Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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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 Preparation of Fine Spinel and Cordierite Ceramic Powders by Mechano-Chemical Techniques(Izmir Institute of Technology, 2004) Yalamaç, Emre; Akkurt, SedatLow temperature synthesis of cordierite and magnesium aluminate spinel powders has been attracting attention in recent years due to new potential applications. The use of mechanochemical methods to achieve partial or complete structural disorder as a tool to lower the sintering temperatures has also been increasingly reported. In this study, spinel was produced by intense milling of a mixture of Mg(OH)2 and Al(OH)3. Detailed phase characterization of the synthesized loose powder spinel was performed using XRD and DTA. SEM was used for the analysis of ground powder morphology and particle size. Amorphization was observed after 50 minutes of grinding at 600 rpm. 110 minutes of grinding led to partial growth of spinel. Temperatures less than 1000oC were able to produce spinel powders. In the second part of the study, cordierite was synthesized by mixing proper amounts of various combinations of alumina or Al(OH)3 (as a source of Al2O3), kaolin (as a source of SiO2 and Al2O3), and talc (as a source of MgO and SiO2). Detailed microstructural characterization of the synthesized pellets was performed by using SEM. Other techniques used for analysis of powder products were XRD, DTA and FTIR. One of the four possible mixture combinations was processed by using mechanochemical synthesis. This technique was analyzed by the use of statistical experimental design (SED) in order to understand the effects of process variables on the amount of synthesized product. Temperature was the most important factor and grinding speed-grinding time interaction was the next significant variable. These results were expected because lower grinding speed and longer grinding time generates a similar amount of grinding action compared to higher speeds and lower times. The cordierite mixture was completely amorphized by grinding at 300 rpm for 60 minutes based on XRD peak intensity measurements. Temperatures as low as 1150oC were able to produce cordierite ceramic. In addition to the mechanochemical technique, the effect of additive use and the combined effect of additive use and grinding on cordierite synthesis were also studied. These factors further decreased the synthesis temperature down to about 1050oC.