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Lead Oxide (PbO) is the main material used for the preparation of the active material for the positive and negative electrodes in the lead acid battery where the electrochemical reaction that provides the electrical energy of the battery takes place. The particle size distribution and surface area characteristics of the lead oxide play a major role in the electrical performance of the completed battery. The two most commonly used processes to manufacture PbO in the lead acid battery industry are the Barton pot and the Ball mill processes. These two processes produce oxides that differ in particle size distribution, particle shape and surface area. It is generally accepted that the Ball mill process produces an oxide with a smaller mean particle size with a higher surface area and better initial electrical performance than the Barton pot process to the detriment of an initial higher capital and running cost. The study showed that it is possible to improve the surface area and particle size distribution characteristics of Barton pot oxide, by subsequently hammer milling the oxide particles before the paste manufacturing process. The results showed that there was an initial reduction in the particle size with an increase in the surface area. This increased the electrochemical performance in terms of the high rate discharge. However, further hammering of the oxide reduced the average particle size only slightly with little change in the surface area and a reduction in the electrochemical performance. The study showed that an improvement in Barton pot oxide can be achieved with a hammering of the oxide in order to obtain a uniform particle size with improved surface area and an improved high rate performance of the electrochemical cells made with such an oxide. As a comparison, the particle size and surface area characteristics of Ball mill lead oxide subjected to the hammer milling process was also studied. The results showed a similar effect to the Barton pot oxide on the particle size distribution. However, there was no appreciable change in the surface area due to the hammer milling process.

The purpose of this study was two-fold: firstly, the MOCVD deposition behavior of Pb(thd)2 was studied in detail and a one-dimensional kinetic model was proposed to successfully predict the effect of processing conditions on the deposition rate profile for PbO. Assuming the surface reaction is the rate-limiting step in the process, the effective activation energy for the process, Ea, was found to be 82 kJ/mol while the preexponential rate constant was found to be 33 g/cm2/min (0.15 moVcm2/min). The process was found to consistently produce a combination of the high temperature, orthorhombic modification of lead monoxide with randomly oriented plates of tetragonal lead monoxide. TEM electron diffraction was used to investigate the crystal orientation of the individual plates which was found to be in the plane normal to the <201> zone. Secondly, the deposition behavior of PbTi03 and the resulting film structure and properties were investigated. Pb(thd)2 was used in conjunction with titanium ethoxide (Ti(OEt)4) as a titanium source. Stoichiometric lead titanate films which were found to be smooth, specular and transparent, and well-adhered were deposited on a variety of substrates by careful control of the experimental conditions. Film structure, composition, and thickness were studied and correlated to changes in various experimental parameters. Additionally, a high temperature regime at which the film stoichiometry is relatively insensitive to experimental conditions was found to occur. The effects of post-annealing on the as-deposited films including compositional changes, morphological changes and crystal structure was also studied. Some problems were obtained with film peeling on the ruthenium oxide (Ru0₂)-coated substrates which could be alleviated somewhat by the use of (100) oriented silicon wafer rather than (111) oriented silicon; a possible mechanism to explain this behavior is also suggested. Optical properties were obtained using UV -VISNIR transmission and reflectance spectroscopy; the ferroelectric hysteresis behavior of the films was observed using standard R T -66 A test equipment. / Master of Science

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Orientador: João Manuel Marques Cordeiro / Resumo: O chumbo, em função de sua alta resistividade é mau condutor de eletricidade, sendo classificado como um metal semicondutor. Já os seus óxidos são muito utilizados na confecção de baterias automotivas, pelo seu comportamento condutor. Dos vários óxidos de chumbo que existem, o dióxido de chumbo (PbO2) é um dos que mais se destacam devido a suas aplicações. O β-PbO2 é um semicondutor com band gap estreito, que recebeu uma grande atenção ultimamente devido à sua potencial utilização como óxidos condutores transparentes (TCO). Os TCO são compostos que combinam as propriedades normalmente mutuamente excludentes da transparência e da condutividade. O desempenho óptico e elétrico dos TCO está intimamente ligado à estrutura de bandas e, desta forma, a distribuição periódica de potencial em um cristal. Neste trabalho procura-se compreender os fundamentos das propriedades elétricas macroscópicas do material β-PbO2 na forma de filmes finos. Para tanto, adotou-se abordagem da mecânica quântica baseada na Teoria do Funcional Densidade (DFT), com potencial híbrido B3LYP, implementada no código CRYSTAL09. Cálculos de estrutura de bandas e densidade de estados mostram que o band gap de filmes de β-PbO2 tendem para o gap do material na forma de bulk e cálculos de energia de superfície permitem concluir que sua face mais estável é a (110). / Mestre

Submitted by ARILSON COSTA ALVES null (arilson33@hotmail.com) on 2016-12-06T18:59:15Z No. of bitstreams: 1 Dissertacao_prop_estrtuturais_eletronicas_b_PbO2_filmes_finos.pdf: 2808420 bytes, checksum: 6ced87859a7fdbd4de3e64c3b5472a0a (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-12-09T12:41:56Z (GMT) No. of bitstreams: 1 alves_ac_me_ilha.pdf: 2808420 bytes, checksum: 6ced87859a7fdbd4de3e64c3b5472a0a (MD5) / Made available in DSpace on 2016-12-09T12:41:56Z (GMT). No. of bitstreams: 1 alves_ac_me_ilha.pdf: 2808420 bytes, checksum: 6ced87859a7fdbd4de3e64c3b5472a0a (MD5) Previous issue date: 2016-11-03 / O chumbo, em função de sua alta resistividade é mau condutor de eletricidade, sendo classificado como um metal semicondutor. Já os seus óxidos são muito utilizados na confecção de baterias automotivas, pelo seu comportamento condutor. Dos vários óxidos de chumbo que existem, o dióxido de chumbo (PbO2) é um dos que mais se destacam devido a suas aplicações. O β-PbO2 é um semicondutor com band gap estreito, que recebeu uma grande atenção ultimamente devido à sua potencial utilização como óxidos condutores transparentes (TCO). Os TCO são compostos que combinam as propriedades normalmente mutuamente excludentes da transparência e da condutividade. O desempenho óptico e elétrico dos TCO está intimamente ligado à estrutura de bandas e, desta forma, a distribuição periódica de potencial em um cristal. Neste trabalho procura-se compreender os fundamentos das propriedades elétricas macroscópicas do material β-PbO2 na forma de filmes finos. Para tanto, adotou-se abordagem da mecânica quântica baseada na Teoria do Funcional Densidade (DFT), com potencial híbrido B3LYP, implementada no código CRYSTAL09. Cálculos de estrutura de bandas e densidade de estados mostram que o band gap de filmes de β-PbO2 tendem para o gap do material na forma de bulk e cálculos de energia de superfície permitem concluir que sua face mais estável é a (110). / Lead, due to its high resistivity, is a poor conductor of electricity and is classified as a semiconductor. On the other hand their oxides are widely used in the manufacture of automotive batteries, because of its conductivity. β-PbO2 is a narrow band gap semiconductor which received great attention lately due to their potential use as a transparent conducting oxide (TCO). The TCO are compounds which combine transparency and conductivity, properties that normally do not coexist. The optical and electrical performance of the TCO are intimately connected to the band structure and thus the potential distribution in a periodic crystal. This work, seeks to contribute for understanding the fundamentals of macroscopic electrical properties of β-PbO2 material in the form of thin films. Therefore, it was adopted the quantum mechanics approach based on Density Functional Theory (DFT), with B3LYP hybrid potential, implemented in the CRYSTAL09 code. Band structure and density of states calculation show that the band gap of β-PbO2 films tend to the bulk band gapsurface energy calculations permit conclude that its most stable face is the (110).