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Low cycle fatigue of nickel superalloy IN713LC with TBC layer at high temperatures
Machala, Jan ; Čelko, Ladislav (referee) ; Juliš, Martin (advisor)
This thesis deals with the low cycle fatigue nickel-based superalloy IN713LC with applied TBC barrier at high temperature. The theoretical part is divided into four sections. The first one focuses on description of fatigue damage. The second one provides the basic characteristics of nickel-based superalloys. The third section describes the use of the surface layers - diffusion layers and thermal barriers and the fourth section deals with the influence of these layers on fatigue properties. Experimental part is focused on the evaluation of low cycle fatigue tests and on the explanation of the mechanisms of initiation and propagation of fatigue cracks. For the experimental part, fatigue samples were prepared by vacuum precision investment casting. TBC barrier was applied by atmospheric plasma spraying and consists of two sublayers - the lower metallic bond coating type CoNiCrAlY and top ceramic coating type YSZ. Low cycle fatigue tests were conducted under strain control at controlled temperature of 900 ° C. Fractographical analysis of fracture surfaces was carried out by using light and electron microscopy. Effect of applied barrier to fatigue life was determined - the parameters of Manson-Coffin and Basquin curve. A cyclic stress-strain curve was also obtained. The curves softening / hardening and number of transit cycles were determined. The obtained parameters and values from fatigue tests were compared with available data from fatigue tests of superalloy IN713LC without the layer, as applied AlSi type diffusion layer, at high temperatures. The initiation site on the fracture surfaces was determined within the fractographic evaluation and the influence of the layer on the initiation and propagation of fatigue cracks was discussed. A helpful tool was the assessment of longitudinal sections using scanning electron microscopy.
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Preparation of Nanocomposites TiOx /Plasma Polymer and Study of Their Properties
Drábik, Martin ; Biederman, Hynek (advisor) ; Čech, Vladimír (referee) ; Špatenka, Petr (referee)
Title: Preparation of Nanocomposites TiOx/Plasma Polymer and Study of Their Properties Author: Mgr. Martin Drábik Department: Department of Macromolecular Physics Supervisor: Prof. RNDr. Hynek Biederman, DrSc. Supervisor's e-mail address: bieder@kmf.troja.mff.cuni.cz Abstract: This thesis concerns a study of nanocomposite films TiOx/plasma polymer prepared by various deposition techniques using different organic precursors. Processes of deposition of the films were diagnosed in-situ by means of OES and measuring the deposition rate by QCM. Properties of the nanocomposite films were studied by various characterization techniques. Wettability of the films was described by means of the contact angle of water. Morphology of the nanocomposites was characterized by AFM, TEM and SEM. Elemental analysis and chemical composition of the films were studied by XPS, RBS, SIMS and FTIR. Crystal structure of TiO2 films was identified by XRD. Optical characterization of the prepared films was done by UV-Vis spectroscopy. Electrical properties of the samples were characterized by I-V and SPV measurements. In the end, 'wet' chemical processes were utilized for preparation of both TiO2 nanostructures and organic films for comparison with vacuum deposition techniques and plasma polymer composite films. Keywords: nanocomposite...
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Investigation of matter transport in porous materials by means of PFG NMR
Peksa, Mikuláš ; Lang, Jan (advisor) ; Hof, Martin (referee)
Title: Investigation of matter transport by means of PFG NMR Author: Mikuláš Peksa Department of low temperature physics Supervisor: doc. RNDr. Jan Lang, Ph.D. Assistant Supervisor: RNDr. Milan Kočiřík, CSc. (ÚFCH JH AV ČR) Abstract: Estimation of transport-structural parameters such as porosity, tortuosity and surface-to-volume ratio of pores in beds of glass beads is the main goal of this study. These parameters were estimated for 5 samples with different distributions of sizes. The second goal is to probe a possibility to use the same approach to describe the self-diffusion in water solution of LiCl confined in two porous materials based on Al2O3 and glass, respectively. The last goal is the measurement of self-diffusion of water molecules in mesoporous geopolymeric material. Its capability of water transport at long scales have been documented. The measurements of apparent self-diffusion coefficients by means of NMR spectroscopy with pulsed field gradients was major methodology of this work. Keywords: porous material, porosity, tortuosity, self-diffusion, NMR
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The preparation of Grafen by method CVD
Procházka, Pavel ; Kromka,, Alexander (referee) ; Mach, Jindřich (advisor)
This diploma thesis is mainly focused on the fabrication of graphene layers on the copper foil by the Chemical Vapor Deposition (CVD). For this purpose the high-temperature chamber for the production of the graphene was completed and fully automated. The production of the high area graphene on the copper foil was experimentally achieved. The Raman microscopy and X-ray photoelectron spectroscopy measurements proved that the produced graphene is mostly a monolayer. Graphene layer was transferred on non-conductive substrate.
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Methods of checking the observance of diagnostic reference levels in the field of radiodiagnostics
KROUPOVÁ, Helena
Methods of Checking the Observance of Diagnostic Reference Levels in the Field of Radio diagnostics Although there is a simultaneous development of diagnostic and therapeutic methods, perfection of instrumentation and means for personnel and patient protection, there is also an effort to reduce applied doses. In this way, medical irradiation caused by ionizing radiation used in medicine represents a significant contribution to the total dose of ionizing radiation that a person is exposed. Today the medical radiation in the Czech Republic comprises more than ninety per cent of radiation from an artificial source and approximately one ninth from the total population radiation. Evaluation of professional doctor radiation and X-ray devices attendance has been safeguarded within the personal dosimetry for many decades. However, systematic monitoring of doses related to medical radiation of the patient is a relatively new problem in the radiodiagnostics sphere. According to the Council directive 97/43/EUROATOM requirement, the SUJB has stated the so called ``diagnostic reference levels{\crqq} within enclosure number 9, Regulation No. 307/2002 Coll., about radiation protection. These ``diagnostic reference levels{\crqq} are dose levels within medical radiation and their exceeding is not expected at the 70 kg adult patient medical examination in the case of correct practice. The systematic exceeding of diagnostic reference levels under clinical practice conditions is the reason for reconsideration of radiation protection optimalization at a given workplace. In accordance with the proposal of the National Radiology Standards for Radiology Physics, the author team recommends the monitoring extension of the patient radiating load related to a particular medical radiation by specifying the local diagnostic reference levels, typical for a given type of workplace at a particular keeper, and their continuous verification within the clinical examination of the standard group of patients. Generally, the doses can be determined in two ways: by exposure parameter calculation or by product measure of area kerma, which is generally implemented by special devices, so called DAP meters. The aim of the work is the description of both methods, their comparison and the evaluation of the method effectiveness at various types of sciagrammatic workplaces.
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Selective growth of GaN on SiN
Hulva, Jan ; Kolíbal, Miroslav (referee) ; Mach, Jindřich (advisor)
This bachelor's thesis deals with the selective growth of gallium and gallium nitride on silicon nitride (SiN) substrates. Thin silicon nitride layers are deposited on silicon substrates. Oxide structures are prepared by the local anodic oxidation method (LAO) on SiN substrates. These surfaces can be editionally modified by etching in hydrofluoric acid. Modified substrates are used for the deposition of gallium or gallium nitride under ultra-high vacuum conditions. Consequently, ordering of deposited material was studied in areas modified by LAO. Chemical state of layers is studied by X-ray photoelectron spectroscopy. Morphology of surfaces is measured by the atomic force microscope (AFM).
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Sol-gel synthesis of ternary ZnxTiyOz nanostructures for applications in solar cell technologies and photonics
Mrázek, Jan ; Nižňanský, Daniel (advisor) ; Pinkas, Jiří (referee) ; Pollert, Emil (referee)
The presented study deals with the sol-gel synthesis of nanocrystalline ternary phases of the general formula ZnxTiyOz, their characterization and potential application in photonics. Achieved results brings new fundamental knowledge about the processes leading to the formation of ZnxTiyOz nanocrystals from amorphous xerogels and gives novel information about structural and opto-electrical properties of prepared materials. Based on the presented results, most of all up-to-date reported ZnxTiyOz compounds with tailored nanocrystalline size and structure can be prepared as powders or thin films. Two sol-gel approaches based on the cluster process and direct heteronucleation were employed to prepare initial sol. Sols were optionally doped by Eu3+ ions to evaluate the effects of rare earth element to crystallization properties of formed compounds. In the first part of our study crystallization properties and structural evolution of thermally treated xerogels were analyzed. As a result a versatile method allowing the preparation of inverse spinel Zn2TiO4, cubic defect spinel ZnTiO3 and rhombohedral ZnTiO3 with tailored nanocrystal sizes was established. Initial composition and thermal annealing allow us to prepare selected ternary phase with tailored nanocrystal size ranging from tens of nanometers up to...
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Titania suspensions for material printing
Svoboda, Tomáš ; Drbohlavová, Jana (referee) ; Dzik, Petr (advisor)
This bachelor‘s thesis deals with the preparation of stable suspensions of titanium dioxide applicable for material printing. A wide range of dispersive environments stabilizing the nanoparticles of titanium dioxide was investigated. Commercially available aqueous dispersion and dry titania powder was used as the source of TiO2.The properties of prepared suspensions were evaluated and the most suitable suspension was used for material printing. This thesis focused on suspension‘s stability, sizes of particles dispersed in them, and in their rheological behavior. Furthermore, we analyzed the studied the properties of printed layers by SEM, optical microscopy, DLS and analytical centrifuge. We also evaluated the photocatalytic activity by monitoring the oxidation rate of coumarin to 7-hydroxycoumarin.
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