Estudo da forma e da distribuição de tamanho de partículas de alumina em dispersões coloidais relacionado a sedimentação gravitacional
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Data
1999-05-17
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Universidade Estadual Paulista (Unesp)
Resumo
Amostras comerciais de alumina foram caracterizadas quanto à estrutura, características de superfície e morfologia. Sais de polifosfato com diferentes tamanhos de cadeia foram isolados por cromatografia por troca iônica, tendo como precursor polifosfato de sódio. Os sais isolados na forma de tetraetilamoniomagnésio foram caracterizados e uma das amostras foi ensaiada como agente dispersante para alumina. As técnicas de caracterização utilizadas foram: análise termogravimétrica e térmica diferencial, difratometria de raios X, espectroscopia vibracional infravermelho, microscopia eletrônica de varredura e de transmissão, medidas de mobilidade eletroforética, área de superfície, ressonância magnética nuclear de 31P no estado sólido e sedimentometria. Sedimentometria de partículas de alumina foi utilizada para verificar a influência da natureza e da concentração de sais de polifosfato como agente dispersante na estabilidade coloidal da dispersão. Também foi investigada a influência da forma da partícula na velocidade terminal de sedimentação de partículas micrométricas, através da relação entre o coeficiente de arraste e o número de Reynolds. Modelos estatísticos, a saber: normal, lognormal e Rosin-Rammler foram ajustados aos perfis de sedimentação facilitando o tratamento dos resultados experimentais e permitindo caracterizar as dispersões através de parâmetros dos modelos teóricos, tais como o desvio padrão, que fornece informações sobre a distribuição do tamanho de partículas com relação à media. Metodologia que permitem a linearização dos dados experimentais através dos modelos estatísticos foram empregados e parece contribuir para definir rapidamente faixas de concentração, cada vez mais restritas, até a concentração ideal, bem como a natureza do agente dispersante que minimize a formação de agregados. Os resultados...
The influence of the nature and concentration of the polyphosphate salts as dispersant agents on the colloidal stability of alumina dispersions by particle gravitational sedimentation was investigated. Shape of colloidal particle influence on the terminal velocity of sedimentation has been correlated using a simple relationship involving the usual drag coefficient and Reynolds number. In order to treat the experimental results, statistic models: normal, lognormal and Rosin-Rammler were adjusted to the sedimentation curves. Theoretical parameters of these models, such as standard-deviation, gives information about the dispersion of the particle size distribution in relationship to average particle size, and are not usually obtained directly from the experimental data set.A linear data set starting from the experimental data by calculation of the statistical models probabilities was obtained. This procedure quickly define dispersion agent concentration range, more and more restricted, up to the ideal concentration, as well as the nature of the dispersant agent that minimizes the aggregates formation. Structure, surface properties and morphology of the commercial alumina samples were characterized.Ion exchange chromatography for separating polyphosphate salts with different chain size was used.The isolated salts as tetraetylammonium magnesium were characterized and tested as dispersion agent for alumina. However, the salt behaved as flocculant agent due to the group of tetraetylammnium.The samples were characterized by thermogravimetry and diferential thermal analysis, X ray diffratometry, infrared spectroscopy, scanning and transmission electron microscopy, electrophoretic mobility and surface area measurements, 31P MAS NMR and sedimentometry.The results showed that the particle shape influences the settling velocity and they allowed to insert a proportionality term in the Stokes’ equation.This term includes the projected area of the particle.
The influence of the nature and concentration of the polyphosphate salts as dispersant agents on the colloidal stability of alumina dispersions by particle gravitational sedimentation was investigated. Shape of colloidal particle influence on the terminal velocity of sedimentation has been correlated using a simple relationship involving the usual drag coefficient and Reynolds number. In order to treat the experimental results, statistic models: normal, lognormal and Rosin-Rammler were adjusted to the sedimentation curves. Theoretical parameters of these models, such as standard-deviation, gives information about the dispersion of the particle size distribution in relationship to average particle size, and are not usually obtained directly from the experimental data set.A linear data set starting from the experimental data by calculation of the statistical models probabilities was obtained. This procedure quickly define dispersion agent concentration range, more and more restricted, up to the ideal concentration, as well as the nature of the dispersant agent that minimizes the aggregates formation. Structure, surface properties and morphology of the commercial alumina samples were characterized.Ion exchange chromatography for separating polyphosphate salts with different chain size was used.The isolated salts as tetraetylammonium magnesium were characterized and tested as dispersion agent for alumina. However, the salt behaved as flocculant agent due to the group of tetraetylammnium.The samples were characterized by thermogravimetry and diferential thermal analysis, X ray diffratometry, infrared spectroscopy, scanning and transmission electron microscopy, electrophoretic mobility and surface area measurements, 31P MAS NMR and sedimentometry.The results showed that the particle shape influences the settling velocity and they allowed to insert a proportionality term in the Stokes’ equation.This term includes the projected area of the particle.
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Palavras-chave
Coloides, Alumina, Colloids
Como citar
VARANDA, Laudemir Carlos. Estudo da forma e da distribuição de tamanho de partículas de alumina em dispersões coloidais relacionado a sedimentação gravitacional. 1999. 132 f. Dissertação (mestrado) - Universidade Estadual Paulista, Instituto de Química, 1999.