work. Compared with the commercial reference electrode, the planar miniaturized AgCl reference electrode module developed in this thesis has displayed its many excellent characteristics and with a dimension only 250 times smaller than the conventional reference electrode.

Le développement de la technologie « piles à combustible » nécessite l'utilisation d'outils de diagnostic adéquats notamment pour le monitoring de l'état de santé des systèmes industriels (stacks) dans les conditions réelles de fonctionnement. L'utilisation des moyens traditionnels de diagnostic nécessite l'arrêt ou la perturbation du fonctionnement du système. Le travail de cette thèse vise le développement d'une approche innovante non intrusive pour le diagnostic des stacks PEM (Proton Exchange Membrane), basée sur la mesure des petites fluctuations électriques (bruits électrochimiques). Pour mesurer les bruits, un système d'acquisition des faibles signaux à haute fréquence a été utilisé sans filtrage analogique préalable. Ces mesures ont été dans le cadre du projet ANR « Propice » pour quatre campagnes de mesures avec la collaboration du FCLAB et du CEA LITEN. Les mesures des bruits électrochimiques, sur plusieurs semaines, ont permis de construire une base de données extrêmement riche. Pour traiter ces données, différents approches statistiques dans le domaine temporel, fréquentiel et tempo-fréquentiel ont été utilisés pour la génération de descripteurs fiables et robustes. Il a été démontré que la mesure des bruits permet d'obtenir une riche signature des stacks PEM dans un vaste domaine fréquentiel. Cette signature reflète les différents phénomènes physico-chimiques et est très sensible aux paramètres de fonctionnement du système. L'évolution de cette signature au court de temps peut être utilisée pour le diagnostic in-situ de d'état de santé des stacks commerciaux dans les conditions réelles de fonctionnement et pour le développement des moyens de pronostic. / Fuel cell technology development requires adequate diagnostic tools, in particular for monitoring the state of health of industrial systems (stacks) under operating conditions. Traditional diagnostic tools require to stop or disrupt the system operating. This thesis aims at the development of an innovative and non-intrusive approach for the diagnostic of PEM (Proton Exchange Membrane) fuel cell stacks. The methodology is based on the measurement of small electrical fluctuations (electrochemical noise). To measure this noise, a high frequency signal acquisition system was used without prior analog filter. These measurements were obtained within the ANR project « Propice » using four measurement campaigns with the collaboration of FCLAB and CEA LITEN. Electrochemical noise Measurements, over several weeks, made it possible to build a rich database. To process these data, different statistical approaches in time, frequency and tempo-frequency domains have been used for the generation of reliable and robust descriptors. It has been shown that the measurement of noise makes it possible to obtain a rich signature of the PEM stacks in a wide frequency range. This signature reflects the various physico-chemical phenomena and it is very sensitive to the operating parameters of the system. The evolution of this signature in short time analysis can be used for an in-situ diagnostic of the state of health of commercial stacks under real operating conditions and for the development of prognostic strategies.