Doktora Tezleri

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"Fine-Sgraffito ware," "Aegean ware" from Anaia: An analytical approach
(Izmir Institute of Technology, 2013) Budak Ünaler, Meral; Akkurt, Sedat
Excavation in Byzantine castle, known as Kuşadası Kadıkalesi, Anaia provided ceramic finds which dates back to mid 12th and 13th century of Mid Byzantine period. These finds were produced as serial products. In first part of the thesis 47 samples with four different decoration repertoire; Fine Sgraffito, Incised-Sgraffito, Incised and Champlevé, were analyzed by Scanning Electron Microscope (SEM-EDX), X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) methods, in order to identify the three distinct layers in cross sections: body, slip and glaze layers. Body was largely composed of SiO2, Al2O3, CaO, Fe2O3, Na2O and K2O along with other less abundant elements. Slip had similar chemistry but with less Fe2O3. The glaze was composed mainly of lead oxide. Between the glaze and the slip some new well formed crystals of lead feldspar were found to precipitate in dimensions of roughly 10-50 m. Statistical analysis tools like Hierarchical Clustering Analysis (HCA) and Principal Component Analysis (PCA) were used to see if any groupings were possible between the samples collected. Dendrograms indicated that these ceramics were made of two different types of clay. In second part of the thesis, replicate samples of earthenware pottery were manufactured in the laboratory to mimic the formation of the glazed pottery. Similar microstructural features were identified. Another HCA study was done to compare the Anaia samples with the literature. Dendrograms obtained showed some similarity. However, it was not possible to strongly and conclusively say that the two sample groups were related.
Improvement of IT-SOFC by tailoring the microstructure of LSCF cathode and GDC electrolyte
(Izmir Institute of Technology, 2019-07) Sındıraç, Can; Akkurt, Sedat; Büyükaksoy, Aligül
The high operating temperature of solid oxide fuel cells (SOFC) brings about some restrictions like the high cost of fuel cell, long start-up time, thermal stress, and decreasing lifetime. Thus, lowering the operating temperature is vital for improvement of SOFC. However, reducing the operating temperature leads to some negative effects on solid oxide fuel cell performance by increasing the electrolyte and electrode resistances. This dissertation focuses on tailoring the cathode and/or electrolyte layers to obtain improved electrochemical performances. For this purpose, some strategies are proposed. These are (i) thin film cathode nanocomposite cathode layer formation, (ii) infiltration of porous GDC by LSCF/LSCF+GDC, (iii) infiltration of porous GDC by GDC solution to improve densification at lower temperature and finally (iv) electrochemical characterization of GDC densified by infiltration.
Sintering, co-sintering and microstructure control of oxide based materials: Zirconia, alumina, spinel, alumina-zirconia and spinel-alumina
(Izmir Institute of Technology, 2010) Yalamaç, Emre; Akkurt, Sedat
Densification and microstructural evolution during co-sintering of alumina (Al2O3) . zirconia (Y-ZrO2) and alumina . spinel (MgAl2O4) co-pressed bimaterials were investigated. First high purity submicron powders of monomaterials of alumina, spinel and zirconia were pressed at 100 to 250 MPa with different dry pressing techniques like UP (uniaxial pressing) and CIP (cold isostatic pressing). The latter was found to provide higher green densities. Before co-sintering of bi-materials, sintering behaviors of their end-members were studied by vertical dilatometer to determine the degree of shrinkage mismatches between the end-members. The effects of precoarsening and two-step sintering on the densification and microstructure of spinel ceramics were tested. Samples were etched both chemically and thermally to better understand their structure. Crack-free bonds were observed in alumina-spinel bi-materials after compaction by UP+CIP. Interfaces between alumina and spinel after treatment at 1400-1500 C were investigated by SEM, EDS, WDS, EBSD. A spinel interlayer with columnar grains of up to 40 .m length and 5 .m width was observed after 16 hours at 1500 C. Growth rate of this interlayer from spinel toward alumina was found to follow parabolic kinetics, controlled by a diffusion mechanism of probably lattice diffusion of O2- ions. Two isothermal steps co-sintering at 1400 C and 1500 C on the interlayer formation was tested. Two separate areas formed in the interlayer spinel. Diffusion couple tests of spinel and alumina produced the same columnar spinel grains at the interface with the same kinetics as in co-sintering experiments. Phase boundaries between the columnar spinel and alumina grains had a characteristic center of curvature located in alumina which was further indication of the direction of growth of the interlayer.
The use of paper processing residues in the development of ceramics with improved thermal insulation properties
(Izmir Institute of Technology, 2010) Sütçü, Mücahit; Akkurt, Sedat
Recycled paper processing residues, those are industrial wastes, are utilized in the manufacture of porous and lightweight ceramics with improved thermal insulation properties for structural brick and refractory firebrick applications. These residues that contained micro-sized calcium carbonate (<5 .m) and cellulose fibers (<20 .m of diameter), were successfully used as an additive to earthenware brick to create porous structure during firing. A solid porous brick and a vertically perforated porous brick had 0.4 W/mK and 0.158 W/mK of thermal conductivity, respectively. This means substantial potential energy savings in houses and other buildings. When the paper residue was added in extreme amounts to the brick clay, it was found that anorthite (CaO.Al2O3.2SiO2) formed in the brick at the high-end of the firing temperatures of 1000-1100 C. This inspired the second part of the thesis which dealt with the production of porous, lower density insulating firebrick. Addition of the paper residue in excessive amounts up to 30% into the clay systems and firing at higher temperatures (1100.1400 C) formed a crystalline anorthite phase. Highly porous anorthite lightweight ceramics from the mixtures with up to 30% sawdust addition (used as additional pore-former) was successfully produced. Thermal conductivities of the samples decreased from 0.25 W/mK (1.12 g/cm3) to 0.13 W/mK (0.64 g/cm3) with increasing sawdust addition. Samples were stable at high temperatures up to 1100 C, and their cold strength was sufficiently high. Two separate porous lightweight ceramics were developed for insulation in buildings to reduce heat losses, and for insulation in high temperature applications.

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