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On the Effective Machining of New Ceramic Materials
Sámelová, Vendula ; Sedlák, Josef (referee) ; Vrba, Vladimír (referee) ; Humár, Anton (advisor)
Advanced ceramics have long held the front of the list of promising materials for high-tech applications. The most common problem is the high cost of design, production and machining of advanced ceramics parts. The main sense of advanced ceramics processing techniques development is affordable, high-volume production. The dissertation is focused on SiC silicon carbide grinding. SiC is used in the design of machine parts due to its excellent properties The deep knowledge of the diamond wheel grinding process is important because it is one of the finishing methods and therefore has a direct impact on the quality and strength of the SiC parts. The key issue here is the overall surface quality of the parts after diamond wheel grinding and the knowledge of the factors that influence the surface quality. These include, in particular, grinding vibrations. The main purpose of the thesis is to create a system of specific scientific and technical information, which will allow applying optimal technological procedures in the processing of ceramic components. The theoretical part of the thesis contains an analysis of the current state of the art in the advanced ceramics machining area, detailed analysis of the ceramics grinding with diamond grinding wheels, signal analysis theory and analysis of surface quality assessment methods. The experimental part contains analysis and discussion of the results obtained during the monitoring of the silicon carbide grinding process with a diamond grinding wheel. Various diagnostic methods have confirmed the presence of vibrations at a frequency close to the speed frequency of the grinding wheel, which had a significant, negative effect on the samples surface quality. Vibration diagnostics has identified a specific source of vibration (clamping of the workpiece) and it has been removed subsequently.
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Processing of Electroceramic Materials for Advanced Applications
Kachlík, Martin ; Petzelt, Jan (referee) ; Bartoníčková, Eva (referee) ; Maca, Karel (advisor)
Disertační práce se zabývá přípravou pokročilých keramických materiálů se zajímavými fyzikálními vlastnostmi. Materiály, připravené v rámci této práce, byly vyrobeny tuho-fázovými popř. hydrotermálními syntézami. První ze zkoumaných materiálů je elektrokeramika EuTiO3 s perovskitovou mřížkou. Absence termodynamických dat tohoto systému vedla k rozsáhlému experimentálnímu výzkumu vhodných podmínek jeho přípravy. Tři směsi práškových prekurzorů (Eu2O3 s Ti2O3 nebo TiO2 – rutil či anatas) byly homogenizovány mletím v planetovém mlýnu a formovány izostatickým tlakem 300 MPa. Vzniklé keramické polotovary diskového tvaru byly slinovány konvenčními metodami v redukčních atmosférách (Ar + 7 % H2 nebo pouze čistý H2) popř. pokročilou slinovací metodou Spark Plasma Sintering (SPS). Následně byl studován vliv slinovací metody, teploty, složení atmosféry a prodlevy na finální hustotu a fázovou čistotu vzorků. Tento výzkum vyústil v úspěšnou přípravu jednofázové EuTiO3 objemové keramiky s relativní hustotou vyšší než 95 % teoretické hustoty (%TH). S ohledem na dostupnou literaturu jsou tyto materiály jedinými publikovanými vzorky fázově čisté EuTiO3 keramiky s tak nízkou porozitou. Důležitost těchto výsledků je podložena čtyřmi publikacemi v impaktovaných časopisech, kde byly vlastnosti měřené na těchto vzorcích prezentovány. Spektra infračervené odrazivosti byla porovnána s výsledky v literatuře. Byla tak demonstrována nezbytnost fázově čistých vzorků s minimálním porozitou pro měření jejich reálných (neovlivněných) fyzikálních vlastností. Další výzkum byl zaměřen na hydrotermální syntézu (HTS) keramického prášku Eu0,5Na0,5TiO3. Prezentované HTS byly uskutečněny ve vysoce zásaditém prostředí vodných roztoků NaOH nebo KOH při teplotách 220 – 250 °C. Experimenty s různými koncentracemi prekurzorů (EuCl3 a TiCl4) a redukčních činidel vedly k přípravě jednofázového práškového perovskitu Eu0,5Na0,5TiO3 s krychlovými částicemi s rozměry pod 1 m. Jiný titaničitan - MgTiO3 – byl syntetizován tuho-fázovou reakcí směsi práškových prekurzorů MgO a TiO2. Směsi byly mechanicky aktivovány v kulovém mlýnu po dobu 0, 10, 40, 80 nebo 160 min. Keramická tělesa byla slinována pomocí dvou různých přístupů a to buď metodou Two-step Sintering (TSS) na teplotách 1300 °C (30 min) a následně 1200 °C (20 h) nebo nejprve konvenčním slinováním při 1300 °C popř. 1400 °C po dobu 30 min a poté ještě pomocí metody Hot Isostatic Press (HIP) na 1200 °C popř. 1280 °C. V případě HIP-ovaných vzorků při 1280 °C po 3 hodiny v inertní Ar atmosféře o tlaku 200 MPa byly získány fázově čisté keramické vzorky MgTiO3 s relativní hustotou nad 93 %TH. Poslední z prezentovaných materiálů je Ba(Ca)Ti(Zr)O3 bezolovnatá piezokeramika, která byla připravena tuho-fázovou reakcí práškových směsí mletých v planetovém kulovém mlýnu za rozdílných podmínek. Keramická tělesa lisovaná izostatickým tlakem (300 MPa) byla dále zhutněna beztlakým slinováním na teplotách 1200, 1300, 1400 popř. 1500 °C po dobu 1 h na vzduchu. Byly studovány potřebné podmínky pro přípravu jednofázové perovskitové Ba0,85Ca0,15Ti0,9Zr0,1O3 keramiky s požadovanou mikrostrukturou. Úspěšně tak byly připraveny vzorky fázově čisté Ba(Ca)Ti(Zr)O3 keramiky o relativní hustotě až 96 %TH. Prezentované výsledky potvrzují význam volby vhodné metody výroby a potřebných parametrů k získání pokročilých elektrokeramických materiálů s požadovanou mikrostrukturou i fázovým složením a tudíž i pro správné stanovení jejich fyzikálních vlastností.
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Non-conventional sintering of advanced ceramic materials
Suchý, Václav ; Kachlík, Martin (referee) ; Pouchlý, Václav (advisor)
This bachelors thesis deals with non-conventional sintering methods of advanced ceramic powders. The theoretical research on the topic of sintering and ceramics materials was done in the first part of this work. The end of theoretical section is devoted to the non-conventiolan sintering methods of ceramic powders. Experiments of sintering ceramic powders (cubic ZrO2 doped by 3mol% Y2O3) enhanced by electromagnetic field were made in practical part of this work. Specifically the method of Flash sintering was used. Results confirmed that it is possible to use Flash sintering method for making advanced ceramics. The material made by this technique had relative density of 95,9% and grain size of 0,22m.
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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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Sintering of Advanced Ceramic Materials
Pouchlý, Václav ; Svoboda, Jiří (referee) ; Ptáček, Petr (referee) ; Maca, Karel (advisor)
Sintering is a one of the key step in a processing of bulk ceramic materials. New sintering methods were invented in the last years. These new sintering methods, according to their authors, can be used for obtaining finer final microstructure of ceramics only by modifying the heating schedule. This work is focused on an influence of the Two Step Sintering method on the final microstructure for oxide ceramics. Obtained experimental results have shown that the effectivity of the Two Step Sintering method is rising with crystallographic symmetry of used material. Thesis is also focused on a high-temperature dilatometry and concept of the Master Sintering Curve. This concept was used for calculation of the activation energy of sintering and finding different sintering mechanisms acting in the intermediate and final stage of sintering. Activation energy of sintering was compared with activation energy of grain growth with target to find the kinetic window. Kinetic window can allow a sintering without a grain growth. Master Sintering Curve method was also used in a pressure assisted unconventional sintering technique Spark Plasma Sintering. Master Sintering Curve applied to a Spark Plasma Sintering technique reveals and quantified different sintering mechanisms acting in Spark Plasma Sintering. These findings led to preparation of transparent tetragonal ZrO2.
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Advanced Heterostructured Ceramic Materials
Drdlík, Daniel ; Lapčík,, Lubomír (referee) ; Veselý, Michal (referee) ; Cihlář, Jaroslav (advisor)
The doctoral thesis is orientated to preparation of advanced ceramic materials by electrophoretic deposition (EPD). The vertical mode of EPD in constant current regime was used in this study. The morphology of prepared materials (image structural analysis), physical properties (EPD yields, relative density, roughness of deposit surface) and mechanical properties (hardness, fracture toughness, elastic module) were characterized on the prepared deposits from alumina (Al2O3), zirconia (ZrO2) or their composites. It was found that the surface charge of alumina or zirconia particles was opposite (inversion charge) in stabilized isopropanolic dispersions than in case of water dispersions. The model of alumina or zirconia particles “inverse” stabilization was proposed. This type of EPD was further studied in presence of different acidic stabilizers. The obtained results from the experimental work (-potential and electric conductivity of dispersions, EPD yields, relative density of deposits, roughness of deposit surface etc.) showed the monochloracetic acid as the optimal type of acidic stabilizer. The kinetic of EPD process from dispersions containing isopropanol, monochloracetic acid and Al2O3 or ZrO2 particles and its influence on the final properties of prepared deposits was studied. The new method of kinetic measurement was developed. Due to good knowledge of EPD kinetic the ceramic laminates (Al2O3/ZrO2) with optimized layer thickness were prepared. The internal stresses and their influence on crack trajectory in ceramic laminates contained 100-150 strongly bonded layers were studied. It was found that the dominant role of crack deflection played the internal compressive stresses, i.e. with increasing of amount of internal compressive stresses the crack deflection was also increased. This work brought a new knowledge in the area of non-aqueous ceramic dispersion stabilization and preparation of heterostructured ceramic materials.
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Influence of uniaxial pressing conditions on final ceramics aimed for ballistic applications
Malý, Martin ; Roleček, Jakub (referee) ; Kachlík, Martin (advisor)
This bachelor thesis is a literary research on the preparation of advanced ceramics with a focus on the uniaxial pressing. The focus is also on the literary review of personal ballistic protection. The experimental part of the thesis was dedicated to the preparation of the Al2O3 ceramics by uniaxial pressing. Relative green density and relative density of sintered samples were measured. The acquired results were discussed in terms of impact of the dimension of the green bodies, pressing pressure and endurance of the pressing pressure. Hardness according to Vickers was measured in a group of chosen samples. The result of the experimental part was successful determination of optimal parameters for the process of uniaxial pressing in terms of relative density and achieved hardness of sintered Al2O3 material. Advanced ceramics prepared this way are suitable for ballistic protection.
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The printing of the complex shapes by DLP technology from the ceramic materials
Popek, Tomáš ; Roleček, Jakub (referee) ; Spusta, Tomáš (advisor)
This work is focused on the characteristics of advanced ceramics, the basic principles of the 3D printing, and the division of methods for the 3D printing of ceramic materials. It also discusses the removal of the binder from the printed samples, subsequent sintering, and associated TGA analysis and high-temperature dilatometry. Al2O3 ceramic powder was used to print ceramic components, from which two suspensions with a weight fill of 60 and 65 % were prepared. These components have been progressively subjected to TGA analysis and high-temperature dilatometry. The results of the two measurements were used to determine the debinding and sintering cycle. Debinding took place in a vacuum at 410 . As a result, the weights decreased to 63.91 ± 0.45% and 68.62 ± 1.08% of the original weights. The parts were sintered for 120 minutes at 1550 and then the relative densities were measured, which were 87.89 ± 1.05 % and 88.36 ± 0.81 %. The complex components were a turbine with a height of h = 4.4 mm and a diameter of d = 27 mm, a hexagon head screw with a length of 20 mm and an M8 thread, and a nut with a height of 6.5 mm and a width of 13 mm with an M8 thread.
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Application of 3D printing for prepartion of advanced ceramic materials
Klusáček, Martin ; Kachlík, Martin (referee) ; Salamon, David (advisor)
In this bachelor thesis there are summarized main 3D printing methods of advanced ceramics. They are compared and their advantages and disadvantages are mentioned. In experimental part of this thesis two different ceramic suspensions were prepared and used for automated silicon form casting and direct 3D printing with financially available 3D printer. The analysis of results was based on reproducibility of the method and sample relative density. The mass accuracy of 5,3 % was reached. It was found out, that the relative density of samples over 98 % can be achieved with accuracy of 1 %.
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The printing of the complex shapes by DLP technology from the ceramic materials
Popek, Tomáš ; Roleček, Jakub (referee) ; Spusta, Tomáš (advisor)
This work is focused on the characteristics of advanced ceramics, the basic principles of the 3D printing, and the division of methods for the 3D printing of ceramic materials. It also discusses the removal of the binder from the printed samples, subsequent sintering, and associated TGA analysis and high-temperature dilatometry. Al2O3 ceramic powder was used to print ceramic components, from which two suspensions with a weight fill of 60 and 65 % were prepared. These components have been progressively subjected to TGA analysis and high-temperature dilatometry. The results of the two measurements were used to determine the debinding and sintering cycle. Debinding took place in a vacuum at 410 . As a result, the weights decreased to 63.91 ± 0.45% and 68.62 ± 1.08% of the original weights. The parts were sintered for 120 minutes at 1550 and then the relative densities were measured, which were 87.89 ± 1.05 % and 88.36 ± 0.81 %. The complex components were a turbine with a height of h = 4.4 mm and a diameter of d = 27 mm, a hexagon head screw with a length of 20 mm and an M8 thread, and a nut with a height of 6.5 mm and a width of 13 mm with an M8 thread.
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