Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 2Citation - Scopus: 2Sintering Under High Heating Rates(Annual Reviews, 2025) Karacasulu, Levent; Maniere, Charles; Vakifahmetoglu, Cekdar; Marinel, Sylvain; Biesuz, MattiaRapid sintering using a high heating rate is growing in technological and scientific interest. This is motivated by the promise of reducing the carbon footprint of sintering and developing materials with properties and microstructures different from those achievable by conventional heating. For instance, rapid heating can induce suppression of grain growth, the possibility of obtaining modified space charges and elemental segregations, and the development of out-of-equilibrium materials. Severe challenges still exist for the industrial exploitation of rapid sintering technologies, and, nowadays, only fast firing can be considered mature. Most of these limitations are related to the homogeneity of the sample and the possibility of obtaining complex shapes. This review investigates developments in rapid sintering by comparing different processes, suggested mechanisms, and future challenges.Article Citation - WoS: 5Citation - Scopus: 8High Entropy (hftizrvnb)b2 Ceramic Particulate Reinforced Al Matrix Composites: Synthesis, Mechanical, Microstructural and Thermal Characterization(Elsevier Ltd, 2024) Süzer,İ.; Özçakıcı,Y.E.; Tekinşen,A.S.; Bayrak,K.G.; Mertdinç-Ülküseven,S.; Balcı-Çağıran,Ö.; Ağaoğulları,D.This study aims to introduce a novel type of particulate reinforced Al matrix composite. High entropy (HfTiZrVNb)B2 ceramic particulate reinforced Al matrix composites were produced via a combined process of different powder metallurgy methods. Firstly, boride compounds (HfB2, TiB2, ZrB2, VB2, NbB2) were synthesized in the laboratory scale using the related metal oxide, boron oxide, and magnesium by mechanochemical synthesis (MCS) and leaching processes under optimum conditions. Secondly, the synthesized and purified boride powders were mixed in equimolar ratios using a planetary ball mill for 72 h, and they were sintered at 2000 °C under 30 MPa via spark plasma sintering (SPS). Thirdly, equimolar high entropy (HfTiZrVNb)B2 bulks were crushed, converted into powder forms, and added into Al powders at different amounts as 1, 2, 5, 10, and 15 wt %. Lastly, these powder blends were mechanically alloyed in a vibratory ball mill for 6 h, cold pressed and pressureless sintered at 630 °C for 2 h. For characterization techniques, X-ray diffractometry (XRD), thermal analysis, scanning electron microscopy/energy dispersive spectrometry (SEM/EDS), density measurements using pycnometer and Archimedes' methods, microhardness and dry sliding wear tests were conducted on the sintered composites. The highest hardness (∼1.5 GPa) and the lowest wear rate (∼0.0012 mm3/Nm) were obtained in the Al-15 wt % (HfTiZrVNb)B2 sample. © 2024 Elsevier Ltd and Techna Group S.r.l.Article Citation - WoS: 13Citation - Scopus: 13On the Temperature Measurement During Ultrafast High-Temperature Sintering (uhs): Shall We Trust Metal-Shielded Thermocouples?(Elsevier Sci Ltd, 2024) Biesuz, Mattia; Karacasulu, Levent; Vakifahmetoglu, Cekdar; Sglavo, Vincenzo M.Temperature measurement upon ultrafast high-temperature sintering (UHS) is a crucial task. Herein, we provide some arguments posing concerns about the use of metal-shielded thermocouples as temperature probes in UHS. The discussion is based on literature data and on some ad hoc experiments. In detail, we show at least two cases in the literature where the use of a shielded thermocouple causes a substantial underestimation of the UHS temperature. The argumentation is based on comparing the thermocouples read and the observed phase and microstructural evolution. Moreover, by means of a simple experimental design, we show that a metal shield on the thermocouple tip can substantially reduce the measured temperature. Since the metal shield is orders of magnitude more thermally conductive than the graphite felt used as heating element in UHS, it efficiently removes heat from the thermocouple tip region. As such, data acquired from shielded thermocouples must be treated with care.Article Citation - WoS: 3Citation - Scopus: 3Effects of Different Precursors on the Aging and Electrocaloric Properties of Mn-Doped Ba0.95sr0.05tio3 Ceramics(Springer, 2023) Karakaya, Merve; Erdem, Emre; Akdoğan, Yaşar; Adem, UmutIn this study, the effects of different types of Mn precursors (MnO2 and Mn2O3) and sintering temperature on the defect dipole formation, ferroelectric aging and electrical properties were investigated by using Ba0.95Sr0.05TiO3 ceramics as the base. Both Mn precursors were substituted to the Ti-site as 1 mol% and two different sintering temperatures of 1325 and 1400 degrees C were used to study the effect of grain size. We deduced that slightly higher amounts of Mn2+ can be incorporated into the perovskite structure when MnO2 is used as the precursor, by using X-ray diffraction and electron paramagnetic resonance spectroscopy. Mn-doped samples sintered at 1325 degrees C age faster than those sintered at 1400 degrees C. Aging caused a decrease in the electrocaloric effect whereas Mn-doping increased it. This study shows that Mn precursor used for the acceptor doping affects the amount of Mn incorporated into the structure and therefore electrical properties of the resulting ceramics.Article Citation - WoS: 37Citation - Scopus: 41Processing and Characterization of Geopolymer and Sintered Geopolymer Foams of Waste Glass Powders(Elsevier, 2021) Polat, Dilan; Güden, MustafaGeopolymer foams of fine and coarse waste glass (WG) powders were prepared using an activation solution of NaOH (8 M) and Na2SiO3. The effects of WG powder particle size, solid/liquid ratio (S/L = 1, 1.5, and 2) and Al foaming agent content (2-20 wt%) on the expansion and temperature behavior of the slurries were determined in-situ using a laser sensor and a thermocouple, respectively. The geopolymer foams processed using a coarse WG powder slurry, S/L = 2, and 2 wt% Al, were further sintered at 600, 700, 725, and 750 degrees C. The compression strengths and thermal conductivities of the geopolymer and sintered geopolymer foams were also determined. The slurry expansions continued until about a maximum, and the temperatures of the slurries increased to a maximum, 85-88 degrees C. At the maximum temperature, the slurry evaporation and the resultant increase in the S/L ratio limited the slurry expansion. Increasing the Al content decreased the final density of the foams (238-555 kg m-3), while the coarse powder slurries resulted in lower densities than the fine powder slurries. Three crystal phases, muscovite, sodium aluminum silicate hydrate, and thermonitrite, were determined in the geopolymer foams. The muscovite formation was noted to be favored at high S/L ratios. During sintering, the partial melting of glass particles started after about 700 degrees C, while sintering above this temperature decreased the final density of the foams. The reduced density above 700 degrees C was ascribed to the release of CO2 due to the decomposition of thermonitrite. Both the compressive strength and thermal conductivity of the geopolymer and sintered geopolymer foams increased with increasing foam density. The highest increase in the compressive strength and reduction in the density were seen in the geopolymer foams sintered at 750 degrees C.