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Application of impedance techniques to the study of living cell monolayers and membranesCoombs, Helen Victoria January 1990 (has links)
No description available.
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Influência dos íons cloreto na cinética de redução eletroquímica dos íons de Bi+3 e CU2+ no eletrodo de mercúrio / Influence of chloride ions on the electrochemical reduction of Bi3+ and Cu2+ ions on mercury electrodeAgostinho, Silvia Maria Leite 03 November 1975 (has links)
A influência de pequenas concentrações de íons cloreto na cinética de redução eletroquímica dos íons Bi3+ e Cu2+ foi estudada através de medidas independentes de adsorção específica e de cinética eletroquímica. A adsorção específica foi determinada por meio das curvas eletrocapilares obtidas com o método do tempo de gota, para soluções aquosas de misturas de ácido clorídrico xM e de ácido perclórico (1 - x)M. Obeservou-se que, em concentrações de cloreto muito baixas, iguais ou inferiores a 10-2 M, a adsorção específica desses íons segue a isoterma de adsorção de Henry. A cinética da redução eletroquímica dos íons de Bi3+ e Cu2+, na presença de pequenas concentrações de íons cloreto, em meio de ácido perclórico 1 M, foi estudada por polarografia com o eletrodo de mercúrio. Os valores das constantes de velocidade foram calculados, a partir da relação existente entre a corrente, medida em cada potencial, e a corrente de difusão, usando as equações relativas a processos de eletrodos irreversíveis. Estes valores mostraram que, para as concentrações mais baixas de cloreto estudadas, esses íons aceleram as reações Bi3+ + 3e → Bi(Hg) e Cu2+ + 2e → Cu(Hg). O mecanismo de redução, por outro lado, permanece o mesmo já observado por outros autores em soluções de ácido perclórico puro, ou seja, os íons Bi3+ e Cu2+ são reduzidos em etapas de um elétron com velocidades comparáveis. No caso do bismuto, para as concentrações mais altas de cloreto estudadas, o efeito da complexação dos íons Cl- e Bi3+ no meio da solução se torna apreciável e a influência dos íons cloreto na velocidade de redução se deve a uma ação combinada da sua adsorção específica sobre o eletrodo e da sua tendência em formar complexos. No caso do cobre apenas a adsorção específica dos íons cloreto é a responsável pelo seu efeito na cinética do processo, em virtude da não complexação dos íons Cl- e Cu2+ presentes na solução. Tanto no caso do bismuto como o do cobre se observou uma relação linear entre os logaritmos das constantes de velocidade de redução e a carga especificamente adsorvida de íons cloreto, a um potencial constante. Esses resultados estão em concordância com os modelos teóricos de PARSONS e de GUIDELLI e FORESTI, sobre a influência de íons não eletroativos especificamente adsorvidos na cinética de reações de eletrodo. presença de uma carga especificamente adsorvida, dependente do potencial do eletrodo, justifica a variação no coeficiente de transferência à medida que se varia a concentração do íon especificamente adsorvido; no caso do cobre, onde apenas a adsorção específica é a responsável pelo aumento da velocidade de redução eletroquímica, a correção no valor do coeficiente de transferência a partir dos dados de adsorção, coincide com os resultados experimentais obtidos a partir da variação do logaritmo da constante de velocidade com o potencial. / In the present work, the effect of chloride ions in small concentrations on the electrochemical reduction of Bi3+ and Cu2+ ions was studied by means of independent measurements of specific adsorption and electrode kinetics. Specific adsorption was calculated irom electrocapillary curve data, obtained by means of the drop time method for aqueous solutions of xM hydrochloric acid and (1 - x)M perchloric acid mixtures. It was observed that, for low chloride concentrations (less than or equal to 10-2M), specific adsorption of these ions on the mercury electrode obeys the Henrys adsorption isotherm. The kinetics of the electrochemical reduction of Bi3+ and Cu2+ ions, in the presence of emall concentrations of chloride ions in 1M HC104 was studied by dropping mercury electrode polarography. The rate constants was calculated from the ratio between the current, measured at each potential, and the diffusion current, using the equations for irreversible electrode processes. It is shown from these rate constansts, that for the smaller chloride concentrations, the velocity of the reaction Bi3+ + 3e → Bi(Hg) and Cu2+ + 2e Cu(Hg) is increased by the presence of chloride ions. The reduction mechanism remains the same as that observed by other investigators in pure HC104, i.e., the reduction occur in one electron steps and the rates of each step are compa¬rable. In the case of bismuth the effect of complexation of Bi3+ by Cl- ions is appreciable for the higher chloride concentrations; the influence of the chloride ions on the reduction velocity thus results from a combination of its specific adsorption on the electrode and its tendency for complex formation. In the case of copper, only the specific adsorption of chloride ions is responsible for their effect on the electrode process kinetics since there is no complexation of the Cu2+ ion by Cl- in solution. For the reductions of bath bismuth and copper ions, a linear relation between the logarithms of the rate constants and the specifically adsorbed charge of Cl- ions is observed at constant potencial. These results agree with the theoretical models of PARSONS and of GUIDELLI and FORESTI describing the effect of non-electroactive, specifically adsorbed ions on the kinetics of electrode processes. The presence of specifically adsorbed charge, that depends on the electrode potential, explains the observed variation of the transfer coefficient as the concentration of the specifically adsorbed ion is increased. For copper, in which only apecific adsorption is responsible for the increase of the velocity, transfer coefficients corrected using the specific adsorption data are in agreement with the experimental results obtained from the variation of the logarithm of the rate constant with the potential.
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Les accumulateurs au sodium et sodium-ion, une nouvelle génération d’accumulateurs électrochimiques : synthèse et électrochimie de nouveaux matériaux d’électrodes performants / Sodium batteries and sodium-ion batteries, a new family of rechargeable batteries : synthesis and electrochemistry of new high performance electrode materialsHuynh, Le Thanh Nguyen 31 October 2016 (has links)
Les accumulateurs au lithium jouent un rôle important comme source d'alimentation pour les appareils électroniques portables en raison de leur forte capacité gravimétrique et volumétrique et leur haute tension. En outre, la technologie lithium-ion est la mieux placée pour une application à grande échelle, telle que le véhicule électrique, ce qui pose un problème de ressource et à terme, de coût. Une des réponses envisagées sur le plan économique et environnemental est le développement d’accumulateurs sodium-ion. Dans tous les cas, le problème scientifique consiste à proposer des matériaux d’insertion des ions sodium avec un caractère réversible de la réaction électrochimique, et une durée de vie compétitive par rapport aux systèmes au lithium. Le travail présenté se situe dans cet effort de recherche. Les potentialités de matériaux dérivés du pentoxyde de vanadium, de structure 2D, sont étudiées comme composés d’intercalation du sodium: le composé de référence V2O5, le bronze performant dérivé de V2O5 de formule K0,5V2O5, ε’-V2O5, ainsi que le composé au manganèse de type lamellaire : la birnessite sol-gel et sa forme dopée au cobalt. Les relations structure-électrochimie sont élucidées à travers une étude combinant propriétés électrochimiques, diffraction des Rayons X et spectroscopie Raman des matériaux à différents taux d’insertion, en fin de réaction et après cyclages galvanostatiques. De nouvelles phases sont obtenues et des capacités spécifiques comprises entre 100 et 160 mAh/g dans le domaine de potentiel 4V-1V peuvent être obtenues avec parfois une stabilité remarquable comme dans le cas de NaV2O5 et ε’-V2O5 / Since commercialization, Li-ion batteries have been playing an important role as power source for portable electronic devices because of high gravimetric, volumetric capacity and high voltage. Furthermore, the lithium-ion technology is best suited for large-scale application, such as electric vehicles, which poses a resource problem and ultimately cost. On the contrary, sodium is a most abundant element, inexpensive and similarly properties as lithium. In order to solve the problem of lithium raw resource, sodium is proposed as a solution for next generation power source storage. This work investigates the potential derivative vanadium pentoxide materials as sodium intercalation compounds: the V2O5 reference compound, the promizing potassium bronze K0,5V2O5, ε'-V2O5, as well as a lamellar manganese oxide: the sol-gel birnessite and its doped cobalt form. The structure-electrochemistry relationships are clarified through a study combining electrochemical properties, X-ray diffraction and Raman spectroscopy of materials at different insertion rate, end of the reaction and after galvanostatic cycling. New phases are highlighted and specific capacities between 100 and 160 mAh / g in the field of 4V-1V potential can be obtained with sometimes remarkably stable as in the case of NaV2O5 and ε'-V2O5
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Influência dos íons cloreto na cinética de redução eletroquímica dos íons de Bi+3 e CU2+ no eletrodo de mercúrio / Influence of chloride ions on the electrochemical reduction of Bi3+ and Cu2+ ions on mercury electrodeSilvia Maria Leite Agostinho 03 November 1975 (has links)
A influência de pequenas concentrações de íons cloreto na cinética de redução eletroquímica dos íons Bi3+ e Cu2+ foi estudada através de medidas independentes de adsorção específica e de cinética eletroquímica. A adsorção específica foi determinada por meio das curvas eletrocapilares obtidas com o método do tempo de gota, para soluções aquosas de misturas de ácido clorídrico xM e de ácido perclórico (1 - x)M. Obeservou-se que, em concentrações de cloreto muito baixas, iguais ou inferiores a 10-2 M, a adsorção específica desses íons segue a isoterma de adsorção de Henry. A cinética da redução eletroquímica dos íons de Bi3+ e Cu2+, na presença de pequenas concentrações de íons cloreto, em meio de ácido perclórico 1 M, foi estudada por polarografia com o eletrodo de mercúrio. Os valores das constantes de velocidade foram calculados, a partir da relação existente entre a corrente, medida em cada potencial, e a corrente de difusão, usando as equações relativas a processos de eletrodos irreversíveis. Estes valores mostraram que, para as concentrações mais baixas de cloreto estudadas, esses íons aceleram as reações Bi3+ + 3e → Bi(Hg) e Cu2+ + 2e → Cu(Hg). O mecanismo de redução, por outro lado, permanece o mesmo já observado por outros autores em soluções de ácido perclórico puro, ou seja, os íons Bi3+ e Cu2+ são reduzidos em etapas de um elétron com velocidades comparáveis. No caso do bismuto, para as concentrações mais altas de cloreto estudadas, o efeito da complexação dos íons Cl- e Bi3+ no meio da solução se torna apreciável e a influência dos íons cloreto na velocidade de redução se deve a uma ação combinada da sua adsorção específica sobre o eletrodo e da sua tendência em formar complexos. No caso do cobre apenas a adsorção específica dos íons cloreto é a responsável pelo seu efeito na cinética do processo, em virtude da não complexação dos íons Cl- e Cu2+ presentes na solução. Tanto no caso do bismuto como o do cobre se observou uma relação linear entre os logaritmos das constantes de velocidade de redução e a carga especificamente adsorvida de íons cloreto, a um potencial constante. Esses resultados estão em concordância com os modelos teóricos de PARSONS e de GUIDELLI e FORESTI, sobre a influência de íons não eletroativos especificamente adsorvidos na cinética de reações de eletrodo. presença de uma carga especificamente adsorvida, dependente do potencial do eletrodo, justifica a variação no coeficiente de transferência à medida que se varia a concentração do íon especificamente adsorvido; no caso do cobre, onde apenas a adsorção específica é a responsável pelo aumento da velocidade de redução eletroquímica, a correção no valor do coeficiente de transferência a partir dos dados de adsorção, coincide com os resultados experimentais obtidos a partir da variação do logaritmo da constante de velocidade com o potencial. / In the present work, the effect of chloride ions in small concentrations on the electrochemical reduction of Bi3+ and Cu2+ ions was studied by means of independent measurements of specific adsorption and electrode kinetics. Specific adsorption was calculated irom electrocapillary curve data, obtained by means of the drop time method for aqueous solutions of xM hydrochloric acid and (1 - x)M perchloric acid mixtures. It was observed that, for low chloride concentrations (less than or equal to 10-2M), specific adsorption of these ions on the mercury electrode obeys the Henrys adsorption isotherm. The kinetics of the electrochemical reduction of Bi3+ and Cu2+ ions, in the presence of emall concentrations of chloride ions in 1M HC104 was studied by dropping mercury electrode polarography. The rate constants was calculated from the ratio between the current, measured at each potential, and the diffusion current, using the equations for irreversible electrode processes. It is shown from these rate constansts, that for the smaller chloride concentrations, the velocity of the reaction Bi3+ + 3e → Bi(Hg) and Cu2+ + 2e Cu(Hg) is increased by the presence of chloride ions. The reduction mechanism remains the same as that observed by other investigators in pure HC104, i.e., the reduction occur in one electron steps and the rates of each step are compa¬rable. In the case of bismuth the effect of complexation of Bi3+ by Cl- ions is appreciable for the higher chloride concentrations; the influence of the chloride ions on the reduction velocity thus results from a combination of its specific adsorption on the electrode and its tendency for complex formation. In the case of copper, only the specific adsorption of chloride ions is responsible for their effect on the electrode process kinetics since there is no complexation of the Cu2+ ion by Cl- in solution. For the reductions of bath bismuth and copper ions, a linear relation between the logarithms of the rate constants and the specifically adsorbed charge of Cl- ions is observed at constant potencial. These results agree with the theoretical models of PARSONS and of GUIDELLI and FORESTI describing the effect of non-electroactive, specifically adsorbed ions on the kinetics of electrode processes. The presence of specifically adsorbed charge, that depends on the electrode potential, explains the observed variation of the transfer coefficient as the concentration of the specifically adsorbed ion is increased. For copper, in which only apecific adsorption is responsible for the increase of the velocity, transfer coefficients corrected using the specific adsorption data are in agreement with the experimental results obtained from the variation of the logarithm of the rate constant with the potential.
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Modélisation électrochimique de la vitesse de corrosion généralisée du fer en milieu poreux : contribution à un modèle prédictif de la durabilité des aciers non alliés en conditions de stockage géologique / Electrochemical modeling of the general corrosion rate of iron in porous medium : contribution to a predictive model of the durability of unalloyed steels in geological storage conditionsMarion, Antoine 03 February 2014 (has links)
Les enveloppes métalliques en acier non allié choisies par l’Andra comme surconteneurs pour le stockage des déchets radioactifs seront principalement soumises à la corrosion généralisée. L’objectif de ce travail est de démontrer qu’il est possible de simuler sur le long terme cette vitesse de corrosion de façon à bien dimensionner les surconteneurs pour qu’ils restent étanches et confinent la radioactivité des déchets qu’ils contiennent pendant plusieurs siècles.La modélisation par la méthode des éléments finis, basée sur la résolution numérique de l’équation de Nernst-Planck en potentiel libre a donc été utilisée pour prévoir le comportement électrochimique de ces aciers sur des durées inaccessibles à des expériences en laboratoire. A partir d’études paramétriques (influence des constantes de cinétique électrochimique, des constantes cinétiques associées aux réactions chimiques, de la température) et en se basant sur plusieurs comparaisons entre expériences de laboratoire et simulations numériques, il a été possible de déterminer l’ensemble des paramètres et des règles de fonctionnement nécessaires pour construire et utiliser un modèle numérique prédictif le plus complet possible.Dans la simulation à long terme, qui constitue le résultat majeur du travail, on constate qu’après épuisement de l’oxygène dissous initialement piégé, la vitesse de corrosion est contrôlée par le recouvrement de la surface métallique dû à l’apparition de produits de corrosion (magnétite, sidérite). Ce phénomène induit une diminution de la porosité totale, identifiée comme déterminante dans le ralentissement de la vitesse de corrosion. / Unalloyed steels selected by Andra for nuclear waste storage would be mainly affected by general corrosion. The aim of this study is to demonstrate that it is possible to simulate the long term corrosion rate in order to estimate the thickness of the containers expected to maintain the confinement for several centuries. Modeling by the finite element method, based on the resolution of Nernst-Planck equation in free potential conditions has been used to predict the electrochemical behavior of these steels impossible to reach at long time through laboratory experiments. From parametric studies (influence of electrochemical kinetic constants, kinetic constants dealing with chemical reactions, temperature) and in the light of several comparisons between laboratory and numerical experiments, it was possible to determine all the parameters and all the rules to build and use the most completed predictive numerical model.The main result of this study is a long term prediction model. After a first step it was established that dissolved oxygen initially trapped is consumed, whereas the corrosion rate is controlled by the fractional coverage of the surface due to the formation of corrosion products (magnetite, siderite). As a consequence, the decrease of the total porosity can be identified as a key parameter in the reduction of the corrosion rate.
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Investigation of Charge Transfer Kinetics in Non–Aqueous Electrolytes Using Voltammetric Techniques and Mathematical ModelingShen, Dai 28 January 2020 (has links)
No description available.
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