|
|
Study of Electric and Thermal Properties of Building Materials with Conductive Additives
Veselá, Jana ; Krouská, Jitka (referee) ; Zmeškal, Oldřich (advisor)
This work focuses on study of electric, dielectric and thermal properties of composite electrically conductive building materials composed of magnesium oxychloride cement and small amount of graphene and graphite admixtures. The aim of this work was to determine thermal properties of materials and create a model of electric current conduction mechanism in material. Electric and dielectric properties were determined with using of transient direct current measurement of resistivity and impedance spectroscopy. Thermal properties were investigated using transient step-wise method and fractal analysis of thermocamera data. Electrical resistivities of materials are determined from the direct current measurements. Model of transport of electrical charge carriers was evaluated by fitting impedance data to an equivalent electrical circuit model. Thermal conductivities and thermal capacities were determined by means of thermal measurements. The presented properties for example can be used for assessment of suitability for specific construction applications.
|
|
| |
|
| |
|
| |
|
|
Nanofibrous Separators for Lithium-Ion Batteries
Pléha, David ; Míka, Martin (referee) ; Janderka,, Pavel (referee) ; Novák, Vítězslav (advisor)
Nanofibrous separators use in lithium-ion batteries brings many advantages. In contrast to contemporary used commercial separators, nanofibrous ones exhibit higher temperature resistance,ionic conductivity and higher electrolyte uptake. Better ionic conductivity is ensured by porous structure and large specific surface. Fibers creates channels for the ionic species motion. Amorphous texture of nanofibers allows quick lithium ionic species motion within the polymeric matrix of separator. Furthermore, these separators exhibit higher volume of uptaken electrolyte. Further advantage of electrospinned nanofibrous separators are both high porosity and chemical stability.
|
|
|
Study of the dielectric properties of perovskite crystals
Mlčkovová, Hana ; Pospíšil, Jan (referee) ; Zmeškal, Oldřich (advisor)
The presented diploma thesis deals with the preparation of perovskite single crystals by inverse thermal crystallization and subsequent study of the basic properties of these hybrid organic-inorganic materials that can be used in various optoelectronic (photodetectors, transistors, lasers, LEDs) or photovoltaic applications. Their behavior in the electric field was studied by impedance spectroscopy. Impedance and capacitance-voltage (C-V) characteristics (frequency dependences) were measured in the dark and in the light. From the impedance dependences for measurements at 0 V voltage in the dark, the equivalent circuit was modeled and its parameters and dielectric constant were determined. From the C-V dependence, Mott-Schottky analysis determined the parameters – "flat-band" potential U_"fb" and charge carrier density N_"C-V" , the parameter – the so-called Warburg coefficient was found, which together with the parameter N_"C-V" was used to calculate the diffusion coefficient D.
|
|
|
Measurement and modeling of real impedance results in dependence on the position the sensing electrodes
Haňka, Jiří ; Maxa, Jiří (referee) ; Novák, Vítězslav (advisor)
ABSTRAKT Obsah této práce je směřován na řešení problematiky měření impedančních charakteristik dielektrických materiálů, zejména keramik, za pomocí simulace připojení elektrod na mě- řený vzorek. V práci je popsáno měření impedancí se zaměřením na metodu impedanční spektroskopie. Cílem práce je seznámení s problematikou měření komplexní impedance a popsání parazitních jevů, vyskytujících se v materiálu. Dále jsou v práci popisovány současné možnosti simulací a simulačních softwarů jako je zejména ANSYS Maxwell. S využitím simulací tohoto softwaru jsou v práci řešeny impedanční charakteristiky vodivé keramiky a jejich závislost na poloze napájecích elektrod. KLÍČOVÁ SLOVA Dielektrické materiály, elektrická polarizace, impedanční spektroskopie, komplexní impe- dance, vodivé keramiky, ANSYS, metoda konečných prvků. ABSTRACT Content of this thesis is aimed to solutions of issues, created due measurement impe- dance characteristics of dielectric materials, mainly ceramics, using simulation electrode position by specific software. In thesis is described impedance measurement with focusing to impedance spectroscopy. Goal of this thesis is to get acquainted with issues of mea- surement complex impedance and explain parasitics effects in ceramics material. Further goals of thesis are described current possibilities of simulation software ANSYS Ma- xwell. Using this simulation software was solved impedance characteristics of conductive ceramics and their dependence of electrodes position.
|
|
|
Synthesis and characterization of sulfurized polymers for electrochemical power sources
Svoboda, Lukáš ; Kazda, Tomáš (referee) ; Čech, Ondřej (advisor)
Batteries based on lithium-sulfur technology have the potential to increase the amount of stored energy in comparison with current lithium-ion systems while maintaining the same weight. Achieving this goal is possible due to the high theoretical energy density of sulfur, which exceeds the values of other materials used in batteries. However, these batteries suffer from several failing, which still hinder the practical use. The use of amorphous sulfur instead of its crystalline form might lead to increasing of durability and charge efficiency. Inverse vulcanization of sulfur seems to be the perspective method for the preparation of polymer sulfur because it prevents its recrystallization and stabilizes amorphous sulfur. The aim of this thesis is the preparation and study of properties of materials made of inverse vulcanized sulfur.
|
|
|
Gel polymer electrolytes with fire retardands
Veselkova, Iuliia ; Jahn, Michal (referee) ; Sedlaříková, Marie (advisor)
This graduate work deals with the study and preparation of gel polymer electrolytes with flame retardants for lithium-ion batteries. The theoretical part describes the types of electrolytes, their features, benefits, how they differ and where they are used in detail. The basis of this section is gel electrolytes with flame retardants, to measure their electrical and electrochemical properties. The experimental part deals with the preparation of samples of gel electrolytes with different percentages of flame retardant, where varied species of flame retardants and measuring their electrical conductivity and potential windows. Impedance spectroscopy, cyclic voltammetry and dynamic-analytical thermal analysis were selected as measuring methods.
|
|
|
Study of optoelectrical properties of organic semiconductor thin film layers of phtalocyanines
Miklíková, Zdeňka ; Vala, Martin (referee) ; Zmeškal, Oldřich (advisor)
Diploma thesis is focused on the study of optoelectric properties of thin layers of organic materials based on phthalocyanines, which can be used as an active layer of photovoltaic cells. Especially are studied the properties of the thin active layers of PdPc and PdPc + IL on the glass or ceramic substrates with aluminium contact, which are prepared by material printing here. On the prepared samples were first measured current-voltage characteristics in the dark and in the light and then were measured impedance spectrums in the dark. The received results will be used to improve the properties and structures of photovoltaic cells.
|
guest ::
