There are many challenges in materializing the applications utilizing inorganic nanoparticles. The primary drawback is the degradation of properties due to aggregation and sintering either due to elevated temperatures or prevailing chemical/electrochemical conditions. In this thesis, various wet chemical synthesis methods are developed to obtain metal nanostructures with enhanced thermal stability. The thesis is organized as below: Chapter 1 presents the problems and challenges in materializing the application of nanomaterials associated with the thermal stability of nanomaterials. A review of the existing techniques to improve the thermal stability and the scope of the thesis are presented. Chapter 2 gives a summary of the various materials synthesized, the method adopted for the synthesis and the characterization techniques used in the material characterization. Chapter 3 presents a general template-less strategy for the synthesis of nanoporous alloy aggregates by controlled aggregation of nanoparticles in the solution phase with excellent control over morphology and composition as illustrated using PdPt and PtRu systems as examples. The Pt-based nanoporous clusters exhibit excellent activity for methanol oxidation with good long term stability and CO tolerance. Chapter 4 presents a detailed study on the thermal stability of spherical mesoporous aggregates consisting of nanoparticles. The thermal stability study leads to a general conclusion that nanoporous structures transform to hollow structures on heating to elevated temperatures before undergoing complete densification. Chapter 5 presents a simple and facile method for the synthesis of single crystalline intermetallic PtBi hollow nanoparticles. A mechanism is proposed for the formation of intermetallic PtBi hollow structures. The intermetallic PtBi hollow structures synthesised show excellent electrocatalytic activity for formic acid oxidation reaction. Chapter 6 presents a robust strategy for obtaining a high dispersion of ultrafine Pt and PtRu nanoparticles on graphene. The method involves the nucleation of a metal precursor phase on graphite oxide surfaces and subsequent reduction with a strong reducing agent. The electrocatalytic activity of the composites is investigated for methanol oxidation reaction. Chapter 7 presents a microwave-assisted synthesis method for selective heterogeneous nucleation of metal nanoparticles on oxide supports leading to the synthesis of high activity catalysts. The catalytic activity of the hybrids synthesized by this method for investigated for H2 combustion. Chapter 8 presents thermal stability studies carried out on nanostructures by in-situ heating in transmission electron microscope. The microstructural changes during the sintering process are observed in real time and the observations lead to the understanding of the mechanism of particle growth and sintering. At the end, the results of the investigations were summarized with conclusions drawn.

La fissuration d’éléments minces en béton dès le jeune âge correspond à une réalité observée sur des ouvrages en construction. Cette fissuration concerne des bétons courants de bâtiments, pour lesquels les matériaux de qualité optimale ne sont pas toujours disponibles, en particulier au niveau des granulats. Le but de cette thèse est de définir une approche expérimentale d’étude de ces phénomènes et de proposer des interprétations pour les sensibilités relatives à la fissuration en fonction de la nature des granulats et de leurs taux de saturation initiaux. La sensibilité des moyens de mesures existants conçus pour des bétons spéciaux (BAP et BHP) a d’abord dû être<p>vérifiée. Un nouveau dispositif expérimental a été développé dans le but de mieux décrire l’évolution de la résistance et de la capacité de<p>déformation en traction du béton jeune. Les indicateurs globaux (macroscopiques) apparaissent plus sensibles que les indicateurs de la microstructure pour rendre compte des différences de comportement observées. L’évolution du module élastique, du retrait plastique et endogène corrélées à l’évolution de la capacité de déformation et de la résistance en traction permettent de mieux caractériser le risque<p>potentiel de fissuration par retrait empêché. La fin de prise correspond à une phase critique. L’influence de la saturation des granulats est<p>indirecte, et résulte des variations du rapport Eau d’ajout/Ciment, à rapport Eau efficace/Ciment constant. La nature des granulats intervient au niveau des évolutions relatives de la résistance en traction et du module élastique. La méthodologie peut être appliquée à l’étude d’autres types de bétons et d’autres paramètres de formulation. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Master`s thesis is divided in to two parts, practical and theoretical. In theoretical part are listed basic information’s about light weight concrete, special emphasis are given to characteristic and practical application of compact light weight concrete with Liapor aggregates. In this study is described influence of high temperature on concrete structure and chemical, mechanical and physical changes, which take place during exposal to high temperatures. Further is evaluated surface permeability of concrete and addition of polypropylene fibres to concretes resistive to high temperatures. The practical part deals with design, production and testing of cement based concrete with use of different aggregates (light weight aggregates Liapor, basalt). The properties and use for applications in high temperatures is also mentioned. The influence of high temperature on strength, absorption, thermal conductivity, changes of surface permeability and degradation of testing specimens due to heat loads according to normative heat curve (ISO 834). For better transparency are experimental tests divided in to five phases and the measured values are evaluated on the end of each phase. In conclusion are resumed all knowledge’s obtained by testing and evaluated the most suitable formulation. The approach for further research is also mentioned.

Constitués de plusieurs composants (granulats naturels et pâte de ciment adhérente), les GBR ne sont à l’heure actuelle pas utilisés largement dans la formulation de nouveaux bétons. Les propriétés médiocres des GBR compliquent considérablement la détermination de la quantité d’eau efficace dans le béton frais. Tout d’abord, une étude bibliographique va mettre en évidence la grande dispersion des résultats des essais de caractérisation des GBR et des propriétés des bétons recyclés à l’état frais et durci. Ensuite, une étude vise à analyser l’hétérogénéité des GBR et des granulats de béton concassé (GBC) par rapport à différents paramètres : aux impuretés granulaires, à la densité et à la teneur en pâte de ciment, au malaxage du béton parent, et au niveau de la capacité d’absorption d’eau des GBC en fonction de leur état de pré-humidification. Enfin, une dernière partie est destinée à améliorer la maîtrise de l’eau efficace réelle dans la fabrication du béton recyclé. La cinétique d’absorption des GBC dans une pâte de ciment est tout d’abord étudiée. Ensuite, l’évolution de l’eau efficace durant le malaxage de bétons à base de GBC est investiguée au moyen d’une méthode originale basée sur le suivi des courbes de puissance du malaxeur. Finalement, l’effet d’un malaxage sous vide relatif sur les propriétés des bétons à base de granulats naturels et des bétons à base de GBC est étudié. / Composed of several components (natural aggregates and adherent cement paste), RCA are not widely recommended in new concrete formulations. Their poor properties considerably complicate the determination of the effective water in fresh concrete. In a first part, a bibliographic study will highlight the wide dispersion of the results of characterization tests of RCA and the properties of fresh and hardened recycled concrete. In a second part, the heterogeneity of RCA and crushed concrete aggregates (CCA) is studied according to different parameters: granular impurities, density, cement paste content, mixing of parent concrete, and water absorption capacity according to their pre-humidification. The third part consists of three experimental studies that intend to improve effective water control in the manufacture of recycled concrete. The absorption kinetics of CCA in a cement paste is first studied. Then, the evolution of effective water in fresh concrete during mixing is studied using an original method based on the power evolution of the mixer. Finally, the effect of vacuum mixing on the properties of ordinary and recycled concretes is investigated.

No description available.

Ground Improvement using vibro stone columns is gaining increasing acceptance on marginal soft clay sites as a sustainable foundation solution, particularly for lightly loaded low-rise structures supported by shallow, narrow footings. Most experience in this context however has been with widespread loads and use of the wet top-feed stone column technique, which has now been largely superseded, on environmental grounds, by the dry bottom-feed technique, and for which no significant published field trial data currently exists in deep soft clay deposits in the context of shallow, narrow footings. This research is therefore principally concerned with evaluating both the ground response to installation of partial depth vibro stone columns using the dry bottom-feed method in a deep moderately sensitive soft clay soil, together with the influence of parameters such as stone column spacing and length, founding depth within a thin surface 'crust', and also foundation shape on the performance of narrow footings subsequently constructed and subjected to incremental loading, over the installed stone columns, at the Bothkennar soft clay research site in Scotland. Comparisons are made with footings constructed within the surface 'crust' at Bothkennar without stone columns. Whilst stone columns were satisfactorily constructed with the dry bottom-feed technique at Bothkennar, it was evident that the vibroflot should not remain in the ground for longer than is necessary, in order to avoid excessive soil disturbance. For this reason construction of partial depth stone columns to a more uniform diameter, without construction of an 'end bulb', is advocated. Stress ratio was found to increase significantly with increasing length of stone column and also applied load, up to a maximum value of around 4.0. Moreover, for a trial footing founded at the base of the 'crust', stresses attracted by the columns were higher than all other columns where founding depth (level) was at shallower depth in the crust. A significant stress transfer was also measured beneath the toe of columns intentionally installed shorter than the minimum design length predicted by the Hughes and Withers (1974) approach at all iii applied loads, but not for columns equal to, or longer than minimum design length, confirming the predictions of this laboratory-based approach at the field scale. The stress measurements recorded by the field instrumentation demonstrate that the behaviour of the composite stone column-soil-foundation system is complex, with simultaneous and interdependent changes in pore pressures, soil stress ratios and resulting stiffness of both soil and columns. Whilst observed settlements exceeded those predicted, with larger foundation settlements observed at low applied loads over stone columns than at the same loading level in untreated ground, principally due to soil disturbance and accelerated consolidation effects during initial loading, at higher applied loadings however the stone columns significantly reduced the rate and magnitude of settlement compared to a foundation in the untreated 'crust'. It is therefore clear that the stone columns 'reinforced' the weak soil, providing a significantly increased factor of safety against bearing failure.

La transplantation d’îlots de Langerhans microencapsulés est un traitement prometteur du diabète de type 1. La microcapsule protège l’îlot du système immunitaire, tout en permettant la diffusion de petites molécules. Comme la microcapsule empêche la revascularisation des îlots, leur oxygénation se fait par diffusion d’oxygène et ils sont exposés à l’hypoxie. Le manque d’oxygène est un facteur limitant dans la survie des îlots microencapsulés. Il est connu que les plus petits îlots sont plus résistant à l’hypoxie à cause d’une meilleure diffusion de l’oxygène. À cette fin, les agrégats de cellules dispersées d’îlots seront étudiés. Lorsque les cellules des îlots sont dispersées, elles ont la propriété de se ré-assembler dans une structure semblable à celle des îlots. La présente étude a permis de mettre au point une technique de formation des agrégats, de les caractériser et de comparer la résistance à l’hypoxie des îlots et des agrégats. Ceux-ci ont une structure semblable aux îlots et ils sont de plus petite taille. Pour cette raison, ils sont plus viables après un choc hypoxique tout en renversant efficacement l’hyperglycémie de souris diabétiques. Les agrégats sont une alternative intéressante pour la transplantation d’îlots microencapsulés puisque leur oxygénation est plus efficace. / Transplantation of microencapsulated islets of Langerhans is a promising treatment for type 1 diabetes mellitus. The microcapsule allows the diffusion of small molecules, while protecting the islet from the antibodies and immune cells. However, microcapsule prevents islet revascularization, thus oxygenation depends on diffusion and islets are exposed to hypoxia. Poor oxygenation is a major limitation in microencapsulated islet survival. It was shown that smaller islets are more resistant to hypoxia because of a better oxygen diffusion. In this study, dispersed islet cell aggregates will be used to improve the oxygenation. When islet cells are dispersed into single cells, they have the ability to re-associate into an islet-like structure. This study allowed to set up a technique to form aggregates, to characterized them and to compare the resistance to hypoxia of islets and aggregates. Aggregates have a similar structure than islets and they are smaller. For this reason, they survive better to a hypoxic treatment, while restoring efficiently normoglycemia in diabetic mices. Aggregates are an interesting solution for microencapsulated islet transplantation because they have a better oxygenation.

L'objectif de ce travail était de mettre au point un système de culture tridimensionnel compartimenté pour la différentiation de cellules neurales et la croissance des neurites en 3D. Les matériaux biomimétiques permettent l'élaboration de microenvironnements contrôlés qui peuvent orienter la réponse cellulaire. Ils sont particulièrement intéressants pour les études fondamentales visant à étudier des voies de signalisation impliquées dans des processus physiologiques ou pathologiques. Nous nous sommes intéressés à la maladie d'Alzheimer, où l'on observe des neurites dystrophiques associés aux plaques amyloïdes. Aucune relation n'a été réellement établie entre l'interaction neurites - agrégats, leur dystrophie et la mort neuronale. Dans un premier temps, nous avons décrit et caractérisé la structure et les propriétés de matrices de collagène fibrillaire d'épaisseur calibrée. Ensuite, nous avons mis au point la fonctionnalisation de ces matrices avec des facteurs de croissance neurotrophiques (NGF et BDNF). Deux techniques ont été étudiées : l'imprégnation/libération et le couplage covalent. Ces matrices fonctionnalisées ont été validées comme support pour la différenciation de cellules nerveuses (PC-12 et SH-SY5Y) par des études de la morphologie cellulaire. Enfin, nous avons caractérisé des agrégats amyloïdes (Aβ) formés à l'intérieur des matrices de collagène par co-précipitation du peptide Aβ avec le collagène et nous avons étudié leur toxicité sur les cellules neurales. / The objective of this work was to develop a 3D compartmented cell culture set-up that allow the differentiation of nerve cells and the growth of neurites in the matrix depth. Biomimetic materials enable the formation of controlled microenvironments that orient cell behavior. They are particularly interesting for fundamental studies that aim to study signaling pathways involved in physiologic or pathologic processes. We focused on Alzheimer's disease, in which dystrophic neurites are associated to amyloid plaques. No direct relationship has yet been established between Aβ aggregates-neurite interaction, neurite dystrophy and cell death. First, we described and characterized the structure and properties of fibrillar collagen matrices with adapted thickness. Then, we adjusted functionalization of these matrices with neurotrophic growth factors (NGF and BDNF). Two methods were studied: impregnation/release and covalent coupling. Cell morphology studies confirmed that these functionalized matrices were efficient supports for nerve cells differentiation (PC-12 and SH-SY5Y). Finally, we have characterized Aβ aggregates that were formed inside collagen matrices by coprecipitation of amyloid peptide and collagen and we studied their toxicity on neural cells.

Esta tese aborda a aplicação da tecnologia dos concretos leves de alto desempenho (CLAD) para a produção de elementos construtivos esbeltos pré-fabricados, tais como painéis estruturais e de vedação e peças para cobertura, apresentando um concreto com propriedades especiais em função da utilização conjunta de látex de estireno butadieno (SB), sílica ativa, superplastificante acelerador e agregados leves nacionais, denominado concreto leve de alto desempenho modificado com SB. Desenvolveu-se um amplo programa experimental para a análise dos concretos, tendo como objetivos o estudo dos processos de dosagem e produção, caracterização das propriedades dos concretos nos estados fresco e endurecido, análise da ductilidade de elementos construtivos esbeltos pré-fabricados submetidos à flexão, assim como a obtenção de informações microestruturais sobre a matriz de cimento e a zona de transição entre o agregado e a matriz de cimento. Os resultados do programa experimental demonstraram que os concretos leves de alto desempenho modificados com SB são extremamente adequados à produção de elementos pré-fabricados esbeltos, devido essencialmente à redução da massa específica e ao excelente desempenho das propriedades relacionadas à resistência mecânica e durabilidade. Nos estudos microestruturais, observou-se que a utilização de sílica ativa e de SB promoveram a diminuição da quantidade e do diâmetro dos poros capilares e da quantidade de hidróxido de cálcio (CH) na matriz de cimento, assim como reduziram a espessura da zona de transição agregado-matriz. Observou-se, também, que os concretos com agregados leves nacionais apresentaram valores da espessura da zona de transição agregado-matriz inferiores aos observados para os concretos com agregados tradicionais. / This dissertation deals with the application of the high performance lightweight aggregate concrete (HPLWAC) for the production of thin precast components, such as structural and insulation panels and elements for covering. A concrete with special properties was presented, once the use of styrene-butadiene latex (SBR), silica fume, accelerating superplastificizer and Brazilian lightweight aggregates, named SBR-modified high performance lightweight aggregate concrete. Our main goals in the experimental program were the study of concrete dosage and production, the characterization of concretes properties, the thin precast components analysis, as well as the microstructural study about both cement paste and the interfacial transition zone (ITZ) between aggregate and cement paste. The main results show that the SBR-modified HPLWAC are extremely appropriate to the production of thin precast components, due essentially to the density reduction and to the high performance of mechanical and durability properties. Besides this, it was viewed that the silica fume and SBR use promote the decrease of the amount and diameter of the capillary pores, as well as the amount of calcium hydroxide (CH) in the cement paste. Additionally, they reduce the thickness of the interfacial transition zone between aggregate and cement paste. It was also observed that the concretes with Brazilian lightweight aggregate presented lower values of the interfacial transition zone thickness than the ones observed for the concretes with traditional aggregates (basalt).

Muitas das ações e das preocupações orientadas para a destinação mais correta dos resíduos sólidos urbanos, particularmente do vidro de embalagens, acabam por não se concretizarem pela falta de informações básicas, geralmente muito simples e que podem ser disponibilizadas com facilidade. Neste trabalho propomos o desenvolvimento de um programa que incentive os usuários de embalagens de vidro a não descartarem, de maneira indiscriminada e inconsciente, este material. Trata-se, portanto, de um programa de incentivo que busca apoiar, técnica e informacionamente, todos aqueles que hoje são consumidores de embalagens de vidro, embora não tenham como garantir o retoro deste material às recicladoras ou à indústria vidreira. Este trabalho pretende se constituir em um instrumento de apoio a uma atuação mais correta das municipalidades e/ou instituições, na busca de uma destinação mais eficiente das embalagens de vidro consumidas em sua área de atuação. Apesar da indústria vidreira afirmar que tem capacidade instalada para reciclar todo o vidro produzido no Brasil, é sabido que mais da metade da produção anual de embalagens de vidro não retorna às fábricas de vidro. A razão principal é que não há comprador de caco de vidro para as cidades localizadas a mais de 500 km dos centros de produção. A proposta desenvolvida neste trabalho, para aquelas cidades e regiões mais distantes dos centros de produção de vidro e das recicladoras, prevê o reaproveitamento do vidro de embalagens na produção de artefatos de concreto. O vidro, adequadamente preparado, será utilizado como agregado na composição do concreto em substituição à areia e ao pedrisco. Para tanto desenvolvemos, em conjunto com a Escola Politécnica da USP, um estudo de composição de traços especialmente elaborados para esta finalidade. Est novo material será utilizado na produção local de peças de mobiliário urbano e de componentes de infra-estrutura. Além disso, para quem tiver interesse em produzir com este novo concreto, disponibilizamos um conjunto de desenhos que incluem peças de mobiliário urbano e de infra-estrutura, bem como as respectivas formas, armaduras e demais especificações técnicas. / Many actions and concerns that aim the propoer destination of urban solid waste, guided to most correct glass packing management, do not get success due to the lack of adequate and very simple basic informations, which can be easily afforded. Trying to miminize the effect of the indiscriminate or unconscious discharge that conduct to an inadequate glass packing management, we developed and suggest a program which main purpose is to incentive the consumer consider other possibilities for it use. This program incentive and give support to all glass packing consumers estabilishing a technical and knowledge system analysis, although we do not have the guarantee that this kind of waste will return to the glass industry or to the recycling one. Our intention with the present work is to estabilish a feasible support instrument to its application, by municipal or others institutions, in effective actions for the glass packages managements. The representants of the brazilian glass industry declares that their recycle capacity is for the entire production, but we know that more than fifty prcent of the anual glass packing prodution do not return to the glass industry. We believe that the main reason for this effect is the inexistance of glass fragment buyers placed more than 500 km away from the production centres. In the present work we suggest to these municipalities and others institutions placed far away from the glass production centres or from the recycles industries units, the incusion of the glass packing reutilization by the concrete industries in its artifacts production. For this purpose we estabilished, in association with the Escola Politécnica da USP, Brazil, an experimental work analysing the mixing concrete composition using the glass fragments in substitution of sand and gravel. This new mixing will be used in a local production of urban furnitures. For this purpose we added, in the present work, the drawigs, shapes and its frameworks for who wants to produce urban furnitures with this new mixture.