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Öğe Effect of concentration of Sm2O3 and Yb2O3 and synthesizing temperature on electrical and crystal structure of (Bi2O3)(1-x-y)(Sm2O3)(x)(Yb2O3)(y) electrolytes fabricated for IT-SOFCs(ELSEVIER SCIENCE BV, 2016) Kayali, Refik; Ozen, Murivet Kasikci; Bezir, Nalan Cicek; Evcin, AtillaFor intermediate temperature solid oxide fuel cells (IT-SOFCs), (Bi2O3)(1-x-y)(Sm2O3)(x)(Yb2O3)(y) ternary systems (x=0.01 and y = 0.11), (x=0.05 andy= 0.07), (x=0.07 and y=0.05), and (x=0.11 and y=0.01) as electrolytes have been fabricated at different temperatures (700, 750, and 800 degrees C) by solid state ceramic technique (SST). The characterization of the samples has been performed by X-ray powder diffractometer (XRD), scanning electron microscopy (SEM), four point-probe method (FPPM), X-ray energy diffraction spectroscopy (EDX), and differential thermal analysis (DTA). XRD measurements have shown that only the samples (Bi2O3)(1-x-y)(Sm2O3)(x)(Yb2O3)(y) (x=0.01, y=0.11 synthesized at 700, 750, and 800 degrees C) and (x=0.05, y=0.07 synthesized at 800 degrees C) have stable fluorite type face centered cubic (FCC) delta-phase. SEM images have shown the morphology of the stable samples. The conductivity and the operation temperature region of the samples have been determined from Arrhenius curves obtained from the FPPM measurements data and they vary from 1.83 to 9.95 x 10(-1) S cm(-1). Moreover, activation energy of the samples have been calculated by means of Arrhenius curves of the samples and relationships between them and the conductivity of the samples have been investigated in detail. The results obtained from XRD and FPPM measurements were confirmed by the DTA measurements. (C) 2016 Elsevier B.V. All rights reserved.Öğe Indium phosphide nanofibers prepared by electrospinning method: Synthesis and characterization(WILEY-V C H VERLAG GMBH, 2014) Evcin, Atilla; Bezir, Nalan Cicek; Kayali, Refik; Ari, Mehmet; Kepekci, Deniz BelkisNine sets of (3 x 3) InP nanofiber samples have been successfully prepared at three different voltages (20, 25, 30 kV) and at three separate heights (5, 7, 10 cm) by electrospinning with a constant precursor flow rate of 0.3 mLh(-1). The crystalline structure, thermal, morphologies and nanostructure, electrical, and optical properties of the samples are characterized by X-ray powder diffractometer (XRD) and thermal gravity-differential scanning calorimeter (TG-DSC), scanning electron microscopy (SEM), by Four-Point Probe Technique (FPPT,) and ultraviolet/visible spectrometry (UV/VIS), respectively. From these measurements, we have found the formation of stoichiometric nanostructured InP with zinc-blende structure and having lattice parameter of a = 5.874 angstrom, weight loss of 64.59% and crystallization temperature of 500 degrees C, average fiber diameter of 65.82 nm, the activation energies, E-a, of the samples, and band gap energy, E-g, of the nanofibers developed at constant applied voltage 30 kV. The band gap energies determined at different distances 5, 7, and 10 cm are found to be as 1.29, 1.37, and 1.30 eV, respectively.Öğe Investigation of structural, electronic and optical properties of pure and Ag-doped TiO2 nanofibers fabricated by electrospinning(WILEY-V C H VERLAG GMBH, 2016) Bezir, Nolan Cicek; Evcin, Atilla; Kayali, Refik; Ozen, Murivet Kasikci; Oktay, AysePure and 1, 2, and 3 wt% Ag doped TiO2 nanofibers were prepared by electrospinning method at different applied voltages and heights at a constant flow rate of 2 mL/h. Characterization of the prepared samples was performed by x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microcopy (AFM),four point probe method (FPPM), the differential scanning calorimetry/the thermal gravimetric analysis (DSC/TGA), ultraviolet/visible spectrometry (UV/VIS), and energy dispersive X-ray spectrometer (EDX). It was found that the thermally untreated pure TiO2 nanofibers and thermally treated (at 500 degrees C) samples have the crystalline phase of anatase (A), and mixed anatase and rutile (A+R) phases, respectively. It was also observed that the content of the silver does not affect the crystal structure, but plays strengthening role in the rutile structure. SEM micrographs showed that all fabricated nanofiber samples have uniform morphologies, and AFM measurements indicated that the nanofibers were formed in three-dimensional coils. The band gap values of the nanofiber samples obtained from UV/VIS measurements revealed that band gap values of the nanofiber samples decrease while the diameter of the nanofiber increases.Öğe Numerical and experimental analysis of a salt gradient solar pond performance with or without reflective covered surface(ELSEVIER SCI LTD, 2008) Bezir, Nalan C.; Donmez, Orhan; Kayali, Refik; Oezek, NuriAn experimental salt gradient solar pond having a surface area of 3.5 x 3.5 m(2) and depth of 2 m has been built. Two covers, which are collapsible, have been used for reducing the thermal energy loses from the surface of the solar pond during the night and increasing the thermal efficiency of the pond solar energy harvesting during daytime. These covers having reflective properties can be rotated between 0 degrees and 180 degrees by an electric motor and they can be fixed at any angle automatically. A mathematical formulation which calculates the amount of the solar energy harvested by the covers has been developed and it is adapted into a mathematical model capable of giving the temporal temperature variation at any point inside or outside the pond at any time. From these calculations, hourly air and daily soil temperature values calculated from analytical functions are used. These analytic functions are derived by using the average hourly and daily temperature values for air and soil data obtained from the local meteorological station in Isparta region. The computational modeling has been carried out for the determination of the performance of insulated and uninsulated solar ponds having different sizes with or without covers and reflectors. Reflectors increase the performance of the solar ponds by about 25%. Finally, this model has been employed for the prediction of temperature variations of an experimental salt gradient solar pond. Numerical results are in good agreement with the experiments. (C) 2008 Elsevier Ltd. All rights reserved.Öğe Simulation of astrophysical jet using the special relativistic hydrodynamics code(ELSEVIER SCIENCE INC, 2006) Donmez, Orhan; Kayali, RefikThis paper describes a multi-dimensional hydrodynamic code which can be used for the studies of relativistic astrophysical flows. The code solves the special relativistic hydrodynamic equations as a hyperbolic system of conservation laws based on high resolution shock capturing (HRSC) scheme. Two standard tests, one of which is the relativistic blast wave tested in our previous paper [O. Donmez, Astrophys. Space Sci. 293 (2004) 323-354], and the other is the collision of two ultra-relativistic blast waves tested in here, are presented to demonstrate that the code captures correctly and gives solution in the discontinuities, accurately. The relativistic astrophysical jet is modeled for the ultra-relativistic flow case. The dynamics of jet flowing is then determined by the ambient parameters such as densities, and velocities of the jets and the momentum impulse applied to the computational surface. We obtain solutions for the jet structure, propagation of jet during the time evolution, and variation in the Mach number on the computational domain at a fixed time. (c) 2006 Elsevier Inc. All rights reserved.Öğe Temperature and Thickness Effects on Electrical Properties of InP Films Deposited by Spray Pyrolysis(IOP PUBLISHING LTD, 2009) Kayali, Refik; Ari, Mehmet; Oeztas, Mustafa; Bedir, Metin; Aksoy, FundaInP film samples are prepared by spray pyrolysis technique using aqueous solutions of InCl(3) and Na(2)HPO(4), which are atomized with compressed air as carrier gas onto glass substrates at 500 degrees C with different thicknesses of the films. The structural properties of the samples are determined by x-ray diffraction (XRD). It is found that the crystal structure of the InP films is polycrystalline hexagonal. The orientations of all the obtained films are along the c-axis perpendicular to the substrate. The electrical measurements of the samples are obtained by dc four-probe technique on rectangular-shape samples. The effects of temperature on the electrical properties of the InP films are studied in detail.Öğe The morphology and structural properties of InP thin films deposited by spray pyrolysis method(PERGAMON-ELSEVIER SCIENCE LTD, 2008) Aksoy, Funda; Kayali, Refik; Oeztas, Mustafa; Bedir, MetinInP film samples were prepared by spray pyrolysis technique using aqueous solutions of InCl3 and Na2HPO4, which were atomized with compressed air as carrier gas onto glass substrates at 500 degrees C with different thicknesses of the films. The structural properties of the samples have been determined by using X-ray diffraction (XRD). It was found that the crystal structure of the InP films is polycrystalline hexagonal. The orientations for all the obtained films are along the e-axis perpendicular to the substrate. It is observed that the crystallite sizes of the films increase with the thickness of the film up to 616 rim. The changes observed in the morphology and structural phases related to the film thickness have been discussed in detail. (C) 2007 Elsevier Ltd. All rights reserved.
