Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4719
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Article Citation - WoS: 3Citation - Scopus: 4Development of Textured Lead-Free Nbt-Based Piezoelectric Materials in a Matrix, Synthesized by an Alternative Route, Via Templated Grain Growth(Springer, 2023) Çoban Tetik, Hatice Şule; Suvacı, Ender; Avcı, A. Murat; Adem, Umut; Karakaya, MerveIn this study, (1−x)(K0.5Bi0.5TiO3-BaTiO3)−xNa0.5Bi0.5TiO3 KBT:BT = 2:1 where x = 0.8 (KBT-BT-NBT) (001) textured lead-free piezoelectric ceramics were fabricated using BT template by templated grain growth with tape casting. Unlike the commonly used matrix preparation method, which is the calcination of all raw materials in one step, the matrix phase was prepared in a different way by first preparing KBT, BT and NBT powders separately and then by calcining the mixtures of these powders, so that effect of the matrix, synthesized by this alternative route, on texture development properties was evaluated. In addition, the effect of BT template content on the grain orientation with different sintering temperature and time, structure evolution, phase stability and piezoelectric properties were investigated to assess the materials’ actuating performance. The highest Lotgering factor of 81% was achieved for the textured ceramics with 10 wt% BT templates sintered at 1150 °C for 48 h. Compared to the one-step synthesis method, similar Lotgering factor values were obtained at lower sintering temperatures in the matrix, synthesized by the alternative 2-step method. The highest piezoelectric constant, remnant polarization, strain value and depolarization temperature were also obtained from the same sample, as ~ 190 pC/N, 30 kV/cm, 25% at 50 kV/cm and ~ 165 °C, respectively. The results show that the textured, lead free K0.5Bi0.5TiO3-BaTiO3-Na0.5Bi0.5TiO3 (KBT-BT-NBT) ceramics that are developed by using the matrix, synthesized by the alternative 2-step method, can be very promising lead-free electroceramics for high performance actuator applications.Article Citation - WoS: 1Citation - Scopus: 1Influence of Processing Method of Cocrmo Dental Alloy on the Corrosion Behavior in Artificial Saliva(Wiley, 2022) Pontes, Joana R.; Pinto, Ana M. P.; Ariza, Edith; Alves, Alexandra C.; Toptan, FatihRemovable or fixed dental frameworks are usually made of CoCr alloys. The CoCr dental alloys are produced traditionally by lost-wax casting. However, alternative processing routes, such as hot-pressing, are being studied for dental applications. The purpose of the present work was to assess the corrosion resistance of CoCrMo dental alloy produced by conventional lost-wax casting and hot-pressing. The corrosion behavior was studied in artificial saliva at 37°C by potentiodynamic polarisation tests. Immersion tests were performed to evaluate the growth of the passive film where electrochemical impedance spectroscopy was used at different immersion periods. Results showed slightly better corrosion resistance in terms of ipass for CoCrMo samples obtained by hot-pressing. On the other hand, the immersion tests showed a more stable and thicker passive film formed on hot-pressed CoCrMo dental alloy, pointing out that hot-pressing may be considered a promising technique to produce CoCrMo dental structures.Article Citation - WoS: 2Citation - Scopus: 1Effects of Electrospraying Parameters on Deposition of La0.3sr0.7fe0.7cr0.3o3−δ Cathode Layer on Gdc(Wiley, 2022) Akkurt, Sedat; Sındıraç, Can; Özmen Egesoy, Tuğçe; Atıcı, Gökçe; Erişman, Elif; Erğen, Emre; Büyükaksoy, AligülHigh performance in intermediate temperature solid oxide fuel cells requires improvements especially in the microstructure of the cathode layer. New cobalt-free cathode materials are used because cobalt-containing cathodes have higher thermal expansion coefficients, poor long-term chemical stability, and lower mechanical stability. Recently cobalt-free cathodes have been proposed to solve these issues by using deposition methods other than electrospray deposition (ESD). In this study, ESD method is used to develop a cobalt-free cathode layer. The electrolyte layer is gadolinium-doped ceria that is deposited with La0.3Sr0.7Fe0.7 Cr0.3O3−δ (LSFCr) prepared by 2-butoxyethanol and ethylene glycol solvents as opposed to conventional solvents. Experimental ESD parameters are tested at different levels and combinations by applying statistical experimental design methods to optimize the microstructure. Coating deposited as such demonstrated higher electrochemical performance than similar electrodes fabricated by other methods.Article Citation - WoS: 49Citation - Scopus: 54Highly Porous Poly(o-Phenylenediamine) Loaded Magnetic Carboxymethyl Cellulose Hybrid Beads for Removal of Two Model Textile Dyes(Springer, 2022) Arıca, Tuğçe Aybüke; Balcı, Fadime Mert; Balcı, Sinan; Arıca, Mehmet YakupEnsuring the removal of complex dyes from wastewater is a topic of great interest as it is vital for the environment. The present study reports a facile preparation method for poly(o-phenylenediamine) [p(o-PDA)] micro-particles loaded to magnetic carboxymethyl cellulose (CMC) hydrogel beads as adsorbents. The prepared products were characterized by FTIR, TGA, VSM, SEM, BET, and zeta sizer. The Fe3O4@p(o-PDA)@CMC beads were used for the removal of Reactive Blue 4 (RB-4) and Congo Red (CR) textile dyes from an aqueous medium. Different factors, such as adsorbent dose, initial pH, ionic strength, contact time, temperatures, and initial RB-4 and CR concentrations were examined. The maximum adsorption capacities of the RB-4 dye and CR at optimum pH 5 reached 398.7 and 524.6 mg/g in 120 min, respectively. The adsorption of RB-4 and CR on the hybrid magnetic beads can be due to the electrostatic, hydrogen bonding, and π-π interactions. Moreover, the magnetic hybrid beads showed easy regeneration ability and good reusability. The adsorbent can be a very good candidate for the efficient removal of micro-pollutant from wastewater.Article Citation - WoS: 4Citation - Scopus: 4Indirect Exchange Interaction in Two-Dimensional Materials With Quartic Dispersion(American Physical Society, 2022) Canbolat, Ahmet Utku; Sevinçli, Haldun; Çakır, ÖzgürWe investigate the indirect magnetic exchange interaction between two magnetic moments in a two-dimensional semiconductor with quartic dispersion, featuring a singularity at the band edge. We obtain the Green's functions analytically to calculate the magnetic exchange interaction at zero temperature. We show that the singularity in the density of states (DOS) for quartic dispersion gives rise to an enhancement in the amplitude of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction as the Fermi energy is swept toward the band edge. Furthermore, a region of finite exchange interaction arises, with a range increasing as the Fermi energy approaches the band edge. The results lay the possibility of an electrical/chemical control over the exchange interactions.Article Citation - WoS: 28Citation - Scopus: 33Cold Sintering as a Promising Isru Technique: a Case Study of Mars Regolith Simulant(Elsevier, 2023) Karacasulu, Levent; Karl, David; Gurlo, Aleksander; Ahmetoğlu, Çekdar VakıfMars regolith simulant (MGS-1) was densified for the first time via a cold sintering process (CSP) as a novel in-situ resource utilization (ISRU) concept. The technique comprises the utilization of NaOH solution as a liquid media during the densification of simulant powder with <100 μm particle size. In as short as 30 min, with the increase in the NaOH concentration (from 3 M to 10 M) and processing temperature (from 150 °C to 250 °C), the relative densities of the regolith compacts and the mechanical properties were enhanced. The artifacts produced with Mars regolith simulant powder at 250 °C using 10 M NaOH solution yielded a relative density of around 88% and compressive strength reaching ∼45 MPa.Article Citation - WoS: 9Citation - Scopus: 9Polymer-derived ceramic molten metal filters(Springer, 2022) Dizdar, Kerem Can; Kulkarni, Apoorv; Dışpınar, Derya; Soraru, Gian Domenico; Ahmetoğlu, Çekdar Vakıf; Semerci, TuğçeThis paper reports the synthesis and the performance of polymer-derived ceramic filters for molten metal filtration. Two different filter types were studied: foam filters produced from flexible polyurethane (PU) foams and additive manufacturing (AM) filters produced from thermoplastic polyurethane (TPU) cellular structure, and the results from all filter types were compared with that of the commercially used SiC foam filters. In both cases, the urethane-based polymeric template was impregnated with the preceramic solution, followed by pyrolysis. The produced ceramic components were then used to filter a molten Al alloy (A357), and the resulting Al samples were characterized for their mechanical properties. When filters were used, more reproducible and reliable mechanical properties were achieved compared to the samples obtained without any filtration. Among the different filters tested, the foam filters demonstrated better performance in comparison with the AM ceramic filters due probably to the three-dimensional interconnected porosity compared with the unidirectional cellular structure of the AM ceramic filters.Article Citation - WoS: 3Citation - Scopus: 4Partial Austenitisation and Tbf Steel Composed of Ferrite, Bainitic Ferrite, and Austenite(Taylor & Francis, 2022) Erişir, Ersoy; Bilir, Oğuz Gürkan; Sözer, Yunus Emre; Ararat, Özge; Davut, KemalA TRIP-aided bainitic-ferritic (TBF) steel with a chemical composition of Fe-0.19C-1.7Mn-1.09Si-0.51Al-0.05Nb (wt-%) was partially austenitised from a hot-rolled martensitic initial microstructure. After the hot rolling, the martensitic specimens were reheated to different intercritical temperatures and then austempered at 350 degrees C. Thus, the effect of the initial microstructure of TBF steel on intercritical austenite formation during partial austenitisation was studied. The microstructures were investigated by scanning electron microscopy and electron backscatter diffraction (EBSD), and the tensile properties were tested. Microstructural observations revealed that a final microstructure of fine ferrite, bainitic ferrite, and retained austenite can be obtained. The steel partial austenitised at 770 degrees C showed a good combination of ultimate tensile strength and total elongation.Article Citation - WoS: 6Citation - Scopus: 6Tribocorrosion-Resistant Ti40nb-Tin Composites Havingtio(2)-Based Nanotubular Surfaces(American Chemical Society, 2022) Çaha, İhsan; Alves, Alexandra Cruz; Chirico, Caterina; Pinto, Ana Maria; Tsipas, Sophia; Gordo, Elena; Toptan, FatihA novel multifunctional material was developed byhard TiN particle reinforcement addition to a beta-type Ti40Nb alloy,followed by surface functionalization, yielding the formation of ananotubular layer. Corrosion and tribocorrosion behaviors wereinvestigated in a phosphate-buffered saline solution at bodytemperature. The results revealed that the Ti40Nb-TiNcomposites presented similaripassandE(i=0)values together withrelatively similarRoxandCox. However, its tribocorrosion resistancedrastically improved (wear volume is almost 15 times lower than anunreinforced alloy) as a consequence of the load-carrying effectgiven by the reinforcement phases. The corrosion and tribocorro-sion behaviors were further improved through surface functionaliza-tion as observed by significantly loweripassand higherRoxvalues andalmost undetectable wear volume loss from tribocorrosion tests dueto the formation of a well-adhered anatase-rutile TiO2-based nanotubular layer.Article Citation - WoS: 8Citation - Scopus: 8Design and Fabrication of Polymer Micro/Nano Composites With Two-Level Mechanical Reinforcing Procedure(Wiley, 2022) Kandemir, Ayşe Çağıl; Dönmez, Fatma; Davut, Kemal; Kaplan Can, HaticeBiocompatible composite production was accomplished by utilizing two-level hierarchical approach for mechanical reinforcement. A well-known commodity polymer; low-density polyethylene (LDPE), which has high-fracture toughness, yet low strength and modulus was used as the main matrix material. As the first step of hierarchy, ductile LDPE was blended with brittle polyvinylpyrrolidone (PVP), which is an eco-friendly, nontoxic and biocompatible polymer. This resulted in slight decrease of strength and drastic reduction of toughness (%70), yet modulus was increased by 78%. As the second level of hierarchy, PVP composites were introduced in LDPE. Nano-scaled Halloysite clay and micro-scaled spherical Silica particles were utilized as additives in the aforementioned PVP composites. The reason for the choice of these particles is that they are nontoxic, low-cost and in the case of Halloysite; abundant in nature. Owing to the implementation of the second level; modulus improvement was further enhanced to 150%, with additional benefits of strength increase up to 17% and less reduction in fracture toughness (minimum 51% reduction). Dynamic mechanical analysis also supported these outcomes that storage modulus of composites are higher than both LDPE and LDPE-PVP blend. The proposed biocompatible composites in the end of this study would be utilized in biomedical applications necessitating mechanical improvements.