Master Degree / Yüksek Lisans Tezleri

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Publisher: search.filters.publisher.Izmir Institute of TechnologySubject: search.filters.subject.Microstructure

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  • Master Thesis
    Production and Characterization of Emulsion Derived Porous Sioc+tio2 Submicron/Nanospheres
    (Izmir Institute of Technology, 2020) Ahmetoğlu, Çekdar Vakıf; Ahmetoğlu, Çekdar Vakıf; 03.09. Department of Materials Science and Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    The water resources are polluted because of the widespread use of dyes in the industry, resulting in a major ecological threat. Among the various water treatment techniques, adsorption and photocatalytic degradation methods are the most preferred owing to their easy applicability, low cost, and high efficiency. Silicon oxycarbide (SiOC), which is a type of polymer-derived ceramic, has the potential to be used in harsh environmental conditions thanks to its strong chemical stability and oxidation resistance, that being said it can also be used as a photocatalyst substrate. Titanium dioxide (TiO2) photocatalysts are extensively used for purification of contaminated waters. And also, TiO2 particles are synthesized with various material groups to investigate the adsorption and photocatalytic effect. In this thesis, initially, submicron/nano SiOC spheres were produced via an oil in water (o/w) emulsion technique by using parameters such as two types of preceramic polymer precursors (silicon oil and resin), mixing types (magnetically and ultrasonically), and different pyrolysis temperature (600-1200 oC). Upon the formation of submicron/nano SiOC spheres, selected samples were impregnated with a different molar of titanium oxide precursor solution (Titanium(IV) n-butoxide (TBT)) and calcined at 450 °C for 4 h. Various amounts of (0-5-10-20 wt.%) TiO2 containing submicron/nano SiOC spheres were produced and then characterized in depth by various techniques. Finally, the effects of pyrolysis temperatures and the amount of TiO2 were investigated in terms of adsorption and photocatalytic performance against aqueous cationic dye (methylene blue) (MB) solution. In the adsorption experiments, pure SiOC submicron/nanospheres (UM1200), pyrolyzed at 1200 oC, showed the best performance at the end of 24 h in the dark with 64% adsorption. In photocatalytic experiments, samples obtained by coating the SiOC substrate produced by pyrolysis at 600 oC with different amounts of TiO2 (UM600T5, UM600T10 and UM600T20) showed 79%, 80%, and 87% photodegradation efficiency.
  • Master Thesis
    Microstructural and Mechanical Characterization of Nitrogen Ion Implanted and Plasma Ion Nitrided Plastic Injection Mould Steel
    (Izmir Institute of Technology, 2003) Onmuş, Ortaç; Öztürk, Orhan; Öztürk, Orhan; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    In this study, high-chromium ferritic plastic injection mould steel (X36CrMo17, similar to AISI-420F) was subjected to plasma nitriding and nitrogen ion beam implantation under various conditions. The effectiveness of conventional plasma nitriding and nitrogen ion beam implantation conditions in improving the tribological properties and mechanical performance was investigated.The experimental results clearly show that plasma nitriding and nitrogen ion beam implantation lead to the development of the various near-surface microstructures and enhanced mechanical properties.Plasma nitriding was performed at a temperature range between 520-540 °C, with a bias voltage of 500 V for 15 to 18 hours under various gas mixtures of N2+H2 in an industrial nitriding facility (micro-pulsed DC). Nitrogen ion beam implantation was carried out with 2x1017 and 1x1018 ion doses with an 85 kV nitrogen ion energy at temperatures 200 a1C. Near-surface phases, compositions, plasma nitrided and nitrogen implanted layer thicknesses and the strength of these layers were studied by a combination of symmetric (0-2.) and grazing incidence x-ray diffraction (XRD and GIXRD), conversion electron and x-ray Mössbauer spectroscopies (CEMS and CXMS), cross-sectional scanning electron microscopy (SEM) and cross-sectional nanohardness measurements. The corrosion behaviour was investigated by a salt spray method and by observation of acid etching during SEM sample preparation. The tribological properties (friction and wear) were examined by a ball-on-disc tribometer.Combined Mössbauer, XRD, and SEM analyses clearly indicate that (Fe,Cr,Mn)-nitrides and CrN are distributed in the top nitrided layers of several micron thickness. The CEMS and CXMS analyses show the nearly complete decomposition of the near surface and deeper crystal structures into pure bcc (Fe), (Fe,Cr,Mn)-nitrides, consisting of Fe3N and Fe4N, and CrN. The XRD, CEMS and CXMS results also show an Fe3C-like carbide phase, (Fe,Cr,Mn)3C, in the nitrided layers, whose presence is attributed to C segregation to the near-surface region and to extra carbon being present in the nitriding system. The nitriding conditions with the gas composition N2/H2.1 produces the thickest nitrided layer (about 135 .m) with an excellent resistance to corrosion. The nanohardness measurements indicate that the cross sectional hardness-depth profiles under all nitriding conditions is found to be plateau-shaped, and the nitrided layer surface hardness values are found to be increased by a factor of about three in comparison to that of the substrate material. This study also showed that the hardening effect in plasma nitrided specimens was due to a fine and homogeneous chromium nitride precipitation. The wear analysis results showed that the nitrided layers have reduced friction coefficient values (20 to 25%) and possess excellent wear resistance in comparison to that of the bulk material.It was also found that nitrogen ion implantation into plastic injection mould steel produces N content rich layers (less than 0.1 .m thick) with enhanced wear and corrosion properties. The surface nanohardness measurements of the low and high dose implanted specimens indicate that the hardness values increase by factors of about 1.4 and 1.6, respectively, compared to the substrate material. The salt spray corrosion analysis (2% NaCl solution in distilled water) experiments showed enhanced corrosion behaviour for the N implanted layers, and that nitrogen ion implantation is a viable method for improving corrosion resistance of plastic injection mould steel.Combined Mössbauer and XRD data reveal that the N implanted layers consist of nitride phase, (Fe,Cr,Mn)2+xN, with both magnetic (x-1) and paramagnetic (x-0) characteristics. Based on the CEMS results, the N implanted layer thicknesses are found to be - 40 and 65 nm for the low dose (2x1017 ions/cm2) and high dose (1x1018 ions/cm2) dose N implanted specimens, respectively.
  • Master Thesis
    Towards the Design of Ultrasound Contrast Agents: Investigation of Monolayer Microstructure
    (Izmir Institute of Technology, 2011) Akıncı, Saliha Zeyneb; Kılıç Özdemir, Sevgi; Kılıç Özdemir, Sevgi; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    This thesis work is focused on the monolayer formation of phospholipid molecules and surfactants by Langmuir-Blodgett thin film technique on air/water or phosphate buffer interfaces. This study is also devoted to find out the effect of surfactants, the mixing ratio of the components, and also the phosphate buffer solutions on the monolayer films. The pH of the phosphate buffer solution that is used in experiments, is 7.2 and is coherent with the human blood plasma. In addition to this technique, a microscopic technique is employed. The monolayer features in different liquid interfaces are investigated by Brewster angle microscopy technique. In this study, the effect of ionic strength coming from the buffer solutions are examined in whole pure components and mixtures. It is aimed to find out to obtain more detailed information from the surface-pressure versus mean molecular area isotherms that are obtained from Langmuir-Blodgett technique. Therefore, the exact behavior of these organic thin films at the air/liquid interfaces are studied. The miscibility behavior and thermodynamic analysis of the mixed monolayers are also examined for each of the mixtures.