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.

Táto práca sa zaoberá prispôsobením (tailoring) mikroštruktúry vybraných pokročilých keramických materiálov (oxid hlinitý, kubický a tetragonálny oxid zirkoničitý) metódou izostatického lisovania za tepla (post-HIPing) s cieľom pripraviť vzorky s teoretickou hustotou and minimálnou veľkosťou zŕn. Vzhľadom na to, že izostatické lisovanie je vo väčšine prípadov používané ako dokončovacia metóda, pred-slinovanie (príprava vzoriek v štádiu uzavretej pórovitosti) bolo tiež dopodrobna študované. Extenzívny teoretický a experimentálny výskum pred-sintrovania pokročilých keramických materiálov ukázal niekoľko výsledkov. Bolo zistené, že uzatváranie pórov je materiálová charakteristika riadená medzi-povrchovými energiami (uzatváranie pórov nastáva pri 92-96 % t.d. pre skúmané materiály), je nezávislé na technológii prípravy keramického polotovaru a je nezávislé na histórii sintrovacieho procesu. Pre analýzu mikroštruktúry skenovacím elektrónovým mikroskopom a výrazné zvýšenie efektivity mikroštruktúrnej analýzy, bola vyvinutá nízkoteplotná metóda termálneho leptania. Táto metóda umožňuje zviditeľnenie leštenej mikroštruktúry pri leptacej teplote 900 °C a výdrži 1 hodina čiastočne sintrovaných a plne hutných vzoriek bez teplotnej kontaminácie (zvýšenie hustoty a veľkosti zŕn). Pred-sintrované vzorky boli post-HIPované nadizajnovaným kombináciami teploty (1200-1400 °C), aplikovaného tlaku (50 a 200 MPa) a času výdrže (0,5 až 9 hodín) s cieľom štúdia vplyvu týchto post-HIPovacích parametrov na mikroštruktúru vzoriek. Najdôležitejší výsledok experimentov je, že aplikovaný tlak vykazuje iba minimálny vplyv na rast zŕn v priebehu post-HIPovania, pričom výrazne posilňuje zhutňovanie. Sintrovacia teplota a čas výdrže tiež vykazovali zhutňovací potenciál, avšak s negatívnym efektom na veľkosť zŕn počas post-HIPovania rešpektujúc kinetickú rovnicu rastu zŕn – exponenciálny rast pre teplotu a parabolický rast pre čas. Tieto výsledky boli použité pre optimalizáciu post-HIPovacích cyklov pre študované materiály. Výsledné vzorky boli zhutnené nad 99,7 % t.d. a s minimálnym (pod 10 %) nárastom veľkosti zŕn v porovnaní s pred-sintrovanou veľkosťou zŕn. Aplikáciou získaných znalostí bola pripravená transparentná korundová keramika dopovaná erbiom s fotoluminiscenčnými vlastnosťami. Pripravená vzorka s tvrdosťou HV 10 26,9 GPa a so skutočnou inline priepustnosťou RIT 56 % vykazuje najlepšie hodnoty tvrdosti a priepustnosti v doposiaľ publikovaných korundových keramických materiáloch dopovaných prvkami vzácnych zemín.

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 thesis is focused first on the research of literature on the topic of phosphate ceramics and then on the search for a suitable synthesis of phosphate binder based on Y2O3-P2O5-H2O and characterization of the resulting products. Various types of syntheses were prepared with subsequent characterization of the phase and chemical composition of the final products. The samples were measured on an electron microscope to determine their surface morphology and also element maps were obtained. The samples were also analyzed by heat microscopy to determine the temperature behavior of the samples. After measurement on a heat microscope, the samples were measured again on an electron microscope, in order to detect changes caused by the action of high temperatures, in particular to assess the presence of binder or sintered phases.

The diploma thesis is related to the preparation of hydroxyapatite complex structures by additive manufacturing known as Lithography based ceramics manufacturing – LCM. A photosensitive suspension containing hydroxyapatite particles was used for 3D printing of ceramic complex structures. The influence of printing parameters on the resulting macrostructure, microstructure, density, and dimensional accuracy was evaluated. The aim was to obtain ceramic components without delamination of the layers and optimise following post-processing steps (cleaning and thermal treatment). It was found that the exposure time has a significant effect on the dimensional accuracy of printed parts. During observation microstructure of printed parts, a microporosity at the interface of printed layers, which can cause delamination of several layers was identified. High-temperature dilatometry showed different temperature of beginning densification process in the longitudinal and perpendicular directions to the layers. That could be an initiation mechanism for delamination of the layers. X-ray diffraction analysis determined a single-phase composition of powder in photosensitive suspension and sintered parts. A commercial product LithaSol 20 was suggested as a suitable cleaning agent and efficiency of the ultrasound field for cleaning was demonstrated. Based on the thermogravimetric analysis an optimized cycle of heat treatment was designed. The optimisation led to time saving (49 hours), while maintaining density, dimensional accuracy and macrostructure of the 3D printed structures.

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.

Course of synthesis of Li2O – Al2O3 – SiO2 (LAS) ceramic via sol – gel process made precursor was investigated. Powder precursor containing LAS components in molar ratio 1:1:4 were prepared by polycondensation technique in aqueous medium using lithium chloride (LiCl), hydrated aluminium nitrate (Al(NO3)39H2O) and silica sol (tosil), respectively. Heated sol was transformed into gel. The resulting gel was dried at temperature 105 °C and xerogel was next calcinated at 750°C. Further was evaluated influence of sintering additives (MgO, ZnO, Ca5(PO4)3OH) on the length of sintering interval. All of them have been stabilized spodumene in the solid solution. The properties of ceramic body prepared by sintering of precursor and grinded Li2CO2, Al2O3 a SiO2 powders were compared. Simultaneous thermogravimety and differential thermal analysis (TG-DTA), X-ray diffractions and heating microscopy were used to study sintering process of LAS ceramic.

The goal of diploma thesis is study of the effect of thermal annealing at different temperatures and different annealing durations on the surface structure of oxide ceramics based on Al2O3 and study of the samples porosity.

This work is focused on Li ceramics and glass-ceramics with low thermal expansion. Composition of these material is based on mineralogical composition of ?-spodumene – Li2O•Al2O3•4SiO2. Sol-gel route of preparation was used for preparation of the material. Sol-gel route is profitable because of production of high purity and controlled grain size powder. Lower sintering temperature, higher degree of homogeneity and shorter time of heat treatment in comparison with traditional approach belong among other advantages of sol-gel route of preparation. Influence of Li+ substitution for K+, which has similar atomic radius, is assessed in this work. These ions are localized in the interstitial position of spodumene structure and are able to maintain the charge balance. Li+ ions were substituted with K+ in the amount of 0; 0,5; 1; 2; 5 and 10 wt. % in view of Li+ weight. In the next step influence of adding mineralizer was specified in the material modified this way. The effect of adding mineralizer on phase transformation and heat treatment tendency was considered. K+ were added to the mixture in the form of potash. Due to this addition forming of orthoclase phase next to spodumene, eucryptit and SiO2 (ss) was detected. Decrease in melting temperature and ability of melt to crystallize were consequence of orthoclase forming. No crystallization appears, when more than 1 wt.% of K+ was added.

This work deals with the fabrication of closed cavities in Low Temperature Co-Fired Ceramics (LTCC). In recent years, the LTCC ceramics have become widely used in the areas of sensors, MEMS and micro-fluidic applications. When fabricating such devices, it is important that the cavities maintain their compactness and dimensions after the manufacturing process . This is achieved primarily with the right choice of lamination process and its parameters and also by appropriate setting of the firing profile. The theoretical part describes the various steps in the production of LTCC structures and the most common technological processes used for creating structures with cavities and micro - channels . In the practical part are selected laminating procedures performed on the test pattern, which contains cavities of different sizes. Emphasis was placed on the correct execution of each method , while gradually modifying the lamination parameters. The achieved results are further discussed in terms of process parameters and their influence on the dimensions of manufactured cavities.