Orientador: Prof. Dr. Sérgio Ricardo Lourenço / Tese ( doutorado)- Universidade Federal do ABC. Programa de Pós-Graduação em Energia, 2016.

Les composés homologues de formule chimique (PbSe)5(Bi2Se3)3m avec m = 1, 2 et 3 se caractérisent par une structure lamellaire où alternent des couches de PbSe avec m couches de Bi2Se3. Ces composés, que l’on retrouve à l’état naturel, ont récemment suscité un intérêt pour la thermoélectricité en raison de leur remarquable aptitude à ne conduire que très faiblement la chaleur. L’objectif des travaux de cette thèse est d’étudier en détail le transport électrique et thermique de ces matériaux et de sonder leurs performances pour la génération d’électricité. Pour atteindre ces objectifs, des techniques de synthèse par métallurgie de poudres ont été mises en œuvre. Les matériaux résultants ont été ensuite caractérisés finement. Les caractérisations ont porté sur des analyses physico-chimiques mais aussi sur des mesures de propriétés électriques et thermiques aussi bien à basses températures (2 – 300 K) pour identifier les mécanismes microscopiques qui gouvernent le transport qu’à hautes températures (300 – 723 K) pour déterminer leur domaine d’application optimal. Une étude détaillée de leur structure cristalline a été menée en combinant des mesures de diffraction des rayons X sur monocristal et des analyses de microscopie électronique à transmission à haute résolution. Les mesures des propriétés physiques de ces composés ont confirmé leur potentiel pour des applications en génération d’électricité à températures moyennes. De nombreuses substitutions ont été entreprises afin de tenter d’optimiser davantage les performances de ces composés. Les éléments en substitution ont été choisi pour soit augmenter (m = 1) ou au contraire diminuer (m = 2 et 3) la concentration en électrons. Ces travaux ont permis de démontrer pour la première fois la possibilité de doper ces matériaux avec de nombreux éléments tels que l’iode, le sodium, l’argent ou le tellure. D’autre part, une étude détaillée des propriétés thermiques de ces matériaux a été réalisée par diffusion inélastique des neutrons sur poudre afin de dévoiler l’origine microscopique des très faibles valeurs de conductivité thermique de réseau mesurées / The homologous series of compounds of general chemical formula (PbSe)5(Bi2Se3)3m with m = 1, 2 et 3 is characterized by a lamellar crystal structure where PbSe layers alternate with m Bi2Se3 layers. These compounds, that can be found as minerals, have recently focused attention for thermoelectric applications owing to their remarkable ability to poorly conduct heat. In order to evaluate their thermoelectric performances, the present work dealt with their synthesis by powder metallurgy techniques followed by measurements of their transport properties not only at low temperatures (2 – 300 K) with the aim to identify the basic mechanisms governing the transport but also at high temperatures (300 – 723 K) to determine their optimum temperature range. A detailed study of their crystalline structure has been carried out by a combination of X-ray diffraction on high-quality single crystals and high-resolution transmission electron microscopy. Measurements of their transport properties have confirmed the potential of these materials for power generation applications at mid temperatures. Numerous substitutions have been studied to optimize further their thermoelectric performances. The elements in substitution have been chosen to either increase (m = 1) or decrease (m= 2 and 3) the electron concentration. This work has demonstrated for the first time the possibility to dope these materials with various elements such as iodine, sodium, silver or tellurium. Moreover, a detailed study of the thermal properties of these compounds has been performed by means of powder inelastic neutron scattering in order to unveil the microscopic origin of the very low lattice thermal conductivity values measured

One-dimensional (1D) nanomaterials are of great importance for a number of potential applications. However, in order to realize this potential a thorough understanding of the charge-carrier dynamics in these materials is required, since these largely determine the optoelectronic properties of the materials in question. This thesis investigates the charge-carrier dynamics of two 1D nanomaterials, single-walled carbon nanotubes (CNTs) and tungsten-oxide nanowires (WOxNWs), with the goal of better understanding the nature of their optoelectronic responses, and how nanomaterial geometry and morphology influence these responses. We do this using terahertz time-domain spectroscopy (THz-TDS) and optical pump - terahertz probe time-domain spectroscopy (OPTP). Firstly, we discuss how to properly analyse and interpret the data obtained from these experiments when measuring 1D nanomaterials. While the data obtained from THz-TDS is fairly straight-forward to analyse, OPTP experimental data can be far from trivial. Depending on the relative size of the sample geometry compared to the probe wavelength, various approximations can be used to simplify the extraction of their ultrafast response. We present a general method, based on the transfer matrix method, for evaluating the applicability of these approximations for a given multilayer structure, and show the limitations of the most commonly used approximations. We find that these approximations are only valid in extreme cases where the thickness of the sample is several orders of magnitude smaller or larger than the wavelength, which highlight the danger originating from improper use of these approximations. We then move on to investigate how the charge-carrier dynamics of our CNTs is influenced by nanotube length and density. This is done through studying the nature of the broad THz resonance observed in finite-length CNTs, and how the nanotube length and density affects this resonance. We do this by measuring the conductivity spectra of thin films comprising bundled CNTs of different average lengths in the frequency range 0.3-1000 THz and temperature interval 10-530 K. From this we show that the observed temperature-induced changes in the terahertz conductivity spectra depend strongly on the average CNT length, with a conductivity around 1 THz that increases/decreases as the temperature increases for short/long tubes. This behaviour originates from the temperature dependence of the electron scattering rate, which results in a subsequent broadening of the observed THz conductivity peak at higher temperatures and a shift to lower frequencies for increasing CNT length. Finally, we show that the change in conductivity with temperature depends not only on tube length, but also varies with tube density. We record the effective conductivities of composite films comprising mixtures of WS2 nanotubes and CNTs vs CNT density for frequencies in the range 0.3-1 THz, finding that the conductivity increases/decreases for low/high density films as the temperature increases. This effect arises due to the density dependence of the effective length of conducting pathways in the composite films, which again leads to a shift and temperature dependent broadening of the THz conductivity peak. Next, we investigate the conflicting reports regarding the ultrafast photoconductive response of films of CNTs, which apparently exhibit photoconductivities that can vastly differ, even in sign. Here we observe explicitly that the THz photoconductivity of CNT films is a highly variable quantity which correlates with the length of the CNTs, while the specific type of CNT has little influence. Moreover, by comparing the photo-induced change in THz conductivity with heat-induced changes, we show that both occur primarily due to heat-generated modification of the Drude electron relaxation rate, resulting in a broadening of the plasmonic resonance present in finite-length metallic and doped semiconducting CNTs. This clarifies the nature of the photo-response of CNT films and demonstrates the need to carefully consider the geometry of the CNTs, specifically the length, when considering them for application in optoelectronic devices. We then move on to consider our WOxNWs. We measure the terahertz conductivity and photoconductivity spectra of thin films compromising tungsten-oxide (WOx) nanowires of average diameters 4 nm and 100 nm, and oxygen deficiencies WO2.72 and WO3 using THz-TDS and OPTP. From this we present the first experimental evidence of a metal-to-insulator transition in WOx nanowires, which occurs when the oxygen content is increased from x=2.72 -> 3 and manifests itself as a massive drop in the THz conductivity due to a shift in the Fermi level from the conduction band down into the bandgap. Furthermore we present the first experimental measurements of the photoexcited charge-carrier dynamics of WOx nanowires on a picosecond timescale and map the influence of oxygen-content and nanowire diameter. From this we show that the decay-dynamics of the nanowires is characterized by a fast decay of < 1 ps, followed by slow decay of 3-10 ps, which we attribute to saturable carrier trapping at the surface of the nanowires.

Submitted by Lucas Kaique Martins Roncaselli (lucaskaiique@hotmail.com) on 2016-03-31T19:01:49Z No. of bitstreams: 1 dissertação - Fabricação e caracterização elétrica de filmes nanoestruturados de derivados do politiofeno.pdf: 2213057 bytes, checksum: 090f4d69287d8df3078f3e9849957e37 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-04-05T13:52:15Z (GMT) No. of bitstreams: 1 roncaselli_lkm_me_prud.pdf: 2213057 bytes, checksum: 090f4d69287d8df3078f3e9849957e37 (MD5) / Made available in DSpace on 2016-04-05T13:52:15Z (GMT). No. of bitstreams: 1 roncaselli_lkm_me_prud.pdf: 2213057 bytes, checksum: 090f4d69287d8df3078f3e9849957e37 (MD5) Previous issue date: 2016-02-19 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho foram utilizados derivados alquilados do politiofeno (P3ATs), sendo eles regioirregulares (RI) e regiorregulares (RR), diferenciados pela organização molecular. Esses materiais apresentam diferentes características quando fabricados usando técnicas diferentes como, a Langmuir-Blodgett (LB) e a Langmuir-Schaeffer (LS). O objetivo fica em fabricar filmes mistos com ambas as técnicas LB e LS, sendo os derivados misturados com ácido esteárico (Stearic Acid, SA), afim de verificar os diagramas de energia de acordo com a organização e condutividade de cada politiofeno. Foram depositados filmes de LB e LS de poli(3-butiltiofeno) (P3BT), poli(3-hexiltiofeno) (P3HT), poli(3-octiltiofeno) (P3OT) e de poli(3-dodectiltiofeno) (P3DDT). Os P3ATs poli(3-alquiltiofenos) foram depositados em ITO (Indium-Tin Oxide), e realizado para a caracterização desses materiais de espectroscopia UV-Visível, eletroquímicas e condutividade. Através dessas medidas foi possível estabelecer uma relação entre a organização, reversibilidade e condutividade desses materiais, possibilitando construir um diagrama de energia para esses derivados alquilados do politiofeno. / In this work we were used alkylated derivatives of polythiophene (P3ATs), and they regioirregulares (RI) andregiorregulares (RR), differentiated by molecular organization. These materials exhibit different characteristics when manufactured using different techniques such as the Langmuir-Blodgett (LB) and Langmuir-Schaeffer (LS). The objective is to manufacture mixed films with both LB and LS techniques, and derivatives mixed with stearic acid (Stearic Acid SA) in order to check the energy diagram according to the conductivity of each organization and polythiophene. LB films were deposited and LS poly(3-butylthiophene) (P3BT), poly(3-hexylthiophene) (P3HT), poly(3-octylthiophene) (P3OT) and poly(3-dodectiltiofeno) (P3DDT). The P3ATs poly(3-alquiltiofenos) were deposited on ITO (Indium-Tin Oxide), and held for characterizing these materials spectroscopy UV-Visible, electrochemical, and conductivity. Through these measures it was possible to establish a relationship between the organization, reversibility and conductivity of these materials, making it possible to build an energy diagram for these alkylated derivatives of polythiophene.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The study of hydraulic conductivity of soil is an important stage in the geotecnical investigations, aiming at the use of compacted soils as impermeabilizing mineral layers, for the base and cover of sanitary land-fill sites. This paper presents the study of hydraulic conductivity (k) of natural and compacted soils of the Santa Maria region, in the area called Caturrita which was chosen for the future installation of the sanitary land-fill of this city, localized near the current solid waste disposal site of Santa Maria (Robaina, 2002). In this place a detailed geological-geotecnical investigation was undertaken. The objective of this investigation was the identification, classification and characterization of the soils of seventeen drilling profiles (P1 to P17) distributed in the area of study; the majority were executed with a manual boring-tool, of which samples were collected for laboratory tests. For all profiles characterization tests were performed (Atterberg limits, granulometric analysis, density of grains). In one typical profile (P1) complementary tests were made such as, chemical tests, X-ray diffraction, compaction and hydraulic conductivity tests with of rigid and flexible walls permeameters. For this study of hydraulic conductivity a flexible wall permeameter with a simplified triaxial chamber was assembled similar to that of Bjerrum and Huder (1957). In situ tests were performed of the following type: infiltration hole, ring infiltrometer, and piezometer, which evaluated the characteristics of soil in its natural condition. Through the investigations two layers (layers 1 and 2) were identified in this area. Layers 1 are more superficial, and constituted of horizon A and finally horizon B. In the lower layer 2 (horizon C), with a reddish colour, the soil shows characteristics of alteration of sedimentary rocks. The results of in situ tests k show similar values between each other, because the infiltration tests have values of k in the order of 10-5 m/s, in the same order of magnitude as the results with piezometer in layer 1. The values of k of layer 2 were in the order of 10-7 and 10-8 m/s in the natural state. The compacted samples had values of k in the order 10-9 and 10-10 m/s. The results of k in the flexible wall permeameter were higher for undisturbed samples, and compacted samples resulted in values in the order of 10-9 m/s. Values of k of this order are indicated as natural impermeabilizing barriers in sanitary land-fills. / O estudo da condutividade hidráulica de solos é uma etapa importante nas investigações geotécnicas, visando a utilização de solos compactados como camadas impermeabilizantes minerais, para base e revestimento de cobertura de aterros sanitários. Este trabalho apresenta o estudo da condutividade hidráulica (k) de solos naturais e compactados da região de Santa Maria, na área denominada Caturrita, a qual foi pré-selecionada como futura instalação do aterro sanitário desta cidade, localizada próximo ao atual local do depósito de resíduos sólidos de Santa Maria, o chamado lixão da Caturrita (Robaina, 2002). Neste local foi realizada uma investigação geológica-geotécnica detalhada. Esta investigação teve como objetivo a identificação, classificação e caracterização de solos através de 17 perfis (P1 a P17) de sondagem distribuídos na área do empreendimento, na maioria executados com trado manual, dos quais coletaram-se amostras para ensaios de laboratório. Em todos os perfis foram realizados ensaios de caracterização (limites de Atterberg, granulometria com e sem defloculante e peso específico real dos grãos). Em um perfil típico (P1) foram realizados ensaios complementares, tais como: ensaios químicos, difração de raios-X, ensaios de compactação e condutividade hidráulica com permeâmetro de parede flexível. Para o estudo da condutividade hidráulica foi montado para esta pesquisa o permeâmetro de parede flexível com câmara triaxial simplificada, similar ao proposto por Bjerrum e Huder (1957). In situ foram realizados ensaios do tipo: cava de infiltração, infiltrômetro de anel, e com a técnica do piezômetro, os quais avaliam as características do solo em condições naturais. Através das investigações foram identificadas na área duas camadas (camadas 1 e 2) para os perfis de solo, sendo que a camada 1 mais superficial é constituída por um horizonte A e eventualmente um horizonte B. Na camada 2 (horizonte C) mais inferior, com coloração avermelhada, possui características de alteração de rochas sedimentares. Os resultados dos ensaios k in situ apresentaram valores semelhantes entre si, sendo que o ensaio de infiltração teve valores na ordem de 10-5 m/s, na mesma ordem dos resultados com piezômetro na camada 1. A camada 2 os valores de k foram da ordem de 10-7 e 10-8 m/s no estado natural. Os corpos compactados tiveram valores de k na ordem 10-9 a 10-10 m/s. Os resultados de k em permeâmetro de parede flexível foram mais elevados para amostras indeformadas, e nos corpos de prova compactados resultaram valores na ordem de 10-9m/s. Valores de k desta ordem são indicados como barreiras naturais impermeabilizantes em aterros sanitários.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The urban environment diagnosis aims at subsidizing the districts in the decisionmaking in the presence of natural resources preservation. This study, specifically, analyze the urban environment aspect of the physical space. The area of this study is the Map of the Geotechnical Engineering Units according to Maciel Filho (1990) of Santa Maria, located in the Central Depression of the State of Rio Grande do Sul. The methodology of this research started with office studies by means of preexisting researchers; geoprocess tools application with the use of the software Spring 4.2 for the thematic maps and cartograms elaboration; identification and characterization of the geotechnical units carried out thereby laboratory assays and 20 assays of hydraulic conductivity (k) the field carried out using the method of excavated piezometer. The study of the aquifer natural vulnerability were accomplished based on GOD method according to Foster and Hirata (1988) and Foster et al. (2003) using data from 36 wells. The spacialization of the tubular wells and the hydraulic conductivity assays in the Map of the Geotechnical Engineering using the Universal Transverse Mercator/UTM coordinate system from Global Position System /GPS. The potentiometer surface was evaluated associated to the cartograms of vulnerability and the potential points of contamination by the use of SURFER 8.0 software adopting mathematical interpolator Kriging. The results shown that related to the characterization geotechnical coherent parameters with the descriptions of the study area and related to the assays of hydraulic conductivity in the field the range of variation was between 10-5 to 10-8 m/s, classifying the units since the high permeability (Gravitational and Fluvial Deposits, Caturrita, Botucatu and Passo das Tropas formations) to the low permeability (Santa Maria Formation, Alemoa Member). For the vulnerability natural index from the aquifers 4 classes were obtained (negligible, low, moderate and high). From all wells analyzed 11 were classified from moderate to high vulnerability situated in the south and north from each geotechnical units of Santa Maria. The results also shown that were identified 35 fuel ranks, 06 cemeteries and 06 areas of garbage deposits. The majority of the potential sources of contamination are prompt and are inserted in sufficiently susceptible areas of ground and the aquifers pollution. The methodology was viable and gave supply to the physical space research. / O diagnóstico ambiental urbano visa subsidiar os municípios na tomada de decisão perante a preservação dos recursos naturais. Especificamente este trabalho estuda o aspecto ambiental urbano do meio físico. A área de estudo é a Carta das Unidades Geotécnicas de Maciel Filho (1990) do município de Santa Maria, localizado na Depressão Central do Estado do Rio Grande do Sul. A metodologia de pesquisa teve inicio com estudos de escritório através de pesquisas pré-existentes; da aplicação de ferramentas de geoprocessamento com o uso do software Spring 4.2 para a elaboração dos mapas temáticos e cartogramas; da identificação e caracterização das unidades geotécnicas realizadas através de ensaios de laboratório e 20 ensaios de condutividade hidráulica (k) in situ com a técnica do piezômetro escavado. O estudo do Índice vulnerabilidade natural dos aqüíferos pelo método GOD de Foster e Hirata (1988) e Foster et al. (2003) com a utilização de dados de 36 poços. A espacialização dos poços tubulares e dos locais dos ensaios de condutividade hidráulica na carta das unidades geotécnicas foi utilizado o sistema de Coordenadas Universal Transversa de Mercator/UTM obtidas com o Global Position System/GPS. Avaliou-se a superfície potenciométrica associada aos cartogramas de vulnerabilidade e aos pontos potenciais de contaminação através do programa SURFER 8.0 adotando-se o interpolador Krigagem matemática. Como resultados obteve-se, quanto à caracterização geotécnica parâmetros coerentes com as descrições da área de estudo, com relação aos ensaios de condutividade hidráulica in situ os valores situaram-se entre 10-5 e 10-9 m/s, classificando as unidades desde permeáveis (Colúvios, Depósitos Fluviais, Caturrita, Botucatu, Passo das Tropas) até impermeáveis (Membro Alemoa da Formação Santa Maria). Para o Índice de vulnerabilidade natural dos aqüíferos obteve-se 4 classes (insignificante, baixa, média e alta). Do total de poços analisados 11 foram classificados de média a alta vulnerabilidade situados ao sul e norte da carta de unidades geotécnicas de Santa Maria. Foram identificados 35 postos de combustíveis, 6 cemitérios e algumas áreas de depósitos de lixo. A maioria das fontes potenciais de contaminação são pontuais e estão inseridas em áreas bastante susceptíveis a poluição dos solos e dos aqüíferos. A metodologia proposta apresentou-se viável e forneceu subsídios para o estudo do meio físico.

Made available in DSpace on 2014-06-11T19:25:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-17Bitstream added on 2014-06-13T19:12:21Z : No. of bitstreams: 1 escanhoelajunior_ca_me_rcla.pdf: 2205069 bytes, checksum: 07cd01b4a104f262986c24bd2a7f874b (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Neste trabalho realizamos a polarização térmica em vidros silicatos com composição (%mol) 22Na2O.8CaO.65SiO2 .5MO2 (M = Si, Ti, Ge, Zr, Sn e Ce). A polarização térmica consiste em aplicar um campo elétrico DC de elevada intensidade (~1 MV/m) em amostras a altas temperaturas. Durante a polarização térmica é gerado um campo elétrico permanente no interior da amostra, na região do anodo, que é responsável por propriedades ópticas nãolineares. Submetemos à polarização térmica amostras dos vidros, com ~1,5 mm de espessura e área de 20 x 20 mm2. Utilizamos eletrodos de Au, com diâmetro de 1 cm. As amostras foram aquecidas no interior de um forno até ~145 oC e aplicamos um campo elétrico de 1 MV/m durante 60 min. Durante a aplicação do campo elétrico, medimos simultaneamente a corrente através do circuito e as temperaturas no forno e na amostra. A corrente elétrica medida no circuito está relacionada com a migração de íons Na+ no interior das amostras do anodo para o catodo. A diminuição da corrente após um determinado tempo de polarização é devido à formação de uma camada com ausência de íons Na+ (camada de depleção) junto ao anodo. Os diferentes cátions tetravalentes, M4+, inseridos no vidro têm funções particulares na estrutura deste e afetam de formas distintas a corrente elétrica. A energia de ativação para a condutividade elétrica em vidros soda-cal-sílica está associada à energia necessária para o íon Na+ transpor a barreira de potencial entre os interstícios adjacentes na rede vítrea. Para determinar a energia de ativação da condutividade elétrica DC, Eσ, destes vidros, submetemos amostras de cada composição a um campo elétrico de 1 MV/m, durante 2 segundos para diferentes temperaturas entre 100 e 220 ºC. Esta energia está relacionada com... / In this work we performed thermal poling in glasses with composition (%mol) 22Na2O.8CaO.65SiO2 .5MO2 (M = Si, Ti, Ge, Zr, Sn and Ce). The thermal poling consist in apply a high intensity DC electric field (~1 MV/m) on samples at high temperatures. During the thermal poling process a permanent electric field is generated in the anode region of the sample, and this field is responsible for nonlinear optical properties of various glasses. We submit to thermal poling samples with ~1.5 mm in thickness and area of 20x20 mm2. We used gold electrodes with a diameter of 1 cm. The samples were heated inside a furnace to ~ 145 oC and an electric field of 1 MV/m was applied for 60 min. During the poling process, we measure simultaneously the current through the circuit and the temperatures in the furnace and of the sample. The electric current of the circuit is related to the migration of sodium ions in the bulk samples from the anode to the cathode. The current decrease with the poling time is due to the formation of a Na+ absent layer (depletion layer) near the anode surface. The different tetravalent cations, M4+, in the glass have different functions in their structures and affect the electrical current in particular manners. The activation energy for electrical conductivity in soda-lime-silica glasses is associated with energy for the Na+ ions to cross the potential barrier, which is submitted to the interstices of the glassy network, and jump into the nearest interstice. The activation energy of DC electrical conductivity, Eσ, of our samples of was determined by applying an electric field of 1 MV/m for 2 seconds, at different temperatures between 100 and 220 ºC. This energy is related to the current, I, through the equation ... The energy calculated is ~0.8 eV. To evaluate the structural and compositional changes of the samples surfaces that were in contact with the ...

Made available in DSpace on 2014-06-11T19:25:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-11-29Bitstream added on 2014-06-13T20:33:19Z : No. of bitstreams: 1 leite_dr_me_araiq.pdf: 1062321 bytes, checksum: 11dd1388d9d38f07bddc258ae780e508 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A influência do Cr na condutividade elétrica e propriedades microestruturais de cerâmicas à base de SnO2-Mn-Nb foi investigada. Também foi estudada a influência do método de preparação nas características dos pós precursores cerâmicos e nas propriedades e características das cerâmicas resultantes. Sistemas SnO2-Mn-Nb com concentrações variadas de Cr foram preparados pelo método convencional de mistura de óxidos e pelo método Pechini (rota orgânica). Foram utilizadas medidas de área superficial (método BET), difração de raios X, espectroscopia vibracional no infravermelho e microscopia eletrônica de varredura a fim de caracterizar os pós preparados. Análises de condutividade elétrica e impedância complexa confirmaram uma diminuição da condutividade em função do aumento da concentração de Cr também relacionado a esta segregação que limita a passagem de corrente pelo contorno de grão. Os sistemas preparados pelo método Pechini mostraram-se mais resistivos nas curvas I-V em relação aos sistemas preparados por mistura de óxidos. A adição de Cr levou a uma diminuição do coeficiente de não-linearidade uma vez que o Cr parece segregar no contorno de grão, diminuindo o tamanho de grão, levando a uma microestrutura porosa e conseqüentemente degradando as propriedades varistoras dos sistemas. / The influence of Cr in the electrical conductivity and in microstuctural properties of SnO2-based ceramics was studied. In addition, the influence of preparation method in the characteristics of ceramics precursor powders and in the characteristics and properties of the resultant ceramics was investigated. SnO2-Mn-Nb systems with varied Cr concentration were prepared by the conventional method of mixture of oxides and by Pechini method (organic route). Surface area measurements (BET method), X-ray diffraction, infrared spectroscopy and scanning electronic microscopy were utilized to characterize the prepared powders. Analysis of electrical conductivity and complex impedance confirm a decrease of conductivity as a function of the increase of Cr concentration also related to this segregation that limits the current passage by the grain boundary. The systems prepared by Pechini method turned out to be more resistive in the I-V curves than systems prepared by mixture of oxides. The Cr addition led to a decrease of non-linear coefficient since the Cr seem to segregate on grain boundary, decreasing the grain size, leading to a porous microstructure and, consequently, degraded of varistors properties of systems.

Made available in DSpace on 2014-06-11T19:26:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-04-28Bitstream added on 2014-06-13T20:14:51Z : No. of bitstreams: 1 pede_maz_me_rcla.pdf: 3116261 bytes, checksum: eef7881b3c61cba9db27744f6f6269e9 (MD5) / A Região Metropolitana de São Paulo apresenta áreas de embasamento cristalino alterado, densamente ocupadas, que sofreram os mais diversos impactos ambientais, comprometendo os aqüíferos presentes. Este trabalho teve por objetivo a caracterização da condutividade hidráulica da porção saturada de dois domínios hidrogeológicos do embasamento cristalino alterado, um relacionado às rochas metassedimentares e outro às rochas gnáissicas. A condutividade hidráulica de ambos os domínios foi determinada através da realização de testes de slug em 63 poços de monitoramento. Os testes foram realizados utilizando-se transdutor de pressão de alta precisão. Os dados obtidos foram armazenados e analisados, utilizando-se os métodos de Hvorslev (1951) e Bower & Rice (1976). Os valores de condutividade hidráulica de cada domínio hidrogeológico, obtidos por ambos métodos, foram comparados através de análises estatísticas. Procurou-se estabelecer a relação entre os valores de condutividade hidráulica e a profundidade do meio saturado, bem como a influência das heterogeneidades presentes nos dois domínios hidrogeológicos. Os resultados dos testes revelaram que a condutividade hidráulica média das rochas gnáissicas alteradas é de 7,51x10-4 cm/s, segundo o método de Hvorslev (1951), e 2,34 x10-3 cm/s para o método de Bouwer & Rice (1976). Para as rochas metassedimentares alteradas foram obtidos valores médios de 5,01x10-5 cm/s e 7,99x10-5 cm/s, respectivamente. / The São Paulo Metropolitan Region (RMSP) is located on crystalline rock areas. The region is highly populated and has suffered different environmental impacts, affecting the aquifers. The objective of this work is to characterize the of the satured portion of two different hydrogeological domains, consisting of weathered basement, one related to the metassedimentary rocks and another to gneissic rocks. The hydraulic conductivities of both domains were determined by a series of slug tests in 63 monitoring wells. The tests were executed using a high precision pressure transducer. The data from the tests were collected, stored and analyzed using new analytical tools based on Hvorslev (1951) and Bower and Rice (1976) methods. The conductivity values obtained from both methods were evaluated using statistical analysis, looking for relationships among hydraulic conductivity, depth of satured zone, as well as heterogeneity present on both hydrogeologic domains. Hydraulic conductivity values for weathered gneiss were 7,51x10-4 cm/s and 2,34 x10-3 cm/s obtained using Hvorslev (1951) and Bower and Rice (1976), respectively. For metassedimentary rocks hydraulic conductivity values were 5,01x10-5 cm/s and 7,99x10-5 cm/s, respectively.

Made available in DSpace on 2014-06-11T19:26:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-23Bitstream added on 2014-06-13T19:55:06Z : No. of bitstreams: 1 panazzolo_f_me_botfca.pdf: 695410 bytes, checksum: 68a4f2852f522f08b7912faf2c61757b (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Universidade Estadual Paulista (UNESP) / A cenoura (Daucus carota L.) é uma hortaliça amplamente empregada na alimentação do brasileiro, constituindo uma rica fonte de cálcio e vitamina A, de fácil digestão e baixo teor de calorias. A cultivar Brasília foi desenvolvido para ser cultivada no verão, apresentando resistência ao calor, com produtividade média de 30 t ha-1 e ciclo médio de 85 a 100 dias. O presente trabalho teve por objetivo avaliar os possíveis efeitos do estresse hídrico e salino no crescimento e nas características morfológicas da cultivar Brasília. O experimento foi conduzido em casa de vegetação, no Departamento de Engenharia Rural da Faculdade de Ciências Agronômicas, Botucatu–SP, nos meses de setembro de 2009 e janeiro de 2010. O manejo hídrico foi estabelecido com base no potencial de água no solo e foram determinados três níveis de água (-0,01; -0,04 e -0,06 MPa), fazendo-se a reposição de água evapotranspirada por pesagem dos vasos. Foram utilizadas quatro doses de cloreto de sódio (1,41; 2,50; 4,50 e 6,45 dS m-1). O ensaio constituiu-se de um fatorial 3x4 (três níveis de água x quatro doses de salinidade). Os parâmetros morfológicos observados foram: altura da parte aérea, massas fresca e seca de parte aérea; massas fresca e seca da parte radicular (bulbo), comprimento da parte radicular (bulbo), diâmetro da parte radicular (bulbo) e produtividade. Foram realizadas três avaliações morfológicas durante os 100 dias após plantio e avaliações diárias de sobrevivência. A análise estatística dos dados foi feita pela análise de variância e teste de Tukey com 5% de probabilidade. Os resultados nas condições deste experimento permitiram as seguintes conclusões: Não foram observadas diferenças significativas... / The carrot (Daucus carota L.) is a vegetable widely used in the Brazilian diet, constituting a rich source of calcium and vitamin A, digestible and low in calories. The cultivar Brasilia was designed to be cultivated in summer, showing resistance to heat, with an average yield of 30 t ha-1 and average cycle from 85 to 100 days. This study aimed to evaluate the possible effects of water stress and salinity on growth and morphological characteristics of the Brasilia cultivar. The experiment was conducted in a greenhouse at the Department of Agricultural Engineering, Faculty of Agronomic Sciences, Botucatu-SP, on September 2009 until January 2010. The water management was based on soil water potential determined and three water levels (-0.01, -0.04 and -0.06 MPa), but with the replacement of water transpired by weighing the pots. We used four doses of sodium chloride (1.41, 2.50, 4.50 and 6.45 dS m-1). The test consisted of a 3x4 factorial (three levels of water salinity x four doses). The morphological parameters were: shoot height, fresh and dry shoot, fresh and dry weight of roots (bulb), length of roots (bulb), diameter of the root (bulb) and productivity. They performed three morphological evaluations during the 100 days after planting and daily assessments of survival. The statistical analysis was performed by ANOVA and Tukey test at 5% probability. The results allowed the following conclusions: there are not observed significant differences on plant development subjected to different minmum soil water potentials (Ψs) = -0,01; -0,04 e -0,06 MPa; the treatments that did not received saline doses showed higher development in relation to aereal part height and bulb length on three available periods (60, 80 e 100 days after planting); the applied saline doses (1,41; 2,50; 4,50 e 6,45 dS m-1 NaCl) did not statistically affect plant development in relation to fresh and dry of aereal... (Complete abstract click electronic access below)