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Interaction between TiAl melt and coated oxide refractories
Dočekalová, Kateřina ; Dlouhý, Antonín ; Zemčík, L. ; Fiala, J.
The present study focuses on reactions between ceramic crucibles and molten TiAl intermetallics. Coating strategies are investigated that exhibit a potential in slowing down the decomposition of the crucible wall. Uncoated crucibles (system TiAl melt - Al2O3 crucible) and crucibles with the coat (system TiAl melt - CaO coat - Al2O3 crucible) were used in melting and casting experiments. The reference state of the coated crucible before the melting trial was also investigated. Results of the SEM, EDAX and X-ray diffraction analysis contributed to the identification of the reaction zone and its chemical composition. The melt contamination with oxide inclusions results from the erosion process in which individual components of the melt diffuse along grain boundaries of the refractory and activate chemical reactions that decompose the crucible wall. Assessment of thermodynamic parameters associated with the chemical reactions helped in identifying the nature of the erosion process.
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Comparison of chemical composition of throughfall and deposited precipitation
Chaloupecký, Pavel ; Špičková, Jitka ; Fišák, Jaroslav ; Skřivan, Petr
Since June 2004 throughfall samples in beech and spruce vegetation have been taken at the observatory Milesovka. Ever since 1998 fog water samples have been taken there as well. In this paper are compared the concentrations of main ions and trace elements in throughfall and in deposited precipitation. The concentrations of main ions and trace elements in throughfal are primarily affected by the volume of samples. The highest concentrations of monitored sustances in throughfall were recorded in September and in October when the lowest rainfall totals were measured. The concentrations of monitored sustances were in throughfall mostly higher in spruce vegetation in comparison with beech vegetation. It is probably due to the thicker treetop in spruce vegetation on Milesovka observatory. Due to the thicker treetop a smaller volume of throughfall is let fall and the substances from ambient air are captured more effectively in comparison with beech vegetation. In the case of main ions the lowest concentrations were measured in fog water samples. For trace elements wasn´t data. From comparison with reference locality Lesni potok is obvious that concentrations of monitored sustances in throughfall on Milesovka exceed sharply concentrations in locality Lesni potok. This difference is considerably higher by spruce vegetation in comparison to beech vegetation which indicate that it is necessary take not only local air quality into account but also type of vegetation and thick of treetop which can very significantly contribute to the chemical composition of throughfall.
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Vakuová metalurgie intermetalik TiAl
Zemčík, L. ; Dlouhý, Antonín ; Król, S. ; Pražmowski, M.
To be able to melt successfully type gamma TiAl alloys it is absolutely necessary to solve the fundamental metallurgical problems associated with the reactions between the melt and the refractories of crucibles and ceramic moulds, with the reactions between the melt and residual gases in the furnace chamber, and with the evaporation of aluminium from the melt. The paper deals with the physico - chemical analyses of the above processes and gives their evaluation based on the results of experimental melts of the type of Ti48Al2Cr2Nb1B (at.%) obtained in vacuum induction furnace. The work also gives the results of oxidation tests for the Ti48Al2Cr2Nb1B(at.%) alloy.
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PM2.5 Chemical Composition at the Rural Background Site Košetice.
Schwarz, Jaroslav ; Cusack, Michael ; Karban, Jindřich ; Chalupníčková, E. ; Havránek, Vladimír ; Smolík, Jiří ; Ždímal, Vladimír
Measurements of atmospheric aerosols at rural background areas are important because they are not influenced by the urban emissions, and are therefore better suited to investigate the influence of long-range transport and trends in concentrations of individual pollutants. Summary of the measurements of total concentration and the concentration of PM10 and PM2.5 components was carried out in the works Putaud et al. (2004, 2010). Although the later work included the measurement of more than 60 stations across Europe, the post-communist countries contained data on PM2.5 from only four locations (Prague, Debrecen, Hungary, and two rural locations). Although Košetice place where this study was made, is also discussed there, it was for only PM10 and total carbon (TC). Therefore, the aim of this study is to fill this information gap, and provide additional information regarding the PM2.5 fraction and composition at the Central European background station Košetice.
Fulltext: content.csg -  PDF
Plný tet: SKMBT_C22016110313110 - PDF
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Sukcese hmyzenek (Protura) a vidličnatek (Diplura) na haldách chemické továrny
Rusek, Josef
Primary succession of Protura and Diplura was studied on deposits of a former chemical factory at Petrovice u Karviné, NE Moravia, Czech Republic, in 1978-1979, 1993 and in 2002-2004. Chemically loaded deposits were 15, 25 and 60 years old in 1979 and a primary succession without plant re-cultivation took place there. The succession was delayed on small humps and slopes where the deposited substrate was covered by terrestrial algae, lichens and mosses. Protura did not enter the primary succession before a moss cover occurred on the 15 years old heap and they were represented only by .i.Acerentulus traegardhi./i.. Three species of Protura were established in the 20 years old grass-covered stage as well as on the 49 years old heap. They occurred in low densities up to the 74 years old stage (and older), in which a proturan community of 4-6 species was established.
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Reoxidation in steel
Kotásek, Petr ; Veselý, Pavel (referee) ; Šenberger, Jaroslav (advisor)
This work is about development and methodology verification of data collection which will be used in the research of the reoxidation in steel castings. To examine reoxidation rate will be measured oxygen activity in the furnace, in the ladle and in the mould. Next it will be evaluated the chemical structure of mould slag, the chemical changes of steel and measured the volume and the area of the casting defects. Each technique is briefly described by the principle of measurement and each method has the results which are analysed. In the conclusion the experiment is summarized and there are mentioned the observations from this experiment.
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Total contents and speciation of arsenic and selenium in plants growing in soils with different physico-chemical properties
Tremlová, Jana ; Száková, Jiřina (advisor) ; Vymazal, Jan (referee)
This dissertation thesis deals with uptake, accumulation and transformation of arsenic and selenium in plants growing on soils with different chemico-physical soil properties. The contents of arsenic were investigated in 99 wild plant species, coming from 27 different families and 6 different vegetables growing in arsenic contaminated soils. The results suggest that there are species-specific mechanisms which protects certain plants from the excessive uptake of arsenic from the soil. On the other hand, there are plants using a strategy of accumulation, which theoretically may increase the risk of arsenic entry into the food chain, whether through grazing cattle and wildlife or through consumption of vegetables growing on arsenic contaminated soils. The most prevalent arsenic compounds are AsV and AsIII. Other arsenic compounds occure as minor species. An important finding was detection of arsenobetaine in Plantago lanceolata L. and Carex praecox Schreb ..
The contents of selenium were examined in 73 species of wild plants, coming from 29 different families. The results suggest that naturally low levels of selenium in the soil of selected locations along with a low capability of selenium uptake via collected plant species lead to the low content of selenium in plant biomass which may contribute to selenium deficient throughout the food chain. Foliar application of selenate on wild plant communities and on some types of vegetables in our case Brassica oleracea var. italica can have a positive impact on increasing the selenium content in the aboveground biomass of these plants and by extension, increase the selenium content in the human diet. Dominant selenium compounds in the aboveground biomass of the analyzed plants were SeVI and selenomethionine, with variable proportion of other commonly occurring organic selenium compounds, which is mainly affected by plant species.
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Noise, Transport and Structural Properties of High Energy Radiation Detectors Based on CdTe
Šik, Ondřej ; Lazar, Josef (referee) ; Navrátil, Vladislav (referee) ; Grmela, Lubomír (advisor)
Poptávka ze strany vesmírného výzkumu, zdravotnictví a bezpečnostního průmyslu způsobila v posledních letech zvýšený zájem o vývoj materiálů pro detekci a zobrazování vysokoenergetického záření. CdTe a jeho slitina CdZnTe. jsou polovodiče umožnují detekci záření o energiích v rozsahu 10 keV až 500 keV. Šířka zakázaného pásma u CdTe / CdZnTe je 1.46 -1.6 eV, což umožňuje produkci krystalů o vysoké rezistivitě (10^10-10^11 cm), která je dostačující pro použití CdTe / CdZnTe při pokojové teplotě. V mé práci byly zkoumány detektory CdTe/CdZnTe v různých stádiích jejich poruchovosti. Byly použity velmi kvalitní spektroskopické detektory, materiál s nižší rezistivitou a výraznou polarizací, detektory s asymetrií elektrických parametrů kontaktů a teplotně degenerované vzorky. Z výsledků analýzy nízkofrekvenčního šumu je patrný obecný závěr, že zvýšená koncentrace defektů způsobí změnu povahy původně monotónního spektra typu 1/f na spektrum s výrazným vlivem generačně-rekombinačních procesů. Další výrazná vlastnost degenerovaných detektorů a detektorů nižší kvality je nárůst spektrální hustoty šumu typu 1/f se vzrůstajícím napájecím napětí se směrnicí výrazně vyšší než 2. Strukturální a chemické analýzy poukázaly, že teplotní generace detektorů způsobuje difuzi kovu použitého při kontaktování a stopových prvků hlouběji do objemu krystalu. Část mé práce je věnována modifikaci povrchu svazkem argonových iontů a jejímu vlivu na chemické složení a morfologii povrchu.
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