Orientador: José de los Santos Guerra / Resumo: Os materiais vítreos a base de TeO2 têm sido amplamente estudados e suas potencialidades requerem particular atenção para o desenvolvimento de novos sistemas vitrocerâmicos. Neste trabalho, com o objetivo de formar nanocristais de BaTiO3 (na fase tetragonal) através da estequiometria do sistema xBaO–xTiO2–(100–2x)TeO2 (BTT), tratamentos isotérmicos foram realizados sob diferentes condições. Desse modo, foram investigadas as propriedades físicas do sistema BTT para as composições x = 7,5, 10,0 e 12,5 mol%, de nomenclaturas 85BTT, 80BTT e 75BTT, respectivamente. As amostras foram obtidas pelo método convencional de fusão, seguido de um rápido resfriamento (quenching). Particularmente, suas propriedades térmicas, estruturais e óticas foram analisadas a partir de Análise Térmica Diferencial (DTA), Difração de raios-X (DRX), Espectroscopia Raman (ER) e de Absorção Ótica (AO). Os resultados revelaram uma forte influência das concentrações de BaO-TiO2 nas propriedades estudadas, que pode ser associada à quebra de simetria da unidade estrutural elementar (TeO4), devido à variação estrutural TeO4TeO3+1TeO3, ao caráter covalente das ligações TeO, a presença do par de elétrons livres na camada de valência do TeO2 e, consequentemente, à formação de oxigênios não ligantes (NBO’s). As bandas de cortes no UV-Vis apresentaram absorção fundamental na região de 400-450nm, onde a rede mais polimerizada da composição 80BTT proporcionou os valores mais elevados do gap indireto (Ei = 2,87eV) e ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: TeO2-based glassy materials have been extensively studied and their potentialities require particular attention for the development of new ceramic-glass materials. In this work, viewing the formation of tetragonal BaTiO3 nanocrystals by considering the xBaO–xTiO2–(100–2x)TeO2 (BTT) stoichiometry formula, isothermal treatments were performed under different conditions. Thus, the physical properties of the BTT system were investigated for compositions with x = 7.5, 10.0 and 12.5 mol%, hereafter labeled as 85BTT, 80BTT and 75BTT, respectively. The samples were obtained by the conventional fusion method followed by rapid cooling (known as the quenching method). Particularly, the thermal, structural and optical properties were studied from Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), Raman Spectroscopy and Optical Absorption (OA) analyses. The results showed a strong influence of the BaO-TiO2 concentrations on the studied properties, which could be related to the symmetry breaking of the elemental structural unit (TeO4), due to the TeO4→TeO3+1→TeO3 structural variation, the covalent character of the Te−O bonds, the presence of the lone-pair valence electrons in the TeO2 and, consequently, the formation of non-binding oxygen (NBO's). The UV-Vis cut-off bands revealed the fundamental absorption in the 400-450nm region, where the most polymerized network of the 80BTT samples has provided the highest indirect (Ei = 2.87eV) and direct (Ed = 2.96eV) gap values. The resu... (Complete abstract click electronic access below) / Doutor

Ce travail de thèse inclut deux parties : i) l'étude fondamentale de la formation de cristaux zéolithiques ; et ii) la préparation de massifs zéolithiques de taille centimétriques à porosité interparticulaire contrôlée. La première partie de ce travail est donc consacrée à l'étude de l'effet de la microstructure (propriétés physiques et texturales) et de la composition chimique du gel sur la vitesse de nucléation et la taille des cristaux formés. Les résultats de cette étude se résument par le rôle important que joue la composition du gel (plus particulièrement sa concentration en hydroxyde de cation alcalin) sur le degré de polymérisation des particules du gel, la détermination de sa microstructure et par conséquent sur la vitesse de nucléation des zéolithes et la taille des cristaux. Les connaissances acquises dans la première partie ont été utilisées dans le développement du deuxième objective. Notamment, la préparation de massifs zéolithiques de taille centimétrique de types structuraux *BEA et MFI. Le contrôle post-synthèse de la porosité interparticulaire de ces massifs était essentiel pour leur utilisation dans des applications bien précises. A cette fin, une méthode en deux étapes, comportant un assemblage de nanocristaux de zéolithes préformés (en présence ou en absence d'un liant) puis un traitement de croissance secondaire pour l'élimination de la porosité interparticulaire, a été mise en œuvre. Plusieurs traitements de croissance secondaire furent évalués selon le type de zéolithe étudié. Une attention particulière fut accordée à l'étude de l'évolution du liant au cours des processus de préparation et de calcination des massifs zéolithiques. / The present study includes two parts: i) fundamental study of zeolite nucleation-crystal growth mechanism; and ii) preparation of zeolite bodies with controlled interparticle porosity.Thus the first part of the present work deals with the study of the effect of physico-chemical characteristics of initial hydrogel on the nucleation and crystal growth kinetics of zeolite crystals. The obtained data revealed that the concentration of alkali metal hydroxide in the initial system controls the rate of polymerization of the aluminosilicate species, the size of initial gel particles, and the textural properties of the gel. Consequently, the following reaction was to great extent predetermined by the events taking place during mixing the initial reactants.The second part of this work was targeted at the preparation of centimeter-sized zeolite bodies of *BEA- and MFI-type with reduced to minimum inter-particle porosity. A preparation method consisting in assembling of zeolite nanocrystals (with or without a binder) was developed and further optimized. The preformed bodies were subjected to a hydrothermal treatrnent in a fresh zeolite synthesis solution in order to till up the inter-particle porosity. Depending onthe zeolite type, different methods of secondary growth treatrnents were employed. A particular attention has been paid on the study of the binder evolution during the calcination and secondary growth processes.