WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 2Citation - Scopus: 3A Full 3(4) Factorial Experimental Design for the Low Energy Building's External Wall(Vinca Inst Nuclear Sci, 2020) Pekdoğan, Tuğçe; Akkurt, Sedat; Başaran, TahsinThe low energy building concept is based on improving the building envelope to reduce heating and cooling loads. Improvements in building envelopes depend not only on climatic conditions but also on insulation. In this study, the thermal performance of external walls was studied by using a three-level full factorial statistical experimental design. An opaque wall in low energy buildings was chosen in order to study the effect of selected factors of city (A), orientation (B), insulation location (C), and month of the year (D) on heat loss or gain. A software was used to calculate the ANOVA table. As a result, all three factors of months of the year, city and orientation of the building facade were found to be significant factor effects for heat transfer. Two-factor interactions of AB, AD, BD, and CD were found to be significant. Therefore, the effects of season, location and orientation were successfully shown to be effective parameters.Article Citation - WoS: 54Citation - Scopus: 58Sintering and Microstructural Investigation of Gamma–alpha Alumina Powders(Elsevier Ltd., 2014) Yalamaç, Emre; Trapani, Antonio; Akkurt, SedatSintering behaviors of commercially available alumina powders were investigated using constant-heating rate dilatometric experiments. Each powder had different proportion of alpha/gamma alumina. Densification behaviors of powders were studied up to 1600 °C with three different heating rates of 1, 3.3 and 6.6 °C/min. Compacts of different gamma content alumina powders exhibited systematic anomalous second peaks in the densification rate curves at certain heating rates and temperatures. At 3.3 °C/min heating rate experiments, densification curves of 10% gamma phase alumina powder compacts reached a plateau after 1450 °C, and did not increase any further at higher temperatures. This phenomenon was double checked to understand powder behavior during sintering. 10% gamma phase alumina powder compacts showed the highest density for each heating rate. It reached 94% theoretical density with 1 °C/min heating rate. But 20% gamma phase alumina powder compacts had the finest grain size of about 1.40 ?m. Final density and porosity of compacts were also tested by image analysis and the results were coherent with Archimedes results. © 2014 Karabuk UniversityArticle Citation - WoS: 14Citation - Scopus: 15Electrochemical Performance of La0.6sr0.4co0.2fe0.8o3-Ce0.9gd0.1o2 Composite Sofc Cathodes Fabricated by Electrocatalyst And/Or Electrocatalyst-Ionic Conductor Infiltration(Springer, 2019) Sındıraç, Can; Büyükaksoy, Aligül; Akkurt, SedatInfiltration of electrocatalyst precursor solutions into previously sintered porous ionic conductor scaffolds has been used recently as an alternative method to the conventional co-sintering route to fabricate electrocatalyst-ionic conductor composites for solid oxide fuel cell (SOFC) cathode applications. However, the aqueous nitrate solutions generally used to perform the infiltration process results in electrocatalyst precipitates that are disconnected from each other, yielding poor electrode performance. In this work, polymeric electrocatalyst (La0.6Sr0.4Co0.2Fe0.8O3-LSCF) precursors that produce interconnected thin films upon heat treatment were used to infiltrate porous ionic conductor Ce0.9Gd0.1O2-delta (GDC) scaffolds to overcome these issues. In addition, for the first time in the literature, a mixture of LSCF and GDC polymeric precursors, which would yield LSCF-GDC nanocomposite coatings on the grains of the porous GDC scaffold were used as the infiltration solution. Thus, further enhancement of the electrocatalyst/ionic conductor interfacial area and achievement of improved electrode performance was aimed. As a result of the optimization studies, the lowest measured area specific polarization resistance (ASR(cathode)) values of 0.47 and 0.73 omega.cm(2) were obtained for polymeric LSCF+GDC and LSCF precursor infiltrations respectively at 700 degrees C, in air. In addition, LSCF+GDC infiltration yielded electrodes with much improved long-term stability in comparison to those obtained by LSCF infiltration. [GRAPHICS] .Article Citation - WoS: 25Citation - Scopus: 26Lowering the Sintering Temperature of Solid Oxide Fuel Cell Electrolytes by Infiltration(Elsevier Ltd., 2019) Sındıraç, Can; Çakırlar, Seda; Büyükaksoy, Aligül; Akkurt, SedatA dense electrolyte with a relative density of over 95% is vital to prevent gas leakage and thus the achievement of high open circuit voltage in solid oxide fuel cells (SOFCs). The densification process of ceria based electrolyte requires high temperatures heat treatment (i.e. 1400-1500 degrees C). Thus, the minimum co-sintering temperatures of the anode-electrode bilayers are fixed at these values, resulting in coarse anode microstructures and consequently poor performance. The main purpose of this study is to densify gadolinia doped ceria (GDC), a common SOFC electrolyte, at temperatures lower than 1400 degrees C. By this aim, an approach involving the infiltration of polymeric precursors into porous electrolyte scaffolds, a method commonly used for composite SOFC electrodes, is proposed. By infiltrating polymeric precursors of GDC into porous GDC scaffolds, a reduction in the sintering temperature by at least 200 degrees C is achieved with no additives that might affect the electrical properties. Energy dispersive x-ray spectroscopy line scan analyses performed on porous GDC scaffolds infiltrated by a marker solution (polymeric FeOx precursor in this case) reveals a homogeneous infiltrated phase distribution, demonstrating the effectiveness of polymeric precursors.Article Citation - WoS: 15Citation - Scopus: 16Fabrication of Lscf and Lscf-Gdc Nanocomposite Thin Films Using Polymeric Precursors(Springer, 2020) Sındıraç, Can; Ahsen, Ali; Öztürk, Osman; Akkurt, Sedat; Birss, Viola, I; Büyükaksoy, AligülLa1-xSrxCoyFe1-yO3 (LSCF) and LSCF-gadolinia-doped ceria (LSCF-GDC) composites are used as solid oxide fuel cell (SOFC) cathodes. In the present study, to maximize the LSCF/gas and LSCF/GDC interfacial area and thus enhance the performance, we fabricated both single-phase LSCF and composite LSCF-GDC thin-film electrodes using a facile and cost-effective polymeric precursor technique. This method involves molecular level mixing of cations in solution form and results in average particle sizes of ca. 72 nm and 60 nm upon annealing at 700 degrees C, respectively. For LSCF, electrochemical impedance spectroscopy measurements indicate very low electrode polarization resistances of ca. 0.6 omega cm(2) per electrode at 600 degrees C. However, the addition of GDC results in poorer electrochemical activity but better microstructural and electrochemical stability, all at 600 degrees C. Surface analysis revealed that Fe surface segregation occurs in the single-phase LSCF, while predominantly Co segregation is observed at the LSCF-GDC composite electrode surface.Article Citation - WoS: 9Citation - Scopus: 10Formation of La1-Xsrxco1 Cathode Materials From Precursor Salts by Heating in Contact With Cgo Electrolyte(Elsevier Ltd., 2016) Sındıraç, Can; Akkurt, SedatThe purpose of this study is to determine the solid state reactions leading to the formation of La0.6Sr0.4Co0.8Fe0.2O3 and La0.6Sr0.4Co0.2Fe0.8O3 which are widely used as cathode material in solid oxide fuel cells (SOFC) from precursor salts. Interactions between the cathode and the electrolyte layers are also investigated while the cathode layer formed upon heating in contact with the surface of cerium-gadolinium oxide (CGO) electrolyte substrates. Almost all combinations of precursor salt mixtures were tested to see if all solid state reactions are completed and what phases eventually formed. Most of the transformation was complete after 1050 °C heat treatment to yield different mixed oxides. 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 influenced the stoichiometry of the resulting cathode layer in varying degrees. Fe was found to diffuse into the substrate.Article Citation - WoS: 126Citation - Scopus: 138Thermal Performance Optimization of Hollow Clay Bricks Made Up of Paper Waste(Elsevier Ltd., 2014) Sütçü, Mücahit; Del Coz Diaz, Juan Jose; Alvarez Rabanal, Felipe Pedro; Gençel, Osman; Akkurt, SedatIn this paper, the thermal behavior of hollow clay bricks made up of paper waste has been studied and their thermal performance has been optimized. On the one hand, both strength and thermal properties of different paper waste concentrations have been obtained by means of laboratory tests. Thermal conductivity of the microporous brick materials with additives produced in this study reduced from 0.68 W/m K to 0.39 W/m K compared with that of the sample without additives. On the other hand, the finite element method (FEM) has been applied to the nonlinear numerical thermal analysis of three different hollow bricks, including radiation and convection phenomena inside holes. Next, using the design of experiments (DOE) over the FEM models, several parameters such as the material conductivity, the convection and radiation properties and the mean brick temperature have been studied. In general, the thermal resistance is a nonlinear function that depends on the geometry of the recesses, the material properties and the temperature distribution. In all analyzed cases, minimizing the material thermal conductivity of bricks and decreasing the recesses surface radiation emissivity caused a lower thermal transmittance in the brick. Finally, the most important conclusions and the main findings of this research are exposed.Article Citation - WoS: 4Citation - Scopus: 4Effects of Catalyst Precursor Type and Preparation Conditions, and Solvent Type on Activity and Selectivity of Pt/Sio2 Catalyst in Citral Hydrogenation(Walter de Gruyter GmbH, 2011) Depboylu, Can Okan; Yılmaz, Selahattin; Akkurt, SedatIn this study, citral hydrogenation reaction in liquid phase over silica gel supported Pt catalysts was investigated. It was desired to hydrogenate carbonyl group selectively to produce valuable unsaturated alcohols, namely geraniol and nerol. Pt/SiO2 catalysts were prepared by impregnation method. The effects of parameters investigated in the present study included Pt precursor type (hexachloroplatinic acid (HCLPA), platinum II acetylacetonate (PAA)), catalyst activation temperature (350°C and 450°C), catalyst activation without calcination, catalyst washing with 0.1 M NaOH and solvent type (ethanol, 2-pentanol). The catalysts activities and selectivities were affected by the type of precursor and activation temperature. The maximum citral conversion (89.50 percent) was achieved at lower activation temperature (350°C) with PAA precursor based catalyst. It was observed that higher activation temperature provided lower citral conversion but higher selectivity to unsaturated alcohols; increasing the activation temperature to 450°C decreased citral conversion to 26.10 percent. But selectivity to unsaturated alcohols, geraniol and nerol, increased from 7.06 to 54.60 percent. Catalyst washing and 2-pentanol prevented acetal formation. Catalyst activation without calcination gave lower citral conversion (20.84 percent) and selectivity to unsaturated alcohols (30.00 percent). Copyright © 2011 The Berkeley Electronic Press. All rights reserved.Article Citation - WoS: 14Citation - Scopus: 14Microstructural Development of Interface Layers Between Co-Sintered Alumina and Spinel Compacts(Elsevier Ltd., 2011) Yalamaç, Emre; Carry, Claude; Akkurt, SedatTests were performed to investigate the microstructure of the interface between alumina and spinel materials after high temperature thermal treatment (1500°C). The first test involved co-sintering of co-pressed alumina and spinel compacts. Microstructures were investigated by SEM, EDS, WDS and EBSD. A microstructurally distinct layer with columnar grains of up to 40μm length and 5μm width was observed after 16h at 1500°C. Growth rate of the columnar spinel grains from parent spinel towards alumina follows parabolic kinetics, controlled by a mixed process of O2- ion diffusion and interface reaction. Diffusion couples of spinel and alumina were investigated. Same columnar spinel grains were observed at the interface which grew into alumina during thermal treatment with the same kinetics as in co-sintering experiments. The shape of the phase boundaries between spinel and alumina can be a further indication of the direction of their growth.Article Citation - WoS: 61Citation - Scopus: 74Production of Anorthite Refractory Insulating Firebrick From Mixtures of Clay and Recycled Paper Waste With Sawdust Addition(Elsevier Ltd., 2012) Sütçü, Mücahit; Akkurt, Sedat; Bayram, Alican; Uluca, UluçProduction of porous anorthite refractory insulating firebricks from mixtures of two different clays (K244 clay and fireclay), recycled paper processing waste and sawdust addition are investigated. Suitability of alkali-containing-clay, low-alkali fireclay, pore-making paper waste and sawdust in the products was evaluated. Prepared slurry mixtures were shaped, dried and fired. Highly porous anorthite ceramics from the mixtures with up to 30% sawdust addition were successfully produced. Physical properties such as bulk density, apparent porosity, percent linear change were investigated as well as the mechanical strengths and thermal conductivity values of the samples. Thermal conductivities of the samples produced from fireclay and recycled paper waste decreased from 0.25 W/mK (1.12 g/cm 3) to 0.13 W/mK (0.64 g/cm 3) with decreasing density. Samples were stable at high temperatures up to 1100 °C, and their cold strength was sufficiently high. The porous anorthite ceramics produced in this study can be used for insulation in high temperature applications. © 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.