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Alkali Activated Systems
Bílek, Vlastimil ; Rovnaník, Pavel (referee) ; Vlček, Jozef (referee) ; Ptáček, Petr (advisor)
This doctoral thesis is focused on the possibilities of alkali-activated slag (AAS) shrinkage reduction, which would together with the use of waste sludge from waterglass production contribute to wider practical utilization of this interesting material. Besides the influence on AAS dimensional changes also effect of various factors on workability, setting time and mechanical properties was investigated. Obtained results were supported by the application of instrumental techniques like izotermal calorimetry, mercury intrusion porosimetry, scanning electron microscopy and X-ray diffraction. The results show the possibilities of reduction of AAS drying shrinkage related to its cracking tendency through the combination of increased dose of waterglass and reduced water to slag ratio (w/b), partial replacement of slag by pulverized fly ash or cement by-pass dust and application of organic admixtures, where significant effect on AAS hydration was observed. On the basis of the obtained results concrete mixtures, where the whole activator was replaced by the waste sludge form waterglass production, were designed and optimized in terms of shrinkage, mechanical properties and price. Selected concretes were also tested in semi-operating conditions.
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Influence of noble earth's elements on Bi based high temperature superconductors phase transition.
Šilhavý, Miroslav ; Havlica, Jaromír (referee) ; Ptáček, Petr (advisor)
The thesis is focused on high-temperature superconducting (HTS) ceramics series of bismuth. Specifically, there is studied Bi2Sr2CaCu2O8+x phase, known as the 2212 phase. The theoretical part describes the basic properties of superconductivity and superconductors, the properties of cuprate ceramics and description of LBCO, YBCO and BSCCO structures. The experimental part deals with the preparation of the precursor own Bi-2212 phase. It is synthesized by a process called sol-gel. Feedstock Bi2O3, CaCO3, SrCO3 and CuSO4 was dissolved in HNO3 and transferred to a complex with ethylenediaminetetraacetic acid (EDTA, Chelaton II). With NH3 pH > 9 was maintained due to the stability of complex. The obtained gel was concentrated, calcinated in a furnace at 860 °C and crushed into powder. Pure powder was subjected to analysis dipping microscope, SEM, XRD, FT-IR, TG-DTA at different atmospheres argon, oxygen and air. Then 1 wt.% of the oxide (La, Y, Sc, Sm) was added to part of the powder precursor and the samples were examined using TG-DTA.
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Gypsum free cements with retarded setting by plastisizer and alkali compond
Sedlařík, Tomáš ; Ptáček, Petr (referee) ; Havlica, Jaromír (advisor)
This thesis deals with preparation of gypsum free cements with retarded solidification. It focuses on their preparation by alkali activation with addition of superplasticizers and without superplasticizers. The main aim of this work is to suggest substitution of gypsum in Portland cement by other materials. Ash after fluidized combustion was chosen as a good compensatory raw material with respect to sustainable development. Milled fluidized bed ash from heating station Třinec was tested. Examined pastes were prepared by alkali activation. 50% solution NaOH and sodium water-glass were used as alkali activators. Trial specimens (20x20x100 mm) were prepared from pastes. Measurements of calorimetric properties of unprocessed pastes tested mixtures were implemented. Bending and compressive strength of pastes were also explored.
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Vanadium corrosion of refractory materials
Florian, Ondřej ; Opravil, Tomáš (referee) ; Ptáček, Petr (advisor)
The bachelor thesis is focused on the influence of vanadium corrosion process on the corrosion and properties of high-alumina refractory products used in gasified on production of synthesis gas from a carbon feedstock, water on oxygen. The composition, properties of refractory product and mutual interaction of corrosion processes was investigated by method of thermal analysis, X-ray diffraction analysis and scanning electron microscopy.
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Possibilities of reducing zinc losses during heat treatment of ferrite ceramics
Buday, Patrik ; Šoukal, František (referee) ; Ptáček, Petr (advisor)
The diploma thesis is focused on the study of the influence of sintering temperature on the evaporation of zinc from Mn-Zn-ferrite ceramics. The main focus of the study is on the reaction kinetics of the zinc evaporation process, at the same time the aim of this work is to propose and verify a method that would limit the evaporation of zinc. The theoretical part summarizes the basic knowledge about the properties, classification, application, and production of Mn-Zn-ferrites. The end of the theoretical part describes the loss of zinc and a possible solution to this undesirable phonomenon. The beginning of the experimental part contains a summary of the principles of infrared spectroscopy, electron scanning microscopy, and X-ray crystallography. The experimental part of the diploma thesis is focused on the description of the production of ferrite samples, the characterization of the input material and the determination of the reaction kinetics of the sintering, and its comparison with the kinetics of the sample treated with a protective layer.
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The influence of barium and its compounds on the formation and properties of Portland clinker
Zezulová, Anežka ; Rovnaníková, Pavla (referee) ; Palou, Martin (referee) ; Ptáček, Petr (advisor)
The work deals with the study of barium cement. Barium cements are used to prepare concrete that protects against ionizing radiation. Barium can be also present in a conventional Portland cement clinker as an impurity from alternative fuels or raw materials, which are increasingly used for clinker production, and thus change the structure and properties of the product. Various methods of preparation of this cement were studied in this work. Barium cements were prepared from raw meals of different composition, but always with the same procedure and burning temperature. Using suitable analytical methods, the work describes the influence of individual admixtures of raw meal on the phase composition of the resulting clinker. Furthermore, the work deals with monitoring the form and location of barium in the prepared clinker. Several experiments are focused on the study of hydration of prepared barium clinkers, the phase transformation is monitored by XRD and supplemented by analyses of hydration products. In this way, it was possible to obtain the data needed to describe the preparation, burning, and hydration of barium cements with different compositions. The work also deals in detail with the real use of barium cements. The ability of pastes and mortars from prepared barium cements to shield various types of ionizing radiation was tested and described experimentally. The results are presented in comparison with reference samples, which were prepared from commonly used Portland cement.
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Noise impact of combustion engine exhaust systems
Ptáček, Petr ; Knotek, Jiří (referee) ; Zubík, Martin (advisor)
This bachelor’s thesis is focused on creating a research study about noise of combustion engine exhaust systems. Introducing of this work coves all parts of common exhaust systems while mostly focused on silencers. It further describes several methods of measuring the noise established by legislation and at its end it deals with a noise impact of exhaust system treatments.
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The formation of gehlenite and anortite in the ceramics body.
Matysová, Dorota ; Šoukal, František (referee) ; Ptáček, Petr (advisor)
This bachelor thesis deals with the study of mechanism and kinetics of gehlenite and anorthite formation in the ceramic body. Methods used for this study were thermal analysis (TG-DTA-EGA), HT-XRD and heating microscopy. The Kissinger equation which belongs to the mechanism-free isoconversional methods was used for the determination of the activation energy, the pre-exponential factor and the Avrami coefficient. Characteristic of reactants kaoline Sedlec Ia and precipitated CaCO3 (Penta, p.a.) using IR spectrometry, thermal analysis (TG-DTA-EGA), SEM and heating microscopy is also included in this thesis.
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Sintering of Advanced Ceramic Materials
Pouchlý, Václav ; Svoboda, Jiří (referee) ; Ptáček, Petr (referee) ; Maca, Karel (advisor)
Sintering is a one of the key step in a processing of bulk ceramic materials. New sintering methods were invented in the last years. These new sintering methods, according to their authors, can be used for obtaining finer final microstructure of ceramics only by modifying the heating schedule. This work is focused on an influence of the Two Step Sintering method on the final microstructure for oxide ceramics. Obtained experimental results have shown that the effectivity of the Two Step Sintering method is rising with crystallographic symmetry of used material. Thesis is also focused on a high-temperature dilatometry and concept of the Master Sintering Curve. This concept was used for calculation of the activation energy of sintering and finding different sintering mechanisms acting in the intermediate and final stage of sintering. Activation energy of sintering was compared with activation energy of grain growth with target to find the kinetic window. Kinetic window can allow a sintering without a grain growth. Master Sintering Curve method was also used in a pressure assisted unconventional sintering technique Spark Plasma Sintering. Master Sintering Curve applied to a Spark Plasma Sintering technique reveals and quantified different sintering mechanisms acting in Spark Plasma Sintering. These findings led to preparation of transparent tetragonal ZrO2.
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Corporate Governance
Ptáček, Petr ; Pelc,, Petr (referee) ; Kocmanová, Alena (advisor)
The aim of the master’s thesis is to analyse the corporate governance in the Cyrrus, a. s. In the first part of the thesis, particular approaches to corporate governance including an approach used in trading companies in the Czech Republic are appointed. Further, in the practical part, theoretical knowledge to a particular company is applied. With the help of the economic analysis and the analysis of compliance with the Code of Corporate Governance Principles, based on the OECD 2004, the work will evaluate the effectiveness of governance in the particular company and propose recommendations that would lead to an improvement of the situation.
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