In several applications of casting, dendritic microstructure is not desirable as it results in poor mechanical properties. Enhancing the fluid flow in the mushy zone by stirring is one of the means to suppress this dendritic growth. The strong fluid flow detaches the dendrites from the solid-liquid interface and carries them into the mold to form slurry. The detached dendrites coarsen in the slurry and form into rosette or globular particles based on processing conditions. This slurry offers less resistance to flow even at a high solid fraction and easily flow into the die-cavity. The above principle is the basis of a new manufacturing technology called “semi-sold forming” (SSF), in which metal alloys are cast in the semi-solid state. This technique has several advantages over other existing commercial casting processes, such as reduction of macrosegregation, reduction of porosity and low forming efforts. A major challenge existing in semisolid manufacturing is the production of metallic slurry in a consistent manner. The main difficulty arises because of the presence of a wide range of process parameters affecting the quality of the final product. An established method of producing slurry is by stirring the alloy using an electromagnetic stirrer. From an elaborate review of literature, it is apparent that solidification in presence of electromagnetic stirring involves a wide range of shear and cooling rates variation. However, the CFD models found in the literature are generally not based on accurate rheological properties, which are known to be functions of the relevant process parameters. Hence, there is a clear need for a comprehensive numerical model for such a solidification process, involving accurate rheological data for the semisolid slurry subjected to a range of processing conditions. The objective of the present work is to develop a numerical model for studying the transport phenomena during solidification with linear electromagnetic stirring. The study is presented in the context of a billet making process in a cylindrical mould using linear electromagnetic stirring. The mould consists of two parts: the upper part of the mould is surrounded by a linear electromagnetic stirrer forming the zone of active stirring, and the lower part of the mould is used to cool the liquid metal. The material chosen for the study is Al-7.32%Si (A356) alloy, commonly used for die casting applications. A complete numerical model will therefore have two major components: one dealing with rheological behavior of the semisolid slurry, and the other involving macroscopic modeling of the process using computational fluid dynamics (CFD) techniques. For the latter part of the model, determination of rheological behavior of the slurry is a pre-requisite. The rheological characteristics of the stirred slurry, as a function of shear rate and cooling rate, is determined experimentally using a concentric cylinder viscometer. Two different series of experiments are performed. In the first series, the liquid metal is cooled at a constant cooling rate and sheared with different shear rates to get the effect of shear rate on viscosity. In the second series of experiments, the liquid metal is cooled at different cooling rates and sheared at a constant shear rate to obtain the effect of cooling rate on viscosity. During all these experiments, the shear rate is calculated from the measured angular velocity of spindle using inductive position sensor; viscosity of the slurry is calculated based on the torque applied to the slurry and angular velocity of the spindle; and the solid fraction is calculated from measured temperature of the slurry based on Schiel equation. From these data, a constitutive relation for variable viscosity is established, which is subsequently used in a numerical model for simulating the transport phenomena associated with the solidification process. The numerical model uses a set of single-phase governing equations of mass, momentum, energy and species conservation. The set of governing equations is solved using a pressure based finite volume technique, along with an enthalpy based phase change algorithm. The numerical simulation of this process also involves modeling of Lorentz force field. The numerical study involves prediction of temperature, velocity, species and solid fraction distribution. First, studies are performed for a base case with a moderate stirring intensity of 250A primary current and 50 Hz frequency. It is found that the electromagnetic forces have maximum values near the mould periphery, which results in an ascending movement of the slurry near the mould periphery. Because of continuity, this slurry comes down along the axis of the mould. Stirring produces a strong fluid flow which results good mixing in the melt. Correspondingly, a homogenized temperature distribution is found in the domain. Because of strong stirring, the solid fraction in the slurry is found to be distributed almost uniformly. It is also found that fragmentation of dendrites increases solid fraction in the slurry with processing time. During processing, the continuous rejection of solute makes the liquid progressively solute enriched. It is predicted from the present study that the remaining liquid surrounding the primary solid phase finally solidifies with a near-eutectic composition, which is desirable from the point of view of semisolid casting. Correspondingly, a set of experiments are performed to validate the numerically predicted results. The numerical predictions of temperature variations are in good agreement with experiments, and the predicted flow field evolution correlate well with the microstructures obtained through experiments at various locations, as observed in the numerical results. Subsequently the study is extended to predict the effect of process parameters such as stirring intensity and cooling rate on the distributions of solid fraction and solute in the domain. It is found, from the simulation, that the solidification process is significantly affected by stirring intensity. At increasing primary excitation current, the magnitude of Lorentz force increases and results in increase of slurry velocity. Correspondingly, the fragmentation of dendrites from the solid/liquid is more during solidification at higher stirring intensity, which increases the fraction of solid in the slurry to a high value. It is also found that the solute and fraction of solid in the liquid mixes well under stirring action. Thus, a near uniform distribution of solute and solid fraction is found in the domain. It is found that stirring at high currents produces high solid fraction in the liquid. Also, at very low cooling rate, the solid fraction in the liquid increases. The present study focuses on the model development and experimental validation for solidification with linear electromagnetic stirring for producing a rheocast billet. Further studies highlighting the effects of various process parameters on the thermal history and microstructure formation are also presented.

Made available in DSpace on 2014-12-17T15:01:51Z (GMT). No. of bitstreams: 1 AristidesFSJ_TESE.pdf: 1616188 bytes, checksum: 162e291640cf71e1607267c17f431e17 (MD5) Previous issue date: 2010-10-15 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The wet oxidation of organic compounds with CO2 and H2O has been demonstrated to be an efficient technique for effluent treatment. This work focuses on the synthesis, characterization and catalytic performance of Fe-MnO2/CeO2, K-MnO2/CeO2/ palygorskite and Fe/ palygorskite toward the wet oxidative degradation of phenol. The experiments were conducted in a sludge bed reactor with controlled temperature, pressure and stirring speed and sampling of the liquid phase. Experiments were performed on the following operating conditions: temperature 130 ? C, pressure 20.4 atm, catalyst mass concentration of 5 g / L initial concentration of phenol and 0.5 g / L. The catalytic tests were performed in a slurry agitated reactor provided with temperature, pressure and agitation control and reactor liquid sampling. The influences of iron loaded on the support (0.3; 7 and 10%, m/m) and the initial pH of the reactant medium (3.1; 6.8; 8.7) were studied. The iron dispersion on the palygorskite, the phase purity and the elemental composition of the catalyst were evaluated by X-Ray Difraction (XRD), Scanning Electron Microscopy (SEM) and X-Ray Flourescence (XRF). The use of palygorskite as support to increase the surface area was confirmed by the B.E.T. surface results. The phenol degradation curves showed that the Fe3+ over palygorskite when compared with the other materials tested has the best performance toward the (Total Organic carbonic) TOC conversion. The decrease in alkalinity of the reaction medium also favors the conversion of TOC. The maximum conversion obtained from the TOC with the catalyst 3% Fe / palygorskite was around 95% for a reaction time of 60 minutes, while reducing the formation of acids, especially acetic acid. With products obtained from wet oxidation of phenol, hydroquinone, p-benzoquinone, catechol and oxalic acid, identified and quantified by High Performance Liquid Chromatography was possible to propose a reaction mechanism of the process where the phenol is transformed into the homogeneous and heterogeneous phase in the other by applying a kinetic model, Langmuir-Hinshelwood type, with evaluation of kinetic constants of different reactions involved. / A oxida??o ?mida de compostos org?nicos a CO2 e H2O tem demonstrado ser uma t?cnica interessante no tratamento de efluentes. Este trabalho tem como objetivo a s?ntese e caracteriza??o dos catalisadores Fe-MnO2/CeO2, K-MnO2/CeO2/paligorsquita e Fe/paligorsquita, assim como, a avalia??o na degrada??o oxidativa do fenol. Os experimentos foram realizados em um reator de leito de lama, com controle de temperatura, de press?o e de velocidade de agita??o e com coleta de amostras da fase l?quida. Os Experimentos foram executados nas seguintes condi??es operacionais: temperatura de 130 oC, press?o de 20,4 atm, concentra??o m?ssica do catalisador de 5 g/L e concentra??o inicial do fenol de 0,5 g/L. Os par?metros avaliados foram: teor de ferro impregnado (0,3; 7 e 10% em massa) e o pH do meio reacional (3,1; 6,8 e 8,7). Os resultados da caracteriza??o por DRX, MEV e FRX mostraram a dispers?o do ferro na paligorsquita, a pureza das fases e, finalmente, a composi??o dos elementos que constituem o catalisador. O uso da paligorsquita como suporte eleva a ?rea especifica superficial do catalisador que foi confirmada por an?lise BET. As curvas de degrada??o do fenol indicam que o catalisador Fe3+ suportado em paligorsquita tem um papel preponderante na convers?o de Carbono Org?nico Total (COT) quando comparado aos demais catalisadores. A diminui??o da alcalinidade do meio reacional favorece tamb?m a convers?o de COT. A convers?o m?xima de COT obtida com o catalisador 3% Fe/paligorsquita, foi em torno de 95 % para um tempo de rea??o de 60 minutos, reduzindo ao mesmo tempo a forma??o de ?cidos, em especial o ?cido ac?tico. Com os produtos obtidos da oxida??o ?mida do fenol, hidroquinona, p-benzoquinona, catecol e ?cido ox?lico, identificados e quantificados por Cromatografia L?quida de Alta Efici?ncia, foi poss?vel propor um mecanismo do processo reacional onde o fenol ? transformado em fase homog?nea e os demais em fase heterog?nea. Aplicou-se um modelo cin?tico, tipo Langmuir- Hinshelwood, com avalia??o das constantes cin?ticas das diferentes rea??es envolvidas

Pour réduire les nuisances et pollutions émises par le transport aérien, une solution consisterait à remplacer les matériaux des pièces chaudes des moteurs d'avions par des composites à matrice céramique (CMC). Pour intégrer ces matériaux dans les moteurs, il est nécessaire de les adapter aux contraintes imposées par ce milieu (température≥1400°C, oxydation/corrosion), tout en garantissant des propriétés égales à celles des superalliages actuels (conductivité thermique, résistance mécanique). L'objectif de la thèse était de proposer une architecture de matériau présentant l'ensemble des propriétés demandées par le cahier des charges, d'élaborer ce composite et de le caractériser. Ce travail a permis d'identifier les phénomènes mis en jeu lors de l'élaboration des composites. L'optimisation du procédé, de l'architecture et de la composition du matériau a permis de fournir un CMC dense. Les caractérisations réalisées ont montré l'intérêt de ces matériaux pour l'application visée. / To reduce pollution emitted by air transport, high temperature materials used in hot parts of aircraft engines could be replaced by ceramic matrix composites (CMC). To integrate these materials, they must support the harsh environment encountered inside the engine (temperature ≥ 1400 ° C, oxidation / corrosion), while having properties equivalent to current superalloys (thermal conductivity, mechanical strength). This work was aimed to establish a material architecture presenting all properties required, and to develop and characterize this composite. This procedure has helped to identify the phenomena involved in the development of composites. Various optimizations, as process, material architecture and composition, have lead to the establishment of a dense CMC. Measured properties have proved that these materials can be used for the intended application.

Résumé confidentiel / Résumé confidentiel

Des réacteurs avec solide en suspension (« slurry »), très répandu dans l'industrie chimique, du laboratoire à la production, offrent des bonnes capacités en transfert de matière et de chaleur. Leur flexibilité facilite le changement de la phase solide et permet une régénération en continue des catalyseurs en cas de désactivation. Cependant, ils présentent un fort rétro-mélange, et donc un désavantage pour des réactions ayant des enjeux de sélectivité et/ou de conversion poussées. L'écoulement segmenté dit de Taylor est souvent mis en œuvre dans les réacteurs micro-structurés (RMS), grâce à ses propriétés intéressantes (capacités de transfert, écoulement, piston). Cependant, l'utilisation des solides catalytiques dans ces RMS est le plus souvent résolue par immobilisation du catalyseur nuisant la flexibilité. L'écoulement « slurry Taylor » (EST) qui utilise les recirculations internes dans les segments liquides pour transporter des particules en poudre, peut potentiellement répondre à cet enjeu. L'objet de cette étude est la conception et la caractérisation de ce nouveau mode de contact gaz-liquide-solide (G-L-S) dans des tubes millimétriques horizontaux et verticaux. Des études hydrodynamiques ont révélé différents régimes d'écoulement dépendant de la vitesse et de l'orientation de l'écoulement. Pour étudier le transfert de matière L-S, une résine échangeuse d'ion a été utilisée et une première corrélation pour le nombre de Sherwood est proposée / Slurry reactors, widely encountered in chemical industry (laboratory scale up to manufactaring), offer good mass and heat transfer capacities and their high flexibility ensures the simple changeover of solid phases enables a continuous online fresh catalyst feed for fast deactivating catalysts. However slurry reactors promote a high degree of backmixing which can be a drawback for reactions with selectivity issues or when very high conversions are required. In microreaction technology, Taylor flow is often employed providing excellent heat and mass transfer and almost ideal plug flow behavior. Solid handing in these small structures is often resolved by immobilizing the solid catalyst which impinges on the flexibility. One possible solution to combine beneficial properties of Taylor flow with the operational flexibility of conventional slurry reactors is a “slurry Taylor” flow (STF) where catalyst particles are suspended and kept in motion by the internal circulations present in the liquid slugs. The focus of this work is the design and characterization of this innovative gas-liquid-solid contactor. Particles were transported in millimetric horizontal and vertical tubing without the risk of clogging. Hydrodynamic studies revealed different flow patterns depending mainly on velocity and flow orientation. Ion exchange resin particles were used to study the liquid-solid mass transfer and first correlation for the Sherwood number in STF is proposed

L’objectif de cette étude est de recycler du slurry, suspension silicatée, utilisé dans le domaine de l’électronique lors du polissage. Deux applications de polissage sont étudiées : le polissage silicium et le polissage tungstène. Pour ces deux applications, une caractérisation physico-chimique des slurries en amont et en aval du procédé de polissage a mis en exergue une importante dilution du slurry par de l’eau déionisée destinée au rinçage des wafers : une collecte ségrégée a ainsi été mise en place. Le procédé d’ultrafiltration permet une reconcentration de la silice. Toutefois ce procédé ne permet pas la récupération des composés dissous du slurry, qui restent pourtant essentiels au polissage et d’autant plus pour l’application tungstène : un ajustement chimique est donc développée avant réutilisation du slurry ainsi retraité. Pour le slurry tungstène, la matrice chimique étant plus complexe, deux types d’ajustement ont été testés dont les proportions ont été optimisées par une méthode de plans d’expériences.Concernant le slurry silicium, un prototype industriel a été installé et les résultats de polissage sont similaires au slurry POU sur un nombre significatif de plaques. La qualification industrielle a été réalisée. Ce prototype permet d’atteindre les objectifs de diminution de 30% de la consommation de slurry et de 40% des volumes d’effluents rejetés vers station d’épuration. / The chemical and mechanical polishing is a costly step in the process of microelectronic chips manufacturing. This study aims for recycle the silicate suspension named slurry by membrane processes. Both polishing applications are studied: the silicium and the tungsten polishing. A physical and chemical characterization before and after polishing process shows an important dilution of slurry by deionized water used for wafers rinsing. From CMP machine, a collect segregation of a concentrated effluent is realised by a diverter valve. Ultrafiltration has been chosen to reconcentrate silica but does not permit to recover the chemical compounds of the slurry which are essential to the polishing mainly to the tungsten application. Thus, retreatment process includes a collect segregation at the CMP outlet to decrease the dilution factor of slurry, an ultrafiltration step to concentrate silica and a chemical adjustment step. About tungsten application, the chemical media is more complex and two types of adjustment have been led. Firstly, a mix of POU and retreated slurry has been tested and secondly, an experiment of design with three important compounds of the slurry has been tested. Most CMP parameters are obtained in industrial specifications with the mix of POU and retreated slurry.Concerning the silicium slurry, an industrial prototype is installed and polishing results are similar to the original slurry for a significant wafers number. The industrial agreement is obtained. This prototype allows reaching a 30% decrease of slurry consumption and a 40% decrease of waste waters.

This dissertation presents a series of studies relating to optimization of kinematics and consumables during chemical mechanical planarization processes. These are also evaluated with the purpose of minimizing environmental and cost of ownership impacts.In order to study diamond micro-wear and substrate wear during planarization processes, a series of static etch tests and wear tests were performed using different types of diamond discs and subjected to various treatments. Scanning Electron Microscopy (SEM) and Inductively Coupled Plasma Membrane Spectroscopy (ICPMS) were used to estimate the extent of diamond micro-wear and substrate wear.Next, the impact of various factors (type of slurry abrasive, pH, abrasive content and abrasive concentration) on pad wear rate during planarization process was studied. Another study in this dissertation focuses on the development of a novel technique of using coefficient of friction (COF) data to distinguish between good and bad diamond discs. This study made use of the innovative tool diamond disc dragging device (DDD-100) designed and developed for the purpose of this study.It is known that the performance of chemical mechanical planarization depends significantly on the polishing pad grooving type and the kinematics involved in the process. Variations in pad grooving type as well as pressure and sliding velocity can affect polishing performance. One study in this dissertation investigates the effect of pressure and sliding velocity on the polishing performance. The study is conducted on multiple pressure and sliding velocity variations to understand the characteristic of each condition. A subsequent study focuses on the impact of pad grooving type on polishing performance.The greatest contribution of this dissertation involves development of the novel slurry injector to optimize the utilization of slurry during planarization processes. Slurry is a critical component in chemical mechanical planarization processes and accounts for approximately 50 percent of the cost of ownership (CoO). The novel injector apart from reducing the consumption of slurry, also contributed in addressing problems associated with foaming, reduced the number of defects and achieved better within wafer non-uniformity (WIWNU).

L’objectif de cette étude est l’élaboration de nanocomposite à base d’un élastomère de styrène et de butadiène (SBR) par l’ajout d’une dispersion aqueuse (slurry) de nanocharges lamellaires de phosphate de zirconium en phase α (α-ZrP ou ZrP). Les travaux s’attardent d’abord sur le mélange entre le SBR à l’état fondu et le slurry de ZrP en absence de traitement de surface. Différents stratégies d’élaboration sont ensuite envisagées afin d’améliorer la dispersion (intercalation exfoliation) des feuillets de ZrP dans le matériau en couplant le traitement de surface du ZrP et les paramètres de mise en œuvre. Différents traitements de surface sont abordés avec l’utilisation d’un agent intercalant métallique (Na+), de deux intercalants alkylamines (propylamine, octadécylamine) et d’un agent d’exfoliation (hydroxyde de tétrabutylammonium). En parallèle, plusieurs procédés de mise en œuvre générant des écoulements complexes sont utilisés. La complémentarité entre la diffraction des rayons X (DRX), la microscopie électronique en transmission (MET) et la spectroscopie mécanique (DTMA) permet d’obtenir une analyse multi-échelle de l’état de dispersion du ZrP et de proposer des scénarii décrivant les mécanismes de dispersion en fonction des paramètres étudiés. Un effort important est apporté pour la compréhension de la relation structure à l’échelle nanoscopique et les propriétés macroscopiques du matériau. Une étude comparative est ensuite proposée entre les valeurs expérimentales de l’effet de renforcement des matériaux et les prédictions des modèles Krieger-Dougherty et Halpi-Tsai / This work focuses on the melt processing of nanocomposite materials obtained from a synthetic lamellar filler, α-zirconium phosphate (α-ZrP), dispersed within a synthetic rubber of the SBR type. The first step is the melt compounding using aqueous slurry of α-ZrP without any treatment. Following, several kinds of surface modifiers such as sodium cation, alkylamines and tetrabutylammonium hydroxide and different melt processing conditions are investigated to improve the level of dispersion of ZrP platelets into the matrix. X-ray diffraction, transmission electron microscopy and dynamical mechanical method are used as a multi-scale analysis to quantify the state of dispersion of the filler within the nanocomposite. Several mechanisms of dispersion are described depend on the surface modifying treatment and the melt processing parameters and the structure-properties relationship are studied. A comparison between the material reinforcement and two models of predictions, Krieger-Dougherty and Halpin-Tsai are discussed

To minimize coastal land loss and create new land, dredged sediment has been in use in coastal Louisiana during the last several years. Engineering properties and material characteristics of dredged material are input parameters in several mathematical models used to predict the long-term hydrodynamic behavior of the coast. Therefore, proper characterization of the dredged material is of utmost importance in the correct design of coastal restoration and land creation projects. The sedimentation characteristics of the dredged material, among other factors, depends on the (a) grain size distribution of the dredged material, (b) salinity (fresh, brackish, or saltwater environment) of the composite slurry, and (c) concentration of the solid particles in the slurry. In this research, dredged sediments obtained from actual coastal restoration projects were characterized. Furthermore, the effects of grain size distribution, salinity and solid particle concentration on sedimentation characteristics have been evaluated.

No presente trabalho são apresentadas sugestões de critérios executivos, fundamentados nos tratamentos efetuados em três obras brasileiras, em especial na Usina de Rasgão. O uso dos recursos da estatística também é proposto para avaliar a injeção de solo-cimento, ainda durante a fase executiva dos trabalhos. As análises realizadas mostram que as médias da pressão de iniciação da ruptura do maciço, em terreno natural, são crescentes com a profundidade. Observa-se também que à medida que o tratamento avança, os valores médios das pressões de ruptura e de injeção crescem nas linhas subseqüentes, tendendo a um valor constante com a profundidade e, conseqüentemente, indicando certa homogeneização do maciço. Destaca-se a performance do ensaio do tipo crosshole, executado ainda que em campo de prova, na avaliação da eficiência do tratamento. Nas paredes de uma trincheira escavada no campo de prova, observam-se fraturas hidráulicas predominantemente subverticais, algumas sub-horizontais e poucas inclinadas. Embora diferentes corantes tenham sido empregados nas caldas para observar as possíveis relações entre as fraturas hidráulicas, o processo de pigmentação adotado parece não ter sido adequado. / Soil-cement slurry grouting has been applied for a long time, although not is commonly used in Brazil, a tropical country where thick layers of soil are frequently found. The present paper is based on the soil mass treatment carried out at three different sites, particularly at Rasgão hydroelectric power plant. Statistics methods were applied in order to analyse the variation of the grouting pressures. They showed that pressure of fracturing were increasingly higher with depth in the natural soil mass. As long as the treatment goes on, it has also noticed that the average values of pressures fracturing and injection in each line of grouting became gradually higher, while the subsequent lines showed values of pressures tending to become constant with depth, suggesting a homogeneity of mechanical strength of the natural soil mass. Field geophysical tests performed before and after the grouting, using cross-hole technique, succeeded in verifying the efficiency of the treatment. The excavation of a trench into the test site indicated that the hydraulic fracturing has developed greatly in a vertical position, other than horizontally. Although different colours of pigments were mixed into the slurry in order to investigate the possible relationship among hydraulic fractures, that procedure proved to be unsuccessful.