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QUANTUM-MECHANICAL STUDY OF INTERNAL STRUCTURAL TRANSFORMATIONS IN Pb-SUPERSATURATED Pb-Sn ALLOYS
Friák, Martin ; Čípek, Petr ; Pavlů, J. ; Roupcová, Pavla ; Miháliková, Ivana ; Msallamová, Š. ; Michalcová, A.
Motivated by a decades-long controversy related to the crystal structure of Pb-supersaturated solid solutions of Pb in Sn, we have performed a quantum-mechanical study of these materials. Focusing on both body-centred-tetragonal beta-Sn and simple-hexagonal gamma-Sn structures, we have computed properties of two alloys with the chemical composition Pb5Sn11, i.e. 31.25 at. % Pb, which is close to the composition of the experimentally found alloy (30 at. % Pb). The 16-atom computational supercells were designed as multiples of the elemental beta- and gamma-Sn unit cells, where the Pb atoms were distributed according to the special quasi-random structure (SQS) concept. Full structural relaxations of both beta- and gamma-phase-based alloys resulted in very significant re-arrangements into structures which do not exhibit any apparent structural features typical for the original alloys, and are, therefore, difficult to classify. The formation energies of the beta- and gamma-phase-originating equilibrium phases are 50 meV/atom and 53 meV/atom, respectively. Therefore, they are not stable with respect to the decomposition into the elemental lead and tin. Moreover, our calculations of elastic constants of both phases revealed that they are close to mechanical instability. Our results indicate that the studied Pb-supersaturated Pb-Sn solid solutions may be prone to structural instability, transformations into different phases and decomposition. Our findings may contribute into the identification of the reason why the subsequent experimental studies did not reproduce the initial published data.
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MINOR PHASES IN TIN-RICH HISTORICAL MATERIALS
Michalcová, A. ; Msallamová, Š. ; Fink, D. ; Friák, Martin
The historical organ pipes used to be manufactured from tin and tin-lead alloys. The tin-rich organ pipes usually contained copper as alloying elements, which make them similar to modern lead free soldering materials. The historical organ pipe materials can be used as model materials for natural ageing of soldering materials. Tin pest is a term for modification from white tin to grey tin, which leads to degradation of tin or tin-rich alloys. The influence of individual alloying elements has not been reliably described, yet. Not only on the concentration of the alloying element, but also the distribution may play the important role. In dependence on heat-treatment, the Cu can be in the Sn matrix present in these forms: i) as large intermetallic particles after casting (Cu6Sn5), ii) as solid solution after homogenization annealing and iii) as fine precipitates after ageing. The microstructure of the real historical organ-pipes material was studied and it was proven that contradictionary to the equilibrium phase diagram the Cu enriched was observed.
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Machining technology with the necessity of manual work
Svoboda, Jakub ; Kupčák, Radim (referee) ; Kalivoda, Milan (advisor)
Manual work is still necessary and often irreplaceable. In most cases, it is combined with machine production. As an example of such work we have chosen the production of tin lead alloy organ pipes, which encompasses several machining processes. All aspects of production were analyzed, including specification of the materials used and the various production processes. A pipe was produced according to these specifications for illustration. Individual chapters presented special manual tools and specific machinery. The difficulty and originality of the given production was outlined. This is professional work requiring manual dexterity, logical thought, attention to detail and an artistic spirit. During production we obtained an image showing a part of the cross-section of the pipe perpendicular to its axis. The image shows the correct shape of the soldered joint and the tangential connection of both sides of the sheet. Several aspects of the pipe were evaluated. The final chapters include feedback from customers and a general assessment of this particular work.
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TOWNHOUSE ON THE WATERFRONT IN PŘEROV
Veselý, Josef ; Wahla, Ivan (referee) ; Nový, Vítězslav (advisor)
Problems arising in the town house near the city center is largely determined by context and situation. The house is not possible to propose no relation to surrounding Material, shape, urban, typology context. Context, therefore, may seem to be anything problematic, but a proper understanding of context and unloading only leads to the correct destination. The house should have all these connections encoded in nature.
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Surveying of stream Lubě between Skalička and Malhostovice
Jirásek, Michal ; Volařík, Tomáš (referee) ; Vondrák, Jiří (advisor)
The aim of this bachelor thesis is planimetry and altimetry measuring tacheometric method part of valley Lubě stream and copy tacheometric plan in scale 1:500. Resultant tacheometric plan is connected to references geodetic systems S-JTSK and Bpv. Output of work was data ready to handover for create DMT at form edit triangulated network. Elaborate of tacheometric plan meets standards ČSN 01 3410 and ČSN 01 3411.
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The issue of determination of tin in environmental matrices
Bušinová, Markéta ; Sommer, Lumír (referee) ; Doležalová Weissmannová, Helena (advisor)
This diploma thesis deals with the retrieval of the content of tin in environmental media, the circulation in them and possibilities of the determination of tin in the environment. Summarizes available information on the properties of tin and its compounds, the occurrence and circulation of tin in environmental and determination of tin in environmental media, attention is paid to the determination of total tin content using method of ET-AAS. The experimental part is focused on optimization methods of determination for the ET AAS and selection of a suitable extraction procedure for determination of total tin content in soils and sediments. The best procedure for the determination of tin in the ET-AAS was applied to samples of soil, sediment and water. As the optimum matrix modifier was chosen the solution of Pd (NO3)2 in 5% ascorbic acid, the optimum pyrolysis temperature was 1400 °C and atomization temperature 2400 ° C. Neither of extraction procedures examined were found to be an appropriate procedure for the determination of tin in environmental samples and further work is necessary to optimize the method of separation.
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Tin and his species in the environment
Bušinová, Markéta ; Moos, Martin (referee) ; Doležalová Weissmannová, Helena (advisor)
Presented bachelor thesis is background research on tin and his species in the environment. Mainly deals with the effects of inorganic and organic compounds of tin on elements of environment. The work resumes accessible information about properties of tin and his compounds, entry of tin and his compounds into the elements of environment, cycle and occurrence of tin speciation in water, soils, sediments and biological materials.
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