Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Sintering and Densification Behavior of Nanoparticle-Infiltrated Alumina Scaffolds(Izmir Institute of Technology, 2023) Özbekler, Meti̇n; Akkurt, SedatThis study explores high-purity Alumina's sintering and densification behavior, specifically the CT3000 SG variation, which traditionally requires high temperatures for full densification. The goal is to lower processing costs by achieving densification at lower temperatures through nanoparticle infiltration. The process involves a two-step heat treatment and infiltration technique. Alumina scaffolds are initially bisque-fired at 1100 °C and then infiltrated with a polymer precursor solution containing Al+3 ions, followed by decomposition at 400 °C to precipitate alumina nanoparticles in the scaffold pores. Multiple infiltration cycles are performed to enhance density. The relative density of furnace-sintered pellets increases with decreasing heating rate and increasing sintering temperature in reference samples. Infiltrated samples and "P" pellets (formed by washing CT3000 SG Alumina loose powder with the polymer precursor solution) follow a similar trend, with higher infiltration numbers leading to increased relative density. However, "P" samples have lower relative densities than reference samples. In-depth analysis using a horizontal dilatometer reveals that the 15 times infiltrated scaffolds exhibit better densification due to early activation of nanoparticles, leading to neck formation, reduced porosity, and altered particle shape. On the other hand, "P" pellets fail to achieve sufficient densification compared to reference samples. In summary, this study investigates lowering the sintering temperature of Alumina by nanoparticle infiltration. It involves bisque firing, multiple infiltration cycles, and a polymer precursor solution. Results indicate that 15 times infiltrated scaffolds achieve better densification, while "P" pellets fall short of achieving adequate densification compared to reference samples.Master Thesis Energy Performance Analysis and Materials Characterization of Aerogel Insulation Blankets(Izmir Institute of Technology, 2022) Alan, Selena; Gökçen Akkurt, Gülden; Akkurt, Sedatİzmir Geothermal Energy Inc. is a geothermal district heating company in İzmirTurkey that circulates hot water throughout the district via a 450 km of piping system and with the help of valves, pipes, and heat exchangers. As the distance traveled by the hot water is excessively long, heat losses are common. Rock wool is used as thermal insulation material, but the performance degraded over time because of water leakage. Instead of rock wool, aerogel insulation blanket use is evaluated in this study. Rock wool and three different aerogel insulation blankets are comparatively studied to assess their structures and thermal performances in two ways: the first is the characterization of materials by various physical and chemical analysis methods in the IZTECH-Integrated Research Center. The second way is to assemble a test setup on-site and make thermal measurements on the test setup for each aerogel insulation material, rock wool, and bare pipe. Heat loss calculations were conducted by EES software. The results are compared based on each characterization and thermal performance calculation. The thermal conductivity values of the insulation materials were calculated. Nonwetting properties were also checked to understand their hygrothermal properties. Compared with bare pipe, with the 10 mm thickness, rock wool decreases heat loss by 48-52%, and with the 10 mm thickness, the aerogel insulation blankets reduce heat loss by 57-61%. Finally, while aerogel insulation blankets have a better performance, they are more expensive than rock wool.Master Thesis Microstructural Analysis of the Corrosion of Al2o3 and Zro2 in Frit Melts(Izmir Institute of Technology, 2007) Şenöz, Ceylan; Akkurt, SedatDense 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 Development of Porous Ceramics for Air Diffuser Applications(Izmir Institute of Technology, 2009) Küçük, Aslı; Akkurt, SedatPorous ceramic for bubbling air into water at 1 bar of pressure was successfully developed. Different compositions were tested. The use of superground alumina was not successful because the particle size was too small and the pores were closed thereby forbidding any air transport through the ceramic. Additions of corn starch to this material did not help much because any contribution of porosity was closed porosity and that was useless in air transport. Limited success was accomplished when clay, quartz and corn starch were used but this time the pressure needed to produce a reasonable amount of bubble in water was higher than 1 bar which was the initially set goal for this project. Bayer alumina was used as a replacement for superground Alcoa alumina to help with porosity because these powders are well known to be agglomerated and to offer high amount of porosity Smaller fraction of quartz was added to help with strength and clay to assist in forming and very good results were obtained. Ceramics made from 50% Bayer alumina and 50% clay provided very good oxygenation of water. However, their strength was not as good as samples made from 50% Bayer alumina, 20% quartz and 30% clay. These latter samples had higher strength and slightly lower oxygenation. The use of these ceramics as air diffusers can help oxygenate water which is needed in a lot of different applications.Key words: Porous ceramic, air diffuser, alumina.Master Thesis Investigation of the Formation of La1-Xsrxc1 Cathode Materials and Their Interaction With Electrolyte Substrates for Potential It-Sofc Applications(Izmir Institute of Technology, 2013) Sındıraç, Can; Akkurt, SedatCathode layers of IT-SOFC (Intermediate Temperature Solid Oxide Fuel Cell) materials are investigated to find out the reactions leading to the formation of La0.6Sr0.4Co0.8Fe0.2O3 and La0.6Sr0.4Co0.2Fe0.8O3 on the surface of either ZrO2 or CGO (Cerium-Gadolinium Oxide) electrolyte substrates. Precursor salt powders were blended, compressed and placed on discs of sintered ceramic electrolytes before being heated in a laboratory furnace at 800oC for 1h. Almost all combinations of LSCF salt mixtures were prepared and analyzed by SEM-EDS, XRD and DTA-TGA to see if all solid state reactions are completed and what new phases eventually formed in LSCF combinations. Most of the transformation was complete after 1050oC heat treatment to yield oxides. According to XRD analysis it was observed that La plays a significant role to enable the formation of new phases. In the absence of La, other salts had significant difficulty to react to form new phases. Also, Sr tends to swap its chloride with nitrate of other salts in salt mixtures after drying in oven. SEM-EDS analysis of the interface between the electrolyte and LSCF showed that there was weak mutual diffusion of the constituent elements between the cathode layer and the electrolyte. The cathode layer was usually in porous form but was found to spread well over the substrate. Uneven diffusion of La, Sr, Co or Fe into the substrate had little influence on the stoichiometry of the resulting coating layer. Unlike 6428 samples, it was possible to form stoichiometric LSCF in 6482 samples.Master Thesis Development of Engobe Compositions for Local Roof Tiles(Izmir Institute of Technology, 2010) Bodur, Hilal; Akkurt, SedatEngobes can be described as a coating layer on ceramic surfaces to produce the desired color. In this thesis a commercial roof tile, which was taken from a company, was used. For good fitting between the engobe and the roof tile their coefficients of thermal expansion (CTE) should be almost the same. One way of adjusting the CTE values, the chemical analysis of the roof tile was analyzed and based on these different engobe recipes with high purity raw materials and frit that was made in the laboratory with high purity raw material were prepared. The roof tiles were rich in SiO2, Al2O3, (Na+K)2O. Therefore, by changing the percentage of these oxides new engobe recipes were prepared to find the most suitable composition for roof tiles. After application on surfaces of roof tiles, the samples were fired at 1000oC for 75 min. 70% SiO2, 20% Al2O3, 10% (Na+K)2O with 10% laboratory frit and 70% SiO2, 20% Al2O3, 10% (Na+K)2O with 30% laboratory frit were found to be two of the most proper engobe compositions for the roof tile. Later these engobe recipes were prepared with lower purity industrial grade raw materials and industrial frit because the cost of producing frit is high for a roof tile manufacturer. The low purity engobes were applied successfully on the surface. However, lower purity raw materials containing little Fe and Ti led to a slightly darker color compared to higher purity engobes. The life cycle of the products were tested with different kinds of acids and temperature tests. And the results showed that the engobe samples were durable against the environmental effects. Finally, metal oxides were used up to 5% in the engobe compositions to give different colors to the roof tiles.Master Thesis The Use of Boron-Containing Additives for Synthesis of Anorthite Ceramic Powders(Izmir Institute of Technology, 2006) Kavalcı, Sedat; Akkurt, SedatAnorthite ceramics have a great potential as a substrate material due to their low thermal expansion coefficient and low dielectric constant. For lowering the sintering temperature of anorthite ceramics several routes like employing additives, sol-gel method and the use of mechanochemical methods have been proposed.In this study, anorthite was synthesized by using mechanochemical methods and boron oxide addition. The raw materials used in this study were Sivas kaolin as a source for Al2O3 and SiO2, calcined alumina or Al(OH)3 as a source for Al2O3 and calcite powder as source for CaO. Phase characterizations of synthesized powders were performed by XRD using CuK radiation. Microstructural characterization was performed by SEM. Statistical experimental design techniques (SED) were used in order to determine and analyze the more important process variables for synthesizing anorthite ceramics. The results of screening experimental design clarified that the temperature was the most important process variable. Second most important process variable was grinding speed which was followed by additive amount and additive type. This study showed that both additive type and additive amount were important process variables because these two factors were related to each other.The effect of both additive use and grinding on anorthite synthesis helped decrease the synthesis temperature down to 900 oC.Master Thesis Development of Dense Ceramic Tiles From Mixtures of Alumina Powders With Different Psd(Izmir Institute of Technology, 2004) Sütçü, Mücahit; Akkurt, Sedat; Akkurt, SedatIn Turkey, domestic alumina powders are generally used as an intermediate product in metallic aluminum production. Recently, its usage as a raw material for technical applications in ceramic industry has gained importance. The properties of domestic powders must be improved in order to be used in technical ceramic applications. Because these powders have coarse particle size with a high amount of sodium oxide as well as incomplete transformation to stable form. Therefore, sodium oxide that has been physically and chemically bound to aluminum oxide during Bayer process must be removed. In this study, sodium oxide (Na2O) content of the domestic powders was decreased to desirable levels (<0.15% Na2O) by hot washing treatments. These powders were calcined to transform into stable alpha form. X-Ray Diffraction (XRD) was preformed to analyze the calcined and as-received powders. Chemical analyses of the powders were done using Atomic Absorption Spectrometry (AAS) and Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). Domestic powders were ground. Scanning Electron Microscopy (SEM) was performed to analyze the morphology and particle size distributions of as-received and ground powders. Particle size distributions (PSD) were plotted using lineal intercept method. In this study, it was aimed to provide maximum packing by blending the powders in different combinations (binary and ternary powder blends). In addition to this, dense ceramic tiles were produced by blending different proportions of the powders that provide maximum packing. In this study, the improved domestic (coarse size-SKA and medium size-SEA) and superground (Alcoa CT3000SG) alumina powders with three different particle size distributions were used. The packing of binary (SEA-CT3000SG) and ternary (SKA-SEA-CT3000SG) blends were predicted by using the softwares, MXENTRY® and MIX10®. These softwares utilized the Dinger-Funk (DF) equation for predictions of packing. Prepared blends were uniaxially dry-pressed and sintered. Archimedes method was used to measure the density and porosity of the pellets. All results showed that the blend contained 100% superground alumina powders achieved almost full density (98%) at 1550C. The binary and ternary blends that contained a relatively higher proportion of fine alumina powders provided higher fired densities. In binary blends, if the proportion of SEA was up to 50%, porosity values of these blends increased. Also the effects of additives such as TiO2 and MnO2 on densification and mechanical properties of pellets were investigated. The additives provided higher fired densities between 91 and 99%. Vickers hardness tests were conducted to determine mechanical properties of the sintered pellets. The samples that contained relatively higher proportions of fine particles provided higher hardness values in a range of 1500 and 2100 kg.mm-2. Also, microstructural characterization of the pellets was done using SEM. Finally, the tiles at desired dimensions were produced based on the blends that give the highest density and hardness values. Porosity and density measurements, microstructural and mechanical characterizations of the tiles were carried out.Master Thesis Artificial Neural Networks and Fuzzy Logic Applications in Modeling the Compressive Strength of Portland Cement(Izmir Institute of Technology, 2004) Can, Sever; Akkurt, SedatPortland cement production is a complex process that involves the effect of several processing parameters on the quality control of 28-day cement compressive strength (CCS). There are some chemical parameters like the C3S, C2S, C3A, C4AF, and SO3 contents in addition to the physical parameters like Blaine (surface area) and particle size distribution. These factors are all effective in producing a single quantity of 28-day CCS. The long duration of 28 day CCS test provided the motivation for research on predictive models. The purpose for these studies was to be able to predict the strength instead of waiting for 28 days for the test to be complete. In this thesis, artificial intelligence (AI) methods like artificial neural networks (ANNs) and fuzzy logic were used in the modeling of the 28-day CCS. The two models were compared for their quality of fit and for the ease of application.Quality control data from a local cement plant were used in the modeling studies. The data were separated randomly into two parts: the first one contained 100 data points to be used in training and the second part had 50 data points to be used in testing stages of the models. In this study, four different AI models were created and tested (3 ANN, 1 fuzzy logic). One of the ANN models (Model A) had 20 input parameters in 20x20x1 architecture with testing average absolute percentage error (AAPE) of 2.24%. The other ANN model (Model B) had four input parameters (SO3, C3S, Blaine and total alkali amount) in 4x4x1 architecture with AAPE of 2.41%. Both of the Model A and the Model B were created in the MatLAB® environment by writinga custom computer code. The last ANN model (Model C) actually refers to 72 differentANN models created in the MatLAB® neural networks toolbox. In order to obtain a model with the lowest error, different learning algorithms, training functions and architectures in combinations were tested. The lowest AAPE among these models appeared to be 2.31%. The fuzzy logic model (Model D) which had four input parameters (SO3, C3S, Blaine and total alkali amount) was created in the MatLAB fuzzy logic toolbox. In order to write the fuzzy rules, the sensitivity analysis of the Model B was utilized. The AAPE of the Model D was 2.69%. The model was compared with the ANN models for its error levels and ease of application. The results indicated that through the application of fuzzy logic algorithm, a more user friendly andmore explicit model than the ANNs could be produced within successfully low error margins.Master Thesis Characterization of Selected Beylikler Period Mortars and Processing of New Intervention Mortars for Restoration Purposes(Izmir Institute of Technology, 2005) Budak, Meral; Akkurt, SedatIn this study, Saruhanlı Emirates period mortars collected from Manisa Çukur Hamam (Bath) and Manisa Hacet Mescidi (Mosque) in Western Turkey were characterized, and the results of characterization tests were used for production of new compatible mortars, which would then be used for conservation of the buildings. For this purpose, physical, mineralogical and chemical compositions of the mortars were characterized by XRD, SEM-EDS, TGA and chemical analysis. The results indicated that the mortars were hydraulic and were produced by the use of pozzolanic aggregates. The use of hydraulic lime mortars can be related to the structural requirements of these buildings. The binder aggregate ratio of mortar samples were in the range of 1:2-1:4. Aggregate particle sizes that are grater than the 1180 .m composed the largest sizes of the total aggregates and aggregates were composed of quartz, albite and anorthite. Lime aggregate ratios (L/Ag) of the produced intervention mortars were in the range of 1:6- 1:1. Standard sand was used as aggregate. The pozzolanic additive was commercial clay, which was heat treated between 25 and 1000oC. It was found that the addition of K-244 clay which was heat-treated above 600oC improved compressive strengths of the mortars.