Dissertations / Theses: 'Processus de dissolution'

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Azzolini-Manouk, Maryvonne. "Le processus de dissolution des firmes post-industrielles." Aix-Marseille 3, 2001. http://www.theses.fr/2001AIX32014.

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Le déclin du système productif fordien a imposé une redéfinition stratégique de la grande entreprise, afin d'y intégrer les nouveaux paramètres relevant d'un processus global de dématérialisation. Les changements majeurs que connaissent les firmes, accentués par le phénomène de la mondialisation, semblent mettre en défaut les principales valeurs issues des doctrines matérialistes de la période antérieure : rationalisme, cartésianisme, mécanisme, positivisme, etc. , grâce auxquelles l'entreprise capitaliste et institutionnelle a pu se développer dans une forme de cohérence, d'ordre, de sécurité et de durabilité, satisfaisante pour la mentalité dominante. Différents signes manifestes permettent de s'interroger sur l'avenir incertain des firmes post-industrielles. La crise de sens et de légitimité qui les affecte est suffisamment préoccupante pour avoir suscité des réactions parmi les chercheurs, et laisse entrevoir qu'elle tend à devenir une donnée première et incontournable pour toute étude de prospective. .
The decline of the "Henry Ford" system of manufacture has led us to make a strategic redefinition of the big business organization, with a view to incorporating in it new parameters which form part of a global process of dematerialisation. The major changes affecting firms - changes that are accentuated by the phenomenom of globalisation - appear to highlight the insufficiency of those key values which come out of materialist doctrines of the previous period : rationalism, cartesianism, mecanism, positivism, etc. , thanks to which the capitalist, institutional business entity was able to form itself in a coherent, orderly, secure and long-lasting, all of which satisfied the prevailing mentality at the time. Various different clear signs enable us to ask questions about the uncertain future of the post-industrial firms. The crisis about sense and legitimacy affecting them is worrying to a point that is has led to reactions amongst researchers, and suggests that this crisis will tend to become a primary and unavoidable fact for anyone studying this matter in depth. .

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Desboeufs, Karine. "Processus de dissolution des aérosols atmosphériques au sein des gouttes d'eau nuageuses." Phd thesis, Université Paris-Diderot - Paris VII, 2001. http://tel.archives-ouvertes.fr/tel-00005175.

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Les nuages sont des éléments essentiels de notre atmosphère qui agissent à la fois sur le bilan radiatif terrestre et sur sa capacité oxydante en transformant chimiquement une grande variété d'espèces solubles. Ces nuages se forment par la condensation de vapeur d'eau sur des particules d'aérosols, appelés noyaux de condensation. La fraction soluble de ces particules conditionne l'hygroscopie des particules et détermine ainsi la taille des gouttes du nuage. Ce paramètre est déterminant pour définir les propriétés optiques des nuages. De plus, la dissolution des particules est la source primaire en phase aqueuse de différentes espèces dont les métaux de transition. Ces éléments sont impliqués dans divers processus d'oxydoréduction et en particuliers dans les processus responsables de la formation des pluies acides. Il est par conséquent très important de connaître, de manière fiable, les processus aboutissant à la solubilisation de l'aérosol dans les gouttes d'eau nuageuses. Le principal objectif de ce travail a donc été de développer un outil expérimental puis une approche de modélisation afin de comprendre et de simuler la dissolution des particules piégées dans une phase nuageuse liquide. Dans un premier temps, ce travail a consisté à mettre en oeuvre un dispositif expérimental, comportant un réacteur de dissolution en circuit ouvert, qui permet de suivre la cinétique de dissolution dans des conditions proches des conditions nuageuses. Cet outil expérimental a ensuite été utilisé pour une caractérisation systématique des différents facteurs d'influence recensés jusqu'alors sur la dissolution, c'est à dire le pH, la nature des aérosols, leur degré d'altération... mais également sur des facteurs jusqu'alors non expérimentés que sont la force ionique, la nature des acides et les cycles d'évapocondensation nuageuse. Les expériences de dissolution menées sous ces différentes conditions nuageuses ont permis de mettre en avant et de quantifier l'effet important des ions H+ et OH- sur la dissolution, ainsi que du degré de solubilisation de la particule. Ces observations ont ensuite été utilisées pour l'élaboration d'un mécanisme de dissolution des particules en phase aqueuse. Une quantification de ce mécanisme a enfin été réalisée en paramétrisant les principaux facteurs impliqués dans la dissolution. La comparaison des résultats calculés et expérimentaux montre une assez bonne adéquation, validant la paramétrisation effectuée. Finalement ce travail permet d'apporter des informations qualitatives et surtout quantitatives des interactions entre l'eau et les particules d'aérosols qui étaient encore manquantes et montrent notamment l'importance du processus de dissolution pour comprendre le rôle des aérosols dans l'implication climatique et chimique des nuages.

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Desboeufs, Karine. "Processus de dissolution des aerosols atmospheriques au sein des gouttes d'eau nuageuses." Paris 7, 2001. http://www.theses.fr/2001PA077020.

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Les nuages sont des elements essentiels de notre atmosphere qui agissent a la fois sur le bilan radiatif terrestre et sur sa capacite oxydante en transformant chimiquement une grande variete d'especes solubles. Ces nuages se forment sur des particules d'aerosols, appeles noyaux de condensation. Le processus de dissolution de ces particules en phase aqueuse conditionne la microphysique du nuage, et donc ses proprietes optiques, et represente egalement une source importante d'especes impliques dans les processus chimiques en phase aqueuse. Il est par consequent essentiel de connaitre les processus aboutissant a la solubilisation de l'aerosol dans les gouttes d'eau nuageuses. Le principal objectif de ce travail a donc ete de developper une approche experimentale puis de modelisation afin de comprendre et de simuler l'alteration des particules piegees dans une phase nuageuse liquide. A partir des travaux menes jusqu'alors, un certain nombre de facteurs pouvant jouer sur la dissolution des particules a deja ete identifie. Toutefois, aucune connaissance precise du processus de solubilisation n'a pu etre apportee du fait de l'utilisation de moyens d'etude peu adaptes a la complexite des systemes nuageux. Dans un premier temps, ce travail a donc consiste a mettre en oeuvre un dispositif experimental, compose d'un reacteur de dissolution en circuit ouvert, qui permet de suivre la cinetique de dissolution dans des conditions proches des conditions nuageuses. Cet outil experimental a ete utilise pour une caracterisation systematique des differents facteurs d'influence recenses sur la dissolution, c'est a dire le ph, la nature des aerosols, leur degre d'alteration mais egalement sur des facteurs jusqu'alors non experimentes que sont la force ionique, la nature des acides et les cycles d'evapocondensation nuageuse. Les experiences de dissolution menees sous ces differentes conditions nuageuses ont permis de mettre en avant des parametres cinetiques qui ont ensuite ete utilises pour l'elaboration d'un modele simple de dissolution des particules en phase aqueuse. Ce modele permet de capturer les parametres essentiels impliques dans la dissolution et ainsi abouti a l'elaboration d'un mecanisme general de solubilisation des particules dans les gouttes nuageuses.

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Wagener, Thibaut. "Le fer à l'interface océan-atmosphère : Flux et processus de dissolution dans l'eau de mer." Phd thesis, Université de la Méditerranée - Aix-Marseille II, 2008. http://tel.archives-ouvertes.fr/tel-00270558.

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L'étude des flux et du devenir du fer atmosphérique dans l'eau de mer est essentielle pour estimer sa contribution au stock de fer dans l'océan de surface et donc sa contribution dans les cycles biogéochimiques. Pour de larges zones océaniques de l'hémisphère Sud, inexplorées en ce qui concerne les aérosols, ce travail montre que les apports de fer atmosphérique sont liés à de très faibles concentrations de particules d'origine lithogénique ayant voyagé sur de très longues distances. Les flux de fer vers l'océan, déterminés au cours de ce travail, sont largement inférieurs (de 1 à 2 ordres de grandeur) aux estimations récentes par des modèles globaux de poussières minérales, qui sont largement utilisés dans les modèles biogéochimiques. En ce qui concerne le devenir du fer atmosphérique dans l'eau de mer, ce travail propose de considérer le processus de dissolution comme la combinaison d'un processus rapide (considéré instantané) et d'un processus lent (à l'échelle de plusieurs jours). Le processus instantané est contrôlé par des paramètres physico-chimiques des particules qui dépendent à la fois de la nature (source) et de l'histoire (transport dans l'atmosphère des particules) des aérosols à l'interface océan-atmosphère. Le processus « lent » dépend de la quantité de ligands libres dans l'eau de mer et est proportionnel à la quantité de matière organique dissoute. La dissolution du fer transporté par les particules atmosphériques est donc liée à la fois aux sources, au transport et à la nature de l'eau de mer où elles se déposent, illustrant l'impossibilité de considérer une valeur unique de dissolution du fer atmosphérique à l'échelle globale. Une paramétrisation intégrant ces différents forçages est proposée. Ce travail, en estimant à la fois les flux et la dissolution, montre que pour certaines zones océaniques, la connaissance des flux présente une incertitude au moins aussi importante que celle de la dissolution.

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Duportal, Malo. "Impact de la concentration en hydrogène sur les processus de dissolution et de passivation d’un acier inoxydable austénitique." Thesis, La Rochelle, 2020. http://www.theses.fr/2020LAROS024.

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De nombreux phénomènes sont susceptibles d’occasionner l’adsorption puis l’absorption d’hydrogène à la surface d’un matériau, modifiant ainsi ses propriétés intrinsèques de cœur comme de surface. En particulier, l’hydrogène introduit peut impacter les processus de corrosion, sujet encore que peu exploré et qui reste à interroger. Dans ce cadre, le présent travail a pour objet d’évaluer l’impact de l’absorption d’hydrogène sur les mécanismes de dissolution et passivation d’un acier inoxydable austénitique AISI 316L. Dans un premier temps, une caractérisation fine de la distribution d’hydrogène a été conduite. Les résultats obtenus ont montré un fort gradient de concentration permettant d’estimer le coefficient de diffusion ainsi que la concentration locale d’hydrogène. De plus, des techniques de caractérisation telles que le MET et la nano-indentation ont révélé que cette localisation induit une augmentation de la dureté, la formation de défauts de type dislocations, ainsi qu’une transformation locale de phase (γ→ε). Dans un deuxième temps, l’impact de l’absorption d’hydrogène sur les processus anodiques de l’alliage a été questionné. En particulier, les essais électrochimiques réalisés ont montré une augmentation des cinétiques dans le domaine anodique après absorption d’hydrogène. En présence du soluté le pic d’activité et la densité de courant passif sont sensiblement augmentés, et la résistance à la corrosion par piqûre est nettement altérée. Des analyses XPS ex-situ ont souligné le peu de modifications de la couche passive alors qu’une diminution significative de résistance a été clairement observée par EIS. Une augmentation des cinétiques de dissolution a clairement été établie par de analyses ICP, même si les poids respectifs de la dissolution et de l’oxydation de l’hydrogène n’ont pu être clairement quantifiés. Les modifications observées après chargement semblent en partie réversibles avec la désorption de l’hydrogène. Les résultats démontrent donc que l’hydrogène mobile est majoritairement responsable des effets observés, et que l’hydrogène piégé irréversiblement et les modifications métallurgiques induites par l’hydrogène et n’ont que peu d’effet sur les processus de corrosion même s’ils peuvent expliquer la non-réversibilité totale des effets observés
Different processes can lead to hydrogen absorption on the surface of the materials and can decrease their inherent materials properties, especially their surface characteristics. Interactions between these modifications and corrosion processes have to be more thoroughly studied. In this context, this work aims to investigate the role of hydrogen absorption on the dissolution and passivation mechanisms of the AISI 316L. First, the total absorbed hydrogen concentration has been quantified after an electrochemical charging process. Then, we evaluated the different hydrogen states in the material and its distribution from surface to the bulk. Results suggest a strong concentration gradient and allows to estimate both an apparent coefficient of diffusion and a local hydrogen concentration. In addition, we observed that the local hydrogen increased hardness enhanced the dislocations density and induced an occasionally phase transformation to martensite (γ→ε). In the second time, the influence of hydrogen on anodic processes on the AISI 316L have been investigated. For that purpose, electrochemical tests have been conducted and show an increase of anodic kinetics after hydrogen absorption. Hydrogen induced an increase of the passive current density while the pitting resistance is widely degraded. XPS analyses attest of a similar passive layer (thickness and composition) before and after H-charging even though EIS results show a decrease of the resistance. Inductively Coupled Plasma showed that hydrogen promotes dissolution processes. The modifications induced by hydrogen are partially reversible with hydrogen desorption. Our results illustrate that mobile hydrogen is mainly responsible for the decrease of the properties and that trapped hydrogen and / or metallurgical modifications induced by electrochemical charging have few effects on the corrosion process even they highlight the partial non-reversibility of the observed effects

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Saad, Alice. "Influence du changement climatique et des conditions extrêmes sur les massifs fracturés : rôle des fluides (H2O, CO2) dans leur processus d’altération." Thesis, Paris Est, 2011. http://www.theses.fr/2011PEST1117/document.

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L'objectif de ce travail est de comprendre le processus d'altération des calcaires oolithiques et d'estimer leur cinétique d'altération en fonction des conditions climatiques présentes en France. Pour y répondre, des cycles de vieillissement accéléré, basés sur les paramètres issus de l'étude bibliographique et sur les données de température et de précipitations réelles, ont été définis. Ensuite, des lots d'échantillons de deux calcaires oolithiques ont subis ces vieillissements. Les mesures réalisées pour déterminer l'endommagement ont été choisies en fonction de leurs caractéristiques métrologiques et de leur pertinence. Les résultats obtenus ont été comparés avec les mêmes mesures réalisées sur des calcaires altérés de façon naturelle prélevés sur site. Ainsi, les liens entre le processus d'altération des calcaires et les caractéristiques mécaniques, physiques et surtout microstructurales des calcaires ont été établis. Cette analyse a également abouti à des cinétiques d'altération. Les résultats ont été validés par l'étude d'un autre calcaire oolithique sous d'autres conditions climatiques. Enfin, l'influence de changements climatiques éventuels sur les cinétiques d'altération a été déterminée à l'aide d'un outil statistique
The objective of this work is to understand the weathering process of oolitic limestone and estimate their weathering kinetics under French climatic conditions. Accelerated ageing cycles, based on parameters deduced from a literature review and on temperature and precipitation data, have been defined. Then samples of two oolitic limestones have undergone these ageing. The measurements used to determine damage were chosen based on their metrological characteristics and their relevance. The results were compared with the same measurements performed on naturally weathered limestone. Thus, the relationships between the weathering process of oolitic limestone and their mechanical, physical and microstructural characteristics have been established. This analysis also led to weathering kinetics. The results were validated by the study of another oolitic limestone under different climatic conditions. Finally, the influence of a potential climate change on the weathering kinetics was determined using a statistical tool

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Devigne, Vincent. "Ecoulements et conditions aux limites particulières appliquées en hydrogéologie et théorie mathématique des processus de dissolution/précipitation en milieux poreux." Phd thesis, Université Claude Bernard - Lyon I, 2006. http://tel.archives-ouvertes.fr/tel-00132036.

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En sciences de l'environnement et plus particulièrement en hydrogéologie les
problèmes de nature phénoménologique nombreux conduisent bien souvent à
l'étude des Équations aux Dérivées Partielles (EDP's) au travers des non
moins nombreux modèles qui en découlent.

Si chaque phénomène physique, mécanique, chimique ou autres pris
indépendamment et à une échelle suffisamment fine est aujourd'hui bien
compris et relativement aisé à modéliser il n'en est pas de même pour les
problèmes multiphysiques, physico-chimique, les écoulements au voisinage de
domaines de structures différentes ou même dans l'appréhension de ces
phénomènes à des échelles plus grandes méso et macroscopique.

La compréhension des conditions aux limites et leur modélisation reste une
étape clef dans l'étude de ces phénomènes naturels.

Nous verrons au travers du (dé)couplage de problèmes multi-domaines par les
lois de paroi (Navier, Beavers et Joseph), des processus chimiques (Modèle de
Duijn-Knabner) ou la dispersion de Taylor comment il est possible de résoudre
numériquement et en partie ces difficultés par des techniques d'analyse
mathématique récentes (homogénéisation, raisonnement multi-échelles et
développements asymptotiques).

Des résultats de simulations réalisées au moyen d'un logiciel de résolution
d'EDP's baptisé SciFEM (Scilab Finite Element Method) conçu pour les besoins
de la thèse illustreront notre démarche.

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Devigne, Vincent. "Écoulements et conditions aux limites particulières appliquées en hydrogéologie et théorie mathématique des processus de dissolution / précipitation en milieux poreux." Lyon 1, 2006. http://tel.archives-ouvertes.fr/docs/00/13/20/36/PDF/UCBL_manuscrit.pdf.

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En sciences de l'environnement et plus particulièrement en hydrogéologie les problèmes de nature phénoménologique nombreux conduisent bien souvent à l'étude des équations aux dérivées partielles (EDP's) au travers des non moins nombreux modèles qui en découlent. Si chaque phénomène physique, mécanique, chimique ou autres pris indépendamment et à une échelle suffisamment fine est aujourd'hui bien compris et relativement aisé à modéliser il n'en est pas de même pour les problèmes multiphysiques, physico-chimique, les écoulements au voisinage de domaines de structures différentes ou même dans l'appréhension de ces phénomènes à des échelles plus grandes méso et macroscopique. La compréhension des conditions aux limites et leur modélisationreste une étape clef dans l'étude de ces phénomènes naturels. Nous verrons au travers du (dé)couplage de problèmes multi-domaines par les lois de paroi (Navier, Beavers et Joseph), des processus chimiques (Modèle de Duijn-Knabner) ou la dispersion de Taylor comment il est possible de résoudre numériquement et en partie ces difficultés par des techniques d'analyse mathématique récentes (homogénéisation, raisonnement multi-échelles et développements asymptotiques). Des résultats de simulations réalisées au moyen d'un logiciel de résolution d'EDP's baptisé SciFEM (Scilab Finite Element Method) conçu pour les besoins de la thèse illustreront notre démarche.

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Rembert, Flore. "Development of geo-electrical methods to characterize dissolution and precipitation processes in a carbonate context." Electronic Thesis or Diss., Sorbonne université, 2021. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2021SORUS114.pdf.

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La précipitation et la dissolution de la calcite sont des processus primordiaux dans les roches carbonatées et le fait de pouvoir les surveiller in situ est un enjeu majeur. Les méthodes hydrogéophysiques sont fondées sur le développement de techniques géophysiques appropriées pour le suivi des processus hydrologiques et biogéochimiques de manière non-intrusive et à faible coût. Parmi les techniques existantes, les méthodes électriques ont déjà prouvé leur capacité à surveiller de tels processus. Pour cette raison, les méthodes du potentiel spontané (PS) et de la polarisation provoquée spectrale (PPS) ont été choisies pour investiguer les processus de dissolution et de précipitation de la calcite. La PS est une technique passive consistant à mesurer le champ électrique naturel généré par les flux d’eau et les gradients de concentration, tandis que la PPS est une méthode active mesurant la conductivité électrique complexe aux basses fréquences (mHz-kHz). Ses composantes réelle et imaginaire peuvent être reliées respectivement à la microstructure et à l’état de surface des minéraux le constituant. Cette thèse présente des développements expérimentaux et théoriques afin d'améliorer l’interprétation des méthodes PS et PPS. Un nouveau modèle de conductivité électrique est développé et montre un bon ajustement avec les résultats numériques de dissolution et de précipitation. Des données PS remarquables ont été obtenues et ont pu être reliées quantitativement grâce à de la modélisation de transport réactif. Les résultats PPS nourrissent la réflexion sur les mécanismes responsables des variations de polarisation engendrés par la réactivité de la calcite
Precipitation and dissolution of calcite are key processes in carbonate rocks and being able to monitor them in situ is a major issue. Hydrogeophysical methods are based on the development of appropriate geophysical techniques for monitoring hydrological and biogeochemical processes in a non-intrusive and low-cost manner. Among the existing techniques, electrical methods have already proven their ability to monitor such processes. For this reason, the methods of self-potential (SP) and spectral induced polarization (SIP) were chosen to investigate the processes of dissolution and precipitation of calcite. SP is a passive technique consisting in measuring the natural electric field generated by water flows and concentration gradients, while SIP is an active method measuring the complex electrical conductivity at low frequencies (mHz-kHz). Its real and imaginary components can be related respectively to the microstructure and surface state of the minerals constituting it. This thesis presents experimental and theoretical developments in order to improve the interpretation of SP and SIP methods. A new electrical conductivity model is developed and shows a good fit with the numerical results of dissolution and precipitation. Remarkable SP data have been obtained and could be quantitatively linked through reactive transport modeling. The SIP results provide further insights into the mechanisms responsible for the polarization variations caused by the reactivity of calcite

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Pauwels, Hélène. "Etude theorique et experimentale du comportement des elements traces lors des processus d'interaction eau-roche." Paris 7, 1988. http://www.theses.fr/1988PA077136.

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Le modele de dissolution d'une solution solide est etendu aux mineraux silicates faisant intervenir des reactions acido-basiques. Ce modele permet une approche theorique du comportement des elements en traces lors des processus d'interaction eau-roche: la dissolution et la precipitation. L'evolution de la solution aqueuse jusqu'a l'etat stationnaire est decrite. Une liste des parametres fixant la concentration des elements traces est donnee. Leur comportement est etudie experimentalement et il est compare a celui des elements majeurs

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Devigne, Vincent Graillot Didier Mikelic Andro Batton-Hubert Mireille. "Écoulements et conditions aux limites particulières appliquées en hydrogéologie et théorie mathématique des processus de dissolution / précipitation en milieux poreux = Flows and Particular Boundary Conditions applied in Hydrogeology and Mathematical Theory of Dissolution/Precipitation process in porous media." Lyon : [s.n], 2006. http://tel.archives-ouvertes.fr/docs/00/13/20/36/PDF/UCBL_manuscrit.pdf.

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Davranche, Mélanie. "Impacts des processus aux interfaces solide/liquide sur la mobilité des éléments : Observations de terrain-Expérimentation-modélisation." Habilitation à diriger des recherches, Université Rennes 1, 2008. http://tel.archives-ouvertes.fr/tel-00289457.

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One of the key research issues in surface geochemistry is to understand the processes responsible of the surface water compositions to both improve fundamental knowledge of controlling mechanisms and protection of water resources. Processes occurring at solid-solution interface are predominant among the known involved chemical mechanisms. Solids, such as soil colloids, particles, sediments or colloids occurring as suspension in waters, present very large specific surfaces. This latter point gives them strong complexation or sequestration properties for elements such as metals, trace elements...These solids include mineral (oxyhydroxydes Fe and Mn, silicates, carbonates ...), organic colloid (humic substances...) and biological cells (algae, bacteria...) bound or not in between them. Sorption, co-precipitation and surface precipitation are the three major processes at interfaces involving these solid surfaces. They partly control the mobility and dissolved concentrations of metals and trace elements in waters and soil solutions. However, these processes are themselves controlled by physico-chemical parameters such as pH, Eh, T..., the solid nature and the interactions in between. The present work has therefore been focused on assessing the influence of these factors on the reactivity of elements at solid/solution interfaces. To address this issue, a combined approach involving laboratory experiments and modelling to answer to the questions identified in the field, was used. Firstly, the impact of redox condition variations on the mobilization of metals sourced in minerals (natural and synthetic oxyhydroxydes Fe and Mn, and slags from metallurgic industry) was experimentally evaluated. In a second step, this work was focused on the in situ monitoring of the iron cycle in a natural wetland soil. This implied the development of an innovative tool allowing the insertion of synthetic iron oxides directly in soil horizons. This research has been conducted to identify the impact of the iron oxides reductive dissolution and/or mineralogical changes on the mobilization of associated trace elements. Since organic matter release is often linked to iron reductive dissolution in wetland soil solutions, two experimental studies were also conducted: (i) on the redox condition impact on the dynamics of organic matter and trace element mobility and (ii) on the impact of organic complexation on the rare earth element (REE) speciation in solution. This work is ended by a research project dedicated to the rare earth element partitioning at solid-water interface and its impact on REE geochemical behaviour and associated fingerprinting properties.

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Laveuf, Cédric. "Les terres rares et le zinc comme traceurs des processus pédogénétiques : application à une séquence de sols issue de calcaires minéralisés." Phd thesis, Université d'Orléans, 2009. http://tel.archives-ouvertes.fr/tel-00452682.

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Ce travail évalue le potentiel du zinc et plus particulièrement des terres rares à tracer les différents processus le long d'une catena issue d'une formation carbonatée constituée d'une succession de bancs marneux et calcaires, et ayant subi des processus de décarbonatation, des conditions redox en lien avec l'hydromorphie et de l'éluviation. L'approche choisie repose (i) sur la spéciation des terres rares, à l'aide de méthodes physiques et chimiques, dans les traits pédologiques formés par les différents processus et des matériaux aux dépens desquels ils se sont développés, (ii) sur la quantification par bilan de masse des flux de terres rares et éléments majeurs associés. Ce travail a nécessité deux mises aux points méthodologiques : une méthode de normalisation des terres rares, basée sur l'enfoncement des fronts de transformation afin de quantifier l'impact des processus successifs sur le fractionnement des terres rares ; une méthodologie de reconstruction des matériaux parentaux pour chacun des horizons, l'approche par bilan de masse nécessitant une connaissance des stocks initiaux. L'impact de deux processus sur les fractionnements de terres rares est ensuite plus particulièrement abordé : la décarbonatation des matériaux parentaux et les processus d'oxydo-réduction. On montre ainsi l'importance de comparer les quantités mises en solution aux flux calculés par les bilans de masse pour prédire le devenir des éléments libérés et l'intérêt des terres rares pour quantifier les cycles de dissolution/précipitation des oxydes de fer et de manganèse.

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Daviray, Maxime. "Fonctionnement biogéochimique des écosystèmes transitionnels colonisés par les bactéries filamentaires électriques : réponse des biocénoses et thanatocénoses de foraminifères benthiques." Electronic Thesis or Diss., Angers, 2024. http://www.theses.fr/2024ANGE0031.

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L’objectif de cette thèse est d’évaluer l’effet de l’acidification provoquée par l’activité des cable bacteria sur la géochimie du sédiment des environnements intertidaux, et les conséquences de ce processus de dissolution sur les communautés de foraminifères benthiques et la préservation de leur test dans les sédiments. Cette étude combine des campagnes de suivis de vasières intertidales dans différents estuaires de la façade atlantique et de la Manche (France) par des approches à haute résolutions et des incubations en conditions contrôlées au laboratoire. L’activité des cable bacteria présente une variabilité saisonnière, avec un maximum d’activité durant la période été-automne, et tend à fortement structurer la succession verticale des zones oxique-suboxique-anoxique. La bioturbation associée à la macrofaune ou au réseau racinaire des zostères introduit de l’hétérogénéité latérale dans la géochimie et génère des microhabitats. L’effet structurant du pH sur la distribution successive des différentes espèces de foraminifères dans le sédiment a été mise en évidence. La réponse des foraminifères à l’acidification de leur environnement apparait espèce-dépendante et implique autant leur particularité métabolique que comportementale.L’activité des cable bacteria engendre une perte importante des tests carbonatés dans l’enregistrement sédimentaire. Leur temps de résidence est estimé à une douzaine de jours.L’accumulation de tests agglutinés et de membranes organiques, à défaut des tests carbonatés, pourraient être utilisée pour fournir une revue historique des processus de dissolution dans les sédiments marins
This thesis aims to assess the effect of acidification caused by cable bacteria activity on the sediment geochemistry in intertidal environments, and the consequences of this dissolution process on benthic foraminiferal communities and the preservation of their shell in sediments. This study combines intertidal mudflats monitoring in various estuaries on the Atlantic coast and in the English Channel (France) using high-resolution approaches and incubation under controlled conditions in the laboratory.. The cable bacteria activity varies according to the season, with maximum activity during the summer-autumn period, and strongly structures the vertical oxic-suboxic-anoxic redox zone succession. Bioturbation associated with macrofauna or the eelgrass roots introduces late--ral heterogeneity into this system and generate microhabitats. The structuring effect of pH on the successive distribution of foraminiferal species within sediment has been demonstrated. The response of foraminifera to the acidification of their environment seems to depend on the species and involves both their metabolic and behavioural characteristics. The activity of the cable bacteria results in a significant loss of calcareous shells in the sedimentary record. Their residence time is estimated about a dozen days. The accumulation of agglutinated shells and organic linings despite of calcareous shells could be used to provide a historical review of dissolution processes in marine sediments

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15

Chen, Tao. "Evolution de la perméabilité d'agrégats de sels sous contrainte liée à des circulations de fluides : dissolution, colmatage, déformation." Phd thesis, Université Joseph Fourier (Grenoble), 1994. http://tel.archives-ouvertes.fr/tel-00743930.

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Le but de ce travail est d'étudier l'évolution de la perméabilité d'agrégats de sels sous contrainte lorsque les fluides circulant dans ces agrégats peuvent réagir avec le solide par des dissolutions et/ou des colmatages. Des essais de circulation de divers fluides à travers des échantillons de briques de sels sous contrainte ont permis de suivre l'évolution de la composition des fluides en cours d'essai. L'évolution des matériaux a été aussi caractérisée en cours d'essai (mesure de vitesse acoustique) et après essai (scanner, microscope optique et à balayage, mesure de porosité mercure). Les résultats ont été discutés d'abord du point de vue de l'équilibre des réactions entre la solution qui percole et les différents minéraux des briques de sels (théorie de l'espace des réactions, modèles thermodynamiques à l'équilibre) . Ensuite a été introduite la notion de cinétique des réactions (processus limitant) pour déboucher sur un modèle d'évolution de la circulation des fluides dans un ouvrage de brique de sels au contact d'un fluide plus ou moins saturé en sels. L'effet des contraintes a été trouvé différent à court terme et à long terme. A court terme, sur des matériaux poreux, les contraintes et des réactions chimiques de mise à l'équilibre induisent des processus instables comme le développement de dissolutions en doigts de gants qui peuvent contribuer à amplifier la perméabilité. En revanche, à long terme les contraintes (au moins avec les valeurs modérées utilisées) ont un effet stabilisateur. La perméabilité décroît par une compaction chimique (dissolution-cristallisation sous contrainte), puis la déformation à long terme tend vers un processus de fluage lent par dissolution-cristallisation sous contrainte.

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16

Saad, Alice. "Influence du changement climatique et des conditions extrêmes sur les massifs fracturés : rôle des fluides (H2O, CO2) dans leur processus d'altération." Phd thesis, Université Paris-Est, 2011. http://tel.archives-ouvertes.fr/tel-00657462.

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L'objectif de ce travail est de comprendre le processus d'altération des calcaires oolithiques et d'estimer leur cinétique d'altération en fonction des conditions climatiques présentes en France. Pour y répondre, des cycles de vieillissement accéléré, basés sur les paramètres issus de l'étude bibliographique et sur les données de température et de précipitations réelles, ont été définis. Ensuite, des lots d'échantillons de deux calcaires oolithiques ont subis ces vieillissements. Les mesures réalisées pour déterminer l'endommagement ont été choisies en fonction de leurs caractéristiques métrologiques et de leur pertinence. Les résultats obtenus ont été comparés avec les mêmes mesures réalisées sur des calcaires altérés de façon naturelle prélevés sur site. Ainsi, les liens entre le processus d'altération des calcaires et les caractéristiques mécaniques, physiques et surtout microstructurales des calcaires ont été établis. Cette analyse a également abouti à des cinétiques d'altération. Les résultats ont été validés par l'étude d'un autre calcaire oolithique sous d'autres conditions climatiques. Enfin, l'influence de changements climatiques éventuels sur les cinétiques d'altération a été déterminée à l'aide d'un outil statistique

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17

Frisby, Brandi N. "Communicative facework in marital dissolution and post-dissolution processes." Morgantown, W. Va. : [West Virginia University Libraries], 2010. http://hdl.handle.net/10450/11241.

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Thesis (Ph. D.)--West Virginia University, 2010.
Title from document title page. Document formatted into pages; contains viii, 159 p. Includes abstract. Includes bibliographical references (p. 108-125).

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18

Moune, Severine. "Volatils mineurs (S, Cl, F) et éléments traces dans les magmas pré-éruptifs et les gaz volcaniques. Etude des processus de dégazage magmatique sur les volcans Hekla (Islande) et Masaya (Nicaragua)." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2005. http://tel.archives-ouvertes.fr/tel-00011542.

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L'axe principal de cette thèse est la caractérisation des processus de dégazage magmatique des éléments traces, du soufre et des halogènes de deux volcans actifs : Hekla (Islande) et Masaya (Nicaragua).
Une étude sur les inclusions magmatiques (MIs) a permis de suivre l'évolution des volatils dissous dans le système volcanique d'Hekla au cours de la différenciation magmatique (cristallisation fractionnée). Ceci a permis d'estimer les concentrations en volatils dissous "attendues" dans le liquide pré-éruptif. Cette approche permet donc de ne pas sous-estimer les concentrations des liquides piégés dans les MIs et améliore ainsi les contraintes sur la masse de volatils émise dans l'atmosphère. Cette étude indique que, lors de l'éruption de février 2000, Hekla a émis dans l'atmosphère 0.1 Mt de HCl, 0.2 Mt de HF et 3.8 Mt de SO2. La chimie de la phase sub-Plinienne de cette éruption a été étudiée, de façon plus approfondie, grâce aux averses neigeuses qui ont traversé le panache volcanique. L'étude de ces neiges a montré que l'enrichissement des éléments volatils est lié à un processus de dégazage sous forme de chlorures, fluorures et sulfates. En revanche, l'enrichissement des éléments réfractaires est expliqué par un processus de dissolution non-stoechiométrique des téphras par la phase gazeuse riche en fluor au sein du panache éruptif.
Une étude basée sur les MIs a permis de confirmer la théorie de Walker et al. (1993) selon laquelle la différenciation des magmas tholéiitiques du Masaya se produit à basse pression à partir d'un magma relativement "sec" de composition homogène dans le temps. La caractérisation physico-chimique des aérosols par MEB et la chimie de la phase éruptive du volcan Masaya suggèrent que la plupart des éléments traces sont dégazés sous forme de chlorures, mais aussi sous forme de sulfates et chloro-sulfates. De plus, la quantification des flux de matière a montré que le dégazage au Masaya est une source importante de pollution atmosphérique.

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19

Najjar, Denis. "Compétition entre les mécanismes de dissolution anodique et de fragilisation par l'hydrogène dans le processus de fissuration par corrosion sous contrainte de l'alliage Al-Zn-Mg-Cu 7150 sollicité en traction lente en milieu chlorure (NaCl 3)." Lille 1, 1994. http://www.theses.fr/1994LIL10098.

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Les alliages d'aluminium alznmg(cu) de la serie 7000 utilises dans l'industrie aeronautique ont fait l'objet de nombreuses etudes en corrosion sous contrainte (csc). Neanmoins, le mecanisme de fissuration est toujours sujet a controverses: dissolution anodique et fragilisation par l'hydrogene sont souvent proposes de maniere mutuellement exclusive. Le principal objectif de ce travail est de faire la part des choses entre ces deux grandes familles de mecanismes lors de la fissuration par csc de l'alliage 7150 sollicite en traction lente en milieu chlorure (nacl 3%). En couplant des essais mecaniques discriminatoires a des observations en microscopie electronique a balayage, nous montrons que dissolution anodique et fragilisation par l'hydrogene operent conjointement. L'influence relative de ces deux mecanismes depend des principaux parametres qui gouvernent la fissuration: l'etat microstructural, le potentiel electrochimique et la vitesse de deformation. En consequence, seule une modelisation qui considere cette influence relative semble appropriee pour rendre compte des resultats experimentaux. Jusqu'a presente, seule la phase de propagation avait fait l'objet d'etudes approfondies et nous proposons d'introduire la notion de defaut critique pour decrire la phase d'amorcage.

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20

Pritchard, Keith L. "Fundamental processes governing calcite dissolution at high pH." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238178.

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21

Adobes, Vidal Maria. "Quantitative and holistic views of crystal dissolution processes." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/95498/.

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This thesis is concerned with the development and application of novel theoretical and experimental methodologies to study crystal dissolution processes across multiple lengthscales. In particular, it presents a versatile in situ multimicroscopy approach, comprising atomic force microscopy (AFM), scanning ion-conductance microscopy (SICM), and optical microscopy (OM) that is readily combined with finite element method (FEM) simulations. The methodology permits the quantitative 3D visualization of microcrystal morphology during dissolution with well-defined, high mass transport rates, enabling both the measurement of face-dependent dissolution rates and the elucidation of the dissolution mechanism. The approach also allows the determination of interfacial concentrations and concentration gradients, as well as the separation of kinetic and mass transport limiting regimes. The high resolving power and versatility of this new methodology is demonstrated on four different crystalline compounds with very different characteristics. First, the dissolution kinetics of individual faces of single furosemide microcrystals are investigated by OM-SICM and FEM modeling. It is found that the (001) face is strongly influenced by surface kinetics, while the (010) and (101) faces are dominated by mass transport. Dissolution rates are shown to vary greatly between crystals, with a strong dependence on crystal morphology and surface properties. A similar approach is then used to investigate changes in both crystal morphology and surface processes during the dissolution of bicalutamide single crystals, achieving high resolution with in situ AFM. It is shown that dissolution involves roughening and pit formation on all dissolving surfaces, and that this has a strong influence on the overall dissolution rate. FEM simulations determine that mass transport contributions increase as dissolution proceeds due to a continuous increase of the intrinsic dissolution rate constant, promoted by the exposure of high index microfacets. The methodology is further developed to show that kinetic data obtained from OMSICM and AFM, which provide differing measures of kinetic parameters, are in good agreement when the different mass transport regimes of the two experimental configurations are accounted for. The robustness of the methodology is verified via studies of L-cystine crystals, while also providing insights into the dissolution mechanism by visualizing hexagonal spirals descending along screw dislocations. Finally, the ability of the methodology to characterize processes with fast surface kinetics is demonstrated by the study of the proton-promoted dissolution of calcite single crystals. The approach allows the accurate determination of the near-interface concentration of all species during dissolution, as well as the intrinsic dissolution rate constant of the {104} faces, showing that surface kinetics play an important role in the dissolution process. Overall, this methodology provides a significant advance in the analysis and understanding of dissolution processes at a single crystal level, revealing the intrinsic properties of crystal faces and providing a powerful platform from which future studies can be developed.

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22

Parker, Alexander S. "Quantitative crystal investigations : surface dissolution and nucleation processes." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/88282/.

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The aim of this thesis is twofold with both elements related to industrially relevant crystal systems and processes. The first element utilized a combined scanning electrochemical cell microscope (SECCM) and atomic force microscopy (AFM) method to study the dissolution of enamel surfaces with controlled proton flux to the surface. This was then extended to investigate the effect of both known surface treatments, fluoride and zinc ions, but also a novel treatment of calcium silicate and its methods of action. The second element investigated the use of a nanopipette to investigate the early nucleation and initial growth of calcium carbonate crystals. For the dissolution of enamel, an SECCM probe to selectively etch a surface for a defined period of time with a high spatial resolution was used. The extent of the etching in the resultant pits was then monitored through AFM to measure the volume of material removed along with other pit dimensions. The method allowed for multiple independent measurements on a single sample, which could be selectively treated to eliminate comparability issues associated with measurements on multiple samples. The system could be modelled via finite element method (FEM) to calculate an intrinsic rate of reaction for the proton induced dissolution of enamel. A proton induced rate constant of dissolution of k0= 0.099 ± 0.008 cm s-1 for bare untreated enamel was established, whereas treatment with 1000 ppm sodium fluoride (NaF) and/or zinc chloride (ZnCl2) decreased this rate constant. The work also characterised the use of calcium silicate as a novel additive in toothpaste and to determine its effect as both a remineralising agent and as a dissolution inhibitor. The release of Ca2+ ions into solution was measured which acts to promote the remineralisation of tooth enamel. The addition of phosphate buffer into this solution combined with micro-Raman spectroscopy was then used to confirm the formation of hydroxyapatite (HAP (Ca10(PO4)6(OH)2)) material. The extent of adhesion of calcium silicate onto rough and polished samples was also observed, showing the preference of particles to adhere to rough surfaces, and was quantified by investigating the effect of infilling of etch pits formed via the SECCM method above, which showed an average pit volume reduction of 77±12%. The second element of the thesis involved investigation into the initial phase of nucleation, nanoprecipitation and growth of calcium carbonate crystals using voltage driven ion migration within a nanopipette (~50 nm opening) geometry to control the mixing of constituent ions to selectively control and induce the nucleation and dissolution of crystals and monitor their growth. This was achieved using oppositely charged CO32- and Ca2+ ions, inside and outside the pipette respectively, which could be either driven together or apart depending on the applied polarity. This process was modelled using FEM to give quantitative information about the growth rate and nanocrystal size during growth as well as analysis of the saturation levels within the probe geometry. The nanocrystals formed were studied in situ using micro-Raman spectroscopy to give information about the polymorph of calcite produced. The effect of the driving bias was demonstrated and rationalised through simulation along with the effect of constituent ion concentration. This method was used to assess the effect of maleic acid as an inhibitor to the formation of calcium carbonate. Its potent effect was shown by the significantly larger time taken to block the pipette by crystal growth. This also provided evidence for the mechanism of crystal growth inhibition by comparison with ion concentrations expected as a result of a pure chelation effect.

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23

Mitchell, Mark J. "Mathematical modelling of carbon dioxide dissolution and reaction processes." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/14502/.

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Carbon dioxide dissolution into water is a ubiquitous chemical process on earth, and having a full understanding of this process is becoming ever more important as we seek to understand the consequences of 250 years of exponentially-increasing anthropogenic C02 emissions to the atmosphere since the start of the Industrial Revolution. We examine the dissolution of C02 into water in a number of contexts. First, we analyse what happens to a range of chemical species dissolved in water following an injection of additional C02. We consider the well-mixed problem, and use the method of matched asymptotic expansions to obtain new expressions for the changes in the species' concentrations with time, the new final chemical equilibrium, and the time scales over which this equilibrium is reached, as functions of time, the parameters and the initial condition. These results can be used to help predict the changes in the pH and concentrations of dissolved carbonic species that will occur in the oceans as a result of anthropogenic C02 emissions, and in saline aquifer formations after pumping C02 deep underground. Second, we consider what happens deep underground in a saline aquifer when C02 has been pumped in, spreads through the pore space, and dissolves into the resident water, when advection, diffusion, and chemical reaction have varying levels of relative importance. We examine the length scales over which the dissolved C02 will spread out through an individual pore, ahead of a spreading drop of C02, and the concentrations of the different chemical species within the pore, in the steady-state case. Finally, some experiments have been carried out to investigate the effect of an injection of gaseous C02 on the chemical composition and pH of a saturated limestone aquifer formation. As the C02 enters the soil, it dissolves into the water, and we model the changes in the chemical composition of the water/limestone mixture with time.

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24

Perry, Amelia Ruth. "Quantitative microscopic methods for crystal growth and dissolution processes." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/73865/.

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The aim of this thesis was to investigate crystal nucleation, growth and dissolution processes, focussing particularly on the behaviour of the crystal surface. To facilitate this various methods of microscopy were used, as well as electrochemical techniques, with the goal to separate mass transport towards the crystal surface and the processes which occur close to the crystal surface, and measure intrinsic growth/dissolution rates. In order to do this, crystal systems were screened for their relevance to applications in industrial processes, and those chosen were related to pharmaceutical crystallization and scale formation in o↵ shore oil wells. For each system, different methods of electrochemical measurement and microscopy were investigated to chose a technique which works best for the problem in hand. Further to the experimental data produced, these were supported by mass transfer models, with the aim of finding out more quantitative information about the surface behaviour of the crystal systems observed. Firstly, salicylic acid micro-crystals were observed in aqueous solution by optical microscopy to visualise growth/dissolution rates of individual faces. It was found from finite element method (FEM) simulations that the most active (001) face was strongly mass transport controlled, and that the (110) and ( ¯ 110) were closer to the surface controlled regime. Salicylic acid crystals were further analysed by scanning electrochemical microscopy (SECM) using 3 dimensional (3D) scans containing a series of approaches to the surface. By inducing dissolution on the crystal surface, and measuring a change in ultramicroelectrode (UME) current, the dissolution rate constant of the (110) face of salicylic acid was determined for this heterogeneous surface. Barite nucleation and growth was observed by optical microscopy, using a flow cell with hydrodynamic flow. High supersaturations were used and the crystals were deposited onto foreign surfaces with differing surface charge. It was found that the flux of material, once initial nucleation was achieved, matched closely to simulated mass transport fluxes. Finally, nanoprecipitation was induced at the opening of a nanopipette (ca. 100 nm) diameter and an ion current was applied to induce the early stages of barite nucleation. It was possible to observe nucleation and blockage of the nanopipette from the current transient produced. This process was used to test the effectiveness of different phosphonate inhibitors.

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25

Noiriel, Catherine. "Contribution à la détermination expérimentale et à la modélisation des différents processus contrôlant l'évolution géochimique, structurale et hydrodynamique des roches fissurées carbonatées." Phd thesis, École Nationale Supérieure des Mines de Paris, 2005. http://tel.archives-ouvertes.fr/tel-00012048.

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Ce travail a porté sur l'application de la microtomographie à rayons X à la caractérisation de la géométrie de fractures et milieux poreux soumis à des réactions de dissolution, afin de mieux comprendre les relations existant entre les réactions chimiques, les modifications de géométrie, et l'évolution des écoulements et du transport réactif. Les observations ont permis de mettre en évidence la nature instable des phénomènes de dissolution, qui peuvent conduire à une augmentation rapide de la perméabilité. L'implication de la minéralogie et de la texture des roches naturelles paraît également déterminante dans l'évolution de la rugosité des surfaces, du transport des éléments à l'interface eau-minéral, et des motifs de dissolution. Le modèle de transport réactif HYTEC a ensuite été utilisé afin de mettre en évidence le rôle de la géométrie, de la relation porosité - diffusivité, et de la valeur des nombres de Damköhler et de Péclet dans l'évolution du transport des espèces en solution.

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26

Rheinheimer, Vanessa. "A nanoscale study of dissolution and growth processes in cement hydrates." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/285965.

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This thesis aims at providing new knowledge on the, otherwise poorly known, molecular-scale mechanisms that operate during hydration of cement phases and dissolution of their hydrates. In order to pursue this objective, a novel approach has been followed, including the development of a new procedure to synthesize thin films of calcium silicates, real time characterization of grain growth and dissolution with liquid-cell atomic force microscopy, and monitoring of their chemical evolution by X-ray photoelectron spectroscopy of thin films hydrated in-situ, avoiding atmospheric contamination. Nanometer-sized films of clinker phases have been prepared using electron-beam evaporation methods. After deposition on silicon substrates, film thicknesses and mineralogical composition were characterized by atomic force microscopy (AFM) or mechanical profilometry and grazing-angle X-ray diffraction (GAXRD), respectively. Chemical composition was determined by X-ray photoelectron spectroscopy (XPS). Results from the GAXRD and XPS analysis show that aluminates phases are not suitable to be evaporated by electron beam technique. However quantitative analysis of calcium silicates samples shows that the Ca:Si ratio of the deposited film is the same as in the bulk starting material, confirming the suitability of the technique for the synthesis of these materials. Calcium silicate thin films with different thicknesses were submitted to hydration in different ways. XPS results describe clear chemical changes when samples are exposed to water vapor by shifts on the silicon peak, broadening on the calcium peak and decreasing on the Ca:Si ratio, related to the silicon polymerization due to the C-S-H formation. In situ hydration in fluid cell followed by AFM in water and calcium hydroxide saturated solution allows observing the formation of C-S-H particles, that happens very fast in C3S, which is dissolved later, and slower in C2S. Finally, Scanning transmission X-ray microscopy (STXM) of samples hydrated in situ with water allows observing the formation of particles with different concentration of calcium and silicon, and different chemical state at some point. The development of this technique of synthesis and the results obtained on the hydration allow improving the knowledge of early stage clinker phase hydration at the molecular level and to better understand the behavior of these materials, shedding some additional light on the complex problem of the hydration mechanisms of cementitious materials.
Aquesta tesi té per objectiu proporcionar nous coneixements sobre els mecanismes, abans poc coneguts, que operen durant la hidratació de les fases de ciment i la dissolució dels seus hidrats a escala molecular. Per tal d'aconseguir aquest objectiu, un nou enfocament ha estat seguit amb l'elaboració d'un nou procediment per sintetitzar pel·lícules primes de silicats de calci, la seva caracterització en temps real del creixement del gra i de la dissolució amb les cel·les de líquid al microscopi de forces atòmiques i el seguiment de l'evolució de la seva composició química per espectroscòpia de fotoelectrons de raigs X de pel·lícules primes hidratades in-situ, evitant la seva contaminació atmosfèrica. S'han preparat pel·lícules nanomètriques de les fases del clínquer utilitzant l'evaporació per feix d'electrons. Després de la deposició en substrats de silici, es van caracteritzar el gruix mitjançant la microscòpia de forces atòmiques (AFM) i la perfilometria mecànica i la composició mineralògica amb la difracció de raigs X d'angle rasant (GAXRD). La composició química es va determinar per espectroscòpia fotoelectrònica de raigs X (XPS). Els resultats del GAXRD i d'XPS mostren que els aluminats no són adequats per a ser evaporats utilitzant l'evaporació assistida amb feix d'electrons. No obstant això, anàlisis quantitatives de les mostres de silicats de calci mostren que la relació Ca:Si de la pel·lícula dipositada és la mateixa que en el material de partida, el que confirma la idoneïtat de la tècnica per a la síntesi d'aquests materials. Les pel·lícules primes de silicat càlcic de gruixos diferents van ser sotmeses a hidratació de diferents maneres. Els resultats d`XPS descriuen canvis químics clars quan les mostres estan exposades al vapor d'aigua com s'infereix dels canvis en el pic del silici, l'eixamplament del pic del calci i la disminució en la relació Ca:Si, que es relaciona amb la polimerització del silici degut ala formació de C-S-H. La hidratació in situ en aigua o solució saturada d'hidròxid de calci a la cel·la de fluid de l'AFM permet observar la formació de partícules de C-S-H. La hidratació ocorre molt ràpidament en el C3S, que després es dissol, i és més lenta en el C2S. Finalment, la microscòpia de transmissió i escaneig de raigs X (STXM) de les mostres hidratades in situ amb aigua permet observar la formació de partícules amb diferents concentracions de calci i silici i, en alguns casos, la variació de l'estat químic . El desenvolupament d'aquesta tècnica de síntesi i els resultats obtinguts en la hidratació permeten millorar el coneixement de la hidratació de les fases del clínquer en estadis inicials a nivell molecular i entendre millor el comportament d'aquests materials, ajudant a aclarir el complex problema dels mecanismes d'hidratació dels materials del ciment

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Hammons, Joshua Aaron. "A study of precipitated films formed during electrochemically driven dissolution processes." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/3165/.

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Precipitated surface films form when metal cations are produced faster than they can move away from the dissolving interface. This build up of cations results in supersaturation conditions, which cause a solid to precipitate. The precipitated solid affects ion transport and thus the dissolution kinetics, which ultimately control the two systems studied here. X-ray diffraction, small angle X-ray scattering and fast radiography were chosen to study the metal/solution interface in-situ, using synchrotron radiation. The AC electrograining system is a widely used industrial process whereby an alternating current is applied to aluminium plates to form a pitted surface. During this process, an Al(OH)3 surface gel (smut) forms within seconds whilst electrograining continues for several minutes in its presence. Although smut formation has been investigated previously, how the smut affects metal dissolution is currently unknown and is the primary goal of this project. The second system is a nickel “artificial pit,” which is commonly used to simulate pit propagation. In this system, a salt film is precipitated by imposing a large overpotential whilst restricting transport through a 1-D pit. Interfacial phenomena that occur during salt film formation are investigated towards an understanding of how the salt film forms.

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28

Yau, Sze Tai. "Electrochemical recovery of copper from waste catalyst residues." Thesis, University of Huddersfield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327142.

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29

Romero, Joseph Vincent 1977. "Experimental analysis and modeling of transient dissolution of RDX through mass transfer processes." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29957.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.
Includes bibliographical references (leaves 79-80).
A simulation study was performed to model the transient behavior of the dissolution of hexahydro-1, 3,5-trinitro-1, 3,5-triazine (RDX) in Composition B. Composition B, also referred to as CompB. CompB is made up of three parts: 54% RDX, 6% HMX and 40% TNT. A numerical simulation was employed to model the overall solute transport equation. The solute transport equation takes into account advection, dispersion, sorption, degradation, mobile-immobile sorption, and a mass transfer source term. Numerical code was developed and this model simulated the following: (1) flow rate, (2) initial mass loading, (3) particle size and (4) field oil. The simulation model results verified laboratory experiments provided by Phelan et. al. [2003] by applying the governing advection-dispersion equation with a linear-driving-force source term of the form kf (C, - C) . The variable k represents the lumped mass transfer coefficient [1/day], which implicitly incorporates specific surface area. The concentration denoted as C [mg/L], represents the effluent chemical concentration present in water at a given time while C, [mg/L] represents the concentration at equilibrium. The mass transfer source term was evaluated by correlating k to the modified Sherwood number. The modified Sherwood number was fitted with a least-squares method that approximated non-aqueous phase liquid (NAPL) dissolution [Miller et. al., 1990]. This study adjusted the constants developed with the obtained modified Sherwood number to model RDX. Modeling development used a modified Sherwood number in the form: ... The simulation code effectively modeled RDX effluent profiles.
by Joseph Vincent Romero.
S.M.

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30

Grant, Gavin P. "The evolution of complex DNAPL releases : rates of migration and dissolution." Thesis, University of Edinburgh, 2005. http://hdl.handle.net/1842/2155.

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A series of local and bench scale laboratory experiments and bench and field scale numerical simulations were conducted to develop a better understanding of the interrelationship between nonwetting phase (NWP) source zones and downgradient aqueous phase concentrations in saturated porous media contaminated by immiscible organic liquids. Specific emphasis was placed on the factors governing the rate of NWP source zone evolution and the factors governing the rate of mass transfer from the NWP to the aqueous phase. Hysteretic NWP relative permeability-saturation (krN-SW) relationships were measured at the local scale for six sands to examine the relationship between krN-SW functions and porous media type. Parameterization of the measured constitutive relationships revealed a strong correlation between mean grain diameter and the maximum value of NWP relative permeability. The measured krN-SW relationships, were validated through a bench scale experiment involving the infiltration, redistribution, and immobilisation of NWP in an initially water saturated heterogeneous porous medium. This match of simulation to experiment represents the first validation of a multiphase flow model for transient, fixed volume NWP releases. Multiphase flow simulations of the bench scale experiment were only able to reproduce the experimental observations, in both time and space, when the measured krN-SW relationships were employed. Two-dimensional field scale simulations of a fixed volume NWP release into a heterogeneous aquifer demonstrate the influence of spatially variable krN-S relationships correlated to porous media type. Both the volume of the NWP invaded porous media, and the length of time during which NWP is migrating, will be under predicted if variable (correlated) kr,N is not accounted for in the numerical model iv formulation. This under prediction is exacerbated as the mean intrinsic permeability of the release location decreases. A new, thermodynamically-based interfacial area (IFA) model was developed for use in the single-boundary layer expression of mass transfer as an alternative to existing empirical correlation expressions. The IFA model considers consistency and continuity of constitutive relationships, energy losses, effective specific interfacial area for mass transfer, and dissolution of residual NWP. A bench scale experiment involving the release and dissolution of a transient NWP source zone in heterogeneous porous media was conducted to evaluate the appropriateness of the developed IFA model when utilised to predict NWP dissolution rates. Comparison of measured downgradient dissolved phase concentrations and source zone NWP saturations in time and space with those from numerical simulations of the experiment reveal that the proposed IFA model is superior to both a local equilibrium assumption and existing empirical correlation expressions. This represents the first mass transfer model validated for the dissolution of a complex NWP source zone. Twodimensional simulations at the field scale of multiphase flow and dissolution suggest that employing existing mass transfer expressions instead of the IFA model lead to incorrect predictions of the life spans of NWP source zones, downgradient dissolved phase concentrations, and the rate of mass flux through a downgradient boundary. The practical implication of this research is that accurate numerical predictions of the evolution of a transient NWP source in porous media require consideration of krN-S relationships and NWP / aqueous phase IFA, as these factors dictate the rates of the key subsurface contaminant processes of migration and dissolution, respectively.

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Zaim, Christiane Yuriko Hamai. "Avaliação do perfil de dissolução de comprimidos de glibenclamida 5 mg obtidos por diferentes processos." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/9/9139/tde-10042015-143023/.

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Fármacos pouco solúveis em água são um dos maiores desafios encontrados em formulação de comprimidos, uma vez que, se não adequadamente formulados, podem apresentar problemas de dissolução e de biodisponibilidade. O presente trabalho teve como objetivo produzir comprimidos de glibenclamida 5 mg (hipoglicemiante oral pouco solúvel) utilizando diferentes processos visando a melhoria da dissolução do fármaco e comparar a liberação in vitro (perfil de dissolução) das formulações entre si, bem como em relação ao medicamento referência no Brasil, Daonil®. Foram obtidas 19 formulações por compressão direta empregando dispersão sólida, complexação com ciclodextrina ou micronização do fármaco. Os comprimidos foram analisados quanto ao aspecto, peso médio, dureza, friabilidade, teor e eficiência de dissolução. Os resultados indicaram que, dentre os processos estudados, a utilização de complexos glibenclamida-β-ciclodextrina e glibenclamida micronizada, promoveram uma melhora da dissolução do fármaco. O superdesintegrante Explocel® promoveu significativa melhoria no perfil de dissolução em todas as formulações em que estava presente. A utilização do complexo glibenclamida-β-ciclodextrina com o Explocel® apresentou perfil de dissolução estatisticamente semelhante ao Daonil®, além de atender aos demais requisitos físico-químicos.
Slightly soluble drugs are one of the largest challenges found in tablet formulation, once, if not appropriately formulated, they can present dissolution and bioavailability problems. The present work had as objective to produce 5 mg glibenclamide (practically insoluble hipoglicemic drug) tablets using different processes which aim at enhancing drug dissolution and to compare the in vitro release (dissolution profile) of these formulations with each other as well as with the reference medicine in Brazil, Daonil®. 19 diferent formulations were obtained through direct compression using solid dispersion, cyclodextrin complexion or micronization of the drug. The tablets were also analyzed in relation to aspect, medium weight, hardness, friability, assay and dissolution eficiency. The results indicated that, among the studied processes, an enhancement of the dissolution rate of the drug have arisen from the use of the glibenclamide-β-cyclodextrin complex and the micronized glibenclamide. The disintegrant Explocel® promoted enhancement in the dissolution rate in all the formulations in which it was present. The use of the glibenclamide-β-cyclodextrin complex with Explocel® have presented the best dissolution profile, statistically similar to Daonil®, besides accomplishing the other physico-chemical requirements.

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Brown, Eric Vincent. "Incinerator ash dissolution model for the system : plutonium, nitric acid and hydrofluoric acid." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/12166.

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Stoor, T. (Tuomas). "Air in pulp and papermaking processes." Doctoral thesis, University of Oulu, 2006. http://urn.fi/urn:isbn:9514280784.

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Abstract A pulp suspension consists of water, fibres, fines, fillers and chemicals, but air or other gases are also present in practically all pulping processes either in dissolved form or as bubbles. Dissolved gases seldom disturb the processes, but they are readily converted to gaseous form when conditions change. The gas bubbles affect the properties of the pulp suspension, reduce the accuracy of certain measurements, interfere with the runability of the papermachine and detract from the quality of the end-product. Gases are removed from the process by either mechanical or chemical means, resulting in increased investments and operational costs. The aim of this work was to study the behaviour of gas in pulp and papermaking processes with laboratory, pilot-scale and mill-scale experiments. Five main areas of the research can be identified: 1. Occurrence of gases in pulp and paper mill processes, 2. Dissolution, precipitation and hold-up of gases in the pulp suspension and mill water, 3. Effects of gases on certain consistency measurements, centrifugal pumping and operation of the hydrocyclone. 4. Measurement of the gas content of the pulp suspension by compression, radiometric, microwave and sonar methods and 5. Removal of gases with a centrifugal pump equipped with vacuum pump or hydrocyclone equipped light reject removal. The results show that the dissolution and precipitation of gas is strongly dependent on the pulp and water properties. Dissolved and colloidal material reduces the solubility potential of gas, but also accelerates the precipitation of dissolved gases in gaseous form. The hold-up of precipitated gas bubbles was found to be much more pronounced in hydrophobic mechanical pulps than in lignin-free chemical pulps. The accuracy of consistency measurements was affected by free gas in the pulp suspension, requiring special attention when assessing the results. The operation of pressure screens and hydrocyclones was affected only at high volumes of free gas in the feed suspension. According to the experiments, a reliable gas content measurement can be achieved by in-line radiometric, microwave or sonar methods, and also by the off-line compression method if a representative sample is obtained. A centrifugal pump equipped with a gas removing unit is designed mainly to ensure undisturbed pumping, whereas its gas removal efficiency remains quite low, especially with small bubbles and at a low gas content. The gas removal efficiency of a hydrocyclone equipped with light reject removal is good, but decreases with small precipitated bubbles. These results offer new information of the behaviour of the gas in pulp suspensions and white water and underline the importance of the bubble generation mechanism in this context.

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Lorenzen, Leon. "A fundamental study of the dissolution of gold from refractory ores." Thesis, Stellenbosch : Stellenbosch University, 1992. http://hdl.handle.net/10019.1/69492.

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Thesis (PhD)--Stellenbosch University, 1992.
ENGLISH ABSTRACT: The dissolution of gold from refractory ores is a complex kinetic problem involving a number of chemical, mass transport and mineralogical factors. In most Witwatersrand ores in South Africa more than 97 % of the gold is dissolved in cyanide medium after a residence time of about 16 hours in pachuca tanks. This high percentage may be the reason why so little fundamental research has been done into the mechanism and kinetics of the leaching process. With the increasingly lower grades of ore mined, the introduction of backfill mining, and the reduction of profit margins, it has become imperative to increase the efficiency of gold dissolution. The effects of the chemistry and particle size on the dissolution of gold in each sample of ore were studied in detail. The emphasis in this study is on the effect of the leaching behaviour of various ore constituents on the rate of gold dissolution. Interferences with the leaching of gold in contact with other minerals or metals could be attributed to the galvanic interaction (electrical conductivity) between the gold and the mineral and to the formation of a surface film on the gold surface. Sulphide minerals and their oxidation products cause the largest decrease in gold dissolution rate. Galena enhances the rate of gold dissolution owing to dissolved Pb(II)-ions. Gold in contact with conductive minerals passivates as a result of the enhanced magnitude of the cathodic cu1Tent. In all experiments the rotating disc of gold passivated so that the rate of dissolution was much slower than that predicted by a mass-transport limiting model. The various films that form on the surface of the gold and associated minerals, as well as the galvanic interaction, depend largely on the pretreatment of the ore. Pre-elimination of host minerals from the gold bearing ore increases the dissolution rate of gold, and explains the kinetics of reaction on the gold surface to a large extent. The selective destruction of the various minerals with oxidative acid leaches destroys and/or decomposes certain minerals which may form films on the gold surface by precipitation. The chemical composition of these films and precipitates depends on the mineralogy of the sample. These films may be oxides, sulphides, carbonates and cyanide complexes. The complexes can be destroyed, depending on the nature of the film, by interstage dilute acid and/or cyanide washes in an agitated vessel. The destruction of the films exposes the gold surface for cyanidation. A simple distribution function similar to the King liberation model is proposed and tested to describe the dissolution step in the multi-step leaching mechanism. For the King model, good agreement is shown with experimental results. For the liberation results obtained by leaching in this study, the trend is co1Tect, but calibration is required for a close fit. A potentially important use for the liberation model by leaching is to predict the leachable or free gold in an ore from the free gold in the complete sample. This approach for studying the leaching behaviour of different gold bearing minerals has provided reasons why some ores leach better than others.
AFRIKAANSE OPSOMMING: Die loging van goud vanuit weerbarstige ertse is 'n komplekse kinetiese probleem wat verskeie faktore soos massa-oordrag, chemiese aspekte en mineralogiese ingeweefdheid insluit. Goud ekstraksies so hoog as 97 % in sianied oplossings in Pachuca reaktore na ongeveer 16 uur logingstyd word behaal in die meeste Witwatersrand ertse in Suid-Afrika. Hierdie hoë ekstraksies mag dalk die rede wees vir die min fundamentele navorsing oor die ekstraksie van goud vanuit minerale in 'n spesifieke erts. Die dalende erts grade, die verlaging van winsgrense en die terugplaas van geloogde erts in die myn noodsaak verbeterde goud ekstraksie. Verkeie faktore nl., chemie, diffusie, partikelgrootte en oplosbaarheid van goud in elke monster erts is in hierdie studie ondersoek. Die sentrale tema was om die logingsgedrag van goud vanuit verskeie minerale in 'n erts te bepaal. Galvaniese interaksie (hou verband met elektriese geleidingsvermoeë) en film vorming is die belangrikste faktore wat die loging van goud in kontak met minerale nadelig beïnvloed. Sulfied minerale en hul oksidasie produkte speel die grootste rol in die verlaging van die tempo van goudloging. Galena verhoog die tempo van goudloging as gevolg van die Pb (II)- ione in oplossing. Goud in kontak met geleidende minerale passiveer as gevolg van die verhoogde katodiese stroomdigtheid. In alle eksperimente met die roterende skyf (goudskyf) apparaat, passiveer die goudskyf in so 'n mate dat die logingstempo baie stadiger is as wat voorspel word met die massa-oordrags model. Die onderskeie films wat vorm op die goud- en geassosieerde minerale se oppervlaktes, asook die galvaniese interaksies, is 'n funksie van die voorafbehandeling van die erts. Die selektiewe eliminering van minerale vanuit 'n gouddraende erts verhoog die tempo van goudloging drasties en dit beskryf die kinetika van goudloging op die goudoppervlak in 'n groot mate. Die selektiewe eliminering van minerale deur gebruik te maak van oksiderende suurlogings, vernietig sekere van die minerale wat films op die goudoppervlakte kan veroorsaak deur middel van presipitasie. Die chemiese samestelling van hierdie films hang af van die mineralogie van die monster. Dit bestaan meestal uit oksiedes, sulfiedes, karbonate en sianiedkomplekse en hulle kan vernietig word deur middel van inter-stadia verdunde suur-en/of sianied wasse. 'n Eenvoudige distribusiefunksie, soortgelyk aan die King bevrydingsmodel word voorgestel en eksperimenteel getoets om die logingstap in die multi-stadia logingsmeganisme te beskryf. Vir bevryding deur loging, is die neiging van King se model korrek, maar kalibrasie word benodig vir goeie passing. 'n Potensiele gebruik van die aangepaste model is om vrye of loogbare goud in 'n spesi fieke partikel grootte fraksie van 'n erts te voorspel as die vry goud in die totale fraksie bekend is. Die resultate uit hierdie studie kan gebruik word om die logingsgedrag van gouddraende minerale te voorspel en te beskryf, en dus veduidelik hoekom goud uit sekere ertse beter loog as uit ander.

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Espriu, Alexandra. "Study of near field processes involved in the oxidative dissolution of the spent nuclear fuel and radionuclides release." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/461973.

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Nowadays nuclear power plants (NPP) and dedicated facilities are storing the spent nuclear fuel (SNF). In the case of Spain, the NPP have enough space in their pools to keep storing the SNF produced from their activity; therefore, it is necessary to provide a final solution for the SNF management. It has been internationally accepted that the safest and most economically viable option to finally dispose the SNF is the Deep Geological Repository (DGR) which is based on the protection and confinement of the SNF by using a multibarrier system. This system considers the SNF as the first barrier where all the radionuclides (RN) are contained due to the physical and chemical properties of the fuel waste. With the goal of assessing the safety of the DGR and determining the SNF behavior under relevant conditions for the repository, in this work, four different scenarios have been selected that might alter the nuclear waste. These scenarios were studied by using non irradiated analogues of the SNF. During the alteration of the barriers of the DGR, the anoxic corrosion of the metallic container will produce high partial pressures of hydrogen that might get in contact with the SNF. At the same time, it is possible that vapor will be produced due to the water entry and the temperature of the SNF. In this work, the effect of water vapor and hydrogen in contact with UO2 has been studied. It was observed that uranium is oxidized in contact with water vapor in anoxic and reducing environment and as a function of the temperature. On the other hand, when palladium nanoparticles were used as analogues of the epsilon and metallic particles of the SNF, no oxidation was observed under H2 atmosphere. At the time when the water gets in contact with the SNF, the RN that are segregated and are more volatile and soluble than UO2 will be released to the water faster than the SNF matrix and will contribute to the Instant Release Fraction (IRF). With the aim of predicting the RN release, a mathematical model and a specific algorithm were designed, in order to identify and quantify the segregation of the RN that contributes to the IRF. Real leaching data was used to discuss the model and the algorithm by using the results obtained that allowed to classify the RN depending on their release source (grain boundary, oxidized phases and matrix). The dissolution rates obtained from the model agree with reported values in the bibliography. Since the alteration mechanisms of the SNF and the UO2 matrix depend on the ground water composition, and given the presence of concrete components in the DGR, this work studied the SNF corrosion in contact with cement waters. A SIMFUEL electrode was used to obtain cyclic voltammograms, potentiostatic and corrosion potential measurements under hyper alkaline conditions in presence of calcium and silicate as a analogue of cementitious water. The results obtained showed that the oxidation of the SIMFUEL was partially avoided in the presence of calcium and silicate. This might be caused by the precipitation of solid phases on the electrode surface or by the stabilization of reduced phases. Finally, saturation conditions might occur in the SNF near field and secondary solid phases might precipitate in the SNF vicinity. In this context, this work studied the influence of two uranyl silicate solid phases (soddyite and uranophane) on the Cs and Sr mobility. It was determined that both solid phases can retain the two RN on their surface and the sorption process proceeds through sorption on active sites. For the sorption of Cs, soddyite has more sorption capacity while in the case of Sr, uranophane has more sorption capacity. Therefore, the formation of these secondary phases might decrease the concentration of Cs and Sr released to the geosphere.
Actualmente en España, las centrales nucleares están acumulando el combustible nuclear gastado (CNG) y apenas disponen de espacio suficiente para seguir almacenando el residuo generado por la actividad de la central. En consecuencia, es necesario adoptar una solución definitiva a la gestión de los residuos nucleares. La opción aceptada internacionalmente para almacenar definitivamente el CNG como la más segura y viable es el Almacenamiento Geológico Profundo (AGP) basado en el confinamiento y la protección del residuo mediante un sistema de multibarrera. Dicho sistema considera el CNG como primera barrera donde están contenidos los radionúclidos (RN) debido a las propiedades físicas y químicas del propio combustible. Con el objetivo de evaluar la seguridad del AGP y determinar el comportamiento del CNG en condiciones relevantes para su almacenamiento definitivo, en el presente trabajo se han planteado cuatro posibles escenarios que podrían provocar la alteración del combustible. Dichos escenarios se han estudiado mediante análogos no irradiados del CNG. En el proceso de alteración de las barreras que componen el AGP, la corrosión anaeróbica de la capsula metálica produce una elevada presión de hidrógeno que podría entrar en contacto con el CNG. A su vez, la entrada de agua en el repositorio y la temperatura a la que se encuentra el CNG podrían hacer aumentar la humedad en las proximidades del residuo. Por lo tanto, en este trabajo se ha estudiado el efecto del vapor de agua en contacto con el UO2 en atmósfera de H2. Los resultados obtenidos muestran que se produce la oxidación del uranio tanto en condiciones anaeróbicas como en condiciones reductoras en función de la temperatura usada. Por otro lado, en presencia de nanopartículas de paladio, análogas a las partículas épsilon del CNG, no se observó oxidación alguna del UO2 en presencia de H2. En el momento en que el agua entre en contacto con el CNG, los RN segregados de la matriz más volátiles y solubles serán lixiviados de forma prácticamente instantánea (IRF) provocando un aumento significativo de radiación en las aguas subterráneas. Con el objetivo de predecir la liberación de dichos RN se ha diseñado un modelo y un algoritmo matemático que ha permitido predecir la liberación de los RN disueltos en la matriz e identificar y cuantificar los RN que forman parte de la IRF de un combustible real. Los resultados obtenidos de la aplicación del modelo concuerdan con resultados experimentales publicados anteriormente. Por lo tanto, se puede concluir que el modelo y el algoritmo cumplen con los objetivos marcados de identificación, predicción y cuantificación de la distribución de los RN en el CNG. Debido a que los mecanismos de alteración del UO2 podrían variar dependiendo de la composición del agua subterránea, se ha estudiado la corrosión del CNG en contacto con aguas de cemento. Para ello se ha usado un electrodo de SIMFUEL con el que se han realizado ciclovoltamogramas, experimentos potenciostáticos y mediciones del potencial de corrosión en condiciones hiperalcalinas y en presencia de calcio y silicato como símil de aguas de cemento. Los resultados muestran una disminución de la corrosión en presencia de calcio y silicato que podría ser provocada por la precipitación de fases sólidas en la superficie del SIMFUEL o por la estabilización de las fases reducidas. Por último, la precipitación de fases sólidas podría ayudar a reducir la concentración de los RN liberados por el CNG. En este contexto, se han estudiado y determinado las capacidades de retención de dos fases sólidas de uranio; la soddiita y la uranofana, en contacto con Cs y Sr en disolución. Se ha determinado que ambos sólidos son capaces de adsorber ambos iones en su superficie, siendo la soddiita el sólido con mayor capacidad de retener Cs y la uranofana la fase sólida con mayor capacidad de retención de Sr. Por tanto, la formación de estas fases podría disminuir la concentración de estos RN liberados a la geosfera.

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Nitschke, Fabian [Verfasser], and T. [Akademischer Betreuer] Kohl. "Numerical and Experimental Characterization of Dissolution and Precipitation Processes in Deep Geothermal Reservoirs / Fabian Nitschke ; Betreuer: T. Kohl." Karlsruhe : KIT-Bibliothek, 2018. http://d-nb.info/1151938637/34.

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Tähtinen, J. (Jaana). "The dissolution process of a business relationship:a case study from tailored software business." Doctoral thesis, University of Oulu, 2001. http://urn.fi/urn:isbn:9514265300.

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Abstract This research aims at developing theory about the dissolution process of business-to-business relationships in tailored software context. Although dissolving business relationships can be viewed as one of the essential themes of marketing, the existing research on dissolution does not provide us with a holistic picture of the dissolution as a process. This research builds an empirically-grounded model of the business relationship dissolution process. First, a theoretical, tentative model of the process of business relationship dissolution is built. Second, empirical knowledge is acquired from a case study of business relationship dissolution in a software context. The case study data has been collected from various sources, from both seller and buyer organisations as well as network actors, through interviews and also from other written and oral sources in order to ensure triangulation. Third, the findings of the case study are compared to the tentative process model and the model is adjusted accordingly, thus developing the empirically-grounded process model. The process model includes three elements: the nature of the relationship, the factors influencing its dissolution, and the dissolution process. It incorporates both the time dimension and the multiplicity of the actors (individuals, companies, other relationships) involved into the model. The nature of the relationship is classified (terminal, continuous, episodic) as are the influencing factors and events (predisposing, precipitating and attenuating). The dissolution process is modelled by using stages, which describe the different action and time periods of the process, and by using levels, which describe the different actors who bring the process about. Six stages are distinguished: the communication stage, consideration stage, disengagement stage, enabling stage, restoration stage, and sensemaking / aftermath stage. The concept of stage is used to divide the complex process into more comprehensible periods and to emphasise that in each stage, managers' actions differ. The dissolution process does not always proceed through all the stages, nor have the stages any particular order.

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Wilson, Tony Keith. "The dissolution of Ag(111) electrodes investigated by in situ scanning tunnelling microscopy." Thesis, University of Warwick, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364612.

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39

Potysz, Anna. "Copper metallurgical slags : mineralogy, bio/weathering processes and metal bioleaching." Thesis, Paris Est, 2015. http://www.theses.fr/2015PESC1201/document.

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Les principaux objectifs étaient d'évaluer la stabilité de l'environnement des scories métallurgiques de Cu résultant de différentes périodes d'activités industrielles et de différentes technologies de fusion. Parmi les scories étudiées, on retrouve: les scories historiques cristallines (SH) ainsi que modernes: les scories de four vertical (SFS), les scories granulées (GS) et les scories de plomb (LS). Les différentes approches adoptées dans ce travail de thèse ont tenu compte de: i) la composition chimique et la phase minérale des scories, ii) la sensibilité à la lixiviation des scories sous l’exposition à différentes conditions de pH en mode statique, iii) l’altération des scories sous exposition aux acides organiques couramment trouvés dans l'environnement du sol, iv ) la bio-altération des scories par les bactéries (Pseudomonas aeruginosa) et v) l’application future de la récupération des métaux provenant des scories étudiées en mettant en œuvre la méthode de lixiviation biologique. Résultats cruciaux: Les résultats des tests de lixiviation dépendant du pH ont montré une libération de métal plus élevée dans des conditions fortement acides (pH 2 et 4), alors que la lixiviation dans des conditions alcalines (pH 10.5) était moins importante pour toutes les scories analysées. L'effet de l’altération par le sol a été démontré, la dissolution des scories est notamment sensible à la présence d'exsudats racinaires artificiels (ARE), d’acides humiques (HA) et d’acides fulviques (FA), la contribution des ARE étant la plus forte. Selon les données recueillies, la dissolution relative des scories est strictement liée à leurs caractéristiques (composition chimique et minéralogique) en fonction des différentes conditions étudiées. L'étude concernant l’effet de l’altération biologique a révélé que Pseudomonas aeruginosa améliore considérablement la libération des éléments majeurs (Si et Fe) et métalliques (Cu, Zn, Pb) par rapport aux effets des facteurs abiotiques, indépendamment de la chimie et de la structure des scories. En outre, une récupération élevée (jusqu'à 90%) des métaux (Cu, Zn, Fe) pourrait être obtenue grâce à la lixiviation avec Acidithiobacillus thiooxidans dans des conditions de laboratoire. Conclusions générales : La stabilité des scories dans l'environnement dépend à la fois des caractéristiques chimiques et de la minéralogie. Cependant, les phases minérales hébergeant les métaux sont les facteurs les plus déterminants concernant l'intensité de la lixiviation des métaux. Pour cette raison, l'examen individuel du comportement des scories est important pour empêcher la contamination de l'environnement et devrait être considéré comme une priorité pour la gestion durable des scories. L’optimisation des paramètres de fonctionnement pour le biolessivage et le développement de la technologie à l'échelle industrielle pourrait permettre une bien meilleure gestion (voir l’exploitation) des scories métallurgiques de Cu
Problem statement: Copper pyrometallurgical slags are inevitable waste by-products of Cu smelting operations. These waste are considered to be important due to their production volume and high residual metal content that are inefficiently recovered during industrial process. Due to the lack of sustainable practices in the past, tremendous volumes of Cu-slags have been disposed in many industrial districts, regardless of the weathering and associated environmental risk. Consequently, there are many areas where slags have been proven to be a source of metallic pollution for the surrounding environment. At the present time, the outstanding contradiction between the sustainable development and environmental pollution encourages to undertake the action regarding this aspect. For this reason, slags are currently being used as supplementary materials for civil engineering purposes (e.g. cement and concrete additives, road bed filling materials, hydraulic construction materials) rather than disposed. Additionally, modern-day management strategies require slags to be thoroughly evaluated with respect to their environmental stability prior undertaking any reuse action. Main objectives were to evaluate environmental stability of Cu-metallurgical slags resulting from different periods of industrial activities and different smelting technologies. Those included: historical crystalline slag (HS) as well as modern: shaft furnace slag (SFS), granulated slag (GS) and lead slag (LS). Different approaches undertaken in this PhD work considered: i) chemical and mineral phase compositions of slags, ii) leaching susceptibility of slags under exposure to different pH-stat conditions, iii) slags weathering under exposure to organic acids commonly found in soil environment, iv) bacterially (Pseudomonas aeruginosa) mediated weathering of slags and v) future application of studied slags for metal recovery by implementing the bioleaching method. Crucial results: The results of the pH-dependent leaching tests showed a higher metal release in strong acidic conditions (pH 2 and 4), whereas leachability at alkaline conditions (pH 10.5) revealed a lower importance for all the slags analyzed. The study considering soil weathering scenario demonstrated that Cu-slags are susceptible to dissolution in the presence of artificial root exudates (ARE), humic (HA) and fulvic acids (FA), whereby ARE were found to have stronger contribution than HA and FA. According to data collected, the different behavior of individual slags is strictly related to their characteristics (chemical and phase composition) reflecting various susceptibilities to dissolution under the investigated conditions. The study considering bio-weathering scenario revealed that Pseudomonas aeruginosa considerably enhances the release of major (Si and Fe) and metallic (Cu, Zn, Pb) elements compared to the effects of abiotic factors, regardless of the slags chemistry and structure. Furthermore, a high gain (up to 90%) of metals (Cu, Zn, Fe) could be credited to bioleaching with Acidithiobacillus thiooxidans under laboratory conditions. General conclusions: The environmental stability of slags depends on both, their bulk chemistry and mineralogy. However, mineral phases harbouring the metals are the key players in metal leachability intensity. For, this reason consideration of individual slags behaviour is important for preventing environmental contamination and should be regarded as priority branch of sustainable slag management. Optimization of operating parameters for bioleaching following development of industrial scale technology is an incentive scheme for future management of Cu-metallurgical slags

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Hupfer, Sarah [Verfasser], Andreas [Akademischer Betreuer] Weller, and S. [Akademischer Betreuer] Kruschwitz. "Spectral induced polarisation for an enhanced pore-space characterisation and analysis of dissolution processes of carbonate rocks / Sarah Hupfer ; Andreas Weller, S. Kruschwitz." Clausthal-Zellerfeld : TU Clausthal, 2020. http://d-nb.info/1231362642/34.

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Damian, Alexis. "In situ STM study of the growth and dissolution processes on bimetallic Pd/Au(111) substrates and of ultrathin alloy layers on Au(111)." Phd thesis, Ecole Polytechnique X, 2009. http://pastel.archives-ouvertes.fr/pastel-00005915.

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Villinski, John Eugene. "Reductive dissolution of manganese (IV) oxides and precipitation of iron (III) : implications for redox processes in an alluvial aquifer affected by acid mine drainage." Diss., The University of Arizona, 2001. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_2001_96_sip1_w.pdf&type=application/pdf.

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CRISAFULLI, RUDY. "Preparação de eletrocatalisadores PtSnCu/C e PtSn/C e ativação por processos de Dealloying para aplicação na oxidação eletroquímica do Etanol." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10183.

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Made available in DSpace on 2014-10-09T12:35:43Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:03:54Z (GMT). No. of bitstreams: 0
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Calapa, Kayla. "Hydrologic alteration and enhanced microbial reductive dissolution of Fe(III) (hydr)oxides under flow conditions in Fe(III)-rich rocks: contribution to cave-forming processes." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1619628782604003.

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Mokni, Nadia. "Deformation and flow driven by osmotic processes in porous materials." Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/6279.

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En el caso del almacenamiento de los residuos radioactivos los flujos osmóticos pueden ser relevantes y requieren un análisis en detalle. El residuo nuclear bituminizado (BW) será almacenado mediante contenedores en cavidades excavadas en la Boom Clay, que es una arcilla marina que presenta propiedades favorables para limitar y retrasar la migración de los contaminantes radioactivos. La interacción entre los dos materiales es un proceso acoplado químico-hidro-mecánico y depende de la respuesta hidromecánica de la Boom Clay y del BW. En condiciones de almacenamiento, el contacto del BW, que contienen cantidades importantes de NaNO3, con el agua subterránea induce la hidratación por gradientes osmóticos y el consiguiente hinchamiento, además de la difusión de la sal disuelta hacia la Boom Clay. Se pueden distinguir dos tipos de afecciones: la perturbación geomecánica causada por el hinchamiento del BW y el aumento de presión en el BW y cambio de las distribución de tensiones en la roca, y la perturbación físico química por la migración de grandes cantidades de sales. El objetivo de esta tesis es: (i) Mejorar la comprensión de los procesos que controlan la absorción de agua y el consecuente hinchamiento del BW que contengan sales (NaNO3), y (ii) Investigar los posibles efectos de la concentración de fluidos de los poros sobre el hinchamiento, la compresibilidad y comportamiento de corte de la Boom Clay. En primer lugar, se ha desarrollado una formulación para el análisis de la deformación inducida por la disolución de sales en medio poroso con contacto con agua. Las ecuaciones planteadas incluyen los flujos acoplados de agua y soluto. Se presenta también un trabajo teórico que ayuda a la comprensión del comportamiento mecánico del BW. Se considera este material como una mezcla de bitumen y cristales de NaNO3. Se ha desarrollado un modelo elasto-viscoplástico que describe el comportamiento de fluencia del BW considerando el comportamiento de fluencia de sus constituyentes. El modelo constitutivo elasto-viscoplástico ha sido implementado en el programa CODE_BRIGHT. Los resultados se han comparado con observaciones experimentales. Se ha estudiado el comportamiento a largo plazo del BW en contacto con agua al simular ensayos de hinchamiento por absorción de agua bajo condiciones confinadas. El análisis numérico ha demostrado ser capaz de proporcionar una representación satisfactoria de los principales patrones observados en su comportamiento. En lo que respecta al segundo objetivo de la tesis, se ha propuesto una formulación para el análisis de las deformaciones inducidas por procesos osmóticos en un medio poroso de doble estructura. Esta formulación distingue dentro del material un nivel micro-estructural y otro macro-estructural con cambios químicos que tienen un efecto significativo en la micro-estructura. Se han obtenido las ecuaciones básicas que describen los flujos acoplados de agua y solutos y el transporte de sus componentes a través de los macroporos así como las ecuaciones de balance de masa para agua y soluto en los macroporos y microporos. La formulación propuesta ha sido aplicada particularmente para analizar cualitativamente el efecto de la succión osmótica sobre el hinchamiento de los suelos arcillosos. Se han analizado los efectos a corto y largo plazo. Se ha investigado también la influencia del aumento de la concentración del fluido en los poros sobre las propiedades geotécnicas y el comportamiento de la Boom Clay no saturada. Se ha llevado a cabo un programa sistemático de investigación experimental, con control de succión osmótica y matricial, con el fin de investigar el efecto del incremento de la concentración del fluido de poros sobre la resistencia de corte y el cambio volumétrico bajo condiciones edométricas. Se ha observado, que bajo condiciones parcialmente saturadas, un cambio en la salinidad provoca una disminución en la compresibilidad y en la resistencia de corte del material.
For deep storage of high-level nuclear waste osmotic flows can be significant and so require a careful analysis. In Belgium, The bituminized nuclear waste (BW) named Eurobitum contained in metallic drums will be placed inside a tunnel or a shaft excavated in the Boom Clay, which is 100 m thick marine clay presenting favourable properties to limit and delay the migration of the leached radionuclides over extended periods of time. In Geological disposal conditions, contact of the bituminized radioactive waste which contains high amounts of highly soluble salt (NaNO3) with groundwater will result in water uptake and swelling of the waste and in subsequent diffusion of the dissolved salt through the host clay formation. Basically, two types of disturbance can be distinguished: A geo-mechanical perturbation, caused by the swelling of the waste and the increase of the pressure in and around the waste and a physico-chemical perturbation by the release of large amounts of NaNO3 and other soluble salts. In this context the aim of this thesis is: (i) to improve the understanding of the processes controlling the water uptake and the subsequent swelling of bituminized waste containing soluble salts (NaNO3), and (ii) to investigate of the possible effects of the increase of pore fluid concentration on swelling, compressibility and shear behaviour of Boom Clay. A formulation has been proposed for the analysis of deformation induced by dissolution of salts in porous media in contact with water. The equations include the effect of coupled transport phenomena and the formulation has been included as an extension in the coupled THM program CODE_BRIGHT. A theoretical and experimental work aiming at understanding the mechanical behaviour of the Bituminized Waste has been presented.This material is considered for this purpose as a mixture of bitumen and crystals of NaNO3. An elasto-viscoplastic model has been developed that describes the creep behaviour of BW considering the constituents' creep behaviour. The elasto-viscoplastic constitutive model has been implemented into CODE_BRIGHT. The modelling results have been compared with the experimental data. The impact of osmotic forces on the swelling of the material has been investigated by simulating water uptake swelling tests under confined conditions and comparing the predictions with experimental results. The numerical analysis has proven to be able to furnish a satisfactory representation of the main observed patterns of the behaviour. In regard to the second objective of this thesis, a formulation has been proposed for the analysis of deformations induced by osmotic processes in double structure porous media. The formulation is based on the distinction within the material of a microstructural and a macrostructural levels with chemical changes having a significant effect on the microstructure. A macroscopic description of the system is provided. Then the basic equations describing coupled flows of water and solutes and the transport of its components through macropores and mass balance equations for water and solute in macro and micro pores have been obtained. The proposed formulation has been particularly applied to analyze qualitatively the effect of osmotic suction on swelling of clayey soils. Transient and long term effects have been analyzed. The influence of pore fluid concentration on the geotechnical properties and behavior of Boom Clay under partially saturated conditions has been investigated. A systematic experimental research program involving osmotic suction and matric suction controlled experiments has been carried to investigate the effect of the increase of pore fluid concentration on shear strength and on the volume change behaviour under odometer stress state conditions. It has been observed that under partially saturated conditions a change in salinity causes a decrease in compressibility and shear strength.

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Ramstedt, Madeleine. "Chemical Processes at the Water-Manganite (γ-MnOOH) Interface." Doctoral thesis, Umeå universitet, Kemi, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-253.

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The chemistry of mineral surfaces is of great importance in many different areas including natural processes occurring in oceans, rivers, lakes and soils. Manganese (hydr)oxides are one important group to these natural processes, and the thermodynamically most stable trivalent manganese (hydr)oxide, manganit (γ-MnOOH), is studied in this thesis. This thesis summarises six papers in which the surface chemistry of synthetic manganite has been investigated with respect to surface acid-base properties, dissolution, and adsorption of Cd(II) and the herbicide N-(phosphonomethyl)glycine (glyphosate, PMG). In these papers, a wide range of analysis techniques were used, including X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) spectroscopy, Fourier transform infra-red (FTIR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), potentiometry, electrophoretic mobility measurements and wet chemical techniques, in order to obtain a more complete understanding of the different processes occurring at the manganite-water interface. From the combined use of these techniques, a 1-pKa acid-base model was established that is valid at pH>6. The model includes a Na+ interaction with the surface: =MnOH2+½ --> =MnOH-½ + H+ log β0 (intr.) = -8.20 = -pHiep =MnOH2+½ + Na+ --> =MnOHNa+½ + H+ log β0 (intr.) = -9.64 At pH<6 the manganite crystals dissolve and disproportionate into pyrolusite (β-MnO2) and Mn(II)-ions in solution according to: 2 γ-MnOOH + 2H+ --> β-MnO2 + Mn2+ + 2H2O log K0 = 7.61 ± 0.10 The adsorption and co-adsorption of Cd(II) and glyphosate at the manganite surface was studied at pH>6. Cd(II) adsorption displays an adsorption edge at pH~8.5. Glyphosate adsorbs over the entire pH range, but the adsorption decreases with increasing pH. When the two substances are co-adsorbed, the adsorption of Cd(II) is increased at low pH but decreased at high pH. The adsorption of glyphosate is increased in the entire pH range in the presence of Cd(II). From XPS, FTIR and EXAFS it was found that glyphosate and Cd(II) form inner sphere complexes. The binary Cd(II)-surface complex is bonded by edge sharing of Mn and Cd octahedra on the (010) plane of manganite. Glyphosate forms inner-sphere complexes through an interaction between the phosphonate group and the manganite surface. The largest fraction of this binary glyphosate complex is protonated throughout the pH range. A ternary surface complex is also present, and its structure is explained as type B ternary surface complex (surface-glyphosate-Cd(II)). The chelating rings between the Cd(II) and glyphosate, found in aqueous complexes, are maintained at the surface, and the ternary complex is bound to the surface through the phosphonate group of the ligand.

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Martins, Inês da Costa. "Desenvolvimento dos relacionamentos entre as agências e os seus clientes." Master's thesis, Instituto Superior de Economia e Gestão, 2017. http://hdl.handle.net/10400.5/15635.

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Mestrado em Marketing
O crescimento da indústria da publicidade tem sido acompanhado por um igual desenvolvimento da sua complexidade, resultando numa crescente tensão nas relações entre agência e cliente. Neste sentido o estudo pretende compreender o desenvolvimento dos relacionamentos entre as agências de publicidade e os seus clientes, nomeadamente os critérios de seleção de uma agência, os processos de interação, troca, adaptação e coordenação. Pretende também averiguar quais os fatores que levam à continuidade e/ou dissolução dos relacionamentos. Foi estudado o modelo de Håkansson et al. (1982), Möller & Wilson (1988) e Baptista (2013) por forma a criar um modelo conceptual de desenvolvimento dos relacionamentos entre agência e cliente. O estudo seguiu uma metodologia qualitativa, e a recolha de dados foi executada através de recurso a entrevistas em profundidade semi-estruturadas junto de uma amostra, não-probabilística, por conveniência. Através dos resultados identificou-se que a troca de informação é feita por ambas as partes, independentemente do relacionamento; que os processos de adaptação são mais evidentes quando existe um relacionamento forte; que dependendo do relacionamento será mais provável a adaptação de novos serviços por parte da agência; para um relacionamento ser duradouro é crucial que exista confiança e que nenhuma das partes se acomode, que exista qualidade e abrangência do serviço e capacidade de dar respostas criativas e inovadoras; e que a insatisfação com o desempenho da agência e os fatores pessoais continuam a ser uma das principais razões para a mudança de agência.
The growth of the advertising industry has been accompanied by an equal development of its complexity, resulting in increasing stress in agency-client relationships. In this sense, the objective of this study is to understand the development of relationships between advertising agencies and their clients, the criteria for selecting an agency, the processes of interaction, exchange, adaptation and coordination. It also investigates which factors lead to the continuity and / or dissolution of relationships. The model of Håkansson et al. (1982), Möller & Wilson (1988) and Baptista (2013) was used in order to create a conceptual model for the development of agency-client relationships. The study followed a qualitative methodology, and data collection was executed using semi-structured in-depth interviews with a non-probabilistic sample, for convenience. The results show that the exchange of information is made by both parts, independently of the relationship; adaptation processes are more evident when there is a strong relationship; depending on the relationship, the adaptation of new services by the agency is the most likely scenario; for a relationship to be long-lasting, it is crucial that there is trust and that neither party settles down, that the service has good quality and scope and that there is an ability to respond creatively and innovatively; and that the dissatisfaction with the performance of the agency and personal factors remain the main reasons for the change of agency.
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Castro, Pollyana Souza. "Desenvolvimento de microssensores eletroquímicos e aplicações no estudo de processos dinâmicos interfaciais utilizando microscopia eletroquímica de varredura." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/46/46136/tde-06042016-145742/.

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O trabalho descrito nesta tese mostra de forma detalhada a fabricação e caracterização de diferentes microssensores eletroquímicos os quais têm sido recentemente utilizados como sondas em grupo de técnicas conhecida como Scanning Electrochemical Probe Microscopy (SEPM). Desta forma, a caracterização de superfícies pode ser feita explorando diferentes fenômenos interfaciais relevantes à Ciência. Neste sentido, as interfaces de materiais cristalinos como hidroxiapatita (materiais dentários) e calcita foram o foco de estudo neste trabalho. Assim, diferentes técnicas SEPM foram exploradas no sentido de se obter informações relevantes relacionadas aos processos dentários, como a erosão ácida e hipersensibilidade. Inicialmente, microeletrodos de platina foram desenvolvidos empregando uma metodologia convencional na qual são utilizados microfibras encapsuladas em capilares de vidro. Scanning Electrochemical Microscopy (SECM) no modo amperométrico foi utilizada para obtenção de informações com relação às alterações de topografia do esmalte dentário causadas pelo contato com substâncias ácidas. Adicionalmente, SECM foi empregada no estudo do transporte de espécies eletroativas em amostras de dentina e investigações relacionadas ao bloqueio dos túbulos empregando-se cremes dentais comerciais foram realizadas. A permeação de peróxido de hidrogênio pela dentina também foi estudada. Os resultados de SECM foram comparados com imagens SEM obtidas nas mesmas condições experimentais. Microeletrodos de membrana ionófora íon-seletiva (Ion Selective Microelectrodes-ISMEs) sensíveis a íons cálcio também foram desenvolvidos e caracterizados, com subsequente aplicação em SECM no modo potenciométrico. A dissolução ácida de esmalte bovino (erosão dentária) foi investigada em diferentes valores de pH (2,5; 4,5; 6,8). Além disso, o transporte de íons cálcio através de membranas porosas sintéticas foi avaliado a uma distância tip/substrato de 300µm. Alterações no fluxo de íons cálcio foram correlacionadas em experimentos realizados na presença e ausência de campos magnéticos gerados por nanopartículas de magnetita incorporadas à membrana porosa. Microcristais de calcita facilmente sintetizados pelo método de precipitação foram utilizados como superfície modelo para investigações interfaciais, cujos resultados podem ser correlacionados aos materiais dentários. Desta forma, nanopipetas de vidro preenchidas com eletrólito suporte foram fabricadas e utilizadas como sonda em Scanning Ion Conductance Microscopy (SICM). O mapeamento topográfico de alta resolução espacial da superfície de um microcristal de calcita foi obtido utilizando o modo de varredura hopping mode. Adicionalmente, sondas multifuncionais ISME-SICM também foram desenvolvidas e caracterizadas para investigações simultâneas com relação às alterações topográficas e quantificação de íons cálcio sobre a superfície de um microcristal de calcita. A adição de reagentes ácidos no canal SICM promoveu a dissolução da superfície do microcristal, sendo obtidos dados cinéticos de dissolução. Investigações em meio neutro também foram realizadas utilizando a sonda ISME-SICM. Os resultados experimentais obtidos também foram comparados com aqueles oriundos de simulação computacional.
The study reported in this thesis shows in details the fabrication and characterization of different electrochemical microsensors which have been employed as probes in SEPM. Thus, the characterization of surfaces can be performed by exploiting different interfacial phenomena that are relevant to life sciences. In this sense, the interfaces of crystalline materials such as hydroxyapatite (dental materials) and calcite were the focus of this study. Thus, different SEPM techniques were explored in order to obtain relevant information related to dental materials processes such as acid erosion and hypersensitivity. Initially, platinum microelectrodes were developed employing conventional methodology that utilizes microfibers encapsulated in glass capillaries. Amperometric SECM mode was used to obtain information regarding the topography changes of tooth enamel caused by contact with acid chemicals. In addition, SECM was used to study the transport of electroactive species in dentin samples. Investigations related to the treatment of dental hypersensitivity and dental whitening were also evaluated. SECM results were compared with SEM images obtained under the same experimental conditions. Ion-selective microelectrode (ISME) based on the ionophore membrane sensitive to calcium ions were also developed and characterized followed by application in SECM potentiometric mode. The acid dissolution of bovine enamel (dental erosion) was investigated at different pH values (2.5; 4.5; 6.8). In addition, the transport of calcium ions through synthetic porous membranes was evaluated at a tip/substrate distance of 300µm. Changes in calcium ion flux were studied in the presence and absence of magnetic fields generated by magnetite nanoparticles incorporated into the porous membrane. Calcite microcrystals easily synthesized by precipitation method were used as a model of an interfacial surface for investigations which can be correlated to the dental materials. Thus, glass nanopipette filled with supporting electrolyte was fabricated and used as SICM probe. The high resolution topographic mapping of the calcite microcrystal was obtained using hopping mode. Additionally, ISME-SICM multifunction probes were developed and characterized for simultaneous investigations related to the topographical changes and quantification of local calcium ions on the surface of a calcite microcrystal. The addition of acidic reagents in the SICM channel promoted the dissolution of the microcrystal surface and dissolution kinetic data were obtained. Investigations in neutral medium were also studied using the ISME-SICM multifunctional probe. The experimental results were also compared with those obtained by computer simulation.

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Serris, Eric. "Influence des conditions de compression sur les propriétés physico-chimiques des comprimés issus de poudres organiques." Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 2002. http://tel.archives-ouvertes.fr/tel-00089185.

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La compression des poudres est un procédé largement répandu et concerne, par exemple, 60% de la production de l'industrie pharmaceutique. Malgré cette importance, les connaissances scientifiques sur cette opération restent encore partiellement empiriques. Nous avons donc tenté au cours de cette thèse d'approfondir la connaissance des phénomènes qui se déroulent lors de la compression. L'objectif de ce travail était d'étudier l'influence des paramètres du procédé sur les propriétés d'usage des comprimé, pour modéliser les phénomènes, et dégager les conditions optimum de fabrication.
Dans un premier temps, nous avons caractérisé tous les phénomènes (réarrangement granulaire, fragmentation, déformations plastiques et visqueuses) qui se déroulent lors du cycle de compression grâce à l'étude de l'émission acoustique produite lors de la compression. L'étude des trois poudres différentes utilisées dans ce travail (aspirine, amidon et produit A) a donné des résultats montrant que la fragmentation et réarrangement granulaire initial sont es responsables majeurs de l'émission acoustique en cours de compression.
L'étude du cycle de compression a été menée pour dégager l'influence de chaque partie du cycle (montée en pression, palier isobare, descente en pression et temps avant démoulage) sur les propriétés (la porosité relaxée et la résistance à la rupture) des comprimés de produits purs, ou de mélanges. De plus, cette étude nous a permis d'améliorer les modèles existants avec notamment une modélisation de l'évolution de la porosité lors du palier isobare ainsi qu'une modélisation géométrique de l'élasticité.
Pour finir une étude de la dissolution des comprimés de mélanges aspirines / amidons a été menée. Comme l'aspirine comprimée seule se dissout lentement, il faut lui adjoindre un délitant comme l'amidon de maïs. Nous avons vérifié que le principal paramètre qui joue sur la vitesse de dissolution des comprimés de mélanges est la fraction massique en amidon. Un modèle de prévision du délitement des comprimés utilisant l'analyse d'image permet de prévoir la taille initiale des fragments d'aspirine en contact avec l'eau et donc de mener à bien une étude cinétique.

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Hauck, Judith [Verfasser], Dieter [Akademischer Betreuer] Wolf-Gladrow, and Birgit [Akademischer Betreuer] Schneider. "Processes in the Southern Ocean carbon cycle: Dissolution of carbonate sediments and inter-annual variability of carbon fluxes / Judith Hauck. Gutachter: Dieter Wolf-Gladrow ; Birgit Schneider. Betreuer: Dieter Wolf-Gladrow." Bremen : Staats- und Universitätsbibliothek Bremen, 2012. http://d-nb.info/1071993844/34.

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Dissertations / Theses on the topic 'Processus de dissolution'

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