Carbon nanotubes were dispersed and functionalized with polyethylene imine (PEI) before incorporation in a polyvinyl acetate matrix. The resulting samples exhibit air-stable N-type characteristics with electrical conductivities as great as 1600 S/m and thermopowers as high as 100 microV/K. Thermopowers and electrical conductivities correlate, in a reversal of the trend found in typical materials. This phenomenon is believed to be due to the increase in the number of tubes that are evenly coated in a better dispersed sample. Increasing the amount of PEI relative to the other constituents positively affects thermopower but not conductivity. Air exposure reduces both thermopower and conductivity, but a stable value is reached within seven days following film fabrication. The atmospheric effects on the electrical conductivity prove to be reversible. Oxygen is believed to be the primary contributor to the decay.

Konstanz, Univ., Diss., 2000.

Konstanz, Univ., Diplomarb., 2001.

abstract: Thermoelectric devices (TED's) continue to be an area of high interest in both thermal management and energy harvesting applications. Due to their compact size, reliable performance, and their ability to accomplish sub-ambient cooling, much effort is being focused on optimized methods for characterization and integration of TED's for future applications. Predictive modeling methods can only achieve accurate results with robust input physical parameters, therefore TED characterization methods are critical for future development of the field. Often times, physical properties of TED sub-components are very well known, however the "effective" properties of a TED module can be difficult to measure with certainty. The module-level properties must be included in predictive modeling, since these include electrical and thermal contact resistances which are difficult to analytically derive. A unique characterization method is proposed, which offers the ability to directly measure all device-level physical parameters required for accurate modeling. Among many other unique features, the metrology allows the capability to perform an independent validation of empirical parameters by measuring parasitic heat losses. As support for the accuracy of the measured parameters, the metrology output from an off-the-shelf TED is used in a system-level thermal model to predict and validate observed metrology temperatures. Finally, as an extension to the benefits of this metrology, it is shown that resulting data can be used to empirically validate a device-level dimensionless relationship. The output provides a powerful performance prediction tool, since all physical behavior in a performance domain is captured using a single analytical relationship and can be plotted on a singe graph. / Dissertation/Thesis / M.S. Mechanical Engineering 2011

Yes / Sensing concrete has the capability to sense its condition and environmental changes, including stress (or force), strain (or deformation), crack, damage, temperature and humidity through incorporating functional fillers. Sensing concrete has recently attracted major research interests, aiming to produce smart infrastructures with elegantly integrated health monitoring abilities. In addition to having highly improved mechanical properties, sensing concrete has multifunctional properties, such as improved ductility, durability, resistance to impact, and most importantly self-health monitoring due to its electrical conductivity capability, allowing damage detection without the need of an external grid of sensors. This tutorial will provide an overview of sensing concrete, with attentions to its principles, properties, and applications. It concludes with an outline of some future opportunities and challenges in the application of sensing concrete in construction industry. / National Science Foundation of China (51978127 and 51908103), the China Postdoctoral Science Fundation (2019M651116) and the Fundamental Research Funds for the Central Universities in China (DUT18GJ203). / National Science Foundation of China (NSFC) (Nos. 51978127 and 51908103), the China Postdoctoral Science Foundation (No. 2019M651116), and the Fundamental Research Funds for the Central Universities in China (No. DUT18GJ203).

No description available.

Cette thèse porte sur le mouvement de particules colloïdales induit par l’effet thermoélectrique (ou effet Seebeck). Dans un électrolyte soumis à un gradient de température, les ions ont tendance à migrer à des vitesse qui différent d'une espèce à l'autre. On observe alors une accumulation de charge aux bords de l’échantillon. Ce déséquilibre induit un champ électrique qui agit sur les colloïdes chargés présents dans la solution. Cette contribution électrophorétique dans le champ de Seebeck s'additionne à la contribution directe de thermodiffusion. Comme résultat principal,nous obtenons la vitesse phorétique en fonction de la fraction volumique des particules et, dans le cas de polyélectrolytes, du poids moléculaire. Dans la seconde partie, nous étudions l’effet thermoélectrique pour une particule chauffée par absorption d’un faisceau laser. Le gradient de température est alors radial et l’effet Seebeck induit une charge nette dans le voisinage de la particule. Enfin, nous discutons les applications possibles de ce phénomène de thermocharge / In this work we study the motion induced in a colloidal dispersion by thethermoelectric or Seebeck effect. As its basic principle, the ions of the electrolytesolution start moving in a temperature gradient. In general, the velocity of one iondiffers from another. As a result, one observes a charge separation and a macroscopicelectric field. This thermoelectric field, in turn, acts upon the charged colloidalparticle present in the solution. Thus thermophoresis of the particle comprises of anelectrophoretic motion in the thermoelectric or Seebeck field. As an important result,we derive how the corresponding velocity of a colloidal particle depends upon thecolloidal volume fraction or on molecular weight for polymers. In a second part, westudy the thermoelectric effect due to a hot colloidal particle where a radialtemperature gradient is produced by the particle itself. In this temperature gradientthe same Seebeck effect takes place in the electrolyte solution. We find that the hotparticle carries a significant amount of charge around it. Whereas the amount ofsurface charges present at the boundaries of the sample container in the onedimensionalcase is rather insignificant. Possible applications of this thermochargingphenomenon are also discussed.

Aujourd’hui, les énergies renouvelables comme l’énergie éolienne, l’énergie solaire, l’énergie hydroélectrique et la thermoélectricité jouent un rôle essentiel dans la couverture de nos besoins en énergie. Parmi ces différentes sources d’énergie, la thermoélectricité, qui permet de convertir la chaleur en électricité ou inversement, attire une grande attention grâce à son large champ d’application. Les actuelles avancées dans la recherche thermoélectrique visent l’amélioration du rendement de conversion des modules thermoélectriques, à travers l’optimisation des propriétés thermoélectriques intrinsèques des matériaux utilisés (coefficient de Seebeck, conductivité électrique et conductivité thermique). Pour cela, différentes approches ont été étudiées (dopage, nouveau alliages, nanostucturation …). Parmi ces approches, la nanostructration des matériaux a été largement étudiée pour mener à bien cet objectif. Dans ce travail de thèse, nous nous sommes intéressés à étudier l’effet de la nanostructuration de surface des matériaux (silicium mesoporeux et oxyde de titane déposé en couches minces) par faisceaux laser ultra-court (picoseconde et femtoseconde) sur l’évolution de leurs propriétés thermoélectriques. Dans un premier temps, nous nous sommes focalisés sur l’étude des différents phénomènes physiques impliqués durant l’interaction laser-matière ainsi que sur la formation des différentes nanostructures résultantes (en forme de ripples, spikes, dots et autres) en fonction de la dose laser appliquée (la fluence et le nombre de pulses). La formation de ces nanostructures a été étudiée suivant deux régimes (stationnaire et dynamique). Après l’optimisation des paramètres conduisant à la formation de ces nanostructures, la caractérisation du coefficient de Seebeck et la conductivité électrique avant et après la nanostructuration de ces matériaux a été réalisée grâce à un nouveau dispositif de mesure (ZT-meter) développé au laboratoire GREMI. Les résultats de mesures montrent une importante amélioration du coefficient de Seebeck et la conductivité électrique après la nanostrucutration. Un facteur d’augmentation de la puissance thermoélectrique a été observé pour les deux matériaux étudiés ; notamment dans le cas de couches minces d’oxyde de titane (jusqu’à 500 fois). / Today, renewable energies such as wind, solar, hydropower and thermoelectricity play an essential role to cover our energy needs. Among these different sources of energy, thermoelectricity, which offers the ability to convert a heat into electricity or vice versa, has attracted a great attention due to its wide field of potential applications. The current advances in thermoelectric research are focusing on the improvement of the conversion efficiency of thermoelectric devices through optimizing and improving the thermoelectric properties of the thermoelectric materials (Seebeck coefficient, electrical conductivity and thermal conductivity). For this, different approaches (doping, new materials, nanostucturing...) have been investigated in the literature. Among these approaches, nanostructuring of materials is the most studied in the literature in order to improve the thermoelectric properties of materials. In this thesis work, we aimed to study the effect of surface nanostructuring of materials (mesoporous silicon and titanium oxide deposited in thin film) by ultra-short laser beams (picosecond and femtosecond) on the evolution of their thermoelectric properties. First, we focused on the study of various physical phenomena involved during the laser-matter interaction that yield to the formation of very different nanostructures in form of ripples, spikes, dots and others as function of the applied laser dose (fluence and number of pulses). The formation of these nanostructures has been studied in two regimes (stationary and dynamic). After optimizing the laser parameters leading to the formation of such nanostructures, a characterization of Seebeck coefficient and the electrical conductivity before and after the nanostructuring of these materials was carried out by using a new experimental setup (ZT-meter) designed and validated in GREMI laboratory. The results of measurements showed an important improvement of Seebeck coefficient and electrical conductivity after nanostructuring. This important improvement observed with the both materials leaded to a strong increase in the thermoelectric power factor (reaching roughly 50000%).

Este trabalho apresenta os estudos técnicos para implantação de um sistema de geração de energia que atenda a demanda dos circuitos eletroeletrônicos de um queimador de biogás, tornando-o autossuficiente energeticamente e viabilizando sua instalação em locais distantes e não atendidos pelo sistema convencional de distribuição de energia. O projeto do sistema de geração de energia tem como base a associação das tecnologias fotovoltaica e termoelétrica direta, tipo efeito Seebeck. O queimador de biogás descrito neste projeto é instalado em miniestações de tratamento de efluentes com produção de biogás, onde o aproveitamento energético da forma tradicional é inviável em função da baixa e inconstante vazão de biogás. O queimador de biogás possui um circuito eletrônico de controle que determina o tempo de combustão do biogás, onde, através de um microcontrolador, recebe informações do circuito eletrônico de controle e registra o volume de biogás queimado, objetivando a obtenção dos créditos de carbono. O queimador de biogás tem como objetivo somente o saneamento, provocando a queima do gás metano (CH4) presente no biogás e permitindo a busca por créditos de carbono, contribuindo para a diminuição dos efeitos provocados pelos gases do efeito estufa (GEE). Durante os estudos, foi constatado que a energia gerada pelo painel fotovoltaico é suficiente para atender a demanda de energia do circuito eletroeletrônico do queimador de biogás, enquanto que o sistema termoelétrico direto obteve resultados desprezíveis. Constatou-se também que parte do circuito do controlador de carga, utilizado nesse estudo, pode futuramente ser inserida no firmware do microcontrolador já existente no projeto, reduzindo assim significativamente os componentes do circuito. / This paper presents the technical studies for the implementation of a system of power generation to meet the energy demand of biogas burner electronics circuits, making it self-sufficient energy and enabling installation in remote locations not served by the conventional system of energy distribution. The design of the power generation system is based on the combination of photovoltaic technologies and thermoelectric direct like Seebeck Effect. The biogas burner described in this project is installed in mini-stations for treatment and biogas production, where energy reuse in the traditional way is not feasible due to the low and variable flow of biogas. The biogas burner has an electronic control circuit which determines the time of combustion of biogas, which, through a microcontroller receives information from the electronic control circuit and registers the volume of biogas flared aiming to get carbon credits. The biogas burner, aims only sanitation, causing burning methane gas (CH4) present in biogas and allowing the search for carbon credits, helping to reduce the effects caused by greenhouse gases (GHG). During the studies, it was found that the energy generated by the photovoltaic panel is enough to attend the energy demand of the electronics circuit of biogas burner, while the direct thermoelectric system obtained a negligible result. It was found that part of the charge controller, used in this study, in the future can be inserted into the firmware of the microcontroller existing of the in the project, reducing therefore the circuit components significantly.

Thermoelektrische Phänomene können in Nanomaterialien im Vergleich zum Volumenmaterial stark modifiziert werden. Die Bestimmung der elektrischen Leitfähigkeit, des absoluten Seebeck-Koeffizienten (S) und der Wärmeleitfähigkeit ist eine wesentliche Herausforderung für die Messtechnik in Hinblick auf Mikro- und Nanostrukturen aufgrund dessen, dass die Transporteigenschaften vom Volumenmaterial sich durch Oberflächen- und Einschränkungseffekte verändern können. Im Rahmen dieser Abschlussarbeit wird der Einfluss von Größeneffekten auf die thermoelektrischen Eigenschaften von dünnen Platinschichten untersucht und mit dem Volumenmaterial verglichen. Dafür wurde eine Messplattform als standardisierte Methode entwickelt, um S einer dünnen Schicht zu bestimmen. Strukturelle Eigenschaften wie Schichtdicke und Korngröße werden variiert. Grenz- und Oberflächenstreuung reduzieren S der dünnen Schichten im Vergleich zum Volumenmaterial. Außerdem wird eine Methode demonstriert um S von einzelnen metallischen Nanodrähten zu bestimmen. Für hochreine und einkristalline Silber-Nanodrähte wird der Einfluss von Nanostrukturierung auf die Temperaturabhängigkeit von S gezeigt. Ein Modell ermöglicht die eindeutige Zerlegung des temperaturabhängigen S von Platin und Silber in einen Thermodiffusions- und Phononen-Drag-Anteil. Des Weiteren werden die thermoelektrischen Transporteigenschaften von einzelnen auf Bismut-basierenden Kern/Hülle-Nanodrähten untersucht. Der Einfluss des Hüllenmaterials (Tellur oder Titandioxid) und der räumlichen Dimension des Nanodrahts auf die Transporteigenschaften wird diskutiert. Streuung an Oberflächen, Einkerbungen und Grenzflächen zwischen dem Kern und der Hülle reduzieren die elektrische und thermische Leitfähigkeit. Eine Druckverformung induziert durch die Hülle kann zu einer Bandöffnung bei Bismut führen, sodass S gesteigert werden kann. Das Kern/Hülle-System zeigt in eine Richtung, um die thermoelektrischen Eigenschaften von Bismut erfolgreich anzupassen. / Thermoelectric phenomena can be strongly modified in nanomaterials compared to the bulk. The determination of the electrical conductivity, the absolute Seebeck coefficient (S) and the thermal conductivity is a major challenge for metrology with respect to micro- and nanostructures because the transport properties of the bulk may change due to surface and confinement effects. Within the scope of this thesis, the influence of size effects on the thermoelectric properties of thin platinum films is investigated and compared to the bulk. For this reason, a measurement platform was developed as a standardized method to determine S of a thin film. Structural properties, like film thickness and grain size, are varied. Boundary and surface scattering reduce S of the thin films compared to the bulk. In addition, a method is demonstrated to determine S of individual metallic nanowires. For highly pure and single crystalline silver nanowires, the influence of nanopatterning on the temperature dependence of S is shown. A model allows the distinct decomposition of the temperature-dependent S of platinum and silver into a thermodiffusion and phonon drag contribution. Furthermore, the thermoelectric transport properties of individual bismuth-based core/shell nanowires are investigated. The influence of the shell material (tellurium or titanium dioxide) and spatial dimension of the nanowire on the transport properties are discussed. Scattering at surfaces, indentations and interfaces between the core and the shell reduces the electrical and the thermal conductivity. A compressive strain induced by the shell can lead to a band opening of bismuth increasing S. The core/shell system points towards a route to successfully tailor the thermoelectric properties of bismuth.