This thesis concerns the formation, sintering and humidity dependent electrical behaviour of the spinel ceramic material nickel germanate, Ni(_2)Ge0(_4).Ni(_2)Ge0(_4) has been prepared via the solid state reaction between NiO and GeO(_2) over a range of temperatures, and characterised using a number of techniques. The sintering behaviour of pressed pellets of Ni(_2)Ge0(_4) has also been investigated, together with a characterisation of the microstructure of the sintered bodies. Substitutional doping of Ni(_2)GeO(_4) with Li as a replacement for Ni is found to promote a high degree of shrinkage in the sintering process, probably due to the formation of a liquid phase. XRD revealed that even when 10 % of the Ni atoms were replaced with Li, no change in the crystal structure could be detected. A C. impedance spectroscopy of Ni(_2)Ge0(_4) samples was used to investigate the humidity sensitivity of this material. Equivalent circuit analysis, based on a network of resistors and constant phase elements, shows that the humidity sensitivity is due to conduction in a surface layer of water, in agreement with the models currently popular in the Uterature. Measurement of the water adsorption isotherm of Ni(_2)Ge0(_4) in pellet form indicates that a single monolayer of water is formed at around 20 %R(_H), with an approximately linear increase in water layer thickness up to around 80 %R(_H), after which capillary condensation causes a large increase in the volume of adsorbed water. The information gained on the thickness of this layer of water has been correlated with the resistance of the layer measured by impedance spectroscopy, and subsequently used to provide evidence for a model of the humidity sensitive conduction. The conduction in the surface layer is thought to be due to dissociation of the water, where the amount of dissociation is exponentially dependent on the humidity.

A concentração de sais na água é um dos principais aspectos a ser observado para se definir uma estratégia de manejo da irrigação, podendo levar a prejuízos pela salinização do solo, com conseqüente redução do rendimento das culturas. Visto que culturas tolerantes à salinidade apresentam maiores teores foliares de certos nutrientes, então a adubação em culturas sensíveis poderia ser conduzida de modo a elevar os teores destes nutrientes nas folhas, promovendo aumento da tolerância da cultura aos sais. Este trabalho teve o objetivo de estudar os efeitos de três doses de N e K na tolerância da cultura do tomateiro à salinidade, bem como avaliar a performance de medidores de íons específicos (MIE) na determinação de nutrientes na solução do solo e na seiva da planta. Mudas de tomateiro, híbrido Facundo, foram transplantadas em 23/10/2001 em vasos contendo 60 kg de solo franco-argilo-arenoso, no espaçamento de 1,0 x 0,5 m, em um ambiente protegido com cobertura de polietileno. Os tratamentos foram compostos pela combinação de três níveis de N (7,5; 15,0 e 22,5 g planta-1) e três níveis de K (8, 16 e 24 gK2O planta-1) aplicados via fertirrigação por gotejamento, no esquema fatorial 3x3 com cinco repetições, sendo que à água de irrigação foram adicionados os sais cloreto de sódio e cloreto de cálcio para obtenção de condutividade elétrica da água de 9,5 dS m-1. Foram realizadas coletas da solução do solo e da seiva do pecíolo para determinações dos nutrientes pelos MIE, cujos valores foram comparados com as determinações pelos métodos-padrões. Não foram observados efeitos significativos dos tratamentos sobre o desenvolvimento e a produtividade das plantas, bem como sobre a qualidade dos frutos. As concentrações de nutrientes na solução do solo determinadas com os MIE apresentaram boa correlação com as determinações pelos métodos-padrões, e as concentrações de nutrientes na seiva do pecíolo foram bem correlacionadas aos teores na matéria seca das folhas. A condutividade elétrica e a concentração iônica na solução do solo não puderam ser estimadas a partir dos valores medidos no extrato de saturação ou na solução 1:2 apenas pela correção de umidade, com exceção do K e Na, cujas estimativas foram satisfatórias para baixas concentrações destes elementos na solução do solo. / The concentration of salts in the water is one of the main aspects to be observed to define a strategy of irrigation management, which could take to damages due to the soil salinization, with consequent reduction of crops yield. Once tolerant crops to salinity present larger tenors of some nutrients in the leaves, then the fertilizing in sensitive crops could be conducted in order to increase the tenors of these nutrients in the leaves to increase the crop tolerance to salts. This work had the objective of studying the effects of three doses of N and K in the tomato tolerance to salinity, as well as to evaluate the performance of cardy-ion meters (CIM) in the determination of nutrients in the soil solution and in the sap of the plant. Tomato seedlings, hybrid Facundo, were transplanted in 10/23/2001 in vases containing 60 kg of a sandy-clay-loam soil, spaced 1.0 x 0.5 m, in a greenhouse covered with polyethylene film. The treatments were composed by the combination of three levels of N (7.5; 15.0 and 22.5 g plant-1) and three levels of K (8, 16 and 24 gK2O plant-1) applied by drip fertigation, in the 3x3 factorial scheme with five replications. Salts (sodium chloride and calcium chloride) were added to the irrigation water for obtaining an electric conductivity of 9.5 dS m-1. Soil solution and petiole sap were collected for determinations of the nutrients with the CIM, whose values were compared with the determinations by the standard methods. Significant effects of the treatments were not observed for the development and yield of the plants, as well as for the fruits quality. The concentrations of nutrients in the soil solution determined with CIM showed good correlations with the determinations by the standard methods, and the concentrations of nutrients in the petiole sap were well correlated to the tenors in the dry matter of the leaves. The electric conductivity and the ionic concentration in the soil solution could not be estimated from the measured values in the saturation extract or in the solution 1:2 only by the correction of the water content, except for K and Na, whose estimates were satisfactory for low concentrations of these elements in the soil solution.

Com o intuito de contribuir para os estudos referentes à tolerância e efeitos da salinidade causada por excesso de fertilizantes nas principais culturas exploradas nacionalmente, o presente trabalho teve como objetivos estudar os efeitos de diferentes níveis de salinidade do solo sobre as variáveis fenológicas e de produção do pepino cultivado em vasos e em ambiente protegido, e averiguar se a manutenção da condutividade elétrica em um determinado nível promove incremento da produção quando contrastada com o manejo tradicional da fertirrigação. Este estudo foi conduzido na experimental do Departamento de Engenharia Rural da ESALQ/USP, Piracicaba, SP. Os tratamentos foram compostos da combinação de dois fatores: 6 níveis de salinidade inicial do solo (S1 = 1,5; S2 = 2,5; S3 = 3,5; S4 = 4,5; S5 = 5,5 e S6 = 6,5 dS m-1) e dois manejos de fertirrigação: tradicional (M1) e com controle da condutividade elétrica da solução do solo (M2). O delineamento estatístico adotado foi o de blocos casualizados completos com quatro repetições, ficando os fatores estudados arranjados no esquema fatorial 6 x 2. A salinização inicial do solo se procedeu por meio da aplicação de soluções salinas preparadas a partir de fertilizantes, sendo que a quantidade de sais a ser adicionada foi determinada tomando por base uma curva de salinização artificial obtida previamente em laboratório. A condutividade elétrica da solução foi medida após o término de cada evento de irrigação, utilizando-se extratores com cápsulas porosas. Os resultados mostram que houve efeito significativo, para todos os fatores estudados e para variáveis respostas estudadas, com exceção da variável altura de plantas. O manejo M1 proporcionou uma maior produção de frutos por planta, total e comercial, em relação ao manejo M2. Embora a literatura cite que a cultura do pepino seja moderadamente sensível a salinidade, o valor encontrado para a salinidade limiar (SL), sob condições do referente estudo, ficou bem acima dos níveis encontrados na literatura. / With intention of contributing for the studies regarding the tolerance and effect of the salinity caused by fertilizer excess in the main explored cultures, the present work has had as objective to study the effect of different levels of ground salinity on the phenology variable and of production of the cucumber cultivated in vases and protected environment, and to check if the maintenance of the electric conductivity in one determined level promotes increment of the production when contrasted with the traditional management of fertirrigation. This study was lead in the experimental area of the Department of rural Engineering of ESALQ/USP, Piracicaba, SP. The treatments had been composed of the combination of two factors: 6 levels of initial salinity of the ground (S1 = 1,5; S2 = 2,5; S3 = 3,5; S4 = 4,5; S5 = 5,5 and 6,5 S6 = dS m-1) and two fertirrigation management: traditional (M1) and with control of the electric conductivity of the solution of the soil (M2). The adopted statistical delineation was of complete random blocks with the four repetitions, being the studied factors arranged in factorial project 6 x 2. The initial salinization of the soil was proceeded by means of the application of saline solutions prepared from fertilizers, being that the amount of salt was to be added was determined based a in curve of artificial salinization previously gotten in laboratory. The electric conductivity of the solution was measured after the ending of each event of irrigation, using extracts with porous capsules. The results show that it had significant effect, for all the studied factors and changeable studied answers, except for the changeable height of plants. The M1 management provided a great yield of fruits per plant, total and negatiable, in relation to management M2. Literature states that the culture of the cucumber is moderately sensitive to the salinity, and the value found for the salinity threshold (SL), under conditions of the referring study, was well above of the levels found in the literature.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / Vita. / Includes bibliographical references. / Ph.D.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O presente trabalho apresenta o desenvolvimento, calibraÃÃo e testes de um tensiÃmetro de leitura eletrÃnica. O dispositivo foi calibrado utilizando como padrÃo de comparaÃÃo o tensiÃmetro de mercÃrio, e testado quanto ao tempo de resposta, efeito de flutuaÃÃes diurnas de temperatura nas leituras de potenciais, sensibilidade e precisÃo. Os ensaios foram conduzidos no LaboratÃrio de MecÃnica e EletrÃnica do Departamento de Engenharia AgrÃcola da UFC. A bancada de ensaio constituiu-se de trÃs caixas plÃsticas preenchidas com solo de densidade 1,4 g.cm3 e textura franco arenosa. Para o desenvolvimento dos testes, nove tensiÃmetros eletrÃnicos e trÃs tensiÃmetros de mercÃrio foram instalados. O tensiÃmetro eletrÃnico difere do tensiÃmetro de mercÃrio por substituir o mercÃrio como manÃmetro de pressÃo por um sensor de pressÃo, disposto em um circuito eletrÃnico juntamente com um sensor de temperatura, o qual foi calibrado antes da instalaÃÃo. O sistema de aquisiÃÃo de dados constituiu-se de um conversor analÃgico/digital, de 12 bits, microcontrolador e microcomputador portÃtil. Durante o perÃodo de um mÃs, foram coletados dados utilizados para gerar equaÃÃes de calibraÃÃo do tipo C = offset + bψ m , onde C à o valor do contador (cont) enviado ao computador e Ψm à o valor de potencial fornecido pelo tensiÃmetro de mercÃrio. Os valores mÃximo e mÃnimo de offset foram de 348,572 e 261,026, respectivamente, e de coeficiente angular de 3,597 e 3,376, respectivamente. Os resultados obtidos para o ajuste de regressÃo linear simplesindicaram a existÃncia de regressÃo a 1% de significÃncia e os coeficientes de correlaÃÃo apresentaram valores nunca inferiores a 0,9994. Para validar as equaÃÃes de calibraÃÃo, deu-se inÃcio a um segundo ciclo de secagem, entre as datas de 01/11/2002 a 13/12/2002, onde se obteve um valor de 0,9957 para o coeficiente de correlaÃÃo mÃnimo entre valores observados e esperados. O desvio entre os valores observados e os esperados deve-se provavelmente ao solo ainda estar passando por processos de agregaÃÃo e/ou estruturaÃÃo. As cÃpsulas porosas foram testadas quanto à condutÃncia e pressÃo de borbulhamento, apresentando valores mÃdios de condutÃncia igual de 2,031x10-3 cm2.s-1 e mÃnimo para pressÃo de borbulhamento de 1,3 atm. Quanto aos testes realizados no tensiÃmetro eletrÃnico, conclui-se que ocorre um aumento do tempo de resposta do equipamento com a diminuiÃÃo no potencial do solo, sendo este o principal fator de modificaÃÃo da resposta dos tensiÃmetros testados. Conclui-se ainda, que o erro nas leituras, decorrentes das flutuaÃÃes diurnas de temperatura, à evidente, principalmente nas horas em que o equipamento registra as maiores temperaturas, e a medida em que os potenciais diminuem. Os trÃs dispositivos testados apresentaram sensibilidades de 42,763, 42,575 e 43.161 mV.kPa-1, e precisÃo de 0,02338 (0,2385), 0,02348 (0,2394) e 0,02317 (0,2362) kPa (cm.c.H2O).

ii ABSTRACT Percolation phenomena involving the electrical conductivity, dielectric constant, Hall coefficient, magnetoconductivity, relative magnetoresistivity, 1/ f noise and thermoelectric power are investigated in graphite (G) and hexagonal boron-nitride (BN) powder mixtures. Two kinds of systems are used in the experiments: highly compressed discs and parallelepipeds, cut from these discs, as well as 50%G-50%BN and 55%G-45%BN powder mixtures undergoing compression. The measured DC conductivities follow the power-laws 0"( <p, 0) ex: (<p-<Pc)t (<p > <Pc) and O"(<p, 0) ex: (<Pc-<Pti (<p < <Pc), and the low frequency (lOOHz & 1000Hz) dielectric constant varies as c( <p, W ~ 0) ex: (<Pc - <P )-S( <P < <Pc), where <Pc is the percolation threshold, t and s are the conductivity exponents, and s is the dielectric exponent. Near the percolation threshold and at high frequencies, the AC conductivity varies with frequency as 0"( <p, w) ex: WX and the AC dielectric constant varies as c( <p, w) ex: w-Y, where the exponents x and y satisfy the scaling relation x + y = 1. The crossover frequency We scales with DC conductivity as Wc ex: O"q( <p, 0) (<p > <Pc), while on the insulating side, Wc ~ 1, resulting in q ~O for the three G-BN systems. The loss tangent tan t5( <p, w) (<p < <Pc) is found to have a global minimum, in contrary to the results of computer simulations. The Hall constant could not be measured using existing instrumentation. The measured magnetoconductivity and relative magnetoresistivity follow the power-laws - 6. 0" ex: (<p - <Pc)3.08 and 6.R/ R ex: (<p - <Pc)O.28 respectively. These two exponents, iii 3.08 and 0.28, are not in agreement with theory. The 1/ f noise was measured for the conducting discs and parallelepipeds. The normalized 1/ f noise power varies as Sv I V2 ex RW with the exponents w = 1.47 and 1.72 for the disc and parallelepiped samples respectively. Furthermore, the normalized noise power near the percolation threshold is, for the first time, observed to vary inversely with the square-root of sample volume. Based on the Milgrom-Shtrikman-Bergman-Levy (MSBL) formula, thermoelectric power of a binary composite is shown to be a linear function of the WiedemanFranz ratio. A scaling scheme for the Wiedeman-Franz ratio for percolation systems is proposed, which yields power-law behavior for the thermoelectric power. The proposed power-laws for the thermoelectric power can be written as (Sm - Md ex (<p - <Pc)h 1 for <P > <Pc and as (Sm - /~1d ex (<Pc - <p)-h2 for <p < <Pc, where Sm is the thermoelectric power for the composites, Afl is a constant for a given percolation system, and hI and h2 are the two critical exponents. The experimental thermoelectric power data for the G-BN conducting parallelepipeds was fitted to the above powerlaw for <p > <Pc. A least squares fit yielded the exponent hI = -1.13 and parameter MI =9.511l V I I< respectively.

Semiconducting properties and related defect disorder for well defined TiO2 single crystal were studies. Semiconducting properties have been determined using simultaneous measurements of two independent electrical properties, including electrical conductivity, ??, and thermoelectric power, S, at elevated temperatures (1073-1323 K) in the gas phase of controlled oxygen activity (10-10 Pa &lt p(O2) &lt 75 kPa). Measurements of s and S were conducted (i) in the gas/solid equilibrium and (ii) during equilibration. Oxygen vacancies have been identified as the predominant defects in TiO2 over a wide range of p(O2). Individual conductivity components related to electrons, electron holes and ions, were determined from the obtained ?? data. The effect of p(O2) on these individual components was considered in the form of a diagram. This work led to the discovery of the formation and diffusion of Ti vacancies. However, the obtained diffusion data indicate that, in the temperature ranges commonly used in studies of semiconducting properties (1000-1400K), the Ti vacancies concentration is quenched and may thus be assumed constant. In addition it was shown that Ti vacancies in appreciable concentrations form only during prolonged oxidation. It was determined that the discrepancies in the reported n-p transition point are related to the concentration and spectrum of impurities as well as the concentration of Ti vacancies. It has been shown that the n-p transition point in high-purity TiO2 is determined by the Ti vacancy concentration. A well defined chemical diffusion coefficient, Dchem, was determined using kinetic data obtained during equilibration. A complex relationship between p(O2) and Dchem was observed. These data showed a good agreement between the obtained diffusion data and defect disorder. Examination of the determined equilibration kinetics, led to the discovery of two kinetic regimes, the result of the transport of defects at different mobilities. The determined data are considered well defined due to the following reasons: 1. The studied specimen was of exceptionally high purity and free of grain boundaries (single crystal) 2. The specimen was studied in the gas phase of controlled and well defined oxygen activity which was continuously monitored. 3. Whenever the experimental data were measured in equilibrium, the gas/solid equilibrium has been verified experimentally. 4. A good agreement between the two, self-confirmatory, electrical properties, including ?? and S has been determined simultaneously and independently. The defect disorder model derived in the present work may be used for tailoring controlled semiconducting properties through the selection of annealing conditions involving the temperature and oxygen activity.

Liquid dispersions of colloidal particles play a big role in nature and as industrial products or intermediates. Their material properties are largely determined by the liquid-mediated particle-particle interaction. In water-based systems, electric charge is ubiquitous and electrostatic particle interaction often is the primary factor in stabilizing dispersions against decomposition by aggregation and sedimentation. Very nonpolar liquids, by contrast, are usually considered free of charge, because their low dielectric constant raises the electrostatic cost of separating opposite charges above the available thermal energy. Defying this conventional wisdom, nonpolar solutions of certain ionic surfactants do support mobile ions and surface charges. Even some nonionic surfactants have recently been found to raise the conductivity of nonpolar oils and promote surface charging of suspended particles, but this counter-intuitive behavior is not yet widely acknowledged, nor is the mechanism of charging understood. The present study provides the first characterization of the electrostatic particle interaction caused by nonionizable surfactants in nonpolar oils. The methods used in this study are video microscopy experiments where particle positions of equilibrium ensembles are obtained and translated into particle interactions. Experimentally, equilibrium particle positions are monitored by digital video microscopy, and subjected to liquid structure analysis in order to find the energy of interaction between two particles. The observed interaction energy profiles agree well with a screened-Coulomb potential, thus confirming the presence of both surface charge and mobile ions in solution. In contrast to recently reported electrostatic particle interactions induced by ionic surfactants in nonpolar solution, the present study finds evidence of charge screening both above and below the surfactant's critical micelle concentration, CMC. Fitted Debye screening lengths are much larger than in aqueous systems, but similar to the Debye length in nonpolar oils reported for micellar solutions of ionic surfactants cite{hsu_charge_2005}. Radial distribution functions obtained from experiments are compared to Monte-Carlo simulations with input potentials obtained from a fit to the interaction measurement. The measured electrostatic forces and fitted surface potentials are fairly substantial and easily capable of stabilizing colloidal dispersions. Although few in number, surface charges formed on polymer particle surfaces submerged in nonpolar solutions of nonionizable surfactants create surface potentials comparable to those in aqueous systems.

Polymer nanocomposites (PNCs) have gained significant interest because they have outstanding performance that allows cost reduction, weight reduction, and product improvement. This research study focuses on the manufacture and characterization of PNCs in order to explore their potential in automotive applications. More specifically, polypropylene (PP) nanocomposites reinforced with xGnP and nanokaolin were fabricated by manufacturing methods that optimize their performances. Exfoliated graphite nanoplatelets (xGnP) are promising nanofillers that are cost effective and multifunctional with superior mechanical, thermo-mechanical and electrical properties. Nanokaolin is a newly introduced natural mineral mind in Georgia that has not been studied as of now. PNCs reinforced with these two nanofillers were characterized in terms of mechanical, thermo-mechanical, and various other properties, and then compared to talc- reinforced PP composites, which are the current state of the art for rear bumpers used by Honda Motor. Characterization results indicated that xGnP had better performance than talc and nanokaolin. Furthermore, the addition of xGnP introduces electrical conductivity in the PNCs, leading to more potential uses for PNCs in automotive applications such as the ability to be electrostatic painted. In order to fabricate PNCs with a desired conductivity value, there is need for a design tool that can predict electrical conductivity. Existing electrical conductivity models were examined in terms of model characteristics and parameters, and model predictions were compared to the experimental data. The percolation threshold is the most important parameter in these models, but it is difficult to determine experimentally, that is why a correlation between thermo-mechanical properties and electrical conductivity is also investigated in this study.

Thesis (M.S.)--University of Central Florida, 2009. / Adviser: Kuo-Chi Lin. Includes bibliographical references (p. 84-92).