National Repository of Grey Literature 66 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Study of microstructure evolution during intermediate stage of sintering of advanced ceramic materials
Jemelka, Marek ; Pouchlý, Václav (referee) ; Maca, Karel (advisor)
Hlavním cílem této diplomové práce byl popis závislosti kritické hustoty (tj. hustota, při které se tubulární póry zcela přemění na póry izolované a uzavřené) a průměrné velikosti zrn při této hustotě na rozdílných rychlostech ohřevu během druhého stádia slinovacího procesu. Dosažené výsledky jsou velice důležité, např. pro produkci transparentních balistických pancířů, vysoce výkonných řezných nástrojů či kostních a kloubních implantátů, jelikož poskytují informace pro výběr nejvhodnější slinovací metody, jejímž výsledkem jsou vzorky v předslinutém stavu s minimální velikostí zrn pro následnou metodu izostatického lisování za tepla (post –HIP). Bylo zjištěno, že kritická hustota všech studovaných oxidových materiálů (Al2O3, tetragonální ZrO2 a kubické ZrO2) není významně závislá na rychlosti ohřevu v rozmezí od 2°C/min do 200°C/min a průměrné hodnoty kritických hustot jsou 96.3 %; 92,4 % a 93,0 % pro Al2O3, t- ZrO2 a c-ZrO2. Výsledky z dosavadní literatury prokázali, že kritická hustota není taktéž závislá na mikrostruktuře keramického polotovaru, a tedy je možné usuzovat, že kritická hustota je materiálovou konstantou závislou na dihedrálním úhlu materiálu. Slinovací trajektorie (tj. závislost průměrné velikosti zrn na relativní hustotě) byly vyhodnoceny jak pro všechny tři způsoby slinování lišící se rychlostí ohřevu (2, 10 a 200 °C/min s dobou výdrže 5 min), tak pro takzvaný způsob slinování- long-dwell (nízké slinovací teploty s dobou výdrže 5 – 10 h). Výsledky nepotvrdily, že by některá z alternativních metod slinování vedla ke snížení průměrné velikosti zrn při kritické hustotě materiálu, a tudíž v současnosti nejvyužívanější metoda pro přípravu materiálů v předslinutém stavu, tzv. metoda konvenčního slinování (rychlost ohřevu 10 °C/min, doba výdrže 5 min), zůstává i nadále vhodnou metodou pro přípravu vzorků s optimální mikrostrukturou pro následný post-HIP proces.
Oxidation barriers prepared by electrochemical procedures
Šťastná, Eva ; Pouchlý, Václav (referee) ; Jan, Vít (advisor)
A process with aim to prepare an oxidically and thermal resistant layer was performed on the samples from clear aluminium (99,99+ %, VÚK čisté kovy, s. r. o.) and on the samples from clear titanium (99,95 % Goodfellow) with a layer from sputtered aluminium (99,99 %, VÚK čisté kovy, s. r. o.), An oxidic layer was prepared on the samples by anodization in the oxalic acid. The layer had fine, hexagonally organized pores with the diameter of 30 nm. During the following processing was the structure prepared for the electrochemical deposition of copper to the pores. The aim of the electrodeposition was preparation of copper nanowires deposited into the pores of the oxidic layer. The process was performed in the solution of copper sulfate and sulfuric acid in water. The controlling parameter of the deposition was voltage which had a very asymmetric period. The period had to be optimized for a successful preparation of the wires. The result of the whole process was structure with oxidic matrix whose most of the pores were filled with copper.
Processing of bulk SiC ceramics by advanced sintering methods
Poczklán, Ladislav ; Pouchlý, Václav (referee) ; Kachlík, Martin (advisor)
In this bachelor's thesis literature search of preparation of advanced ceramic materi-als was made. The influence of pressure, temperature and time on final microstruc-ture of non-oxide SiC ceramics was studied. The experimental part was devoted to processing of bulk SiC ceramics especially by spark plasma sintering.
Influence of plasma activation of ceramic particles on ceramic technology and properties
Klevetová, Tereza ; Ráheľ,, Jozef (referee) ; Pouchlý, Václav (advisor)
This thesis is focused on the study of the influence of plasma activation of powder ceramic materials on sintered microstructure. In this experiment Diffuse Coplanar Surface Barrier Discharge (DSCBD) device was used for plasma treatment and two materials were chosen to be investigated – Al2O3 (TAI) and ZrO2 doped with 3 mol % Y2O3 (TZ). Two methods of powders dispergation in suspension were used – ultrasound and ball milling. The effect of using of DCSBD on alumina and zirconia powders was investigated by mercury intrusion porosimetry, dilatometry and by evaluation of final relative densities and grain sizes. Generally, was investigated that plasma surface activation of ceramic particles has measurable influence on the final microstructure. In comparison with the non-plasma treated alumina powders, plasma activated powders disperged with ultrasound and ball milling achieved lower values of grain size at comparable relative densities. In case of zirconia powders was observed that plasma treated powders achieve higher relative densities, if ultrasound was used. On the other hand, plasma treated zirconia powders disperged with ball milling achieve lower relative densities compared with non-plasma treated zirconia powders. Final sintering trajectory of plasma treated TZ powders disperged with ultrasound is comparable to the sintering trajectory of non-plasma treated zirconia powders disperged with ball milling and vice versa. Plasma surface treatment is the way of more ecological friendly preparation of suspension and its stabilization than the conventional stabilization methods using chemical additives.
Lamination of ceramic tapes
Smiešková, Jana ; Pouchlý, Václav (referee) ; Trunec, Martin (advisor)
This master’s thesis deals with ways of lamination of ceramic tapes prepared by gel–tape casting method. The thesis is divided into two parts. The first part, a literary recherche, describes methods of production of thin ceramic layers. The main focus is on the tape casting method. The second, experimental, part of the thesis describes the preparation of ceramic suspensions, the fabrication of thin ceramic layers by gel–tape casting method, the preparation of laminated bodies from thick-walled discs and laminated tapes and it also shows a possibility of creating of ceramic layers by the spin coating method used on polycrystalline ceramic substrate.
Processing and properties of transparent polycrystalline ceramic materials
Tásler, Jan ; Pouchlý, Václav (referee) ; Maca, Karel (advisor)
The presented diploma thesis is focused on the preparation and properties of transparent polycrystalline ceramic materials based on Al2O3. Theoretically, the most important technological aspects of the processing of these materials are presented. Detailed attention is given to transparent Al2O3 polycrystalline ceramics doped with rare earth elements. The influence of microstructural parameters on the optical properties (represented by RIT) is investigated on Al2O3 samples doped and codoped with dysprosium, terbium and chromium. A significant effect of the average grain size on the light transmittance of all samples is observed. The highest RIT = 55 % (measured by a laser beam with a wavelength of 632,8 nm) was achieved by an optimized preparation process for a sample doped with 0,05 at. % of dysprosium. For all samples photoluminescent properties are also analysed. The photoluminescent emission spectra correspond to the activation of doping elements. In case of the terbium and chromium codoped samples, the differences in the activation of individual dopants depending on different excitation wavelengths were demonstrated, resulting in different colour emissions for different excitation wavelengths.
The influence of heating rate on two step sintering of advanced ceramic materials
Klevetová, Tereza ; Maca, Karel (referee) ; Pouchlý, Václav (advisor)
Recently, there has been growing interest in new technologies and procedures to improve the microstructure of advanced ceramic materials. One of the most commonly used sintering methods is Two step sintering (TSS), Rapid rate sintering (RRS) and Spark plasma sintering (SPS). Within the framework of this bachelor thesis number of experiments were carried out for the research of the microstructure interconnecting the Two step sintering with the Rapid rate sintering and non-preassure Spark plasma sintering. The aim of this work was to determine the influence of the heating rate on the size of final relative density and the average grain size for ceramic materials based on ZrO2. The results of the study show that occurrence of the „core-shell“ structure on the ZrO2 doped by 3 mol.% Y2O3 (TZ-3Y) tend to production of non-homogenous microstructure with a fully compacted surface and a porous center. In the case of ZrO2 doped by 8 mol.% Y2O3 (TZ-8Y) this structure was detected only in several cases at higher heating rates. An the same time it was found that the final relative density decreases with increasing heating rate. Using cubic ZrO2 with larger grain size (TZ-8YSB), the „core-shell“ structure did not appear, however a lower relative densities of about 98 % t.d. was always achieved, regardless of the applied temperature profile. The best results were obtained with TZ-8Y using Spark plasma sintering and Rapid rate sintering. Smaller grain size was obtained as compared with conventional methods of other authors. The difference in grain size was just within the framework of the standart deviation. This work doesn’t show any positive influence of Rapid rate sintering on the resulting grain size.
Transparent polycrystalline ceramic materials with cubic lattice structure
Kučera, Jan ; Pouchlý, Václav (referee) ; Maca, Karel (advisor)
The presented work is focused on the study of the influence of preparation parameters on the optical properties of polycrystalline cubic ZrO2 (stabilized with 8 mol.% Y2O3). Furthermore, the work deals with the doping of c-ZrO2 with TiO2 and its effect on the luminescence properties of ZrO2. The examined samples were prepared by uniaxial pressing (10 MPa), followed by a cold isostatic pressing (300 and 700 MPa), pressureless sintering (1340–1380 °C, 10 min), and hot isostatic pressing (1200–1400 °C, 4 h, 200 MPa). In this work, it is shown that the optical properties are significantly affected by the temperature of the hot isostatic pressing, the thickness of the sample, and also by the wavelength of the incident light. A maximum real in-line transmission of 68.8 % was achieved, which is 90.5 % of the theoretical limit for c-ZrO2 at an incident radiation wavelength of 632.8 nm. A low-pressure infiltration method and a powder mixing method were used to prepare the doped ZrO2 ceramic sample. With doping, the maximum of the excitation spectrum shifted from 295 nm (4.20 eV) for the undoped ZrO2 to 320 nm (3.87 eV) for the doped samples. Doping led to an increase in emission intensity compared to a pure ZrO2 by up to 23 times. The maximum emission intensity at 545 nm wavelength was achieved for samples doped by infiltration method with a nominal 0.1 mol.% TiO2 content.
Preparation of transparent advanced ceramic base on Al2O3.MgO
Chvíla, Martin ; Maca, Karel (referee) ; Pouchlý, Václav (advisor)
Ceramic materials are in general characterized by high hardness, high modulus of elasticity, excellent abrasion resistance, etc. These properties make ceramics among others useful in optically transparent applications. An ideal form of optically transparent ceramic material is monocrystalline. However, the monocrystalline fabrication is expensive and/or time consuming. From this point of view polycrystalline ceramics is preferred. But the polycrystalline transparent ceramics fabrication is fraught with complications such as porosity, inappropriate grain size and insufficient purity. These circumstances could be solved by using sintering additives. This master’s thesis compiles literature research summarizing modern technologies of advanced ceramics sintering and ceramic polycrystalline microstructure dependence on its optical properties. The experimental part of this thesis focuses on the fabrication parameters of polycrystalline advanced ceramics based on Al2O3MgO and evaluation of their optical properties. Polycrystalline magnesium-aluminate spinel with sintering additive contents 0; 0.3 and 0.6 weight % LiOH was fabricated by optimalisation of Spark Plasma Sintering cycle. Fully dense ceramic samples of polycrystalline magnesium-aluminate spinel with favourable optical properties in visible spectrum radiation were achieved. Real In-line Transmission RIT and Total Forward Transmittance TFT were analysed. RIT exceeded 84 % at wavelength of 633 nm and TFT exceeded 83 % at wavelength above 860 nm. The decisive factors in terms of the optical properties of ceramics sintered with sintering additives were the amount of time-spending at high temperatures and the purity of ceramic powders.
Processing of compact polycrystalline YAG ceramics
Kaplan, Lukáš ; Pouchlý, Václav (referee) ; Kachlík, Martin (advisor)
In the literary part of this master thesis a research on various methods of preparation of dense polycrystalline YAG ceramics and the effects of sintering on the densification and other desired properties of such prepared YAG ceramics was carried out, the transparency after addition of dopant elements was also discussed. In the experimental part of the thesis, samples of dense polycrystalline YAG ceramics were prepared by SSR method and the effect of sintering on the densification and porosity of the YAG ceramic samples was studied. Relative density, porosity, phase purity and transparency were measured on the sintered samples. These measurements were compared with the results of the works reported in the literature section.

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