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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.
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Study of the synthesis and processing conditions on the structure and properties of (Ba,Ca)(Ti,Zr)O3 lead-free ceramics
Bijalwan, Vijay ; Liedermann, Karel (referee) ; Olhero,, Susana Maria Henriques (referee) ; Button, Timothy William (advisor)
V poslední době je snahou nahradit klasickou komerční olovnatou piezoelektrickou keramiku bezolovnatou, z důvodu zvýšeného zájmu o ochranu životního prostředí a zdraví. Různé typy materiálů již byly navrženy, jako například (K, Na) NbO3 (KNN), (Bi, Na) TiO3 (BNT), (Bi, Na) TiO3 – BaTiO3 (BNT-BT), ale jejich piezoelektrické vlastnosti zatím nedosáhly takových hodnot jako u olovnatý chkeramik (např. olovnatý titanát olova ((Pb Zr)TiO3). Nejvíce se olovnatým materiálů blíží bezolovnatý systém na bázi (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 nebo (Ba, Ca) (Zr, Ti) O3 ((1-x)BZT-xBCT, BCZT) a to díky vysokým piezoelektrickým a dielektrickým parametrům. Nevýhodou tohoto prostředku je jeho velmi vysoká teplota slinování (1520 ° C) za účelem dosažení vysokých piezoelektrických vlastností (např. Piezoelektrické konstanty d33 > 600 pC / N). Tato práce se zabývá bezolovnatou keramikou na bázi BCZT, její výrobou a vylepšením piezoelektrických vlastností dopováním CeO2. Přidáním CeO2 (y wt.%) do (Ba0.85Ca0.15) (Zr0.1Ti0.9) O3 se výrazně snížila slinovací teplota a došlo ke zhutnění při 1350°C. U této kompozice se Curieova teplota pohybovala kolem TC~105°C a velikost zrn byla v rozmezí ~ 10-13 m. Fázový přechod z romboedrické struktury na tetragonální (R-T) byl zjištěn pomocí rentgenové spektroskopie u y = 0 - 0.1 wt.%, což koreluje s výsledky Ramanovy spektrální analýzy. Mikrostrukturní a strukturní charakteristiky byly detailně studovány v korelaci s dielektrickými, feroelektrickými a piezoelektrickými vlastnostmi. Nejlepší funkční vlastnosti byly dosaženy pro keramiku BCZT – 0.07 wt.% CeO2. Tato keramika vykazovala piezoelektrický nábojový koeficient d33 = 507±20pC/N, elektromechanický planární koeficient kp = 51.8 %, dielektrickou konstantu r = 4091±100, ztrátový činitel tan = 0.02, remanentní polarizaci Pr = 13.58C/cm2, intenzitu koercitivního pole EC = 2.13kV/cm při normovaném napětí, d33* nebo Smax/Emax = 840pm/V. Dvoustupňovou kalcinační technikou bylo docíleno homogenního růstu zrn s vysokou relativní hustotou (~ 99% teoretické hustoty). Tato kompozice BCZT- CeO2 vykazovala stálé feroelektrické, dielektrické a piezoelektrické vlastností i při velikosti zrn 10 µm. Bezolovnatá piezoelektrická keramika (Ba0.85Ca0.15-y Cey) (Zr0.1Ti0.9) O3 (BCCeZT) byla dále dopována CeO2 s cílem substituce Ce4+ v místě A krystalické mřížky. Posunutí rentgenových vrcholů k vyšším úhlům naznačuje kontrakce mřížky, což by mohlo způsobit obsazení iontů ceru v místech A této soustavy. Bylo zjištěno, že velikost zrn kolem 10 - 12 m je významná pro vysokou piezoaktivitu bezolovnaté BCCeZT keramiky. Nejvyšší piezoelektrické vlastnosti tato keramika vykazovala při y;Ce = 0.00135 a slinovaná na teplotě 1350°C/4h, kdy piezoelektrické parametry byly d33 = 501±10 pC/N, kp = 38.5±1.92 %, Pr = 12.19 C/cm2, TC = 108.1 °C a s maximální deformací S do 0.14 %. Pro další studium substituce v místě A, byly vyrobeny keramické materiály (Ba1-x-y Cax Cey) (Zr0.1 Ti0.9) O3 (x:Ca = 0.05, 0.10, 0.15, 0.20 a y;Ce = 0.00135). Opět se ukázalo, že pokud byla velikost zrn ~13um, tak keramika vykazovala vysoké piezoelektrické vlastnosti (d33 = 457pC/N) pro x = 0.15 % kalcinované na teplotě 1425 °C. Když se se velikost zrn zvýšila nad 16 um, piezoelektrický nábojový koeficient d33 klesl na 200 pC/N. Rentgenová analýza ukázala změnu fázové struktury z rombické na tetragonální při zvýšení obsahu vápníku.
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Biodegradable bone implants based on iron
Müller, Petr ; Kazda, Tomáš (referee) ; Sedlaříková, Marie (advisor)
The present work deals with the comparison of the properties of metallic biomaterials in terms of their suitability for use as a temporary metal implant. In the work is judged biocompatibility of materials, they are comparing the corrosion rates and the influence of additives in the iron alloy to change biocompatibility and corrosion rate. In a part of this work is suggesting a method of preparing biodegradable metallic samples with different alloying elements and determine the methods, processes and measuring the corrosion rates. Part of this work is the chapter dealing with the function and effect of iron in the human body and any complications that may occur when a surplus caused by the release of part of the implant during its degradation or corrosion products. The outcome of this work is sort of created an iron-based samples in terms of their electrochemical corrosion potential, corrosion rate of samples exposed in various corrosive solutions, spectroscopic elemental analysis and outputs from the microscopic observation of the structures.
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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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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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Machining of ceramic bodies using CAD-CAM
Kaplan, Lukáš ; Částková, Klára (referee) ; Kaštyl, Jaroslav (advisor)
The literature part of bachelor's thesis deals with ceramic materials based on Al2O3 and ZrO2, methods of sample preparation for consequent machining, different methods of machining, especially the technology of CNC machining in non-sintered and sintered state with their comparison. The thesis presents possible examples of the use of ceramic parts. The experimental part of the thesis deals with the machining of ceramic based on ZrO2 using different types of ceramic powders, methods of preparation and the choice of the sintered temperature in relation to its properties. The best results were achieved with SZ-3Y ceramic material sintered at 1550 °C for 2 hours, strength values were 1203 MPa, roughness of surface Ra was 126 nm a grain size was 382 nm.
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The effect of modification of cermic surface on the sintering of advanced ceramic materials
Vykydal, Adam ; Spusta, Tomáš (referee) ; Pouchlý, Václav (advisor)
This thesis is focused on the effect of modification of ceramic surface on the sintering of the advanced ceramic materials. To modify the surface of ceramic materiál was used method atomic layer deposition. For the research we used materiál TiO2 and materiál TiO2, which was modified using gas in an ALD chamber. To determine the appropriate sintering temperature we used high-temperature dilatometry, where we found that the sintering temperature is about 800 °C. Moreover, the coefficient of thermal expansion (CTE) was determined using subsequent calculation with the data of shrinkage from sintering densification curve. The samples were placed in a kiln where they were sintered on the mentioned temperature on four different dwell times to find effective dwell time for the best value of density of material. Using a scanning electron microscope, the surface-modified material was found to have a uniform structure when sintered to 800 ° C. At a sintering temperature of 1500 ° C, it can be observed that the ZrO2 did not remain only at the grain boundaries, but is more or less evenly distributed. The core-shell structure was not preserved in the structure, however ZrO2 was agglomerated into particles and in the vicinity of these particles titanium dioxide and zirconia react according to the phase diagram. Based on the diagram, it can be stated that this is the ZrTiO4 phase. The occurrence and size of this pase can be verified by RTG analysis.
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Powder Metallurgy and Fundamentals of Sintering Process
Foltýnek, Jaroslav ; Pouchlý, Václav (referee) ; Čelko, Ladislav (advisor)
The bachelor thesis deals with the powder metallurgy and sintering process of metallic materials. The work is a recherche on this topic and includes a basic comprehensive insight into the entire production process consisting of the overview on the material powder processing techniques, introduction of the basic parameters of sintering process and mechanisms involved during sintering influencing the final compact product formation. The sintering process is in work divided into two basic categories, solid state and liquid-phase sintering.
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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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