Master Degree / Yüksek Lisans Tezleri

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  • Master Thesis
    Preparation and Characterization of Alumina Powders and Suspensions
    (01. Izmir Institute of Technology, 2000) Şakar, Aylin M.; Polat, Hürriyet
    This study involves the preparation of fine alumina powders derived from Bayer gibbsite and also aqueous alumina suspensions by using tri block copolymers. Preparation of alumina powders was performed by decomposition of gibbsite into transition alumina phase followed by controlled transformation to alpha phase. To increase transformation rate.. to a-alumina in transition phase hence influence the nucleation and growth rate of the solid-solid phase transformation ball milling and ultrasonication was applied. Gibbsite was thermally treated at 900°C to reach a transition form of alumina. In some cases a heat treatment at 350 °C was applied to create a network of submicroscopic cracks in the heated gibbsite that may help grinding. Ball milling and ultrasonic treatment before calcination at 1100, 1200 °C and 1450 °C followed these heat treatments. Characterizations of the powders were performed with XRD, FTIR, thermal analysis, density measurements and particle size determinations. According to the XRD patterns, complete transformation to alpha form occurred in powders previously heat treated at 900°C, mechanical treated and then cfllcined at 1200 °C in 8 hours and 1450 °C in 2 hours. Powders that were calcined at 1100 °C and 1200 °C in 1-2 hours contained considerable amount of kappa form together with alpha. The effect of the polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO/PPO/PEO) blockcopolymers on the dispersion behaviour of alumina powder suspensions in water were investigated at <1>.0.125,1.0,14 and 50 vol% solid loadings by rheological and turbidity measurements. To compare the effects of block copolymers with other type of dispersants, measurements of some other well known dispersants were also conducted at 10-7 to 10-3 M. The results indicated that type block copolymers with high EO percentage have a positive effect when they are used with ultrasonic treatment on the agglomerated alumina suspensions. But it was not able to create stable dispersions ll1 the absence of ultrasonic bath application. Turbidity measurements at <1>.0.5 wt% showed that some dispersants gave higher dispersion but the stability was reached after a time period. Ultrasonic treatment created stability but lowered the turbidity values.
  • Master Thesis
    Microstructural Analysis of the Corrosion of Al2o3 and Zro2 in Frit Melts
    (Izmir Institute of Technology, 2007) Şenöz, Ceylan; Akkurt, Sedat
    Dense alumina and zirconia crucibles manufactured in the laboratory by slip casting were tested for their resistance to corrosive attack by opaque and transparent frits between 1400-1500oC. Interface between the crucible and the frit was investigated by Scanning Electron Microscopy (SEM, Philips XL-30S FEG) equipped with EDS (Energy Dispersive Spectroscopy) unit, X-ray diffraction (XRD, Philips X.Pert Pro), and Optical Microscope (OM, Nikon Eclipse L150). Formation of a continuous band of zinc aluminate (gahnite) crystals was observed at the interface between the alumina crucible wall and the contained opaque and/or transparent frit melt. When opaque frit was used, isolated pockets of zirconia were present adjacent to the zinc aluminate band inside the frit. Deeper inside the frit incompletely dissolved zircon were observed. On the other hand zirconia crucible failed against both of the corrosive frits, resulting in complete penetration of frit species into zirconia crucible wall. Thermodynamic predictions based on the use of phase diagrams also produced similar conclusions with the practically observed results. Crucibles with 50 wt% zirconia and 50 wt% alumina were also manufactured and tested for their corrosion resistance against the frit. It was found that the alumina crucibles could be safely used for corrosion testing with minimal aluminum contribution to the frit melt.
  • Master Thesis
    Gelcasting of Alumina Ceramics With Gelatin and Carrageenan Gum and Investigation of Their Mechanical Properties
    (Izmir Institute of Technology, 2013) Koçlar, Galip Sarper; Çiftçioğlu, Muhsin; Çiftçioğlu, Muhsin
    In this study, use of gelatin and carrageenan gum as gel formers in gelcasting process of alumina ceramics was aimed. The effects of each gel former on the mechanical properties of gelcasted alumina ceramics were distinctly investigated. Firstly, an experimental design was made according to pre-experimental studies and researches. In this experimental design, it was determined what the factors should be and how the levels of factors should change. Two groups of gelcasting slips were prepared with alumina powder. One of them was the group that contained gelatin with changing ratios from 3 to 6 wt%. Other was the group that contained carragenan gum with changing ratios from 1 to 2 wt%. Alumina powder amounts of the slips in also each group were the same and changing from 47 to 53 vol%. Furthermore, in order to see the direct effect of each gel former type and amount on mechanical properties and compare the methods of gelcasting and slip casting, alumina slips that contained no gelatin or carrageenan gum were also prepared. Green alumina samples in suitable shapes for mechanical tests were obtained by gelcasting method from the prepared slips. After green samples were dried, half of them were sintered at 1550 oC. Rest of them weren’t subjected to any heat treatment. Green samples in block shape were cut in suitable dimensions for 3-point bending test before they were sintered. Shrinkage and densification ratios of the alumina samples after drying and sintering were measured and calculated. At the end of the mechanical tests applied on green and sintered alumina ceramics, data about change in their bending strength, compressive strength and hardness values due to varying gel amount and sintering were obtained. These data were analyzed, then the obtained results were interpreted. While optimum gel former amount needed for maximum compressive and bending strength of gelatin-gelcasted alumina samples was 5 wt%., this amount for that of gum-gelcasted alumina samples was 1.7 wt%. The effect of alumina solid loading on mechanical properties of gelcasted alumina samples was unclear. After sintering of gelatin-gelcasted alumina samples, the densification reached to a maximum of 95.80%.
  • Master Thesis
    The Use and Characterization of Composite Alumina-Titania Membranes for Gas Separation
    (Izmir Institute of Technology, 2002) Topuz, Berna; Çiftçioğlu, Muhsin
    The preparation, characterization and pure gas permeation of sol-gel derived alumina and silica membranes were investigated in this work. The effects of various parameters on sol particle size and unsupported membranes pore structure were investigated by laser light scattering particle size and N2 adsorption-desorption analysis .-alumina membranes were prepared on ZrO2 supports by successive dipping into boehmite sols. Almost proportional decreases in sol particle size and membrane pore diameter were determined with increasing acid content during the boehmite sol preparation. Increasing the H+/Al3+ mole ratio from 0.1 to 0.25 caused the hydrodynamic particle size and BJH pore size to decrease from 65 to 30 nm and 3.6 to 2.9 nm, respectively. The pore size increased from 2.8 nm to 3 nm upon increasing the calcination temperature from 500 to 600oC. Unsupported membranes were heat treated in the 200 to 1200 oC range for the characterization of the phase structure. Boehmite was the dominant phase below 500 oC, gamma being the dominant phase up to 900 oC and pure .-Al2O3 phase was obtained upon heat treatment at 1200oC. Pinhole and crack free alumina membranes about 3 .m (double layer) in thickness were observed from SEM pictures with insignificant infiltration. The CO2 permeability through the double layer .-Al2O3 membrane calcined at 600 oC was about 2.25*10-7 mol/m2.s.Pa, and had a slight pressure dependence which may indicate Knudsen Diffusion and Laminar Flow as the effective transport mechanisms. Upon the calcination of a similar double layer alumina membrane at 500oC, the CO2 permeability decreased to 1.51*10-8 mol/m2.s.Pa and was independent of pressure. Silica membranes were prepared by a sol-gel technique. These sols were prepared by acid catalysed hydrolysis and condensation of tetraethylorthosilicate in the presence of a solvent. The effects of processing parameters like the acid type and amount utilized during sol preparation, sol aging, heat treatment conditions, dipping time on the membrane pore structure and the permeation of pure gases were investigated. The supported membranes were heat treated in the 50-400 oC range. The N2 and CO2 permeabilities of silica membranes varied in the 2.2 * 10-10 . 2.7 * 10-8 mol / m2.s.Pa and 1.2*10-9 . 6.95*10-8 mol / m2.s.Pa range for single layer membranes dipped for 10 seconds into the sol. The sols became viscous and gelled in 16 hours at 50 oC. The O2 permeability increased with aging time. The optimum dipping time during processing was determined to be 10 seconds. The permeabilities of these membranes increased significantly with the sol acid content. The thickness of the silica membranes were determined to be about 2.m and significant infiltration into the support was observed from the SEM pictures.
  • Master Thesis
    Oxidation of Ethanol and Carbon Monoxide on Alumina-Supported Metal/Metal Oxide Xerogel Catalysts
    (Izmir Institute of Technology, 2011) Ateş, Selcan; Şeker, Erol
    The main goal of the study is to investigate the effect of metal type, metal oxide type and metal/oxide loading on the conversion as a function of temperature for the complete combustion of ethanol and CO in air over single step sol-gel made Al2O3 supported metal and mixed metal oxides. Two types of catalysts, Pt/Al2O3 (1, 2, and 3 % Pt loaded) and CuO-Mn2O3/Al2O3, with Cu/Mn molar ratio of 1:1, 5:1 and 12:1, and 50, 70, and 90% metal loading, were synthesized by impregnation and single step sol-gel methods, respectively. In addition, by synthesizing CuO/Al2O3, Mn2O3/Al2O3 and Pd-Mn2O3/Al2O3, the catalytic activity relationship between metal and metal oxides were clarified. Characterization of the samples was performed by XRD, BET, and FT-IR techniques and it was observed that among the metal oxide catalysts, CuO-Mn2O3/Al2O3 (70 wt%; (Cu/Mn)molar=1) showed the highest activity due to the formation of Cu1.5Mn1.5O4 phase while 3% Pt loaded alumina was the catalyst demonstrated the highest catalytic activity among the noble metal catalysts. Also, Pd addition enhanced the activity of metal oxide catalyst by lowering the temperature at which ~99% ethanol conversion was obtained. Moreover, deactivation of CuO-Mn2O3/Al2O3 mixed oxides was observed due to the irreversible adsorption of CO2 on catalyst surface at low temperatures. Except for Pt containing catalysts, the catalysts that showed high catalytic activity in ethanol oxidation was also tested for CO oxidation and CO2 formation was detected qualitatively at varying operating temperatures.