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: 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 UniversityConference Object Citation - WoS: 3Citation - Scopus: 3Co-Sintering Behaviors of Oxide Based Bi-Materials(American Ceramic Society, 2010) Carry, Claude; Yalamaç, Emre; Akkurt, SedatBi-materials have attracted attention due to combination of properties that such structures can offer. A strong bond between two co-sintered oxide ceramics can provide novel properties. This study focused on the densification and the microstructural evolution during co-sintering of alumina (Al2O3)zirconia (Y-ZrO2) and alumina-spinel (MgAl2O4) bi-materials, produced by co-pressing of powders. High purity submicron powders were uniaxially pressed or co-pressed (150 or 250 MPa). The sintering behaviors of mono and bi-material bodies were investigated using a vertical dilatometer under constant heating rate conditions (from 1 to 10 degrees C/min up to 1580 degrees C). Microstructural characterizations focused on the interface and diffusion layers of bonded bi-materials. Best bonding without cracks were observed on alumina-spinel bi-materials. Macroscopic and microscopic observations are analyzed, interpreted and discussed considering shrinkage and thermal expansion mismatches, residual stresses, diffusion kinetics and oxide phase diagrams.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: 59Citation - Scopus: 71Additive and Intensive Grinding Effects on the Synthesis of Cordierite(Elsevier Ltd., 2006) Yalamaç, Emre; Akkurt, SedatCordierite was mechanochemically synthesized by mixing proper amounts of kaolin, talc and Al(OH)3. Full factorial experiments were planned, conducted, and the results were analyzed by the use of statistical techniques in order to understand the effects of process variables on the amount of synthesized product. The powder products were analyzed by XRD, DTA, and SEM-EDS. As a result of the statistical analysis, temperature was found to be the most important factor. Based on XRD peak intensity measurements, the cordierite mixture was completely amorphized by grinding at 300 rpm for 60 min. Cordierite was successfully produced at temperatures as low as 1150 °C by using the mixture after intensive grinding. The combined effect of magnesium borate additive and grinding on cordierite synthesis was also studied. These factors successfully decreased the synthesis temperature down to 1000 °C.Article Citation - WoS: 36Citation - Scopus: 43Effects of Boron Addition and Intensive Grinding on Synthesis of Anorthite Ceramics(Elsevier Ltd., 2008) Kavalcı, Sedat; Yalamaç, Emre; Akkurt, SedatAnorthite ceramics were synthesized starting from mixtures prepared by using mechanochemical methods with boron oxide addition. The raw materials used in this study were Sivas Kaolin, calcined alumina/Al(OH)3 and calcite. Statistical experimental design techniques (SED) were used in order to determine and analyze the more important process variables for synthesizing anorthite ceramics. Phase characterizations of synthesized powders were performed by XRD using Cu Kα radiation. Microstructural characterization was performed by SEM. The results of screening experimental design clarified that the temperature was the most important process variable. Second most important process variable was grinding speed of starting mixture which was followed by additive amount and additive type. The effect of both additive use and grinding on anorthite synthesis helped decrease the synthesis temperature down to 900 °C. © 2007 Elsevier Ltd and Techna Group S.r.l.Conference Object Citation - WoS: 8Citation - Scopus: 8Low Temperature Synthesis of Spinel Powders by Mechanical Grinding(Trans Tech Publications, 2004) Yalamaç, Emre; Akkurt, Sedat; Çiftçioğlu, MuhsinLow temperature synthesis of spinel powder via intense mechanical grinding was performed. A dramatic decrease in the synthesis temperatures of ground powders was achieved. We were able to produce partially crystallized spinel at room temperature via a 110 minute grinding. Characterization of the synthesized powders was performed using SEM, XRD and DTA. Each stage of synthesis was analyzed using these techniques. Mixtures of Mg(OH)2 and Al(OH) 3 were used for synthesis. Temperatures as low as 800°C were able to produce bumps in the XRD patterns of ground powders at the 2θ angles for spinel crystals.