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RISS 인기검색어
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- 저자 : Cengiz Tatar (검색결과 4 건)
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Cengiz Tatar,Dilek Bagci,Omer Kaygili 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.5
In the present study, the effects of high amounts of Al and Zn additives on the crystal structure, phase composition andmicrostructure of hydroxyapatite (HAp) samples synthesized by sol-gel route were investigated by X-ray diffraction (XRD),Fourier transformation infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) techniques. The values of thecrystallinity percent, crystallite size, lattice parameter of a and volume of the unit cell decrease gradually with increasingamount of the co-additives. The formation of the new phases is observed and these phases become dominant with increasingamount of Al and Zn. The morphology of HAp, shape and size of the particles are also affected by the amount of Al and Zn. As expected, a gradual decrease in the Ca/P molar ratio is observed.
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Cengiz Tatar,Sefa Kazanc 한국물리학회 2012 Current Applied Physics Vol.12 No.1
Thermoelastic phase transformations and thermodynamic properties of CuAlNi alloys at 0, 1, 2 and 3 GPa pressures were investigated by using MD simulation in this study. The interactions between atoms were modelled by SuttoneChen type of embedded atom method (SCEAM) that is based on many-body interaction. It was observed that thermoelastic phase transformation in the ternary alloy system occurred at the end of thermal process. Radial distribution function (RDF) was used in order to analysis the structures obtained from MD simulation using the simulation techniques’ thermodynamic parameters. The transformation temperatures, enthalpy and entropy of the ternary alloy system have been observed to be changing with the applied pressure. In addition, it was found that the elastic energy has been decreased about 22% by applied pressure whereas Gibbs free energy has been increased about 60% by applied pressure. The values of the thermodynamical parameters obtained in this study were observed to be in close agreement with the experimental study. Thermoelastic phase transformations and thermodynamic properties of CuAlNi alloys at 0, 1, 2 and 3 GPa pressures were investigated by using MD simulation in this study. The interactions between atoms were modelled by SuttoneChen type of embedded atom method (SCEAM) that is based on many-body interaction. It was observed that thermoelastic phase transformation in the ternary alloy system occurred at the end of thermal process. Radial distribution function (RDF) was used in order to analysis the structures obtained from MD simulation using the simulation techniques’ thermodynamic parameters. The transformation temperatures, enthalpy and entropy of the ternary alloy system have been observed to be changing with the applied pressure. In addition, it was found that the elastic energy has been decreased about 22% by applied pressure whereas Gibbs free energy has been increased about 60% by applied pressure. The values of the thermodynamical parameters obtained in this study were observed to be in close agreement with the experimental study.
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Thermoelastic Transition Kinetics of a Gamma Irradiated CuZnAl Shape Memory Alloy
Soner Ozgen,Cengiz Tatar 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.6
Many types of shape memory alloys have been used in nuclear reactors and aerospace applications where they are exposed to high levels of various kinds of radiation. The effect of gamma irradiation on the transformation kinetics of thermoelastic transformations in a shape memory CuZnAl alloy was investigated by differential scanning calorimetry (DSC) with heating/cooling rates of 10, 20, 30 and 40 °C/min. Irradiation doses of 10, 20, 30 and 40 kGy were applied to the samples of the alloy. Changes in Gibbs free energies,entropies and elastic energies were calculated. Reverse transition temperatures As and Af systematically decreased with increasing doses, although forward transition temperatures Ms and Mf underwent a minimum value at a dose of 20 kGy. Hysteresis in the transition temperatures changed as an inverse parabolic function of the irradiation dose. The activation energies of transformations were calculated by using Kissinger and Osawa methods.
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Dielectric and thermal properties of Na2O-CaO-SiO2- MgO-Al2O3-TiO2 glass-ceramic
Omer Kaygili,Fahrettin Yakuphanoglu,Cengiz Tatar 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.8
The Na2O-CaO-SiO2-MgO-Al2O3-TiO2 (NCSMAT) glass-ceramic having the composition of 49 Na2O, 19 CaO, 31 SiO2,0.25 MgO, 0.50 Al2O3 and 0.25 TiO2 (wt.%) was prepared by conventional method. The crystal structure, phase composition,microstructural, chemical, thermal and dielectric properties of the glass-ceramic were investigated. Using the X-ray diffraction(XRD) results, biphasic structure of the glass-ceramic sample was detected, the crystallite size was found to be 13.21 nm forNa4CaSi3O9 phase and 11.02 nm for Na8Al4Si4O18 phase, and the crystallinity percent was calculated to be 86.74 %. Scanningelectron microscope (SEM) observations show that the NCSMAT glass-ceramic has the fine-grained particle distribution withthe smaller particles than 1 µm. The stretching modes of Si-O-Si bound were detected from Fourier transform infrared (FTIR)spectrum. The NCSMAT glass-ceramic is thermally stable from room temperature to 1173 K and the mass loss of the samplein this range is 1.05%. The density was calculated to be 2,751 kg m−3. The relative permittivity at 1 kHz was found to be 85.35. The alternating current conductivity increases with increasing frequency and obeys the universal power law.
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