D. Tech. Chemical, Metallurgical and Materials Engineering / This study provides experimental data and new perspectives on selective precipitation of platinum group metals (PGMs) in the presence of base metals while at the same time reviewing the mass transfer characteristics and models associated with metal sulphides precipitation in liquid-liquid and gas-liquid systems. In this study, the objective was to investigate and validate the concept of selective precipitation of platinum from chloride media using sulphur-bearing liquids or gases.

Lorsque des champs électriques sont appliqués à des mélanges eau-huile, les petites gouttelettes d'eau sont attirées entre elles et se regroupent en gouttes plus grosses. Ce processus d’électrocoalescence rend plus efficace la séparation huile-eau par sédimentation.Des données expérimentales sur l’électrocoalescence de très petites gouttelettes sont nécessaires pour améliorer la compréhension de la dynamique de l'interface eau-huile et pour valider les modèles numériques. La configuration simple étudiée dans ce travail de thèse concerne une petite paire de gouttelettes tombant dans une cuve d'huile modèle et soumise à un champ électrique aligné avec l’axe de symétrie des gouttes et la gravité.La première partie du travail a consisté à générer de façon contrôlée d’une paire de très petites gouttelettes (dans la gamme de diamètres 20-200 microns) alignée avec le champ électrique. La génération de goutte à la demande, par méthode éléctrohydrodynamique (EHD) a été améliorée pour un meilleur contrôle du diamètre et de la charge électrique des gouttelettes injectées à partir d'une aiguille métallique unique. Ceci a été obtenu en appliquant à un ménisque d'eau pendant à l’extrémité de l’aiguille des impulsions électriques de forme optimisée.La caractérisation électrique et hydrodynamique des paires de gouttelettes et leur coalescence sont alors principalement déduites de l'analyse des vitesses de chute, avec et sans application d’un champ électrique à courant continu. Des données complètes de positions des gouttelettes et de leur vitesse en fonction du temps sont déduites de prises de vues vidéo. Une attention particulière a été accordée aux visualisations de très petites gouttelettes tombant à petites vitesses, associant des angles multiples de prise de vue, de forts zooms et des vidéos à grande vitesse.La modélisation des différents termes d'interactions hydrodynamiques et électrostatiques entre les gouttelettes permet de déduire des vitesses enregistrées leur masse charge électrique respectives. Quand se produit une coalescence des deux gouttelettes, un enregistrement de la vitesse de la gouttelette résultante, avec et sans tension électrique appliquée, permet de contrôler la conservation de la masse et de la charge électrique, et la validation du procédé.Un premier ensemble de données est constitué d'environ 70 cas différents, avec différentes paire des gouttelettes (dans une plage de diamètre limitée de façon à ce que les vitesses de chute soient comprises entre 0,1 et 0,3 mm/s) et en faisant varier la tension appliquée à courant continu ou alternatif. L'analyse des résultats et des incertitudes expérimentales et un exemple de comparaison possible avec des simulations numériques utilisant le logiciel Comsol Multiphysics ™, permettent d'effectuer des recommandations pour les travaux futurs.Ce travail a été financé par le projet “Fundamental understanding of electrocoalescence in heavy crude oils”; coordonné par SINTEF Energy Research. Le projet a été soutenu par The Research Council of Norway, dans le cadre du contrat n °: 206976 / E30, et par les partenaires industriels suivants: Wärtsilä Oil & Gas Systems AS, Petrobras et Statoil ASA. / When electric fields are applied in oil-water mixtures small water droplets are attracted to others and merge in larger drops. This electrocoalescence process makes more efficient the oil-water separation by sedimentation.Experimental data on the electrocoalescence of very small droplets will be useful to improve the understanding of the dynamics of water-oil interface and to validate numerical models. The simple configuration studied consists in a small droplet pair falling in stagnant model oil, under electric field aligned with the symmetry axis of the droplet pair and the direction of gravity.First part of the work consisted in the well-controlled generation of very small droplet pair (range 20-200 microns) aligned with electric field. Droplet-on-Demand generation by EHD method was improved for a better control of the diameter and electric charge of droplets injected from a single metallic needle. This was obtained by applying to a pendant water meniscus optimized multistage high voltage electric pulses.Electrical and hydrodynamic characterization of the droplet pairs and their coalescence are then mainly deduced from the analysis of falling velocities, with and without applied DC electric field. A complete data set of droplet position and velocity is deduced from video. A special attention was paid to the visualizations of very small droplet and small falling velocities, involving multiple angle of view, strong zooming and high speed video.Modelling the different terms of hydrodynamic and electrostatic interactions between droplets allows deducing from the recorded velocities their respective mass and electric charge. When coalescence occurs, a record of the resulting single droplet velocity, with and without applied voltage, allows controlling the mass and charge conservations and validating the method.A first data set was constituted of about 70 different cases, with varying droplets pair (with a limited diameter range to remain with falling velocities between 0.1 and 0.3 mm/s) and varying applied DC or AC voltage. Analyses of the results and experimental uncertainties, and example of possible comparison with numerical simulations using Comsol Multiphysics™ software, allow performing some recommendations for future work.This work was funded by the project “Fundamental understanding of electrocoalescence in heavy crude oils”; co-ordinated by SINTEF Energy Research. The project was supported by The Research Council of Norway, under the contract no: 206976/E30, and by the following industrial partners: Wärtsilä Oil & Gas Systems AS, Petrobras and Statoil ASA.

abstract: Ionic liquids (ILs), or low-temperature liquid salts, are a class of materials with unique and useful properties. Made up entirely of ions, ILs are remarkably tunable and diverse as cations and anions can be mixed and matched to yield desired properties. Because of this, IL/water systems range widely—from homogeneous mixtures to multiphasic systems featuring ionic liquid/liquid interfaces. Even more diversity is added when particles are introduced to these systems, as hard particles or soft-matter microgels interact with both ILs and water in complex ways. This work examines both miscible ionic liquid/water mixture and two-phase, immiscible ionic liquid/water systems. Extensive molecular dynamics (MD) simulations are utilized in conjunction with physical measurements to inform theoretical understanding of the nature of these systems, and this theoretical understanding is related to practical applications—in particular, the development of a low-temperature liquid electrolyte for use in molecular electronic transducer (MET) seismometers, and particle self-assembly and transport at ionic liquid/liquid interfaces such as those in Pickering emulsions. The homogenous mixture of 1-butyl-3-methylimidazolium iodide and water is examined extensively through MD as well as physical characterization of properties. Molecular ordering within the liquid mixture is related to macroscopic properties. These mixtures are then used as the basis of an electrolyte with unusual characteristics, specifically a wide liquid temperature range with an extremely low lower bound combined with relatively low viscosity allowing excellent performance in the MET sensor. Electrolyte performance is further improved by the addition of fullerene nanoparticles, which dramatically increase device sensitivity. The reasons behind this effect are explored by testing the effect of graphene surface size and through MD simulations of fullerene and a silica nanoparticle (for contrast) in [BMIM][I]/water mixtures. Immiscible ionic liquid/water systems are explored through MD studies of particles at IL/water interfaces. By increasing the concentration of hydrophobic nanoparticles at the IL/water interface, one study discovers the formation of a commingled IL/water/particle pseudo-phase, and relates this discovery to previously-observed unique behaviors of these interfaces, particularly spontaneous particle transport across the interface. The other study demonstrates that IL hydrophobicity can influence the deformation of thermo-responsive soft particles at the liquid/liquid interface. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2016

No description available.

<p dir="ltr">A major goal of applied electrocatalysis research has been the development of electrode materials that are active, selective, stable, and cost effective in producing electricity or desired products. In recent years, developments in <i>ab initio</i> methods for the simulation of catalyst surfaces, and electrochemical reactions occurring on them, have enabled the development of a fundamental understanding of the processes occurring at the solid-liquid interface at an atomistic scale. In combination with experiments, these calculations are helpful in elucidating design principles that can then inform electrocatalyst design. In this work, we describe the application of density functional theory, <i>ab initio</i> molecular dynamics, and high throughput materials informatics approaches to understand oxygen and carbon based electrochemistries, with relevance to electricity conversion and environmental protection. We also introduce an approach, based on a Born-Haber cycle analysis, to quantify adsorbate stabilization from solvent molecules that are ubiquitous for any electrochemical reaction occurring at solid-liquid interfaces.</p><p dir="ltr">The oxygen reduction reaction (ORR) occurs at the cathode in hydrogen fuel cells and, in conjunction with the hydrogen oxidation reaction (HOR) at the anode, produces electricity and water. While platinum group metals are the current state-of-the-art catalysts for the ORR, their high cost has necessitated an extensive search for alternatives. To this end, we investigated iron-nitrogen-carbon (Fe-N-C) catalysts, which are platinum group metal-free and have been shown experimentally to have reasonable activity compared to platinum. Despite their potential as cost effective materials, however, these catalysts are not durable over long-term operation of fuel cells, impeding their commercial adoption. The mechanisms of deactivation of the iron-nitrogen-carbon catalysts under aqueous acidic electrochemical reaction conditions remain debated, and deciphering them is complicated due to the complex structure of the catalyst. We attempt to address these challenges by first examining the structural aspects of the catalyst, sampling numerous potential active site configurations, determining their in-situ structure, and linking them to intrinsic activity and intrinsic stability descriptors. Our findings reveal that an activity-stability tradeoff exists, with the most active sites being most prone to stability issues. Additionally, we explored the role of hydrogen peroxide, a side product of ORR, in degrading Fe-N-C catalysts. This analysis demonstrated that hydrogen peroxide strongly oxidizes the catalyst surface, resulting in an activity loss in the catalyst. Based on these insights, we propose design principles to enhance the activity and stability of Fe-N-C catalysts.</p><p dir="ltr">In additional work, we compared the predictions for the Fe-N-C catalysts with ORR analysis on platinum catalysts, and we further analyzed the oxygen evolution reaction (OER) on iridium oxides and the carbon dioxide reduction reaction (CO₂R) on copper catalysts in water electrolyzers. For ORR on platinum, we identified the formation of hydroxyl and water adsorbate rings on stepped surfaces, akin to hexagonal rings found on terraces but largely absent on Fe-N-C catalysts. The ORR follows an associative mechanism involving proton coupled electron transfer to these ring structures. Furthermore, we provided activity descriptors that aligned with experimental observations, showing a higher activity on stepped surfaces compared to terraces. For OER on iridium oxides, we examined transformations of IrO₂ (110) surfaces, and we pinpointed oxidation of bridge and coordinatively unsaturated top sites as key charge transfer steps that correlate with peaks in cyclic voltammograms. Finally, for CO₂R on copper, we investigated the role of water as a proton source under neutral or alkaline conditions, providing insights into the effect of coverages of surface species on the kinetics of water dissociation that, in turn, can provide protons for CO₂ reduction and the competing hydrogen evolution reaction.</p><p dir="ltr">Through this work, we have gained a deeper understanding of the properties of various catalytic materials under conditions specific to each type of electrochemistry. We elucidated the relationships between the in-situ structure, activity, and stability for the electrocatalysts, and identified key factors influencing catalyst performance. Integrating such insights from a computational perspective with experimental approaches holds great potential in making significant advancements in developing sustainable energy technologies and ultimately contributing to a greener and more energy-efficient future.</p>

Ce manuscrit se concentre sur l’étude de la dynamique de drainage de gouttes d’eau dans une phase continue d’huile de paraffine. Les gouttes sont de taille millimétrique, déformables et évoluent dans un domaine de simulation carré de 1 cm de coté. La simulation du comportement de tels systèmes pose le problème général de la description numérique des écoulements multiphasiques non stationnaires. Un modèle simplifié dans une géométrie à deux dimensions est proposé et simulé en volumes finis. Il inclut les propriétés physico-chimiques des interfaces et notamment les phénomènes de coalescence et l’évolution d’un tensioactif soluble dans les gouttes. L’effet des conditions aux limites sur le drainage d’une unique goutte est étudié. Le rôle de la coalescence sur ce drainage est également décrit pour un modèle de deux gouttes. Quelques simulations sont enfin proposées avec des systèmes dispersés plus complexes. / This manuscript focuses on the description of the settling dynamics of water droplets in a continuous phase of paraffin oil. Droplets are of millimetre size, deformable and evolve in a square simulation domain of 1 cm side. The simulations of the behaviour of such systems raise the general problem of the numerical description of the flows occurring in multiphase unsteady systems. A simplified model in a two dimensional geometry is used and integrated with a finite volume numerical technique. It includes the interfacial mechanical and chemical properties and in particular the coalescence phenomena and the evolution of a water soluble surfactant. The effect of the boundary conditions on the drainage of a unique droplet is studied. The role of drop-drop coalescence on this drainage is also described for a model with two droplets. Some simulations are finally proposed with more complex dispersed systems.

The classical theory of colloids and surface science has universally been applied in modeling and calculations involving solid-liquid interfaces encountered in natural and engineered environments. However, several discrepancies between the observed behavior of charged solid-liquid interfaces and predictions by classical theory have been reported in the past decades. The hypothesis that the mean-field, pseudo-one-component approximation adopted within the framework of the classical theory is responsible for the differences observed is tested in this work via the application of modeling and experimental techniques at a molecular level. Silica and silicon nitride are selected as model charged solid surfaces, and mixtures of symmetric and asymmetric indifferent and non-indifferent electrolytes are used as liquid phases. Canonical Monte Carlo simulations (CMC) of the electrical double layer (EDL) structure of a discretely charged planar silica surface, embedded in solutions of indifferent electrolytes, reveal the presence of a size exclusion effect that is enhanced at larger values of surface charge densities. That effect translates into an unexpected behavior of the interaction forces between a charged planar surface and a spherical particle. CMC simulations of the electrostatic interactions and calculations of the EDL force between a spherical particle and a planar surface, similarly charged, reveal the presence of two attractive force components: a depletion effect almost at contact and a long-range attractive force of electrostatic origin due to ion-ion correlation effects. Those two-force components result from the consideration of discreteness of charge in the interaction of solid-liquid interfaces, and they contradict the classical theory predictions of electrostatic repulsive interaction between similarly charged surfaces. Direct interaction force measurements between a charged planar surface and a colloidal particle, performed by atomic force microscopy (AFM), reveal that, when indifferent and non-indifferent electrolytes are present in solution, surface charge modification occurs in addition to the effects on the EDL behavior reported for indifferent electrolytes. Non-uniformity and even heterogeneity of surface charge are detected due to the action of non-indifferent, asymmetric electrolytes. The phenomena observed explain the differences between the classical theory predictions and the experimental observations reported in the open literature, validating the hypothesis of this work.

Multi-chip integration with emerging technologies such as a 3D IC stack or 2.5D interposer is primarily enabled by the off-chip interconnections. The I/O density, speed and bandwidth requirements for emerging mobile and high-performance systems are projected to drive the interconnection pitch to less than 20 microns by 2015. A new class of low-temperature, low-pressure, high-throughput, cost-effective and maufacturable technologies are needed to enable such fine-pitch interconnections. A range of interconnection technologies are being pursued to achieve these fine-pitch interconnections, most notably direct Cu-Cu interconnections and copper pillars with solder caps. Direct Cu-Cu bonding has been a target in the semiconductor industry due to the high electrical and thermal conductivity of copper, its high current-carrying capability and compatibility with CMOS BEOL processes. However, stringent coplanarity requirements and high temperature and high pressure bonding needed for assembly have been the major barriers for this technology. Copper-solder interconnection technology has therefore become the main workhouse for off-chip interconnections, and has recently been demonstrated at pitches as low as 40 microns. However, the current interconnection approaches using copper-solder structures are not scalable to finer feature sizes due to electromigration, and reliability issues arising with decreased solder content. Solid Liquid Inter-Diffusion (SLID) bonding is a promising solution to achieve ultra-fine-pitch and ultra-short interconnections with a copper-solder system, as it relies on the conversion of the entire solder volume into thermally-stable and highly electromigration-resistant intermetallics with no residual solder. Such a complete conversion of solders to stable intermetallics, however, relies on a long assembly time or a subsequent post-annealing process. To achieve pitches lower than 30 micron pitch, this research aims to study two ultra-short copper-solder interconnection approaches: (i) copper pillar and solder cap technology, and (ii) a novel technology which will enable interconnections with improved electrical performance by fast and complete conversion of solders to stable intermetallics (IMCs) using Solid Liquid Diffusion (SLID) bonding approach. SLID bonding, being a liquid state diffusion process, combined with a novel, alternate layered copper-solder bump structure, leads to higher diffusion rates and a much faster conversion of solder to IMCs. Moreover this assembly bonding is done at a much lower temperature and pressure as compared to that used for Cu-Cu interconnections. FEM was used to study the effect of various assembly and bump-design characteristics on the post-assembly stress distribution in the ultra-short copper-solder joints, and design guidelines were evolved based on these results. Test vehicles, based on these guidelines, were designed and fabricated at 50 and 100 micron pitch for experimental analysis. The bumping process was optimized, and the effect of current density on the solder composition, bump-height non-uniformity and surface morphology of the deposited solder were studied. Ultra-short interconnections formed using the copper pillar and solder cap technology were characterized. A novel multi-layered copper-solder stack was designed based on diffusion modeling to optimize the bump stack configuration for high-throughput conversion to stable Cu3Sn intermetallic. Following this modeling, a novel bumping process with alternating copper and tin plating layers to predesigned thicknesses was then developed to fabricate the interconnection structure. Alternate layers of copper and tin were electroplated on a blanket wafer, as a first demonstration of this stack-technology. Dies with copper-solder test structures were bonded using SLID bonding to validate the formation of stable intermetallics.

Orientador: David Mendez Soares / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-28T00:49:55Z (GMT). No. of bitstreams: 1 Gomes_WyllersonEvaristo1983-_D.pdf: 5303870 bytes, checksum: ba3a86db4d3713f9b80b91fba5545795 (MD5) Previous issue date: 2015 / Resumo: Neste trabalho, pesquisamos o uso de filmes autoorganizados sobre o eletrodo de ouro da microbalança de cristal de quartzo eletroquímica, EQCM. Focamos a pesquisa na interação física da superfície sólida funcionalizada com o meio líquido. Desenvolvemos uma metodologia para compreender a dinâmica de variação dos parâmetros medidos, pela EQCM durante um experimento (perturbação) em meio líquido. Introduzimos a representação bidimensional da variação da freqüência de ressonância e da resistência de ressonância do cristal de quartzo da EQCM, ?f e ?R respectivamente, durante uma perturbação, usando o tempo como parâmetro. A metodologia foi utilizada para soluções aquosas de sais, álcool, líquidos apolares como ciclohexano, n-hexano, soluções de sacarose. Mostramos que líquidos reais apresentam viscoelasticidade. Também testamos a perturbação causada pela aplicação de campo elétrico nas interfaces sólido/soluções iônicas em condições em que o eletrodo é polarizável. Mostramos a possibilidade de formação de nanoestruturas gasosas, nanobolhas. Estendemos a pesquisa para a superfície do ouro funcionalizado com filmes de tiol, S-layers (proteínas de membrana de bactéria), e adsorção de lipossomos zwiteriônicos. A interface sólido/líquido também foi estudada relativamente às características hidrofóbicas da funcionalidade devido à sua microestrutura superficial (superfície superhidrofóbica). Usamos as técnicas de microscopia de força atômica, AFM, e de Raman confocal, paralelamente às nossas pesquisas com a EQCM. Para complementar o estudo de campos elétricos aplicados a interfaces, estudamos também os efeitos macroscópicos da aplicação desses campos a líquidos dielétricos como a água. Pesquisamos o fenômeno da ponte líquida usando líquidos dielétricos isolantes apróticos / Abstract: In this work, we have studied the use of self-assembling films onto gold electrode of the electrochemical quartz crystal microbalance, EQCM. The main objective is to understand the physical interaction of the functionalized solid surface with the liquid medium. We have developed a methodology to understand the dynamics of variation of the parameters measured by the EQCM in liquid medium. We also have introduced the two-dimensional representation of the variation of resonance frequency and resonance resistance of the quartz crystal of the EQCM, ?f and ?R respectively. The measurements were taken during a perturbation, using time as parameter. The methodology was used for aqueous salt solutions, alcohol, nonpolar liquids such as cyclohexane, n-hexane and sucrose solutions. We showed that real liquids exhibit viscoelasticity. We also tested the perturbation caused by the application of electric field at solid interfaces/ionic solutions, under conditions in which the electrode is polarizable. We showed the possibility of formation of gaseous nanostructures, nanobubbles. We extended the study to gold electrode thiol-functionalized surfaces, gold surfaces covered by S-layers films (membrane proteins of bacteria), and then adsorption of zwitterionic liposomes. The solid/liquid interface was also studied in relation to hydrophobic functionality due to its surface microstructure (superhydrophobic surface). We use the atomic force microscopy, AFM, and confocal Raman techniques, parallel to our research with EQCM. In addition to the study of electric fields applied to interfaces, we also studied the macroscopic effects of the application of these fields to the dielectric liquids like water. We researched the phenomenon of liquid bridge using insulating dielectric aprotic liquids / Doutorado / Física / Doutor em Ciências / 2010/140031-3 / CNPQ

No description available.