Princípios físicos da impedância de uma célula eletroquímica e sua aplicação na determinação da condutividade de soluções de moléculas de fulerenol

• Ano de defesa: 2011
• Autor(a) principal: Roberto Batista Sardenberg
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Física; Impedância (Célula eletrolítica); Condutividade elétrica nos sólidos; Moléculas de fulerenois
• Link de acesso: http://hdl.handle.net/1843/BUOS-8H2N9C

This work presents an impedance model based on the transport equations (diffusion and migration), and the Poisson equation. We introduced a variable that we call distributed impedance. As a result the impedance of an electrolytic cell was calculated as an integral over the cell length of the distributed impedance. This way we showed that thetotal cell impedance is the sum of several partial impedances, each one defined in a specific region and reflecting the local transport properties. The use of the distributed impedance concept shows the existence of a correlation between the impedance spectral decomposition and the local proprieties and charge distribution. This opens the possibility ofretrieving information concerning the structure of a sample using this technique. Systematic impedance experiments were performed in an electrolytic cell with the aim of testing this formalism. Several kinds of ionic solutions with several concentration values were tested. The impedance model developed is capable of explain with good precision all experimental data we got. As an application of this technique, several impedance measurements were made in aqueous solutions of fullerenol molecules. We observed in some cases a non-linear dependence of the conductivity as function of concentration. In order to explain this nonlinear behavior we utilized the Debye-Hkel and Onsager theory which predicts a concentration dependent mobility. In consequence some fullerenol transport parameters as the hydrodynamic radius, the ionic mobility, the valence and the passivation number were obtained.