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Dielectric Properties Of Natural Oils From Different Oilseeds
Spohner, Milan
This paper describes analysis of perspective, ecological and environmentally-friendly electrical insulating liquids for electrical engineering. In the experimental part, dielectric properties of the most common vegetable oils were analyzed and compared with frequently used noninhibited mineral oil (TrafoN): soybean oil, sunflower oil, rapeseed oil, peanut oil and two types of olive oils (extra virgen and pomace). Dielectric properties were measured using the high-resolution Novocontrol Alpha-A Frequency Analyzer in the frequency range 1 Hz – 1 MHz in the temperature interval 243 K – 363 K.
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Phase transformation in magnesium MgZnAl-based alloys
Kodetová, Veronika ; Vlach, Martin (advisor)
In the present work, there was analyzed thermal evolution of the phase transformation in the MgZnAl and MgZnAlCa alloys with different concentration of the Zn and Ca. The grains were occupied by the phase with quasicrystaline icosaedral structure in the as-cast alloys and after isochronal annealing up to 240 řC. The thermal measurements revealed two exothermic effects in the MgZnAl alloy and three exothermic effects in the MgZnAlCa alloy during linear heat treatment in the temperature range of 100 - 250 řC. In agreement to the thermal response, two and three stages of electrical resistivity decrease were observed in the same temperature range. The lower thermal changes, absolute resistivity changes and microhardness were observed in the alloy with Ca-addition and lower concentration of Zn.
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determination of kinetic parameter of reactions using DSC
Kopecký, Jan ; Kouřil, Miloslav (referee) ; Jan, Vít (advisor)
The master thesis deals with DSC measurments a calculation of kinetic parameters. In the theoretical part, iron alotropy is briefly described, followed by a description of the DSC analysis itself. The thesis also includes division and derivation of isoconversional methods for calculating the activation energy. In the experimental part, a series of measurments is perfomed on pure iron prepared by Cold Spray method. In the paper the influence of deformation on the Curie temperature of the magnetic transformation in -Fe and transformation > is investigated. The activation energy is calculated for transformation > for different degrees of deformation. The degree of deformation is monitored by channeling contrast.
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Phase transformation in bio-compatible Mg-based alloys
Hornát, Bohumil ; Vlach, Martin (advisor) ; Mathis, Kristián (referee)
ÙÖÖ ÒØ Ñ Ø Ö Ð Ö × Ö × Ó Ò Ò ÑÔÖÓÚ Ò Ú ÓÖ Ó Ð ØÛ Ø Ñ ¹ Ò × ÙÑ ÐÐÓÝ Û Ú Û Ù× ×Ô ÐÐÝ Ò ØÖ Ò×ÔÓÖØ Ò Ù×ØÖÝ Ò Ñ ¹ Ò ž Å ¹Ê ¹Ë ¹ÅÒ × ÐÐÓÝ× Ò ÓÒ× Ö × ÔÖÓÑ × Ò Ñ Ø Ö Ð ÓÖ Ø × ÔÔÐ Ø ÓÒמ ÁÒ Ø ÔÖ × ÒØ ÛÓÖ ¸ Ø Ö Û × ×ØÙ Ø ÖÑ Ð ÚÓÐÙØ ÓÒ Ó Ø Ô × ØÖ Ò× ÓÖÑ Ø ÓÒ× Ò Å ¹Ê ¹Ë ¹ÅÒ × ÐÐÓÝ× Ý Ö ÒØ Ð × ÒÒ Ò ÐÓ¹ Ö Ñ ØÖÝ Ò Ñ ×ÙÖ Ò Ñ ÖÓ Ö Ò ×מ Ì Ø ÖÑ Ð Ö ×ÔÓÒ× × Ø Ö ÒØ Ø Ò Ö Ø × Û Ö Ó × ÖÚ Ò Ø Ø Ú Ø ÓÒ Ò Ö × Ó Ø ÔÖÓ ×× × Û Ö Ð ÙÐ Ø ž Ì Ø ÖÑ Ð Ö ×ÔÓÒ× × Û Ö ××Ó Ø Û Ø Ò Ú Ù Ð ÔÖ Ô Ø Ø ÓÒ ÓÖ ×ÓÐÚ ÒØ ÔÖÓ ×× × × ÓÒ ÓÑÔ Ö ×ÓÒ Û Ø Ð Ø Ö ØÙÖ ž ÈÖ Ô Ø Ø ÓÒ × ÕÙ Ò Ó ×Ý×Ø Ñ Å ¹ Û Ö Ó × ÖÚ Ò Ñ Ø Ö Ð× Å ½Ë ½ÅÒ Ò Å ½¼ ½Ë ½ÅÒž ÈÖ ¹ Ô Ø Ø ÓÒ × ÕÙ Ò Ó ×Ý×Ø Ñ Å ¹ Û Ö Ó × ÖÚ Ò Ø Ñ Ø Ö Ð Å ½Ë ½ÅÒž ÈÖ Ô Ø Ø ÓÒ Ó Ô ÖØ Ð × ÅÒ¾Ë Ò Ô ÖØ Ð × ÓÒØ Ò Ò ÅÒ Ò Ê Û Ö Ø ¹ Ø Ò ×ØÙ ÐÐÓÝמ À Ö Ò Ò Û Ö ÒÓØ Ó × ÖÚ Ò Ú ÖØ Ð ×× Ø Ö Û Ö ÒÓØ × Ò ÒØ Ö × × Ó Ö Ò ×× Ò Ø ÙÖ Ò ÒÒ Ð Ò ÙÔ ØÓ ½¼ ž
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Phase transformation in magnesium MgZnAl-based alloys
Kodetová, Veronika ; Vlach, Martin (advisor) ; Mathis, Kristián (referee)
In the present work, there was analyzed thermal evolution of the phase transformation in the MgZnAl and MgZnAlCa alloys with different concentration of the Zn and Ca. The grains were occupied by the phase with quasicrystaline icosaedral structure in the as-cast alloys and after isochronal annealing up to 240 řC. The thermal measurements revealed two exothermic effects in the MgZnAl alloy and three exothermic effects in the MgZnAlCa alloy during linear heat treatment in the temperature range of 100 - 250 řC. In agreement to the thermal response, two and three stages of electrical resistivity decrease were observed in the same temperature range. The lower thermal changes, absolute resistivity changes and microhardness were observed in the alloy with Ca-addition and lower concentration of Zn.
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Influence of minor solutes on thermal properties of MgYNd-based alloys
Kodetová, Veronika ; Vlach, Martin (advisor) ; Kekule, Tomáš (referee)
The development of magnesium alloys has the growing trend and leads mainly to the transport industry and modern medicine. The use of the alloying elements, especially rare- earth elements, is a way to improve the material utility. In the present work, there was studied thermal evolution of the phase transformations in the MgYNd alloys containing additional elements by differential scanning calorimetry. The thermal responses at different heating rates were observed and the activation energies of the processes were calculated. On the basis of confrontation with literature the precipitation and dissolution of stable, metastable phases were assigned to the observed processes. The thermal response corresponding to the precipitation of the stable β phase was observed in all materials. The activation energies of the stable β phase precipitation are practically identical for all materials investigated.
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First-principles studies of the electronic and structural properties of Lead Zirconate Titanate (PZT)
Planer, Jakub ; Friák, Martin (referee) ; Bartošík, Miroslav (advisor)
This work is focused on Density Functional Theory (DFT) calculations of oxygen vacancy diffusion barriers in mixed perovskite lead zirconate titanate and its pure counterparts. We found out that barrier heights are different in lead titanate and lead zirconate caused by the different localization of the excess electrons due to the oxygen vacancy formation. Diffusion barriers were also determined for titanium-rich mixed phases and compared to experimental values. This work contributes to clarify unusually low experimentally measured diffusion coefficients in PZT. We found out that the induced vacancy states are forming localized bonds to the lead atoms which causes the oxygen vacancies to become immobile due to the increase of the activation energy of the diffusion process.
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Phase transformations in Mg-Gd alloys
Stíbal, Adam ; Vlach, Martin (advisor) ; Mathis, Kristián (referee)
ývoj hořčíkový h slitin má ekonomi koEekologi ké opodst-tněníF yužití tě hto slitin je n- vzestupné tenden i - z-s-huje zejmén- do tr-nsportního pr·mysluD -le svoje upl-tnění n- hází i v medi íněF tedn- z metod zlepšení vl-stností hořčíku je legování jinými prvkyF vláš¡' do rý h výsledk· dos-huje legování prvky vzá ný h zeminF "ento typ slitinD kde legují ím prvkem je g-doliniumD jsou studovány v předklád-né prá i ve tře h tl-kově litý h slitiná h do kon entr- e IS hmF7F ředmětem prá e ylo studium fázový h tr-nsforE m- í při žíhání m-teriálu pomo í metody diferenční skenov- í k-lorimetrie při neizotermi kém žíháníF fyly pozorovány tři pro íh-jí í pro esy - spočteny jeE ji h -ktiv-ční energieF "ěmto pro es·m ylo n- zákl-dě srovnání s liter-turou přiř-zeno kl-strování -tom· qd - pre ipit- e met-st- ilní h fází β - β F I
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Controlled life-time polypropylene
Demková, Eva ; Petruš, Josef (referee) ; Tocháček, Jiří (advisor)
The master´s thesis is focused on the characterization of degradation process of polypropylene and polypropylene with statistic copolymer into which manganese (II) stearate and cobalt (II) stearates were added at 0.05, 0.10 and 0.20 wt.% loadings. The aim of the thesis was to prepare the controlled life-time polypropylene. The degradation was studied at varying temperatures and prodegradant loadings. The prodegradants were synthetized and characterized using the FTIR and DSC techniques. Thermooxidation of the tested samples induced the changes in crystallinity, melting points and melt-flow indexes. Tensile strength and other mechanical properties were determined by means of the tensile test. The carbonyl index was determined using FTIR, the thermooxidation stability test was used to determine the activation energies of reactions. The changes in morphology of degraded samples were observed by SEM analysis.
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