Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
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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: 5Ultrafast High-Temperature Sintering of Yttria-Stabilized Zirconia in Reactive N<sub>2</Sub> Atmosphere(Elsevier Sci Ltd, 2025) Karacasulu, Levent; de Beauvoir, Thomas Herisson; De Bona, Emanuele; Cassetta, Michele; Vakifahmetoglu, Cekdar; Sglavo, Vincenzo M.; Biesuz, MattiaSo far, ultrafast high-temperature sintering (UHS) has always been carried out in an inert environment. In the present work, we investigated UHS of 3YSZ in nitrogen and argon atmosphere showing that "the atmosphere matters". Highly densified samples can be obtained in both environments but densification and grain growth are significantly retarded in N-2. Moreover, the phase evolution is strongly atmosphere-dependent with the samples treated in Ar remaining tetragonal and those treated under N-2 progressively reducing their tetragonality, eventually converting into cubic zirconia and rock salt oxynitride. The results can be explained by the incorporation of nitrogen within the ZrO2 lattice. Electrochemical impedance spectroscopy demonstrates that while the ionic bulk conductivity are marginally influenced by the sintering atmosphere, the grain boundaries' capacitive behavior strongly changes. After UHS under 30 A, excellent ionic conductors were obtained without substantial grain boundary-blocking effects.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: 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.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: 103Citation - Scopus: 110Cold Sintering of Ceramics and Glasses: a Review(Elsevier Ltd., 2020) Ahmetoğlu, Çekdar Vakıf; Karacasulu, LeventTraditionally ceramic artifacts are processed at high temperatures (> 1000 degrees C) by classical sintering techniques such as solid state, liquid phase and pressure-assisted sintering. Recently, inspired from the geology, novel sintering approaches that allow the densification of ceramic components at relatively low temperatures <= 400 degrees C have been proposed. While initial efforts for such low temperature densification concept were developed in the mid-70s, the topic has become increasingly prominent in the last decade. Currently, these low temperature methods can be classified into four main groups: (i) hydrothermal reaction sintering (HRS), (ii) hydrothermal hot pressing (HHP), (iii) pressure-assisted densification techniques: room-temperature densification (RTD), cold sintering (CS), warm press (WP), and finally no-pressure assisted method called (iv) reactive hydrothermal liquid phase densification (rHLPD). Above named techniques are commonly assisted by an aqueous solution used as either reactant or transient liquid phase to assist densification. Starting from the background in traditional sintering processes, this review aims to explore in depth the existing literature about low temperature densification approaches along with their advantages & disadvantages, and probable application areas.Article Citation - WoS: 6Citation - Scopus: 6The Expansion Behavior of Slurries Containing Recycled Glass Powder Carboxymethyl Cellulose, Lime and Aluminum Powder(Elsevier, 2020) Zeren, Doğuş; Şentürk, Ufuk; Güden, MustafaThe rheology and foaming/expansion of the slurries of a waste/recycled glass powder with 50, 55 and 60 wt% of solid (glass powder) were experimentally investigated. The glass powder slurries were foamed using aluminum powder as foaming agent (0.75 wt%) and calcium hydroxide as activator (1 wt%). Sodium carboxymethyl cellulose (CMC) was added to the slurries as a binder with the amounts between 0 and 4 wt%. The expansions of the slurries were measured in-situ using a laser sensor and reported as percent volume expansion. The CMC-addition increased the viscosities of the slurries, particularly the fine size powder slurries. The slurries with the relatively low-viscosity exhibited lower initial expansion rates compared to the slurries with the relatively high-viscosity. The maximum expansions of the slurries increased from 300 to 350%, when the viscosity increased to 5 Pa s and reached a steady value around 400% between 5 and 50 Pa s. The expansions of the slurries could not be achieved above 50 Pa s since they became too thick to be foamed. The foam samples made from the slurries with 55 and 60 wt% of solid and sintered at 700 and 750 degrees C for 30 min had the average densities between 355 and 530 kg m(-3) and the average compressive strengths between 0.2 and 0.5 MPa. Increasing sintering time to 60 min at 750 degrees C increased the average compressive strength from 0.5 to 1.5 MPa for the foam samples made from the slurry with 60 wt% of solid. These proved that both sintering temperature and time were effective in increasing the compressive strengths of the foamed structures. The thermal conductivities of the sintered foam samples with the densities of 355 and 504 kg m(-3) were measured 0.042 and 0.057 W m(-1) K-1, respectively. (C) 2019 Elsevier Ltd. All rights reserved.Article Citation - WoS: 19Citation - Scopus: 17Preparation and Characterization of Nanocrystalline Titania Powders by Sonochemical Synthesis(Elsevier Ltd., 2012) Çağlar Duvarcı, Özlem; Çiftçioğlu, MuhsinNanocrystalline mesoporous titania powders were synthesized by hydrolyzing titanium isopropoxide in ethanol-water mixtures which were ultrasonically treated without using any templates or chemicals. Titanium isopropoxide-ethanol mixture was added dropwise to a water-ethanol mixture placed in an ultrasonic bath. The properties of the sonochemically synthesized powder were compared with those of the powders prepared without ultrasonic treatment along with Degussa P-25 titania powder. The phase structure, crystallite size, surface area, particle size, powder density were determined and sintering behavior was analyzed in this work. The nanotitania powder prepared during ultrasonic induced hydrolysis (TiO 2-U) was determined to be formed from a mixture of anatase and brookite phases at 25°C. The brookite phase in nanotitania powder prepared without ultrasonic treatment (TiO 2-NoU) was detected at 70°C. The anatase-rutile phase transformation was completed in the 500-700°C range for both powders. The average crystallite sizes of the powders at 25°C were determined as 10 and 5nm for TiO 2-NoU and TiO 2-U, respectively. The surface area decreased from 238 to106m 2/g for TiO 2-NoU and from 287 to 82m 2/g for TiO 2-U when the calcination temperature was increased from 200 to 500°C. The evolution of the N 2 adsorption-desorption behavior with calcination temperature and the corresponding pore size distributions/volumes was attributed to the formation of closely packed submicron aggregates during powder synthesis and calcination. The sintering behavior was concluded to be controlled by 7-10nm crystallites and the submicron aggregates. The determination of the densification behavior of titania powders prepared by different methods with various levels of dopants may prove to be very useful for a better understanding of the phase/pore structure evolution which is crucial for a significant number of applications.Article Citation - WoS: 7Citation - Scopus: 9Preparation of the Pb(mg1/3nb2 Films by Aqueous Tape Casting(Elsevier Ltd., 2009) Şakar-Deliormanlı, Aylin; Çelik, Erdal; Polat, MehmetLead magnesium niobate (PMN) is a relaxor ferroelectric material. Because of its high dielectric constant and superior electrostrictive properties it is commonly used in the manufacture of multilayer electronic devices which is typically produced by tape casting. However, preparation of PMN slurry formulations to use in aqueous tape casting process is not investigated in detail yet. Therefore, in this study aqueous PMN formulations were developed for tape casting and its relation with the final properties of PMN films were investigated. The slurries were prepared using poly(acrylic acid)-based comb polymer as the dispersant, nonionic acrylic latex as the binder and the hydroxypropyl methyl cellulose as the wetting agent. The results showed that it is possible to prepare flexible, crack-free PMN films using highly concentrated suspensions without using any plasticizer. The study gives guidelines for the aqueous tape casting of PMN and can be adapted to processing of other multi-component metal oxides.