Dissertations / Theses on the topic 'Electrical conductivity'
To see the other types of publications on this topic, follow the link: Electrical conductivity.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Electrical conductivity.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Zhang, Yuxi Ph D. Massachusetts Institute of Technology. "Electrospun nanofibers with tunable electrical conductivity." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81690.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 114-117).
Electrospinning is a convenient method to produce nanofibers with controlled diameters on the order of tens to hundreds of nanometers. The resulting nonwoven fiber mats are lightweight, highly porous, and have high specific surface areas around 1 to 100 m2/g. Combined with the high electrical conductivity of intrinsically conductive polymers, conductive electrospun fiber mats are promising for a variety of applications, such as multifunctional textiles, resistance-based sensors, flexible reversibly hydrophobic surfaces, organic photovoltaics, scaffolds for tissue engineering, and conductive substrates for surface functionalization and modification Intrinsically conductive polymers, such as polyaniline (PAni), however, are relatively hard to Intrinsically conductive polymers, such as polyaniline (PAni), however, are relatively hard to process compared to most other polymers. They have fairly rigid backbones due to the high aromaticity, and are usually available only in relatively low molecular weight forms, so that the elasticity of their solutions is insufficient for it to be electrospun directly into fibers. Considerable amount of recent work has been reported trying to make electrospun polymeric nanofibers with intrinsically conductive polymers or composites. However, a large fraction of the work only showed the morphology and did not characterize the actual performance of these fibers, nor did they test the variability of the fibers and mats from a wide range of processing conditions and resulting structures. Therefore, this thesis aims to make a comprehensive study of the electrical tunability of electrospun fibers with intrinsically conductive polymers and its composites, to establish a clear processing-structure-property relationship for these fibers and fiber mats, and to test the resultant fibers with the targeted applications such as gas sensing. We have first developed a reliable method to characterize fiber electrical conductivity using interdigitated electrodes (IDE) and high-impedance analyzers with contact-resistance corrections, and applied to electrospun conductive polymer nanofibers. This method was shown to be reliable and sensitive, as opposed to some of the other methods that have been reported in literature. Facing with the challenge of overcoming the relatively low elasticity of the conductive polymer solutions to achieve electrospinnability, we have fabricated electrospun fibers of PAni and poly(3,4-ethylenedioxythiophene) (PEDOT), blended with poly(ethylene oxide) (PEO) or poly(methyl methacrylate) (PMMA) over a range of compositions. Pure PAni (doped with (+)- camphor-i 0-sulfonic acid (HCSA)) fibers were successfully fabricated for the first time by co-axial electrospinning and subsequent removal of the PMMA shell by dissolution. This allowed for the pure electrospun PAni/HCSA fibers to be tested for electrical performances and its enhancement as well as gas sensing application. The conductivities of the PAni-blend fibers are found to increase exponentially with the weight percent of doped PAni in the fibers, to as high as 50 ± 30 S/cm for as-electrospun fibers of 100% PAni/HCSA. This fiber conductivity of the pure doped PAni fibers was found to increase to 130 ± 40 S/cm with increasing molecular orientation, achieved through solid state drawing. The experimental results thus support the idea that enhanced molecular alignment within electrospun fibers, both during the electrospinning process and subsequent post-treatment, contributes positively to increasing electrical conductivity of conductive polymers. Using a model that accounts for the effects of intrinsic fiber conductivity (including both composition and molecular orientation), mat porosity, and the fiber orientation distribution within the mat, calculated mat conductivities are obtained in quantitative agreement with the mat conductivities measured experimentally. This correlation, along with the reliable method of fiber conductivity measurement by IDE, presents a way to resolve some of the inconsistencies in the literature about reporting electrical conductivity values of electrospun fibers and fiber mats. Pure PAni fibers with different levels of doping were also fabricated by co-axial electrospinning and subsequent removal of the shell by dissolution, and shown to exhibit a large range of fiber electrical conductivities, increasing exponentially with increasing ratio of dopant to PAni. These fibers are found to be very effective nanoscale chemiresistive sensors for both ammonia and nitrogen dioxide gases, thanks to this large range of available electrical conductivities. Both sensitivity and response times are shown to be excellent, with response ratios up to 58 for doped PAni sensing of ammonia and up to more than 105 for nitrogen dioxide sensing by undoped PAni fibers. The characteristic times for the gas sensing are shown to be on the order of 1 to 2 minutes. We have also developed a generic time-dependent reaction-diffusion model that accounts for reaction kinetics, reaction equilibrium, and diffusivity parameters, and show that the model can be used to extract parameters from experimental results and used to predict and optimize the gas sensing of fibers under different constraints without the need to repeat experiments under different fiber and gas conditions.
by Yuxi Zhang.
Ph.D.
2
Kim, Yeon Seok. "Electrical conductivity of segregated network polymer nanocomposites." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1880.
Full text
3
Fisher, Craig Andrew James. "Electrical conductivity of brownmillerite-structured oxide ceramics." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318598.
Full text
4
Tibaldi, Pier Silvio. "Self-Assembly and Electrical Conductivity of Colloids." Thesis, Uppsala universitet, Materialfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-272198.
Full textAbstract:
Self-assembly is an astonishing phenomenon at the base of organized structures’ formation from disordered systems. It occurs in nature from atomic and molecular lengths to galactic distances. Nowadays self-assembly of colloidal solutions can be used to fabricate photonic crystals and metamaterials. This paper analyses the self-assembly and its effect on the electric conductivity of a colloid made up of carbon nanotubes and magnetite microparticles controlled by electrostatic potentials and magnetic fields. Alignment of the carbon nanotubes and creation of sparks and short-circuits are observed when the electrostatic field is applied. The magnetic field induces time-dependent and memory effects in the sample’s structure and conductivity. At constant potential, the electric current through the sample is reported to increase four times during and after the application of the magnetic fields.
5
Hundermark, Rodney. "The electrical conductivity of melter type slags." Master's thesis, University of Cape Town, 2003. http://hdl.handle.net/11427/5316.
Full textAbstract:
Bibliography: p. 219-226.This thesis details an investigation into the factors affecting the electrical conductivity of slags containing some or all of the following components: Ah03, cae, Cr203, FeOx, MgO and Si02. The interest in the electrical properties of these slags originated from problems being experienced in the electrical control of the melter type furnaces of the platinum producers in South Africa. A large amount of literature on the electrical conductivity of slags was collected and analysed. The key research areas identified through the literature review were: the effect of iron oxide on slag conductivity in terms of ionic and electronic mechanisms, the effect of oxidation state on the conductivity of iron-containing slags and the effect of chromium on the electrical conductivity of melter type slags. Measurements of the electrical conductivities of various slags were conducted in order to gain an understanding of these effects.
6
Su, Bin. "Electrical, thermomechanical and reliability modeling of electrically conductive adhesives." Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-12192005-124641/.
Full textAbstract:
Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2006.Qu, Jianmin, Committee Chair ; Baldwin, Daniel, Committee Member ; Wong, C. P., Committee Member ; Sitaraman, Suresh, Committee Member ; Jacob, Karl, Committee Member.
7
Spurio, Eleonora. "Electrical conductivity of single Be-doped GaAs nanowires." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/19295/.
Full textAbstract:
In this thesis the measurement of the current-voltage characteristics of single nanowires in their as-grown geometry is presented. The studied sample is composed by Be-doped GaAs nanowires grown on Si substrate by molecular beam epitaxy. The measurements have been performed using the two terminal and the four terminal geometry, respectively in the laboratories of Universität Siegen and of Leibniz Universität Hannover. For applications of nanowires in optoelectonic applications the knowledge of electronic properties is fundamental for device optimization. The first aim of this work is the investigation of electric properties of individual nanowires onto the same substrate. The electrical characterization has been performed measuring the current-voltage characteristics of single nanowires in the 2-terminal and 4-terminal geometry. The resistance of single nanowires onto the same substrate has been calculated by fitting the obtained characteristics using thermionic emission theory. The obtained values are different from nanowire to nanowire, meaning differences in conductivity of nanowires on the same substrate. Then, the resistance profile along single nanowires has been measured in the 2-terminal geometry. This measurement shows a quasi-exponential decrease in nanowire conductivity from the bottom to the top part of individual nanowires. The experimental results are in good agreement with numerical simulations obtained using Finite Element Method calculations. The correct implantation of nanowires onto real devices also requires the knowledge of the correlation between the mechanical stress applied to single nanowires and their electric properties. The analysis of this correlation has been performed using the 2 terminal configuration, by applying different mechanical stress to the same nanowire and measuring the current-voltage characteristic at each step. The results show an increase in conductivity of the single nanowire with the increase of the applied tension.
8
Jasbinschek, dos Reis Pinheiro Katia. "Mantle electrical conductivity estimates from geomagnetic jerk observations /." Zürich : ETH, 2009. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=18259.
Full text
9
Ozkan, Koray Ozdal. "Multi-frequency Electrical Conductivity Imaging Via Contactless Measurements." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607071/index.pdf.
Full textAbstract:
A multi-frequency data acquisition system is realized for subsurface conductivity imaging of biological tissues. The measurement procedures of the system at different frequencies are same. The only difference between the single frequency experiments and the multi-frequency experiments is the hardware, i.e. the sensor and the power amplifier used in the single frequency experiments was different than that were used in the multi-frequency experiments. To avoid confusion the measurement system with which the single frequency experiments were performed is named as prototype system and the measurement system with which the multi-frequency experiments were performed is named as multi-frequency system. This system uses magnetic excitation (primary field) to induce eddy currents inside the conductive object and measures the resulting magnetic field due to eddy currents (secondary field). For this purpose, two differential-coil sensors are constructedone is for the single frequency measurements and the other is for the multi-frequency measurements. Geometrically the coils are same, the only difference between them is the radius of the wires wound on them. The sensor consists of two differentially connected identical receiver coils employed to measure secondary field and in between the receiver coils is placed a transmitter coil, which creates the primary field. The coils are coaxial. In the prototype system the transmitter coil is driven by a sinusoidal current of 300 mA (peak) at 50 kHz. In the multi-frequency system the transmitter coil is driven by a sinusoidal current of 217 mA (peak), 318 mA (peak), 219 mA (peak) and 211 mA (peak) at 30 kHz, 50 kHz, 60 kHz and 90 kHz, respectively. A data acquisition card (DAcC) is designed and constructed on a printed circuit board (PCB) for phase sensitive detection (PSD). The equivalent input noise voltage of the card was found as $146.80 hspace{0.1 cm}nV$. User interface programs (UIP) are prepared to control the scanning experiments via PC (HP VEE based UIP, LabVIEW based UIP) and to analyze the acquired data (MATLAB based UIP). A novel sensitivity test method employing resistive ring phantoms is developed. A relation between the classical saline solution filled vessel (45mm radius, 10 mm depth) phantoms and the resistive ring phantoms is established. The sensitivity of the prototype system to saline solutions filled vessels is 13.2 $mV/(S/m)$ and to resistive rings is 155.02 mV/Mho while the linearity is 3.96$%$ of the full scale for the saline solution filled vessels and 0.12$%$ of the full scale for the resistive rings. Also the sensitivity of the multi-frequency system is determined at each operation frequency by using resistive ring phantoms. The results are in consistence with the theory stating that the measured signals are linearly proportional with the square of the frequency. The signal to noise ration (SNR) of the prototype system is calculated as 35.44 dB. Also the SNR of the multi-frequency system is calculated at each operation frequency. As expected, the SNR of the system increases as the frequency increases. The system performance is also tested with agar phantoms. Spatial resolution of the prototype system is found 9.36 mm in the point spread function (PSF) sense and 14.4 mm in the line spread function (LSF) sense. Spatial resolution of the multi-frequency system is also found at each operation frequency. The results show that the resolving power of the system to distinguish image details increases as the frequency increases, as expected. Conductivity distributions of the objects are reconstructed using Steepest-Descent algorithm. The geometries and the locations of the reconstructed images match with those of the real images. The image of a living tissue, a leech, is acquired for the first time in the literature. Magnetic conductivity spectroscopy of a biological tissue is shown for the first time in electrical conductivity imaging via contactless measurements. The results show the potential of the methodology for clinical applications.
10
Ningelgen, Oliver Peter. "GoC : Gulf of Carpentaria electrical conductivity anomaly experiment /." Title page, contents and abstract only, 2001. http://web4.library.adelaide.edu.au/theses/09SB/09sbn7149g.pdf.
Full text
11
Uribe-Salas, Alejandro. "Process measurements in flotation columns using electrical conductivity." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=70295.
Full textAbstract:
Techniques based on electrical conductivity to estimate interface level, gas holdup and bias rate in flotation columns were developed.A conductivity probe and associated data acquisition system for locating the froth/collection zone interface in flotation columns were developed and tested. The level detection technique is based on the collection of a conductance profile around the interface and on the location of the position at which a sharp change in conductance occurs. Such a change in conductance across the interface is caused by the difference in the effective conductivity of the froth and collection zone, primarily due to their difference in gas holdup.
A conductivity cell to measure the effective conductivity of water-air, water-mineral, and water-mineral-air systems was developed. The cell consisted of two grid-electrodes covering the entire cross-sectional area of the cylinder containing the two or three phase system. Such an arrangement allowed the free movement of the phases and provided conditions for uniform potential and current (electrical) fields. It was found that Maxwell's model (1892) predicted the holdups of the non-conductive material reasonably well from the conductivity measurements.
Conditions encountered in industrial flotation columns allowed the use of conductivity to trace the flows of feed water and wash water across the interface, and therefore, to determine the bias rate. Alternative parameters to bias rate as measures of metallurgy such as fraction of feed water in the overflow water (called here feed water entrainment), feed water recovery, and conductance profiles, were explored.
12
Zhang, Maomao. "Permittivity and conductivity imaging in electrical capacitance tomography." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687378.
Full textAbstract:
Electrical capacitance tomography (ECT) is a technology that images the dielectric permittivity distribution of materials under test. ECT has been used as a tool for process monitoring in particular for two-phase flow measurement. These applications mainly focus on the dielectric samples, whose conductivity is negligibly small. This thesis studies ECT imaging with conductivity considerations. The conductive materials will affect the capacitance measurements and introduce difficulties in the ECT image reconstruction. This thesis presents solutions based on ECT to image material of different values of conductivity in different practical process or monitoring scenarios: the conductivity within materials under test is considered to be higher than 10^6 S/m, or less than 10 S/m. This work consists of the following innovative steps. (i) Through an ECT monitoring, floating (i.e., electrically non-grounded) metallic samples are imaged as dielectric illusions and the analysis of capacitance measurements over the conductors is delivered. (ii) Magnetic induction tomography (MIT) is firstly used for locating grounded metallic samples, thereafter as an assistant method to guide ECT to image the dielectric components. (iii) In low conductivity case MIT, as an indicator of conductive material again, helps ECT to solve multiphase flow problems. (iv) The multi-frequency complex ECT measurement provides a potential method to improve the ECT imaging ability for both conductive and dielectric materials. The first three ideas have been testified by both simulated and experimental results, while the fourth part is simulation-based results only on current stage.
13
Su, Bin. "Electrical, thermomechanical and reliability modeling of electrically conductive adhesives." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/10425.
Full textAbstract:
The first part of the dissertation focuses on understanding and modeling the conduction mechanism of conductive adhesives. The contact resistance is measured between silver rods with different coating materials, and the relationship between tunnel resistivity and contact pressure is obtained based on the experimental results. Three dimensional microstructure models and resistor networks are built to simulate electrical conduction in conductive adhesives. The bulk resistivity of conductive adhesives is calculated from the computer-simulated model. The effects of the geometric properties of filler particles, such as size, shape and distribution, on electrical conductivity are studied by the method of factorial design.
The second part of the dissertation evaluates the reliability and investigates the failure mechanism of conductive adhesives subjected to fatigue loading, moisture conditioning and drop impacts. In fatigue tests it is found that electrical conduction failure occurs prior to mechanical failure. The experimental data show that electrical fatigue life can be described well by the power law equation. The electrical failure of conductive adhesives in fatigue is due to the impaired epoxy-silver interfacial adhesion. Moisture uptake in conductive adhesives is measured after moisture conditioning and moisture recovery. The fatigue life of conductive adhesives is significantly shortened after moisture conditioning and moisture recovery. The moisture accelerates the debonding of silver flakes from epoxy resin, which results in a reduced fatigue life. Drop tests are performed on test vehicles with conductive adhesive joints. The electrical conduction failure happens at the same time as joint breakage. The drop failure life is found to be correlated with the strain energy caused by the drop impact, and a power law life model is proposed for drop tests. The fracture is found to be interfacial between the conductive adhesive joints and components/substrates.
This research provides a comprehensive understanding of the conduction mechanism of conductive adhesives. The computer-simulated modeling approach presents a useful design tool for the conductive adhesive industry. The reliability tests and proposed failure mechanisms are helpful to prevent failure of conductive adhesives in electronic packages. Moreover, the fatigue and impact life models provide tools in product design and failure prediction of conductive adhesives.
14
Tran, Sam, Niklas Lindborg, Souza Vivedes Danilo De, Johanna Sjölund, Veronica Enblom, and Mattias Sjödin. "Theoretical models of thermal conductivity and the relationship with electrical conductivity for compressed metal powder." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-387636.
Full textAbstract:
This Independent Project reviews literature about the effect of pressure and temperature on thermal conductivity in packed beds and its relationship with electrical conductivity. Exploring the relationships between thermal conductivity, porosity and pressure can give useful knowledge for further improvements in manufacturing processes in the field of powder metallurgy. The resulting theoretical models describing the effective thermal conductivity show that gas and contact conductance dominate at lower temperatures and that radiation gains dominance as the temperature increases. Modifications of the models covered in this report can be made in order to simulate the process of interest more accurately. It was also shown that Wiedemann-Franz law could be of interest when wanting to quantify the thermal conductivity in a powder compact. Furthermore, a lab manual for a future Independent Project was developed.
15
Oh, Tae-il. "Electrical conductivity and related defect structures in reduced rutile." Full text open access at:, 1985. http://content.ohsu.edu/u?/etd,90.
Full text
16
Yu, Shuaibo. "Study of Electrical Conductivity of Epoxy/Graphene Platelet Nanocomposites." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31447.
Full textAbstract:
Polymer nanocomposites are prepared by appropriately dispersing nanoscale fillers into polymer matrices. Graphene, a two-dimensional nano-carbon material with outstanding physical properties, has been widely studied as a conductive filler for nanocomposites. In this work, a gum Arabic aqueous solution was proposed as a new media to exfoliate graphite into few-layer graphene by liquid-phase sonication. Successful exfoliation was confirmed by Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. Four types of graphene nanoplatelets were used to study the effects of the filler's aspect ratio. The one with the largest aspect ratio showed the best performance, where the conductivity of neat epoxy was increased by five orders of magnitude at 10 wt.%. Using a hot sonication technique and adding a small amount of second fillers further improved the electrical conductivities. The highest conductivity obtained in this study was 0.025 S/cm, which met the requirements of electromagnetic shielding material.
17
Ismail, Bakar Bin. "Electrical conductivity measurements in evaporated cadmium telluride thin films." Thesis, Keele University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293964.
Full text
18
Major, AndraÌs G. "Contactless determination of the electrical conductivity in levitated liquids." Thesis, University of Bristol, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404079.
Full text
19
Navas, Pérez Carlos Justo 1971. "Synthesis, electrical conductivity and nonstoichiometry of dopped layered perovskites." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85242.
Full text
20
Mashiko, V. V., and I. P. Studenyak. "Electrical conductivity of “liquid crystal – Cu6PS5I superionic nanoparticles” composites." Thesis, Sumy State University, 2017. http://essuir.sumdu.edu.ua/handle/123456789/64321.
Full textAbstract:
One of the promising methods to extend the liquid crystal (LC) functionality is introduction of the nanoparticles. Thus, nanoparticles of superionic conductors with argyrodyte structure, in particular Cu6PS5I, can help to extend functional properties of LC. They are characterized by high electrical conductivity as well as ferroelastic and nonlinear optical properties. Therefore, the aim of this work was to study the influence of Cu6PS5I nanoparticles on the electrical conductivity of 6СВ and 6СНВТ liquid crystals.
21
Kress, Oliver Herbert. "Mechanical Tension and Electrical Conductivity of Liquid Crystal Filaments." Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1437752455.
Full text
22
Freire, Ricardo Satuf 1962. "Short fiber composites with high electrical and thermal conductivity." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278242.
Full textAbstract:
This research describes the preparation of electrically and thermally conductive polymer composites. The filler used is short carbon fibers. These were dispersed in methyl methacrylate (MMA) and settled under different vibrational and gravitational forces, resulting in well packed sediments. To improve further the dispersability of the fiber/MMA system, steric stabilization was attempted by using organic dispersants of increasing chain length. Subsequent polymerization of the dense sediments produced composites with high fiber volume fractions. The electrical and thermal conductivities of these composites were studied. Fiber size, distribution, orientation and volume fraction are shown to have a profound influence on these properties. A general effective media equation, which relates percolation and effective media theories, is shown to describe the electrical conductivity of the composites. The specific thermal conductivity of the high fiber fraction composites is greater than that of stainless steel. Applications include electronic packaging and electromagnetic interference shielding.
23
Isarn, Garcia Isaac. "New epoxy composites with enhanced thermal conductivity keeping electrical insulation." Doctoral thesis, Universitat Rovira i Virgili, 2019. http://hdl.handle.net/10803/668084.
Full textAbstract:
La tendència creixent a la indústria electrònica de fer aparells cada vegada més petits, més lleugers i que treballin més ràpid provoca un augment de calor generat per efecte Joule, degut a l’augment de freqüència del pas d’electrons. Eliminar aquest excés de calor requereix la millora de la conductivitat tèrmica dels materials ja existents, ja que el mantenir la temperatura de treball d’aquests dispositius està directament relacionat amb l’eficiència, el temps de vida útil i la prevenció de fallades prematures dels equips. Alguns elements dels dispositius electrònics es recobreixen amb reïnes termoestables epoxídiques. Per aquesta raó, augmentar la conductivitat tèrmica d’aquestes reïnes, aïllants per naturalesa, mantenint l’aïllament elèctric, resulta de gran importància en diverses indústries com l’electrònica i l’elèctrica. El mètode més senzill i econòmic per assolir aquest propòsit és mitjançant l’addició de partícules a la matriu polimèrica. En aquesta tesis doctoral s’han utilitzat diferents tipus de partícules per aconseguir els objectius en diverses matrius epoxídiques: nitrur de bor (BN), alúmina (Al2O3), nitrur d’alumini (AlN), carbur de silici (SiC), grafit expandit (EG) i nanotubs de carboni (CNTs). Experimentalment, s’ha determinat la influència que cada material afegit té sobre les propietats finals dels materials compostos, especialment de les característiques mecàniques, tèrmiques i elèctriques. El millor resultat obtingut pels objectius proposats ha estat la combinació del 70 % en pes de BN i un 2.5 i 5 % en pes de EG, arribant a més d’un 1600 % de millora en conductivitat tèrmica respecte el material de partida. Les conductivitats tèrmiques obtingudes han estat de 2,08 i 2,22 W/m·K, respectivament. A més, aquests materials han mantingut resistivitats elèctriques prou bones, al voltant de 10^10 i 10^6 Ω·m respectivament.La tendencia de la industria electrónica de crear dispositivos cada vez más pequeños, más ligeros y que trabajen más rápido lleva a un aumento en la producción de calor generado por efecto Joule, debido al aumento de la frecuencia de paso de los electrones. Eliminar este exceso de calor lleva a la necesidad de mejorar la conductividad térmica de los materiales ya existentes, ya que limitar la temperatura de trabajo de los dispositivos está directamente relacionada con su eficiencia, su tiempo de vida útil y previene la aparición de fallos prematuros de los equipos. Algunos elementos de estos dispositivos están recubiertos de resina termoestable epoxídica. Por esta razón, aumentar la conductividad térmica de estas resinas, aislantes por naturaleza, resulta de gran importancia en varias industrias como la electrónica y la eléctrica. El método más simple y económico para alcanzar este propósito es mediante la adición de partículas a la matriz polimérica. En esta tesis doctoral se han utilizado diferentes tipos de partículas en varias matrices epoxídicas: nitruro de boro (BN), alúmina (Al2O3), nitruro de aluminio (AlN), carburo de silicio (SiC), grafito expandido (EG) y nanotubos de carbono (CNTs). Se ha determinado experimentalmente la influencia de cada material añadido en las propiedades finales de los materiales compuestos, especialmente en sus características mecánicas, térmicas y eléctricas. El mejor resultado obtenido en cuanto a los objetivos propuestos ha sido la combinación del 70 % en peso de BN y un 2.5 y 5 % en peso de EG, alcanzando más de un 1600 % de mejora en conductividad térmica respecto al material de partida. Las conductividades térmicas alcanzadas han sido de 2,08 y 2,22 W/m·K respectivamente. Además, estos materiales han mantenido unas resistividades eléctricas suficientes, alrededor de 10^10 y 10^6 Ω·m, respectivamente.
The tendency in electronics to produce smaller and lighter devices with higher power output causes an increase of the generated heat (Joule effect) by the increase in the frequency of electrons. Evolve this exceeding heat cause the need to improve some properties that existent materials do not meet, since keeping the working temperature of these devices is directly related to efficiency, useful lifetime and prevention of premature equipment failures. Some elements of these devices are coated by epoxy resins and this is the reason why enhance the thermal conductivity of them, insulators by nature, is of great importance in several industries such as electronics and electrical. The most economic and simple technique to face this issue is still today through the addition of high thermal conductive fillers. In this doctoral thesis, boron nitride (BN), alumina (Al2O3), aluminum nitride (AlN), silicon carbide (SiC), expanded graphite (EG) and carbon nanotubes (CNTs) have been used. Experimentally, the influence of each filler has been determined in the final composites, especially in the thermal, mechanic and electric characteristics. The materials with the best performances in the proposed objectives were those of homopolymerized cycloaliphatic epoxy resin with the combined addition of 70 wt. % of BN platelets and 2.5 and 5 wt. % of EG. The values of thermal conductivity improved by more than 1600 % in reference to the neat epoxy and were 2.08 and 2.22 W/m·K, respectively. These materials also kept enough electrical insulation, in the range of 10^10 and 10^6 Ω·m, respectively.
24
Tighineanu, Alexei [Verfasser], and Patrik [Akademischer Betreuer] Schmuki. "Electrical Conductivity of TiO2 Nanotubes / Alexei Tighineanu. Gutachter: Patrik Schmuki." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2015. http://d-nb.info/1076673813/34.
Full text
25
Tu, Kai-Ming. "Spatial-Decomposition Analysis of Electrical Conductivity in Concentrated Ionic Systems." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199125.
Full text
26
Pires, Ellis John. "Electrical conductivity of single organic molecules in ultra high vacuum." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/56796/.
Full textAbstract:
Measurement of the I(V ) characteristics of single molecules is the first step towards the realisation of molecular electronic devices. In this thesis, the electronic transport properties of alkanedithiol (ADT) and alkylthiol-terminated oligothiophene molecules are investigated under ultra high vacuum (UHV) using a scanning tunnelling microscope (STM). Two techniques are employed that rely upon stochastic molecular bridge formation between gold STM tip and substrate; a novel I(V; s) method is proven to be a powerful alternative to the well-known I(s) method. For ADTs, three temperature-independent (180 - 390 K) conduction groups are identified, which arise from different contact-substrate coordination geometries. The anomalous reduction of conductance at small chain lengths reported by other groups for non-UHV conditions is far less pronounced here; all groups closely follow the anticipated exponential decay with chain length, β = (0.80 ± 0.01) Å ¹, until a small deviation occurs for the shortest molecule. Thus, the likely explanation for the anomalous effect is hydration of thiol groups. The I(V ) curves were fitted using a rectangular tunnel barrier model, with parameters in agreement with literature values; m = (0.32 ± 0.02) m, φ = 2 eV. For the oligothiophene molecules, one common temperature-independent (295-390 K) conduction group was identified; the conductance decays exponentially with molecular length, with different factors of β = (0.78 ± 0.15) Å ¹ and β = (0.16 ± 0:04) Å ¹ for length changes to the alkylthiol chains and thiophene backbone, respectively. An indented tunnel barrier model, anticipated from the physical and electronic structure of the molecules, was applied to fit the measured I(V ) curves; φ1 = φ3 = 2 eV, φ2 = 1.3 to 1.6 eV, m = 0.17 to 0.24 m. These UHV measurements provide an important baseline from which to better understand recent reports indicating hydration-dependent, and hydration-induced temperature-dependent, transport properties.
27
Shearwood, C. "The electrical conductivity and Hall coefficient of sputtered metallic glasses." Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383901.
Full text
28
Atashpendar, Arshia [Verfasser], and Tanja [Akademischer Betreuer] Schilling. "Geometric percolation and electrical conductivity in suspensions of conductive nanoparticles." Freiburg : Universität, 2021. http://d-nb.info/1227187483/34.
Full text
29
Harinarayana, Tirumalachetty. "Lithospheric electrical conductivity structure across Southern Scotland and Northern England." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/10936.
Full text
30
Mitscherling, Johannes [Verfasser], and Walter [Akademischer Betreuer] Metzner. "Electrical conductivity in quantum materials / Johannes Mitscherling ; Betreuer: Walter Metzner." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2021. http://d-nb.info/1233681362/34.
Full text
31
Neto, OdÃlio Coimbra da Rocha. "Hiperspectral data applied for estimating electrical conductivity in salty soils." Universidade Federal do CearÃ, 2016. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=16620.
Full textAbstract:
CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel SuperiorA interpretaÃÃo de dados do sensoriamento remoto fundamenta-se, basicamente, na anÃlise do comportamento da reflectÃncia espectral dos materiais no intervalo de comprimento de onda do visÃvel ao infravermelho de ondas curtas (400 a 2500 nm). Para isso, pode-se usar a espectrorradiometria de reflectÃncia, que à uma tÃcnica capaz de medir, em diferentes comprimentos de ondas, a energia eletromagnÃtica refletida da superfÃcie dos materiais e representÃ-la na forma de um grÃfico denominado curva de reflectÃncia espectral. O poder analÃtico desta tÃcnica advÃm do fato da informaÃÃo espectral se correlacionar diretamente com a composiÃÃo quÃmica e com as caracterÃsticas fÃsicas das substÃncias contidas no alvo. No entanto, o grande volume de informaÃÃes contidas em uma assinatura espectral aumenta a dificuldade de analisÃ-la, principalmente quando se trabalha com imagens. Com isso, o emprego de modelos computacionais se mostra como uma saÃda viÃvel para a anÃlise de curvas espectrais. Dessa forma, o objetivo desta tese à avaliar o desempenho de diferentes modelos computacionais como: mÃnimos quadrados (MQ), rede neural artificial do tipo perceptron de mÃltiplas camadas (MLP) e mÃquina de aprendizagem extrema (ELM), treinados em laboratÃrio para estimar a condutividade elÃtrica do solo, e aplicÃ-los em imagens de alta resoluÃÃo espectral. Esta tese foi separada em trÃs etapas onde foram avaliados: a capacidade dos modelos computacionais em estimar a condutividade elÃtrica do extrato de saturaÃÃo (CEes) a partir de amostra de condutividade elÃtrica 1:1 (CE1:1); as estratÃgias computacionais que melhor estimam a condutividade elÃtrica de amostras de solo a partir de leituras espectrais de solos obtidas em laboratÃrio; e testar desempenho da melhor estratÃgia obtida no passo anterior, aplicando-a em uma imagem do sensor aerotransportado SpecTIR, coletado na regiÃo do PerÃmetro Irrigado de Morada Nova. Para avaliaÃÃo dos algoritmos, foram coletadas amostras de solos na regiÃo de Morada Nova com histÃrico de Ãreas afetadas por sais. Estas amostras foram utilizadas para a calibraÃÃo e validaÃÃo dos modelos. Dados espectrais foram obtidos utilizando o espectrorradiÃmetro FieldSpec 4 Hi-Res, entre 350 a 2500 nm. Foi avaliado o ganho de performance dos modelos matemÃticos pela transformaÃÃo dos dados atravÃs da anÃlise por componente principal e pela anÃlise derivativa. Com os resultados obtidos, pÃde-se observar que as melhores respostas foram alcanÃadas pelo modelo linear dos mÃnimos quadrados aplicados aos dados puros, onde as bandas selecionadas para estimar a condutividade elÃtrica foram de 395, 1642 e 1717 nm. Para estimar a condutividade elÃtrica do solo na imagem do sensor SpecTIR sobre a Ãrea de estudo, o modelo calibrado em laboratÃrio se mostrou interessante, produzindo um RPD de 1,46 e um coeficiente de correlaÃÃo de Pearson de 0,80. Com isso, conclui-se que os modelos calibrados utilizando amostras em laboratÃrio sÃo satisfatÃrios para estimar a CE de imagens hiperespectrais.
Remote sensing data interpretation is based primarily on the spectral reflectance analysis of materials for wavelength ranging from visible to short wave infrared (400 to 2500nm). For this, one can use reflectance spectroscopy which is a technique capable of measuring, at different wavelengths, the electromagnetic energy reflected from the surface of materials and represent it in the form of a graph called spectral reflectance curve. The analytical power of this technique derives from the spectral information being correlated directly with the chemical composition and physical characteristics of the substances that makes the target. However, the large volume of information contained in a spectral signature increases the difficulty of analyzing it, especially if the dataset is made of images. Thus, computational models are expected to be a viable means of analyzing these spectral curves. The refore, the objective of this thesis is to evaluate the performance of different computational models, such as least squares (LS), multilayer perceptron (MLP) and extreme learning machine (ELM) artificial neural networks, trained on laboratory data to estimate the electrical conductivity of salty soils, and to apply them to a hyperspectral image of the field . This thesis was organized in three parts: first, the ability of computer models to estimate the electrical conductivity of saturation extract (ECse) based on electrical conductivity data from a 1:1 dilution (EC 1:1) is assessed; second, computing strategy for best estimating the electrical conductivity of soil samples using their spectral readings under laboratory conditions are evaluated; and finally, the performance of the best found model applied to an airborne SpecTIR sensor hyperspectral image collected at the Irrigated District of the Morada Nova was evaluated. To evaluate the proposed algorithms, soil samples were collected in the Morada Nova Irrigation District with a history of salinity. These samples were used for model calibration and validation. Spectral data were obtained using the spectroradiometer FieldSpec 3Hi-Res, from 350 to 2500nm. In an attempt to improve the performance of the models, data transformation was applied using either principal component analysis or derivative analysis. The results show the best performance was produced by the linear model fitted by least squares algorithm applied to the raw data (no transformation), and the spectral bands selected to estimate the electrical conductivity were 395, 1642 and 1717 nm. To estimate the soil's electrical conductivity from SpecTIR's image sensor data, the model calibrated in the laboratory has proved to be feasible, generating a value o f 1.46 for RPD, and 0.80 for the Pearson correlation coefficient. Therefore, one can conclude that the calibrated models using samples in the laboratory are satisfactory for estimating EC based on hyperspectral images.
32
Asgari, Mohammadreza. "FULLY-INTEGRATED CMOS PH, ELECTRICAL CONDUCTIVITY, AND TEMPERATURE SENSING SYSTEM." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1533827604228324.
Full text
33
Stewart, Douglas Norman. "Geomagnetic impulses and the electrical conductivity of the lower mantle." Thesis, University of Leeds, 1991. http://etheses.whiterose.ac.uk/1238/.
Full textAbstract:
This thesis is an investigation of the changes in the magnetic field as measured at the surface of the Earth on the time-scale of months to decades. In particular the phenomena of geomagnetic "impulses" or "jerks" are investigated. Vigorous discussion has surrounded these phenomena since they were first suggested to have been of global scale, of short duration and originating within the core (Courtillot et a/, 1978), primarily because of their implications for lower mantle conductivity. A major point of discussion has been whether they were of internal or external origin, and to what extent external fields determine their apparent time-scale. A large quantity of monthly means of the geomagnetic field is analysed here to investigate the contribution from external and induced fields. A model of the disturbance fields on the time-scale of months and years is derived. Using the oa geomagnetic index to represent the temporal dependence, the spatial morphology is found to be primarily dipolar aligned with the Earth's main dipole. This model allows a better representation of the core field to be obtained. Seasonal fluctuations in the field are also quantified. The results are found to be consistent with an insulating mantle down to about 600fcm and a conductivity of about 0.15m-1 to 15m"1 below that. A new method is developed to analyse the time-dependence of the improved representation of the core-field and is applied to a large set of geomagnetic annual means. This method determines the periods oftime for which the field, as measured at different locations, can be represented by a quadratic time-dependence. Such a representation is found to be valid typically for 10 years at a time and valid for 93% of the data. Dates at which the changes from one quadratic time-dependence to another occur are found, to a certain extent, to be globally synchronous. Particular dates when this occurs are found to be 1970, 1978 and 1983, the latter events being similar in character to the 1970 jerk, and are thought to arise from impulses in the third time-derivative of the core field. Spherical harmonic models of the main field with a quadratic time-dependence are then derived for epochs 1965.5,1974.5, 1981.5 and 1986.5 using the technique of stochas-tic inversion. These models are then used to map the changes in secular acceleration associated with the 1970, 1978 and 1983 jerks. The global extent of the 1978 and 1983 jerks have not previously been investigated. The 1983 jerk is found to be much weaker than the others and the 1978 jerk appears anti-correlated with the 1970 jerk. The role of electromagnetic coupling between the core and mantle is considered in the presence of a thin conducting layer at the base of the mantle. Time-dependent torques are computed for the period 1900 to 1980 and found to correlate closely with the torque required to explain the decade fluctuations in the length of day. If electro magnetic coupling is solely responsible for the decade fluctuations then this implies the conductance of the layer must be ~ 7 x 1085. Various other pieces of evidence relating to lower mantle conductivity are also discussed.
34
Imashuku, Susumu. "Electrical Conductivity of Grain Boundary in Accepter Doped Barium Zirconate." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/78014.
Full text
35
Uppal, Rajeev. "Effect of TiO₂ on the electrical conductivity of Al₂O₃." Thesis, University of Bath, 2000. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323708.
Full text
36
Fraser, Iain Stuart. "Electrical conduction in macroscopic carbon nanotube assemblies." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609756.
Full text
37
Munro, Brian. "Electrical and spectroscopic studies of new silver gallium thiophosphate glasses." Thesis, University of Aberdeen, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290249.
Full textAbstract:
New silver gallium thiophosphate glasses in the Ag2S-Ga2S3-'P4S8' system were studied employing a.c. impedance, Raman and IR spectroscopy. 'P4S8' does not exist and is used so that the compositions can be conventionally expressed in terms of network modifier and network formers. The glasses were in fact prepared from the elements. The trends in conductivity of other series of glasses were also studied including glasses with added AgI and mixed Ag-Na glasses. These glasses are interesting in that the phosphorus is formally in a IV+ oxidation state whereas other thiophosphate glasses previously reported in the literature contain phosphorus in a V+ oxidation state. Also, Raman spectroscopy has shown that these glasses contain hypothiodiphosphate units (P2S64-) which could be described as octahedral (the P-P occupies the place of the central atom). The phosphate and thiophosphate glasses studied thus far, have had structures based on meta(thio)phosphate chains of corner-sharing tetrahedra. Therefore these hypothiodiphosphate glasses are different in several respects to other thiophosphate glasses. Raman and IR studies of the 0.33Ag2S-0.33Ga2S3-0.33'P4S8' glass (or AgGaP2S6 as it is more usually referred to in this thesis) suggest that the glass is composed of linear chains of -(Ga1/2P2S6Ga1/2)- units as proposed by Wibbelmann. Studies on the Ag(1+x)Ga(1-x/3)P2S6 series lend weight to this model of the structure. The partial depolymerisation as Ga was replaced by Ag along the series could be followed by Raman spectroscopy. It was possible to relate the increase in conductivity (decrease in activation energy) along the series of changes in local structure. It was found that the compositional trends in activation energy can be explained in terms of the modified Anderson-Stuart model of Martin and Angell and in particular in terms of changes in the jump distance.
38
Schroeder, Wade Anthony. "Conductivity Sensor Circuit." University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1429537491.
Full text
39
Casanova, Martínez Ana. "Synthetic strategies for the preparation of nanoporous carbons with improved electrical conductivity." Thesis, Orléans, 2020. http://www.theses.fr/2020ORLE3093.
Full textAbstract:
A côté d’une grande variété de concurrents tels que les métaux (nobles ou non) ou les oxydes métalliques, les carbones nanoporeux apparaissent comme des matériaux clés dans de nombreuses applications électrochimiques. Ils permettent une grande diversité d’architectures de pores contrôlées combinées à des nombreuses propriétés, en particulier, la stabilité chimique et mécanique, la biocompatibilité, une chimie de surface riche et, surtout, une conductivité électrique relativement élevée.Bien que certains carbones (comme le graphite ou le graphène) présentent des propriétés électroniques proches de celles des électrodes métalliques, cette caractéristique dépend fortement de la disposition spatiale des atomes de carbone. En effet, la plupart des carbones nanoporeux sont des matériaux avec un faible degré d'ordre structurel et, par conséquent, avec une conductivité limitée. En vue d’améliorer cette conductivité, des efforts sont donc nécessaires pour préparer des carbones nanoporeux avec un degré élevé d’organisation structurale sans compromettre la structure poreuse.Pour cela, plusieurs stratégies ont été explorées: (i) le dopage des hétéroatomes; (ii) le revêtement avec une phase conductrice; (iii) la synthèse d'architectures 3D de type graphène nanoporeux, et (iv) l'incorporation d'un additif conducteur dans les encres appliquées pour la préparation des électrodes. Cette dernière option est pratique courante dans la plupart des applications électrochimiques, le noir de carbone étant l'additif conducteur le plus utilisé.Ce doctorat a consisté à explorer diverses approches synthétiques pour obtenir à la fois, des carbones nanoporeux avec des réseaux très poreux et une conductivité accrue en incorporant diverses nanostructures de carbone comme additifs conducteurs. Dans une première approche, l'additif a été incorporé pendant la synthèse des carbones nanoporeux eux-mêmes. Dans une seconde approche, des structures 3D de type graphène nanoporeux ont été obtenues par des approches hydrothermiques.Les carbones nanoporeux ont été obtenus modifiant la polycondensation des mélanges de résorcinol et de formaldéhyde décrite dans la littérature. Cette approche permet d'obtenir des matériaux très poreux avec des propriétés accordables, ce qui représente un avantage par rapport aux méthodes conventionnelles qui génèrent des matériaux avec une distribution de taille de pores plus large. Afin d’améliorer leur conductivité électrique, diverses nanostructures de carbone ont été utilisées comme additifs conducteurs: noir de carbone, graphite, graphène et dérivés d'oxyde de graphène.L'effet de divers paramètres tels que la nature, la quantité, le caractère hydrophobe et la composition de l'additif a été évalué. L'étude a révélé le rôle important de la nature de l'additif, non seulement sur la conductivité du composite gel de carbone/additif, mais aussi sur le développement de la porosité. Les additifs carbonés de nature hydrophobe favorisent le développement d'architectures de pores multimodales avec une prédominance des grands mésopores. Les additifs hydrophiles rendent les matériaux moins poreux. Concernant la conductivité, les composites ont montré des valeurs améliorées avec des seuils de percolation d'environ 8 wt.% pour le noir de carbone.Dans la seconde approche, différents carbones nanostructurés ont été soumis à un traitement hydrothermal pour améliorer leur porosité. Tout d'abord, la synthèse du graphène par décomposition par plasma de l'éthanol a été optimisée avec de bons taux de production et de qualité pour des débits de 2 à 4 g/h. L'oxyde de graphène a également été synthétisé par une méthode Hummers modifiée.Dans l'ensemble, des carbones nanoporeux avec une porosité élevée et une conductivité améliorée ont été obtenus par l’incorporation de faibles quantités de noir de carbone, graphite et graphène pendant la synthèse. Ces matériaux présentent un intérêt en tant qu'électrodes dans les applications électrochimiquesNanoporous carbons are key materials in many electrochemical applications over a wide variety of competitors (such as noble metals, non-noble metals or metal oxides) due to the diversity of materials with controlled pore architectures combined with adequate properties; particularly, chemical and mechanical stability, biocompatibility, rich surface chemistry and, most importantly, relatively high electronic conductivity.Although some carbons (e.g., graphite, graphene) present electronic properties close to those of metallic electrodes, this feature depends strongly on the spatial arrangement of the carbon atoms. Indeed, most nanoporous carbons are non-polycrystalline materials with a low degree of structural order and, as a consequence, with limited conductivity. Thus, efforts are yet needed to prepare nanoporous carbons with high and well defined pore architectures combining high electrical conductivity without compromising the porous structure.To increase the conductivity of nanoporous carbon electrodes without compromising the porosity, several strategies have been explored such as: (i) heteroatoms’ doping; (ii) coating with a conductive phase; (iii) synthesizing 3D nanoporous graphene-like architectures, and (iv) incorporating a conductive additive in the formulation of carbon electrodes inks. The latter is the common practice for the manufacturing of the electrodes in electrochemical applications, being carbon black the most popular conductive additive.The approach in this PhD consisted in exploring various synthetic approaches to obtain nanoporous carbons with high porous networks and enhanced conductivity upon incorporating various carbon nanostructures as conductive additives. In a first approach, the additive was incorporated during the synthesis of the nanoporous carbon material itself, rather than as percolator in the inks typically used in the preparation of electrodes (e.g., carbon material, binder and percolator). In a second approach, 3D nanoporous graphene-like architectures were obtained by hydrothermal approaches.The synthesis of the nanoporous carbons was carried out by a modification of the polycondensation of resorcinol and formaldehyde mixtures well reported in the literature for the preparation of carbon gels. This approach allows obtaining highly porous materials with tuneable properties compared to conventional activation methods that usually render materials with broad pore size distributions. To overcome the drawback of their low electrical conductivity, various carbon nanostructures were used as conductive additives: carbon black, graphite, graphene and graphene oxide derivatives.The effect of various parameters such as the type, amount, hydrophobic/hydrophilic character and composition of the additive was explored. The study revealed the important role of the nature of the additive not only on the conductivity of the carbon gel/additive composite, but also on the development of the porosity during the synthesis. Carbon additives of hydrophobic nature act as a porogen, favouring the development of multimodal pore architectures, with predominance of large mesopores. Hydrophilic additives rendered materials with lower porosity. Regarding conductivity, the composites showed enhanced values, with percolation thresholds of ca. 8 wt.% for carbon black.In the second approach, various nanostructured carbons were subjected to a hydrothermal treatment. First, graphene synthesis by plasma decomposition of ethanol was optimized, with good production rates and quality for flows of 2-4 g/h. Graphene oxide was also synthesized by a modified Hummers method. The hydrothermal treatment rendered materials with improved porosity.Overall, highly nanoporous carbons with controlled mesopore architectures and enhanced conductivity were obtained. Such materials are of interest as electrodes in electrochemical applications (e.g, energy storage, supercapacitors, electrochemical sensors)
40
Yang, Fan. "Electrical and thermal properties of yttria-stabilised zirconia (YSZ)- based ceramic materials." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/electrical-and-thermal-properties-of-yttriastabilised-zirconia-ysz-based-ceramic-materials(82568afe-ffcb-4a38-9166-e5de83337763).html.
Full textAbstract:
Electrical and thermal conductivities of the yttria-stabilised zirconia/alumina (YSZ/Al2O3) composites and the yttria-zirconia-ceria (YSZ-CeO2) solid solutions are studied in this thesis. The electrical conductivity of the YSZ/Al2O3 composites decreases with an increase in the volume fraction of Al2O3 and exhibits typical percolation behaviour. The electrical conductivity of the YSZ/Al2O3 interface is higher than that of the YSZ grain boundary, but lower than that of the YSZ grains. The thermal conductivity of the YSZ/Al2O3 composites increases with an increase in the Al2O3 volume fraction, and it can be fitted well to the Maxwell theoretical model, which indicates the absence of obvious interfacial thermal resistances in the composites. The low interfacial thermal resistance of the YSZ/Al2O3 interface is due to the 'clean' and coherent nature of the YSZ/Al2O3 interface, along with the small difference between the elastic properties of YSZ and Al2O3. The electrical conductivity of the [(ZrO2)1-x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions has a 'V-shape' variation as a function of the mole ratio of CeO2 (x). In the ZrO2-rich region (x < 0.5), CeO2 doping increases the concentration of defect associates which limits the mobility of the oxygen vacancies; in the CeO2-rich region (x > 0.5), the increase of x increases the lattice parameter, which enlarges the free channel for oxygen vacancy migration. A comparison of the YSZ-CeO2 solid solutions with the YSZ-HfO2 series indicates the ionic radius of the tetravalent dopant determines the composition dependence of the ionic conductivity of the solid solutions.The thermal conductivity of the [(ZrO2)1-x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions also has a 'V-shape' variation as a function of the mole ratio of CeO2 (x), which indicates an incorporation of Zr4+ and Ce4+ can effectively decrease the thermal conductivity of the end members YSZ and yttria-doped ceria (YDC). In the ZrO2-rich region (0 ≤ x ≤ 0.5), the thermal conductivity is almost temperature independent; in the CeO2-rich region (0.5 ≤ x ≤ 1), it decreases obviously with increasing temperature. By calculating the phonon scattering coefficients, it is concluded that the composition dependence of the thermal conductivity in the ternary solid solutions is dominated by the mass difference between Zr and Ce at the cation sites, whereas the temperature dependence is determined by the order/disorder of oxygen vacancies at the anion sites.
41
Sasaki, Kazunari. "Phase equilibria, electrical conductivity, and electrochemical properties of ZrO₂-In₂O₃ /." Zürich, 1993. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10331.
Full text
42
Saleem, Swilem. "Electrical conductivity measurements of strongly coupled tungsten, titanium and silver plasmas." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=96361262X.
Full text
43
Ndegwa, Anne W. "Biodegradation and electrical conductivity of amine-contaminated soil, a laboratory study." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ65006.pdf.
Full text
44
Carella, Catherine A. "Electrical conductivity as a surrogate for dissolved bromide stream tracer samples." Thesis, University of Colorado at Boulder, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1546530.
Full textAbstract:
The coupling of the stream tracer technique with transient storage modeling is a well-established approach to characterizing solute transport processes of complex stream systems. Stream tracer studies require a large number of samples and the associated chemical analyses are costly. Sampling and analytical demand would be significantly reduced if electrical conductivity - a robust, easy-to-measure, water-quality property- was used as the primary measure of tracer breakthrough and converted to bromide tracer concentrations for breakthrough curve analysis and transient storage model parameter optimization. The advantages of collecting electrical conductivity data as a surrogate for dissolved bromide tracer samples are (1) reduced cost of laboratory analysis, (2) high-frequency data collection by field instruments, and (3) well-defined breakthrough curves for enhanced transient storage model simulations.
This method was tested by collecting electrical conductivity data and dissolved tracer samples during an instantaneous sodium bromide (NaBr) injection experiment in Fourmile Creek, Boulder County, Colorado. Concentrations of bromide were calculated from electrical conductivity data using equations that relate electrical conductivity of natural waters to their chemical composition. Models of transient storage were simulated for both the tracer data derived from electrical conductivity and the measured tracer data.
Small changes in background electrical conductivity caused the highest error (%) in the breakthrough curves. The method was robust in stream reaches where changes in background electrical conductivity could be accounted for. The use of high-frequency calculated bromide data within the transient storage model provided improved parameter estimates.
45
Jamil, Nawfal Yousif. "A study of growth, electrical conductivity and diffusion in (CdMn)Te." Thesis, University of Hull, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314717.
Full text
46
Glover, Paul W. J. "Electrical conductivity of rock samples subjected to high temperatures and pressures." Thesis, University of East Anglia, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236438.
Full textAbstract:
The field determinations of crustal electrical conductivity/depth profiles show anomalously high conductivities in the lower crust. This has yet to be explained by a consistent theory and interpretation of field results is difficult due to the lack of laboratory conductivity measurements of saturated rocks at lower crustal temperatures. A cell was designed to measure the electrical conductivity of saturated rocks up to the lower crustal conditions of; confining pressures of 1 GPa, pore-fluid pressures of 1 GPa and temperatures of 900°C. This complex exercise required the use of a metal sleeve and the use of guard-ring techniques to remove leakage currents induced by the sleeve. The development of the cell involved several years work and is a breakthrough in measurement techniques as it has enabled the measurement of saturated rock conductivities at lower crustal temperatures and high pressures for the first time. The conductivity of 14 samples of acidic and metabasic rocks was measured at a variety of confining pressures (<0.2 GPa), porefluid pressures (<0.2 GPa), temperatures (<900°C) and saturation fluids. The pressure variations showed that the basic rocks had a conductivity too high to be explained by conduction through saturating electrolyte alone. The temperature variation showed a dramatic difference between acidic and basic rocks. The acidic rocks showed large decreases in conductivity above 350°C after initial rapid increases in conductivity. The basic rocks showed no such reduction in conductivity indicating that a conduction mechanism in addition to pore-fluid conduction was present. Results indicate that saturated -rocks at high temperatures have 7/ conductivities sufficient to explain the high conductivity layers in the upper lower crust whereas acidic rocks do not. The results also demonstrate that graphite may be an important additional conduction mechanism possibly accounting for the moderately high conductivities in the lower lower crust even in the absence of electrolyte conduction
47
Veras, Johann. "Electrical Conductivity Imaging via Boundary Value Problems for the 1-Laplacian." Doctoral diss., University of Central Florida, 2014. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6377.
Full textAbstract:
We study an inverse problem which seeks to image the internal conductivity map of a body by one measurement of boundary and interior data. In our study the interior data is the magnitude of the current density induced by electrodes. Access to interior measurements has been made possible since the work of M. Joy et al. in early 1990s and couples two physical principles: electromagnetics and magnetic resonance. In 2007 Nachman et al. has shown that it is possible to recover the conductivity from the magnitude of one current density field inside. The method now known as Current Density Impedance Imaging is based on solving boundary value problems for the 1-Laplacian in an appropriate Riemann metric space. We consider two types of methods: the ones based on level sets and a variational approach, which aim to solve specific boundary value problem associated with the 1-Laplacian. We will address the Cauchy and Dirichlet problems with full and partial data, and also the Complete Electrode Model (CEM). The latter model is known to describe most accurately the voltage potential distribution in a conductive body, while taking into account the transition of current from the electrode to the body. For the CEM the problem is non-unique. We characterize the non-uniqueness, and explain which additional measurements fix the solution. Multiple numerical schemes for each of the methods are implemented to demonstrate the computational feasibility.Ph.D.
Doctorate
Mathematics
Sciences
Mathematics
48
Ohlendorf, Gerd, Denny Richter, Jan Sauerwald, and Holger Fritze. "High-temperature electrical conductivity and electromechanical properties of stoichiometric lithium niobate." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-192902.
Full textAbstract:
High temperature properties such as electrical conductivity (σ) and resonance behaviour of stoichiometric lithium niobate (LiNbO3) are
determined in the temperature range from 20 to 950 °C.
The activation energy of the conductivity is found to be 0.9 and 1.7 eV in the temperature range from 500 to 750 °C and from 800 to 950 °C, respectively. During thermal treatments in ambient air up to 950 °C and back, the conductivity remains unchanged at a given temperature, i.e., the crystal is stable under these conditions. The oxygen partial pressure (pO2) dependence of the conductivity shows two distinct ranges. At 750 °C, the property remains unchanged down to 10−15 bar. Below 10−15 bar, the conductivity increases according to σ ~ (pO2)−1/5. Z-cut LiNbO3 plates can be excited to thickness mode vibrations up to at least 900 °C. At this temperature, the quality factor Q is found to be between 30 and 100. As for changes of the conductivity, a decrease of the resonance frequency is observed below 10−15 bar indicating a correlation of both properties. In order to evaluate the lithium evaporation,
the crystals are tempered at 900 °C in ambient air for 24 h. A depth profile of the constituents does not indicate lithium loss within the accuracy of the secondary ion mass spectroscopy. The preliminary results underline the potential of stoichiometric LiNbO3 for high-temperature applications and justify its closer investigation.
49
Amato, Alessandro. "Temperature dependence of the electrical conductivity in the quark-gluon plasma." Thesis, Swansea University, 2014. https://cronfa.swan.ac.uk/Record/cronfa42946.
Full text
50
Amruthaluri, Sushma. "Synthesis of copper carbon nanotube composite and its electrical conductivity measurement." FIU Digital Commons, 2008. http://digitalcommons.fiu.edu/etd/1283.
Full textAbstract:
The matrices in which Multi Walled Carbon Nanotubes (MWCNTs) are incorporated to produce composites with improved electrical properties can be polymer, metal or metal oxide. Most composites containing CNTs are polymer based because of its flexibility in fabrication. Very few investigations have been focused on CNT-metal composites due to fabrication difficulties, such as achievement of homogeneous distribution of MWCNTs and poor interfacial bonding between MWCNTs and the metal matrix. In an effort to overcome poor interfacial bonding for the Cu - MWCNT composite, silver (Ag) and nickel (Ni) resinates have been incorporated in the ball milling stage. Composites of MWCNT (16, 12, and 8 Vol %) - Cu+Ag+Ni were pelleted at 20,000 psi (669.4 Mpa) and sintered at 950 °C. The electrical conductivity results measured by four probe meter showed that the conductivity decreases with increase in the porosity. Moreover from these results it can also be stated that an addition of optimum value of (12 Vol %) MWCNT leads to high electrical conductivity (9.26E+07 s-m"), which is 50% greater than the conductivity of Cu. It is anticipated that the conductivity can be increased substantially with hot isostatic pressing of the pellet.