Uso das técnicas de difusão em filmes finos por gradiente de concentração (DGT) para avaliação de metais disponibilizados em passivos de mineração de Urânio

The objective of this work is to use the technique of diffusion by concentration gradient films (DGT) for evaluation of dissolved urano in hydro bodies. For this we chose this work as a systems investigation of water bodies in the region of Poços de Caldas, state of Minas Gerais, because, there is a large amount of mining of uranila. The technique to be used to evaluate the potential for dissolved metals analysis involves the use of passive samplers with application in in situ. This allows detection with excellent sensitivity and selectivity allowing the determination of the labile fraction of dissolved metals

Propriedades físicas de vidros Sb2O3-P2O5

This work presents experimental results of some physical properties of antimony phosphate glasses with compositions (x) Sb2O3 - (1-x) P2O5 (x = 0.75, 0.85, 0.90). Mechanical, thermal, optical and electrical properties were investigated: density, elastic moduli (Young's moduli and Poisson's ratio), Vickers microhardness, coefficient of thermal expansion, glass transition temperature, refractive index and electrical conductivity (for x = 0.75). There was no evidence of electronic conductivity by bipolaron hopping. Measurements of energy dispersive spectroscopy (EDS) showed that volatilization of Sb2O3 takes place during the glass melting

Preparo (calibração e tratamento) de Dosímetros Termoluminescetes de Flureto de Lítio (TLD-LiF)

A Dosímetria Termoluminescente (TLD) é uma ferramenta extremamente versátil para a avaliação da dose absorvida por tecidos humanos, devido à interação dos mesmos com a radiação ionizante. As características termoluminescentes (TL) do fluoreto de lítio (LiF) foram estudadas extensivamente primeiramente por apresentar número atômico muito próximo ao do tecido humano e, portanto, conseguir quantificar com fidelidade a radiação recebida na ordem de μGy (micro Gray) a kGy (kilo Gray) . Foram abordados os princípios físicos envolvido no procedimento de calibração e tratamento dos dosímetros (total de 224 pastilhas), os quais foram separados, após tratamento, em 75 grupos. Este trabalho foi de suma importância na aplicação dos conceitos físicos abordados durante a formação da graduação no curso de Bacharelado em Física Médica, e pode auxiliar em projetos, em andamento, junto ao grupo de pesquisa de Física Aplicada ao Radiodiagnóstico

Propriedades estruturais de géis de sílica preparados com adições de dodecil sulfato de sódio

This work aims to study the structural characteristics of silica gels obtained from the acid hydrolysis of tetraethoxysilane (TEOS) in water solutions with different concentrations of sodium dodecyl sulfate (SDS). The structural characteristics were studied in stages ranging from the wet gel to the dry stages of the gels (aerogels and xerogels). Aerogels were obtained by ambient pressure drying (APD) after silylation process using trimethylchlorosilane (TMCS) as silylating agent. Xerogels were obtained by conventional evaporating the liquid phase from non silylated gels. The samples were characterized by nitrogen adsorption and small angle X-ray scattering (SAXS). The structure of the wet gels and of the aerogels prepared with the surfactant exhibited characteristics of mass-fractal structures with fractal dimension D in the range 2.1-2.2 for the wet gels and 2.3-2.4 for the aerogels. The characteristic size  of the fractal domain reduces while the size a0 of the primary silica particle composing the fractal structure increases with the drying of the gels, in a process in which share of the porosity is eliminated. Aerogels exhibited typical values for the specific surface of 900 m2g-1 and of 3.5 cm3.g-1 for the total pore volume. These values are correspondingly comparable to those of the aerogels prepared by supercritical drying, since the silylation process replaces hydrophilic –OH groups by hydrophobic –Si-R3 ones, inhibiting the porosity elimination on drying. The silica particle size also increases lightly with the silylation because the attachment of the –Si-R3 groups on the silica surface. The pore size distribution curves of the aerogels are similar for all samples exhibiting a maximum in around 40 nm, independent the concentration of surfactant. This suggests that the characteristic size of 40 nm is due to the association of surfactant micelles... (Complete abstract click electronic access below)

Propriedades térnicas de géis e xerogéis híbridos de sílica/orgânico à base de GPTS-TEOS com diferentes concentrações de GPTS

In the present work the thermal characteristics of gels and xerogels of Silica/organic hybrids derived from different concentrations of GPTS-TEOS were investigated by thermal analysis (TG, DTA, and DSC). The preparation of gels of the Silica/organic hybrid matrix was held through the sol-gel process, consisting by the hydrolysis of alkoxides GPTS and TEOS in proportion (1:1) and (1:2) that was promoted in acidic conditions under reflux and stirring at 80oC/2h, producing the matrix in the colloidal state (sol). Gels were prepared by addition of NH4OH to the sol, promoting gelation of sol in sealed plastics containers. Part of the gels samples was analyzed by TG, DTS and DSC techniques in order to characterize water loss and degradation of the polymeric “epoxy” groups present in the structure of the silica derived from the GPTS alkoxide. Another set of samples was dried at 80oC/48h to obtain xerogels (dried gels) and analyzed by the same techniques. We obtained the characteristics temperatures of the matrix by the techniques DTA, DSC and TG, under measurements of thermal analysis until 800oC and 600oC in case of DSC. By thermal analysis (TG, DTA, and DSC) the main endothermic events (loss of water, melting, pyrolysis) and exothermic events (burning of the polymer) of the GPTS-TEOS matrix were determined

Avaliação da membrana de troca aniônica DE 81 como ligante ba técnica de difusão em filmes finos por gradientes de concentração (DGT) para a determinação de Cromo VI

It is known that there is a wide variety of bioavailable trace metals in aquatic systems, and its determination is fundamental to predict impacts to organisms in these environments. However, the determination of the total concentration of chemicals in aquatic systems, despite its importance, does not provide necessary information for decision making or even may lead to misinterpretation of the procedures and potential risks to the system in question. This study aimed to use the technique of diffusion in thin films by concentration gradients (DGT) to evaluate the anion exchange membrane Whatman DE 81 as binder alternative in determining Cr (VI). Experiments were carried out to determine the diffusion coefficients for the material used diffusion (agarose gel). The behaviors of the binders were analyzed before the main variables of the systems, immersion time, pH and ionic strength. Then was made the assessment of potential interferences, to finally proceed with testing using actual samples in the laboratory and in situ

Análise estrutural de aerogéis via espalhamento de luz a baixo ângulo

The sol-gel process is a method for obtaining vitreous or vitro-ceramic materials which, are prepared a sol and by drying the liquid phase. This technique has been used extensively for the preparation of glassy gels, films, fibers and particles from the hydrolysis and polycondensation reactions of metal alkoxides. The usual methods for drying are: evaporation drying (xerogels), freeze drying (criogéis) and via supercritical CO2 extraction (aerogels). In the present work, we studied the preparation of silica gels by the sol-gel process from the hydrolysis of alkoxides tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTS). The hydrolysis was promoted from GPTS and TEOS in proportion (4: 1) under acidic conditions. The hydrolysis reaction was promoted inside a Becker at room temperature. After hydrolyses the prepared sol had pH 2, and kept under mechanical agitation for a period of 1 hour. In order to accelerate the polycondensation reaction, the pH was corrected to a value near 5 by slowly adding NH4OH. Then the sols were leaked in sealed polycarbonate containers and maintained for 20 days at 40°C for gelation. Silica aerogels were prepared via supercritical CO2 extraction of the wet gel at temperature and pressure higher than 31°C and 74 atm, in an autoclave specially developed for the process. The structural characteristics were studied in the dry gel (aerogel). Aerogels were then characterized by nitrogen adsorption and small angle light scattering. The nitrogen adsorption data were analyzed for the determination of the BET specific surface (SBET), the total pore volume Vp, the pore mean size (lP=4Vp/SBET), the particle mean size (lS) and the pore size distribution (PSD). And the data from small angle light scattering were analyzed to determine the correlation function (γ'), the area per unit volume (S/V), average pore size (l ) and the average particle size...

Materiais híbridos de sílica/orgânico dopados com rodamina-B: estudo da luminescência e preparação de filmes finos para aplicações em fotônica

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Características estruturais de aerogéis hidrofílicos e hidrofóbicos de sílica modificados com Dodecil Sulfato de Sódio

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Medidas de condutividade A.C. e constante dielétrica na perovskita dupla Ca1.2 La0.8 FeIrO6

This work introduces the results from the performing of impedance spectroscopy on the transition metals oxide Ca1.2La0.8FeIrO6. It was sought to understand the behavior of one sample from its impedance spectra for different AC voltages and temperature values and if an applied external magnetic field at room temperature would cause some change on it. The results revealed that the Ca1.2La0.8FeIrO6 at high temperatures shows conductive and inductive behavior and that the resistance increases with frequency, phenomenon known as Kelvin effect. At 150 K, the spectrum real part no longer consists with the theoretical prediction of Kelvin effect, starting to be influenced by the utilized voltages, condition that inexists on theory. At low temperatures (10, 20, 30 K) it was observed resistive and capacitive behavior, being possible on these conditions, associate to the sample a paralel RC circuit in series with a contact resistance with a fitting from the ZSim software. This fitting allowed the obtaining of capacitance, DC resistance and contact resistance values. The application of a 700G magnetic field at room temperature didn't cause changes on the spectra

Espectroscopia de impedância em Fe3O2BO3 e α-MnO2 dopado com cobre

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Sulfur Radicals as Tethers for the Adsorption of Aromatic Molecules on Silicon Surface

In this work we employ the state of the art pseudopotential method, within a generalized gradient approximation to the density functional theory, to investigate the adsorption process of benzenethiol and diphenyl disulfide with the silicon (001) surface. A direct comparison of different adsorption structures with Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) allow us to identify that benzenethiol and diphenyl disulfide dissociatively adsorb on the silicon surface. In addition, theoretically obtained data suggests that the C6H5SH:Si(001) presents a higher Schottky barrier height contact when compared to other similar aromatic molecules.

Variabilidad de la temperatura superficial del mar en el sureste del Atlántico Norte

Programa de Oceanografí­a Fí­sica y Fí­sica Aplicada

Importancia relativa del forzamiento atmosférico y topográfico de remolinos oceánicos por las islas

Programa de Oceanografía física y Física aplicada

Modelo tridimensional de camino aleatorio para un derrame de petróleo : aplicación al derrame producido por el North Cape

Doctorado en Ciencias Físicas. Programa de Oceanografía y Física aplicada.