Orientador: Miguel Jafelicci Junior / Banca: Sonia R. H. Mello Castanho / Banca: Daniel Rodrigues / Banca: Sidney José Lima Ribeiro / Banca: Celso Valentim Santilli / Resumo: Partículas magnéticas de ferrita de Ítrio (YIG) foram preparadas através da heterocoagulação da sílica sobre a ferrita de ítrio. A ferrita de ítrio foi obtida através do processo de nucleação homogênea, controlando a rota química a partir da hidrólise de cátions em meio ácido. A heterocoagulação foi induzida pela hidrólise do tetraetilortosilicato (TEOS) em diferentes meios de dispersão da ferrita de ítrio. Os produtos dispersos foram calcinados e caracterizados por magnometria de amostra vibrante, espectroscopia fotoeletrônica de raios X, microscopias eletrônicas de varredura e de transmissão, difração de elétrons, análise térmica diferencial, difratometria de raios X e mobilidade eletroforética. A camada de sílica que recobre a ferrita de ítrio foi identificada por microscopia eletrônica de transmissão. Difração de elétrons permitiu distinguir a fase policristalina da ferrita de ítrio e a sílica. A ausência dos picos de Fe e Y no espectro de XPS das partículas confirmam que o processo de heterocoagulação foi efetivo. Comparando as propriedades magnéticas da ferrita de ítrio e do sistema sílica/ferrita de ítrio infere-se que as propriedades de magnetização de saturação (Ms) e de campo coercivo (Hc) variaram em função da camada de sílica. / Abstract: Yttrium iron garnet (YIG) particles were coated with silica for control of their synthesis, improving the performance of system and stabilization of magnetic properties. Well-defined magnet particles were prepared by heterocoagulating silica on yttrium iron garnet. Yttrium iron garnet was obtained by homogeneous nucleation process, controlling the chemical routes from cation hydrolysis in acid medium. The heterocoagulation was induced by hydrolysis of tetraethylorthosilicate (TEOS) in appropriate yttrium iron garnet dispersion medium. Dispersed calcinated product was and characterized by vibrating sample magnetometry, X-ray photoemission spectroscopy, transmission and scanning electron microscopies, small area electron diffraction, differential thermal analysis, X-ray diffractometry and electrophoretic mobility. The pure systems YIG and Silica particles dispersions show appropriated physical-chemistry characteristics to be heterocoagulated. The shell of silica on YIG was identified by transmission electron microscopy and small area electron diffraction allowed to distinguish both silica and polycrystalline YIG phases. The absence of Fe and Y peaks on the particle surface XPS measurements confirmed that the heterocoagulation process was carried out by X-ray photoemission spectroscopy Comparing the magnetic measures of the YIG and silica on YIG samples, the magnetic properties of Ms were reduced and of Hc varied in function of the cover layer. / Doutor

Orientador: Devaney Ribeiro do Carmo / Banca: Urquisa de Oliveira Bicalho / Banca: Everaldo Carlos Venancio / Resumo: No presente trabalho, a 3-cloropropil sílica gel (SG) e o octa-(3-cloropropil)silsesquioxano (SS) foram preparados e organofuncionalizados com grupos imidazol e os materiais obtidos da funcionalização foram descritos como SGI e SSI, respectivamente. Os materiais funcionalizados foram preliminarmente caracterizados por técnicas tais como: espectroscopia na região do infravermelho (FTIR), difração de raios-X (DRX), microscopia eletrônica de varredura (MEV), além de análise de área superficial e porosidade para o precursor SG e o produto SGI. Foram realizados estudos de adsorção de íons metálicos (Cu2+ e Cd2+) para o SGI e SSI em diferentes meios, tais como: aquoso, etanol 42% e etanol 99%. Determinou-se o tempo de equilíbrio de adsorção para todos os meios e posteriormente, determinou-se a capacidade de adsorção (Nf) através de isotermas com diferentes concentrações molares dos íons metálicos, onde se observou que o SSI possui uma capacidade adsorvente maior que o SGI e ambos os adsorventes tem uma capacidade de adsorção maior para íons Cu2+ do que para os íons Cd2+. Os valores de Nf aumentaram de acordo com a seguinte ordem de solventes: água < etanol 42% < etanol 99%. Em uma segunda etapa do trabalho, após a adsorção dos íons metálicos (Cd2+ e Cu2+) pelo SGI e pelo SSI, reagiu-se os mesmos com ferricianeto de potássio (hexacianoferrato de potássio - HCF) formando-se assim os materiais CdHSGI, CuHSGI, CdHSSI e CuHSSI, respectivamente. Estes materiais foram caracterizados por espectroscopia na região do infravermelho (FTIR), difração de raios-X (DRX), espectroscopia na região do UV-visível (Reflectância difusa) e voltametria cíclica, além de serem testados na determinação eletrocatalítica de substâncias de interesse biológico. Foram realizados estudos voltamétricos da oxidação... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In the present work, 3-chloropropyl silica gel (SG) and octa-(3-chloropropyl)silsesquioxane (SS) were organofunctionalized with imidazole groups and the materials obtained of the functionalization were described as SGI and SSI, respectively. The functionalized materials were preliminarily characterized by very techniques such as: infrared spectroscopy (FTIR), X- ray diffraction (XRD), scanning electron microscopy (SEM), and also analysis of surface area and porosity for the precursor SG and the product SGI. Studies of adsorption were carried for metal ions (Cu2+ and Cd2+) for SGI and SSI in different media, such as: aqueous, ethanol 42% and ethanol 99%. It was determined the adsorption equilibrium time for all media and posteriorly, it was determined adsorption capacity (Nf) through isotherms with different molar concentrations of metal ions, where it was observed that SSI has an adsorption capacity greater than the SGI and both adsorbents have a superior adsorption capacity for ions Cu 2+ than ions Cd2+. The values of Nf increased according the following order of solvents: water < ethanol 42% < ethanol 99 %. After adsorption of metal ions (Cd2+ and Cu2+) by SGI and SSI, it was reacted with potassium ferricyanide (potassium hexacyanoferrate - HCF) thus forming the materials CdHSGI, CuHSGI, CdHSSI and CuHSSI, respectively. These materials were characterized by infrared spectroscopy (FTIR), X-ray diffraction (XRD), spectroscopy in the UV-visible (diffuse reflectance) and cyclic voltammetry and tested in the electrocatalytic determination of biologically important substances. Voltammetric studies of the electrocatalytic oxidation of ascorbic acid were carried out using CdHSGI and CdHSSI modified carbon paste electrodes, respectively. The CdHSGI modified electrode was sensitive to... (Complete abstract click electronic access below) / Mestre

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An investigation was conducted on the reaction between silica glass and the refractory metals, Mo, V, Nb, Ta, Ti and Zr. The metals were heated to 1650°C under vacuum (5x10⁻⁴m.m. of Hg.) in contact with the silica. The interface was examined metallographically. The formation of compounds was examined by X-ray diffraction technique. A liquid layer was formed by reaction of the metals with silica. This reaction was responsible for bonding between the two phases. Vanadium and tantalum showed the best bonding characteristics. Niobium formed only a fair bond. In the case of molybdenum and titanium little adhesion occurred. Experimental observations and theoretical considerations indicated that in most cases the liquid was a low fusible silicate. The nature of the reaction was found to be essentially oxidation of the metal followed by solution of the oxides in the glass. Vanadium oxides are rapidly dissolved in silica causing extensive corrosion of the metal. The oxides of niobium and tantalum do not dissolve so rapidly. Only molybdenum showed good corrosion resistance under experimental conditions. The oxides found at room temperature were respectively VO₀․₉, Nb₂O₅, Ta₂O₅ and MoO₉. X-Ray data showed that tantalum - silica interface contained other species that could be silicon, silica, sub-oxides, silicides and crystallised silicates. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Silica (inorganic)-g-polymer (organic) hybrid materials with a large variety of functionality have been studied intensively because of the improvement in their physical and chemical properties (e.g., thermal, mechanical, electrical, magnetic properties, etc.) with respect to conventional organic and inorganic materials. 1–3 This research work introduces a new strategy based on in situ formation of poly(methyl methacrylate) block copolymer grafted silica nanoparticles. The thesis is divided into two major parts. In the first part, the atom transfer radical polymerization (ATRP) method was used to synthesize poly(methyl methacrylate-b-trimethoxysilyl propyl methacrylate) (PMMA-b-PTMSPMA); and poly(methyl methacrylate-b-trimethoxysilyl propyl acrylate) (PMMA-b-PTMSPA) block copolymers. Gel permeation chromatography (GPC) was performed to determine the number-average molecular weight (Mn) and polydispersity index (Đ) of PMMA-b PTMSPMA and PMMA-b-PTMSPA. In addition, proton nuclear magnetic resonance spectroscopy (1H NMR) was used to confirm the successful synthesis of the above copolymers. In the second part, the copolymers were used to form silica nanoparticles grafted with poly(propyl methacrylate-b-methyl methacrylate) [silica-g-(PPMA-b PMMA)] and silica nanoparticles grafted with poly(propyl acrylate-b-methyl methacrylate) [silica-g-(PPA-b-PMMA)]. Fourier transform infrared spectroscopy (FT-IR) and 29Si solid-state NMR were performed to confirm the formation of silica-g-(PPMA-b PMMA) and silica-g-(PPA-b-PMMA). Additionally, thermogravimetric analysis (TGA) was performed to assess the thermal decomposition of silica-g-(PPMA-b-PMMA) and silica-g-(PPA-b-PMMA). Multiple microscopic techniques such as TEM, cryo-TEM, SEM, and AFM were used to study micellization of the silica-g-(PPMA-b-PMMA) and silica-g-(PPA-b-PMMA) in tetrahydrofuran (THF) and chloroform

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