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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Vysoce porézní keramické materiály připravené metodou Spark Plasma Sintering / Highly porous ceramic materials prepared by Spark Plasma Sintering

Barančíková, Miriama January 2021 (has links)
Porous ceramic materials are an interesting group of materials due to a wide range of physical properties, low density, and good permeability. Production of a monolith with a shape stability that would also have a high specific surface area and high porosity is a common problem with porous ceramics. The goal of this work was to maintain the high specific surface area and to produce a monolith with a shape stability. Two forms of porous silica nanofibers (as prepared and milled) were used and partially sintered using the Spark Plasma Sintering method (SPS). Different sintering times and temperatures for SPS were tested. The findings revealed that the best SPS conditions were as follows: temperature: 600 °C, sintering time: 5 minutes, pressure: 3 MPa, and the heating rate: 144 °C/min. These sintering conditions resulted in a stable silica based machinable monolith made from fibers or milled fibers. The monoliths have the specific surface area of up to 470 m^2/g and porosity of 72 %, or the specific surface area of up to 422 m^2/g and porosity of 69 % for as prepared fibers and milled fibers, respectively.
2

DESIGN AND FABRICATION OF HIGH CAPACITY LITHIUM-ION BATTERIES USING ELECTRO-SPUN GRAPHENE MODIFIED VANADIUM PENTOXIDE CATHODES

Amirhossein Ahmadian (7035998) 17 December 2020 (has links)
<p>Electrospinning has gained immense interests in recent years due to its potential application in various fields, including energy storage application. The V<sub>2</sub>O<sub>5</sub>/GO as a layered crystal structure has been demonstrated to fabricate nanofibers with diameters within a range of ~300nm through electrospinning technique. The porous, hollow, and interconnected nanostructures were produced by electrospinning formed by polymers such as Polyvinylpyrrolidone (PVP) and Polyvinyl alcohol (PVA), separately, as solvent polymers with electrospinning technique. </p> <p> </p> <p>In this study, we investigated the synthesis of a graphene-modified nanostructured V<sub>2</sub>O<sub>5</sub> through modified sol-gel method and electrospinning of V<sub>2</sub>O<sub>5</sub>/GO hybrid. Electrochemical characterization was performed by utilizing Arbin Battery cycler, Field Emission Scanning Electron Microscopy (FESEM), X-ray powder diffraction (XRD), Thermogravimetric analysis (TGA), Mercury Porosimetery, and BET surface area measurement. </p> <p> </p> <p>As compared to the other conventional fabrication methods, our optimized sol-gel method, followed by the electrospinning of the cathode material achieved a high initial capacity of <b>342 mAh/g</b> at a high current density of 0.5C (171 mA/g) and the capacity retention of ~80% after 20 cycles. Also, the prepared sol-gel method outperforms the pure V<sub>2</sub>O<sub>5 </sub>cathode material, by obtaining the capacity almost two times higher.</p> <p>The results of this study showed that post-synthesis treatment of cathode material plays a prominent role in electrochemical performance of the nanostructured vanadium oxides. By controlling the annealing and drying steps, and time, a small amount of pyrolysis carbon can be retained, which improves the conductivity of the V<sub>2</sub>O<sub>5</sub> nanorods. Also, controlled post-synthesis helped us to prevent aggregation of electro-spun twisted nanostructured fibers which deteriorates the lithium diffusion process during charge/discharge of batteries.</p>

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