Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Remelting Behaviour of Pure and Az63 Magnesium Chips(01. Izmir Institute of Technology, 2023) Yörük, Pınar; Gökelma, Mertol; Akkurt, SedatMagnesium is a widely used light metal in many areas such as the automotive, aerospace, and medical industries. Magnesium has become widely used in industrial applications despite its poor corrosion resistance and high cost. It has great machinability, weldability, and remarkable mechanical properties such as lightweight, strength, and creep resistance. Magnesium is considered by the European Union as a critical raw material. The demand for magnesium has been increasing and it is used as a substitute for other heavy materials in many applications. Thus, recycling magnesium scrap is important due to limited raw material accessibility and environmental concerns. Secondary sources of magnesium should contribute to the economy and the procedure should be as efficient as possible to prevent metal loss. Magnesium is typically remelted under a salt flux (chloride and fluoride mix) which removes the surface oxides and other contaminants from the metal or under a cover gas that covers the surface against oxidation. This research studies the effects of salt composition, different fluorides, and the compaction degree of turnings on the recovery efficiency of pure and AZ63 magnesium alloy chips that were remelted under different chemical compositions of NaF, CaF2, MgCl2, KCl, and NaCl salt fluxes. The purpose is to minimize the metal loss and increase the coalescence ability of the metal. Metal yield and coagulation efficiency were reported XRD, SEM-EDX, XRF, and TGA analysis were performed for the characterization of chips and remelted samples. The melting point and density of the salt fluxes were determined by the FactSage software.Master Thesis Synthesis and Characterization of Mgb2 Superconducting Wires(Izmir Institute of Technology, 2008) Horzum Polat, Nesrin; Özgen, TamerkanIn this study, the superconducting properties of laboratory synthesized MgB2 was investigated. In the first part, MgB2 synthesis using commercial magnesium and boron (95-97% purity), and its microstructural and electrical characterization was investigated.Effects of sheath material and annealing temperatures were also examined. The microstructural studies showed that when Cu tubes were used as sheath material, MgCu2 forms instead of MgB2 even at 700oC, while on Fe clad cores, the major phase was MgB2 with minor MgO constituent. The transition temperatures of Fe clad wires were measured between 39K and 40K, whereas no transition temperature was observed for Cu clad wires. The Ic value of the Fe clad MgB2 wire was about 25 A at 4K, while the copper clad wire could not carry current and formed resistance. In Fe clad wires, better results were obtained at annealing temperature of 800°C for 30 minutes. In the second part, MgB2 synthesis using commercial magnesium and boron (90% purity) was tried. 0-5-10-15 wt% of Mg doping and, additionally annealing temperatures were examined. Powder-In-Tube method was used for wire production. 10 wt% Mg addition was seen to be beneficial as compared to the stoichiometric MgB2. 750°C was found to be the most suitable temperature for the formation of MgB2 phase. The Ic value of the wire was measured as 13 A at 4K and it showed a broader transition with non-zero resistivity, transition temperature of 24K.In the third part, 200 m long four filament MgB2/Cu wire was successfully produced in laboratory conditions.Master Thesis Synthesis of Magnesium Hydride and Sodium Borohydride at Low Temperatures(Izmir Institute of Technology, 2006) Akyol, Emel; Özgen, TamerkanIn this study, experimental conditions for production of magnesium hydride and sodium borohydride by low temperature grinding are investigated. In the first set of experiments, it was attempted to confirm the information presented in the literature that magnesium hydride could be produced by heating at 350oC for 24 hours under 10 atmospheres of pressure. The results obtained in this study indicated that even a higher temperature heating at 400oC under 10 bar hydrogen pressure was insufficient for magnesium hydride formation. Heating and grinding time were selected as the most effective parameters by which a full-factorial experimental design methodology was implemented. Statistical analysis results indicated that a combination of grinding and a 50oC heating was most effective. Hence, grinding was identified as the most significant factor effect on the production of magnesium hydride. Two different mills were used, in this study, and it was found that disc mill was more effective than ball mill. Different combinations of dehydrated borax, sodium carbonate, magnesium, hydrogen gas, sodium hydride and sodium metaborate were tested without success to produce sodium borohydride. In the final set of experiments, sodium borohydride could be successfully produced by using trimethyl borate and sodium hydride in a disc mill at 50oC under 10 bars hydrogen pressure.Master Thesis Effects of Trace Elements on the Production of Baker's Yeast(Izmir Institute of Technology, 2002) Üzelyalçın, Berna; Harsa, Hayriye ŞebnemBaker.s yeast has been used widely in traditional bakeries to produce different kinds of baked products and for many biotechnological purposes. The principal raw materials used in producing baker.s yeast are the pure yeast culture and molasses. Cane molasses and beet molasses contain 45 to 55 % sugar in the forms of sucrose, glucose, and fructose. Molasses, which is a rich carbon and mineral source, contains most of the nutrients and minerals required for baker.s yeast production. Nutrients and trace elements (magnesium, copper and zinc) that are not present in sufficient quantities in molasesses are added to the fermentation medium. In this study, the effects of Ca2+, Mg2+, Cu2+ and Zn2+ on baker.s yeast production were investigated. The method of Food Composition Laboratory (FCL), Human Nutrition Research Center, Beltsville, US, was used for the preparation of the fermentation samples prior to ICP-AES analysis. The concentrations of Ca2+, Mg2+, Cu2+, Zn2+ were determined in the raw materials entering the fermentors and the products. FCL digestion method was evaluated on precision and accuracy; linear standard curves were obtained for the studied concentration ranges of Ca2+, Mg2+, Cu2+ and Zn2+. Standard addition curves for each element in 45 brix molasses and dry yeast samples were constructed and spike recovery percentages were calculated. High spike recovery percentages were obtained for all elements in both dry yeast and molasses with the FCL method. In industrial fermentations, uptakes of Ca2+, Cu2+, Mg2+ and Zn2+ by the yeast cells were calculated as mg/kg dry yeast at 4h time intervals. The uptake rates were evaluated based on the available element concentration in the medium and the uptake of the elements. Results showed that, as the uptake of Ca2+ increased with time, uptake of Mg2+, Cu2+ and Zn2+ decreased. The yeast cells used the available elements with decreasing uptake rates except Ca2+. During the first hours of fermentation, uptake rates were high. The maximum uptake rates observed for each element in two different industrial fermentations were: 17.73-23.32 mg Cu2+/ kg dry yeast cells , 195.64-413.46 mg Zn2+ / kg dry yeast cells, 2106.46-2051.74 mg Mg2+ / kg dry yeast cells. Ion concentrations of biomass in industrial fermentations revealed that same amounts of Mg were taken by the cell from the fermentation medium under similar conditions. This was verified by the studies done in lab-scale using pure culture of S.cerevisiae, grown on different concentrations of Mg2+. It was found that uptake of Mg2+ was constant and very close to the uptake values of industrial fermentations. 806.7 mM Mg2+ was taken by 1 kg of dry yeast cells. This is in agreement with the stated Mg2+ uptake concentration range 500-1000 mM of Saccharomyces cerevisiae in literature. In the industry, magnesium is added in the form of Mg.SO4.7H2O to the fermentation medium. SO42- ions coming from the MgSO4.7H2O cause settling problems in the waste treatment system of the plant. Generally, molasses contain sufficient concentration of Mg2+ ions required for baker.s yeast production in the industrial scale. Since Mg2+ has toxic effects at high concentrations and its addition is increasing the cost of the process and causing difficulties in the waste treatment of the plant, it may be concluded that addition of Mg2+ as MgSO4.7H2O to the fermentation medium should be done after determining the Mg2+ concentration of molasses. Instead of using excessive amounts of MgSO4.7H2O, only the required quantity should be added to the fermentation medium.