Researcher:
Altıntaş, Zerrin

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Zerrin

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Altıntaş

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Altıntaş, Zerrin

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2018 - 201932020 - 20225

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Now showing 1 - 8 of 8
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    Crystalline Co-Fe-b nanoparticles: Synthesis, microstructure and magnetic properties
    (Elsevier, 2019) Schmidt, Marcus; Bobnar, Matej; N/A; N/A; Department of Chemistry; Department of Chemistry; Khoshsima, Sina; Altıntaş, Zerrin; Somer, Mehmet Suat; Balcı, Özge; Researcher; Researcher; Faculty Member; Researcher; Department of Chemistry; Koç University AKKİM Boron-Based Materials & High-technology Chemicals Research & Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); Koç University AKKİM Boron-Based Materials & High-technology Chemicals Research & Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); N/A; N/A; N/A; N/A; College of Sciences; College of Sciences; N/A; N/A; 178882; 295531
    A new approach for in-situ synthesis of crystalline Co-Fe-B nanoparticles was presented in which low temperature methods were developed by using metal chlorides and NaBH4 in an inorganic molten salt environment. Effects of different reaction systems/conditions on the phase formation, thermal behavior and microstructure were investigated. The melting point of reactants and impurities in final powders were reduced by the use of molten salt technique. After a reaction of CoCl2, FeCl3 and NaBH4 at 850 degrees C in sealed tubes, CoB and Fe3B phases formed separately. After a reaction under Ar flow; however, CoFeB2 solid solution nano powders were obtained in one step at 850 degrees C with an average size of 60 nm. After annealing at 1100 degrees C, stable and highly crystalline (CoFe)B-2 solid solution phase with a Co:Fe molar ratio of 1:1 was achieved. As-synthesized particles exhibited ferromagnetic property, and possessed a narrow hysteresis curve characteristic of soft magnetic materials. Extended reaction temperature from 650 to 850 degrees C is seen to produce coercivity enhancement up to 500 Oe without significant reduction in saturation magnetization. On the other hand, after an annealing process and subsequent phase and chemical change, crystalline (CoFe)B-2 particles exhibited superparamagnetic property.
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    Synthesis of cobalt-nickel-boron based composite powders using metal chloride powder blends
    (TANGER, 2018) N/A; N/A; N/A; Department of Chemistry; Department of Chemistry; Khoshsima, Sina; Altıntaş, Zerrin; Somer, Mehmet Suat; Balcı, Özge; Researcher; Researcher; Faculty Member; Researcher; Department of Chemistry; Koç University AKKİM Boron-Based Materials & High-technology Chemicals Research & Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); N/A; N/A; College of Sciences; College of Sciences; N/A; N/A; 178882; 295531
    This study reports an alternative route for obtaining crystalline metal boride composite powders at low temperatures using various chemical reactions. The ternary system of Co-Ni-B was studied by using anhydrous metal chlorides and sodium borohydride powder mixtures. The reactions were carried out in a sealed reactor under autogenic pressure, placed in a chamber furnace. The unwanted chloride phases were removed by hot water leaching after reaction. Some of the purified powders were annealed at 1100 °C to improve the crystallinity. Effects of different reaction conditions on the formation and microstructure of the final powders were investigated. Phase, chemical and microstructural characterizations and particle size measurements of the synthesized and annealed powders were conducted using X-ray diffractometer (XRD), X-ray fluorescence spectrometer (XRF), scanning electron microscope (SEM/EDX) and dynamic light scattering technique. The results revealed the positive effect of inorganic molten salt mixture (LiCl/KCl eutectic mixture) on the formed phases during the reaction between CoCl 2 , NiCl 2 and NaBH 4 powder blends. After their reaction at 750°C in a sealed reactor under autogenic pressure, crystalline cobalt-nickel-boron based composite powders were achieved with an average particle size of 60 nm.
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    The synthesis of binary and ternary cobalt based metal borides by inorganic molten salt technique
    (TENMAK Bor Araştırma Enstitüsü, 2020) N/A; N/A; Department of Chemistry; Department of Chemistry; Altıntaş, Zerrin; Khoshsima, Sina; Somer, Mehmet Suat; Balcı, Özge; Researcher; Researcher; Faculty Member; Researcher; Department of Chemistry; Koç University AKKİM Boron-Based Materials & High-technology Chemicals Research & Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); N/A; N/A; College of Sciences; College of Sciences; N/A; N/A; 178882; 295531
    Crystalline metal boride powders were synthesized via low temperature method in inorganic molten salt medium, and binary and ternary metal boride composite powders were investigated using anhydrous metal chlorides and sodium borohydride powder mixtures. The reactions were carried out in an aluminum crucible placed in a silica tube under argon which was put in a vertical tube furnace. At the end of the reaction, the resulting powder mixture was leached with hot water to remove any undesirable chloride phases. In order to improve crystalline properties, some of pure powders were selected and annealed at 1100°C. Characterization of synthesized and annealed powders was carried out using X-ray diffractometer (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM / EDX) and dynamic light scattering technique (DLS). The results showed the positive effect of inorganic molten salt technique (LiCl/ KCl eutectic mixture) on the formation of phases during the reaction between CoCl2 , NiCl2 and NaBH4 powder mixtures. Following the reactions at between 750-950 °C, the binary and ternary metal boride powders consisting of CoB-Ni2 BCoBx , CoB-Ni4 B3 ve CoB-NiB-Ni2 Co0.67B0.33 phases were obtained. The measured particle size of the final particles had an average of 60 nm. / Öz: Kristalin metal borür tozları inorganik ergimiş tuz ortamında düşük sıcaklık yöntemi ile sentezlenmiş, ikili ve üçlü metal borür kompozit tozlarının eldesi susuz metal klorürler ve sodyum borhidrür toz karışımları kullanılarak incelenmiştir. Reaksiyonlar, argon altında dikey bir tüp fırında silika tüp içine yerleştirilmiş alüminyum pota içinde gerçekleştirilmiştir. Reaksiyon sonunda elde edilen toz karışımına sıcak su ile liç işlemi yapılarak istenmeyen klorür fazları giderilmiştir. Seçilen bazı saf tozlar, kristalin özelliği geliştirmek amacıyla 1100°C’de tavlama işlemine tabi tutulmuştur. Sentezlenen ve tavlanmış tozların karakterizasyonu, X-ışını difraktometresi (XRD), X-ışını floresans spektrometresi (XRF), taramalı elektron mikroskobu (SEM/EDX) ve dinamik ışık saçma tekniği (DLS) kullanılarak analiz edilmiştir. Sonuçlar, inorganik ergimiş tuz tekniğinin (LiCl/KCl ötektik karışımı) CoCl2 , NiCl2 ve NaBH4 toz karışımları arasındaki reaksiyon sırasında oluşan fazlar üzerindeki olumlu etkisini ortaya koymuştur. 750-950°C sıcaklıkları arasında gerçekleşen reaksiyonlarda CoB-Ni2 B-CoBx , CoB-Ni4 B3 ve CoB-NiB-Ni2 Co0.67B0.33 fazlarını içeren ikili ve üçlü metal borür tozları nano boyutta elde edilmiştir. Sentezlenen tozların partikül boyutu ortalama 60 nm civarında hesaplanmıştır.
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    Enhanced hardness and wear resistance of Al-based hybrid MMCs by using of composite metal boride reinforcement particles
    (Elsevier, 2022) Mertdinç, Siddika; Ağaoğulları, Duygu; N/A; N/A; N/A; Department of Chemistry; Khoshsima, Sina; Motallebzadeh, Amir; Altıntaş, Zerrin; Balcı, Özge; Researcher; Researcher; Researcher; Researcher; Department of Chemistry; Koç University AKKİM Boron-Based Materials & High-technology Chemicals Research & Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A; N/A; College of Sciences; N/A; N/A; N/A; 11611; 295531
    Composite metal boride particles were synthesized and then used as the reinforcement material for fabricating Al-based hybrid metal matrix composites (MMCs). Mechanical alloying and pressureless sintering methods were used to produce the Al - 2 wt % Co-Ni-B/Co-Ti-B hybrid composites. Mechanically alloyed powders and sintered composites were characterized in terms of physical, microstructural and mechanical properties. The low crystallite size of Al particles and high density of the composites provided improved microstructures without needle-shaped secondary phases, and increased nanohardness values of Al matrix, and hence resulted in enhanced mechanical properties. The lowest indentation depths (both for matrix and reinforcement phases), the highest hardness (similar to 2 GPa) and the lowest wear volume loss (similar to 0.13 mm(3)) were obtained from the Al-based MMCs reinforced with Co-Ni-B particles containing CoB and Ni2Co0.67B0.33 phases. Studies revealed that the synergetic effect of the binary and ternary boride phases in the composite reinforcements had a positive role on the hardness and wear resistance of hybrid composites.
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    Cob-tib2 crystalline powders: synthesis, microstructural analysis and their utilization as reinforcement agent
    (Elsevier, 2020) Burkhardt, Ulrich; Schmidt, Marcus; Prashanth, K. G.; N/A; N/A; Department of Chemistry; Department of Chemistry; Khoshsima, Sina; Altıntaş, Zerrin; Somer, Mehmet Suat; Balcı, Özge; Researcher; Researcher; Faculty Member; Researcher; Department of Chemistry; Koç University AKKİM Boron-Based Materials & High-technology Chemicals Research & Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); N/A; N/A; College of Sciences; College of Sciences; N/A; N/A; 178882; 295531
    Due to promising mechanical and chemical properties, transition metal borides have attracted attention, and numerous studies have investigated various combinations of transition elements in hopes of acquiring a final product with desired properties combined. In this study, novel low-temperature approach was adopted for the synthesis of cobalt-titanium-boron based crystalline powders. The method was based on the single-step direct reaction of CoCl2(s), TiCl4(l) and NaBH4(s) in a sealed reactor under autogenic pressure. After the reaction of the precursors at 850 degrees C by using the molar ratios of metal chlorides to NaBH4 as 1:3, CoB and TiB2 phases were formed in-situ. The subsequent annealing process at 1100 degrees C achieved a full conversion of metal chlorides to CoB-TiB2 composite nanostructures. It was concluded that the binary forms of the borides tend to form as separate phases, which is illustrated in the SEM/EDS analyses with different morphologies. Amorphous boron layer surrounded TiB2 particles with an average particle size of 60 nm, whereas the CoB particles formed agglomerates with an average size of 450 nm. The use of synthesized composite powders as reinforcement in metal matrices resulted in enhanced hardness (506 HV) and compressive strength (1682 MPa) of the Ti6Al4V bulk samples.
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    PublicationOpen Access
    Evolution of magnetic properties of crystalline cobalt-iron boride nanoparticles via optimization of synthesis conditions using hydrous metal chlorides
    (Elsevier, 2021) Schmidt, Marcus; Bobnar, Matej; Burkhardt, Ulrich; Department of Chemistry; Altıntaş, Zerrin; Khoshsima, Sina; Somer, Mehmet Suat; Researcher; Researcher; Researcher; Department of Chemistry; Koç University AKKİM Boron-Based Materials _ High-technology Chemicals Research _ Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); College of Sciences; N/A; N/A; 295531
    Chemical synthesis of crystalline and nanoscale cobalt-iron metal boride powders was studied using hydrous metal chlorides and NaBH4. The effects of precursor concentration and optimized synthesis conditions on the phase formation, microstructure, and magnetic properties were investigated. After applying a reaction of CoCl2·6H2O-FeCl3·6H2O-NaBH4 at 850 °C, (CoFe)B2, (CoFe)B, Co2B, Fe3B, and Fe0.71Co0.29 boride phases were obtained from different synthesis conditions applied under autogenic pressure or Ar flow atmosphere. Oxychloride impurities were the reason for the reduced magnetization values. The highest saturation magnetization of 183 emu/g belongs to obtained nanoparticles containing (CoFe)B2 and (CoFe)B pure phases. High temperature magnetic measurements marked synthesized powders as soft magnetic materials up to 795 K while no Tc was reached for the obtained phases.
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    PublicationOpen Access
    Self-assembled poly(2-ethyl-2-oxazoline)/malonic acid hollow fibers in aqueous solutions
    (Elsevier, 2019) Department of Chemistry; Department of Chemical and Biological Engineering; Miko, Annamaria; Altıntaş, Zerrin; Ijaz, Aatif; Demirel, Adem Levent; Adatoz, Elda Beruhil; Teaching Faculty; Researcher; Researcher; Faculty Member; Department of Chemistry; Department of Chemical and Biological Engineering; College of Sciences; Graduate School of Sciences and Engineering; 163509; N/A; N/A; 6568; N/A
    Well-defined poly(2-ethyl-2-oxazoline) (PEOX)/Malonic Acid (MA) fibers having hollow tubular morphology were shown to form in aqueous solutions at 25 degrees C by complexation induced self-assembly between PEOX and MA. The fibers had diameter of similar to 1-3 mu m and a wall thickness of -40 nm. Different interactions between PEOX and MA were identified for complexation as a function of pH. At pI-12, when both ends of MA were protonated, H-bonded complexation was the driving interaction in the fiber formation. IR data showed both PEOX -C=0 band and MA -COOH band in dried fibers formed at pH2. The downshift in the -C=0 stretching of PEOX by as much as 15 cm(-1) confirmed the H-bonded complexation. The interaction enthalpy of PEOX and MA was determined by isothermal titration Calorimetry (ITC) as -49.39 kJ/mol which is consistent with H-bonding. Thermogravimetric analysis (TGA) of the fibers showed two distinct decomposition temperatures one between 100 and 150 degrees C corresponding to MA and the other one at 350-450 degrees C corresponding to PEOX which also indicated the presence of both components in the fibers. At pH4, when one end of MA was protonated and the other end was ionized, electrostatic complexation between carboxylate (-COO-) group of MA and the amide group of PEOX was the driving interaction in the fiber formation. At pH7, when both ends of MA were ionized, fiber formation was significantly hindered. The results are important in understanding the role of different interactions in the hollow fiber formation mechanism as a function of pH. pHresponsive hollow fibers have great potential to be used in biomedical applications for drug delivery and release purposes.
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    PublicationOpen Access
    Nanocrystalline cobalt-nickel-boron (metal boride) catalysts for efficient hydrogen production from the hydrolysis of sodium borohydride
    (Elsevier, 2021) N/A; Department of Chemical and Biological Engineering; Department of Chemistry; Paksoy, Aybike; Altıntaş, Zerrin; Khoshsima, Sina; Öztulum, Samira Fatma Kurtoğlu; Dizaji, Azam Khodadadi; Uzun, Alper; Balcı, Özge; Researcher; Researcher; Faculty Member; Researcher; Department of Chemical and Biological Engineering; Department of Chemistry; Koç University AKKİM Boron-Based Materials _ High-technology Chemicals Research _ Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; N/A; N/A; N/A; N/A; N/A; 59917; 295531
    Innovative metal boride nanocatalysts containing crystalline Co-Ni based binary/ternary boride phases were synthesized and used in the hydrolysis of NaBH4. All the as-prepared catalysts were in high-purity with average particle sizes ranging between similar to 51 and 94 nm and consisting of different crystalline phases (e.g. CoB, Co2B, Co5B16, NiB, Ni4B3, Ni2Co0-67B0.33). The synergetic effect of the different binary/ternary boride phases in the composite catalysts had a positive role on the catalytic performances thus, while the binary boride containing phases of unstable cobalt borides or single Ni4B3 were not showing any catalytic activity. The Co-Ni-B based catalyst containing crystalline phases of CoB-Ni4B3 exhibited the highest H-2 production rate (500.0 mL H-2 min(-1) g(cat)(-1)), with an apparent activation energy of 32.7 kJ/mol. The recyclability evaluations showed that the catalyst provides stability even after the 5th cycle. The results suggested that the composite structures demonstrate favorable catalytic properties compared to those of their single components and they can be used as alternative and stable catalysts for efficient hydrogen production from sodium borohydride.