Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Coating of La0.3sr0.7fe0.7cr0.3o3-Δ and La0.3ca0.7fe0.7cr0.3o3-Δ Cathode Layers on Gdc Ceramics by Electrospray Deposition (esd)(01. Izmir Institute of Technology, 2023) Erğen, Emre; Akkurt, Sedat; Ahmetoğlu, Çekdar VakıfHigh temperatures are needed to rapidly transfer of oxygen ions between layers during the chemical energy to electrical energy conversion in solid oxide fuel cells (SOFC). Nevertheless, intermediate-temperature SOFCs are preferred to increase their lifetime and reduce maintenance and production costs. The performance of IT-SOFCs depends particularly on the microstructure and electrochemical properties of the cathode layer. In this study, cobalt-free La0.3Sr0.7Fe0.7Cr0.3O3-δ and La0.3Ca0.7Fe0.7Cr0.3O3-δ cathode layers were coated on GDC ceramic pellets by ESD method. The aim of the thesis was to have better structural and electrochemical properties of coatings than the literature. ESD provides the atomization of liquids with the help of electrical forces. ESD is an effective method for forming coatings with desired compositions. By changing ESD parameters, different structural properties such as reticular, cracked, and dense were obtained. Reticular structures are useful for easier oxygen transfer with increased surface area. Effects of parameters were examined by Plackett-Burman design, and the most effective parameter was found as flow rate. The quality of the coatings was evaluated by quantitative scoring. The 16th sample, which was coated with solution E, got the best score. Parameters of 16th sample were used in the investigation of the effects of different solutions on the coatings. 8 different solutions named A to H were prepared with different solvents and precursor salts. Coating by solution E shows better EIS results than the literature as 0.22 Ω.cm2. Coatings by solution G and A show close values to the literature as 0.29 Ω.cm2, and 0.34 Ω.cm2, respectively.Master Thesis Comparison of Powder Synthesis Methods for the Production of Potassium Sodium Niobate (knn)(Izmir Institute of Technology, 2021) Pişkin, Cerem; Ahmetoğlu, Çekdar Vakıf; Adem, UmutAlkali niobate-based, i.e., potassium sodium niobate, KxNax-1NbO3 at x=0.5 (the composition at the morphotropic phase boundary (MPB)), based materials have been reported as promising lead-free piezoelectrics to be substituted with the most extensive lead-based, i.e., lead zirconate titanate (PZT) ones. In this thesis, KNN particles were obtained using three discrete powder synthesis routes: conventional solid-state reaction, hydrothermal synthesis, and sol-gel processing. The as-synthesized powders were characterized via several techniques to provide a comparative study and underline the difficulties upon KNN synthesis. In the conventional method, the phase pure K0.5Na0.5NbO3 powders were obtained at 850°C with 382 ∓ 68 nm particle size. Unfortunately, the process cannot be considered sustainable due to the high risk of non-perovskite impurity phase formations. Also, the results demonstrated that single phase KNN powder having the MPB composition could not be accomplished via a one-step hydrothermal reaction process because of the inevitable formation of the second NaNbO3 phase. Instead, post-heat treatment of biphasic (K-rich (x>0.5) KNN and NaNbO3) samples lead to induction of sodium incorporation into the crystal lattice, and eventually, phase-pure KNN particles with high proximity (x=0.58) to MPB were achieved. The KNN powder with the smallest particle size (145 nm) was obtained using the sol-gel method at 500°C. However, the samples showed carbonate impurities resulting from the reaction of unreacted alkali cations (K+ and/or Na+) with the ambient CO2. Hence, the KNN samples needed to be stored under inert atmosphere to ensure purity.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 Optimisation of Organic Phase Pre-Neutralisation Stage in Purification Studies With Solvent Extraction for Mhp (mixed Hydroxide Precipitate) Produced From Gördes Laterite Ore and Investigation of Its Effect on Extraction(01. Izmir Institute of Technology, 2021) Kaya, Ezgi; Ahmetoğlu, Çekdar VakıfIntermediate products such as MHP (Mixed Hydroxide Precipitate) are processed by solvent extraction which is a continuous process in industry for obtaining final product such as nickel metal or nickel sulphate. Nickel is used essentially in stainless steel industry and cobalt is used in super alloys. Both metals are used in lithium-ion battery technologies especially electrical vehicles. A preliminary stage of solvent extraction process is called as pre-neutralisation and it is based on partial neutralisation of the acidic organic reactant to prevent pH fluctuations in extraction due to the H+ ions release aqueous phase, and it provides an exchange mechanism to enable loading of the metals to the organic phase. In this thesis study, it is aimed to optimise the organic phase pre-neutralisation percent in further purification treatment of MHP leach solution (PLS-Pregnant Leach Solution) from Gordes nickel laterites and investigate its effect on extraction by D2EHPA and Cyanex 272 organic reactants. NaOH and Na2CO3 solutions were used in pre-neutralisation with 35%, 40% and 45% in D2EHPA and 30%, 35% and 40% in Cyanex 272. The optimum pre-neutralisation results were found as 35% for D2EHPA and 30% for Cyanex 272.Master Thesis Production and Characterization of Emulsion Derived Porous Sioc+tio2 Submicron/Nanospheres(Izmir Institute of Technology, 2020) İçin, Öykü; Ahmetoğlu, Çekdar VakıfThe 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 Spreadability and Characterization of Metal Powders for Additive Manufacturing(Izmir Institute of Technology, 2020) Hasdemir, Beyza; Ahmetoğlu, Çekdar Vakıf; Yasa, EvrenPowder Bed Fusion (PBF) is one of the Additive Manufacturing (AM) techniques, in which metal powders are used as feedstock. AM process enables the production of lightweight structures, design freedom in 3D printed parts, short cycle time, etc. AM made part properties are affected by the powder characteristics used to form the component. A part comprises hundreds of spread layers; however, a homogeneous layer is crucial for obtaining the necessary final part properties. Spreadability can be defined as a method to quantify the powder distribution through the layer. Although it has not been standardized yet, currently, it is merely controlled by following the powder flowability, a standardized characterization method for AM. This thesis investigates the spreadability of the utilized powders for AM (here only Laser-Powder Bed Fusion will be used), with the image processing algorithms in MATLAB. Besides, it also aims to examine the spreadability correlation with the other characteristics such as flow rate, apparent density, angle of repose, and thus the final 3D printed components. Samples in six different particle size distribution were characterized, and spreadability tests were performed with the L-PBF machine. The powder characterization results demonstrated that an increase in fine particle ratio by volume (below 20 µm) enhances the angle of repose (AOR). The tests demonstrated that irregularities on the spread layer could be quantified with the image processing algorithms. The 3D printed samples were found porous. The reason for porosity in the sample might base on a combination of various factors, poor spreadability, spatter formation, and other L-PBF processing parameters might be the reasons for such microstructural development.Master Thesis Manufacturing of Fire Resistant Porous Ca-Silicate Ceramics(Izmir Institute of Technology, 2019) Oğur, Ezgi; Ahmetoğlu, Çekdar Vakıf; Adem, UmutCalcium silicate hydrates are a group of materials belonging to the calcium silicate family. Calcium silicate hydrates are crucial materials in the building industry, especially for thermal insulation and fire-resistant applications. Tobermorite and xonotlite, calcium silicate hydrates, are the most popular materials in the literature due to their structural properties. These material are synthesized by hydrothermal processes. In some publications, several pre-treatments are applied to the starting materials before hydrothermal synthesis. In this thesis, the effects of these processes on different starting materials and how does changing the parameters affect the process are examined. Besides, the main objective of the thesis is to produce the xonotlite phase using recycling materials as economically as possible. Calcium silicate hydrates powders containing approximately 61 wt. % xonotlite was produced with using lime and recycled glass by hydrothermal synthesis method. The obtained product has a mainly fibrous morphology due to the main phase is xonotlite. According to phase analysis, tobermorite, scawtite, and the trace of calcite phases are also present in the general structure. The thermogravimetric analysis demonstrated that approximately 20% loss is observed up to 800˚C (at about that temperature transformation of the xonotlite to the wollastonite phase is occur.). The mass change remained constant between 800˚C and 1200˚C. Calcium silicate powder (obtained by thermal treatments from CSH) was also thermally analyzed and consequently remained stable up to 1200˚C, (the loss was approximately <1%).Master Thesis Fabrication and Characterization of Ceramic Fibers From Preceramic Polymers(Izmir Institute of Technology, 2019) Özmen, Ecem; Ahmetoğlu, Çekdar Vakıf; Demir, Mustafa MuammerCeramic fibers which are classified as oxide and non-oxide fibers are preferred to use in applications which are carried out at high temperature since they have high strength, low thermal expansion, corrosion, and oxidation resistance. Non-oxide fibers are generally produced using preceramic polymers by the spinning method. The production of ceramic materials using preceramic polymers by spinning method is more advantageous than other methods since the production of complex materials could be achieved at lower temperatures. The preceramic polymer family is basically classified as polysiloxane, polysilazane and polycarbosilane. In this thesis, it was aimed to obtain ceramic fiber in the most economical way. In this context, a spinning device was designed and made. Additionally, polysiloxane which is the most economical preceramic polymer was used to produce ceramic fiber. Polysiloxanes were spun by melt spinning. Obtained fibers were cured by different methods. As a result of pyrolysis, 65-130 μm thickness SiOC fibers were achieved.Master Thesis Production and Characterization of Porous Ceramics for Aircraft Arresting Systems(Izmir Institute of Technology, 2019) Çapraz, Furkan; Ahmetoğlu, Çekdar Vakıf; Adem, UmutDespite developments in aviation, accidents still occur and lead to loss of lives. Technical or environmental factors may cause overrun accidents. In the case of aircraft that fail to stop along the runway distance during take-off or landing, such accidents are called overrun. Aircraft stopping systems (AAS) are passive safety systems used to prevent to take damage of passengers and aircraft during overrun. In the literature, foamed concrete was generally used as the AAS material. However, some studies have also been carried out on other materials that may be used as the AAS material. In present thesis, the aim was to produce porous calcium silicates instead of foamed concrete in AAS. The slip casting method was used to produce porous calcium silicate monoliths. The main components used in the manufacturing of porous wollastonite were xonotlite (as a matrix material), polymethyl methacrylate (as a sacrificial pore former, PMMA), polyvinyl alcohol (as a binder, PVA), Dolapix CE 64 (as a dispersing agent) and distilled water. Three different xonotlite ratios (8, 9 and 10% by volume) have been studied with four different xonotlite/ PMMA ratios (1, 0.82, 0.54 and 0.33 by volume). Also, specimens without PMMA were produced for each xonotlite ratio. The suspensions were stirred for 3 h at 750 rpm and then casted into the gypsum mold. The samples which were dried at room temperature (RT) were heat treated at 1000 oC. After production step microstructural, structural and mechanical analysis o the porous calcium silicates were carried out. Cold Crushing Strength (CCS) tests were performed out for determining mechanical properties. CCS values of the porous monolith parts ranged between 1376 kPa and 53.2 kPa depending on xonotlite/ PMMA ratios. In addition, the porosity values ranged from 93.38 to 87.82%. The resuts showed that some of these porous calcium silicate monoliths are suitable to use instead of foamed concrete as the AAS material.