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Archaeological analogs for verification of container lifetime models for deep radioactive waste repositories : Final report of project TK01010040
Stoulil, J. ; Mukhtar, S. ; Lhotka, M. ; Bureš, R. ; Kašpar, V. ; Šachlová, Š. ; Pecková, A. ; Havlová, V. ; Danielisová, Alžběta ; Malyková, Drahomíra ; Barčáková, Ludmila ; Machová, Barbora ; Březinová, Helena ; Ottenwelter, Estelle ; Němeček, J. ; Němeček, J.
More than 200 artefacts from 15 localities were studied within the scope of this project. 4 localities were crucial, because those were pond beds with continual flooding. Soils at all localities were coarser compared to bentonites and lacked swelling ability. Pore solutions of the soils were very similar to bentonite pore solutions. They differ in cation composition, but anion composition was similar, which is more important for corrosion behaviour. The environment was not completely anaerobic, what influenced the composition of corrosion products. The compounds were oxides and oxohydroxides. Very low oxidation-reduction potential (fully anaerobic environment) is necessary for the formation of carbonate-based corrosion products, that were detected as major corrosion products in the previous lab and in situ experiments on another projects. Nevertheless, the oxygen transport was very slow and the contribution of aerobic corrosion was negligible compared to anaerobic corrosion. The evaluation of archaeological artefacts revealed very important factors influencing corrosion mechanism in latter stage of soil burial. Precipitation of corrosion products is a driving phenomenon for transport limitation and decrease of corrosion rate in the early stage of burial, while the ferrous species transport is limited extensively within the latter stage resulting in mechanical stress of inner corrosion products layers to previously formed corrosion products and subsequent cracking. This mechanical damage is repeated in the cycle. The mechanical properties of corrosion products are poor, they are easily deformable and very porous. The project has revealed a very important phenomenon, necessary for the right lifetime estimation, which would not be obvious based on the short-term experiments data.
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ELECTROCHEMICAL CHARACTERISTICS OF ADVANCED MAGNESIUM ALLOYS PROCESSED BY POWDER METALURGY
Minda, Jozef ; Nový, František (referee) ; Stoulil, Jan (referee) ; Hadzima,, Branislav (advisor)
The subject of the present dissertation is basic research in the field of advanced magnesium-based materials with high potential for medical applications prepared by powder metallurgy. These materials are evaluated in terms of corrosion behaviour in corrosive media by chemical composition and set conditions simulating the physiological environment of the human body (Hank's Balanced Salt Solution was used in this work). The aim is to analyze the influence of the processing parameters, chemical composition and structure on electrochemic characteristics of theprepared materials. For this purpose, a deeper of the the corrosion behavior, to obtain electrochemical characteristics and to investigate the degradation properties of the studied materials by means of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), with elemental analysis by energy-dispersive spectroscopy (EDS) and other complementary methods. The materials for the experiments are prepared using powder metallurgy, which allows the formation of composites with compositions that do not match conventional manufacturing technologies. Thus, pure Mg samples were prepared at process parameters with pressing pressures of 100 and 500 MPa at 400 °C and also samples pressed at 500 MPa and room temperature were tested. Furthermore, MgZn composites prepared at a pressing pressure of 500 MPa and a temperature of 300 °C with a Zn content of 1, 5, 10 and 15 wt.% or MgZn composites pressed at a pressure of 500 MPa and a temperature of 400 °C with a Zn content of 1, 5 and 10 wt.%. Composites of the Mg-hydroxyapatite binary system pressed at 500 MPa and 400 °C with hydroxyapatite contents of 10, 20, 30 and 40 wt.% were also studied. The degradation mechanisms of these materials were investigated using the above mentioned methods and the basic electrochemical parameters and their evolution during the time of exposure were determined. From the results, the influence of process parameters, chemical composition and the corrosive environment itself on the studied materials is evaluated. Several materials that appear to be most suitable for the medical application are described and the causes of degradation behaviour at the level of the structure of the materials and their electrochemical interaction with the corrosive environment are also discussed in the dissertation thesis. Compaction and densification positively influenced pure Mg samples, where samples pressed at 500 MPa and 400 °C are further selected as reference material. Increasing Zn content positively electrochemically affects the corrosion resistance of MgZn series of samples pressed at 500 MPa and 300 °C, on the contrary, in the combination of electrochemical - microgalvanic and structural effects, low Zn content is optimal for MgZn composites pressed at 500 MPa and 400 °C. For Mg-hydroxyapatite materials, in agreement with the literature, it was shown that the most stable corrosion product layers with the best corrosion properties and evolution in time are formed for samples with hydroxyapatite content up to 10 wt.%.
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Combined coatings against mechanical wear and corrosion low carbon steel
Brožek, Vlastimil ; Pokorný, P. ; Kolísko, J. ; Vokáč, M. ; Mastný, L. ; Stoulil, J.
In this study, special ceramic coatings were prepared on low carbon steel (1.0060 - EN 10027-2) via the plasma spraying technique using a WSP®-H plasma generator with output of up to 40 kg/h of aluminum oxide. Corundum coatings were deposited directly on the surface of steel plungers equipped with an anti-corrosion interlayer of zinc phosphate. Coating adhesion properties were tested using pin-off tests (modified ISO 4624) and reached a maximum value of 26 MPa. Corrosion resistance was evaluated by measurements of impedance spectra in the 100 kHz - 10 mHz range in a water solution of sodium sulfate. The capacity of electric double-layer varied depending on the porosity and thickness of the coating. Low-porosity coatings of >1.5 mm thickness had RCT 1.29·105 Ω·m2. The abrasive resistance of coatings was measured by rotary/machining test with SiC cutting knives, using a downforce of 50 kg·cm-2. Abrasion losses decreased with the quality of finish - starting at 0.00266 g cm-2 min-1 down to virtually zero losses after polishing the surface below Ra = 0.55 micro m.
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Corrosion behavior of plasma coatings CuAl10 and CuAl50 on magnesium alloy AZ 91
Kubatík, Tomáš František ; Stoulil, J. ; Stehlíková, K. ; Slepička, P. ; Janata, Marek
The most common magnesium alloy AZ 91 is widely used as a structural material, but its use is limited at higher temperatures and high humidity. Plasma spraying is a technology that allows to prepare protective metallic and non-metallic coatings on a wide variety of substrates including magnesium and its alloys. In this study, CuAl10 and CuAl50 were plasma sprayed on magnesium alloy AZ 91 with the aim to study corrosion resistance of the plasma sprayed coatings. The corrosion resistance of layers was evaluated by the method of electrochemical potentiodynamic measurement as well as long-term corrosion tests in a condensation chamber with 0.5 mol\nNaCl at the temperature of 35 °C for 1344 hours. Layers with 1, 2, 5 passes and passes of CuAl10 with the thickness ranging from 75 to 716 mm and CuAl50 with the thickness ranging from 64 to 566 mm were prepared. The increased corrosion velocity was observed in the case of thin layers of 2 and 5 passes due to the development of a galvanic corrosion couple. The CuAl10 layer prepared with ten passes has an outstanding corrosion resistance.
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