Browsing by Author "Cavdar S."

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A study on nucleation, crystallization kinetics, microstructure and mechanical properties of Ru-Bi partial substituted BSCCO glass ceramics
(2016-02-01) Ozturk O.; Gokcen T.; Cavdar S.; Koralay H.; Tasci A.T.
This study deals with the effects of Ru-Bi partial substitutions on the thermal, structural and mechanical properties of Bi1.8-x Ru x Pb0.2Sr2CaCu2O10+δ (x = 0.0, 0.025, 0.050, 0.075) system, produced by using glass ceramics method. The effects of Ru-Bi partial substitutions on glass transition, nucleation and crystallization temperature were analyzed via differential thermal analyzer (DTA). Besides, microstructure and micromechanical properties of Ru-Bi partially substituted BSCCO glass ceramics were also investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Vickers microhardness measurements. From the DTA results, nucleation kinetics were studied by using Ozawa, Augis-Bennett, Takhor and Kissinger equations. In addition to this, activation energies and Avrami parameters were also calculated. According to the results of the thermogravimetric analyses, the amount of oxidation was seen to be increased with increasing Ru concentration. Moreover, the lattice parameters, volume fractions and surface morphologies of our newly produced glass ceramics were investigated by XRD and SEM measurements, respectively. RISE behavior obtained from the microhardness measurements for all samples. Microhardness, elastic modulus, yield strength and fracture toughness values decreased with increasing Ru doping.
Comparison of Vickers microhardness of undoped and Ru doped BSCCO glass ceramic materials
(2018-03-01) Ozturk O.; Asikuzun E.; Tasci A.; Gokcen T.; Ada H.; Koralay H.; Cavdar S.
In this study, effect of substitution ratio on the mechanical and structural properties of Bi1−xRuxPb0.2Sr2CaCu2O10+δ system, that is prepared in the ratios of x = 0.0, 0.025, 0.050, 0.075, is investigated. Samples are prepared with glass ceramic method and sintered at 845 °C. XRD and SEM measurements are performed for structural analyses, and Vickers micro-hardness measurements are carried out at different applied load (0.245 ≤ F ≤ 2.940 N) in order to investigate the mechanical performance of the Ru doped Bi1−xRuxPb0.2Sr2CaCu2O10+δ system. Experimental results of Vickers micro-hardness analyses are performed using the Meyer’s law, the proportional samples resistance model, the elastic/plastic deformation model, the Hays–Kendall approach and the indentation induced cracking (IIC) model. All analyses results are exhibited reverse indentation size effect behavior. The measured hardness values increase with increasing the applied load. Finally, IIC model is determined as the most successful model describing the mechanical properties of our samples.
Effect of Zn content on microstructure and mechanical performance in Bi1.8Sr2Ca2Cu3.2-xZn xO10+δ glass ceramic
(2014-01-01) Koralay H.; Hicyilmaz O.; Cavdar S.; Asikuzun E.; Tasci A.; Ozturk O.
In this study, we have investigated the effects of Zn doping on structural and mechanical properties of Bi1.8Sr2Ca2Cu 3.2-xZnxO10+δ ceramic samples with x = 0.0, 0.1, 0.5, 1.0. The prepared samples were characterized by using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray powder diffractometer (XRD) and static microhardness indenter. Surface morphology, orientation of grains and elemental composition analysis of the samples were investigated by SEM and EDS measurements, respectively. Texturing and lattice parameters a, b and c were determined from the XRD measurements. In this work we focused on Vickers microhardness measurements in order to characterize the mechanical properties. Experimental results of Vickers microhardness measurements were analyzed by using Meyer's law, the elastic/plastic deformation model, proportional sample resistance model (PSR), modified PSR model, Hays-Kendall (HK) approach and indentation induced cracking (IIC) model. According to the obtained results, HK approach is the most suitable model for the CZn00 sample showing indentation size effect behavior and IIC Model is the most suitable model for the CZn01, CZn05 and CZn10 samples showing reverse indentation size effect behavior. © 2014 Springer Science+Business Media New York.
Evaluation of superconducting features and gap coefficients for electron–phonon couplings properties of MgB2 with multi-walled carbon nanotube addition
(2022-03-01) Kaya N.; Cavdar S.; Ozturk O.; Yildirim G.; Koralay H.
In this study, the samples are prepared by solid state reaction method at different weight ratios (0–4%). The characterization of materials produced is conducted with the aid of powder X-ray diffraction (XRD), temperature-dependent electrical resistivities (ρ-T) and magnetization (M–H) measurements. Moreover, the change in the scattering/breaking of cooper-pairs in the small homogeneous clusters in the superconducting paths with the addition of multi-walled carbon nanotube is also examined by the energy gap coefficients. All the experimental findings show that the weight ratio of wt 2% is observed to be the optimum addition level. The XRD results indicate that the MgB2 material prepared by the optimum level crystallizes better in hexagonal symmetry. The critical current density is found to increase from 1.0 × 104 to 2.3 × 104A cm−2 depending on the increment in the magnetization values. On the other hand, the addition mechanism is noted to degrade slightly the general electrical features, critical transition temperatures, lattice cell constants and crystallite size of MgB2 material. Regardless, although the carbon nanotube addition seems to be negative effect on some general properties, the fundamental characteristic properties (the crystallinity with smoother crystallographic transition, magnetization values, coupling of adjacent layers, degree of broadening and especially formation of effective nucleation centers for the flux pinning ability) improve seriously at the optimum dopant level. Thus, the MgB2 prepared with the optimum carbon nanotube concentration can exhibit higher performance against the magnetic field and current in larger magnetic field strengths applied.
Experimental and theoretical approaches for magnetic, superconducting and structural characterization of Bi1.75Pb0.25Sr2Ca2Cu3-xSnxO10+y glass ceramics
(2017-12-01) Koralay H.; Cavdar S.; Arslan A.; Ozturk O.; Tasci A.T.; Tugluoglu N.
In this work, the effect of the partial substitution of Sn for Cu on structural, electrical and magnetic properties in the superconducting ceramic glass Bi1.75Pb0.25Sr2Ca2Cu3-xSnxO10+y system (x = 0, 0.1, 0.5) has been examined. The structural characterization of samples produced by glass-ceramic technique were done by X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. The electrical and magnetic properties were determined by resistance-temperature (R-T) measurement and magnetization-magnetic field measurement (M-H) in the low temperature by using vibrating sample magnetometer (VSM), respectively. From the results of R-T measurement, the value of critical temperature (Tcoffset) has been decreased from 98 K to 73 K with increasing Sn- concentration. The critical current density has also been decreased with increasing magnetic field intensity. It has been observed from M-H plots that it was decreased with increasing the value of temperature. We have observed from M-H curves that the area size of the hysteresis curve decreases with increasing the value of temperature.
Experimental and theoretical approaches on thermal and structural properties of Zn doped BSCCO glass ceramics
(2016-03-01) Koralay H.; Hicyilmaz O.; Cavdar S.; Ozturk O.; Tasci A.
Thermal properties of Cu-Zn partially substituted Bi1.8Sr2Ca2Cu3.2-xZnxO10+δ (x = 0, 0.1 and 0.5) glass-ceramic systems have been investigated with the help of a differential thermal analyzer (DTA) by using Johnson-Mehl-Avrami-Kolmogorov (JMAK) approximation. Non-isothermal crystallization kinetics of the samples has been tested. The calculated values of activation energy of crystallization (E) and Avrami parameter (n) ranged between 306.1 and 338.3 kJ·mol-1 and 1.29 and 3.59, respectively. Crystallization kinetics was compared following the partial substitution, before and after Zn doping of the sample. In addition, by using a scanning electron microscope (SEM) and X-ray powder diffractometer (XRD), structural properties of Zn doped BSCCO glass-ceramic samples were determined. Surface morphology of the samples was studied by SEM measurements. Lattice parameters and volume of the samples were calculated from the XRD measurements.
Structural and mechanical characterization of Bi1.75Pb 0.25Sr2Ca2Cu3-xSnxO 10+y superconductor ceramics using Vickers microhardness test
(2013-11-01) Koralay H.; Arslan A.; Cavdar S.; Ozturk O.; Asikuzun E.; Gunen A.; Tasci A.T.
In this work we investigated the role of Sn doping on mechanical and structural properties of Bi1.75Pb0.25Sr2Ca 2Cu3-xSnxO10+y (x = 0.0, 0.1, 0.3 and 0.5) superconducting ceramic material. All samples were fabricated with glass ceramic method. The prepared samples were characterized by using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray powder diffractometer (XRD) and static microhardness indenter. Surface morphology, orientation of grains, and elemental composition analysis of the samples were made by SEM and EDS measurements, respectively. Texturing and lattice parameters a and c were determined by XRD measurements. Load dependent and load independent microhardness, elastic modulus, yield strength and fracture toughness were obtained by hardness measurements. In this work we focused on Vickers microhardness measurements in order to characterize the mechanical properties of our samples. Experimental results of Vickers microhardness measurements were analyzed by using Meyer's law, the elastic/plastic deformation model, proportional sample resistance model (PSR), modified PSR model and Hays-Kendall (HK) approach. From these analyses, HK approach was determined as the most successful model describing the mechanical properties of our samples. Finally in this study, the changes on the mechanical and microstructural properties of Sn doped Bi-2223 superconductors and their possible reasons were also discussed in detail. © 2013 Springer Science+Business Media New York.
Structural, electrical and mechanical properties of selenium doped thallium based high-temperature superconductors
(2016-01-01) Cavdar S.; Kol N.; Koralay H.; Ozturk O.; Asikuzun E.; Tasci A.
In this study, highly-refined chemical powders were synthesized by having them ready in appropriate stoichiometric proportions with conventional solid state reaction method so that they would produce the superconductor TlPb0.3Sr2Ca1-xSexCu2Oy (x = 0; 0.4; 0.6; 1.0). This study aims to understand effect of the selenium doping on the superconducting, structural and mechanical properties of the aforementioned superconducting material. The effect of the doping rates on the structural and electrical properties of the sample has been identified. Electrical characteristics of the TlPb0.3Sr2Ca1-xSexCu2Oy material were measured using standard four point probe method. Structural characteristics were examined with the powder X-ray diffractometer (XRD) and scanning electron microscope (SEM). Mechanical properties were analyzed with Vickers microhardness measurements on the sample surface. According to the results, it was observed that the reflection comes from the (00l) and parallel planes increased with Se doping. Particle size increases with increasing doping ratio. According to results of the mechanical measurements, all samples exhibit indentation size effect (ISE) behavior. Comparing the obtained results with theoretical studies, it was understood that Hays Kendall approach is the best method in determination of mechanical properties and analyzing microhardness of the materials.
The effect of pbse addition on the mechanical properties of Bi-2212 superconductors
(2012-10-01) Cavdar S.; Deniz E.; Koralay H.; Ozturk O.; Erdem M.; Gunen A.
The effects of PbSe addition and heat treatment on the structure and mechanical properties of Bi-2212 superconductors are analyzed. Glass ceramic method is used to produce PbSe added samples. The mechanical properties are derived using Vickers microhardness measurement results. Well known analysis methods like Meyer's law, PSR (Proportional Sample Resistance) Model, EDP (Elastic/ Plastic DeformationModel), Hays-Kendall approach and IIC (Indentation-Induced Cracking Model) are used to calculate load independent microhardness values of the samples. HK approach produces successful results for the samples A, E, F, G and H indicating ISE (Indentation Size Effect) behavior. The IIC model successfully explains RISE (Reverse Indentation Size Effect) behavior for the samples B, C and D. RISE behavior is observed only for the samples where the plastic deformation is dominant. ISE behavior is observed for the samples where both elastic and plastic deformation are produced. The results of XRD and SEM analysis show improvement with PbSe addition in the crystal structures and surface morphologies of superconducting samples. © Springer Science+Business Media, LLC 2012.