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Preparation of polyethylene terephthalate model microplastics
Hrušková, Adéla ; Fojt, Jakub (referee) ; Kučerík, Jiří (advisor)
Microplastics are ubiquitous in all ecosystems and for that reason they became a subject of many studies in recent years. Due to their stability, potential release of harmful additives and ability to adsorb pollutants, they pose a threat to the environment. It was found that certain microplastics can, under certain conditions, have toxic effects on fauna, flora and human health. Most of studies include laboratory or mesocosmos testing, therefore, it is important to master their preparation. To study the environmental impact of microplastics, it is essential to be able to prepare these particles, especially required type, shape and size. This bachelor thesis deals with the preparation of model polyethylene terephthalate particles using physical and chemical methods. The physical preparation is based on the cryomilling, in which individual milling parameters are tested and it is investigated their effect on the milling efficiency and the size of the milled particles. The chemical preparation method is based on the dissolution of polyethylene terephthalate in a solvent and subsequent precipitation. In this case, the size, shape of the prepared particles and the content of residual solvent adsorbed on the particles were monitored. At the end of the work, it was concluded that the tested preparation methods are not suitable to prepare microplastics useable for environmental studies because the prepared particles do not have the required size or contain the residues of the used solvent.
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Titanium and titanium alloys prepared by cryogenic milling
Kozlík, Jiří ; Stráský, Josef (advisor) ; Janeček, Miloš (referee)
Ultra-fine grained materials are presently thoroughly investigated due to their enhanced mechanical properties. Cryogenic milling is one of the severe plastic deformation methods, which allow production of these materials. Titanium powder was processed by cryogenic milling in liquid nitrogen and argon and consequently consolidated via spark plasma sintering method. In this work, the influence of milling conditions (liquid nitrogen vs. liquid argon, material of balls, duration and speed of milling, usage of stearic acid) on size and shape of powder particles, contamination and mechanical properties was investigated. Particle size reduction was generally not observed, while their morphology changed significantly. Using liquid nitrogen as a cooling medium leads to strong contamination of prepared material and consequently to its hardening and embrittlement. Stearic acid supresses cold welding of particles during milling and enhances its efficiency. It is possible to eliminate stearic acid from powder by cleaning in acetone before sintering, to prevent contamination of processed material. Microhardness increased, depending on milling efficiency (in liquid argon), from original 178 HV to 200-300 HV range. Increase of yield and ultimate stength was observed in compression tests while maintaining ductility....
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