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Atomization of volatile germanium species in hydride generation atomic absorption spectrometry
Slota, Alexandra ; Kratzer, Jan (advisor) ; Štádlerová, Barbora (referee)
The aim of this thesis was to optimize the atomization conditions of volatile Ge species for hydride generation atomic absorption spectrometry (HG-AAS). The selected species were inorganic germanium (iGe) and its methyl-substituted forms: monomethylgermanium (MMGe) and dimethylgermanium (DMGe). The atomizers for which optimizations were performed included diffusion flame (DF), multi-atomizer (MMQTA), dielectric barrier discharge (DBD) either with sinusoidal modulation of the high voltage source and glued electrodes (REF-SIN) or sputtered electrodes with rectangular high voltage waveform modulation (SE-SW), and finally atmospheric pressure glow discharge (APGD). Under optimal atomization conditions, the highest sensitivity, around 10 ms/ng, was found in DBD atomizers. The advantage of the SE-SW configuration, compared to the REF- SIN arrangement, is better peak shape and repeatability of the measurements. Atomizers such as DF and MMQTA provided mutually comparable sensitivity, which was about 5 times lower than in DBD. The APGD atomizer was the only atomizer studied in which the sensitivity was not comparavle among Ge species. The sensitivity for both methylated species was about half that for iGe (3.0 ms/ng). As part of the mechanistic study, high Ge deposition rates in all types of atomizers,...
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Measuring the retention curve of rocks: the example of sandstone from the Jizera formation
Fataciune, Sotir ; Slavík, Martin (advisor) ; Ondovčin, Tomáš (referee)
Retention curve describes the ability of an unsaturated porous medium to retain water at different suction pressures. It thus plays an important role in providing information on the movement and occurrence of water in the vadose zone. While the determination of the retention curve for soil is common, it is far less common in the case of rocks. The aim of this bachelor thesis is to determine the retention curve of sandstone from the Jestrebicka jehla in Kokorinsko using the tensiometer - weight method. A partial aim is to compare this curve with two previous measurements on the same sandstone: i) measurements by student A. Studencová, using the tensiometer - weight method, and ii) measurements made by the laboratory of Research Institute for Soil and Water Conservation, according to a slightly modified method of CSN ISO 11274. There were notable differences between the retention curves. The retention curve according to the CSN for a given suction pressure showed lower moisture values, which is probably due to insufficient saturation of the sample and air entrapment in the rock pores. Relatively large differences in the retention curve between two independent tensiometer - weight method measurements were also found, which are probably due to insufficient contact between the tensiometer and the porous...
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Mg-hydroxyapatite composite materials prepared by powder metallurgy
Řičánek, Adam ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
This bachelor thesis focuses on the preparation of magnesium-hydroxyapatite composite by powder metallurgy methods. The theoretical part of bachelor thesis deals with magnesium, magnesium alloys and magnesium materials. Furthermore, the theoretical part of the bachelor thesis deals with the basics of powder metallurgy, processing of materials prepared by powder metallurgy and metal matrix composites. In the experimental part of the bachelor thesis, two series of composites were made with different quantities of hydroxyapatite. Composites were made by mixing Mg with filler and by mixing and milling Mg with filler. Both series of composites were characterised by investigation of microstructure and element composition, hardness, compressive strength and corrosion resistance. Composites of mixed and milled series showed a highly homogenous structure. Hardness, compressive strength and corrosion resistance increased with increasing amounts of hydroxyapatite. Composites of mixed series showed heterogeneous structures. Hardness did not increase with increasing amount of hydroxyapatite. Corrosion resistance slightly increased with increasing amount of filler. Compression strength decreased with the increasing amount of filler due to lower cohesion and incompactness of the structure.
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Low energy cements based on clinker phases
Šmeral, Miloslav ; Koplík, Jan (referee) ; Bartoníčková, Eva (advisor)
This thesis deals with low-energy cements and the effect of dopants on their hydration, specifically copper and sulfur. The theoretical part summarizes the general information about clinker minerals, their low-energy/low-carbon alternatives and sustainability in the cement industry. Additionally, possible synthesis of clinker minerals are described. In the experimental part, methods for the preparation of doped tricalcium aluminate and the analysis of the synthesized products are presented. The sulfur doped tricalcium aluminate had the highest hydration heat. On the other hand, copper doped tricalcium aluminate and tricalcium aluminate in combination of these dopants exhibited lower hydration heat. The presence of the dopants also affected the composition of the hydration products.
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Mechanical properties of entropy stabilized ceramic materials
Ronschak, Johana ; Mařák, Vojtěch (referee) ; Salamon, David (advisor)
This work focuses on the topic of the currently novel high entropy materials (HEM). The focus is put primarily on high entropy carbides (HEC) and the effect of carbon content in the matrix of a high entropy alloy (HEA) on its microstructure and hardness. Additionally, the effect of mechanical preparation, sintering temperatures and carbon diffusion from within the sintering die is observed on the samples. Several samples were sintered using the Spark Plasma Sintering (SPS) method under different temperatures. Density, phase and structure analyses were put in correlation to Vickers hardness tests, X-Ray Diffraction (XRD) analysis as well as on some samples to nanohardness tests and Energy Dispersive Spectroscopy (EDS) analysis. Powder milling has been implemented in order to reduce the final material’s porosity, which could negatively impact the accuracy of the hardness reading. Thus, a higher density of the HEA VNbTaMoW has been reached compared to literature by 7 %. Additionally, this result was obtained using lower sintering temperatures. The milled VNbTaMoW had a density of 100 % along with a hardness of 6,9 GPa. Two single-phase HEC materials VNbTaMoW-C0,8 and VNbTaMoW-C0,9 reached hardnesses of 20,46 GPa and 16,87 GPa respectively, whilst densities of 100 % and 97,9 % were observed. The heterogeneous material of VNbTaMoW-C0,5 showed an average hardness of 16,83 GPa. Within this material, nanohardness was measured of the lamellar areas as 20,4 GPa whilst the homogenous areas reached up to 29,3 GPa. The effect of the C diffusion was observed on all samples with the most significant being that of the VNbTaMoW and VNbTaMoW-C0,5 microstructures, where a heterogeneous and homogenous phase of the VNbTaMoW-C0,8 composition was created respectively. C has reached a depth of ~180 m within the VNbTaMoW through diffusion and ~200 m in VNbTaMoW C0,5, where an increase of hardness was observed from 18,4 GPa in the core material to 22,6 GPa on the surface. This work observed a positive impact of mechanical powder milling on the final microstructure and density. Additionally, the implementation of milling has resulted in a lower needed sintering temperature than reported in literature, whilst reaching higher densities. An increase of hardness has been observed in the HEC depending on the C content, with the highest being measured on the VNbTaMoW-C0,8. The material VNbTaMoW-C0,9 showed lower hardness, most likely due to its higher porosity, which lowers the effective hardness of the material. This points towards a possible direction of further studies in regard to the optimalization of HEC powder preparation and sintering temperatures with the goal of obtaining a full-density material with content of C > 80 mol %.
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High-speed shaft production design
Polesný, Pavel ; Jaroš, Aleš (referee) ; Kalivoda, Milan (advisor)
In the bachelor's thesis, a production process of the crankshaft of a single-cylinder two-stroke engine is designed. The flywheel has a diameter of 20.5 mm, the crank pin has a diameter 9 g6, the connecting rod pin has a diameter 4 g6, and the total length is 63.5 mm. Due to the production batch of 1000 pieces, the machining method was selected. The crankshaft will be produced as a monolith. Then the grooves at the ends of the ground surfaces 9 g6 and 4 g6 were addressed. Due to the wall thickness of 1.25 mm, the surfaces will be without grooves, and a radius or chamfer will be in the corners. The axial bearing and the connecting rod have an internal chamfer of 0.7x45°, thus grooves are unnecessary. The chosen material is 15.142 steel, tempered to a lower strength, supplied in 25x3000 mm bars by ZJP, s.r.o. The semifinished part will be manufactured on a Swiss-type lathe Manurhin K'MX EVO 732. After nitriding, the part will be ground on a Bernardo URS 500 N grinder. For the machining on the EVO 732, OPTIMA EXTREMECUT 46 mineral oil was chosen, and for grinding, a 2% concentration emulsion mixed from BITOL M petroleum emulsion oil was selected. Then the technological process was developed, and operational instructions were created. Calculations determined that 26 bars are needed for the production of the specified series. The entire series production will take just under 4 shifts.
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Preparation of layered double hydroxides on Mg-hydroxyapatite-based substrates
Knoflíček, Milan ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
The aim of this bachelor thesis was the preparation and characterization of coatings based on layered double hydroxides (LDH) on Mg composite substrates prepared by powder metalurgy. Hydroxyapatite (HAp) was used as a filler. The deposition of MgAl-LDH coatings on the surface of composites was carried out in a reaction mixture containing Al(NO3)3 at pH 10 and a temperature of 95 °C. The morphology and structure of the samples were characterized using scanning electron microscopy (SEM). The elemental composition of both composites themselves and the prepared coatings were characterized by energy dispersive spectroscopy (EDS). Analysis of the structure of Mg-HAp composites revealed that the frequency of HAp agglomerates increased with increasing reinforcement concentration. The highest frequency of agglomerates was detected in samples containing 20 and 50 wt. % HAp filler, where unlike the other samples, a significant deterioration of corrosion properties was also observed. In contrast, the best corrosion resistance was shown by the sample with 1 wt. % of filler. Other samples with filler contents from 0 to 10 wt. % were relatively similar in terms of corrosion resistance. Potentiodynamic tests demonstrated that coated samples exhibited significantly higher corrosion resistance compared to the uncoated samples. A uniform layer of LDH was observed in the coated samples with HAp content up to and including 10 wt. %. The presence of cracks related to the presence of bulky HAp agglomerates was detected on samples with higher reinforcement content, i.e. 20 and 50 wt. % HAp. Lower coating adhesion was also observed at these locations. It was found that to achieve high quality of LDH coatings, the optimum amount of HAp reinforcement of mixed and subsequently pressed Mg-HAp composites is up to 5 wt. % HAp. Higher HAp content in the samples generally led to the formation of defects and deterioration of corrosion properties.
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Heat exchanger using structured material
Simon, Jakub ; Čížek, Petr (referee) ; Vaverka, Ondřej (advisor)
The aim of this work was to develop and describe a design method of a heat exchanger using Triply Periodic Minimal Surfaces (TPMS) structures and to validate it by design, fabrication, and experimental testing of a working sample. It is an oil-water cooler fabricated additively by Laser Powder Bed Fusion on an SLM 280 HL machine from AlSi10Mg material. After a series of analyses and tests, a cubic diamond structure with a minimum wall thickness of 0.7 mm and a range of relative densities of 15 to 25 % (cell edge length 11.1÷18.5 mm) was chosen for the developed method. The method also includes a prediction script of the performance of the proposed heat exchanger, which was created from data measured during testing of samples with different cells configurations. The method itself guides the user step-by-step from the selection of input requirements, through the estimation of performance, to the two-step parametric modelling of the TPMS exchanger itself (explicit and implicit). The functional sample created using this method achieved heat flows of 315,25 W, which is 4.2 % higher than the reference plate exchanger. The TPMS exchanger also has a 78 % smaller heat transfer body and 62 % less total mass. The differences between predicted and actual heat flows were up to 18%. In its current state, the method is suitable for the design of TPMS heat exchangers with heat flow of 50 to 230 W. However, it is generally versatile and can also be used to map other areas, thus making it more accurate.
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Influence of some microbiogenic elements on carotenogenic yeasts
Pulkrábek, Josef ; Holub, Jiří (referee) ; Obračaj, Jan (advisor)
Carotenogenic yeasts of the genus Rhodotorula are well known for their production of a variety of economically valuable and otherwise difficult to produce compounds such as fatty acids, carotenoids, ergosterol, and ubiquinone. This study investigates the effect of the addition of select microbiogenic elements (Fe, Se, I) and their combinations into mineral cultivation media on the production of the mentioned valuable metabolic products and the rate of element sorption into the biomass of the strains of Rhodotorula mucilaginosa, Rhodotorula kratochvilovae, and Rhodotorula toruloides. Additionally, the sorption of zinc oxide, ferrous fumarate, and selenomethionine into previously cultivated biomass was measured with sorption times of 2 and 24 hours. Fatty acid content was determined using GC-FID, while carotenoids, ergosterol, and ubiquinone were analyzed using HPLC-DAD, with element content being quantified using ICP-OES and IC. With a few exceptions, the production of metabolic products was decreased with the addition of elements into the media and inversely correlated with their concentration. Higher concentrations generally showed greater absolute amounts of sorbed elements but lower relative amounts, which, combined with reduced production of metabolic products shows that the media are not ideal for the cultivation of the given species. The elemental contents were such that biomass supplemented with individually sorbed elements would vaguely align with ESFA dietary reference values, but cultivation in media with a mixture of added elements could result in the biomass containing either insufficient iron or excessively high levels of selenium. Sorption levels were relatively low (5 to 22 % for iron and 0.5 to 2.5 % for selenium). Indicating that cultivation in media with lower concentrations of elemental additives is a promising area for future research.
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Testing of sliding coatings for space applications
Velička, Jan ; Pouzar, Josef (referee) ; Košťál, David (advisor)
This bachelor thesis deals with sliding coatings for use in space applications. In the experimental part, the number of cycles to wear for a molybdenum disulfide based coating was investigated. This coating was deposited on a beryllium copper CuBe substrate. The coating was tested for its possible application to bolt threads. The coefficient of friction of all samples was measured on a tribometer in an atmospheric environment. The specimens were loaded with a normal force of 35 N during the measurement. The number of cycles to wear was compared for specimens differing in coating time. The number of cycles was found to be similar for lower coating times. Then the number of cycles to wear started to increase with the coating time. From the findings, it can be said that increasing the coating time increases the coating life. Such a coating is suitable for the protection of bolts against galling.
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