Made available in DSpace on 2014-10-09T12:30:36Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:36Z (GMT). No. of bitstreams: 1 00497.pdf: 2001599 bytes, checksum: c898aaf8d6641324c22c0d5bb1204f9d (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Energia Atomica - IEA

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Made available in DSpace on 2014-10-09T12:27:21Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:37Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Os efeitos decorrentes da adição de NiO na densificação, na microestrutura e na condutividade elétrica da zircônia totalmente estabilizada com ítria foram sistematicamente estudados. Zircônia-8% mol de ítria (8YSZ) comercial e acetato, trihidróxi-carbonato, nitrato e óxido de níquel foram utilizados como materiais de partida. Os teores de Ni variaram entre 0,5% e 5% em mol e as composições foram preparadas por mistura dos materiais precursores a partir das concentrações estequiométricas. Estudos de densificação realizados por meio de medidas de densidade geométrica e dilatometria revelaram que a retração total até 1400ºC varia de ~16 até ~20% dependendo do precursor de níquel. No segundo estágio de sinterização a retração linear aumentou com o aumento no teor do aditivo (precursor: trihidróxi-carbonato de níquel). No estágio inicial de sinterização a energia de ativação para a difusão via contornos de grão varia de acordo com o precursor de níquel utilizado sendo menor para o óxido e maior para o trihidróxi-carbonato. No estágio secundário de sinterização prevalece a sinterização volumétrica. Neste estágio, as temperaturas de máxima retração são independentes do precursor de níquel, exceto para o acetato. O tamanho médio de cristalito variou com o tipo de precursor empregado sendo menor para o trihidróxi-carbonato e maior para o óxido de níquel. O limite de solubilidade do NiO determinado por difração de raios X é 1,48% em mol a 1350ºC. Para teores acima do limite de solubilidade o aditivo permanece aleatoriamente distribuído como uma fase secundária na forma de NiO. O principal efeito do aditivo na microestrutura é aumentar o tamanho médio de grãos. Os resultados de medidas elétricas revelaram que a adição de NiO não produz alterações significativas na condutividade intragranular da 8YSZ para diversos tempos de sinterização, exceto quando o precursor é o óxido de níquel, para o qual a condutividade elétrica aumenta com o tempo de sinterização evidenciando a dificuldade na formação de solução sólida, quando o material precursor possui tamanho de cristalito superior ao da matriz. Entretanto, a condutividade intragranular nas amostras preparadas com o trihidróxi-carbonato de nickel é pouco inferior à das demais amostras. Nas amostras sinterizadas por 15 h a 1350ºC um terceiro semicírculo foi associado com a formação de fase tetragonal na 8YSZ, devido à aceleração pelo níquel na cinética da transformação de fase cúbica para tetragonal. A condutividade intergranular varia com o tempo de sinterização devido à diminuição na fração de interfaces (contornos de grão) que ocorre com o aumento no tamanho médio de grãos. A condutividade intergranular microscópica da 8YSZ não varia significativamente com a adição de NiO. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP:07/56298-7

While the laws of ionization and conductivity in polar systems are well understood and appreciated in the art, theories related to nonpolar systems and their conductivities remain elusive. Currently, multiple conflicting models, with limited experimental verification, exist that aim to explain and predict the mechanisms by which ionization occurs in nonpolar media. A historical overview of the field of nonpolar electrochemistry, dating back to the 1800’s, is presented herein with a focus on the work of prominent scientists such as Fuoss, Bjerrum, and Onsager, who’s pioneering discoveries serve as the scientific foundation for our understanding of ionization in nonpolar systems, from which our knowledge of ion-pairs (i.e. re-associated solvated ions which do not contribute to the overall conductivity of the system) stems. Recent work in the field of nonpolar electrochemistry has focused on ionization models such as the Disproportionation Model and the Fluctuation Model, which ignore ion-pair formation and the existence of these neutral entities altogether. While, the “Ion-Pair Conductivity Model”, the novel conductivity model introduced and explored herein, primarily focuses on the critical role these neutral entities play with regards to the electrochemistry in these systems. The “Ion-Pair Conductivity Model” for predicting and modeling the conductivity of mixtures of nonpolar liquids, arises from the Dissociation Model, a third ionization model for predicting conductivity in nonpolar systems which accounts for ion-pair formation, and is rooted in the foundational work of Fuoss, Bjerrum, Onsager, and others. The Ion-Pair Conductivity Model’s relationship to and derivation from the Dissociation Model is provided, including the justified assumptions and simplifications of the model to create a more concise approach for predicting conductivity in nonpolar systems that can be readily applied to real-world scenarios. In order to substantiate this model as a reliable method for predicting conductivity in nonpolar solutions, experimental results from studies examining various two-component solutions comprised of an amphiphile and nonpolar liquid, analyzed under a variety of conditions, across the entire concentration spectra, from pure nonpolar liquid to pure amphiphile, are compared to the Ion-Pair Conductivity Model. The role additional properties such as water contamination, ion size, concentration of free ions, range of ion-pair existence, shear and longitudinal rheology in these nonpolar solutions are also explored. The fitting of the experimental data and theoretical model demonstrates the ability of the Ion-Pair Conductivity Model to accurately predict conductivity in two-component solutions of an amphiphile and nonpolar liquid. Furthermore, it emphasizes the importance that ion-pairs play in the conductivity of such a system. Lastly, it reinforces the usefulness of the Ion-Pair Conductivity Model as a tool for investigating the mechanisms by which ionization in nonpolar media occur. Ultimately, the goal of this study is to validate the Ion-Pair Conductivity Model as a robust and precise model for characterizing conductivity in nonpolar solutions across a diverse set of nonpolar systems. Allowing us, and others, to better understand and exploit the intrinsic properties of conductivity in these systems to advance a number of technologies in the field electrochemistry, such as a-polar paints, electrophoretic inks, and electrorheological fluids.

The effects of pentachlorophenol (PCP), a widely used pesticide, on the electrical characteristics of lipid bilayer membranes has been studied. When a small amount of PCP (even at a concentration of a few micromoles per liter) is present in the electrolytic solution surrounding the membrane, the electrical conductivity of the membrane significantly increases. The present work was concerned with detailed measurements of the changes in the conductivity caused by PCP under chemically controlled conditions. The experimental results were analyzed to determine the permanent species in the membrane, and an attempt was made to correlate the data with existing models of transport.

In this project the author has attempted to determine the specific conductance of a gel of known composition; the changes, if any, of conductance in a gel as it sets; and the changes in conductance due to the diffusing of an electrolyte through the gel.

A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science / The role of intersite electron correlation effects and the possible occurrence of the metal-insulator transition in carbon-ion implanted type IIa diamond samples have been studied at very low temperatures, using four- and two-point probe contact electrical conductivity measuring techniques. The measurements were extended to ruthenium oxide thin films in the presence and absence of a constant magnetic field of B = 4.0 T down to 100 mK, using a 3He-4He dilution refrigerator. The effect of the Coulomb gap in the variable range hopping regime has been well studied by other workers. The results tend to follow the Efros-Shklovskii behaviour with a trend towards the Mott T- 114 law for diamond samples far removed from the metal insulator transition, on the insulating side at low temperatures. / Andrew Chakane 2019

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