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Sintering of advanced ceramic materials
Průdek, Miloš ; Trunec, Martin (referee) ; Maca, Karel (advisor)
V předložené diplomové práci bylo studováno slinování hexagonálního Al2O3 a kubického MgAl2O4 pomocí slinovacích cyklů složených z beztlakého předslinutí metodou dvojstupňového slinování s následným doslinutím s využitím tlaku (HIPováním). Cílem bylo pokusit se snížit (při zachování vysoké dosažené hustoty) střední velikost zrn a tím zvýšit tvrdost keramiky popř. optickou transparenci. Hlavní úsilí bylo věnováno optimalizaci předslinutí pomocí různých slinovacích cyklů. Přestože bylo vyzkoušeno velké množství různých kombinací teplot a prodlev dvojstupňového slinování, nepodařilo se výrazným způsobem zvýšit výslednou tvrdost vzorků. V případě kubického MgAl2O4 bylo dosaženo hustot blížících se teoretické hustotě, což se projevilo v optické transparentnosti vzorků.
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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.
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Evolution of pores during sintering of advanced oxide ceramic materials
Spusta, Tomáš ; Kaštyl, Jaroslav (referee) ; Maca, Karel (advisor)
The goal of this bachelor’s thesis is to experimentally specify behaviour of pores in oxide ceramic materials (Al2O3, t-ZrO2, c-ZrO2), particularly to describe the transition from open to close porosity. Ceramics powders made by different producers and with different initial particle size (Al2O3 – AKP30, REYNOLDS, TAIMICRON; ZrO2 + 3 mol.% Y2O3 – TZ3Y, TZ3YSB; ZrO2 + 8 mol.% Y2O3 – TZ8Y, TZ8YSB) were used. Samples were pressed by cold isostatic pressing CIP at pressures of 100MPa and 300MPa, and pressureless sintered up to relative densities up to 88-96%. The obtained results show, that evolution is mainly affected by material, independently of size of initial particles neither by initial shaping pressure. Elimination of open pores occurs in cubic ZrO2 at 91-92 % of relative density, in tetragonal ZrO2 at 92-93 % of relative density and in Al2O3 at 94 % of relative density.
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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.
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Fast sintering of advanced ceramic materials
Prajzler, Vladimír ; Salamon, David (referee) ; Maca, Karel (advisor)
The bachelor thesis is dealing with fast sintering of advanced ceramic materials, such as tetragonal zirconia and alumina in conventional resistance furnace. This approach is made possible by special superkanthal furnace, which is capable to reach a heating rate of 200 °C/min. Samples obtained through fast sintering reached relative density higher than 93% for zirkonia and 97% for alumina, without forming any cracks in samples. Achieved relative density in the case of tetragonal zirconia was higher for samples with larger pores in the green body. This behavior is different of conventional sintering and leads to considerations of heat transfer mainly by radiation.
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Transparent ceramic materials
Krupa, Filip ; Drdlík, Daniel (referee) ; Maca, Karel (advisor)
This Bachelor thesis deals with processing of transparent cubic ZrO2 ceramic doped by 8 mol% Y2O3. Technology used in this Bachelor thesis are uniaxial pressing, cold isosatic pressing, SPS and hot isostatic pressing. Microstructure, real in-line transparency and hardness were evaluated for sintered transparent materials.
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Synthesis of functional ceramic powder materials
Čípová, Eva ; Maca, Karel (referee) ; Částková, Klára (advisor)
The theme of the work is electroceramic materials, particularly materials based on perovskites. The theoretical part describes electroceramic materials, their applications and possibilities of their synthesis. The experimental part focuses on the synthesis methods in liquid media and solid phase of barium strontium titanate. The prepared powders were characterized by morphology, phase composition and particle sinterability. It was found that weakly agglomerated particles with a single phase composition, perspective for the preparation of dense bulk ceramics, were prepared by the metod in liquid phase, especially by precipitation.
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The microstructure evaluation of advanced oxide ceramics during fast sintering
Prajzler, Vladimír ; Chlup, Zdeněk (referee) ; Maca, Karel (advisor)
The diploma thesis deals with influence of fast pressure-less sintering on the microstructure of advanced ceramic materials, namely -Al2O3 and tetragonal ZrO2 (doped by 3 mol% Y2O3) with particle sizes ranging from 60 nm to 270 nm. Fast and controlled heating rate was enabled by utilization of the special superkanthal furnace with moving sample holder. Defect-free bulk and dense samples were prepared using heating rates in order of 100-200 °C/min. Higher densities reached the samples pressed by higher pressures; the specimens with densities higher than 99 % t.d. were prepared within tens of minutes for alumina as well as for zirconia with very low thermal conductivity. Different behavior was observed only for material TZ-3Y, which exhibited core-shell structure with dense surface and porous centre after sintering at heating rates higher than 10 °C/min. It was shown in this work that such behavior was not primarily caused by the high thermal gradient resulting from high heating rates. Its creation was probably caused by chlorine impurities. The mechanism of desintering of these samples was described and eliminated by calcination of the samples at 1000 °C for 10 hours prior to fast sintering at 1500 °C, so even this material could be fast sintered up to 99.9 % theoretical density.
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Sintering of Advanced Cubic Ceramic Materials
Hrubý, Jan ; Pouchlý, Václav (referee) ; Maca, Karel (advisor)
This bachelor's thesis deals with the literature search on preparation of advanced ceramic materials. It compares the sintering and properties of cubic ceramics with ceramic materials with different crystal structures. The experimental section is devoted to preparing tetragonal ZrO2 ceramic (doped with 3 mol% Y2O3) and cubic ZrO2 ceramic (doped with 8 mol% Y2O3). These ceramics were prepared using two-step sintering combining pressure-less sintering with hot isostatic pressing (HIP). The goal was to prepare dense ceramics with homogenous microstructure. Another studied material was Y2O3 with micrometer sized particles. Microstructure and optical properties of studied materials were evaluated.
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Study of microstructure evolution during final stage of sintering of advanced ceramic materials
Hrubý, Jan ; Salamon, David (referee) ; Maca, Karel (advisor)
This diploma thesis deals with the study of microstructure development during the final stage of sintering of two zirconia based ceramic materials (tetragonal ZrO2 doped with 3 mol% of Y2O3 and cubic ZrO2 doped with 8 mol% of Y2O3). Conventional, microwave and SPS sintering methods were used. Achieved relative densities and mean grain sizes were evaluated for sintered materials. It was found that the non-conventional sintering methods are capable of rapid processing of ceramics with improved microstructure compared to conventional sintering.
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