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Publication Metadata only Preparation and x-ray characterization of the mixed oxides (Gd1-xREx)2O3, (RE=Ho, Yb and Y) as powder and thin films buffer layers for YBCO coated conductors(INT UNION CRYSTALLOGRAPHY, 2007) Heiba, Z. K.; Arda, L.; Egyptian Knowledge Bank (EKB); Ain Shams University; Bahcesehir UniversityPublication Metadata only Field dependence of the critical current density of MgB2/Cu wire for coil development(IOP PUBLISHING LTD, 2007) Arda, L.; Sacli, O. A.; Tomsic, M.; Dur, O.; Hascicek, Y. S.; State University System of Florida; Florida State University; Bahcesehir University; Ministry of Transport, Maritime & Communications - Turkey; Turksat ASThe critical current density ( J(c)) of monofilament Cu/ MgB2 wire was measured between 4.2 and 30 K with a variable temperature insert ( VTI) in a 20 T superconducting magnet using the DC pulse four-wire method with a 1 mu V cm(-1) 1 criterion. The critical current density, Jc, was measured to be 0.83 x 10(4) A cm(-2) at 3 T at 21 K and 0.66 x 10(4) A cm(-2) at 8 T at 4.2 K for the MgB2 sample, which was annealed at 700 degrees C for 30 min with 5.8 degrees C min(-1) heating rate under 4% H-2-Ar gas flow. Scanning electron microscopy ( SEM), electron dispersive spectroscopy ( EDS) and x-ray diffraction ( XRD) analysis were used to characterize the microstructure of the samples.Publication Metadata only Sol-gel insulation coatings on Monel/Fe/MgB2 wires for coil development(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008) Arda, L.; Boyraz, C.; Sacli, O. A.; Tomsic, M.; Hascicek, Y. S.; Bahcesehir University; Marmara University; State University System of Florida; Florida State UniversityIn this study, preparation, structure, morphology and thermal properties of ceramic insulation coating on Monel/Fe/MgB2 wires, which were fabricated by Hyper Tech Research Inc., using Continuous Tube Forming and Filling (CTFF) process were studied for coil development. Ceramic insulation coatings were prepared by reel-to-reel sol-gel method using solutions of Y and Zr based organometallic compounds. The coating thickness was controlled by number of coating, withdrawal speed and solution chemistry. 29 meter of Monel/Fe/MgB2 wire was insulated by Y2O3-ZrO2 using sol-gel method. Monel/Fe/MgB2 coil was layer wounded and impregnated with stycast. Sister samples of coil were tested between 4.2 K and 30 K with a Variable Temperature Insert (VTI) in a 20 T superconducting magnet using the analog DC pulse four-wire method with 1 (mu V/cm) criterion. The sample had a J(c) of 0.16 x 10(5) (A/cm(2)) at 4 T at 21 K. The surface morphologies and microstructure of sister samples of coil were characterized by ESEM, EDS, DTA, TGA and XRD. Resistance was measured by using HP 4339A High Resistance Meter.Publication Metadata only Preparation and Thermal Stress Analysis of Al2O3 Insulation Coatings on SS-304 Tape(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2009) Ataoglu, S.; Arda, L.; Kadioglu, N.; Cakiroglu, O.; Bulut, O.; Gulluoglu, A. N.; Belenli, I.; Istanbul Technical University; Bahcesehir University; Istanbul University; Marmara University; Abant Izzet Baysal University; Hakkari UniversityAl2O3 insulation coatings are grown on long-length stainless steel (SS) tapes using reel-to-reel sol-gel method for applications of HTS/LTS coils and magnets. Various ceramic solutions are prepared from Al based precursors, solvent and chelating agent, the coating are fabricated on SS substrates. Al2O3 solution was successfully obtained using Al-sec-butoxide precursor, and isopropanol and acetylacetone as solvent and chelating agents, respectively. In order to improve adhesion of Al2O3 on the SS-304 tapes, triethanolamine was used in the solution. The residual stresses are investigated at different temperature ranges, between (630, 600, 580, and 550 degrees C) and room temperature for different thicknesses (12, 10 and 7 mu m). The maximum stress values are obtained as 0.756 GPa as tension on substrate (SS) for the 12 mu m coating and 1.0 GPa as compression for the 7 mu m Al2O3 coating at 630 degrees C. The surface morphology and microstructure of samples are characterized by a scanning electron microscope (SEM). SEM observation revealed that Al2O3 coatings have crack and mosaic structure.Publication Metadata only X-ray diffraction analysis of powder and thin film of (Gd1-xYx)2O3 prepared by sol-gel process(WILEY-V C H VERLAG GMBH, 2008) Heiba, Z. K.; Arda, L.; Egyptian Knowledge Bank (EKB); Ain Shams University; Bahcesehir UniversityThe mixed oxide (Gd1-xYx)(2)O-3 (0-0 <= x <= 1.0) were synthesized, as powder and thin film, by a sol-gel process. X-ray diffraction data were collected and crystal structure and microstructure analysis were performed using Rietveld refinement method. All samples were found to have the same crystal system and formed solid solutions over the whole range of x. The cationic distribution, Gd3+ and Y3+, over the two non-equivalent sites 8b and 24d of the space group la! is found to be random for all values of (x). The lattice parameter is found to vary linearly with the composition (x). Replacing Gd3+ and Y3+ by each other introduces a systemic decrease in the x-coordinate of cation position (24d) and slight changes in the oxygen coordinates. Crystallite size and microstrain analysis is performed along different crystallographic directions and anisotropic changes are found with the composition parameter (x). The average crystallite size ranges from 75 to 149 nm and the r.m.s strain from 0.027 to 0.068 x 10(-2). Textured Gd1.841Y0.159O3 (400) buffer layers, with a high degree of alignment in both out-plane and in-plan, are successfully grown on cube textured Ni (001) tape substrates by sol-gel dip coating process. The resulting buffer layers are crack-free, pinhole-free, dense and smooth. YbBa2Cu3O7-x (YbBCO) thin film could be (00l) epitaxially grown on the obtained buffer layer using sol-gel dipping technique. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Publication Metadata only Structural properties of Zn1-xMgxO nanomaterials prepared by sol-gel method(WILEY-V C H VERLAG GMBH, 2009) Heiba, Z. K.; Arda, L.; Egyptian Knowledge Bank (EKB); Ain Shams University; Bahcesehir UniversityThe mixed oxides Zn1-xMgxO (ZMO) were prepared as nano-polycrystalline powders and thin films by a simple sol-gel process and dip coating method. Thermogravimetric (TG) and differential thermal analysis (DTA) were used to study the thermal chemistry properties of dried gel. Structural and microstructural analysis was carried out applying x-ray diffraction (XRD) and Rietveld method. Analysis showed that for x < 0.25, Mg replaces Zn substitutionally yielding ZMO single phase, while for x >= 0.25 two phases are identified ZMO and MgO. Replacing Zn2+ by Mg2+ distorts the cation tetrahedrons and decreases the lattice constants ratio c/a of the wurtzite ZMO which deviate the lattice gradually from the hexagonal structure as Mg2+ increases. These distortions are attributed to the difference in electronic configuration of the two cations which suppress the paraelectric-ferroelectric phase transition in the ZMO wurtzite. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimPublication Metadata only Stress analysis of ceramic insulation coating on Cu/MgB2 wires for W&R MgB2 Coils(ELSEVIER SCIENCE SA, 2009) Arda, L.; Ataoglu, S.; Abdulaliyev, Z.; Sacli, O. A.; Bahcesehir University; Istanbul Technical University; Istanbul Technical University; Istanbul Arel UniversityCeramic insulation coatings were produced on Cu/MgB2 wires, which were fabricated by Hyper Tech Research Inc., using Continuous Tube Forming and Filling (CTFF) process, from the solution of Zr, and Y based organometalic compounds, solvent and chelating agent using reel-to-reel sol-gel technique for MgB2 Coils. Y2O3-ZrO2/Cu/MgB2 wires were annealed at 700 degrees C for 30 min with 5.8 degrees C/min heating rate under 4% H-2-Ar gas flow. Residual stresses were examined for Cu/MgB2 wire and YSZ coatings with varying thicknesses. It was observed that displacement values are independent from YSZ thicknesses and the maximum effective stress value is in the Cu region. The surface morphologies and microstructure of samples were characterized using SEM. SEM micrographs of the insulation coatings revealed cracks, pinholes and mosaic structure. (C) 2008 Elsevier B.V. All rights reserved.Publication Metadata only Residual stress analysis of multi-layered buffer layers on Ni substrate for YBCO coated conductor(ELSEVIER SCIENCE SA, 2007) Arda, L.; Ataoglu, S.; Sezer, S.; Abdulaliyev, Z.; Bahcesehir University; Istanbul Technical University; Yildiz Technical University; Istanbul Technical UniversityCeO2/YSZ/CeO2 buffer layer structure is one of the preferred buffer layers for fabrication of coated conductors. Textured CeO2/YSZ/CeO2 buffer layers are grown on biaxially textured Ni (100) substrate from the solution of Zr, Y, and Ce based organometalic compounds, solvent and chelating agent using reel-to-reel sol-gel technique. The film thickness is controlled by number of coating withdrawal speed and solution chemistry. Residual stresses arise during the manufacturing process of buffer layers depending on some factors. One of the most important is due to temperature variation. Effects of the temperature variation and coating thickness on residual stress in CeO2/YSZ/CeO2 buffer layers structure annealed at high temperature are analyzed theoretically. It is observed that the stress magnitudes reach high levels in the region of interlayer of different materials. The surface morphologies and microstructure of sample are characterized by ESEM and AFM. ESEM and ATM micrographs of the films revealed pinhole-free, crack-free, smooth and dense microstructures in the used manufacturing process. (c) 2007 Elsevier B.V. All rights reserved.Publication Metadata only Electrical characterizations of MgO-ZrO2 high temperature sol-gel insulations coatings on different types of epoxies(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008) Cakiroglu, O.; Arda, L.; Boyraz, C.; Sacli, O. A.; Istanbul University; Bahcesehir University; Marmara UniversityThe sol-gel MgO-ZrO2 electrical insulations were coated on Stainless-Steel-304 (SS) tapes by reel-to-reel process for investigation of electrical properties under various pressure at room temperature (298 K) and liquid nitrogen temperature (77 K) for HTS/LTS high field insert coil. Solutions consist of Mg and Zr based precursors, solvent and chelating agent. The electrical insulation was made on long-length SS substrate. Insulation thickness for 4, 8, and 9 dippings were determined 7, 12, and 13 mu m, respectively. Three different types of stycast, 2850 FT/24 LV Black and Blue, and White Buecher Epoxide Resin were studied. Stycast thicknesses were varied from 33-20 mu m, when the pressure was applied from 0 to 0.54 GPa. The thicknesses of high temperature insulation coatings and epoxsies were measured by using Environmental Scanning Electron Microscope (ESEM). Resistance, capacitance and High Voltage Breakdown (HVbd) Of the samples were measured by using standard machines Model 6517A Electrometer/High Resistance Meter, 161 analog digital capacitance meter and Model 200-02R High Voltage Power Supply, respectively. The results were presented graphically.Publication Metadata only Nonvacuum deposition of silver doped YBCO coated conductor on %100 lattice match buffered Ni tapes(AMER INST PHYSICS, 2007) Arda, L.; Cakiroglu, O.; Keskin, S.; Sacli, O. A.; Cetin, SA; Hikmet, I; Bahcesehir University; Marmara University; Istanbul University; Marmara UniversitySilver doped YBa2Cu3O7-delta (YBCO) coated conductors were fabricated on Gd1.624Ho0.O-376(3) (100 % lattice match with YBCO) textured buffer layers on Ni tape by reel-to-reel sol-gel dip coating system. Sample were prepared with different wt(1-5) % Ag doped ratio. The surface morphologies and microstructure of all sample were characterized by ESEM, EDS and XRD. Pole figure texture analyses have been done to characterize texture of buffer layer and YBCO superconducting film. The critical current I-c measurement was performed using four wire method with the 1 mu V/cm criterion. The critical current density, J(c) was measured to be 2.2 x 10(4) A/cm(2) at 77 K self field for 1 wt % Ag doped YBCO sample.
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