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In-situ Raman spectroelectrochemistry of graphene and related materials in concentrated aqueous electrolytes
Abbas, Ghulam ; Frank, Otakar (advisor) ; Kunc, Jan (referee) ; Voiry, Damien (referee)
The complex interplay between the material's properties and the electrochemical process often taking place at its ubiquitous edges makes it difficult to discriminate the role of single defects in the charge transfer processes in the material. Therefore, we have performed in-situ μ-droplet Raman spectroelectrochemistry (SEC) to identify the localized charge transfer processes through the basal plane and defects in a selected localized area of 10-20 μm2 of defect-free and defective monolayer graphene. It is noticed that two distinctive electron transfer processes of slower and faster rates exist side-by-side in the same sample but they are confined in the defect-free and defect-rich regions, respectively. Furthermore, in order to explore the electrochemical ion intercalation mechanism for rechargeable batteries, in-situ Raman SEC in a macro SEC cell was performed. It was observed that structural properties such as the lateral domain size (La), degree of graphitization (g), inter-defect distance (LD) and defect density (nD) have substantial influence on the electrochemical (de)intercalation of anion into natural and kish graphite during charge/discharge process. It was also revealed that ultrasound treatment of natural graphite reduces the La which enhances the reversibility of the anion...
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Structure and mechanical properties of thin wall nodular iron castings
Chýlková, Adéla ; Mores, Antonín (referee) ; Roučka, Jaromír (advisor)
The purpose of this final thesis is experimental verification of the influence of graphitic inoculants containing different amounts of trace elements on the structure, mechanical properties and internal homogeneity of thin-walled ductile iron casting. This thesis describes the issue with casting of thin-walled ductile iron. Two melts of thin-walled test plates with thickenesses of 3-, 5- and 8 mm were done in experimental part. A total of six types of inoculations with different content of trace elements were tested. Subsequently, an X-ray irradiation analysis was performed on the samples and hardness, tensile strength and ductility were evaluated. Futhermore, the amount of graphite in structure, graphite shape, graphite size, nodularity, graphite nodule count and volume phases of ferrite and perlite in matrix were analysed in thin-walled ductile cast iron by computer-based image analyzer. Finally, the measurement data were processed into tables and charts and conclusions were formulated. An X-ray analysis proved, that all thin-walled test plates containned shrinkage porosity. Furthemore it was confirmed, that content of manganese in inoculant increases tensile strength and hardness. Also content of zirconium in inoculant increases graphite nodule count.
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Study of the influence of fillers and external conditions on the resistivity of cement composites
Kejda, Dalibor ; Melichar, Jindřich (referee) ; Černý, Vít (advisor)
The progress of new materials is important for the construction industry. Modern materials include cement composites with reduced resistivity. This is achieved by adding suitable electrically conductive fillers. If there is enough of these fillers, the so-called percolation threshold occurs. Suitable fillers (Condufit C4 and Supragraphite C300) have been proposed. Recipes have been designed to be before and after the percolation threshold. The tests were performed on beams measuring 40x40x160 mm with built-in electrodes for measuring their resistivity. The aim of the work was the research of influencing external conditions on cement composites. The effect of temperature was verified. The lowest values of resistivity were evaluated at temperatures of 50 ° C and the resistivity increased with decreasing temperature. The effect of humidity on the resistivity was then verified. Reference samples and samples with a smaller proportion of graphite powder showed larger differences in resistivities with increasing humidity. The samples above the percolation threshold were not much affected by increasing humidity. Finally, the effect of loading on the resistivity of the samples was verified. Almost all samples with increasing compressive stress showed an increasing value of resistivity.
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Sodium-ion batteries: research of carbon based negative electrode materials
Homolka, Tomáš ; Máca, Josef (referee) ; Libich, Jiří (advisor)
This work focuses on the research of hard carbon as a promising negative electrode material for sodium-ion batteries. The first part deals with electrochemical cells and their development in general. Then lithium-ion cells, their history and the materials currently used are mentioned. The next section discusses sodium-ion cells, their development so far, current issues and differences compared to lithium-ion cells, as they appear to be one of the promising post-lithium technologies with the potential for rapid commercialization. In the practical part, properties of some material samples are tested with a focus on their capacity and coulombic efficiency.
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Negative Electrode for Sodium-ion batteries
Šimek, Antonín ; Bača, Petr (referee) ; Libich, Jiří (advisor)
This master’s thesis is focused on the research of negative electrode materials for sodium-ion batteries. It contains a general introduction to the issue of batteries, their brief historical development, basic operating principles, key parameters and classification. Attention is paid to lithium-ion batteries, which are the most used technology today. Sodium-ion batteries as their potential replacement, especially in the field of energy storage from renewable sources, are based on lithium-ion technology. Promising candidates for the material for the negative electrode of sodium-ion batteries are sodium titanates. Their synthesis and subsequent electrochemical characterization of electrodes using sodium titanate as the active material are included in the practical part of this work.
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Silicate Conductive Composites with Graphite Fillers
Baránek, Šimon ; Drochytka, Rostislav
Electroconductive composites are modern materials that are commonly used in many industries such as construction industry and machine-building industry. For example, these materials can be useful as sensors for monitoring changes in constructions, shielding stray currents from electrification networks, shielding electromagnetic radiation in operating rooms, cathodic protection against moisture or overvoltage protection of buildings. The topic of this post is the research of electrically conductive silicate composites with graphite-based fillers. In this research, composites with different ratios and types of graphite were tested and electroconductive properties such as impedance were monitored, as well as physical-mechanical properties such as strength. It was found that by adding 10 wt. graphite into the mixture reduces the impedance of the composites by 50 % and the compressive strength is reduced by approximately 40 %.
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Flame retardant treated thermosets for composite materials used in transport industry
Novotný, Kamil ; Kučera, František (referee) ; Poláček, Petr (advisor)
First part of this bachelor‘s thesis contains a literature review, which describes basic mechanisms of flame retardancy, distribution of flame retardants into groups based on their composition and commercially available compounds. Experimental part studied the change of thermal stability and flammability of a thermoset resin with the adition of flame retardants. Change in mechanical properties of the resin was investigated as well. Epoxy resin was selected as a specimen of the resin group due to its excellent properties, which make it widely used in transportation industry. The main disadvantage of epoxy is its high flammability. The effect of two low cost, eco-friendly, easily applicable flame retardants was observed, namely expanded graphite and magnesium hydroxide. Materials were evaluated by a burning test, tensile test and thermogravimetric analysis. Overall, the additives caused a decrease in mechanical properties. Material with a combination of both compounds was found to be the least flammable, but had the worst mechanical properties.
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Low energy excitations in oriented graphite by THz magneto-optical spectroscopy
Dubský, Jan ; Kunc, Jan (referee) ; Vrba, Radimír (advisor)
This master’s thesis deals with the modelling of electronic properties of graphite crystal, which are measurable using a spectrometer based on high frequency electron paramagnetic resonance (HFEPR for short) located in laboratories of CEITEC BUT. This is especially the band structure of graphite and its Landau levels. The theoretical part of the thesis describes key effects and connections from quantum mechanics and definitions of important terms from solid state physics, which are used to describe the crystalline structure of graphite and its electronic properties. Furthermore, the project describes the HFEPR spectrometer and its functional principle. In the practical part of the thesis, there are numerical models of the band structure of graphite and of its Landau levels and description of the preparation of a graphite sample for measurement. At the end of the practical part there is the analysis of measurements results, namely the cyclotron resonance and Shubnikov-de Haas oscillations, thanks to which it is possible to determine physical parameters of the sample, such as effective mass of charge carriers and fundamental frequency.
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Negative Electrode for Sodium-ion batteries
Šimek, Antonín ; Jaššo, Kamil (referee) ; Libich, Jiří (advisor)
This bachelor thesis contains general introduction to the issue of batteries, their basic principles and distribution. It is mainly focused on the research of electrode materials for negative electrodes of sodium-ion batteries, which do not use lithium for their function. Thesis is also focused on lithium-ion batteries, because their development is closely linked to sodium-ion batteries. The practical part mainly contains the synthesis and characteristics of sodium metatitanate, which is used as active material in negative electrode mass.
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Study of intercalation properties of electrode materials based on expanded graphite
Vencelides, Lukáš ; Máca, Josef (referee) ; Libich, Jiří (advisor)
The diploma thesis deals with the issue of electrochemical cells and deals in detail with lithium-ion batteries. The thesis describes the history of development of lithium-ion batteries, basic information about lithium and basic types of electrochemical cells. The work is devoted in detail to the description of characteristics and operating principle of lithium-ion batteries with emphasis on the negative electrode and negative electrode materials. Of the negative electrode materials, both the most widely used material graphite and modern materials with a great potential for the future are described. In the measurement methods the work describes methods CV, GCPL and EIS. Great emphasis is placed on the explanation of the principle of the function of electrochemical impedance spectroscopy and its application in measurement of electrochemical properties of materials used in lithium-ion batteries. There is also described the procedure of calculation of diffusion coefficients using the results of electrochemical impedance spectroscopy. In the practical part, two methods are used to calculate the diffusion coefficients of lithium ions into the negative electrode made of expanded flake graphite using the results of a series of electrochemical measurements.
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