Dissertations / Theses: 'Conductivity'

1

Tardieu, Giliane. "Thermal conductivity prediction." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/10014.

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Schroeder, Wade Anthony. "Conductivity Sensor Circuit." University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1429537491.

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Sylvan, Keith. "RF electrolytic conductivity transducers." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/11450.

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4

Martin, Ana Isabel. "Hydrate Bearing Sediments-Thermal Conductivity." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6844.

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The thermal properties of hydrate bearing sediments remain poorly studied, in part due to measurement difficulties inside the hydrate stability envelope. In particular, there is a dearth of experimental data on hydrate-bearing sediments, and most available measurements and models correspond to bulk gas hydrates. However, hydrates in nature largely occur in porous media, e.g. sand, silt and clay. The purpose of this research is to determine the thermal properties of hydrate-bearing sediments under laboratory conditions, for a wide range of soils from coarse-grained sand to fine-grained silica flour and kaolinite. The thermal conductivity is measured before and after hydrate formation, at effective confining stress in the range from 0.03 MPa to 1 MPa. Results show the complex interplay between soil grain size, effective confinement and the amount of the pore space filled with hydrate on the thermal conductivity of hydrate-bearing sediments.

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Mensah-Brown, Henry. "Thermal conductivity of liquid mixtures." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362870.

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Peralta, Martinez Maria Vita. "Thermal conductivity of molten metals." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391505.

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Jawad, Shadwan Hamid. "Thermal conductivity of polyatomic gases." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367922.

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Williams, Oliver Aneurin. "Surface conductivity on hydrogenated diamond." Thesis, University College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405246.

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Valter, Mikael. "Thermal Conductivity of Uranium Mononitride." Thesis, Linköpings universitet, Tunnfilmsfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-122337.

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Thermal conductivity is a crucial parameter for nuclear fuel, as it sets an upper limit on reactor operating temperature to have safety margins. Uranium mononitride (UN) is a prospective fuel for fast reactors, for which limited experimental studies have been conducted, compared to the currently dominating light-water reactor fuel, uranium dioxide. The aim of this thesis is to determine the thermal conductivity in UN and to determine its porosity dependence. This was done by manufacturing dense and porous high-purity samples of UN and examining them with laser flash analysis, which with data on specific heat and thermal expansion gives the thermal conductivity. To analyse the result, a theoretical study of the phenomenology of thermal conductivity as well as a review and comparison with previous investigations were carried out. The porosity range was 0.1–31% of theoretical density. Thermal diffusivity data from laser flash analysis, thermal expansion data and specific heat data was collected for 25–1400 C. The laser flash data had high discrepancy at higher temperatures due to thermal instability in the device and deviations due to graphite deposition on the samples, but the low temperature data should be reliable. As the specific heat data was also of poor quality, literature data was used instead. As for the thermal diffusivity data, the calculated thermal conductivity for lower temperatures are more accurate. A modified version of the porosity model by Ondracek and Schulz was used to analyse the porosity dependence of the thermal conductivity, taking into account the different impacts of open and closed porosity.
Värmeledningsförmåga är en avgörande egenskap för kärnbränslen, eftersom det begränsar den maximala drifttemperaturen i reaktorn för att ha säkerhetsmarginaler. Uranmononitrid (UN) är ett framtida bränsle för snabba reaktorer. Jämfört med det dominerande bränslet i lättvattenreaktorer, urandioxid, har endast begränsade experimentella studier gjorts av UN. Målet med detta arbete är att bestämma värmeledningsförmågan i UN och bestämma dess porositetsberoende. Detta gjordes genom att tillverka kompakta och porösa prover av UN och undersöka dem med laserblixtmetoden, vilket tillsammans med värmekapacitet och värmeutvidgning ger värmeledningsförmågan. För att analysera resultatet gjordes en teoretisk studie av värmeledning såväl som en genomgång av och jämförelse med tidigare undersökningar. Provernas porositet sträckte sig från 0.1% till 31% av teoretisk densitet. Värmediffusivitetsdata från laserblixtmetoden, värmeutvidgningsdata och värmekapacitetsdata samlades in för 25–1400 C. Värdena från laserblixtmätningen hade hög diskrepans vid höga temperaturer p.g.a. termisk instabilitet i anordningen och avvikelser p.g.a. grafitavlagring på proverna, men data för låga temperaturer borde vara tillförlitliga. Eftersom resultaten från värmekapacitetsmätningen var av dålig kvalité, användes litteraturdata istället. Som en konsekvens av bristerna i mätningen av värmediffusivitet är presenterade data för värmeledningsförmåga mest exakta för låga temperaturer. En modifierad version av Ondracek-Schulz porositetsmodell användes för att analysera värmeledningsförmågans porositetsberoende genom att ta hänsyn till olika inverkan av öppen och sluten porositet.

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Anderson, Stephen Ashcraft. "The thermal conductivity of intermetallics." Master's thesis, University of Cape Town, 1996. http://hdl.handle.net/11427/18185.

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Includes bibliographical references.
The thermal conductivity of titanium aluminide and several ruthenium-aluminium alloys has been studied from room temperature up to 500°C. Ruthenium aluminide is a B2-type intermetallic which is unusual and of special interest because of its toughness, specific strength and stiffness, oxidation resistance and low cost. The possible use of ruthenium aluminide in high temperature industrial applications required an investigation of the thermal properties of this compound. Apparatus, capable of measuring thermal conductivity at elevated temperatures has been designed and constructed. This study represents the first experimental results for the thermal conductivity of ruthenium aluminide alloys. The electrical resistivity of the intermetallic compounds has been measured using apparatus based on the Van der Pauw method. The Weidman-Franz ratio of the ruthenium aluminide alloys has been calculated and this indicates that the primary source of heat conduction in these alloys is by electronic movement and that the lattice contribution is minor. The electrical and thermal properties of ruthenium aluminide are shown to be similar to that of platinum and nickel aluminide. This has important implications for the use of these alloys in high temperature applications.

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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.

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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.

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He, Xiaoyan. "Carbon-rich ruthenium complexes and photochromic units : luminescence and conductivity modulations." Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S117.

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Ce travail est consacré à la synthèse et à la caractérisation de commutateurs et de fils moléculaires. La première partie est une étude bibliographique qui présente les avantages et les applications des unités moléculaires utilisées dans le contexte de l’électronique moléculaire. La deuxième partie de ce manuscrit traite de la préparation, des études électrochimiques et photophysiques de complexes de ruthénium bimétalliques portant un coeur triarylamine. Le but est ici de moduler la luminescence de ce cœur en changeant l’état redox des groupements acetylure de ruthénium. Dans la troisième partie, des combinaisons de précurseurs de complexes de Ln (Ln = Eu ou Yb) et de groupements vinyl-ruthénium redox-actifs ont été formées afin de moduler la luminescence des centres Ln via l’oxydation des groupements vinyl-ruthénium. La quatrième partie décrit l'association d'un précurseur de complexe de Ln (Ln = Eu ou Yb) à un ligand portant une unité dithienylethene (DTE), afin de commuter l'émission de lumière du centre Ln. Ces composés ont été synthétisés avec succès et leur luminescence a été reversiblement modulée par irradiation lumineuse. Dans la dernière partie, nous décrivons la synthèse d'une série de fils moléculaires composée de complexes bis(acetylure) de ruthénium (II) terminés par des groupes fonctionnels amine, et comprenant un complexe bimétallique photochrome avec une unité DTE. Ces molécules ont été conçues de manière à être insérées entre deux électrodes de graphène pour étudier leur conductance dans les différents états redox. En outre, le complexe photochrome doit pouvoir permettre la commutation de la conductance par voie optique et électrochimique dans des jonctions moléculaires de graphène
This work is devoted to the synthesis and characterization of novel molecular switches and wires that incorporate ruthenium organometallic moieties. First, a bibliographic chapter presents the advantages and applications of the building blocks used in the following chapters and discuss the general context of molecular electronics. The second part of this manuscript deals with preparation, electrochemical and photophysical studies of bimetallic ruthenium complexes bearing a triarylamine core. The goal is to modulate the luminescence of this core by changing the states of the redox-active ruthenium acetylide moieties. In the third part, combinations of Ln (Ln = Eu or Yb) complexes and redox-active ruthenium vinyl bipyridine moieties were formed in order to tune the luminescence of Ln center via oxidation of the redox-active ruthenium vinyl moieties. The fourth part describes an association of a Ln (Ln = Eu or Yb) precursor and a ligand bearing a dithienylethene (DTE) unit, in order to commute the light emission of the Ln center. These DTE-Ln compounds were successfully synthesized and their luminescence was reversiblely modulated by photo irradiation. In the last part, we report the synthesis of a series of redox-active molecular wires, which are ruthenium (II) bis(σ-arylacetylide) complexes terminated with amine functional groups, one of them including a photochromic DTE unit. These molecules are designed to covalently bridge a gap between graphene electrodes for probing the electrochemical gating of conductance via oxidation of the molecules. Furthermore, the photochromic complex should allow combined optical and electrochemical conductance switching in single molecule graphene junctions

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13

Marpaung, Fivman. "Investigation of the effect of gel residue on hydraulic fracture conductivity using dynamic fracture conductivity test." Texas A&M University, 2007. http://hdl.handle.net/1969.1/85866.

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The key to producing gas from tight gas reservoirs is to create a long, highly conductive flow path, via the placement of a hydraulic fracture, to stimulate flow from the reservoir to the wellbore. Viscous fluid is used to transport proppant into the fracture. However, these same viscous fluids need to break to a thin fluid after the treatment is over so that the fracture fluid can be cleaned up. In shallower, lower temperature (less than 250°F) reservoirs, the choice of a fracture fluid is very critical to the success of the treatment. Current hydraulic fracturing methods in unconventional tight gas reservoirs have been developed largely through ad-hoc application of low-cost water fracs, with little optimization of the process. It seems clear that some of the standard tests and models are missing some of the physics of the fracturing process in low-permeability environments. A series of the extensive laboratory "dynamic fracture conductivity" tests have been conducted. Dynamic fracture conductivity is created when proppant slurry is pumped into a hydraulic fracture in low permeability rock. Unlike conventional fracture conductivity tests in which proppant is loaded into the fracture artificially, we pump proppant/ fracturing fluid slurries into a fracture cell, dynamically placing the proppant just as it occurs in the field. Test results indicate that increasing gel concentration decreases retained fracture conductivity for a constant gas flow rate and decreasing gas flow rate decreases retained fracture conductivity. Without breaker, the damaging effect of viscous hydraulic fracturing fluids on the conductivity of proppant packs is significant at temperature of 150°F. Static conductivity testing results in higher retained fracture conductivity when compared to dynamic conductivity testing.

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14

Abidi, Sonia. "Matériaux composites à haute tenue thermique : influence de la micro-nanostructure sur les transferts moléculaires, électroniques et thermiques." Thesis, Toulon, 2014. http://www.theses.fr/2014TOUL0019/document.

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Les matériaux de protection incendie sont largement utilisés pour assurer la sécurité des usagers des infrastructures. Les normes de protection incendie évoluant régulièrement, les matériaux doivent être de plus en plus performants. Ceux-ci sont généralement des mortiers constitués d’oxydes réfractaires et isolants. L’objectif de ce travail est de mettre au point un composite coupe-feu 4 h applicable par projection mais également de déterminer ses propriétés thermiques et mécaniques.Dans une première partie, cette étude reprend les différentes étapes de l’élaboration d’un matériau de protection incendie, après la présentation de la démarche qui a guidé l’élaboration de nos matériaux, nous nous sommes intéressés plus particulièrement à la composition chimique de la matrice ainsi que celle du ciment. Leurs propriétés thermiques et mécaniques ont été passées en revue.Les matières premières nécessaires à l’élaboration d’un mortier ont ensuite été sélectionnées. L’évolution, respectivement de la conductivité thermique, de la diffusivité, de la porosité, de la chaleur spécifique et des propriétés mécaniques des mortiers choisis en fonction de la nature et de la quantité de charges incorporées à la matrice a été étudiée. Une description des divers modèles analytiques et numériques permettant la représentation de la conductivité thermique et du module d’Young des matériaux a permis de développer un modèle capable de prédire le comportement thermique et mécanique des composites en fonction de la nature et de quantité de charges ajoutées.Dans une seconde partie, la cinétique de la réaction d’hydratation du plâtre afin de maîtriser les temps de prise et pour faciliter la production des projetés dans la chaîne industrielle a été étudiée. L’influence sur la cinétique d’hydratation, de la composition chimique du plâtre, de sa granulométrie et de l’ajout d’adjuvants couramment utilisés dans l’industrie plâtrière, a également été traitée.10A l’issue de cette étude, deux formulations de composites projetables ont été mises au point
Fire protection materials are widely used to ensure the safety of users of the infrastructure. Standards of fire protection regularly operating, the materials must be more efficient. These are generally composed of refractory mortar and insulating oxides. The objective of this work is to develop a firewall composite 4 h applied by projecting but also to determine the thermal and mechanical properties.In the first part, this study describes the various stages of the development of a fire protection material, after the presentation of the approach that has guided the development of our materials, we are interested especially in the chemical composition of the matrix and that of the cement. Their thermal and mechanical properties have been reviewed.The raw materials for the preparation of mortar were selected. The evolution respectively of thermal conductivity, diffusivity, porosity, specific heat and the mechanical properties of mortars chosen according to the nature and amount of the fillers incorporated in the matrix has been studied. A description of the various analytical and numerical models for the representation of the thermal conductivity and Young's modulus of the materials led to the development of a model able to predict the thermal and mechanical behavior of composites based on the nature and amount of charges added.In a second part, the kinetics of the hydration reaction of gypsum to control setting time and to facilitate the production of the composite in the industrial chain was studied. The influence on the kinetics of hydration, of the chemical composition of the gypsum, particle size distribution and the addition of adjuvant commonly used in the plaster industry, has also been treated.At the end of this study, two formulations of composites applied by projection were developed

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Mutnuri, Bhyrav. "Thermal conductivity characterization of composite materials." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4468.

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Thesis (M.S.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains vii, 62 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 61-62).

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Lukaschewitsch, Michael. "Geoelectrical conductivity problems on unbounded domains." Universität Potsdam, 1998. http://opus.kobv.de/ubp/volltexte/2007/1470/.

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This paper deals with the electrical conductivity problem in geophysics. It is formulated as an elliptic boundary value problem of second order for a large class of bounded and unbounded domains. A special boundary condition, the so called "Complete Electrode Model", is used. Poincaré inequalities are formulated and proved in the context of weighted Sobolev spaces, leading to existence and uniqueness statements for the boundary value problem. In addition, a parameter-to-solution operator arising from the inverse conductivity problem in medicine (EIT) and geophysics is investigated mathematically and is shown to be smooth and analytic.

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17

Shegelski, Mark Raymond Alphonse. "Hopping conductivity in lightly doped semiconductors." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/27529.

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In lightly doped semiconductors (LDSs), electrons can exist in localized states around impurities and dc electronic conduction can occur by electrons hopping between localized states. Such hopping is the dominant mechanism for conduction if the temperature is so low that the contribution from band electrons is negligible. According to theories of hopping conduction, at low enough temperature T, the conductivity σ will be o=σ₀e⁻(T₀/T)¼ where T₀ is a temperature which depends on the material. Experimental work on doped semiconductors which exhibits this form of σ is scarce. Recently, however, conductivities which were clearly of this form were reported for lightly doped n-GaAs and lightly doped n-InP. The experimental results were surprising in that the temperature ranges were well above, and the T₀ values well below, the limits set by the theories. To understand these experimental results, hopping in LDSs is modelled in this dissertation using a resistor network. This dissertation is unique in that the conductivity of the unabridged resistor network is examined in a temperature range (called "the high temperature regime") where kT is comparable to the spread ∆ε in the energies of localized electrons. A numerical simulation is performed and an analytic theory based on percolation methods is presented. In this dissertation, an analytic approach is developed for the first time for studying how, in the high temperature regime, the conductivity of the unabridged resistor network depends on the density of localized states. It is found that, in either two or three dimensions, if the density of states is flat, σ is of the activated form o=σ₀e ⁻εa/kt. The activation energies are found to be εa=0.28∆ε in two dimensions and εa =0.20∆ε in three dimensions. These values are considerable improvements over the estimates of previous workers, who used the low temperature asymptotic form of the resistance in the high temperature regime. It is also revealed that σ can be o=µσ₀e ⁻(T₀/T)¼ in the high temperature regime if the density of states decreases with |ε⁻µ₀| for energy e far enough away from the zero temperature chemical potential µ₀, These results are in accord with the experimental results described above.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

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18

Zaki, Athraa J. "Conductivity studies of single protein molecules." Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/95883/.

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A fundamental step for future uses of biomolecules in electronics is the study of the bonding, orientation and conductance of a single molecule attached to a conductive substrate, which is the building block of electronic materials and devices based on molecular conduction. This work provides an in-depth examination of morphology and electrical properties of different molecules anchored to Au(111) and to sustainable carbon materials (graphite and graphene). Cytochrome b562 (Cyt b562), TEM beta-lactamase and the superfolded green uorescent protein engineered with phenyl azide were exposed to UV irradiation to transform the azide compound into the nitrene radical, which enabled successful molecule linking to graphene. The UV-based approach was tested on the above molecules to ascertain its robustness against the specificity of the protein used. The efficiency of the procedure was inspected by imaging via atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). By repeated sample preparation and imaging, we established suitable protein concentrations to enable single-molecule measurements on the resulting samples (e.g., the concentration range optimal for cyt b562 on gold was 0.025-0.5 μM). We used a home-built environmental cell in combination with STM to study the conductance of differently engineered cyt b562 proteins on Au(111), as well as the conductance of oligothiophene on gold, under different humidity and temperature conditions. We found that the conductance of cyt b562 is smaller at lower relative humidity and further decreased when also temperature is reduced. Measuring the conductance as a function of the tip-substrate distance in both tip approaching and retracting modes revealed the occurrence of hysteresis. The engineered cyt b562 with two thiols in the long axis led to less hysteresis in the conductance and larger protein height on gold (from AFM) compared to the protein with thiols in the short axis. Our results stress the importance of protein engineering to control the electrical properties of functionalized surfaces. This study meets the growing demand for achieving more efficient molecule linking to conductive substrates, and studying environmental effects on the electrical response of functionalized surfaces (which is relevant, e.g., to sensing applications).

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Foroozan, Farshad. "Discrete inverse conductivity problems on networks." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3542.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.
Thesis research directed by: Applied Mathematics and Scientific Computation Program. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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Avala, Usha Kranthi. "Ionic Conductivity in Non-Ionic Compounds." TopSCHOLAR®, 2013. http://digitalcommons.wku.edu/theses/1279.

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The main objective of this work is to investigate the ionic conductivity of the drugs under certain conditions and also to compare the ionic conductivities of drugs determined by single surface sensors and parallel plate sensors. The ionic conductivity of various materials at their pre-melt and melt states are studied in order to further study a recently discovered phenomenon. Polar solids like Lidocaine, Ketoconazole, Procainamide and Nifedipine were examined in this study. Experimental studies show an increase in ionic conductivity in both pre-melt (20 -30 °C below melting temperature) and melt transition regions. Results of ionic conductivity of both parallel plate and single surface sensor at different frequencies are compared. At 1000 Hz, all the samples show an increase in ionic conductivity with both parallel plate and single surface sensor, but at 0.1 Hz frequency, no increase in ionic conductivity is observed with parallel plate sensor except for Nifedipine.

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Wei, Xiaohao, and 魏晓浩. "Nanofluids: synthesis, characterization and thermal conductivity." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B44765861.

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Jiang, Wei, and 姜为. "Synthesis and thermal conductivity of nanofluids." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45518063.

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Ashby, Gwyn Tudor. "Directional vibration conductivity in beam structures." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263393.

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Freeman, J. J. "The thermal conductivity of amorphous polymers." Thesis, University of Leeds, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355947.

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Olsen, Tyler J. (Tyler John). "Continuum modeling of particle suspension conductivity." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101480.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 91-94).
A suspension of network-forming, electrically conductive particles imparts electrical conductivity to an otherwise insulating medium. This effect can be used to great effect in many industrial applications. The ability to describe these networks and to predict their physical properties is a key step in designing systems that rely on these properties. In addition, many times these networks are suspended in a flowing fluid, which disrupts existing networks and forms new ones. The extra layer of complexity introduced by flow requires more sophisticated tools to model the effect on the network and its properties. In the first chapter, we derive a model for the full, tensorial effective conductivity of a particle particle network as a function of a local tensor description of the particle network, the "fabric tensor." We validate our model against a large number of computer-generated networks and compare its performance against an analogous existing model in the literature. We show that the model accurately predicts the isotropic magnitude, deviatoric magnitude, and deviatoric direction of a particle network. In the second chapter, we set out to model the effects of flow on a particle network. We propose two frame-indifferent constitutive equations for the evolution of the fabric tensor. We perform conductivity measurements of real flowing carbon black suspensions and fit our models to the results by using the conductivity model derived in chapter 1. We find that our models are able to reproduce out-of-sample experimental results with a high degree of accuracy.
by Tyler J. Olsen.
S.M.

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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.

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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.

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27

Square, Lynndle Caroline. "Proton conductivity stability studies by modelling." University of the Western Cape, 2016. http://hdl.handle.net/11394/6121.

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Philosophiae Doctor - PhD (Physics)
In this thesis, some of the challenges experienced by high temperature polymer electrolyte membrane fuel cells are explored through material modelling techniques. A very important aspect for a fuel cell is that it should have high proton conductivity. As hydrogen enters a fuel cell it gets broken down into its constituents, protons and electrons. The electrons travel to an external load, whilst the protons travel through a diffusive layer, catalyst layer and membrane area, before recombining with oxygen to form water and leave the system. In this particular study, polytetrafluoroethylene and carbon form the diffusive layer, platinum the catalyst and poly(2,5-benzimidazole) doped with phosphoric acid the membrane area. The effects to proton conductivity are investigated as a result of the mixing of materials and adsorption of the phosphoric acid on the platinum active sites. A third study as an alternative avenue for proton conductivity improvements, is also explored. The results from these investigations promotes the idea that polytetrafluoroethylene, which is found in the ionomer layer, should be replaced as its mechanical properties decrease significantly with increase in temperature. Increasing pressure would further promote proton transfer over the doped polymer membrane region.

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Dudnik, S. F., A. I. Kalinichenko, and V. E. Strel’nitskij. "On Thermal Conductivity of Anisotropic Nanodiamond." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35196.

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Dependence of thermal conductivity of nanocrystalline diamond coating on grain size and form is theoretically investigated. Nanodiamond is considered as two-phase material composed of dielectric diamond grains characterizing by three main dimensions and segregated by thin graphite layers with electron or phonon thermal conductivity. Influence of thermal conductance type and thickness of boundary layer on nanodiamond thermal conductivity is analysed. Derived dependences of thermal conductivity on grain dimensions are compared with experimental data. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35196

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Webber, Christina Marie. "Prosthetic Sockets: Assessment of Thermal Conductivity." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1404224355.

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Lanauze, Javier A. "Transient Electrohydrodynamics of Low–Conductivity Drops." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/841.

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Beck, Michael Peter. "Thermal conductivity of metal oxide nanofluids." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26488.

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Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Teja, Amyn S.; Committee Member: Abdel-Khalik, Said I.; Committee Member: Meredith, Carson; Committee Member: Nair, Sankar; Committee Member: Skandan, Ganesh. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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32

Jones, Todd J. Tombrello Thomas A. "Radiation-induced conductivity in amorphous carbon /." Diss., Pasadena, Calif. : California Institute of Technology, 1989. http://resolver.caltech.edu/CaltechETD:etd-02022007-131335.

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Tlili, Radhouan. "Études des transferts dans les matériaux hétérogènes." Thesis, Paris Est, 2010. http://www.theses.fr/2010PEST1092.

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L'usage des matériaux composites dans les différents domaines technologiques (microélectronique, aéronautique, transports…) ne cesse de croître. Une telle augmentation vient du fait qu'il est possible de développer de nouveaux matériaux avec des propriétés adaptées à une application bien préc ise en combinant les propriétés physiques des différents constituants. Dans le travail de thèse, nous nous intéressons à l'étude des propriétés thermophysiques, électriques et diélectriques de composites à base de matrice polymère chargée avec des fibres naturelles et/ou de particules minérales. L'objectif final étant d'une part d'accroître notre connaissance sur le mécanisme de transfert (thermique, électrique et diélectrique) au sein des matériaux composites et d'autre part, de développer une méthode de mesure des propriétés thermophysiques des matériaux à différentes températures (-20°C etlt; T etlt; 180°C)
The use of composite materials in various fields of technology (microelectronics, aerospace, transportation ...) continues to grow. Such an increase is that it is possible to develop new materials with properties tailored to a specific application by combining the physical properties of different constituents.In the thesis, we focus on the study of thermophysical properties, electrical and dielectric of composites based on polymer matrix loaded with natural fibers and/or mineral particles.The final goal is to increase our knowledge on the mechanism of transfer (thermal, electrical and dielectric) in composite materials and secondly, to develop a method for measuring thermophysical properties of materials at different temperatures (-20°C etlt; Tetlt; 180°C)

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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.

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Huldén, Pierre. "Conductivity measurement on thick insulating plaque samples." Thesis, KTH, Elektroteknisk teori och konstruktion, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-150956.

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The conductivity is one of the main properties of HVDC cable insulation materials and needs to be evaluated carefully. Since measurement on cables is time consuming, often thin specimens and normal conductivity measurement cells are used to compare the materials. In this way however, the bulk effects will be less represented in the measurement and the results will be less representative. Instead, one needs to perform the measurements on thick plate samples and with higher voltage levels. This work focuses on the conductivity measurements on thick HVDC insulation plate samples subject to a high electric field and carefully controlled conditions. In the literature, there are many different methods of measuring the leakage current such as dielectric spectroscopy, PD, IV and PEA measurements. In this thesis a three electrode setup is used to measure the leakage current where the electrodes are placed inside the oven. This is to be able to control both temperature and high voltage under similar and different conditions where it is possible to change these two parameters during measurement. This was made by two Labview programs; one for creating a schedule and one control program which controls the equipment in the cell. The task was to make sure that the cell functioned by obtaining repeatable and reasonable measurements. The results that were obtained were reasonable and verified that the cell functioned. The executed measurements were performed in order to achieve a better understanding of error factors in the measurement system, ranging from preparing the sample to measuring the leakage current. The purpose with the cell is it to investigate the quality of the HVDC insulation by conductivity measurements on millimetre thick plate samples.
Den elektriska konduktiviteten är en av de viktigaste egenskaperna av HVDC kablars isolationsmaterial, XLPE, och den måste utvärderas noggrant. Mätning på fullskaliga kablar är tidskrävande och för att jämföra material används istället ofta tunna prover och normerade konduktivitetmätningsceller. En nackdel med denna metod är att bulkeffekterna blir mindre framträdande i mätningen och resultaten kommer att vara mindre representativa. Istället måste man utföra mätningen på tjockare prover och vid högre spänning. Detta examensarbete fokuserar på mätning av ledningsförmåga hos tjocka HVDC- isolationsprover under noggrant kontrollerade förhållanden och starka elektriska fält. I litteraturen finns det många olika metoder att mäta läckströmmar på, till exempel dielektrisk spektroskopi, PD, IV och PEA mätningar för att nämna några. I denna avhandling kommer ett tre-elektrod system att användas där en temperatursensor är monterad på ena elektroden. Systemet används för att både mäta läckströmmar och temperatur vid provet. Detta gör det möjligt att kontrollera temperatur och spänning oberoende av varandra vilket gjordes med hjälp av två Labview program. Det ena för att skapa ett schema och det andra användes som kontrollprogram för att styra utrustningen i cellen. Uppgiften var att kontrollera cellens funktion genom att erhålla rimliga repeterbara mätningar. Mätningarna gav rimliga resultat vilket indikerade att cellen fungerar tillfredställande. Syftet med mätningarna var att få en bättre förståelse för felfaktorer i mätsystemet som kan vara allt från att förbereda provet till att mäta läckström. Syftet med cellen är att undersöka isolationsegenskaperna på millimetertjocka pressade XLPE prover.

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Bihari, Kathleen L. "Analysis of Thermal Conductivity in Composite Adhesives." NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20010808-130536.

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BIHARI, KATHLEEN LOUISE. Analysis of Thermal Conductivity in Composite Adhesives (Under the direction of H. Thomas Banks). Thermally conductive composite adhesives are desirable in many industrial applications, including computers, microelectronics, machinery and appliances. These composite adhesives are formed when a filler particle of high conductivity is added to a base adhesive. Typically, adhesives are poor thermal conductors. Experimentally only small improvements in the thermal properties of the composite adhesives over the base adhesives have been observed. A thorough understanding of heat transfer through a composite adhesive would aid in the design of a thermally conductive composite adhesive that has the desired thermal properties.In this work, we study design methodologies for thermally conductive composite adhesives. We present a three dimensional model for heat transfer through a composite adhesive based on its composition and on the experimental method for measuring its thermal properties. For proof of concept, we reduce our model to a two dimensional model. We present numerical solutions to our two dimensional model based on a composite silicone and investigate the effect of the particle geometry on the heat flow through this composite. We also present homogenization theory as a tool for computing the ``effective thermal conductivity" of a composite material.We prove existence, uniqueness and continuous dependence theorems for our two dimensional model. We formulate a parameter estimation problem for the two dimensional model and present numerical results. We first estimate the thermal conductivity parameters as constants, and then use a probability based approach to estimate the parameters as realizations of random variables. A theoretical framework for the probability based approach is outlined.Based on the results of the parameter estimation problem, we are led to formally derive sensitivity equations for our system. We investigate the sensitivity of our composite silicone with respect to the thermal conductivity of both the base silicone polymer and the filler particles. Numerical results of this investigation are also presented.

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37

Brandell, Daniel. "Understanding Ionic Conductivity in Crystalline Polymer Electrolytes." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5734.

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38

Kruglova, Olga Viktorovna. "Discotic liquid crystals : from dynamics to conductivity /." Amsterdam : IOS Press, 2007. http://www.loc.gov/catdir/toc/fy0803/2007464234.html.

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39

Kartoatmodjo, Rudjuk Sinung Trijana. "A model for finite conductivity horizontal wellbores /." Access abstract and link to full text, 1994. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9522755.

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40

Ford, Theodore Robert. "Thermal conductivity of bonded hollow-sphere monoliths." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/20045.

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41

Church, Benjamin Cortright. "High conductivity alloys for extruded metallic honeycomb." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/21283.

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42

Wagner, Ingo. "Algebraic approach towards conductivity in ergodic media." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-164715.

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This thesis is about an operator algebraic approach towards the derivation of the electrical conductivity in disordered solid states based on the theory of quantum many-particle systems. Such an approach is of interest since it allows for the description of interacting electron gases, which is a feature not present in previous work. In the context of the description of ergodic media, new concepts are introduced, such as covariant states and covariant morphisms. Moreover, the concept of covariant states is combined with the well-known concept of KMS states. In its covariant form, KMS states describe electron gases in ergodic media at thermal equilibrium. Such states are the starting point of the electron gases considered here. An external electric field is applied to the system, influences the electron gas and causes internal electric currents. Thus, the equilibrium position of the system is disturbed, leading to a time evolution of the system, which is described by covariant automorphisms. Summing up, the system is given in a time dependent, covariant state that acts on the algebra of bounded and local operators on the fermionic Fock space defined over some given one-particle Hilbert space. For a discrete model of an extended electron gas in one space dimension with a pair interaction of finite range, explicit constructions of the above states are presented. In addition, for the special case of non-interacting electron gases, the construction of the time dependent covariant state is carried out in arbitrary space dimension. Since measurements in a quantum system are implemented by the action of its state on bounded, local and self-adjoint operators, the concept of a current density operator is introduced. The current density is then defined as the result of the measurement of the current density operator. By an application of Birkhoff’s ergodic theorem, the transformation law of the current density operator together with the covariant transformation law of the state of the electron gas implies the almost sure existence of the spatial mean of the current density. Moreover, the spatial mean current density is almost surely independent of the concrete realisation given. The electric current density describes the linear dependence of the spatial mean current density on the external electric field, for small strengths. Via linear response theory for the noninteracting model of an electron gas, an explicit expression for the current density is derived in terms of a so called Kubo formula. For the derivation the system needs to satisfy a localisation condition, which is specifically designed for non-interacting electron gases. In view of a linear response theory of interacting electron gases, candidates for a generalisation of this localisation criterion that also apply to interacting systems are introduced.

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43

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.

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44

Russell, Carissa Don. "INTERFACIAL THERMAL CONDUCTIVITY USING MULTIWALL CARBON NANOTUBES." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_theses/30.

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Shrinking volume, coupled with higher performance, microprocessors and integrated circuits have led to serious heat dissipation issues. In an effort to mitigate the excessive amounts of waste heat and ensure electronic survivability, heat sinks and spreaders are incorporated into heat generating device structures. This inevitability creates a thermal pathway through an interface. Thermal interfaces can possess serious thermal resistances for heat conduction. The introduction of a thermal interface material (TIM) can drastically increase the thermal performance of the component. Exceptional thermal properties of multiwall carbon nanotubes (MWCNTs) have spurred interest in their use as TIMs. MWCNTs inherently grow in vertically-oriented, high aspect ratio arrays, which is ideal in thermal interface applications because CNTs posses their superior thermal performance along their axis. In this paper, laser flash thermal characterization of sandwich‐bonded and cap‐screw‐bonded aluminum discs for both adhesive-infiltrated and “dry”, 100% MWCNT arrays, respectively. Thermal contact resistances as low as 18.1 mm2K/W were observed for adhesive‐infiltrated arrays and, even lower values, down to 10.583 mm2K/W were measured for “dry” MWCNT arrays. The improved thermal performance of the arrays compared to thermal adhesives and greases currently used in the electronics and aerospace industries, characterize MWCNT arrays as a novel, lighter‐weight, non‐corrosive replacement.

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45

Regan, Simon Edmund. "The low temperature thermal conductivity of polymers." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277153.

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46

Young, Kevin Edward. "Ionic conductivity in silicate - containing solid electrolytes." Thesis, University of Exeter, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335654.

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47

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.

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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.

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48

Gray, David John. "Conductivity studies of selected anionic composite electrolytes." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47453.

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Zalaf, M. "The thermal conductivity of electrically-conducting liquids." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47321.

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Schulz, Eric Clinton. "Conductivity of proppant mixtures." Thesis, 2014. http://hdl.handle.net/2152/26439.

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Hydraulic fracturing is a physically complex phenomenon, and there are many variables, both environmental and operational, that affect the overall success of a fracture treatment. Amongst the operational variables, the process of proppant selection is key to ensuring that the induced fractures remain open and permeable. A variety of physical mechanisms act to degrade the permeability of a given proppant packing after deposition in a fracture, the most important of which is the magnitude of the confining stress. The goal of this work is to understand how mixtures of unlike proppants behave under various stress conditions. Specifically, the permeability and conductivity of various mixtures of unlike proppants are measured as a function of confining stress. A secondary investigation is also made into the dependence of permeability on the areal concentration of proppant. Choices of proppants are restricted to those which are currently most common in industry, in terms of both material and size. To that end, mixtures consisted of primarily ceramics and sands with appropriate grain size distributions. Additionally, a light-weight plastic proppant was included in the study. Simple laboratory methods are employed to measure the permeability of the various proppant packings. Values obtained from direct experimentation are compared with values obtained from an independent analytical model. Given the assumptions which are inherent in the analytical model, the experimental and analytical results are in satisfactory agreement. Also, a correlation is developed for single proppants and binary mixtures which predicts permeability as a function of stress, grain size, material, and weight fraction. One key conclusion is that for a binary mixture of proppants, the mixture permeability will not generally be a weighted linear combination of the pure proppant permeabilities. In other words, the permeability of a mixture comprised of 50% (by weight) of one component and 50% of the second component will generally not be halfway between the permeabilities of the single components. A hypothesis is presented which posits that there are threshold weight fractions for each proppant pair that control the permeability of the mixture.
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Dissertations / Theses on the topic 'Conductivity'

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