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Determination ignition temperature of flammable liquids in different conditions
SABELA, Marek
This master thesis named Determination of ignition temperature at flammable liquids under various conditions deals with atmospheric as well as specific technological, non-atmospheric, conditions. The measurements proved that the ignition temperature at luquids decreases with increasing preassure in a vessel. Based on comparison with foreign sources, it was possible to prove that even size of a vessel influences the ignition temperature. The bigger the vessel the lower the ignition temperature. The measurements are carried out in a closed vessel under isochronic conditions. This method guarantees there is no air exchange between vessel and the surroundings. To equip such measurements the Technical Institute of Fire Protection built specific facility capable of providing necessary conditions. The main goal of the experiments is to determine ignition temperature at selected flammable liquids under variable initial pressures and under various oxygen concentration and to compare the results with available sources in literature. Heptan and Pentan were chosen for this comparison and the experiments were carried out at various initial pressures of 100 kPa, 200 kPa, 500 kPa in a vessel. Apart from comparison of measured values by Technical Institute of Fire Protection along with cooperating institute PTB Braunschweig, this thesis focuses on determination of the lowest oxygen concentration at various initial pressures under which no ignition of tested flammable chemicals happens. Our experiments proved that when the atmospheric pressure in a closed vessel reaches 10%, the tested flammable liquid is not ignitable. When the measures are carried out under higher initial preassures in the vessel the oxygen percentage in the vessel is significantly lower.
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Pressure effects on physical properties of a selected Ce-based compound
Staško, Daniel ; Klicpera, Milan (advisor) ; Míšek, Martin (referee)
Presented thesis focuses on the study of transport properties of two intermetallic compounds, CeRhSi3 and CeCuAl3, under high external pressure. High-pressure dependence of previously reported pressure induced superconductivity in CeRhSi3 is studied closely up to 4.6 GPa, focusing on the, so-far-unstudied, pressure region above 3 GPa. After reaching maximal value at 2.9 GPa, the critical temperature of superconducting transition is gradually suppressed by further pressure application. Extensive search for possible pressure induced superconductivity in CeCuAl3 is conducted, employing solid-pressure-medium Bridgman anvil cells with theoretical pressure limit of 12 GPa. No pressure induced superconductivity is observed up to 4.5 GPa and down to 8 mK. Additionally, a calibration study of three liquid pressure exchange media from Daphne Oil 7000 series is carried out in order to advance high pressure experimental techniques. Comprehensive results about hydrostaticity, solidification, pressure drop and compressibility of individual pressure media are presented.
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Pressure effects on physical properties of a selected Ce-based compound
Staško, Daniel ; Klicpera, Milan (advisor) ; Míšek, Martin (referee)
Presented thesis focuses on the study of transport properties of two intermetallic compounds, CeRhSi3 and CeCuAl3, under high external pressure. High-pressure dependence of previously reported pressure induced superconductivity in CeRhSi3 is studied closely up to 4.6 GPa, focusing on the, so-far-unstudied, pressure region above 3 GPa. After reaching maximal value at 2.9 GPa, the critical temperature of superconducting transition is gradually suppressed by further pressure application. Extensive search for possible pressure induced superconductivity in CeCuAl3 is conducted, employing solid-pressure-medium Bridgman anvil cells with theoretical pressure limit of 12 GPa. No pressure induced superconductivity is observed up to 4.5 GPa and down to 8 mK. Additionally, a calibration study of three liquid pressure exchange media from Daphne Oil 7000 series is carried out in order to advance high pressure experimental techniques. Comprehensive results about hydrostaticity, solidification, pressure drop and compressibility of individual pressure media are presented.
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Adsorption study of waste materials as potential adsorbents for pollutant removal and storage
Řimnáčová, Daniela ; Vorokhta, Maryna ; Vöröš, Dominik ; Borecká, Lenka ; Bičáková, Olga
The study shows how changing the experimental conditions during carbonization of a waste material such as sewage sludge influences textural properties and the CO2adsorption capacity of final carbonized productsin their potential use for removaland storage of pollutantssuch as carbon dioxide. The CO2adsorption measurements were done with gravimetric and manometric sorption devices in a wide range of pressures and temperatures. Further, CO2adsorption capacities of other materialssuch as activated carbon prepared from black carbon and a Czech Silurian shalewere compared toadsorption capacities of the studied carbonized sewage sludge. These two compared materials were chosen according to their compositionsand porosity.The porosityof the studied materials was determined from the N2sorption isotherms and measurements of their skeletal density with He.The adsorption capacity depended on the ratio of micropores and mesopores in the carbonized sewage sludge, because CO2fillsmicropores and mesopores at lowand highpressures, respectively, and was decreasing with the temperature increase atconstant pressure.The adsorption capacity of the carbonized sewage sludgewas increased by increase inthe carbonization temperature.The obtained adsorption capacities showed that the carbonization of sewage sludge can lead to preparation of perspective adsorbents for CO2capture and storage.
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Compressibility of an intermetallic compound
Staško, Daniel ; Prchal, Jiří (advisor) ; Kaštil, Jiří (referee)
Title: Compressibility of an intermetallic compound Author: Daniel Staško Department: Department of Condensed Matter Physics Supervisor: RNDr. Jiří Prchal, Ph.D., Department of condensed matter physics Abstract: This work focuses on the method of using miniature strain gages for the measurement of volume change and strain in hydrostatic pressure. Two state variables are involved in the changes - temperature and pressure. A copper reference material was used to determine the pressure and temperature corrections for the specific type of strain gage used it this work. To demonstrate this method, a pressure dependence of strain was measured up to 2.3GPa for the CeCuAl3 single crystalline sample along particular crystallographic directions. It is studied for its interesting magnetic properties and this work aims to contribute to its complex study. Temperature dependencies of strain under low and high pressure were also measured. Keywords: high pressure, compressibility, strain gage, CeCuAl3
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Experimental and Theoretical Comparative Study of Monolayer and Bulk MoS2 under Compression
del Corro, Elena ; Morales-García, A. ; Peňa-Alvarez, M. ; Kavan, Ladislav ; Kalbáč, Martin ; Frank, Otakar
Recently, a new family of 2D materials with exceptional optoelectronic properties has stormed into the scene of nanotechnology, the transition metal dichalcogenides (e.g., MoS2). In contrast with graphene, which is a zero band gap semiconductor, many of the single layered materials from this family show a direct band-gap in the visible range. This band-gap can be tuned by several factors, including the thickness of the sample; the transition from a direct to indirect semiconductor state takes place in MoS2 when increasing the number of layers from 1 towards the bulk. Applying strain/stress has been revealed as another tool for promoting changes in the electronic structure of these materials; however, only a few experimental works exist for MoS2. In this work we present a comparative study of single layered and bulk MoS2 subjected to direct out-of-plane compression, using high pressure anvil cells and monitoring with non-resonant Raman spectroscopy; accompanying the results with theoretical DFT studies. In the case of monolayer MoS2 we observe transitions from direct to indirect band-gap semiconductor and to semimetal, analogous to the transitions observed under hydrostatic pressure, but promoted at more accessible pressure ranges (similar to 25 times lower pressure). For bulk MoS2, both regimes, hydrostatic and uniaxial, lead to the semimetallization at similar pressure values, around 30 GPa. Our calculations reveal different driving forces for the metallization in bulk and monolayer samples.
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EXPERIMENTAL APPARATUS FOR MEASUREMENT OF DENSITY OF SUPERCOOLED WATER AT HIGH PRESSURE
Hrubý, Jan ; Hykl, Jiří ; Peukert, Pavel ; Šmíd, Bohuslav
Thermodynamic behavior of supercooled water (metastable fluid water existing transiently below the equilibrium freezing point) at high pressures was subject to many recent theoretical studies. Some of them assume that a second critical point of water exists, related to two liquid phases of supercooled water: the low-density liquid and the high-density liquid. To test these theories, an original experimental cryogenic apparatus is being developed. The volume changes are measured optically in custom-treated fused-silica capillary tubes. The capillaries are placed in a metal vessel designed for pressures up to 200 MPa. The vessel is connected to a circulation thermostat enabling a rapid change of temperature to prevent freezing. A new high-vacuum device was developed for degassing of the ultrapure water sample and filling it into the measuring capillaries. The experiments will contribute to fundamental understanding of the anomalous behavior of water and to applications in meteorology, aerospace engineering, cryobiology etc.
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Ultrasonic pulsations of pressure in a tool for water jet cutting
Říha, Zdeněk ; Foldyna, Josef
Water flow in a tool for water jet cleaning and cutting is evaluated in this paper. There are ultrasonic pulsations of high pressure in the given domain. The efficiency of the amplification of high pressure pulsations in the transitional space between larger and smaller pipes is analysed. Three types of transitional spaces are compared in the paper: step change, conical and radius change of pipe diameters.
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