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Study of electric properties of nanocomposites
Libra, Miroslav ; Rozsívalová, Zdenka (referee) ; Polsterová, Helena (advisor)
The present master´s thesis deals with the electrical properties of nanocomposite materials. Samples for the experiment are made epoxi resin and oxides TiO2 and Al2O3 as nanofillers in different percent performace. The samples nanocomposites are measured temperature dependence of the resistivity inside, dissipation factor and relative permittivity. It discusses the effect of the filler on the resulting electrical properties of the polymer.
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Electrical and thermal characteristics of lead-free solder joints
Jurásek, Matěj ; Adámek, Martin (referee) ; Schnederle, Petr (advisor)
This wok is focused on the issue of soldering. The theoretical part describes the basic requirements for materials and solders alloys, which enter into this process. Further also factors that have a major impact on the quality of joints and methods, that are used for final testing of electrical and optical properties. The aim of the practical part of this work will be monitoring changes in electrical properties depending on the base material, surface finish PCB contact surfaces, the type of solder alloy and residual oxygen concentration in the atmosphere. The resulting values are compared, and they will draw the final recommendations for the method of soldering used alloys
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Processing and properties of piezo-dielectric ceramic composites
Kučera, Ondřej ; Drdlík, Daniel (referee) ; Maca, Karel (advisor)
The diploma thesis deals with piezoelectric materials combining dielectric and piezoelectric ceramics. The first part of this diploma thesis summarizes the preparation of ceramic materials and thermodynamic of sintering. The electric properties of ceramic materials and current knowledge in BCZT ceramics are summarized. The second part of this diploma thesis describes BCZT ceramics preparation process from raw materials in powder form through the reaction of the precursors to sintering the experimental material into the compact body. The properties of prepared BCZT samples such as density, grain size, hardness, relative permittivity, piezoelectric constant and dielectric loss are summarized in the thesis.
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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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Novel materials for organic and hybrid electronics and photonics
Kratochvíl, Matouš ; Yumusak,, Cigdem (referee) ; Táborský, Petr (referee) ; Weiter, Martin (advisor)
Obor organické elektroniky nabízí jedinečnou možnost masové výroby levné a ekologicky přívětivé elektroniky. Otevírá dveře novým funkcím a tvarům zařízení, které standardní elektronika na bázi kovu a křemíku neumožňuje Možnosti dané povahou organických látek a pokrok ve výzkumu syntézy nás zásobují novými materiály pro fotonické aplikace. Hlavní motivací této práce je hledání nových materiálů a zkoumání vztahu mezi jejich molekulární (a krystalickou) strukturou a vlastnostmi. Tato práce je zaměřena na studium optických a/nebo elektrických vlastností nových materiálů pro fotonické aplikace. Materiály prezentované v práci jsou organické i hybridní organicko-anorganické, u nichž je snaha získat to nejlepší z obou světů. Výzkum prezentovaný v této práci se skládá ze tří samostatných částí, které jsou propojeny cílem studovat vztah mezi strukturou materiálu a jeho vlastnostmi a metodami používanými ke studiu těchto vlastností. První část si klade za cíl představit materiály vykazující účinnou fluorescenci v pevné fázi (Solid-State Fluorescence, SSF). V této práci jsou prezentovány dvě série materiálů vykazujících SSF. Barva emise je řízena změnami skupin přitahujících elektrony v push-pull systémech molekul. Výsledky ukazují efektivní (>10%) emise pokrývající většinu viditelného spektra (~450–650 nm). Druhá část prezentovaného výzkumu zkoumá vliv thionace na známou skupinu nízkomolekulárních polovodičů – diketopyrrolopyrrolů (DPP). Prezentované výsledky ukazují ve studovaných molekulách výraznou preferenci n-typové chování následkem thionace, s řádovým zvýšením pohyblivosti elektronů, a také působivě nízko ležící hladiny LUMO (~ 4,5 eV). Třetí část uvedených výsledků je zaměřena na perovskitové materiály pro fotonické aplikace. Hybridní materiál – organo-olovnato-halogenidový perovskit je již téměř půldruhého desetiletí v centru pozornosti výzkumníků v oblasti pokročilé fotoniky. Perovskitové solární články prokazují pozoruhodnou účinnost, avšak jejich využití stále brání problémy se stabilitou. V této práci je prezentována studie stability jako referenční bod pro další výzkum v této oblasti a pro získání vhledu do procesů ovlivňujících stabilitu perovskitových materiálů a solárních článků. Následně je navržen a otestován přístup ke zvýšení stability a výkonu článků, využívající materiály studované ve druhé studii.
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Effect of moisture on the electrical properties of silicate composites
Karlíková, Helena ; Kusák, Ivo (referee) ; Rovnaník, Pavel (advisor)
This work deals with study on the dependence of electrical properties on the moisture content in silicate composites. The theoretical part contains information about the electrical properties of cement-based and alkali-activated binders, as well as knowledge on moisture parameters and the presence of moisture in the material structure. Samples of cement-based mortars and alkali-activated slag with a graphite powder in the range of 0–18 per cent by weight were produced and quartz sand was used as filler in the experimental part. The samples were provided with copper electrodes and saturated with water after hardening. The electrical properties of the mortars were monitored by means of impedance spectroscopy during the gradual drying of the samples. The effect of microstructure has been studied using scanning electron microscopy and mercury intrusion porosimetry. The results indicate that a significant increase in electrical resistance occurs only when the relative sorption humidity content is below 20 per cent in the 40–5000 Hz frequency range.
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Testing of MV Distribution Transformers
Czajtányi, Róbert ; Pelikán, Luděk (referee) ; Krbal, Michal (advisor)
The aim of this thesis was to get acquainted with the electrical properties of distribution transformers, which are used in the area of high voltage technology. Further aim was to describe the existing diagnostic methods according to the standards and to introduce the measuring workstation. Finally, the diagnostic of transformer was performed, and the results were evaluated.
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Dielectric properties of epoxy resins
Matoušová, Klára ; Novák, Vítězslav (referee) ; Kazelle, Jiří (advisor)
This diploma thesis deals with the fundamental properties of epoxide mixtures, as determining of these fundamental properties of epoxide mixtures could in the case of favorable results lead to diminishing the amount of defects in epoxide-embedded instrument transformers. As the influence of effects in the manufacturing process of transformers causing poor quality is very extensit, the biggest emphasis is laid capitally on the influence of the epoxide casting mixture composition. The thesis describes the manufacture technology including used methodics and materials. The compositions of epoxide resins and the mechanisms of their curing. Also, the definitions of fundamental properties of dielectric materials and the description of diagnostic methods used to relative permitivity, dissipation factor and inner resistivity are included. suitable casts of acquired samples were set and dried out within the experimental part, followed by measurement of fundamental electrical properties in temperature and frequency relations. Hereafter a comparison of individual samples and the evaluation of their electrical properties will be carried out.
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