|
|
Influence of plasma activation of ceramic particles on ceramic technology and properties
Klevetová, Tereza ; Ráheľ,, Jozef (referee) ; Pouchlý, Václav (advisor)
This thesis is focused on the study of the influence of plasma activation of powder ceramic materials on sintered microstructure. In this experiment Diffuse Coplanar Surface Barrier Discharge (DSCBD) device was used for plasma treatment and two materials were chosen to be investigated – Al2O3 (TAI) and ZrO2 doped with 3 mol % Y2O3 (TZ). Two methods of powders dispergation in suspension were used – ultrasound and ball milling. The effect of using of DCSBD on alumina and zirconia powders was investigated by mercury intrusion porosimetry, dilatometry and by evaluation of final relative densities and grain sizes. Generally, was investigated that plasma surface activation of ceramic particles has measurable influence on the final microstructure. In comparison with the non-plasma treated alumina powders, plasma activated powders disperged with ultrasound and ball milling achieved lower values of grain size at comparable relative densities. In case of zirconia powders was observed that plasma treated powders achieve higher relative densities, if ultrasound was used. On the other hand, plasma treated zirconia powders disperged with ball milling achieve lower relative densities compared with non-plasma treated zirconia powders. Final sintering trajectory of plasma treated TZ powders disperged with ultrasound is comparable to the sintering trajectory of non-plasma treated zirconia powders disperged with ball milling and vice versa. Plasma surface treatment is the way of more ecological friendly preparation of suspension and its stabilization than the conventional stabilization methods using chemical additives.
|
|
|
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.
|
|
|
Milling optimization of ceramic blanks
Ráčková, Jana ; Pouchlý, Václav (referee) ; Trunec, Martin (advisor)
The master thesis deals mainly with the optimization of machining of ceramic semi-finished products from ZrO2 and Al2O3. The first part with literary research, which describes the steps of the technology of forming ceramic bodies, especially the gelcasting method. The thesis describes possibilities of milling of ceramic materials using CNC technology. The thesis describes the dependence of acquired roughness on bodies and used machining strategies. The best roughness parameters on ZrO2 samples were obtained after they were calcined at 900 ° C, while the lowest roughness was obtained on the samples in the unprotected state for the Al2O3 samples. Samples machined with a spherical milling cutter showed surface roughness Ra = 1 m for ZrO2 and Ra = 1.3 m for Al2O3. It also describes the possibility of machining sharp-edged shapes and fine details where the best results are achieved on ZrO2 samples engraved at 900 and 1100 °C. Tool wear was particularly important when machining samples of Al2O3 ignited at temperatures above 800 °C.
|
|
|
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.
|
|
|
Microstructure revealing and analysis of partially sintered oxide ceramic materials
Jemelka, Marek ; Salamon, David (referee) ; Spusta, Tomáš (advisor)
The goal of this bachelor’s thesis is to experimentally determine appropriate etching conditions for etching of partially sintered advanced ceramic materials (Al2O3, ZrO2 + 3mol % Y2O3, ZrO2 + 8mol % Y2O3) with emphasis on minimal influence on the final surface microstructure. The obtained results show, that the optimal etching way of selected materials is thermal etching under conditions: Al2O3 (rel. 95,7 ± 0,9 %)- Te = 1015 C (Ts – 350 C), tetragon. ZrO2 (rel. 94,5 ± 0,6 %)- Te = 1005 C (Ts – 350 C), cubic. ZrO2 (rel. 94 ± 0,5 %)- Te = 1105 C (Ts – 350 C). The applying of chemical etching in H3PO4 for 60s led to revealing of the microstructure of Al2O3 and cubic ZrO2 in shorter times, but the procedure carries its difficulties of etching conditions determination and execution itself, which put it in the second place. Microstructure revealing via using focused ion beam was experimentally determined as inappropriate due to time and personnel demands.
|
|
|
Composite Dental Biomaterials - Structure, Analysis and Properties
Matoušek, Aleš ; Vaněk,, Jiří (referee) ; Lapčík,, Lubomír (referee) ; Cihlář, Jaroslav (advisor)
The aim of this work is to define relations between grain size and bioaktivity of oxide ceramics, specifically ZrO2, Al2O3 and HA. Ceramic materials with grain size from 100 nm up to 10 m, with various surface roughness, were tested for its bioactivity. Ceramography analysis was performed for all tested materials to precisely describe microstructures. Biological properties of the ceramic materials were tested via dilation tests directly in-vitro and by in-vitro extraction. Three cell culturing lines: osteoblast MG63, fibroblast L929, and epithelioid HeLa, were used for our testing. An influence of the grain size on the biological response was only found for the ceramic materials which had been thermally etched. The thermally etched nanocrystalline samples had larger areas covered by cells than ceramics with coarse grain microstructure. Biological tests on layered composites Al2O3×ZrO2 showed the cell selection determined by the type of material, where ZrO2 surfaces were preferably covered. Improved biological response of nanocrystalline ZrO2 was demonstrated on ceramic ZrO2, Al2O3 and SiO2 substrates with nanocrystalline coating of ZrO2. In this work a novel technological process for the formation of defect-free coatings was developed. Sintered coatings were tested using in-vitro technique with cell line HeLa, L929 and MG63 for up to 72 hours. The results of the biological tests of nanocrystalline coatings were consistent with results from the bulk nanocrystalline thermally etched ZrO2 ceramics.
|
|
|
Study of Sintering of Nanoceramic Materials
Dobšák, Petr ; Hanykýř, Vladimír (referee) ; Havlica, Jaromír (referee) ; Šída, Vladimír (referee) ; Cihlář, Jaroslav (advisor)
The topic of the Ph.D. thesis was focused on the process of sintering alumina and zirconia ceramic materials with the aim to compare kinetics of sintering sub-micro and nanoparticle systems. Zirconia ceramic powders stabilized by different amount of yttria addition in the concentration range of 0 – 8 mol% were used. The different crystal structure (secured by yttria stabilization) of zirconia, as found, did not play statistically proven role in the process of zirconia sintering. The possible influence was covered by other major factors as particle size and green body structure, which does affect sintering in general. According to the Herrings law, the formula predicting sintering temperature of materials with different particle size was defined. The predicted sintering temperatures were in good correlation with the experimental data for zirconia ceramic materials prepared from both, coarser submicrometer, and also nanometer powders. In case of alumina ceramics the predicted and experimentally observed sintering temperature values did not match very well. Mainly the nanoparticle alumina materials real sintering temperature values were markedly higher than predicted. The reason was, as shown in the work, strong agglomeration of the powders and strong irregularities of particle shape. The major role of green body microstructure in the sintering process was confirmed. The final density of ceramic materials was growing in spite of sintering temperature, which was decreasing together with pore - particle size ratio (materials with similar particle size were compared). Sintering temperature was increasing together with growing size of pores trapped in the green body structure. Clear message received from the above mentioned results was the importance of elimination of stable pores with high coordination number out off the green body microstructure during shaping ceramic green parts. Same sintering kinetics model was successfully applied on the sintering process of submicro- and also nanometer zirconia ceramics. Activation energy of nanometer zirconia was notably lower in comparison to submicrometer material. For the sintering of nanoparticle zirconia was typical so called “zero stage” of sintering, clearly visible on kinetic curves. It was found out, that processes running in zirconia “green” material during zero stage of sintering are heat activated and their activation energy was determined. Pores of submicrometer zirconia were growing in an open porosity stage of sintering just a slightly (1.3 times) compared to the nanoparticle zirconia, where the growth was much higher (5.5 times of the initial pore diameter). This difference was most probably caused by preferential sintering of agglomerates within the green bodies and by particle rearrangement processes which appears in the zero stage of sintering of nanoparticular ceramics. The technology of preparation of bulk dense ytria stabilized zirconia nanomaterial with high relative density of 99.6 % t.d. and average grain size 65nm was developed within the thesis research.
|
|
|
Coextrusion of laminated ceramic bodies
Kaštyl, Jaroslav ; Cihlář, Jaroslav (referee) ; Trunec, Martin (advisor)
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.
|
|
|
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.
|
|
|
Propagation of inclined cracks to the interface of ceramic laminates
Novotná, Lenka ; Trunec, Martin (referee) ; Chlup, Zdeněk (advisor)
Composite materials with laminated structure provide advantages which are utilised during component design. Low density, temperature and chemical stability are the profitable properties predetermining application of ceramic laminates. The main obstacle for wide spread of ceramic materials is their inherent brittleness. Therefore, in this thesis, the crack propagation in ceramics laminates has been extensively studied. Laminated structures with various volume fractions of components (alumina and zirconia) were prepared by electrophoretic deposition. Evaluation of crack propagation through the interface and determination of basic mechanical properties was conducted on the basis of extensive literature search. Crack deflection originated in both presence of internal stresses and differences in elastic modulus during the crack interface passing was monitored. A special type of specimen geometry was employed with the aim to set arbitrary angle between crack and interface. It was experimentally found that the degree of crack deflection is dependent on entering angle and volume fraction of components. Higher crack deflection was already found in the bulk of the test piece comparing to the test piece surface. The 3D fracture surface reconstruction generated using laser confocal microscopy was used in this detailed crack propagation study. Further basic elastic and strength characteristics of laminates were determined and compared to those obtained from monolithic materials. The validity of the mix rule for elastic characteristics was confirmed by comparing of elastics modulus. The most reliable method for elastic modulus determination was marked the dynamic resonance method due to low scatter and consistency in measurement. The flexural strength of all laminates tends to be close to the flexural strength of the weakest component. Therefore the mix rule is not applicable for flexural strength estimation on the contrary of elastic characteristics. The change of component volume fraction leads only to change of flexural strength scatter. Thanks to gained knowledge about crack propagation and basic characteristic determination will be possible to design ceramic laminates more efficiently for given needs of application.
|
guest ::
