Coextrusion of laminated ceramic bodies

V diplomové práci byl vypracován literární přehled metody termoplastické koextruze a na jeho základě bylo studováno vytlačování homogenních a jednovrstevných keramických těles na bázi materiálů ZrO2, Al2O3, ZTA a ATZ. Pro termoplastické vytlačování byl upraven kapilární reometr, navrženy a vyrobeny vytlačovací trysky. Metodou termoplastické koextruze byly připraveny homogenní keramické tyčinky a jednovrstevné tyčinky se strukturou jádro/vrstva: ZrO2/Al2O3, ZrO2/ATZ a ZTA/Al2O3. U vrstevnatých těles byla hodnocena kvalita rozhraní a defekty vznikající při zpracování. Pro zhodnocení struktury a defektů vrstevnatých těles byly využity technologické parametry a vlastnosti homogenních těles připravených z jednotlivých materiálů. Termoplastickou koextruzí bylo možné připravit keramické jednovrstevné tyčinky se strukturou jádro/vrstva: ZrO2/ATZ a ZTA/Al2O3 o průměru ~ 2,5 mm a délce ~ 45 mm s drobnými defekty.In the diploma thesis, an overview of the existing literature focused on the thermoplastic co-extrusion method was worked out and based on the findings, extrusion of the monolayer and homogenous bodies from ZrO2, Al2O3, ZTA a ATZ was studied. For thermoplastic extrusion the capillary rheometer was modified and the nozzle was designed and fabricated. Applying the co-extrusion method, homogenous ceramic rods and monolayer rods in structure core/layer: ZrO2/Al2O3, ZrO2/ATZ and ZTA/Al2O3 were fabricated. In monolayer rods, the interface quality and defects that originate during preparation were evaluated. Technological parameters and properties of homogenous rods were used to rate the structure and defects in monolayer rods. Monolayer rods ZrO2/ATZ and ZTA/Al2O3 with 2.5 mm diameter and 45 mm length (containing small defects) were prepared by thermoplastic co-extrusion.

Thermoplastic extrusion of ceramic materials with ionic and mixed conductivity

V bakalářské práci byl vypracován literární přehled metody termoplastického vytlačování a na jeho základě byly optimalizovány podmínky pro extruzi směsí oxidu zirkoničitého pro výrobu tyčinek s požadavkem na rozměrovou a tvarovou přesnost keramického dílu. Keramické směsi byly připraveny dvěma způsoby – pomocí hnětení a rozpouštěním. Způsoby přípravy se porovnávaly na základě výsledků reologických měření tokových vlastností, mikrostruktury a rozměrové přesnosti slinutých tyčinek. Po ověření přípravy směsi rozpouštěním byl tento způsob použit pro přípravu směsí s rozdílným obsahem celulózy a pojiva.In the bachelor thesis, an overview of the existing literature focused on thermoplastic extrusion method was worked out and based on the findings; the conditions for extrusion of mixtures with zirconia were optimized in order to produce rods. Great attention was paid to dimensional and shape precision of ceramic parts. Two methods were applied when preparing the ceramic mixtures – mixing and dissolving. These methods have been compared on the basis of the results achieved in rheological measurements of flow properties, microstructure and dimensional accuracy of the sintered rods. Having verified the efficiency of mixture dissolving, this method was used to prepare mixtures with different contents of cellulose and binder.

Core-Shell Ceramic Structures Prepared by Thermoplastic Co-Extrusion Method

V disertační práci byla připravena dvouvrstevná keramická tělesa s „core-shell“ geometrií pomocí metody termoplastické koextruze a na těchto kompozitních tělesech byly studovány mechanické vlastnosti. Pro studium koextruze a mechanických vlastností byly navrženy dva kompozitní systémy. První systém ZTA-A kombinoval hutné jádro ZTA (oxidu hlinitého zhouževnatěného oxidem zirkoničitým) s hutnou vrstvou Al2O3. Druhý systém ZST-Z se skládal z porézního jádra a hutné vrstvy v obou případech ze ZrO2. V práci byla studována reologie keramických termoplastických suspenzí a jejich vzájemné ovlivnění během koextruze. Následně byl studován průběh odstraňování pojiv a slinování a na základě optimalizace všech technologických kroků byla získána bezdefektní „core-shell“ tělesa. Na slinutých tělesech byly stanoveny mechanické vlastnosti (modul pružnosti, tvrdost a pevnost v ohybu). Pro odhad napětí v „core-shell“ tělesech namáhaných ohybem byl využit vztah uvažující rozdílné moduly pružnosti jádra a vrstvy. U těles systému ZTA-A došlo k navýšení pevnosti oproti pevnostem nevrstevnatých těles jednotlivých složek. Byla tedy získána tělesa s vysokou povrchovou tvrdostí vrstvy Al2O3 a navíc vykazující vysokou lomovou sílu při namáhání ohybem. U těles systému ZST Z byl snížen efektivní modul pružnosti až o 25 % oproti modulu pružnosti hutných nevrstevnatých vzorků. Stejného efektivního modulu pružnosti bylo možné u „core-shell“ těles dosáhnout při zachování výrazně vyšší lomové síly než u nevrstevnatých porézních těles nebo trubek.In the doctoral thesis, the bi-layer ceramic bodies with core-shell geometry were prepared by thermoplastic co-extrusion method and for these composite bodies the mechanical properties were studied. For study of co-extrusion and mechanical properties were designed two composite systems. First system ZTA-A combined the dense core ZTA (zirconia-toughened alumina) and the dense shell Al2O3. Second system ZST-Z consisted of porous core and dense shell made from ZrO2 for both cases. In the thesis, the rheology of ceramic thermoplastic suspensions and their mutual influence during co-extrusion was studied. Subsequently, the debinding process and sintering were studied, and based on the optimization of all process steps were obtained defect-free bodies with core-shell geometry. The mechanical properties (elastic modulus, hardness and bending strength) were determined for sintered bodies. To estimate the stress path in the core shell bodies loaded in bending, the relationship considering different elastic moduli of the core and the shell was used. For bodies of ZTA-A system was increased the strength in comparison with monolithic bodies of the individual components. Thus, bodies with high surface hardness of shell from Al2O3 and moreover having high fracture strength in bending were obtained. The effective elastic modulus was decreased for bodies of ZST-Z system up to 25 % in comparison with the elastic modulus of dense monolithic samples. The same effective modulus of elasticity was possible to achieve with core-shell bodies while maintaining significantly higher fracture strength than monolithic porous bodies or pipes.

Machinability and properties of zirconia ceramics prepared by gelcasting method

The machinability of newly developed zirconia ceramics for computer numerically controlled milling (CNC) was investigated. The zirconia blanks were prepared by the gelcasting method and tested in the green and two pre-sintered states. All blanks exhibited uniform sintering shrinkage in all directions. The blanks were investigated from the viewpoint of surface milling roughness, quality of milled edges and sharp tips, and machinability of thin structures. The best milling results were obtained for the blanks pre-sintered at 900?C/1?h. Mechanical properties of zirconia blanks, such as biaxial flexural strength, microhardness, indentation elastic modulus, and fracture toughness were determined in the green and pre-sintered states (900 and 1100?C/1?h) and the correlation with the milling results was discussed. The biaxial strength tests of sintered discs showed the advantage of optimised surface milling over conventional polishing

Transparent LiOH-doped magnesium aluminate spinel produced by spark plasma sintering: Effects of heating rate and dopant concentration

The effects of LiOH doping of magnesium aluminate spinel powders and various Spark Plasma Sintering (SPS) schedules on densification behavior and final transparency of polycrystalline magnesium aluminate spinel were studied. Two commercial magnesium aluminate spinel powders, with different specific surface areas, were doped with up to 0.6 wt% of LiOH and consolidated using SPS with slow (2.75 °C/min) and fast (100 °C/min) heating rates. The slow heating rate was optimal for undoped magnesium aluminate spinel (LiOH-free) with the best real in-line transmittance (RIT) of 84.8% (measured at 633 nm on a disc 0.8 mm thick). For the magnesium aluminate spinel doped with 0.3 wt% of LiOH, the fast heating rate was beneficial, and an RIT of 76.5% was achieved. μ-Raman analysis confirmed that the addition of LiOH suppressed carbon contamination

Structure Tuning and Electrical Properties of Mixed PVDF and Nylon Nanofibers

The paper specifies the electrostatic spinning process of specific polymeric materials, such as polyvinylidene fluoride (PVDF), polyamide-6 (PA6, Nylon-6) and their combination PVDF/PA6. By combining nanofibers from two different materials during the spinning process, new structures with different mechanical, chemical, and physical properties can be created. The materials and their combinations were subjected to several measurements: scanning electron microscopy (SEM) to capture topography; contact angle of the liquid wettability on the sample surface; Raman spectroscopy; X-ray photoelectron spectroscopy (XPS); and Fourier-transform infrared spectroscopy ({FT-IR}) to describe properties and their changes at the chemical level. Crystallization events were determined by differential scanning calorimetry (DSC). Furthermore, the contact angle of the wettability of the liquid on the surface was measured for the materials, and the permittivity was measured to observe the dielectric properties. The advantage of the addition of co-polymers was to control the properties of PVDF samples and understand the reasons for the changed functionality. The innovation point of this work is the complex analysis of PVDF modification caused by mixing with nylon PA6. Here we empathize that the application of nylon during the spin influences the properties and structure (polarization, crystallization) of PVDF

Coextrusion of laminated ceramic bodies

In the diploma thesis, an overview of the existing literature focused on the thermoplastic co-extrusion method was worked out and based on the findings, extrusion of the monolayer and homogenous bodies from ZrO2, Al2O3, ZTA a ATZ was studied. For thermoplastic extrusion the capillary rheometer was modified and the nozzle was designed and fabricated. Applying the co-extrusion method, homogenous ceramic rods and monolayer rods in structure core/layer: ZrO2/Al2O3, ZrO2/ATZ and ZTA/Al2O3 were fabricated. In monolayer rods, the interface quality and defects that originate during preparation were evaluated. Technological parameters and properties of homogenous rods were used to rate the structure and defects in monolayer rods. Monolayer rods ZrO2/ATZ and ZTA/Al2O3 with 2.5 mm diameter and 45 mm length (containing small defects) were prepared by thermoplastic co-extrusion

Overview of the Current State of Gallium Arsenide-Based Solar Cells

As widely-available silicon solar cells, the development of GaAs-based solar cells has been ongoing for many years. Although cells on the gallium arsenide basis today achieve the highest efficiency of all, they are not very widespread. They have particular specifications that make them attractive, especially for certain areas. Thanks to their durability under challenging conditions, it is possible to operate them in places where other solar cells have already undergone significant degradation. This review summarizes past, present, and future uses of GaAs photovoltaic cells. It examines advances in their development, performance, and various current implementations and modifications