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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
621

Vliv velikosti částic a způsobu přípravy na hydrataci vápenato-hlinitých fází / The influence of particle size and methods of preparation of calcium aluminate phases on their hydration

Ohaňka, Zdeněk January 2018 (has links)
This work focuses on the hydration of four calcium aluminate phases – C3A, C12A7, CA and CA2. Above all, the influence of particle size and method of preparation on hydration behaviour were studied. Influence of these factors on hydration products were also investigated. Calcium aluminates were prepared by solid state synthesis and amorphous citrate method. Both methods were described in detail. The particle size was determined by laser diffraction. Isothermic calorimetry was used to investigate the process of hydration. Hydration products were identified by X-ray diffraction analysis and simultaneous thermogravimetric and differential thermal analysis.
622

Charakterizace rašelin / Characterization of peat

Freithová, Štěpánka January 2019 (has links)
Peatlands are considered to be valuable ecosystems on the Planet and play an important role in many processes globally likewise and in the landscape. They are important for maintaining a global biodiversity, play an important role in landscape hydrology and can be a source of drinking water. They can help minimize floods and contribute to climate change mitigation. The peat bogs are one of the largest terrestrial carbon reservoirs. They have been storing carbon for centuries. Many of peat functions are affected due to human activities. It can result into release of greenhouse gases into atmosphere and the excretion of organic carbon into watercourses. The subject of the thesis is understanding of the mechanisms of water binding in peat and exploring possible dependencies within the depth profile of the peatlands using thermal analytical methods, more preciously using thermogravimetry (TG) and differential scanning calorimetry (DSC). The stability of water molecule bridge (WaMB) was investigated. It was found out that the minimum temperature required for WaMB abatement decrease and the whole structure becomes less stable with increasing peat layer depth. Water release processes were evaluated with the meaning of the TGA measurements. A decreasing trend in the degradation of thermolabile substances and an increasing trend in thermostable substances within the peat profile were observed.
623

Aplikace metamastku v anorganických materiálech / Meta-talc Application in Inorganic Materials

Bednárek, Jan January 2019 (has links)
This thesis is focused at possibilities of preparation and characterization of XRD-amorphous delaminated and dehydroxylated talc phase – meta-talc, which can have its potential application and a starter material for a preparation of magnesium-silicate analogues of geopolymers. Changes in structure and morphology of talc ore were observed during this work. For the purposes of this research, two various talc ores – chloritic and dolomitic were examined. Whole process of meta-talc preparation was examined with whole scale of instrumental techniques such as X-ray diffraction, simultaneous thermogravimetric a differential thermal analysis, infrared spectroscopy, scanning electron microscopy or laser analysis of particle size. Meta-talc can be obtained via mechanochemical activation of talc ore with subsequent calcination. Mechanochemical treatment lead to destruction of original crystal structure and breaking of original bonds, i.e. the product of this treatment was almost amorphous and delaminated. Most of hydroxyl groups were converted to molecules of water which remained adsorbed or coordinated in ore structure. These molecules were removed during calcination step.
624

Studium chování nanočástic platiny ve složkách životního prostředí / The study of behavior of platinum nanoparticles in environmental compartments

Berka, Michal January 2020 (has links)
Platinum nanoparticles pose a risk to environmental compartments. The aim of this diploma thesis is to conduct research on the influence of platinum nanoparticles in a wide range of concentrations on soil properties at different humidities. Specifically, it is about influencing the stability of water molecular bridges, the content of aliphatic crystallites, the retention capacity of water in the soil and the strength of water binding. Furthermore, the amount of nanoparticles sorbed on the soil was also measured. These indicators give us more information about the influence of platinum nanoparticles on evapotranspiration and soil deterioration. Methods of thermal analysis (differential scanning calorimetry) and optical methods (atomic absorption spectrometry) were used for these researches. The theoretical part of the work is devoted to a comprehensive introduction to platinum and its nanoparticles, as well as aqueous molecular bridges. It has been found that 200 nm platinum nanoparticles affect the strength of aqueous molecular bridges, have no effect on aliphatic crystallite content, have minimal effect on soil water retention, and that the water bond strength decreases due to platinum nanoparticles at high relative humidity. With 200 nm platinum nanoparticles, complete adsorption to soil occurs over the entire concentration range. With 3 nm nanoparticles, the soil is supersaturated at higher concentrations and larger amounts are not adsorbed. The results show that the larger the size of the platinum nanoparticles, the lower the negative effect on evapotranspiration and soil function itself.
625

Vliv nanočástic různých forem oxidu titaničitého na vlastnosti půdní organické hmoty / Influence of different forms of titanium dioxide nanoparticles on soil organic matter properties

Miklasová, Marta January 2020 (has links)
Nanoparticles present potential risk for environmental compartments including soil. Previous works have been focused on negative effects of nanoparticles on soil biota, however studies about the influence of nanoparticles on soil properties are still limited. This thesis investigates an impact of 20 nm titanium dioxide nanoparticles on selected water properties in soil organic matter exposed to air with various relative humidity. Indeed, at 43, 70 and 95 % dominate different water types, i.e. water adsorbed on soil organic matter, water in water molecular bridges and phase water, respectively. Differential scanning calorimetry (DSC) was used in the study. An important finding is that nanoparticles reduce the stability of water molecular bridges under 70% relative air humidity and generally reduce evaporation enthalpy of water, which represents the ability of the soil to retain water. In the next part the influence of nanoparticles on total water in soil was observed. Under low relative humidity, rutile and anatase affected soil in different ways due to their various hydrophilicity. Under higher relative humidity this effect disappeared. In the last part, ice melting and water evaporation enthalpies of nanoparticle solutions were measured to confirm the presumed effect of nanoparticles on water. The ice melting enthalpy of the solutions was higher relatively to pure water, while the evaporation enthalpy showed a reverse trend (decrease). This confirmed the effects of nanoparticles both for pure water and soil water.
626

Optimalizace povrchových úprav polymerů pro mikroskopická pozorování / Optimizing of Polymer Surface Treatment for Microscopic Examination

Horská, Pavlína January 2011 (has links)
Supramolecular structure of eight commercial types of iPP, its blends with poly(L-lactide) (PP-PLLA) and copolymers with ethylene-propylene rubber (PP-EPR) together with four types of polyethylene (LDPE, HDPE) was uncovered and observed in this work. The spherulitic structure of iPP and PE homopolymers and PP copolymers was uncovered by etching of six different solutions of mineral acids with KMnO4 and by dissolution in four selected solvents. The latter was found to be ineffective. The structure of PP-PLLA blends was uncovered only after recrystallization (the change of structure by annealing and cooling rate). The uncovered crystalline structure was observed directly by confocal laser scanning microscope (CLSM) and SEM. Crystallinity together with a size distribution of crystallites was determined by DSC. It was proved that spherulitic supramolecular structure was easy to uncover by chemical etching only for molded samples and for fracture surfaces of injected samples. The efficiency of etchants varied but, generally, the samples with high degree of crystallinity were etched earlier. The etchants containing nitric acid and high content of sulphuric acid uncovered fine details of shperulites with respect to mixtures containing orthophosporic acid. It was also observed that not only the etchant (especially with nitric acid) itself but also its vapors were effective. The structure was revealed later but the appearance was plastic (3D) and the structure was very fine. The supramolecular structure of PP-PLLA blends differed with amount of each component. The ethylene-rubber phase came forth with increasing time of etching while PP spherulites disappeared in PP-EPR samples. CLSM was shown to be very good tool for observing supramolecular structure of studied samples with respect to SEM, which was proved to be entirely unsuitable for polyolefines. DSC is recommended to be performe before uncovering supramolecular structure for basic information about proportion of amorphous/crystalline phase and size of crystallites.
627

Tepelný komfort a jeho stanovení / Thermal comfort and its estimation

Žáková, Monika January 2015 (has links)
This paper summarizes the problems of human thermoregulation and its measurement, with a focus on the method of indirect calorimetry in resting conditions at different ambient temperatures and during physical activity. It also introduces the issue of human thermal comfort and the methodology of its monitoring using thermal manikin. It describes PowerCube Ergo (Ganshorn, Germany) and Cardiovit AT-104 (Schiller, Switzerland), the diagnostic devices used to spiro-ergometry measurements. It introduces the options to export data. The work proposes the protocol for measuring the thermoregulation of the small group of volunteers, which is realized by the practical part. According to the same protocol is monitored thermal comfort of the thermal manikin. In MATLAB is created the application, allowing clear analysis of measurement records. The data are evaluated and discussed.
628

Spalné teplo čistírenských kalů / Higher Heating Value of Sewage Sludge

Mikluš, Michal January 2010 (has links)
The thesis is focused on problems of thermal treatment of sludge from wastewater treatment plants. The main objective is to establish a formula for calculating higher heating value (HHV) and lower heating value (LHV) of sludge based on its chemical analysis. The work is divided into two main parts: The theoretical part deals with the characteristics of sludge, thermal treatment of sludge, it isn´t omitted higher heating value and lower heating value. The main topic of a practical part is formulation of eguations for HHV and LHV calculation. Chemical analysis of sludge samples were supplied by TÜV NORD Czech s.r.o., together with the values of HHV and LHV. The calculations were verified by the program MINITAB.
629

Studium krystalické struktury polyhydroxybutyrátu a nukleační aktivity vybraných typů aditiv / SStudy of crystalline structure of polyhydroxybutyrate and nucleating activity of selected additives

Sedláček, Zbyněk January 2016 (has links)
This diploma thesis deals with study of crystalline structure of polyhydroxybutyrate (PHB), which contains different types of additives for studying of their nucleation activity and which were prepared by mixing. It is about boronitrid (BN), sacharin, hydroxapatit, plasticizer Tegmer a tree types of talc. Crystal structure was analysed by differential scanning calorimetry and x-ray diffraction, supramolecular structure was observed by optical microscopy (polarized and confocal laser scanning). Nucleating activity was evaluated by isothermal and non-isothermal crystallization made on calorimeter and heated table of optical microscope. There is not influence of additives on crystallographic structure, but additives affects number and size of spherulites including crystal domains defects, which can have impact on final mechanical properties. BN and talcs react as nucleating agents, other additives during low and high cooling speeds (vc) inhibit nucleation and in middle cooling speeds are without effect. Nucleating activity is not evaluated by numerically, because decrease of crystallization temperature together with vc is not linear. Results of direct methods are based on picture analysis, which is great benefit for understanding of crystal behaviour of PHB.
630

Charakterizace vybraných polyelektrolytových komplexů metodami strukturní a termické analýzy / Characterization of polyelectrolyte complexes using structural and thermal analysis

Řiháčková, Barbora January 2016 (has links)
This master thesis deals with study of chitosan-lignohumate, chitosan-polystyrenesulfonate, chitosan-alginate and chitosan-carrageenan polyelectrolyte complexes. The work was motivated by research of finding suitable alternative substance for lignohumate. The molecular weights of substances were characterized using SEC-MALLS. A degree and a character of the interactions between polyelectrolyte were studied by isothermal titration calorimetry and dynamic light scattering method. The calorimetric experiments proved that decreasing concentration of samples causes decreasing of heat flow. The best calorimetric measurements were provided by adding chitosan into polymer solution. The interactions between chitosan and polyanions and influence of mixing order were proved also by measuring intensity of zeta potential, Z-average of particle size and turbidity. New chitosan-based materials have a big potential in agriculture and medicine.

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