Researcher:
Somer, Mehmet Suat

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Mehmet Suat

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    Effect of ambient and cryogenic milling on the microstructure and properties of tungsten matrix composites fabricated by activated sintering
    (Sivas Cumhuriyet Üniversitesi, 2019) Ağaoğulları, Duygu; Öveçoğlu, M. Lütfi; Department of Chemistry; Department of Chemistry; Balcı, Özge; Somer, Mehmet Suat; Researcher; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; 295531; 178882
    Tungsten matrix composites reinforced with TiB2 and Y2O3 particles were fabricated by milling under ambient/cryogenic conditions and Ni activated sintering. Powder blends constituting the W - 1 wt. % Ni - 2 wt. % TiB2 - 1 wt. % Y2O3 composition were mechanically milled for 12 h under ambient condition or cryomilled for 10 min or sequentially milled under ambient and cryogenic conditions. Milling was carried out in a high-energy ball mill under ambient condition whereas cryogenic milling was conducted in externally circulated liquid nitrogen. Milled powders were compacted using a hydraulic press and the pellets were sintered at 1400°C for 1 h under Ar / H2 gas flowing conditions. The effects of different milling types on the microstructural and mechanical properties of the sintered composites were investigated. After sintering, in addition to dominant W phase, small amounts of WB and NiW phases were detected in all sintered samples. The application of cryomilling after milling at ambient condition provided the disappearance of the clustered TiB2 and Y2O3 particles in the sintered sample: They were located at the grain boundaries of W1Ni matrix and homogeneously distributed through the microstructure. Sequentially milled and sintered composite had the highest relative density (95.77 %) and the highest microhardness (7.23 GPa) values among the samples. Nanoindentation tests showed that there was an improvement in the hardness and elastic modulus of W matrix phase, which yielded the values of 8.9 and 373.7 GPa, respectively. / Özet: Bu çalışmada, Ni ile aktive edilerek sinterlenen tungsten esaslı matrisin TiB2 ve Y2O3 partikülleri ile takviye edilmesiyle, tungsten esaslı kompozit malzeme üretimi gerçekleştirilmiştir. W - % 1 ağ. Ni - % 2 ağ. TiB2 - % 1 ağ. Y2O3 kompozisyonundan oluşan toz harmanları, normal koşullarda 12 sa mekanik olarak öğütülerek ya da 10 dk kriyojenik ortamda öğütülerek ya da normal ve kriyojenik şartlarda ardışık olarak öğütülerek hazırlanmıştır. Normal şartlarda öğütme yüksek enerjili bir değirmende uygulanırken; kriyojenik şartlarda öğütme sıvı azot ile dışarıdan çevrelenen bir sistemde yapılmıştır. Öğütülmüş tozlar hidrolik pres kullanılarak preslenmiş ve pekiştirilen bünyeler Ar/H2 gazaltı şartlarında 1400°C’de 1 sa sinterlenmiştir. Farklı öğütme koşullarının sinterlenen kompozit malzemelerin mikroyapısı ve özellikleri üzerindeki etkisi incelenmiştir. Sinterlenme sonrasında, baskın W fazına ek olarak düşük mikarda WB ve NiW fazları oluşumu gözlemlenmiştir. Normal şartlarda öğütme sonrası uygulanan kriyojenik öğütme, sinter malzemelerin mikroyapısındaki TiB2 ve Y2O3 partiküllerin topaklanmasının yok olmasına neden olmuştur: Partiküllerin W1Ni matrisinin tane sınırlarında ve homojen olarak mikroyapıda dağılması sağlanmıştır. Ardışık olarak öğütülmüş ve sinterlenmiş kompozitler, numuneler arasında en yüksek rölatif yoğunluk (% 95,77) ve mikrosertlik değerlerini (7,23 GPa) sunmuştur. Nano-indentasyon testleri sayesinde, W matris fazının sertlik ve elastisite modül değerlerinin sırasıyla 8,9 ve 373,7 GPa değerlerine kadar iyileştirildiği kanıtlanmıştır.
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    The first alkaline-earth azidoaurate(III), Ba[Au(N-3)(4)](2) center dot 4 H2O
    (Wiley, 2023) Prots, Yurii; Jach, Franziska; Afyon, Semih; Höhn, Peter; Department of Chemistry; Department of Chemistry; Department of Chemistry; Subaşı, Yaprak; Tekin, Elif Sena; Somer, Mehmet Suat; Researcher; Undergraduate Student; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; 178882
    Transparent, dark orange Ba[Au(N-3)(4)](2) center dot 4 H2O was synthesized by reaction of Ba(N-3)(2) and AuCl3 or HAuCl4 in aqueous solution. The novel barium tetraazidoaurate(III) tetrahydrate crystallizes in the monoclinic space group Cc (no. 9) with a=1813.68(17) pm, b=1737.95(11) pm, c=682.04(8) pm and beta=108.849(4)degrees. The predominant structural features of Ba[Au(N-3)(4)](2) center dot 4 H2O are two crystallographically independent discrete anions [Au(N-3)(4)](-) with gold in a tetragonal planar coordination by nitrogen. Vibrational spectra show good agreement with those of other azidoaurates(III). Upon drying, this salt was shown to be a highly explosive material.
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    Crystal structure of sodium tetrastrontium tris (dinitridoborate), NaSr4[BN2]3
    (R Oldenbourg Verlag, 2000) Carrillo-Cabrera, Wilder; Peters, K. von Schnering, Hans Georg; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882
    B3N6NaSr4, cubic, Im (3) over bar m (NO. 229), a = 7.568(1) Angstrom, V = 433.5 Angstrom(3), Z = 2, R-gt(F) = 0.053, wR(F) = 0.043, T = 293 K.
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    Structures and properties of NbOF3 and TaOF3 - with a remark to the O/F ordering in the SnF4 type structure
    (Wiley-V C H Verlag Gmbh, 2002) Köhler, J; Simon, A; van Wullen, L; Cordier, S; Roisnel, T; Poulain, M; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882
    Powder samples of NbOF3 und TaOF3 were prepared by heating mixtures of NbO2F and NbF5 or TaO2F and TaF5, respectively, in the corresponding stoichiometric ratio in platinum crucibles under argon atmosphere (180-220degreesC). Both oxide fluorides are coulourless with a slight greyish tinge. They are sensitive to moisture and decompose in air at room temperature within hours. Both, NbOF3 and TaOF3 crystallize as a variant of the SnF4 type structure, space group 14/mmm. The structures have been refined from X-ray powder diffraction data using the Rietveld method (a = 3.9675(1) Angstrom, c = 8.4033(1) Angstrom, R-B = 3.60%, R-p = 4.58% for NbOF3 and a = 3.9448(1) Angstrom, c = 8.4860(1) Angstrom, R-a = 2.07%, R-p = 2.44% for TaOF3). Characteristic building units are sheets of corner sharing MX6 octahedra which are stacked via van der Waals interactions to a three dimensional framework. The occupancy of the two crystallographic sites for the anions by O and F is discussed on the basis of structure refinements, bond order summations, IR and NMR data and calculations of the Madelung parts of the lattice energy.
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    Nanoparticle silicalite-1 crystallization from clear solutions: nucleation
    (Elsevier Science Bv, 2009) Tokay, Begüm; Erdem-Şenatalar, Ayşe; Schueth, Ferdi; Thompson, Robert W.; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882
    Despite much effort spent by various research groups, there remain many aspects of nanoparticle silicalite-1 crystallization from clear solutions which require further investigation. In order to shed light, especially on the nucleation of silicalite-1, particle growth at 100 degrees C from several starting compositions known to yield colloidal silicalite-1, which have been studied previously by other researchers using various techniques, was followed in this study by laser light scattering using scattering angles of 90 degrees and 173 degrees, and zeta potential and pH measurements. Crystallinity was monitored by X-ray diffraction, Fourier transform infrared analysis and transmission electron microscopy. Thermogravimetric analyses and density measurements were also used to characterize the products obtained at various times during the syntheses. The results demonstrate that the distinct time of sudden jump in the effective diameter of the nanoparticles in solution, as observed more clearly by using the back-scattering device, and which marks the beginning of the constant linear growth rate of the particles, corresponds to the nucleation of the silicalite-1 crystal structure. This time was also shown to coincide with the exo-endo thermal switch time of the reaction mechanism, which has been observed previously by another research group. Nucleation was accompanied by an aggregation of a population of smaller particles, as indicated by the broadening of the particle size distribution, and the variation of the pH and zeta potential values during synthesis.
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    FT-Raman, FT-IR and NMR spectra, vibrational assignments and density functional studies of 1,3-bis(benzimidazol-2-yl)-2-thiapropane ligand and its Zn(II) halide complexes
    (2008) Aghatabay, Naz Mohammed; Tulu, Metin; Yılmaz, Ayberk; Department of Chemistry; Department of Chemistry; Somer, Mehmet Suat; Haciu, Durata; Faculty Member; Teaching Faculty; Department of Chemistry; College of Sciences; College of Sciences; 178882; N/A
    1,3-bis(benzimidazol-2-yl)-2-thiapropane (L) ligand and its zinc halide ZnX2 (X = Cl, Br, I) complexes have been synthesized. The compounds were characterized using the elemental analysis, molar conductivity, FT-Raman, FT-IR (mid i.r., far i.r.), 1H and 13C NMR spectra, and quantum chemical calculations performed with Gaussian 03 package program set. The optimized geometries and vibrational frequencies of the ligand and [Zn(L)Cl2] complex were calculated using the DFT/B3LYP method with a 6–31g(d) basis set. The geometry optimization of [Zn(L)Cl2] yields a slightly distorted tetrahedral environment around Zn ion, while the molecule clearly reveals the Cs symmetry. The molar conductivity data reveals that the complexes are neutral. The ligand is bidentate, via two of the imine nitrogen atoms in the bis-imidazole ring units, and together with the monodentate coordination of the two halides to the metal centre.
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    Crystal structure of bis[µ2-(3-benzimidazol-2-yl)-2-ethanethiolato-N,S,S)- chloro-palladium(II)], [(C6H4N2HCCH2CH2S)PdCl]2 C2H5OH
    (Walter de Gruyter GmbH, 2005) Agh-Atabay, N.M.; Borrmann, H.; Department of Chemistry; Department of Chemistry; Somer, Mehmet Suat; Haciu, Durata; Faculty Member; Teaching Faculty; Department of Chemistry; College of Sciences; College of Sciences; 178882; N/A
    C20H24Cl2N4OPd2S2, triclinic, P1 (no. 2), a = 8,796(1) Å, b = 9.844(1) Å, c = 14.718(2) A, α = 94.330(6)°, β = 98.546(6)°,γ = 99.258(7)°, V= 1237.3 Å3, Z= 2, Rgt(F) = 0.068, wRref(F2)= 0.142, T= 295 K.
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    The isotope effect of boron on the carbon doping and critical current density of (MgB2)-B-11 superconductors
    (Royal Society of Chemistry (RSC), 2017) Cheng, Fang; Liu, Yongchang; Ma, Zongqing; Al Hossain, M. Shahriar; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882
    Previous works mainly focused on the isotope effect of boron on the Tc performance and superconducting mechanism of MgB2 superconductors but were never concerned with its effect on the chemical doping and critical current density (J(c)) performance of MgB2, which is of great importance in terms of electromagnetic applications. In the present work, the isotope effect of B-11 on carbon doping and Jc of MgB2 superconductors was for the first time studied systemically. It is found that as the chemical activity of B-10 is higher than B-11, the substitution of B by C can more easily occur on B-10 than on the B-11 site of the MgB2 lattice. This is why carbon doping fails to increase the Jc value of isotope (MgB2)-B-11 superconductors. Our result is quite different from the case in carbon doped normal MgB2 superconductors with a natural boron source (composed of B-10 -18.98% and B-11 -81.02%) reported in most previous studies, where C can substitute a part of B-10 and thus significantly improve Jc performance at high fields. Our results provide a deeper understanding on the boron isotope effect and chemical doping mechanism in MgB2 superconductors.
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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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    Crystal structure of tetrasodium octaeuropium(ii) [octaphosphido(3-)]-bis[diphosphido(4-)]tetraaluminate(iii),NA 4EU8[AL4P8(P2) 2]
    (Walter de Gruyter, 1998) Carrillo-Cabrera, W.; Peters, K.; Von Schnering, H.G.; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882
    N/A