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Electrospinning of ceramic fibers
Nemčovský, Jakub ; Kaštyl, Jaroslav (referee) ; Částková, Klára (advisor)
This diploma thesis focuses on the fabrication of ceramic fibres by electrospinning. The theoretical part of the thesis summarizes the currently available information regarding ceramic fibres, their properties, applications and fabrication. The theoretical part also describes the process of electrospinning as one of the most frequently used methods of nanofibre fabrication, as well as the parametres influencing this process. The experimental part is aimed at the fabrication of ceramic fibres based on titania, pure non-doped zirconia and yttria-doped zirconia by electrospinning and at the characterization of thus fabricated fibres. Ceramic precursors based on propoxide and polyvinylpyrrolidone were subjected to electrospinning. The experimental part of this diploma thesis also describes the influence of precursor composition, process conditions and calcination temperature on the morphology and phase composition of the fibres. Precursors were characterized by viscosity measurements. Thermogravimetric analysis (TGA), Röntgen analysis (RTG) and scanning electron microscopy (SEM) were used to describe the fibres. By performing electrospinning of precursors based on titanium propoxide and subsequent calcination at 500-1300 °C, TiO2 fibres with thickness of 100-2500 nm were fabricated. The phase composition changed with calcination temperature from 500 °C from anatase phase through rutile blend to pure rutile at 900 °C. By performing electrospinning of precursors based on zirconium propoxide and subsequent calcination at 550-1100 °C, 0 – 8 mol% Y2O3 doped ZrO2 fibres with thickness of 50-1000 nm were fabricated. An analysis of fibres based on non-doped ZrO2, calcined at 550 °C showed a composition of predominantly monoclinic phase. An analysis of 3 or 8 mol% Y2O3 doped ZrO2 fibres calcined at 900 °C showed a composition of predominantly tetragonal phase or purely cubic phase, respectively. With the increasing calcination temperature, the morphology of the fibres changed from porous nanostructure to chain-like non-porous structure consisting of micrometer grains of TiO2 or ZrO2. The ZrO2 fibres calcined at 700 °C remained flexible as well as the spun ones, while their fragility increased with the increase in calcination temperature.
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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.
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Study of bioceramic materials for dental applications
Lokvenc, Martin ; Matoušek, Aleš (referee) ; Novotná, Lenka (advisor)
This thesis deals with bioceramics used in dentistry. The biocompatibility, which is the characteristic property of biomaterials, is described in the opening chapter of the thesis. Advantages and disadvantages of advanced ceramics are also discussed. The main attention was paid particularly to the dental bioceramics, which can be divided according to different criteria. The used classification was based on microstructure, which significantly influences behaviour and properties of biomaterials. The ceramic is viewed as a composite material, where the glass matrix is filled with different amount of crystal phase. The thesis also includes the use of the individual types of bioceramics for the manufacture of dental restorations.
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Influence of parameters of electrophoretic deposition on properties of ceramics
Husák, Roman ; Čelko, Ladislav (referee) ; Hadraba, Hynek (advisor)
Electrophoretic deposition is experimentally undemanding shaping method enabling preparation of ceramic material from stable suspension of ceramic particles by means of direct electric current. The aim of the work was to describe effect of electric current magnitude on velocity and final microstructural and mechanical properties of the ceramics. The alumina and zirconia layers were prepared by electrophoretic deposition from stable suspensions of ceramic particles in the isopropanol stabilised with monochloracetic acid. It was found that the real time dependance of particle deposition differs from the theoretical predisction for given electrical conditions. By precise measurement of kinetics of the electrophoretic deposition the actual electrophoretic mobility of the particles and the actual amount of particles taking part in the deposition process were found. It was found that with increasing the electrical current the actual electrophoretic mobility was decreased and actual amount of particles taking part in the deposition process was increased. The increasing velocity of particles under higher electrical currents led to the detorioration of particle arrangement in the elctrode and thus to the increasing of the pore sizes and final densities of the deposits. These microstructural changes reflected in the lowering of the hardness of the deposited ceramics of about 300HV5 in the case of alumina.
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Bioceramic Materials and Their Biocopatibility with Bone Tissues
Novotná, Lenka ; Trunec, Martin (referee) ; Cihlář, Jaroslav (advisor)
The thesis concerns the study of ceramic coatings of zirconia nanoparticles deposited on alumina, zirconia and glass substrates by ultrasonic spraying. The quality of deposits was investigated in dependence on the type of substrate (composition, temperature, roughness) and concentration of ceramic suspension. The best results were received by the deposition of suspension of low concentration on rough substrates at low temperatures. The biocompatibility was tested in vitro. Good cytocompatibility of ceramics with nanostructure coatings was found.
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Abrasives and possibilities of increase in efficiency of abrasive waterjets
Martinec, Petr ; Sitek, Libor
The contribution focuses on the research into abrasive materials and possibilities of adjustment of their properties in order to increase the efficiency of the processes of machining and cutting with abrasive waterjets. Cutting ability of commonly available garnet concentrates and nontraditional products which are starting to access to the Czech market were tested and compared. In addition, entirely new garnet products which are not commercially available yet, recycled abrasives, abrasives with various sizes of grains and heat-affected abrasives or abrasives coated with a thin plastic layer were studied.
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Příprava a charakterizace tenkých vrstev oxidů zirkonu a titanu
Krejčíková, Simona ; Matějová, Lenka ; Matěj, Z. ; Jirkovský, Jaromír ; Šolcová, Olga
Titania and zirconia belong to nanoporous materials with huge application potential in photocatalysis, dye-sensitized photoelectrochemical cells, electrochromic devices, sensors and other applications, especially in the form of nanolayers. Differences in surface morfology, texture and crystallinity influence their catalytic impact. Therefore special attention is focused on the detailed textural and structural characterizations of thin titania-zirconia nanolayers prepared by sol-gel templated route.
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Plazmové stříkání nanokeramiky - oxidu hlinitého a zirkoničitého
Chráska, Tomáš ; Neufuss, Karel ; Nohava, Jiří ; Dubský, Jiří
A novel material has been plasma sprayed by water stabilized plasma torch (WSP®) in order to achieve nanocrystalline microstructure. The new material is composed of three main compounds, namely corundum (alpha Al2O3), baddeleyite (monoclinic ZrO2), and glassy phase (SiO2). The ratio of Al2O3 – ZrO2 compounds is close to that of their respective eutectic alloy. Both dense coatings and free standing parts were produced with the new material, which sprays very well by WSP®. Spraying parameters were varied and molten particles were monitored in flight. The coatings exhibit very low porosity and high hardness. The as-sprayed material is mostly amorphous with some nanocrystalline grains of aluminum and zirconium oxide present. The microstructure of the newly sprayed material was studied by electron microscopy (SEM, TEM) and was found to be very complex. Upon annealing, the as-sprayed material fully crystallizes at around 950ºC. Selected mechanical properties were measured as well.
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