The effects of metastable tetragonal zirconia on the properties of Ordinary Portland Cement were observed during which the effect of crystallite size pH on the preparation solution, precursor salt, and the presence of co-precipitates, Fe(OH)3, SnO2 and SiO2 on the crystallization temperature, enthalpy and crystal structure, immediately following the crystallization exothermic burst phenomenon in ZrO2 were measured. Thermal analysis and x-ray methods were used to determine crystallite sizes and structures immediately following the exothermic burst. Comparisons were made for zirconias prepared from oxychloride, chloride and nitrate solutions. The existence of tetrameric hydroxidecontaining ions in oxychloride precursor is used to rationalise low values of crystallization enthalpy. The position of the crystallization temperature, Tmax was not dependent on crystallite size alone but also on the pH at which the gel was made, the surface pH after washing, and the presence of diluent oxides. Enthalpy v r1/2 and Tmax v (diluent vol)1/3 relationships indicate that surface coverage effects dominate a surface nucleated phenomenon. The data established for ZrO2 systems was used to develop tetragonal-ZrO2-SnO2 powders capable of improving the mechanical properties of Ordinary Portland Cement discs. The ZrO2-OPC discs were prepared by powder mixing, water hydration and uniaxial pressing. Vicat needle tests showed that tetragonal-ZrO2 increases the initial setting rate. Microscopy indicated that porosity distribution changes near to ZrO2 particles. Zirconia has also been introduced into OPC discs by vacuum infiltration methods developed for solutions and colloidal suspensions. Comparisons between OPC discs and the OPCtetragonal ZrO2 composites have been made on the basis of diametral compression strength, Young’s modulus, hardness and toughness (K1c), as estimated by the cracked indentation method. Bell-shaped curves are found for the way the mechanical properties are changed as a function of Zirconia content.

<p> This dissertation describes the recent advancements in micromechanical testing that inform how deformation mechanisms in austenitic stainless steels (SS) are affected by the presence of irradiation-induced defects. Austenitic SS is one of the most widely utilized structural alloys in nuclear energy systems, but the role of irradiation on its underlying mechanisms of mechanical deformation remains poorly understood. Now, recent advancement of microscale mechanical testing in a scanning electron microscope (SEM), coupled with site-specific transmission electron microscopy (TEM), enables us to precisely determine deformation mechanisms as a function of plastic strain and grain orientation.</p> <p> </p> <p>We focus on AISI 304L SSs irradiated in EBR-II to ~1-28 displacements per atom (dpa) at ~415 °C and contains ~0.2-8 atomic parts per million (appm) He amounting to ~0.2-2.8% swelling. A portion of the specimen is laser welded in a hot cell; the laser weld heat affected zone (HAZ) is studied and considered to have undergone post-irradiation annealing (PIA). An archival, virgin specimen is also studied as a control. We conduct nanoindentation, then prepare TEM lamellae from the indent plastic zone. In the 3 appm He condition, TEM investigation reveals nucleation of deformation-induced <i>α</i>’ martensite in the irradiated specimen, and metastable <i>ε</i> martensite in the PIA specimen. Meanwhile, the unirradiated control specimen exhibits evidence only of dislocation slip and twinning; this is unsurprising given that alternative deformation mechanisms such as twinning and martensitic transformation are typically observed only near cryogenic temperatures in austenitic SS. Surface area of irradiation-produced cavities contribute enough free energy to accommodate the martensitic transformation. The lower population of cavities in the PIA material enables metastable <i>ε</i> martensite formation, while the higher cavity number density in the irradiated material causes direct <i>α</i>’ martensite formation. In the 0.2 appm He condition, SEM-based micropillar compression tests confirm nanoindentation results. A deformation transition map with corresponding criteria has been proposed for tailoring the plasticity of irradiated steels. Irradiation damage could enable fundamental, mechanistic studies of deformation mechanisms that are typically only accessible at extremely low temperatures. </p>

Les réfractaires électrofondus, qui constituent l’objet de ce travail, appartiennent au système alumine-zircone-silice. Ils sont obtenus par coulée dans des moules à des températures supérieures à 2000°C, rendant très difficile toute instrumentation. De nombreux phénomènes intrinsèques au matériau interviennent lors du refroidissement qui suit la coulée. Parmi ces derniers, cette recherche a essentiellement porté sur la transformation de phase (de tétragonale à monoclinique) de la zircone et aux phénomènes associés (gonflement, plasticité,…).A partir d’essais mécaniques à haute température réalisés en laboratoire, les lois de comportements thermiques et mécaniques ont été caractérisées et modélisées en cours de transformation de la zircone. La plasticité à très bas seuil de contrainte observée a, en particulier, été décrite par une vitesse de déformation dérivée du modèle de Leblond, une fonction de rendement de type Cam-clay sans consolidation et une fonction de rendement définissant l’avancement de la transformation en fonction de la température. Après implémentation dans un code de calcul par éléments finis et validation par confrontation avec des résultats d’essais sous contraintes multiaxiales, ce modèle a été assemblé aux autres composantes du comportement mécanique (fluage, élasticité,…), pour décrire l’ensemble des phénomènes thermomécaniques observés lors du refroidissement.Parallèlement, des coulées de blocs en laboratoire, instrumentées par des thermocouples et des capteurs d’émission acoustique, ont permis de reconstruire par simulation numérique l’évolution du champ de température à l’intérieur de la dalle au cours du refroidissement. L’enthalpie de solidification et celle associée à la transformation de phase, préalablement quantifiée par ATD, ont été prises en compte. L’application du modèle mécanique complet, associant toutes les composantes du comportement, a permis de calculer l’évolution du champ de contraintes généré par les gradients thermiques en fonction du temps et, en particulier, de mettre en évidence le rôle essentiel joué par la transformation de phase sur la relaxation des contraintes. / Fused-cast refractories, which are concerned by this work, belong to the alumina-zirconia-silica system. They are obtained by casting in molds at temperatures higher than 2000°C, that make very difficult any instrumentation. Many phenomena intrinsic to the material occur during cooling-down after casting. Among these latter, this research essentially focused on the phase transformation (from tetragonal to monoclinic) of zirconia and the associated phenomena (swelling, plasticity,...).From high temperature mechanical tests performed in laboratory, the thermal and mechanical behavior laws were characterized and modeled during the zirconia transformation. Plasticity at very low stress threshold was observed. A Leblond type model has been extended by introducing a Cam-clay yield function without consolidation. In this model, the progress of the transformation is controlled by the evolution of the temperature. This model was complemented by other components of the mechanical behavior (creep, elasticity, ...). It has been validated by experimental tests under multiaxial loadings that replicate the main thermomechanical phenomena observed during cooling.In parallel, blocks casted in laboratory conditions, instrumented with thermocouples and acoustic emission sensors, allowed a numerical simulation of the change in temperature field within the block during cooling-down. This simulation took into account the solidification enthalpy and the enthalpy associated to the phase transformation, previously quantified by DTA. The implementation of the complete mechanical model integrating all the behavior components led to a calculation of the stress field changes generated by thermal gradients as a function of time and, in particular, to highlight the essential role played by the phase transformation on stress relaxation.

Neste trabalho, propõe-se um modelo numérico-computacional representativo dos processos de tratamento térmico, que seja uma ferramenta eficiente e forneça meios para um entendimento efetivo do mecanismo de geração de tensões residuais durante a têmpera de aços. Foram investigados os fenômenos térmicos, mecânicos e de transformação de fase observados na têmpera, bem como o acoplamento entre esses três fenômenos. O modelo utiliza o Método dos Elementos Finitos (MEF) e o programa ABAQUS®, além de rotinas numéricas em FORTRAN responsáveis pela resolução do problema termo-mecânico-microestrutural acoplado. A utilização de sub-rotinas, que implementam uma alteração na formulação (matemática e numérica) do programa de Elementos Finitos, permite incluir no modelo as informações presentes em uma curva CRC (curva de resfriamento contínuo) do aço SAE 4140, implementando o cálculo de deformações da peça simulada de modo incremental e cumulativo. Os resultados mostram que a utilização das sub-rotinas desenvolvidas neste trabalho permitiu implementar, conjuntamente com o programa ABAQUS®, o cálculo das frações volumétricas, durezas, distorções e tensões que surgem em um tratamento térmico de têmpera, simulando as transformações martensítica, perlítica, bainítica e ferrítica. Os resultados dos modelos foram equivalentes aos relatados pela literatura, principalmente no que se refere às durezas e tensões associadas a cada transformação de fase. Em particular, os resultados indicam que a transformação martensítica está sempre associada à formação de tensões compressivas. Ensaios experimentais foram realizados a fim de validar os modelos computacionais propostos, utilizando-se um teste Jominy adaptado e instrumentado, de modo a permitir a amostragem da variação de temperaturas no material. Ensaios metalográficos permitiram correlacionar as frações volumétricas transformadas durante a têmpera do corpo de prova Jominy aos valores calculados pelo modelo numérico acoplado. / The objective of this work is to analyze residual strains and stresses and volumetric expansion due to phase transformations that occur during quenching of a steel body, as well as to predict these phase transformations. The coupled thermo-mechanical-phase transformation problem was analyzed, specifically in terms of the quenching process. Different computational models were presented, based on the finite element software ABAQUS® and on the use of FORTRAN subroutines. The continuous-cooling-transformation (CCT) diagrams of SAE 4140 steel are represented differently in each model, depending on the transformed phases and correspondent volumetric expansion. These subroutines include information from the CCT diagrams of SAE 4140 into a FORTRAN code. The subroutine calculates all the microstructures resulting from quenching (ferrite, pearlite, bainite, and martensite), depending on cooling rate. The numerical analysis conducted in this work provided results in terms of the temperature and stresses developed during quenching. The properties determined in this work are hardness, yield strength, volumetric fraction and distortion. Hardness has been predicted by the use of analytical equations. The finite element analyses were able to explain and reproduce phenomena observed during quenching of a steel cylinder. In particular, numerical results indicated that martensite formation is always related to a compressive stress field. The results of the models are in qualitative agreement with data provided by literature, particularly, in relation to the stresses originated by each different phase transformation during quenching process. Experimental testing was conducted, based on the analysis of the quenching of a Jominy probe, in order to validate the computational model developed in this work.

A proposta da modificação química da superliga MAR-M247 através da substituição do Ta pelo Nb (em átomos) foi baseada nas seguintes informações: (1) O Nb desempenha funções muita parecidas com as do Ta nas superligas à base de Ni, como endurecedor via solução sólida da fase ? e elemento formador de fases secundárias (?? e carbonetos); (2) O Brasil tem as maiores reservas de Nb do mundo e (3) O Nb já é adicionado em diversas classes de superligas à base de Ni - fundidas convencionalmente e solidificadas direcionalmente e monocristalinas. Neste trabalho o objetivo principal foi de avaliar a viabilidade da substituição do Ta pelo Nb na superliga à base de Ni MAR-M247. As amostras da MAR-M247 e da liga modificada - MAR-M247[Nb] utilizadas na caracterização microestrutural foram obtidas por solidificação direcional no forno a vácuo do tipo forno Bridgman (Lab. de Solidificação/FEM-UNICAMP) nas seguintes condições de processamento: v = 5, 10 e 18 cm/h e G = 80°C/cm. As simulações de cálculo termodinâmico utilizando o programa Thermo-Calc foram realizadas com o objetivo de se avaliar se as temperaturas de transformação mudariam com a substituição do Ta pelo Nb. Para avaliação das propriedades mecânicas em alta temperatura e a estabilidade estrutural da superliga MAR-M247[Nb] foram realizados ensaios de fluência a 750 e 850 °C nas tensões de 840, 780 e 440 MPa. A estabilidade microestrutural da MAR-M247[Nb] foi testada por meio de ensaios de oxidação isotérmica a 1000 °C no intervalo de tempo de 30 minutos a 100 h. A substituição do Ta pelo Nb promoveu mudanças significativas principalmente nas temperaturas de formação do eutético ?/??, solvus - ?? e de fusão incipiente. As microestruturas das ligas após os experimentos de solidificação direcional a v = 5, 10 e 18 cm/h eram constituídas por dendritas da fase gama - ? e precipitados coerentes da fase gama linha - ?? (morfologia cuboidal). Na região interdendrítica da MAR-M247 e MAR-M247[Nb] solidificadas a v = 5 e 10 cm/h foram encontrados os eutéticos ?/?? e ?/Ni5(Hf,Zr). Na v = 18 cm/h a região interdendrítica era constituída apenas do eutético ?/??. A exposição a 1250 °C por 15 e 30 dias promoveu a decomposição total e a re-precipitação de carbonetos do tipo MC. No entanto, devido à contaminação por oxigênio e nitrogênio durante os tratamento térmicos, não foi atingido o equilíbrio termodinâmico em decorrência de mudanças das composições dos carbonetos MC. Nos ensaios de fluência a 750 °C, os tempos de ruptura foram de 49 h para MAR-M247 e de 39,4 h para MAR-M247[Nb] apesar dos elevados valores das tensões terem sido superestimados. A 850 °C o tempo de ruptura da MAR-M247[Nb] (trup = 359 horas) foi reduzido em 32 % em relação ao valor observado para MAR-M247 (trup = 476 horas). Os resultados dos ensaios de oxidação a 1000 °C da superliga MAR-M247[Nb] mostraram que o período transiente foi de 20 h com ganho de massa expressivo. A partir de 50 h o efeito do descolamento das camadas oxidadas durante o resfriamento das amostras foi significativo e promoveu uma variação de massa importante no intervalo de tempo de 50 a 100 h. Ensaios de oxidação em tempos mais longo deverão ser feitos para determinação da estrutura de formação das camadas e seus respectivos constituintes. / The chemistry modification in the Ni-based superalloy MAR-M247 through the replacing all Ta by Nb was based on in these statements: (1) Nb does the same function in Ni-based superalloys as Ta does, solid solution strenghtening and ?? e carbides element formers, (2) Brazil has the major ores of Nb in the world and (3) Nb has been added in all classes of Ni superalloy conventional casting, columnar and single crystal processed by directional solidification. In this study the main focus was to evaluate the feasibility of replacing Ta by Nb in the Ni - based superalloy MAR-M247. The samples of MAR-M247 and the Nb modified MAR-M247[Nb] were produced by directional solidification in a Bridgman vacuum furnace at the Solidification Research Lab/FEM - UNICAMP) in the following processing conditions: v = 5, 10 and 18 cm/h and G = 80 °C/cm. The thermodynamic simulations using Thermo-Calc program were performed to evaluate whether or not the transformation temperatures would change with the replacing of Ta by Nb. For the evaluation of mechanical properties at high temperature were performed creep rupture tests at 750 and 850 °C under the stress values of 840, 780 and 440 MPa. The isotermal oxidation tests at 1000 °C were done during the time interval of 30 min to 100 h. The replacing of Ta by Nb promoted some changes in eutectic-?/??, ??-solvus and incipient melting temperatures. After the directional solidification experiments at the v = 5, 10 and 18 cm/h the microstructural characterization has shown that for all condition the microstructures were composed by dendrites - ? and ?? - cuboidal precipitates in it. In the interdendritic region was observe the ?/?? and ?/Ni5(Hf,Zr) eutectics for v = 5 and 10 cm/h and only the ?/?? eutectics for v = 18 cm/h. The exposure at 1250 °C for the extended times promoted the formation of fine MC carbides but the equilibrium compositions have not been achieved due to the oxygen and nitrogen contamination. In the creep rupture tests at 750 °C the MAR-M247[Nb] have shown more shorter lifetime than the MAR-M247 even with overestimated tensile stress. At 850 °C the lifetime for MAR-M247[Nb] (trup = 359 h) was reduced by 32 % compared to the MAR-M247 (trup = 476 h). It was discussed that the changes in the composition of the ? phase induced Ta by Nb replacing which would led to the weakness of matrix in the MAR-M247[Nb]. The samples were oxidized at 1000 °C showed 20 h to the transient period and significant weight gain in that time. However at the extended period the weight gain had changed significantly and was precluded to predict the structure formation of oxides layer properly.

A proposta da modificação química da superliga MAR-M247 através da substituição do Ta pelo Nb (em átomos) foi baseada nas seguintes informações: (1) O Nb desempenha funções muita parecidas com as do Ta nas superligas à base de Ni, como endurecedor via solução sólida da fase ? e elemento formador de fases secundárias (?? e carbonetos); (2) O Brasil tem as maiores reservas de Nb do mundo e (3) O Nb já é adicionado em diversas classes de superligas à base de Ni - fundidas convencionalmente e solidificadas direcionalmente e monocristalinas. Neste trabalho o objetivo principal foi de avaliar a viabilidade da substituição do Ta pelo Nb na superliga à base de Ni MAR-M247. As amostras da MAR-M247 e da liga modificada - MAR-M247[Nb] utilizadas na caracterização microestrutural foram obtidas por solidificação direcional no forno a vácuo do tipo forno Bridgman (Lab. de Solidificação/FEM-UNICAMP) nas seguintes condições de processamento: v = 5, 10 e 18 cm/h e G = 80°C/cm. As simulações de cálculo termodinâmico utilizando o programa Thermo-Calc foram realizadas com o objetivo de se avaliar se as temperaturas de transformação mudariam com a substituição do Ta pelo Nb. Para avaliação das propriedades mecânicas em alta temperatura e a estabilidade estrutural da superliga MAR-M247[Nb] foram realizados ensaios de fluência a 750 e 850 °C nas tensões de 840, 780 e 440 MPa. A estabilidade microestrutural da MAR-M247[Nb] foi testada por meio de ensaios de oxidação isotérmica a 1000 °C no intervalo de tempo de 30 minutos a 100 h. A substituição do Ta pelo Nb promoveu mudanças significativas principalmente nas temperaturas de formação do eutético ?/??, solvus - ?? e de fusão incipiente. As microestruturas das ligas após os experimentos de solidificação direcional a v = 5, 10 e 18 cm/h eram constituídas por dendritas da fase gama - ? e precipitados coerentes da fase gama linha - ?? (morfologia cuboidal). Na região interdendrítica da MAR-M247 e MAR-M247[Nb] solidificadas a v = 5 e 10 cm/h foram encontrados os eutéticos ?/?? e ?/Ni5(Hf,Zr). Na v = 18 cm/h a região interdendrítica era constituída apenas do eutético ?/??. A exposição a 1250 °C por 15 e 30 dias promoveu a decomposição total e a re-precipitação de carbonetos do tipo MC. No entanto, devido à contaminação por oxigênio e nitrogênio durante os tratamento térmicos, não foi atingido o equilíbrio termodinâmico em decorrência de mudanças das composições dos carbonetos MC. Nos ensaios de fluência a 750 °C, os tempos de ruptura foram de 49 h para MAR-M247 e de 39,4 h para MAR-M247[Nb] apesar dos elevados valores das tensões terem sido superestimados. A 850 °C o tempo de ruptura da MAR-M247[Nb] (trup = 359 horas) foi reduzido em 32 % em relação ao valor observado para MAR-M247 (trup = 476 horas). Os resultados dos ensaios de oxidação a 1000 °C da superliga MAR-M247[Nb] mostraram que o período transiente foi de 20 h com ganho de massa expressivo. A partir de 50 h o efeito do descolamento das camadas oxidadas durante o resfriamento das amostras foi significativo e promoveu uma variação de massa importante no intervalo de tempo de 50 a 100 h. Ensaios de oxidação em tempos mais longo deverão ser feitos para determinação da estrutura de formação das camadas e seus respectivos constituintes. / The chemistry modification in the Ni-based superalloy MAR-M247 through the replacing all Ta by Nb was based on in these statements: (1) Nb does the same function in Ni-based superalloys as Ta does, solid solution strenghtening and ?? e carbides element formers, (2) Brazil has the major ores of Nb in the world and (3) Nb has been added in all classes of Ni superalloy conventional casting, columnar and single crystal processed by directional solidification. In this study the main focus was to evaluate the feasibility of replacing Ta by Nb in the Ni - based superalloy MAR-M247. The samples of MAR-M247 and the Nb modified MAR-M247[Nb] were produced by directional solidification in a Bridgman vacuum furnace at the Solidification Research Lab/FEM - UNICAMP) in the following processing conditions: v = 5, 10 and 18 cm/h and G = 80 °C/cm. The thermodynamic simulations using Thermo-Calc program were performed to evaluate whether or not the transformation temperatures would change with the replacing of Ta by Nb. For the evaluation of mechanical properties at high temperature were performed creep rupture tests at 750 and 850 °C under the stress values of 840, 780 and 440 MPa. The isotermal oxidation tests at 1000 °C were done during the time interval of 30 min to 100 h. The replacing of Ta by Nb promoted some changes in eutectic-?/??, ??-solvus and incipient melting temperatures. After the directional solidification experiments at the v = 5, 10 and 18 cm/h the microstructural characterization has shown that for all condition the microstructures were composed by dendrites - ? and ?? - cuboidal precipitates in it. In the interdendritic region was observe the ?/?? and ?/Ni5(Hf,Zr) eutectics for v = 5 and 10 cm/h and only the ?/?? eutectics for v = 18 cm/h. The exposure at 1250 °C for the extended times promoted the formation of fine MC carbides but the equilibrium compositions have not been achieved due to the oxygen and nitrogen contamination. In the creep rupture tests at 750 °C the MAR-M247[Nb] have shown more shorter lifetime than the MAR-M247 even with overestimated tensile stress. At 850 °C the lifetime for MAR-M247[Nb] (trup = 359 h) was reduced by 32 % compared to the MAR-M247 (trup = 476 h). It was discussed that the changes in the composition of the ? phase induced Ta by Nb replacing which would led to the weakness of matrix in the MAR-M247[Nb]. The samples were oxidized at 1000 °C showed 20 h to the transient period and significant weight gain in that time. However at the extended period the weight gain had changed significantly and was precluded to predict the structure formation of oxides layer properly.

L’objectif fondamental de cette étude est de montrer la faisabilité de l’élaboration des couches épaisses de zircone non dopée, en contrôlant la microstructure et l’état mécanique, par MOCVD et par Sol-Gel. Dans un premier temps, nous avons essayé d’optimiser les conditions de dépôt de MOCVD, en faisant varier ou en jouant sur les différents paramètres du procédé, conduisant à l’obtention des couches de ZrO2 micrométriques et denses. La stabilité de la phase quadratique de la zircone est conditionnée par la pression partielle en oxygène, la température du substrat ainsi que l’épaisseur du dépôt. La texture cristallographique de type {100} est obtenue pour les dépôts réalisés à une température de substrat T ≤ 850°C et pour de faibles pressions totales. Concernant l’état mécanique des couches de zircone, l’augmentation de l’épaisseur de la couche peut relaxer les contraintes résiduelles de tension au sein du dépôt. Ce phénomène s’accentue au-delà d’une épaisseur critique suite à la création des espacements entre les colonnes de croissance de la couche. Parallèllement, nous avons montré que la qualité des dépôts Sol-Gel est maitrisée par le choix du substrat, l’utilisation de « sols » vieillis, la multiplication du nombre de couches « spin-coating », le mode de dépôt ainsi que la température de recuit. Certaines propriétés caractéristiques du dépôt telles que la cristallisation, la composition de phase et l’adhérence sont aisément contrôlées respectivement par l’âge du sol, la température de recuit et le coefficient de dilatation thermique associé au substrat utilisé. La microstructure (changement de phases, taille des cristallites, texture cristallographique) et les contraintes internes (thermiques et intrinsèques) ont été caractérisées. Le Sol-Gel présente l’avantage de proposer des couches de zircone très peu contraintes par rapport aux films obtenus par le procédé MOCVD. Quel que soit le procédé de dépôt, MOCVD et/ou Sol-Gel, l’élaboration des films de ZrO2 orientés demeure fonction de la température du traitement. La tentative d’élaborer des multicouches de zircone par un couplage MOCVD/Sol-Gel montre la possibilité de sélectionner des paramètres de dépôt propices à la fabrication d’un film présentant un état microstructural et mécanique contrôlé et voulu. / The fundamental purpose of this study is to demonstrate the feasibility to obtain an undoped zirconia thick film, by controlling the microstructure and mechanical state, using MOCVD and Sol-Gel technique. Firstly, we try to optimize the MOCVD deposition conditions, by varying the different process parameters, leading to the production of ZrO2 micrometric and dense films. The stability of the tetragonal zirconia phase depends on the oxygen partial pressure, the substrate temperature and the film thickness. The crystallographic texture of {100} type is obtained for the deposits obtained under a substrate temperature T ≤ 850°C and a low total pressure. Concerning mechanical state of the zirconia films, the thickness increasing can relax the tensile residual stress within the deposit. This phenomenon accents beyond a critical thickness due to the creation of columns spaces during film growth. In the second part, we show that the quality of the Sol-Gel deposition is controlled by substrate origin, use of aged sol, increase of “spin-coating” layers number, deposition mode and annealing temperature. Some deposit characteristics such as crystallization, phase composition and film adhesion are easily controlled by sol aging, annealing temperature and thermal expansion coefficient associated to the used substrate, respectively. The microstructure (phase change, crystalline size, crystallographic texture) and the internal stresses (thermal and residual) were characterized. The Sol-Gel technique has the advantage of providing zirconia films with low stress level compared to the films obtained by MOCVD. Regardless of the deposition process, MOCVD and / or Sol-Gel, the development of ZrO2 oriented films is in function of the treatment temperature. The attempt to get multilayer zirconia by coupling MOCVD/Sol-Gel methods shows the possibility to choose the deposition parameters in order to produce films with controlled and wanted microstructure and mechanical state.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-05-05T19:45:04Z No. of bitstreams: 1 RicardoSousaFerreira.pdf: 2802747 bytes, checksum: 0d4bf284379fe32714f3b112e464cf64 (MD5) / Made available in DSpace on 2017-05-05T19:45:04Z (GMT). No. of bitstreams: 1 RicardoSousaFerreira.pdf: 2802747 bytes, checksum: 0d4bf284379fe32714f3b112e464cf64 (MD5) Previous issue date: 2016-03-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão (FAPEMA) / Currently, the amino acid salt crystals are extensively studied, primarily because of their possible application in opto-electronic devices. Many amino acids complexed with chlorine crystals were synthesized and characterized, and suggested as promising materials in frequency conversion. However, the characterization of L-isoleucine hydrochloride monohydrate crystals (L-Ile.H2O.HCl) is poor because to date, one article has been published and only the authors determined the crystal structure of the synthesized material. Thus, the objective of this study was to synthesize crystals of L-Ile.HCl.H2O by the method of slow evaporation and characterize them by X-Ray Fluorescence (XRF), Differential Thermal Analysis (DTA), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TG), X-Ray diffraction (XRD) as a function of temperature and time, Raman scattering as a function of temperature and heat treating the material in a sealed glass tube with argon atmosphere for 24h at 170 °C. The XRF confirms the presence of chlorine. The XRD at 25 oC shows that the crystal belongs to orthorhombic system with lattice parameters a = 5.873 (3) Å, b = 24.814 (4) Å, c = 6.873 (5) Å. The TG, DTA and DSC indicated that the material loses water of solvation and crystallization at approximately 55 °C and 132 °C, respectively .The DRX a function of temperature, the material shows phase transformation starts at 60 oC and 155 oC extends to. The XRD at 140 oC shows that after 32h, the crystal loses water and chlorine. Raman spectra as a function of temperature, confirm the phase transformation at 60 °C and 100 °C. The material when subjected to 170 °C, for a period of 24 sealed in a glass tube with an inert atmosphere (Ar) and undergoes vaporization sublimate the same orthorhombic phase, when it has its temperature reduced to 25 °C. Therefore, the L-Ile.HCl.H2O crystal is not a material suitable for use in optical devices due to their low thermal stability. / Atualmente, os cristais de sais de aminoácidos são amplamente estudados, principalmente devido à sua possível aplicação em dispositivos opto eletrônicos. Muitos cristais de aminoácidos complexados com cloro foram sintetizados, caracterizados e sugeridos como materiais promissores na conversão de frequência. No entanto, a caracterização de cristais de L-isoleucina hidroclorídrica monohidratada (L-Ile.H2O.HCl) é deficiente, pois até o momento, um único artigo foi publicado e os autores apenas determinaram a estrutura cristalina do material sintetizado. Dessa forma, o objetivo do presente trabalho foi sintetizar cristais de L-Ile.HCl.H2O pelo método de evaporação lenta e caracterizá-los por Fluorescência de Raios-X (FRX), Análise Térmica Diferencial (DTA), Calorimetria Exploratória Diferencial (DSC), Análise Termogravimétrica (TG), Difração de Raios-X (DRX) em função da temperatura e do tempo, espalhamento Raman em função da temperatura e tratar termicamente o material em um tubo de vidro selado com atmosfera de argônio por 24h a 170 oC. A FRX confirmou a presença de cloro. O DRX a 25 oC mostrou que o cristal pertence ao sistema ortorrômbico, com parâmetros de rede a = 5,873(3) Å, b = 24,814(4) Å, c = 6,873(5) Å. O TG, DTA e DSC indicaram que o material perde água de solvatação e cristalização em aproximadamente 55 oC e 132 oC, respectivamente. O DRX em função da temperatura, revelou que o material inicia transformação de fase em 60 oC e se estende até 155 oC. O DRX a 140 oC mostrou que após 32h, o cristal perdeu água e cloro. Os espectros Raman em função da temperatura, confirmaram as transformações de fase em 60 oC e 100 oC. O material quando submetido a 170 oC, por um período de 24h selado em um tubo de vidro com atmosfera inerte (Ar), sofreu vaporização e ressublimou na mesma fase ortorrômbica, quando teve sua temperatura reduzida a 25 oC. Portanto, o cristal de L-Ile.HCl.H2O não é um material indicado para ser utilizado em dispositivos ópticos devido a sua baixa estabilidade térmica.

The thesis consists of two parts. Part 1 deals with the preparation of thin films and sub-micron powders of complex metal oxides by nebulized spray pyrolysis (NSP) and Part 2 consists of Brillouin scattering studies of solid materials exhibiting interesting phase transitions. The simple technique of NSP has been employed to prepare thin films of A12O3, PbTiO3, Pb(Zr0.5Ti0.5)O3 (PZT) and PbZrO3 on single crystal substrate. The films were characterized by various techniques for their composition, structure, morphology and dielectric properties. Ferroelectric (FE) films of the configuration FE/LaNiO3/SiO2/Si (FE = PbTiO3 and PZT), wherein the LaNiO3 barrier electrode was also deposited on the SiO2/Si substrate by NSP, have been investigated. The films exhibit satisfactory ferroelectric properties. PbZrO3 films deposited on LaNiO3/SiO2/Si substrates show good features, including a reversible AFE ↔ FE transition. Sub-micron particles of TiO2, ZrO2, Pb(Zr0.5Ti0.5)O3, Al2O3, S1O2 and mullite have been prepared by NSP and characterized by various techniques. Brillouin scattering has been used, for the first time, not only to characterize the Peierls transition but also the incommensurate to commensurate transition in the one-dimensional blue bronze, K0.3M0O3. The charge density wave transition in NbSe2 has also been investigated by Brillouin scattering. The charge ordering and antiferromag-netic transitions in single crystals of the rare earth manganates, Nd0.5Ca0.5MnO3 and Pr0.63Ca 0.37MnO3, have been investigated by Brillouin scattering. It is noteworthy that the temperature variation of the Brillouin shift and intensity parallel to that of the magnetization, thereby throwing light on magnetic excitations in charge-ordered state. Brillouin scattering investigations of C60 and C70 films have yielded values of the elastic moduli.

Agitated dispersions of one liquid in another immiscible liquid are widely used in chemical industry in operations such as liquid-liquid extraction, suspension polymerisation, and blending of polymers. When holdup of the dispersed phase is increased, in an effort to increase the productivity, at a critical holdup, the dispersed phase catastrophically becomes the continuous phase and vice versa. This phenomenon is known as phase inversion. Although the inversion phenomenon has been studied off and on over the past few decades, the mechanism of phase inversion (PI) has yet not become clear. These studies have however brought out many interesting aspects of PI, besides unravelling the effect of physical and operational variables on PL Experiments show that oil-in-water (o/w) and water-in-oil (w/o) dispersions behave very differently, e.g water drops in w/o dispersions contain oil droplets in them, but oil drops in o/w dispersions contain none, dispersed phase hold up at which inversion occurs increases with agitation speed for w/o dispersions but decreases for o/w dispersions. A common feature of both types of dispersions however is that as agitation speed is increased to high values, inversion holdups reach a constant value. A further increase in agitation speed does not change inversion hold up. Although this finding was first reported a long time ago, the implications it may have not received any attentions. In fact, the work reported in the literature since then does not even mention it. The present work shows that this finding has profound implications. Starting with the finding that at high agitation speed inversion hold up does not change with agitation speed, the present work shows that inversion hold up also does not change with agitator diameter, type of agitator and vessel diameter. In these experiments, carried out in agitated vessel, energy was introduced as a point source. The experiments carried out with turbulent flow in annular region of two coaxial cylinders, inner one rotating, in which energy is introduced nearly uniformly throughout the system, show that the inversion holdup remains unchanged. These results indicate that constant values of inversion holdups for a given liquid-liquid systems (o/w and w/o) are properties of the liquid-liquid systems alone, independent of geometrical and operational parameters. A new hypothesis is proposed to explain the new findings. Phase inversion is considered to occur as a result of imbalance between breakup and coalescence of drops. Electrolytes, which affect only coalescence of drops, were therefore added to the system to investigate the effect of altering coalescence of drops on phase inversion. The experiments performed in the presence of electrolyte KI at various concentrations indicate that addition of electrolyte increases the inversion holdup for both o/w and w/o dispersions for three types of systems: non polar-water, polar-water and immiscible organic-organic. Higher the concentration of electrolyte used, higher was the holdup required for phase inversion. These findings indicate that while the addition of electrolyte increases coalescence of drops in lean dispersions, it has exactly opposite effect on imbalance of breakage and coalescence of drops at high holdups near phase inversion point. The opposite effect of electrolytes in lean and concentrated dispersions could be explained qualitatively, but only in part in the light of a new theory, involving multi-particle interactions. The phase inversion phenomenon is quantified in a simple manner by testing the breakage and coalescence rate expressions available in literature. It has been found that, equilibrium drop size (where breakage and coalescence events are in dynamic equilibrium) approaches infinity near phase inversion holdup which is not an ex perimentally observed fact. To capture the catastrophic nature of phase inversion, two steady state approach is proposed. The two steady states namely the stable steady state and unstable steady state, are achieved by modifying the expression for coalescence frequency on the basis of (i) shear coalescence mechanism and, (ii) recognising the fact that at high dispersed phase holdup the droplets are already in contact with each other at all times and hence rendering the second order coales cence process to a first order one. Using two steady states approach, catastrophic phase inversion is shown to occur at finite drop size.