Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Coating of Spinel Layers on Alumina by Electrostatic Spray Deposition (esd)(01. Izmir Institute of Technology, 2023) Demirkol, İrem; Akkurt, SedatMgAl2O4 spinel layer was coated on dense alumina pellets by advantageous ESD among the other deposition methods in terms of providing a simple, inexpensive setup and good control of the layer morphology. The main goals are successfull deposition of spinel layers on alumina pellets by ESD, to investigate the effect of ESD parameters (working distance, flow rate of precursors, applied voltage) on coating microstructure by conducting full factorial design experiments and to determine the best experimental conditions for a porous layer. Besides, MgCr2O4 layer was coated on dense alumina and MgAl2O4 layer was deposited on bisque-fired alumina pellet to extend the scope of the work. Alumina powders were compressed and sintered, respectively to obtain pellets. MgAl2O4 spinel precursor solution was sprayed on the alumina pellets by changing the parameters accordingly the full factorial design. MgAl2O4 and MgCr2O4 solutions were also sprayed on the bisque-fired and the dense alumina pellets with the parameters given the best porous layer. Elemental analysis of the residues obtained after evaporation of the solutions by energy dispersive X-ray spectroscopy (EDX), both unheated and post-heated residual powders of solutions by X-ray diffraction (XRD) and surface morphologies of coated pellets by scanning electron microscopy (SEM-EDS) were analyzed. Spinel layers on alumina pellets were successfully coated by ESD, which could provide variable surface morphologies. The optimum conditions for a porous layer were obtained as working distance of 15 mm, flow rate of 0.25 mL/h and applied voltage of 6 kV in this study. The coatings on the pellets before further heating were amorphous. Post-heating of the pellets were required to obtain crystalline spinel structure.Master Thesis Formation of Srtio3[tio2] Ceramic Composites at Low Temperatures(01. Izmir Institute of Technology, 2021) Karataş, Esin; Adem, Umut; Ahmetoğlu, Çekdar VakıfStrontium titanate ceramics are materials belonging to the perovskite material group with the formula ABO3. Strontium titanate ceramics have been a preferred material in many areas, such as the electroceramics industry, due to its high dielectric constant and high chemical stability and generally produced by manufacturing processes such as solid-state synthesis, hydrothermal method, and sol-gel. SrTiO3 ceramics have been produced in the literature with different temperatures, times, and starting materials. For ceramic products, a sintering step is required after the powder production step. Traditional sintering methods, which have been used for many years, are used to densify powders with high temperatures. Recently developed low-temperature densification methods enable the sintering process to be carried out at relatively lower temperatures. For this purpose, in this thesis, SrTiO3-TiO2 ceramic composites were produced at different reaction temperatures and times using the rHLPD method, which combines powder production and sintering steps in a single process. In the studies, the reaction temperature, time, and the effect of adding mineralizer to the prepared solution for the hydrothermal reaction on the final product were investigated. The aim of the thesis is to produce SrTiO3 from TiO2 green body using the rHLPD method. In addition, the production of SrTiO3-TiO2 ceramic composites with as high mole conversion and relative density values as possible was targeted with different parameters such as reaction temperature, reaction time, and addition of NaOH to the solution. As a result of the studies carried out with different parameters, SrTiO3-TiO2 ceramic composites with a final relative density value of approximately 81 % were produced. Consequently, in the XRD and Rietveld analysis, it was seen that the main phase was SrTiO3. In addition, there was a TiO2 phase in the structure. Finally, the SrCO3 phase was not detected in the structure.Master Thesis Preparation and Characterization of Inorganic Membranes by Using Sol-Gel Techniques(01. Izmir Institute of Technology, 2000) Yelken, Gülnihal; Çiftçioğlu, MuhsinIn this research the preparation of ceramIC membranes for gas separation applications by using sol-gel techniques were investigated. The effects of water/alkoxide ratio, H+/alkoxide ratio on the catalysis of the hydrolysis-condensation reactions and the peptization process were investigated by using N2 adsorptiondesorption isotherms, thermogravimetric analysis and FfIR (Fourier Transform Infra Red). The performance and the potential use of these materials in gas separation applications depend mainly on the ability in controlling-designing the microstructurepore network in these materials.The alumina and silica sols were prepared by using aluminium isopropoxide and tetraethylorthosilicate. Sols with different H+/ AI+3 and H20 / AI+3 ratios were prepared.These peptized clear boehmite sols were used for the preparation of unsupported Ah03 membranes at 600°C. The similar ratios were varied for the preparation of clear silica sols and these sols were further dried and heat treated at 400 C.The thermogravimetric analjsis has shown that the weights of the unsupported membranes were stable at the above temperatures. The boehmite was observed to decompose to the y-Alz03 phase at about 425°C. The FfIR analysis have proved the formation of boehmite in the sols and all the organic solvent peaks disappeared upon heat treatment.The y-Alz03 membranes all displayed Type IV isothems typical of mesoporous materials. Hysteresis loops were present in all these isotherms and fast desorption took place in the 0.4-0.6 PlPo range. The BJH pore size distributions were sharp for all the samples.The desorption pore size distributions were found to become wider at an intermediate acid content membrane which also had the lowest BET surface area. The BET particle sizes of these membranes were estimated to be in the 70-100 A0 range.The throat and pore cavity sizes of monosize sphere packings for this particle size range were observed to be in close agreement with the experimentallly determined adsorptiondesorption pore sizes.The silica samples all displayed Type I isotherms with no hysteresis typical of microporous materials. The HK (Horvoath Kawazoe) pore sizes were in the 4-5 AO range. An effect of the water content of these acid-catalyzed sols on the pore size were also detected.Master Thesis The Preparation Characterization and Sintering of Nanocrystalline Ceramics(01. Izmir Institute of Technology, 1999) Çağlar, Özlem; Çiftçioğlu, MuhsinNanocrystalline Titania was prepared by a chemical synthesis technique commonly known as sol-gel method. In the sol gel method, Titanium (IV) Isopropoxide was mixed with Isopropanol and Nitric Acid solution in predetermined ratios. A rapid hydrolysis reaction occurs between Titanium (IV) Isopropoxide and water in the Nitric Acid solution resulting in the formation of Titan oxide (Titania). The sols were clear sols and then gelled without any change in its clarity.Nanocrystalline Titania were tried to prepare by two different techniques in this work. The first technique involved the drying of the gel and subsequent sintering of the dried gel. A number of organic additives (oxalic acid, acetic acid, polyacrylic acid and stearic acid) were mixed into the sol before gelation in order to control drying (drying control chemical addives-DCCAs). Powders was prepared from sols and gels by several processes and a solid form was obtained by dry pressing and subsequently sintered in second technique. Oxalic acid was the most efficient DCCA among the others.The dried gels and powder compacts were sintered at 650, 700, 750, 800, and 850C. The sintering behaviors of them were examined. Relative densities of the dried gels were between 79-99% depending on the sintering temperature. The green body density of the pellets were varied between 41-52%. Their relative densities after sintering were varied between 55-83% depending on the sintering temperature. The pellets were pressed at different pressures to observe the pressure effect on the densification. Increase in pressure improve the densification behavior. The best route for the nanocrystalline powder preparation was the Route 4. This powder had smaller size of agglomerate most probably the agglomerates were broken during the ultrasonic radiation.The pore size analyses showed the pore structure of the gel. The pore size of the gels are about 35 nm. FTIR Spectra gave the crystal structure of the sols gels and powders. As a result, the sintering behavior of the dried gels is better than the powder compacts. The pellets can be densified to higher densities by appropriate forming technique. Although, the dried gels have significantly high densities, the shape and the weight of the gels can not be controlled.