Дисертації: "Insulating polymer materials"

1

Sim, Alec. "Unified model of charge transport in insulating polymeric materials." Thesis, Utah State University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3606878.

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Presented here is a detailed study of electron transport in highly disordered insulating materials (HDIM). Since HDIMs do not lend themselves to a lattice construct, the question arises: How can we describe their electron transport behavior in a consistent theoretical framework? In this work, a large group of experiments, theories, and physical models are coalesced into a single formalism to better address this difficult question. We find that a simple set of macroscopic transport equations--cast in a new formalism--provides an excellent framework in which to consider a wide array of experimentally observed behaviors. It is shown that carrier transport in HDIMs is governed by the transport equations that relate the density of localized states (DOS) within the band gap and the occupation of these states through thermal and quantum interactions. The discussion is facilitated by considering a small set of simple DOS models. This microscopic picture gives rise to a clear understanding of the macroscopic carrier transport in HDIMs. We conclude with a discussion of the application of this theoretical formalism to four specific types of experimental measurements employed by the Utah State University space environments effects Materials Physics Group.

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2

Kashfipour, Marjan Alsadat. "Thermal Conductivity Enhancement Of Polymer Based Materials." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron156415885613422.

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3

Castrovilli, Matteo. "Characterization of the dipole processes of insulating materials used in aeronautical cables." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.

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The studies of this thesis are focused on aeronautic Polymers materials and their dielectric properties, in order to analyze the relaxation times for the materials of interest under an applied electric field, and in order to increase the work operations of the Novocontrol dielectric spectroscopy measurement machine available in the LAPLACE laboratory. In this context, the research team DSF in collaboration with MDCE, from LAPLACE laboratory, has developed in 2019 a numerical model taking into account the polar mechanisms of the polymer insulators used in the aeronautic industry. However, this theoretical model, is not yet validated. Therefore the aim of this thesis, is to make it possible to validate this theoretical model, then by a series of measurements with dielectric spectroscopy(D.S.) for different materials of interest, different frequencies and temperatures; the measurements consist on the measuration of the phase difference between current and voltage applied to the samples, in order to calculate the permittivity values under different working conditions. The permittivity trend is therefore analyzed to find the polar relaxation under thermoelectrical stresses, and the model will then have to calculate the current density (and from the current density is directly calculated the dissipated energy) of the measured data with dielectry spectroscopy, and the validation will be done if the future measurement values of the current density correspond to the calculated one by the model. For this reasons, the main part of the work for this thesis consist in measurements trought the dielectric spectroscopy (using the following polar materials: Polyimide(PI) and PTFE ) under different working conditions and analyze the results in order to evidence polarization phenomena, because the purpose of this part of the validation process is to have the better polar relaxation data for the future work.

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4

Neumann, Andreas C. "Electronic transport in highly resistive materials in strong magnetic fields :nonlinear dynamics in semi-insulating GaAs and magnetoresistance of carbon-black polymer composites." Doctoral thesis, Universite Libre de Bruxelles, 1997. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212185.

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5

Adetunji, Oludurotimi Oluwaseun. "The nature of electronic states in conducting polymer nano-networks." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1206218304.

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6

Silva, Igor. "Propriétés des matériaux isolants pour application dans les appareillages moyenne tension à tension continue." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALT043.

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Les récentes avancées dans la technologie du courant continu, du côté du transport à haute tension et de la consommation à basse tension, ont propulsé le courant continu de moyenne tension (MVDC) au premier plan. Cette thèse explore les propriétés isolantes en courant continu de deux matériaux couramment utilisés dans l'équipement de distribution : de l'époxy chargé en micro-silice et le silicone elastomère.Dans une configuration monocouche, chaque matériau a fait l'objet d'une enquête approfondie, mettant l'accent sur les caractéristiques de sorption d'eau et la conduction électrique. Des mesures de courant ont été effectuées pour analyser la conduction dans divers niveaux de champs, à différentes températures et conditions d'absorption d'eau. De plus, la méthode Laser Pressure Pulse (LIPP) a été utilisée pour des mesures de charge d'espace en tant que technique complémentaire. L'étude s'est étendue à une configuration bicouche, combinant les deux matériaux, nous permettant ainsi de confirmer un modèle prédisant les propriétés du multicouche et sa distribution de champs en fonction des valeurs des monocouches.La conduction en courant continu dans l'époxy a montré une forte dépendance à l'absorption d'eau, l'humidité influençant la non-linéarité et modifiant le mécanisme de conduction. À l'inverse, le silicone a démontré une conduction limitée par l'électrode, avec des variations de courant liées à la sorption d'eau par le biais d'un mécanisme limité par saturation. Dans une configuration bicouche hypothétique, où l'époxy représente un manchon et le silicone sert de terminaison de câble, le champ est censé se concentrer dans l'époxy dans des environnements secs, passant au silicone à mesure que l'humidité augmente. La thèse se conclut par des discussions sur les stratégies de sélection des matériaux et la conception de configurations multicouches
Recent advancements in direct-current technology from the high-voltage transport and low-voltage consumption have brought medium-voltage DC (MVDC) to the forefront. This thesis delves into the insulating DC properties of two commonly used materials in distribution equipment: epoxy filled with silica and silicone rubber.In a monolayer configuration, each material underwent extensive investigation, focusing on water sorption characteristics and electrical conduction. Current measurements were conducted to analyze conduction under various fields, temperatures, and water uptake conditions. Additionally, the Laser Pressure Pulse (LIPP) method was employed for space charge measurements as a complementary technique. The study extended to a bilayer configuration, combining both materials, with insights from monolayer experiments informing the properties of the bilayer and predicting field distribution.The DC conduction in epoxy exhibited high dependence on water absorption, with moisture influencing non-linearity and altering the conduction mechanism. Conversely, silicone demonstrated electrode-limited conduction, with current variations tied to water sorption through a saturation-limited mechanism. In a hypothetical bilayer configuration, where epoxy represents a type-C bushing and silicone serves as the cable termination, the field is expected to concentrate in the epoxy in dry environments, shifting to silicone as humidity increases. The thesis concludes with discussions on material selection strategies and the design of multi-layer configurations

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7

Gawryla, Matthew Daniel. "Low Density Materials through Freeze-Drying:Clay Aerogels and Beyond…" Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1247013426.

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8

Sim, Alec. "Unified Model of Charge Transport in Insulating Polymeric Materials." DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/2044.

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Charge transport, charging, and subsequent electrostatic discharge due to interactions with the space environment are primary concerns of spacecraft designers. Developing a physical understanding of the interactions of charge with the multitude of materials that spacecraft are composed of is a critical step in understanding and mitigating both short-term and long-term spacecraft degradation. In particular, the study of charge transport in highly insulating materials is critical as they store charge longer, with higher capacity, and with greater destructive capability than other materials.The Utah State University Materials Physics Group, with the funding of the NASA James Webb Space Telescope project and Rocky Mountain Space Consortium, have developed a complete and consistent theoretical model that predicts short-term and long-term storage capabilities based on physical material parameters. This model is applicable across a wide range of experimental systems designed to test specific behaviors that characterize charging phenomena.Modeling and understanding the complex relationships between the spacecraft and its surroundings are fundamentally based on detailed knowledge of how individual materials store and transport charge. The ability to better understand these effects will help make exploring the edges of the universe more stable, reliable, and economic.

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9

Elbuzedi, Mohamed. "Material study and properties of polymers used in composite high voltage insulators." Thesis, Stellenbosch : Stellenbosch University, 2007. http://hdl.handle.net/10019.1/17749.

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Thesis (MSc)--University of Stellenbosch, 2007.
ENGLISH ABSTRACT: Silicone rubber, particularly poly(dimethylsiloxane) (PDMS), has been increasingly used in the manufacture of outdoor high voltage insulators in the recent years. PDMS offers several advantages that make it suitable for outdoor use, such as low weight, a hydrophobic surface, stability, and excellent performance in heavily polluted environments. PDMS surfaces can, however, become progressively hydrophilic due to surface oxidation caused by corona discharge, UV radiation and acid rain. In this study, PDMS samples of controlled formulations as well as six commercial insulator materials four PDMS based and two ethylene propylene diene monomer (EPDM) based were exposed to various accelerated weathering conditions for various periods of time in order to track changes in the material over time. The ageing regimes developed and used to simulate the potential surface degradation that may occur during in-service usage included needle corona and French corona ageing, thermal ageing, UV-B irradiation (up to 8000 hours) and acid rain (up to 200 days). Both the chemical and physical changes in the materials were monitored using a wide range of analytical techniques, including: static contact angle measurements (SCA), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), gas chromatography (GC), gas chromatography/mass spectroscopy (GC/MS), size-exclusion chromatography (SEC), Fourier-transform infrared photoacoustic spectroscopy (FTIR-PAS) and slow positron beam techniques (PAS). A low molecular weight (LMW) uncrosslinked PDMS model compound was used to further study the chemical effects of corona exposure on PDMS materials. PDMS showed far better performance than EPDM, in terms of resistance to the various ageing regimes and “hydrophobicity recovery”.
AFRIKAANSE OPSOMMING: Silikoonrubber, spesifiek polidimetielsiloksaan (PDMS), is gedurende die afgelope paar jaar toenemend gebruik in die vervaardiging van buitelughoogspanningisolators. PDMS het baie voordele vir gebruik in elektriese isolators soos ‘n laer massa, ŉ hidrofobiese oppervlak, stabiliteit en uitstekende werking in hoogsbesoedelde omgewings. Die hidrofobiese oppervlakte kan egter gelydelik hidrofilies word weens oppervlakoksidasie as gevolg van korona-ontlading, UV-bestraling en suurreën. In hierdie studie is PDMS monsters van verskillende samestellings sowel as ses kommersiële isolators (vier PDMS en twee etileenpropileenrubber (EPDM)) blootgestel aan verskillende versnelde weersomstandighede vir verskillende periodes om die veranderinge in die materiale te monitor. Die verskillende materiale is gerangskik volgens hulle werking oor ‘n periode van tyd. Dit het ook ‘n geleentheid gebied om die eienskappe van die verskillende samestellings te bestudeer. Die tegnieke wat ontwikkel is om die moontlike oppervlakdegradasie te simuleer, het naald-korona, “French” korona, UVB-bestraling (tot 8000 uur) en suurreën (tot 200 dae) ingesluit. Beide die chemiese en die fisiese veranderinge in die materiale is gemonitor met behulp van verskeie tegnieke soos statiese kontakhoekbepaling, optiese mikroskopie, skandeerelektronmikroskopie, energieverspreidingsspektroskopie, gaschromatografie, grootte-uitsluitingschromatografie, foto-akoestiese Fouriertransforminfrarooi (PASFTIR) en stadige-positronspektroskopie (PAS). ŉ Lae molekulêre massa PDMS modelverbinding is gebruik om die chemiese effek van korona te bestudeer. Die PDMS materiale het baie beter vertoon teenoor die EPDM materiale in terme van hulle herstel van hidrofobisiteit.

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10

Sokotun, Zh, and O. Koshelieva. "Evaluation durability of polymeric insulating material of electric cables." Thesis, Київський національний університет технологій та дизайну, 2017. https://er.knutd.edu.ua/handle/123456789/6714.

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11

Shinko, Andrew. "Structure and Morphology Control in Polymer Aerogels with Low Crosslink Density." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430399529.

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12

Bandaru, Venkata Raghava Sunil Kumar Reddy. "Deformation and Durability Studies of Insulation Polymers." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1227191899.

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13

Zhang, Hui. "Aging characteristics of solid polymeric materials used for electrical insulation." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0018/MQ52685.pdf.

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14

Goss, Ben. "Degradation and life time prediction of high voltage insulation materials." Thesis, Queensland University of Technology, 2001.

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15

Andersen, Allen. "The Role of Recoverable and Non-Recoverable Defects in DC Electrical Aging of Highly Disordered Insulating Materials." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/7047.

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Electrical insulation under high voltage can eventually fail, causing critical damage to electronics. Such electrostatic discharge (ESD) is the primary source of anomalies or failures on spacecraft due to charged particles from the Sun or planetary radiation belts accumulating in spacecraft insulators. Highvoltage direct current power distribution is another example of a growing industry that needs to estimate the operational lifetime of electrical insulation. My research compares laboratory tests of ESD events in common insulating materials to a physics-based model of breakdown. This model of breakdown is based on the approximation that there are two primary types of defects in structurally amorphous insulators. One of the two defect modes can switch on and off depending on the material temperature. This dual-defect model can be used to explain both ESD and less-destructive transient partial discharges. I show that the results of ESD tests agree reasonably well with the dual defect model. I also show that transient partial discharges, which are usually ignored during ESD tests, are closely related to the probability of catastrophic ESD occurring. Since many partial discharges are typically seen during one ESD test, this relationship suggests that the measurements of partial discharges could accelerate the testing needed to characterize the likelihood of ESD in insulating materials.

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16

Hergert, Alexander [Verfasser]. "Test methods for evaluating the dynamic properties of hydrophobicity of polymeric insulating materials / Alexander Hergert." München : Verlag Dr. Hut, 2017. http://d-nb.info/1135597049/34.

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17

Khan, Amir. "Vibro-acoustic products from re-cycled raw materials using a cold extrusion process : a continuous cold extrusion process has been developed to tailor a porous structure from polymeric waste, so that the final material possesses particular vibro-acoustic properties." Thesis, University of Bradford, 2008. http://hdl.handle.net/10454/4289.

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A cold extrusion process has been developed to tailor a porous structure from polymeric waste. The use of an extruder to manufacture acoustic materials from recycled waste is a novel idea and the author is not aware of any similar attempts. The extruder conveys and mixes the particulates with a reacting binder. The end result is the continuous production of bound particulates through which a controlled amount of carbon dioxide gas that is evolved during the reaction is used to give the desired acoustic properties. The cold extrusion process is a low energy consuming process that reprocesses the post manufacturing waste into new vibro-acoustic products that can be used to meet the growing public expectations for a quieter environment. The acoustical properties of the developed products are modelled using Pade approximation and Johnson-Champoux-Allard models. Applications for the developed products are widespread and include acoustic underlay, insulation and panels in buildings, noise barriers for motorways and railway tracks, acoustic insulation in commercial appliances and transport vehicles.

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18

Ariffin, Azrul Mohd. "The measurement and modelling of electroluminescence in high voltage polymeric cable insulation materials." Thesis, University of Southampton, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494683.

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Since space charge plays a significant role in long-term electrical degradation of polymeric insulation in high voltage cables, there is growing interest in the measurement of the energy dissipation of mobile and trapped charges in the dielectric molecules. The dissipation process is associated with the emission of visible photons, a process known as electroluminescence (EL) and can be used, potentially, as an indicator for the inhibition of electrical ageing of insulation. This thesis is based on an investigation into the occurrence of EL in dielectric materials as a result of applying high ac stresses. The phenomenon has been observed and analyzed for different types of thin polymeric films using a charge coupled device (CCD) detection system. This unique experimental setup enables a range of measurements to be performed including the imaging of EL, its temporal behaviour, spectral analysis and phase-resolved measurements using the same detector. The effects of several factors such as the types of material under study and local gas environment have been assessed based on the results obtained. Previously, different research groups have monitored the occurrence of EL under ac conditions by applying a sinusoidal electric field across the polymer but in this project, the emission is also examined under the influence of triangular and square voltage waveforms, together with their asymmetrical counterparts. In addition to this, a dynamic bipolar charge recombination model has been developed in order to simulate studies of EL under an alternating field. By comparing experimental results with the stimulation, the theories relating to the processes responsible for the occurrence of EL have been evaluated and a good agreement was found between the simulation and experimental results.

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19

Guffond, Raphaël. "Characterization and modeling of microstructure evolution of cable insulation system under high continuous electric field." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS039/document.

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Le sujet de cette thèse porte sur la compréhension et la modélisation du comportement électrique de système d'isolation soumis à un fort champ électrique continu. Les propriétés électriques du polymère sont directement pilotées par ses hétérogénéités chimiques et physiques présentes à plusieurs échelles. Dans cette étude, un nouveau modèle est développé ayant pour but de simuler l'évolution de la microstructure de polymère avec la température, le champ électrique et le temps et de simuler l'impact de cette évolution sur les propriétés électriques du polymère. Dans ce modèle, des matrices sont utilisées pour décrire la distribution de chacune des hétérogénéités et propriété électriques d'un polymère semi-cristallin. L'évolution de ces matrices de microstructure suit des lois génétiques dont la définition a été obtenue à partir d'une caractérisation fine des propriétés physicochimiques et électriques de matériaux spécifiques en fonction de la température et du champ électrique. Ces lois implémentées sont basés sur des calculs simples permettant un temps de résolution plus rapide comparativement aux autres modèles préexistants. Basée sur ces lois d'évolutions génétiques, le comportement électrique sous champ électrique continue de polymère isolant peut être simulé uniquement à partir d'une caractérisation physique et chimique de ce polymère. Le modèle est ainsi capable de reproduire le comportement électrique de plusieurs polymères semi-cristallins et de suivre les données expérimentales mesurées par ailleurs. Le modèle intègre plusieurs physiques tels que la diffusion, le transport ionique et le transport électronique, lui permettant ainsi de prendre en compte l'influence d'un grand nombre d'hétérogénéités
This thesis presents a research work on understanding and modeling the electrical behavior of insulation system in cables subjected to high DC constraints. Electrical properties of polymeric insulation are directly related to their chemical and physical heterogeneities present at several scales. In this work, a new model is developed to simulate the modification over time of the microstructure in insulation polymers under electric field and temperature as well as the subsequent impacts on electrical properties. In this model, matrices are used to describe the distribution of each heterogeneity and electrical property in semi-crystalline polymer. When stressed under electric field and at temperature, matrices of microstructure evolve from implemented genetic laws. This simulated microstructure evolution yields to the simulation of electrical property changes over time at transient and steady state. To define these genetic laws, a detailed characterization of the physical, chemical and electrical properties of specific materials as a function of temperature and electric field is experimentally performed. Genetic laws are notably implemented to take into account the impact of the semi-crystalline structure and the presence of chemical residues in polymer electrical properties. Based on these genetic evolution laws, this modeling approach allows simulating DC electrical behavior of polymers only from their physical and chemical characterizations and reproduce accurately experimental electrical behavior with a faster solving time compared to other simulation methods

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20

Santana, Anderson Marques de. "Desenvolvimento de sistema para medição de hidrofobicidade em materiais poliméricos." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/18/18133/tde-12052017-104427/.

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Isoladores poliméricos têm crescentemente competido com os isoladores cerâmicos nas aplicações em sistemas elétricos de potência e é esperado que dominem as aplicações externas em alta tensão em um futuro próximo. Entretanto, há ainda algumas questões pendentes acerca do envelhecimento dos polímeros sobre estresse elétrico e climático. Dessa forma, a estabilidade da hidrofobicidade deve ser medida para estender o tempo de vida do isolador. Por esta razão, o desenvolvimento de um sistema de medição da degradação tem se tornado um fator relevante. Este trabalho apresenta e discute o desenvolvimento de um sistema para avaliação da hidrofobicidade em materiais poliméricos. São também discutidos os testes realizados em novas resinas derivadas do óleo de mamona.
Polymeric isolators have been competing increasingly with ceramic isolators in electric power system applications and is expected to dominate in the near future high voltage outdoor applications. However, there are still some outstanding questions regarding aging of polymers under climatic and electrical stresses. In this way, hydrophobicity has to been measured for to extend the life time of these insulators. For these reasons, the development of a degradation measurement system has become a relevant factor. This work presents and discusses the development of a hydrophobicity estimation system to polymeric materials. Also discussed are the tests carried out on the new castor oil resin.

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21

Nagashima, Haroldo Naoyuki. "Migração de carga espacial em copolímeros P(VDF/TrFE)." Universidade de São Paulo, 1992. http://www.teses.usp.br/teses/disponiveis/54/54132/tde-14012009-102720/.

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Este trabalho apresenta um modelo teórico que procura explicar a origem de um pico anômalo de corrente, observado na fase faraeletrica do copolímero P(VDF/TrFE), nos processos de descarga. Quando uma voltagem tipo V(t) = Vo S(t) é aplicado em materiais isolantes, correntes elétricas observadas em medidas, de carga-descarga decaem aproximadamente com T-n e obedecem ao principio da superposição linear (PSL). Esse comportamento e também observado em polímeros dielétricos. Entretanto, nos processos de descarga, acima da temperatura de Curie do copolímero p (VDF/TrFE), surge um pico anomalo de corrente que viola, aparentemente, o (PSL). Apresentamos um modelo de migração de cargas de espaço em presença de armadilhas, que pode ser responsável pelo pico de corrente e que estaria superposta a corrente de descarga da absorção dielétrica, conforme o modelo, durante os processos de carga, impurezas extrínsecas seriam varridas, pelo campo, do volume da amostra e ficariam, preferencialmente, presas em armadilhas de superfície. Nos processos de descarga, essas cargas se deslocariam em direção ao interior da amostra, devido a repulsão Coulombiana. Esse mecanismo de condução gera um pico de corrente. A aplicação do modelo, permitiu-nos inferir valores de parâmetros como a mobilidade dos portadores de carga e o tempo de transito.
A model based on space charge migration to explain an anomalous electric current peak on films of P (VDF/TrFE) copolymer in its paraelectric phase is presented. In general step-voltage current measurements of insulating polymeric materials obey the Principle of Linear Super-position. However, an unexpected anomalous peak was observed in discharge currents in measurements performed with P (VDF/TrFE) above the Curie temperature. We have assumed that space charges were dragged from the bulk of the sample by the external field during the charge measurement, and trapped close to the surface of the sample in a region where the concentration of traps would be very high. Two methods were developed to calculate the magnitude of the current peak: I) assuming a given space charge distribution during the discharge measurement, and II) considering the movement of thin discrete layers of charge under the influence of the internal field.

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22

Mokni, Marwa. "Optimisation et analyses des propriétés physico-chimiques et diélectriques du parylène D." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY080/document.

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Ce travail est consacré à l’élaboration et à la caractérisation de couches minces de parylène D déposées par dépôt chimique en phase vapeur (CVD) sous forme de films de quelques microns d’épaisseur. L’objectif de l’étude est d’évaluer les potentialités de ce polymère en remplacement des parylènes de type N ou C pour des applications spécifiques ou encore pour l’intégrer dans de nouvelles applications. Une première étude a consisté à évaluer l’impact des paramètres des dépôts CVD (température de sublimation, température de pyrolyse, température du substrat d’accueil du film déposé) sur les changements physico-chimiques, structuraux et diélectriques du parylène D. Pour cela, nous nous sommes appuyés sur des analyses FTIR, XRD, DSC, TGA, AFM, SEM, DMA. Nous avons également appliqué des stress thermiques au parylène D dans le but d’évaluer leur performance à haute température (>200°C) ainsi que les changements opérés au niveau de la structure cristalline (taille des cristallites, pourcentage de cristallinité,…) ou encore la stabilité des propriétés thermiques (température de transition vitreuse, température de cristallisation, température de fusion) et diélectriques (constante diélectrique e’, facteur de dissipation tand et conductivité basse fréquence s’) Enfin, des analyses diélectriques en fréquence (de 0,1Hz à 100 kHz) sur une large plage de température de fonctionnement (-140°C – 350°C) ont permis de mettre en évidence la présence de trois mécanismes de relaxations (a, b, g), une polarisation d’interface de type Maxwell-Wagner-Sillars et une polarisation d’électrode. Les performances diélectriques sont également discutées par comparaison aux parylènes de type N et C plus couramment utilisés aujourd’hui dans les applications industrielles. Cette étude permet ainsi de disposer maintenant de paramètres de dépôt CVD bien contrôlés pour le dépôt de films de parylènes D aux propriétés souhaitées pour une application spécifique
This work is mainly focused on the elaboration and the characterization of parylene D thin films of few micrometers deposited by chemical vapor deposition (CVD). The goal of this study is to evaluate the potentialities of this polymer in order to replace the parylene N or C for specific applications or to integrate it in new applications. A first study consisted in evaluating the impact of the CVD process parameters (temperature of sublimation, temperature of pyrolysis, substrate temperature) on the surface morphology, the molecular structure and dielectric changes of parylene D. For that, we were based on several analyzes techniques as FTIR, XRD, DSC, TGA, AFM, SEM, DMA. Thermal stresses were applied to parylene D to evaluate their performance at high temperature (>200°C) and the changes on the crystal structure (size of crystallites, percentage of crystallinity,…) or the stability of the thermal properties (temperature of transition, temperature of crystallization, melting point) and dielectric properties (the dielectric permittivity, the dissipation factor, the electrical conductivity and the electric modulus). Dielectric and electrical properties of Parylene D were investigated by dielectric spectroscopy in a wide temperature ranges from -140°C to 350°C and frequency from 0.1 Hz to 1 MHz, respectively. (a, b and g)-relaxation mechanisms, interfacial polarization related to Maxwell-Wagner-Sillars and electrode polarization have been identified in this polymers. The dielectric performances of Parylene D have been also compared with parylenes N and C which are used in wide industrial applications. Optimized and controlled conditions of the CVD process of parylenes D are proposed in this work in relation to the properties. The obtained results open a new way for specific applications

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23

Abraham, Berhane Teclesenbet. "Degradation and recovery of polydimethylsiloxane (PDMS) based composites used as high voltage insulators." Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/49902.

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Thesis (MSc)--Stellenbosch University, 2004.
ENGLISH ABSTRACT: Polydimethylsiloxane (PDMS) compounds are utilized in outdoor high voltage insulation due to their low weight, vandalism resistance, better anti-contamination performance and their superior hydrophobic nature. Under severe environmental conditions and over prolonged service time, however, the hydrophobic surface can gradually become hydrophilic and then recover with adequate resting period. In this study, room temperature vulcanized (RTV) PDMS samples were prepared with different formulations and then exposed to corona discharge to evaluate its effect. The influence of different additives, such as different types and amount of fillers and additionally added low molar mass silicone oils, on the hydrophobicity recovery of the material was investigated. The effects of two types of corona treatment were also evaluated. Hydrophobicity recovery of corona and UV-C aged PDMS samples was evaluated by means of static contact angle measurements. Positron annihilation spectroscopy (PAS) gave important information on the micro structural change after corona treatment of RTV PDMS as well as naturally aged high temperature vulcanized (HTV) PDMS samples. The different formulations of the RTV PDMS samples and the effect of the additives were studied with this technique. The formation of a thin, highly crosslinked inorganic silica-like (SiOx) layer was confirmed even at the early stage of degradation. It was also possible to estimate the thickness of the silica-like layer formed during corona exposure that is responsible for the loss and recovery of hydrophobicity. The surface hardness and hydrophilicity change of PDMS samples due to corona treatment were studied simultaneously with force distance measurements by atomic force microscopy (AFM). The adhesive force calculated from the pull-off force-distance curves showed that the adhesive force between the probe and the sample decreased with increasing corona treatment time, indicating hydrophobicity recovery. In addition to this, the increase in hardness after corona exposure provides indirect evidence of the formation of a silica-like layer. In all cases the hydrophilicity and the surface hardness of the PDMS samples increased directly after corona treatment and recovered with time. Two types of FTIR spectroscopy were used to analyse the surface of the polymer.
AFRIKAANSE OPSOMMINGS: Polidimetielsiloksaan (PDMS) word in buitelug hoogspanninginsulasie gebruik as gevolg van sy lae massa, weerstand teen vandalisme, verbeterde anti-kontaminasie werkverrigting en superieure hidrofobiese karakter. Die hidrofobiese oppervlakte kan egter gelydelik hidrofillies word onder uiterste omgewingsomstandighede en oor langdurige dienstyd. PDMS materiaal herstel egter nadat dit genoeg rustyd toegelaat is. Kamertemperatuur-gevulkaniseerde (KTV) PDMS met verskillende formulasies is in hierdie studie voorberei, aan korona ontlading blootgestel, geëvalueer en vergelyk. Die invloed van bymiddels soos verskillende tipes en hoeveelhede vuiler, asook addisionele lae molekulêre massa silikoonolie, op die herstel van hidrofobisiteit van die materiaal is ondersoek. Twee verskillende metodes van korona behandeling is ook geëvalueer. Die herstel van hidrofobisiteit van korona en UV-C verouderde PDMS monsters is met statiese kontakhoekmeting geëvalueer. Positronvernietigingspektroskopie (PVS) is 'n kragtige tegniek wat belangrike inligting oor die mikrostrukturele verandering van korona behandelde van KTV PDMS sowel as natuurlik-verouderde hoë temperatuur gevulkaniseerde (HTV) PDMS monsters gee. Die verskillende formulasies van die KTV PDMS monsters, sowel as die effek van die vullers, is met behulp van hierdie tegniek ondersoek. Die vorming van 'n dun, hoogskruisgebinde, anorganiese silika-agtige (SiOx) laag op die PDMS oppervlak, selfs tydens die vroeë stadium van degradasie, is bevestig. Dit was ook moontlik om die dikte van die silika-agtige laag wat gedurende die korona blootstelling gevorm het, en wat verantwoordelik is vir die verlies aan hidrofobisiteit, te bepaal. Die oppervlakhardheid en hidrofilisiteit verandering van PDMS monsters as gevolg van korona behandeling, was gelyktydig met krag-afstand metings deur middel van atoomkragmikroskopie (AKM) bestudeer. Die kleefkrag, soos bereken van aftrek kragafstandkurwes, dui daarop dat kleefkragte tussen die taster en die monster afneem met toenemende korona behandelingstyd, wat beduidend is op die herstel van hidrofobisiteit. Daarbenewens is die toename van oppervlakhardheid na korona blootstelling "n indirekte bewys van die formasie van 'n silika-agtige laag. In alle gevalle het die hidrofilisiteit en die oppervlakhardheid van die PDMS monsters toegeneem direk na afloop van korona behandeling en gevolglik herstel met tyd. Twee tipes IR spektroskopie metodes is gebruik vir die chemiese-oppervlak analises

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24

CAVASIN, MATTEO. "Study on accelerated exposure testing and thermal insulation for a Glass Fibre Reinforced Polymer in simulated Oil & Gas environment." Doctoral thesis, Politecnico di Torino, 2019. http://hdl.handle.net/11583/2751272.

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25

El, Yamani Hamza. "Caractérisation du comportement mécanique de matériaux isolants sous choc." Electronic Thesis or Diss., Bourges, INSA Centre Val de Loire, 2021. http://www.theses.fr/2021ISAB0007.

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Анотація:

La réduction des risques, sur des sites Seveso et leurs alentours, face aux sollicitations accidentelles ou malveillantes, passe par la sécurisation des bâtiments aux sollicitations dynamiques de type surpression et impact. L’utilisation d’une isolation par l’extérieur, de type matériau isolant et bardage métallique par exemple, semble une piste intéressante techniquement et économiquement permettant d’allier protection face aux risques technologiques et rénovation énergétique.Dans ce travail, deux matériaux représentatifs des isolants thermiques plastiques et minéraux ont été retenus, une mousse polyisocyanurate et une laine de verre. La caractérisation mécanique de ce type de matériaux complexes et à très faible masse volumique, demeure, dans le contexte de sollicitations dynamiques, largement incomplète à l’heure actuelle et les essais mal maîtrisés.Des essais de compression simple et œdométrique en régime statique sont réalisés et un suivi par imagerie à haute résolution associé à de la corrélation d’images numérique permet d’identifier les propriétés mécaniques, d’observer l’hétérogénéité des déformations et de suivre la propagation de fronts de compaction dans le matériau.Des essais dynamiques aux barres de Hopkinson, complétés d’essais DMA, permettent d’étudier la sensibilité à la vitesse de la réponse et de mettre notamment en évidence une dépendance à la vitesse de la contrainte plateau et une insensibilité à la vitesse de la déformation à la densification. Un suivi par imagerie à haute vitesse associé à de la corrélation d’images numérique permet également d’observer l’hétérogénéité des déformations et de déterminer la célérité du front de compaction dans le matériau.Le comportement mécanique des isolants est reproduit au moyen de lois empiriques ou par assemblage de modèles rhéologiques. Une modélisation simplifiée est proposée pour analyser l’effet potentiel d’un dispositif de protection constitué d’un ensemble bardage et isolant face à une sollicitation dynamique transitoire. Elle montre que si un effet atténuateur est possible, son efficacité va dépendre tout à la fois de la signature de la sollicitation et des caractéristiques physiques et géométriques du système de protection
Risk reduction on Seveso sites, particularly for the protection of industrial buildings in the event of an explosion scenario, is a matter of concern. In the context where the insulation of industrial buildings is becoming more widespread, one solution would be to combine thermal insulation and building protection, by exploiting the absorption capacity of common thermal insulation materials. This solution would be interesting from an economic point of view.The aim of this PhD thesis is to experimentally characterise the mechanical behaviour of two insulating materials commonly used in France: a polyisocyanurate foam and a glass wool. Various devices were used to determine the mechanical behaviour, in particular the Split Hopkinson Pressure Bars device, which allows to characterise the mechanical behaviour at high speed loading.The polyisocyanurate foam was characterised in static and dynamic regimes, in unconfined compression and confined compression. These tests showed a sensitivity to the strain rate of the plateau stress in the material, and showed, by using the digital image correlation technique, the heterogeneity of the deformation in the material. The behaviour of the foam was modelled in two ways: firstly with an empirical law and secondly with a rheological model to simulate a dynamic compression test. The glass wool was characterised in simple static compression, and its behaviour was modelled empirically.The modelling based on empirical laws allowed us to carry out some simple simulations of a dynamic stress of explosion type on a cladding-material-structure assembly. The rheological model, which only concerns the polyisocyanurate foam, was used to identify the viscoplasticity coefficient

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26

Vallet, Magali. "Etude des phénomènes limitant l'étalement de solutions aqueuses sur des films de polymères par électromouillage." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10136.

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L'application d'un champ electrique a un systeme compose d'une goutte de liquide conducteur posee sur un film isolant, permet d'observer une evolution reversible et de grande amplitude de l'etalement du liquide. Mais, sous haut champ, l'avancee du liquide est stoppee, avant d'atteindre la transition de mouillage. Differents phenomenes limitants tels que la saturation de l'angle de contact, l'irreversibilite plus ou moins marquee et des instabilites de la ligne de mouillage sont etudiees. L'utilisation d'eau pure, provoque, a haut champ, l'apparition d'instabilites au voisinage de la ligne de mouillage, caracterisee par une fragmentation de la goutte mere en gouttelettes. Une analyse theorique de la stabilite de la ligne de mouillage, qui semble en bon accord avec les seuils d'apparition des gouttelettes est presentee. Cependant, l'ajout de sels en solution semble inhiber totalement ces instabilites, sans que la transition de mouillage soit atteinte. Une etude experimentale permet de correler la saturation de l'angle de contact avec l'ionisation de l'air. On montre que celle-ci est localisee au voisinage du bord de la goutte et qu'elle est a l'origine de la saturation de l'etalement du liquide. Ceci constitue apparemment une limitation fondamentale de l'effet d'electromouillage.

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27

Pallon, Love. "Polyethylene/metal oxide nanocomposites for electrical insulation in future HVDC-cables : probing properties from nano to macro." Doctoral thesis, KTH, Polymera material, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193591.

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Nanocomposites of polyethylene and metal oxide nanoparticles have shown to be a feasible approachto the next generation of insulation in high voltage direct current cables. In order to reach an operationvoltage of 1 MV new insulation materials with reduced conductivity and increased breakdown strengthas compared to modern low-density polyethylene (LDPE) is needed.In this work polyethylene MgO nanocomposites for electrical insulation has been produced andcharacterized both from an electrical and material perspective. The MgO nanoparticles weresynthesized into polycrystalline nanoparticles with a large specific surface area (167 m2 g–1). Meltprocessing by extrusion resulted in evenly dispersed MgO nanoparticles in LDPE for the silane surfacemodified MgO as compared to the unmodified MgO. All systems showed a reduction in conductivityby up to two orders of magnitude at low loading levels (1–3 wt.%), but where the surface modifiedsystems were able to retain reduced conductivity even at loading levels of 9 wt.%. A maximuminteraction radius to influence the conductivity of the MgO nanoparticles was theoretically determinedto ca. 800 nm. The interaction radius was in turn experimentally observed around Al2O3 nanoparticlesembedded in LDPE using Intermodulation electrostatic force microscopy. By applying a voltage on theAFM-tip charge injection and extraction around the Al2O3 nanoparticles was observed, visualizing theexistence of additional localized energy states on, and around, the nanoparticles. Ptychography wasused to reveal nanometre features in 3D of electrical trees formed under DC-conditions. Thevisualization showed that the electrical tree grows by pre-step voids in front of the propagatingchannels, facilitating further growth, much in analogy to mechanical crack propagation (Griffithconcept). An electromechanical effect was attributed as possible mechanism for the formation of the voids.
Nanokompositer av polyeten och metalloxidpartiklar anses vara möjliga material att använda i morgondagens isolationshölje till högspänningskablar för likström. För att nå en transmissionsspänning på 1 MV behövs isolationsmaterial som i jämförelse med dagens polyeten har lägre elektrisk ledningsförmåga, högre styrka mot elektriskt genomslag och som kan kontrollera ansamling av rymdladdningar. De senaste årens forskning har visat att kompositer av polyeten med nanopartiklar av metalloxider har potential att nå dessa egenskaper. I det här arbetet har kompositer av polyeten och nanopartiklar av MgO för elektrisk isolation producerats och karaktäriserats. Nanopartiklar av MgO har framställts från en vattenbaserad utfällning med efterföljande calcinering, vilket resulterade i polykristallina partiklar med en mycket stor specifik ytarea (167m2 g-1). MgO-nanopartiklarna ytmodifierades i n-heptan genom att kovalent binda oktyl(trietoxi)silan och oktadekyl(trimetoxi)silan till partiklarna för att skapa en hydrofob och skyddande yta. Extrudering av de ytmodifierade MgO nanopartiklarna tillsammans med polyeten resulterade i en utmärkt dispergering med jämnt fördelad partiklar i hela kompositen, vilket ska jämföras med de omodifierade partiklarna som till stor utsträckning bildade agglomerat i polymeren. Alla kompositer med låg fyllnadsgrad (1–3 vikt% MgO) visade upp till 100 gånger lägre elektrisk konduktivitet jämfört med värdet för ofylld polyeten. Vid högre koncentrationer av omodifierade MgO förbättrades inte de isolerande egenskaperna på grund av för stor andel agglomerat, medan kompositerna med de ytmodifierade fyllmedlen som var väl dispergerade behöll en kraftig reducerad elektrisk konduktivitet upp till 9 vikt% fyllnadshalt. Den minsta interaktionsradien för MgO-nanopartiklarna för att minska den elektriska konduktiviten i kompositerna fastställdes med bildanalys och simuleringar till ca 800 nm. Den teoretiskt beräknade interaktionsradien kompletterades med observation av en experimentell interaktionsradie genom att mäta laddningsfördelningen över en Al2O3-nanopartikle i en polyetenfilm med intermodulation (frekvens-mixning) elektrostatisk kraftmikroskop (ImEFM), vilket är en ny AFM-metod för att mäta ytpotentialer. Genom att lägga på en spänning på AFM-kantilevern kunde det visualiseras hur laddningar, både injicerades och extraherades, från nanopartiklarna men inte från polyeten. Det tolkades som att extra energinivåer skapades på och runt nanopartiklarna som fungerar för att fånga in laddningar, ekvivalent med den gängse tolkningen att nanopartiklar introducera extra elektronfällor i den polymera matrisen i nanokompositer. Nanotomografi användes för att avbilda elektriska träd i tre dimensioner. Avbildningen av det elektriska trädet visade att tillväxten av trädet hade skett genom bildning av håligheter framför den framväxande trädstrukturen. Håligheterna leder till försvagning av materialet framför det propagerande trädet och förenklar på det sättet fortsatt tillväxt. Bildningen av håligheter framför trädstrukturen uppvisar en analogi till propagering av sprickor vid mekanisk belastning, i enlighet med Griffiths koncept.

QC 20161006

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28

Xie, Wa. "Surface Topography and Aesthetics of Recycled Cross-Linked Polyethylene Wire and Cable Coatings." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc799512/.

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Our research focuses on re-using a waste a material, cross-linked polyethylene abbreviated XLPE, which is a widely used coating for wires. XLPE is strong and has excellent thermal properties due to its chemical structure - what leads to the significance of recycling this valuable polymer. Properties of XLPE include good resistance to heat, resistance to chemical corrosion, and high impact strength. A wire is usually composed of a metal core conductor and polymeric coating layers. One creates a new coating, including little pieces of recycled XLPE in the lower layer adjacent to the wire, and virgin XLPE only in the upper layer. Industries are often wasting materials which might be useful. Mostly, some returned or excess products could be recycled to create a new type of product or enable the original use. This method helps cleaning the waste, lowers the costs, and enhances the income of the manufacturing company. With the changing of the thickness of the outer layer, the roughness changes significantly. Moreover, different processing methods result in surfaces that look differently.

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29

Hammal, Redouane. "Décharges partielles dans les condensateurs tout-film imprégnés." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10006.

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Les decharges partielles ont ete mesurees sur des modeles de condensateurs tout-film dont le dielectrique est du polypropylene (pp) impregne. Ces cellules ont ete alimentees en haute tension alternative. L'influence de l'epaisseur de dielectrique ou des armatures ainsi que les effets de la temperature et du vieillissement ont ete examines. Les representations n() et q#m#o#y() du nombre et de l'amplitude des decharges dans la phase de la tension alternative servent a caracteriser la source de ces decharges : decharges en bord d'armature dans un modele de condensateur sans defaut ou decharges generees par des defauts artificiellement introduits dans la cellule d'etude (defaut d'impregnation, defaut de contact, cavite dans un film de pp, film de pp plie). Le but de cette caracterisation est la constitution d'une base de donnees qui servira a la reconnaissance de la source des decharges sur des appareils industriels et permettra d'estimer la duree de vie de ces appareils. Les tensions d'apparition et d'extinction des decharges partielles (tadp et tedp), l'evolution des decharges en fonction du temps ou de la tension appliquee sont des elements qui servent a la caracterisation des decharges. Cette tache se fait egalement au moyen de parametres calcules a partir des distributions n() et q#m#o#y(). Ces parametres peuvent etre les moments d'ordre 3 et 4 ou bien les parametres que nous avons introduits dans cette etude et qui sont les parametres de position et le parametre d'efficacite energetique. Ces deux derniers parametres sont les plus efficaces car ils permettent a eux seuls de differencier la plupart des cas etudies.

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30

PERRIN, GERALDINE. "Elaboration par pvd et caracterisation de couches minces ferromagnetiques sur film souple pour des applications hyperfrequence." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10199.

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Ce travail concerne l'elaboration et l'etude de nouveaux materiaux magnetiques destines a des applications radiofrequences et hyperfrequences entre 1 mhz et 20 ghz. Jusqu'a present, les materiaux preferes dans les applications radiofrequences et hyperfrequences ont ete les ferrites. Il s'agit de materiaux isolants mais ferrimagnetiques donc a faible aimantation spontanee. Or les alliages ferromagnetiques ont des proprietes bien superieures aux ferrites en particulier des aimantations 3 a 4 fois superieures. Mais ce sont des conducteurs metalliques qui ne peuvent etre utilises sous forme massive aux frequences elevees a cause de l'effet de peau. Le present travail transpose la solution du feuilletage aux hyperfrequences et demontre que des composites stratifies du type metal ferromagnetique - isolant peuvent concurrencer les ferrites et meme etre plus performants dans nombre de cas a condition de realiser des taux de charge convenables. Dans ce but, nos composites sont constitues d'empilements de films minces de polymere revetus du depot magnetique. Nous demontrons la possibilite de recouvrir par pulverisation magnetron au deroule de grandes surfaces de polymere (mylar ou kapton d'epaisseur 12 microns voire 3. 5 microns) par des alliages amorphes a base de cobalt, ayant en particulier une anisotropie uniaxiale planaire bien definie et controlee. Les proprietes dynamiques prevues (notamment la violation de la limite de snoek) sont verifiees et differentes solutions sont proposees pour modifier a volonte le spectre de permeabilite. Enfin, deux exemples de realisation de composants hyperfrequences utilisant ces materiaux sont donnes. Sur le plan theorique, nous corrigeons le modele classique de rytov et donnons les caracteristiques electromagnetiques effectives du composite. Nous calculons la contribution magneto-elastique a l'anisotropie dans le cas ou les contraintes sont anisotropes et la rigidite du substrat du meme ordre de grandeur que celle de la couche

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31

Najem, Johnny F. "Gecko-Inspired Electrospun Flexible Fiber Arrays for Adhesion." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1340465711.

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32

Singha, Santanu. "Studies On The Dielectric And Electrical Insulation Properties Of Polymer Nanocomposites." Thesis, 2008. https://etd.iisc.ac.in/handle/2005/842.

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Анотація:

Today, nanotechnology has added a new dimension to materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials and even though they show tremendous promise for dielectric/electrical insulation applications (“nanodielectrics” being the buzzword), the understanding related to these systems is very premature. Considering the desired research needs with respect to some of the dielectric properties of polymer nanocomposites, this study attempts to generate an understanding on some of the existing issues through a systematic and detailed experimental investigation coupled with a critical analysis of the data. An epoxy based nanocomposite system is chosen for this study along with four different choices of nano-fillers, viz. TiO2, Al2O3, ZnO and SiO2. The focus of this study is on the properties of nanocomposites at low filler loadings in the range of 0.1 - 5% by weight and the properties under investigation are the permittivity/tan delta behaviors, DC volume resistivity, AC dielectric strength and electrical discharge resistant characteristics. Significant efforts have also been directed towards addressing the interface interaction phenomena in epoxy nanocomposites and their subsequent influence on the dielectric properties of the material. The accurate characterization of the dielectric properties for polymer nanocomposites depends on the dispersion of nanoparticles in the polymer matrix and to achieve a good dispersion of nanoparticles in the epoxy matrix for the present study, a systematic design of experiments (DOE) is carried out involving two different processing methods. Consequently, a laboratory based epoxy nanocomposite processing methodology is proposed in this thesis and this process is found to be successful in dispersing nanoparticles effectively in the epoxy matrix, especially at filler concentrations lower than 5% by weight. Nanocomposite samples for the study are prepared using this method and a rigorous conditioning is performed before the dielectric measurements. The dielectric properties of epoxy nanocomposites obtained in the present study show interesting and intriguing characteristics when compared to those of unfilled epoxy and microcomposite systems and few of the results are unique and advantageous. In an unexpected observation, the addition of nanoparticles to epoxy is found to reduce the value of nanocomposite real permittivity below that of unfilled epoxy over a wide range of frequencies. Similarly, it has been observed that irrespective of the filler type, tan delta values in the case of nanocomposites are either same or lower than the value of unfilled epoxy up to a filler loading of 5% by weight, depending on the frequency and filler concentration. In fact, the nanocomposite real permittivities and tan delta values are also observed to be lower as compared to the corresponding microcomposites of the same constituent materials at the same filler loading. In another significant result, enhancements in the electrical discharge resistant characteristics of epoxy nanocomposites (with SiO2/Al2O3 nanoparticles) are observed when compared to unfilled epoxy, especially at longer durations of discharge exposures. Contrary to these encouragements observed for few of the dielectric properties, the trends of DC volume resistivity and AC dielectric breakdown strength characteristics in epoxy nanocomposites are found to be different. Irrespective of the type of filler in the epoxy matrix, it has been observed that the values of both AC dielectric strengths and DC volume resistivities are lower than that of unfilled epoxy for the filler loadings investigated. The results mentioned above seem to suggest that there has to be an interaction between the nanoparticles and the epoxy chains in the nanocomposite and therefore, glass transition temperature (Tg) measurements are performed to characterize the interaction phenomena, if any. The results of Tg for all the investigated nanocomposites also show interesting trends and they are observed to be lower than that of unfilled epoxy up to certain nanoparticle loadings. This lowering of the Tg in epoxy nanocomposites was not observed in the case of unfilled and microcomposite systems thereby strongly confirming the fact that there exists an interaction between the epoxy chains and nanoparticles in the nanocomposite. Considering the variations obtained for the nanocomposite real permittivity and Tg with respect to filler loading, a dual nanolayer interface model is utilized to explain the interaction dynamics and according to the model, interactions between epoxy chains and nanoparticles lead to the formation of two epoxy nanolayers around the nanoparticle. Analysis shows that the characteristics of the interface region have a strong influence on the dielectric behaviors of the nanocomposites and the suggested interface model seems to fit the characteristics obtained for the different dielectric/electrical insulation properties rather well. Further investigations are performed to understand the nature of interaction between nanoparticles and epoxy chains through FTIR studies and results show that there is probably an occurrence of hydrogen bonding between the epoxide groups of the epoxy resin and the free hydroxyl (OH) groups present on the nanoparticle surfaces. The results obtained for the dielectric properties of epoxy nanocomposites in this study have widened the scope of applications of these functional materials in the electrical sector. The occurrence of lower values of real permittivity for nanocomposites is definitely unique and unexpected and this result has huge potential in electronic component packaging applications. Further, the advantages related to tan delta and electrical discharge resistance for these materials carry lot of significance since, electrical insulating materials with enhanced electrical aging properties can be designed using nanocomposite technology. Although the characteristics of AC dielectric strengths and DC volume resistivities are not found to be strictly advantageous for epoxy nanocomposites at the investigated filler loadings, these properties can be optimized when designing insulation systems for practical applications. In spite of all these advantages, serious and systematic research efforts are still desired before these materials can be successfully utilized in electrical equipment.

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33

Singha, Santanu. "Studies On The Dielectric And Electrical Insulation Properties Of Polymer Nanocomposites." Thesis, 2008. http://hdl.handle.net/2005/842.

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Анотація:

Today, nanotechnology has added a new dimension to materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials and even though they show tremendous promise for dielectric/electrical insulation applications (“nanodielectrics” being the buzzword), the understanding related to these systems is very premature. Considering the desired research needs with respect to some of the dielectric properties of polymer nanocomposites, this study attempts to generate an understanding on some of the existing issues through a systematic and detailed experimental investigation coupled with a critical analysis of the data. An epoxy based nanocomposite system is chosen for this study along with four different choices of nano-fillers, viz. TiO2, Al2O3, ZnO and SiO2. The focus of this study is on the properties of nanocomposites at low filler loadings in the range of 0.1 - 5% by weight and the properties under investigation are the permittivity/tan delta behaviors, DC volume resistivity, AC dielectric strength and electrical discharge resistant characteristics. Significant efforts have also been directed towards addressing the interface interaction phenomena in epoxy nanocomposites and their subsequent influence on the dielectric properties of the material. The accurate characterization of the dielectric properties for polymer nanocomposites depends on the dispersion of nanoparticles in the polymer matrix and to achieve a good dispersion of nanoparticles in the epoxy matrix for the present study, a systematic design of experiments (DOE) is carried out involving two different processing methods. Consequently, a laboratory based epoxy nanocomposite processing methodology is proposed in this thesis and this process is found to be successful in dispersing nanoparticles effectively in the epoxy matrix, especially at filler concentrations lower than 5% by weight. Nanocomposite samples for the study are prepared using this method and a rigorous conditioning is performed before the dielectric measurements. The dielectric properties of epoxy nanocomposites obtained in the present study show interesting and intriguing characteristics when compared to those of unfilled epoxy and microcomposite systems and few of the results are unique and advantageous. In an unexpected observation, the addition of nanoparticles to epoxy is found to reduce the value of nanocomposite real permittivity below that of unfilled epoxy over a wide range of frequencies. Similarly, it has been observed that irrespective of the filler type, tan delta values in the case of nanocomposites are either same or lower than the value of unfilled epoxy up to a filler loading of 5% by weight, depending on the frequency and filler concentration. In fact, the nanocomposite real permittivities and tan delta values are also observed to be lower as compared to the corresponding microcomposites of the same constituent materials at the same filler loading. In another significant result, enhancements in the electrical discharge resistant characteristics of epoxy nanocomposites (with SiO2/Al2O3 nanoparticles) are observed when compared to unfilled epoxy, especially at longer durations of discharge exposures. Contrary to these encouragements observed for few of the dielectric properties, the trends of DC volume resistivity and AC dielectric breakdown strength characteristics in epoxy nanocomposites are found to be different. Irrespective of the type of filler in the epoxy matrix, it has been observed that the values of both AC dielectric strengths and DC volume resistivities are lower than that of unfilled epoxy for the filler loadings investigated. The results mentioned above seem to suggest that there has to be an interaction between the nanoparticles and the epoxy chains in the nanocomposite and therefore, glass transition temperature (Tg) measurements are performed to characterize the interaction phenomena, if any. The results of Tg for all the investigated nanocomposites also show interesting trends and they are observed to be lower than that of unfilled epoxy up to certain nanoparticle loadings. This lowering of the Tg in epoxy nanocomposites was not observed in the case of unfilled and microcomposite systems thereby strongly confirming the fact that there exists an interaction between the epoxy chains and nanoparticles in the nanocomposite. Considering the variations obtained for the nanocomposite real permittivity and Tg with respect to filler loading, a dual nanolayer interface model is utilized to explain the interaction dynamics and according to the model, interactions between epoxy chains and nanoparticles lead to the formation of two epoxy nanolayers around the nanoparticle. Analysis shows that the characteristics of the interface region have a strong influence on the dielectric behaviors of the nanocomposites and the suggested interface model seems to fit the characteristics obtained for the different dielectric/electrical insulation properties rather well. Further investigations are performed to understand the nature of interaction between nanoparticles and epoxy chains through FTIR studies and results show that there is probably an occurrence of hydrogen bonding between the epoxide groups of the epoxy resin and the free hydroxyl (OH) groups present on the nanoparticle surfaces. The results obtained for the dielectric properties of epoxy nanocomposites in this study have widened the scope of applications of these functional materials in the electrical sector. The occurrence of lower values of real permittivity for nanocomposites is definitely unique and unexpected and this result has huge potential in electronic component packaging applications. Further, the advantages related to tan delta and electrical discharge resistance for these materials carry lot of significance since, electrical insulating materials with enhanced electrical aging properties can be designed using nanocomposite technology. Although the characteristics of AC dielectric strengths and DC volume resistivities are not found to be strictly advantageous for epoxy nanocomposites at the investigated filler loadings, these properties can be optimized when designing insulation systems for practical applications. In spite of all these advantages, serious and systematic research efforts are still desired before these materials can be successfully utilized in electrical equipment.

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34

Preetha, P. "Studies On Epoxy Nanocomposites As Electrical Insulation For High Voltage Power Apparatus." Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2543.

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Анотація:

High voltage rotating machines play a significant role in generation and use of electrical energy as the demand for power continues to increase. However, one of the main causes for down times in high voltage rotating machines is related to problems with the winding insulation. The utilities want to reduce costs through longer maintenance intervals and a higher lifetime of the machines. These demands create a challenge for the producers of winding insulations, the manufacturers of high voltage rotating machines and the utilities to develop new insulation materials which can improve the life of the equipment and reduce the maintenance cost. The advent of nanotechnology in recent times has heralded a new era in materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials that exhibit unique combinations of physical, mechanical and thermal properties which are advantageous as compared to the traditional polymers or their composites. Even though they show tremendous promise for dielectric/electrical insulation applications, there are no studies relating to the long term performance as well as life estimation of the nanocomposites. Considering this, an attempt is made to generate an understanding on the feasibility of these nanocomposites for electrical insulation applications. An epoxy based nanocomposite system is chosen for this study along with alumina (Al2O3) and silica (SiO2) as the nanofillers. The first and the foremost requirement for studies on polymer nanocomposites is to achieve a uniform dispersion of nanoparticles in the polymer matrix, as nanoparticles are known to agglomerate and form large particle sizes. A laboratory based direct dispersion method is used to process epoxy nanocomposites in order to get well dispersed samples. A detailed microscopy analysis of the filler dispersion using Scanning Electron Microscope (SEM) has been carried out to check the dispersion of the nanofiller in the polymer. An attempt is made to characterize and analyze the interaction dynamics at the interface regions in the epoxy nanocomposite by glass transition temperature (Tg) measurements and Fourier transform infrared (FTIR) spectroscopy studies. The values of Tg for the nanocomposites studied decreases at 0.1 wt% filler loading and then starts to increase gradually with increase in filler loading. This Tg variation suggests that there is certainly an interaction between the epoxy chains and the nanoparticles. Also no new chemical bonds were observed in the spectra of epoxy nanocomposite as compared to unfilled epoxy. But changes were observed in the peak intensity and width of the –OH band in the spectrum of epoxy nanocomposite. This change was due to the formation of the hydrogen bonding between the epoxy and the nanofiller. The thermal conductivity of the epoxy alumina and the epoxy silica nanocomposites increased even with the addition of 0.1 wt% of the filler. This increase in thermal conductivity is one of the factors that make these nanocomposites a better option for electrical insulation applications. The dielectric properties of epoxy nanocomposites obtained in this investigation also reveal few interesting behaviors which are found to be unique and advantageous as compared to similar properties of unfilled materials. It is observed that the addition of fillers of certain loadings of nanoparticles to epoxy results in the nanocomposite permittivity value to be lower than that of the unfilled epoxy over the entire range of frequencies [10-2-106 Hz] considered in this study. This reduction has been attributed to the inhibition of polymer chain mobility caused by the addition of the nanoparticles. The tan 𝛿 values are almost the same or lower as compared to the unfilled epoxy for the different filler loadings considered. This behavior is probably due to the influence of the interface as the strong bonding at the interface will make the interface very stable with fewer defects apart from acting as charge trapping centres. From a practical application point of view, the surface discharge resistant characteristics of the materials are very important and this property has also been evaluated. The resistance to surface discharge is measured in the form of roughness on the surface of the material caused by the discharges. A significant enhancement in the discharge resistance has been observed for nanocomposites as compared to unfilled epoxy/ microcomposites, especially at longer exposure durations. The partial discharge (PD) measurements were carried out at regular intervals of time and it is observed that the PD magnitude reduced with discharge duration in the case of epoxy alumina nanocomposites. An attempt was made to understand the chemical changes on the surface by conducting the FTIR studies on the aged surface. For all electrical insulation applications, materials having higher values of dielectric strengths are always desired and necessary. So AC breakdown studies have also been conducted. The AC breakdown strength shows a decreasing trend up to a certain filler loading and then an increase at 5 wt% filler loading for epoxy alumina nanocomposites. It has been also observed that the type of filler as well as the thickness of the filler influences the breakdown strength. The AC dielectric strength of microcomposites are observed to be lower than the nanocomposites. Extensive research by long term aging studies and life estimation are needed before these new nanocomposites can be put into useful service. So long term aging studies under combined electrical and thermal stresses have been carried out on unfilled epoxy and epoxy alumina nanocomposite samples of filler loading 5 wt%. The important dielectric parameters like pemittivity, tan  and volume resistivity were measured before and after aging to understand the performance of the material under study. The leakage current was measured at regular intervals and tan  values were calculated with duration of aging. It was observed that the tan  values increased drastically for unfilled epoxy for the aging duration considered as compared to epoxy alumina nanocomposites. The life estimation of unfilled epoxy as well as epoxy nanocomposites were also performed by subjecting the samples to different stress levels of 6 kV/mm, 7 kV/mm and 8 kV/mm at 60 oC. It is observed that the epoxy alumina nanocomposite has an enhanced life which is nine times the life of the unfilled epoxy. These results obtained for the nanocomposites enable us to design a better material with improved dielectric strength, dielectric properties, thermal conductivity, resistance to surface discharge degradation and enhanced life without sacrificing the flexibility in the end product and the ease of processing. Dry type transformers and stator winding insulation need to be cast with the above material developed and tested before practically implementing these in the actual application.

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35

Preetha, P. "Studies On Epoxy Nanocomposites As Electrical Insulation For High Voltage Power Apparatus." Thesis, 2012. http://etd.iisc.ernet.in/handle/2005/2543.

Повний текст джерела

Анотація:

High voltage rotating machines play a significant role in generation and use of electrical energy as the demand for power continues to increase. However, one of the main causes for down times in high voltage rotating machines is related to problems with the winding insulation. The utilities want to reduce costs through longer maintenance intervals and a higher lifetime of the machines. These demands create a challenge for the producers of winding insulations, the manufacturers of high voltage rotating machines and the utilities to develop new insulation materials which can improve the life of the equipment and reduce the maintenance cost. The advent of nanotechnology in recent times has heralded a new era in materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials that exhibit unique combinations of physical, mechanical and thermal properties which are advantageous as compared to the traditional polymers or their composites. Even though they show tremendous promise for dielectric/electrical insulation applications, there are no studies relating to the long term performance as well as life estimation of the nanocomposites. Considering this, an attempt is made to generate an understanding on the feasibility of these nanocomposites for electrical insulation applications. An epoxy based nanocomposite system is chosen for this study along with alumina (Al2O3) and silica (SiO2) as the nanofillers. The first and the foremost requirement for studies on polymer nanocomposites is to achieve a uniform dispersion of nanoparticles in the polymer matrix, as nanoparticles are known to agglomerate and form large particle sizes. A laboratory based direct dispersion method is used to process epoxy nanocomposites in order to get well dispersed samples. A detailed microscopy analysis of the filler dispersion using Scanning Electron Microscope (SEM) has been carried out to check the dispersion of the nanofiller in the polymer. An attempt is made to characterize and analyze the interaction dynamics at the interface regions in the epoxy nanocomposite by glass transition temperature (Tg) measurements and Fourier transform infrared (FTIR) spectroscopy studies. The values of Tg for the nanocomposites studied decreases at 0.1 wt% filler loading and then starts to increase gradually with increase in filler loading. This Tg variation suggests that there is certainly an interaction between the epoxy chains and the nanoparticles. Also no new chemical bonds were observed in the spectra of epoxy nanocomposite as compared to unfilled epoxy. But changes were observed in the peak intensity and width of the –OH band in the spectrum of epoxy nanocomposite. This change was due to the formation of the hydrogen bonding between the epoxy and the nanofiller. The thermal conductivity of the epoxy alumina and the epoxy silica nanocomposites increased even with the addition of 0.1 wt% of the filler. This increase in thermal conductivity is one of the factors that make these nanocomposites a better option for electrical insulation applications. The dielectric properties of epoxy nanocomposites obtained in this investigation also reveal few interesting behaviors which are found to be unique and advantageous as compared to similar properties of unfilled materials. It is observed that the addition of fillers of certain loadings of nanoparticles to epoxy results in the nanocomposite permittivity value to be lower than that of the unfilled epoxy over the entire range of frequencies [10-2-106 Hz] considered in this study. This reduction has been attributed to the inhibition of polymer chain mobility caused by the addition of the nanoparticles. The tan values are almost the same or lower as compared to the unfilled epoxy for the different filler loadings considered. This behavior is probably due to the influence of the interface as the strong bonding at the interface will make the interface very stable with fewer defects apart from acting as charge trapping centres. From a practical application point of view, the surface discharge resistant characteristics of the materials are very important and this property has also been evaluated. The resistance to surface discharge is measured in the form of roughness on the surface of the material caused by the discharges. A significant enhancement in the discharge resistance has been observed for nanocomposites as compared to unfilled epoxy/ microcomposites, especially at longer exposure durations. The partial discharge (PD) measurements were carried out at regular intervals of time and it is observed that the PD magnitude reduced with discharge duration in the case of epoxy alumina nanocomposites. An attempt was made to understand the chemical changes on the surface by conducting the FTIR studies on the aged surface. For all electrical insulation applications, materials having higher values of dielectric strengths are always desired and necessary. So AC breakdown studies have also been conducted. The AC breakdown strength shows a decreasing trend up to a certain filler loading and then an increase at 5 wt% filler loading for epoxy alumina nanocomposites. It has been also observed that the type of filler as well as the thickness of the filler influences the breakdown strength. The AC dielectric strength of microcomposites are observed to be lower than the nanocomposites. Extensive research by long term aging studies and life estimation are needed before these new nanocomposites can be put into useful service. So long term aging studies under combined electrical and thermal stresses have been carried out on unfilled epoxy and epoxy alumina nanocomposite samples of filler loading 5 wt%. The important dielectric parameters like pemittivity, tan  and volume resistivity were measured before and after aging to understand the performance of the material under study. The leakage current was measured at regular intervals and tan  values were calculated with duration of aging. It was observed that the tan  values increased drastically for unfilled epoxy for the aging duration considered as compared to epoxy alumina nanocomposites. The life estimation of unfilled epoxy as well as epoxy nanocomposites were also performed by subjecting the samples to different stress levels of 6 kV/mm, 7 kV/mm and 8 kV/mm at 60 oC. It is observed that the epoxy alumina nanocomposite has an enhanced life which is nine times the life of the unfilled epoxy. These results obtained for the nanocomposites enable us to design a better material with improved dielectric strength, dielectric properties, thermal conductivity, resistance to surface discharge degradation and enhanced life without sacrificing the flexibility in the end product and the ease of processing. Dry type transformers and stator winding insulation need to be cast with the above material developed and tested before practically implementing these in the actual application.

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36

Kanwal, Alokik Paul. "All organic memory devices utilizing C60 molecules and insulating polymers." 2008. http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.17337.

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37

I-FenTsai and 蔡宜芬. "Numerical Analysis for Effect of Material Properties and microstructure on the Sound Insulation of Foamed Inorganic Polymers." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/92722992754276781439.

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Анотація:

碩士
國立成功大學
土木工程學系碩博士班
100
Here, a commercial finite element package ABAQUS with different types of elements was used to numerically analyze the sound transmission losses of foamed inorganic polymers. It is found that solid element can effectively simulate the transmission loss of a solid plate while acoustic medium with a volumetric drag can effectively simulate the low-frequency acoustic response of a foamed inorganic polymer. In addition, three types of models were employed to investigate the sound insulation of foamed inorganic polymers with different microstructures: (a) a closed-cell microstructure with a single cell size; (b) a closed-cell microstructure with different cell sizes; (c) a closed-cell microstructure with tunnels. Furthermore, foamed inorganic polymer specimens with three different pore-size distributions were produced and tested to measure their sound transmission losses. Experimental results indicate that the variation of sound transmission losses is insignificant if the porosity and surface density of foamed inorganic polymers are the same. Also, numerical results suggest that the effect of microstructural geometry on the sound transmission losses of foamed inorganic polymers with the same surface density is negligible, consistent with the experimental results. Therefore, the proposed 2D numerical model can be utilized to partially replace tedious experimental works when experimental cost and consuming-time are concerned.

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38

Vas, Joseph Vimal. "Studies On Silicone Rubber Nanocomposites As Weathershed Material For HVDC Transmission Line Insulators." Thesis, 2011. https://etd.iisc.ac.in/handle/2005/2057.

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Анотація:

Outdoor insulators are one of the most important parts of a power system. The reliability of a power system depends also on the reliability of the insulators. The main functions of an insulator used for outdoor applications are to give the necessary insulation, provide the necessary mechanical support to the transmission line conductor and also to resist the various environmental stresses like pollution, ultra violet rays etc. Traditionally porcelain and glass insulators have been used for outdoor insulator applications. They are good insulators under normal conditions and the cap and pin arrangement allows them to take up the mechanical load of the line. But owing to their large weight and brittle nature they are susceptible to vandalism and also they have increased cost of installation and commissioning. But the main problem of porcelain and glass insulators is its performance under polluted environmental condition. Under wet and polluted conditions, the porcelain insulators allow the formation of a conducting layer on the surface which results in setting up of leakage current, dry band arcing and power loss. This problem is further augmented under dc voltages where the stress is unidirectional and the contaminant deposition is higher as compared to ac. Polymeric insulators are a good alternative for porcelain and ceramic insulators for use especially under dc voltages because of their good pollution performance. The property of surface hydrophobicity resists the setting up of leakage currents and hence polymeric insulators help in reducing power loss. They are also light in weight and vandalism resistant and hence easier to install. But being polymeric, they form conductive tracks and erode when exposed to high temperatures which occur at the surface during dry band arcs and when exposed to corona discharges. The surface hydrophobicity is also temporarily lost when exposed to different electrical stresses. Silicone rubber is the most popular among the various choices of polymers for outdoor insulator applications. They have good surface hydrophobicity and tracking performance. But polymers in their pure form cannot be used as insulators because of their poor mechanical strength. Adding inorganic fillers into the polymer matrix not only improves its mechanical properties but also its erosion resistance. Micron sized Alumina Trihydrate (ATH) is used traditionally to improve the tracking and erosion resistance of polymeric insulators. A very high loading (up to 60%) is used. Adding such a high filler loading to the base polymer hampers its flexibility and the material processing. With the advent of nanotechnology, nano fillers have come into vogue. Studies conducted on nano filled polymers showed exciting results. A small amount of nano fillers in the polymer matrix showed significant improvement in the mechanical strength without hampering its flexibility. The electrical properties like tracking and erosion also improved with filler loading. Hence the use of nano filled silicone rubber is a good alternative for use as a high voltage insulator especially under dc voltages. Reports suggest that adding nano fillers into the silicone rubber matrix improves the tracking and erosion resistance and the corona degradation as compared to the unfilled samples under ac voltages. The literature on the dc performance of silicone rubber nano composites is scarce. So the present study aims to evaluate the performance of silicone rubber nano composites for tracking and erosion resistance and corona degradation under dc voltages. The tracking and erosion resistance under dc voltages was measured using the Inclined Plane Tracking and Erosion Resistance set up as per ASTM D2303 which was modified for dc voltage studies. The performance of nano Alumina and nano Silica fillers were evaluated under negative dc and the performance was compared with micron sized Alumina Trihydrate filled samples. The effect of filler loading was also studied. It was seen that the performance of the silicone rubber improved with filler loading. A small loading percentage of nano fillers were enough to give performance similar to silicone rubber filled with micron sized ATH filler. The silicone rubber performed better under negative dc as compared to ac and positive dc. The positive dc tests showed a migration of ions from the electrodes onto the sample surface. The increased surface conductivity resulted in very heavy erosion in the case of positive dc tested samples. The corona aging studies were also conducted on silicone rubber nano composites. Nano silica was used as filler in this case. Different filler loadings were employed to understand the effect of filler loading. The corona was generated using a needle plane electrode and samples were exposed to both positive and negative dc corona. The samples were exposed to corona for different time intervals – 25 and 50 hours to study the effect of exposure time. The hydrophobicity, crack width and surface roughness were measured after the tests. Adding nano fillers into the polymer matrix improved the corona performance. With filler loading, the performance improved. The samples exposed to positive dc corona performed better than those under negative dc corona. The loss of hydrophobicity, surface cracks and the surface roughness was less in the case of positive dc corona tested samples. With exposure time, the performance of silicone rubber became poorer for positive dc corona tested samples. For the negative dc corona tested samples, the performance seemed to improve with exposure time. The tracking and erosion resistance and the corona aging studies conducted showed that the performance of silicone rubber is improved by adding nano fillers into the polymer matrix. A small amount of nano filler loading was enough to perform similar to a heavily loaded micron filled sample. Hence nano fillers can be used as a good functional material to improve the performance of silicone rubber insulators especially under wet and polluted conditions.

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39

Vas, Joseph Vimal. "Studies On Silicone Rubber Nanocomposites As Weathershed Material For HVDC Transmission Line Insulators." Thesis, 2011. http://hdl.handle.net/2005/2057.

Повний текст джерела

Анотація:

Outdoor insulators are one of the most important parts of a power system. The reliability of a power system depends also on the reliability of the insulators. The main functions of an insulator used for outdoor applications are to give the necessary insulation, provide the necessary mechanical support to the transmission line conductor and also to resist the various environmental stresses like pollution, ultra violet rays etc. Traditionally porcelain and glass insulators have been used for outdoor insulator applications. They are good insulators under normal conditions and the cap and pin arrangement allows them to take up the mechanical load of the line. But owing to their large weight and brittle nature they are susceptible to vandalism and also they have increased cost of installation and commissioning. But the main problem of porcelain and glass insulators is its performance under polluted environmental condition. Under wet and polluted conditions, the porcelain insulators allow the formation of a conducting layer on the surface which results in setting up of leakage current, dry band arcing and power loss. This problem is further augmented under dc voltages where the stress is unidirectional and the contaminant deposition is higher as compared to ac. Polymeric insulators are a good alternative for porcelain and ceramic insulators for use especially under dc voltages because of their good pollution performance. The property of surface hydrophobicity resists the setting up of leakage currents and hence polymeric insulators help in reducing power loss. They are also light in weight and vandalism resistant and hence easier to install. But being polymeric, they form conductive tracks and erode when exposed to high temperatures which occur at the surface during dry band arcs and when exposed to corona discharges. The surface hydrophobicity is also temporarily lost when exposed to different electrical stresses. Silicone rubber is the most popular among the various choices of polymers for outdoor insulator applications. They have good surface hydrophobicity and tracking performance. But polymers in their pure form cannot be used as insulators because of their poor mechanical strength. Adding inorganic fillers into the polymer matrix not only improves its mechanical properties but also its erosion resistance. Micron sized Alumina Trihydrate (ATH) is used traditionally to improve the tracking and erosion resistance of polymeric insulators. A very high loading (up to 60%) is used. Adding such a high filler loading to the base polymer hampers its flexibility and the material processing. With the advent of nanotechnology, nano fillers have come into vogue. Studies conducted on nano filled polymers showed exciting results. A small amount of nano fillers in the polymer matrix showed significant improvement in the mechanical strength without hampering its flexibility. The electrical properties like tracking and erosion also improved with filler loading. Hence the use of nano filled silicone rubber is a good alternative for use as a high voltage insulator especially under dc voltages. Reports suggest that adding nano fillers into the silicone rubber matrix improves the tracking and erosion resistance and the corona degradation as compared to the unfilled samples under ac voltages. The literature on the dc performance of silicone rubber nano composites is scarce. So the present study aims to evaluate the performance of silicone rubber nano composites for tracking and erosion resistance and corona degradation under dc voltages. The tracking and erosion resistance under dc voltages was measured using the Inclined Plane Tracking and Erosion Resistance set up as per ASTM D2303 which was modified for dc voltage studies. The performance of nano Alumina and nano Silica fillers were evaluated under negative dc and the performance was compared with micron sized Alumina Trihydrate filled samples. The effect of filler loading was also studied. It was seen that the performance of the silicone rubber improved with filler loading. A small loading percentage of nano fillers were enough to give performance similar to silicone rubber filled with micron sized ATH filler. The silicone rubber performed better under negative dc as compared to ac and positive dc. The positive dc tests showed a migration of ions from the electrodes onto the sample surface. The increased surface conductivity resulted in very heavy erosion in the case of positive dc tested samples. The corona aging studies were also conducted on silicone rubber nano composites. Nano silica was used as filler in this case. Different filler loadings were employed to understand the effect of filler loading. The corona was generated using a needle plane electrode and samples were exposed to both positive and negative dc corona. The samples were exposed to corona for different time intervals – 25 and 50 hours to study the effect of exposure time. The hydrophobicity, crack width and surface roughness were measured after the tests. Adding nano fillers into the polymer matrix improved the corona performance. With filler loading, the performance improved. The samples exposed to positive dc corona performed better than those under negative dc corona. The loss of hydrophobicity, surface cracks and the surface roughness was less in the case of positive dc corona tested samples. With exposure time, the performance of silicone rubber became poorer for positive dc corona tested samples. For the negative dc corona tested samples, the performance seemed to improve with exposure time. The tracking and erosion resistance and the corona aging studies conducted showed that the performance of silicone rubber is improved by adding nano fillers into the polymer matrix. A small amount of nano filler loading was enough to perform similar to a heavily loaded micron filled sample. Hence nano fillers can be used as a good functional material to improve the performance of silicone rubber insulators especially under wet and polluted conditions.

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40

Lionel, Flandin. "Multiscale Relationships in Polymer-Based Heterogeneous Systems: Experiments and Simulations." Habilitation à diriger des recherches, 2006. http://tel.archives-ouvertes.fr/tel-00454578.

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I have worked on many projects, but there are several things that they all had in common. First, nearly all projects involved searching for the structural parameters that governed the macroscopic properties of the polymers and composite materials. A second common denominator is that even though my work was performed in an “academic context”, the goals were targeted toward industrial needs. Lastly, the methods and procedures were similar; they were all based on experimental results obtained for various scales of measurement (see Fig. 1). Hence, multi-scale modeling was very useful and beneﬁcial for these projects. The models developed (mainly numerical and sometimes analytical) were initially derived from experimental evidence and then validated and improved with further experimentation. The reﬁned models provided an eﬃcient means of: (i) optimizing the composites according to speciﬁc needs, (ii) better understanding the hierarchical relations between the diﬀerent scales, (iii) controlling the micro or meso structure and thereby the macroscopic properties. This study of the relations between structure and properties was performed on a wide variety of physical properties and materials. However, the electric and dielectric properties of composites constituted the major- ity of it and will be presented in this report. The remaining property investigations provided supplemental but valuable information. This work often requires altering various conventional experimental techniques or using well-known techniques for new purposes. I also developed, when needed, several unconventional but necessary measurement techniques. This report contains two major parts which are separated according to the nature of the ﬁllers: Part I : Conducting ﬁllers. In the ﬁrst part, the main interest both for application and fundamental point of view, is related to the changes in properties in the vicinity of the sharp percolation transition. After a brief introduction to the percolation theory, this part will be subdivided in three chapters: Chapter 1. presents a numerical method that correlates the mesostructure to the macroscopic electrical properties both in two and three dimensions. Chapter 2. will show that an external variable (the mechanical stress) may largely alter the microstruc- ture of the percolating network within composites as revealed the macroscopic conductivity. The understanding of the mesoscale changes will be based on the chemical structure of the polymer matrix. Chapter 3. is devoted to the description of a unique case in term of percolation behavior, which made possible the control of the phase arrangement within the composite and thereby the control of the macroscopic resistivity. p. 2 Multiscale relationships in polymer–based heterogeneous systems. . . Part II : Insulating ﬁllers. In the second part, the main interest is to obtain good electrical insulators, i.e. that can withstand large electric ﬁelds. This part thus starts with a brief introduction to the common failure mechanisms, associated with the dielectric breakdown and is also divided in three chapters: Chapter 4. is devoted to the description of a numerical simulation of the relationships between mesostructure and dielectric breakdown. Chapter 5. reveals the inﬂuence of the processing conditions of a composite utilized in the industry on the microstructure and the quantitative consequences on breakdown properties. Chapter 6. presents the aging of these composites under “real word” conditions which will further be compared to accelerated aging performed in controlled conditions, in the laboratory. A comparison of the two aging situations will furnish a quantitative understanding of the relative inﬂuence of the chemical and physical contributions to the aging process. This report will then be concluded with a description of the current and future projects.

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Дисертації з теми "Insulating polymer materials"

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