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Preparation of Tobermorite
Dlabajová, Lucie ; Palou, Martin (referee) ; Martinec, Petr (referee) ; Ptáček, Petr (advisor)
This doctoral thesis is focused on the study of reactions in the CaO–SiO2–H2O complex system, primarily to the synthesis of crystalline tobermorite. Hydrothermal conditions are necessary for the formation of crystalline tobermorite, whereas the course of the reaction is influenced by several factors. The main studied factor was the choice of the silica sources differing in means of solubility, crystallinity, particle size distribution, specific surface area, and purity. The water-to-solid ratio turned to be also an important factor as the length of the hydrothermal reaction. The influence of the mechanochemical pretreatment of starting materials to the final phase composition of samples was studied as well. The obtained results show that the crystallinity of the silica source is the main factor influencing the reaction rate and the purity of the synthesized tobermorite. While using the crystalline silica source the shorter silicate chains are formed and the formation of tobermorite structure is easier. Using the amorphous silica sources and the mechanochemical pretreatement of starting materials prolong the hydrothermal reaction. The prepared samples are always the mixture of crystalline or semicrystalline calcium hydrosilicates instead of the phase pure tobermorite.
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Synthesis and fabrication of lead-free piezoceramics
Řeháková, Bára ; Pouchlý, Václav (referee) ; Částková, Klára (advisor)
The topic of this thesis is synthesis and preparation of lead-free pizoceramic with perovskite structure, in particular potassium-sodium niobate (KNN). In theoretical part are described possibilities of KNN synthesis and of it’s shaping and sintering. Experimental part deals with three types of synthesis described in the theretical part – solid state reaction, hydrothermal synthesis, sol-gel synthesis, and subconsequentional shaping of prepared powders by uniaxial pressing, cold isostatic pressure method, sintering (classical in oven, in some cases SPS – spark plasma sintering) of such green body and their following properties like relative density, grain size or charge constant. Preparation of KNN powder by each described method took place, followed by shaping and sintering. Best properties were shown by SPS sintered samples, which reached the highest density and lowest grain growth.
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Fabrication of ceramic materials for piezoelectric applications
Karkuszová, Karina ; Spusta, Tomáš (referee) ; Částková, Klára (advisor)
The content of this thesis is about preparation and processing of lead-free piezoceramic materials with perovskite structure. Potassium sodium niobate (KNN) powder was prepared by solid state reaction (SSR) and liquid phase reaction (sol-gel reaction). The powders were formed by uniaxial and isostatic pressing and further sintered. The density, grain size and morphology were determined on the sintered samples. The powder, synthesised by SSR and sintered in a conventional furnace, was chosen as a standard. The maximum density achieved on samples after optimization of sintering cycle was 93 %TD. The sintering optimization involved a homogenization step at 950 °C, which promotes the correct development of the phase composition and microstructure, followed by sintering at 1120 °C. The same approach and sintering cycle were used for sintering the samples, prepared by sol-gel synthesis. The maximum density of the samples prepared by sol-gel reaction and sintered in a conventional way, was 92 %TD. For further comparison, both of the synthesised powders were sintered using SPS (spark plasma sintering), which increased their final density up to 97 %TD. The approximate value of the piezoelectric coefficient d33 (pC/N) has been measured on selected SSR samples with pure phase composition ((K0,5Na0,5)NbO3). The best measured value of d33 was around 100 pC/N.
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Sol-gel synthesis and properties of piezoceramic nanoparticles on the base of (BaxCa1-x)(TiyZr1-y)O3
Vacek, Petr ; Matoušek, Aleš (referee) ; Cihlář, Jaroslav (advisor)
The aim of the work was sol-gel synthesis of piezoceramic nanoparticles on the base of BaxCa1-xTiyZr1-yO3 (BCTZ), preparation of sintered samples and analysis of their structure and properties. Theoretical part includes information about piezoelectricity, piezoelectric materials and preparation of ceramics. Experimental part describes sol-gel synthesis of BCTZ nanoparticles and achieved phase composition and particle size. The next topic of experimental part was preparation of sintered BCTZ samples and analysis of their properties.
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Preparation and properties of ferroelectric ceramic materials
Vykoukalová, Tereza ; Maca, Karel (referee) ; Částková, Klára (advisor)
The aim of the work was a processing of ceramic material based on BST for ferroelectric application. Wet chemical techniques based on precipitations and sol-gel methods with ultrasound, hydrothermal or mechanochemical treatment supporting deaglomeration and reducing particle growth were used for BST ceramic powder synthesis. Suitable powders were selected by the evaluation of particle morphology, size and agglomeration, from these powders BST bulk ceramic with defined phase composition and morphology applicable for ferroelectric applications was prepared. It was found, that the most suitable method for preparation of phase pure and nanosized BST powder was sol-gel synthesis with solvothermal treatment (200 °C/48 h). Ceramic with relative density of 85 % TD and with the average grain size of about 1, 22 µm was prepared by pressing and sintering of the powder synthesized by the sol-gel method.
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Highly porous ceramic oxide materials for environmental catalysis
Husťák, Miroslav ; Částková, Klára (referee) ; Cihlář, Jaroslav (advisor)
As far as the replacement of fossil fuels with more environmentally friendly options is concerned, hydrogen is considered as the most promising source of energy. Currently, hydrogen is mainly produced through the method of methane reforming. This method requires the utilisation of catalysts made of precious metals. This master's degree thesis therefore investigates perovskite materials SmCoO3, Sm0,8Ca0,2CoO2,9, SmCo0,8Al0,2O3 and Sm0,8Ca0,2Co0,8Al0,2O2,9, which could be utilised as catalysts in the production of hydrogen by methane reforming. Methane reformation occurs on the surface of a catalyst. Therefore, it is desirable to ensure that the specific surface area of a catalyst material is as large as possible. For that reason, the aforementioned perovskite materials were prepared by two sol-gel methods, which are expected to create perovskites with large specific surface areas. It was investigated in the course of the work how the method of synthesis affects the structure and catalytic properties of individual materials. The SmCo0,8Al0,2O3 material prepared by a sol-gel synthesis with propylene oxide as a gelation agent demonstrated the best results - the measurement of catalytic activity showed that the methane conversion had achieved the value of 99%.
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Highly porous ceramic oxide materials for environmental catalysis
Husťák, Miroslav ; Částková, Klára (referee) ; Cihlář, Jaroslav (advisor)
As far as the replacement of fossil fuels with more environmentally friendly options is concerned, hydrogen is considered as the most promising source of energy. Currently, hydrogen is mainly produced through the method of methane reforming. This method requires the utilisation of catalysts made of precious metals. This master's degree thesis therefore investigates perovskite materials SmCoO3, Sm0,8Ca0,2CoO2,9, SmCo0,8Al0,2O3 and Sm0,8Ca0,2Co0,8Al0,2O2,9, which could be utilised as catalysts in the production of hydrogen by methane reforming. Methane reformation occurs on the surface of a catalyst. Therefore, it is desirable to ensure that the specific surface area of a catalyst material is as large as possible. For that reason, the aforementioned perovskite materials were prepared by two sol-gel methods, which are expected to create perovskites with large specific surface areas. It was investigated in the course of the work how the method of synthesis affects the structure and catalytic properties of individual materials. The SmCo0,8Al0,2O3 material prepared by a sol-gel synthesis with propylene oxide as a gelation agent demonstrated the best results - the measurement of catalytic activity showed that the methane conversion had achieved the value of 99%.
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Preparation of Tobermorite
Dlabajová, Lucie ; Palou, Martin (referee) ; Martinec, Petr (referee) ; Ptáček, Petr (advisor)
This doctoral thesis is focused on the study of reactions in the CaO–SiO2–H2O complex system, primarily to the synthesis of crystalline tobermorite. Hydrothermal conditions are necessary for the formation of crystalline tobermorite, whereas the course of the reaction is influenced by several factors. The main studied factor was the choice of the silica sources differing in means of solubility, crystallinity, particle size distribution, specific surface area, and purity. The water-to-solid ratio turned to be also an important factor as the length of the hydrothermal reaction. The influence of the mechanochemical pretreatment of starting materials to the final phase composition of samples was studied as well. The obtained results show that the crystallinity of the silica source is the main factor influencing the reaction rate and the purity of the synthesized tobermorite. While using the crystalline silica source the shorter silicate chains are formed and the formation of tobermorite structure is easier. Using the amorphous silica sources and the mechanochemical pretreatement of starting materials prolong the hydrothermal reaction. The prepared samples are always the mixture of crystalline or semicrystalline calcium hydrosilicates instead of the phase pure tobermorite.
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Fabrication of ceramic materials for piezoelectric applications
Karkuszová, Karina ; Spusta, Tomáš (referee) ; Částková, Klára (advisor)
The content of this thesis is about preparation and processing of lead-free piezoceramic materials with perovskite structure. Potassium sodium niobate (KNN) powder was prepared by solid state reaction (SSR) and liquid phase reaction (sol-gel reaction). The powders were formed by uniaxial and isostatic pressing and further sintered. The density, grain size and morphology were determined on the sintered samples. The powder, synthesised by SSR and sintered in a conventional furnace, was chosen as a standard. The maximum density achieved on samples after optimization of sintering cycle was 93 %TD. The sintering optimization involved a homogenization step at 950 °C, which promotes the correct development of the phase composition and microstructure, followed by sintering at 1120 °C. The same approach and sintering cycle were used for sintering the samples, prepared by sol-gel synthesis. The maximum density of the samples prepared by sol-gel reaction and sintered in a conventional way, was 92 %TD. For further comparison, both of the synthesised powders were sintered using SPS (spark plasma sintering), which increased their final density up to 97 %TD. The approximate value of the piezoelectric coefficient d33 (pC/N) has been measured on selected SSR samples with pure phase composition ((K0,5Na0,5)NbO3). The best measured value of d33 was around 100 pC/N.
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Synthesis and fabrication of lead-free piezoceramics
Řeháková, Bára ; Pouchlý, Václav (referee) ; Částková, Klára (advisor)
The topic of this thesis is synthesis and preparation of lead-free pizoceramic with perovskite structure, in particular potassium-sodium niobate (KNN). In theoretical part are described possibilities of KNN synthesis and of it’s shaping and sintering. Experimental part deals with three types of synthesis described in the theretical part – solid state reaction, hydrothermal synthesis, sol-gel synthesis, and subconsequentional shaping of prepared powders by uniaxial pressing, cold isostatic pressure method, sintering (classical in oven, in some cases SPS – spark plasma sintering) of such green body and their following properties like relative density, grain size or charge constant. Preparation of KNN powder by each described method took place, followed by shaping and sintering. Best properties were shown by SPS sintered samples, which reached the highest density and lowest grain growth.
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