Tıbbi Hizmetler ve Teknikler Bölümü

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https://hdl.handle.net/20.500.12491/10788

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Investigation of hybrid wires combining superconductive MgB2 and ultra-conductive Graphene/Cu sheath
(Elsevier Science Sa, 2024) Karaboğa, Fırat; Farhangmehr, Mojtaba; Özmen, Ahmet; Yetiş, Hakan; Belenli, İbrahim; Ertuğrul, Mehmet
In our study, hybrid wires with ultra-conductive Graphene/Copper(GCu) sheath and superconducting MgB2 core were produced and experimentally examined. Cu tubes with outer/inner diameters of 15/12 mm were first coated with multi-layered graphene by chemical vapour deposition (CVD) method. Then, the ultra-conductive G/ Cu tubes were filled with Mg+ 2B powder and they were gradually drawn into wires with a diameter of 1.94 mm. According the analysis results, the graphene coating process was successfully completed and the hybrid wires were produced by achieving MgB2 superconducting phase formation after annealing at 650 circle C for 1 h. In this study, a graphene-coated copper tube with a CVD process was used for the first time to manufacture a superconducting wire. The ampacity value of industrial G/Cu sample has been improved in hybrid wires about 75% despite Cu exposed to mechanical deformations throughout the wire production process after graphene coating.
The h-index and the problem of measuring academic success: Stressing to overcome deficiencies and limitations
(Mehmet Akif Ersoy Univ, 2023) Fırat, Serhat; Alramazanoğlu, Buket Oğuz; Genç, Gülşen; Karaşin, Yusuf; Kurutkan, Mehmet Nurullah
The aim of this study is to determine the deficiencies of the h-index, to produce solutions in this direction and to reveal the limits of the h-index. In this study, document analysis, which is included in secondary data analysis, was used. Except for the H-index, indices used in the scientific world are generally examined in 3 groups. In this direction, a total of 33 indexes were examined by 3 scientists, each index type being compared. The publications and citations of scientists are based on the October 2021 period via Google Scholar. Although the h-index, developed by Hirsch, in which n citations to n publications of a scientist is presented as output, is the most used criterion in the scientific world, it has been determined that there are missing aspects. In the study, it was seen that the scientist with a low h-index may have a higher value in other index types. It has been concluded that the other indexes examined in the study are alternatives to the h-index and that a new type of index should be developed that exceeds all limitations..
Annealing-induced modifications on structural, surface chemical bonding, and electrical characteristics of p-NiO/n-TiO2 heterostructure
(Springer, 2023) Kaya, Şenol; Soykan, Uğur; Sunkar, Mustafa; Karaboğa, Seda; Doğan, Muhsin Uğur; Terzioğlu, Rıfkı; Yıldırım, Gürcan; Terzioğlu, Cabir
The influences of annealing temperatures on the electrical characteristics of a p- NiO/n-TiO2 heterojunction diode were thoroughly investigated, taking into account changes in microstructure, morphology, and surface chemistry of the p-NiO/n-TiO2 films, which were deposited on an insulating SiO2/ Si layer. During different annealing processes, considerable stress variations were observed in the p-NiO/n-TiO2 films due to the crystalline evolution of p-NiO and n-TiO2. Notably, the crystallization of the TiO2 layer, which serves as the intermediary between the back contact materials and NiO, led to the evident formation of grain structures. As the annealing temperature increased, the surface roughness also grew from 5.4 to 8.7 nm. At an annealing temperature of 500 degrees C, the formation of a parasitic NiTiOx phase was observed, particularly at the interface between NiO and TiO2. Conversely, the study also revealed that annealing temperature played a significant role in the rectifying behavior, barrier potential, and ideality factor of the diode. Among the various annealing processes, the most favorable results were achieved after annealing at 400 degrees C. At this temperature, the diode demonstrated the lowest ideality factor of 1.89, accompanied by superior rectifying behavior and a barrier potential of 0.70 eV. The findings clearly indicate that any alterations in the surface chemistry and microstructure of the film directly impact the diode's characteristics. Thus, optimizing the annealing temperature becomes crucial for enhancing the performance of the p-NiO/n-TiO2 heterojunction diode.
Evolution of basic features of Bi1.8Pb0.4Sr2Ca2.2Cu3Oy ceramic systems with NiO impurity
(Springer, 2023) Kara, Emre; Doğan, Muhsin Uğur; Kaya, Şenol; Terzioğlu, Rıfkı; Yıldırım, Gürcan; Terzioğlu, Cabir
In the current work, we have investigated the role of different nickel oxide (NiO)(x) impurity addition levels (0 & LE; x & LE; 1.2) on the fundamental crystallographic, morphological, electrical, magnetic, critical current density, and superconducting features of Bi1.8Pb0.4Sr2Ca2.2Cu3Oy (Bi-2223) by the temperature-dependent electrical resistivities (& rho;-T), X-ray diffraction data (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and magnetic hysteresis (M-H) measurements for the first time. The NiO-added Bi-2223 ceramics have been produced by the standard solid-state reaction method at 840 & DEG;C for 36 h in the air atmospheric conditions. EDX investigations have demonstrated that there appear no extra contamination and additional phases for any anionic or cation-including phases. Besides, the Ni impurity concentration has been observed to increase systematically depending on the impurity amount. Thus, the NiO impurities have been added to the ceramic matrix as requested. Similar findings have been confirmed by the XRD examinations. The experimental results have pointed out the multiple substitution reaction of Ni-sites with the Bi-sites, Ca-sites, and Cu-sites in the Bi-2223 system. Moreover, the experimental results have shown that all the fundamental features are strongly dependent upon the NiO addition level due to the variation of Cu-O-2 interlayer bonding forces, grain alignment distributions, mobile carrier concentrations in the in-plane Cu-O-2 layer x(2)-y(2) bands, and coupling probabilities between the adjacent layers in the crystal structure. Similarly, the induction of new impurity phase formations, grain boundaries, modulation of Bi-O double layers, spin fluctuations, inhomogeneities, structural defects, and non-recoverable structural problems have also triggered the decrease in the main characteristic quantities. On this basis, the microstructural morphology and related crystallographic features have been noted to degrade with the impurity. Furthermore, the presence of NiO impurity has resulted in a decrement in the flux-pinning centers due to the increase in the lower resistance regions against the flux drifts in the bulk crystal system. All in all, the addition of NiO impurity in the Bi-2223 ceramic matrix is not a good idea for the improvement in the fundamental features of the Bi-2223 superconducting structure.
Evolution of operable slip systems, lattice strain fields and morphological view of Bi-2223 ceramic system with optimum NiO addition
(Elsevier, 2023) Mercan, Ali; Kara, Emre; Doğan, Muhsin Uğur; Kaya, Şenol; Terzioğlu, Rıfkı; Erdem, Ümit; Yıldırım, Gürcan; Terzioğlu, Cabir
The current work extensively reveals the influence of different nickel oxide (NiO) impurity addition levels on the morphological, microstructural, key mechanical performance, and mechanical characteristic properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Oy (Bi-2223) ceramics using scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and Vickers micro-indentation (Hv) hardness measurements. It was observed that the addition of NiO impurity in the Bi-2223 crystal structure affected seriously the fundamental characteristic features. In the case of the optimum NiO concentration level of x = 0.1, the Bi-2223 materials exhibited the best crystallinity quality and coupling strengths between the adjacent layers, the most uniform surface view, and the densest, and the smoothest crystal structure. Similarly, the compound was noted to possess the hardest, highest mechanical strength, durable tetragonal phase, resistance toward failure by fatigue, and elastic recovery properties. Besides, it was observed that the characteristic Bi-2223 superconducting phase fraction and stabilization of the tetragonal crystal system reached the maximum level for the optimum concentration. Moreover, optimum NiO particles brought about a considerable increase in the number of operable slip systems, surface residual compressive force regions, and lattice strain fields. Correspondingly, the mobility of defects was blocked significantly depending on the preference of defects through transcrystalline regions. Additionally, optimum addition strengthened the typical indentation size effect due to the improvement of the recovery mechanism. In this regard, the NiO-added sample exhibited the least response to the applied loads. Thus, the Bi-2223 sample with the optimum NiO concentration was found to present the highest hardness parameter of 0.496 GPa, greatest elastic deformation value of 16.493 GPa, largest stiffness value of 1.044 MN/m, and smallest contact depth of 5.849 mu m. On the other hand, after the optimum concentration level of x = 0.1, there appeared serious increase in problems including internal defects, impurity residues, microscopic structural problems, and connection problems between the grains. All experimental findings were theoretically supported by semi-empirical mechanical methods. To sum up, the addition of NiO particles was noticed to increase the potential application areas of Bi-2223 ceramic
Improvement in deformation degree of Zr surface-layered Bi-2223 ceramics by diffusion annealing temperature
(Elsevier Sci LTD, 2023) Mercan, Ali; Terzioğlu, Rıfkı; Doğan, Muhsin Uğur; Kaya, Şenol; Erdem, Ümit; Yıldırım, Gürcan; Terzioğlu, Cabir; Varilci, Ahmet
This study investigated the effects of different annealing temperatures (650 degrees C <= T <= 840 degrees C) on the surface morphological and mechanical performance properties of Zr surface-layered Bi-2223 materials with scanning electron microscopy (SEM) images, Vickers microhardness (Hv) measurements, and semi-empirical mechanical approaches. It was observed that the ceramic compound exposed to 650 degrees C annealing temperature exhibited the superior performance features due to the enhancement in the deformation degree. This is because the Zr ions behaved as the nucleation centers to prevent the propagations of cracks and dislocations throughout the main matrix depending on the decrease in the degree of granularity and distributions of crystal structure problems over a wider area. Similarly, the SEM pictures indicated that the diffusion mechanism increased the random distributions of the thinner plate-like granular structures (serving as nucleation centers), leading the decrease in the coupling problems between the grains. Among the materials, the highest surface densification was observed for the compound exposed to 650 degrees C. Namely, surface morphological analysis showed a strong correlation be-tween microstructure and mechanical performances. Further, the zirconium ions were found to decrease in the non-recoverable stress concentration sites, crack-initiating defects, and dislocations in the ceramic system. Accordingly, the sensitivity to the applied test load was noted to decrease dramatically. Shortly, crack growth size and velocity were observed to be more easily under control. Correspondingly, the Zr ions delayed consid-erably the beginning points of saturation limit (load-independent) regions for the bulk Bi-2223 superconducting materials. Additionally, the Zr ions led to the change in the mechanical characteristic behavior from typical indentation size effect to reverse indentation size effect. Lastly, the microindentation hardness measurements were semi-empirically analyzed by the different models. According to the comparison, Hays-Kendall mechanical model was noted to provide the closest parameters to the load-independent microhardness results.
Current-voltage characteristics of nano whisker ZnO/Si heterojunction under UV exposition
(Elsevier Science Sa, 2022) Koç, Nevin Soylu; Altıntaş, Sevgi Polat; Gökçen, Muharrem; Doğruer, Musa; Altuğ, Cevher; Varilci, Ahmet
In/ZnO/p-Si heterojunction diode was produced to investigate the photo-responsivity and electrical features under ultraviolet (UV) light. A hydrothermal synthesis technique was used to coat the ZnO layer on the p-Si single crystal as nanowhisker/rods. The formation of surface and nanowhisker properties of the ZnO layer were investigated by scanning electron microscope (SEM). The I-V (current-voltage) analysis of the In/ZnO/p-Si diode was realized in dark and under UV (290-400 nm) illumination. Further, the main electrical parameters of the diode; such as reverse bias saturation current (I-V), ideality factor (n), zero bias barrier height (Phi(Bo)), resistance (R) and interface state density (N-ss) were obtained from the experimental I-V measurements by thermionic emission (TE) and Card and Rhoderick's function. Also, the power law of the photocurrents (I-PC), photoresponsivity (PR) and response time were extracted. Photo-responsivity and response time values of In/ZnO/p-Si heterojunction diode were obtained as 2.0 A/W and (rise/decay) 160/200 ms, respectively.
Increased systemic inflammatory response with mast cell activation in elder children with cerebral palsy
(Marmara University, Institute of Health Sciences, 2022) Demir, Cemalettin; Kılınç, Yasemin Baranoğlu; Kılınç, Erkan
Objective: Increased systemic inflammatory response during intrauterine period or period before the age of 3 is associated with cerebral palsy (CP) pathogenesis; however, effects of inflammatory processes involving mast cell activation in elder children with CP remain unclear. We aimed to investigate the role of mast cells and proinflammatory cytokines in children with CP at 3-18 years of age. Methods: In this cross-sectional study, venous blood samples were obtained from 30 volunteers with CP and 26 healthy volunteers at 3-18 years of age. Plasma levels of proinflammatory cytokines (IL-1 beta, IL-6 and IL-9) and mast cell biomarkers (histamine and tryptase beta-2) were determined using ELISA. Results: IL-1 beta, IL-6 and histamine levels were higher in individuals with CP compared to healthy controls. Likewise, IL-1 beta, IL-6, IL-9 and histamine levels were higher in the female patients with CP compared to the male patients, and in the female patients in adolescence compared to the female patients in pre-adolescence. Conclusion: Our findings indicate that the increased inflammatory response contributes to the pathogenesis of the disease in children with CP who are older than 2 years of age. Moreover the increased inflammatory response is more effective in female patients than in male patients, suggesting that there may be a gender difference in CP. Additionally mast cell activation contributes to the exacerbation of systemic inflammatory response in children with CP at 3-18 years of age.
Refinement of some basic features of Zr surface-layered Bi-2223 superconductor with diffusion annealing temperature
(Springer, 2022) Orhan, Emre; Kara, Emre; Kaya, Şenol; Doğan, Muhsin Uğur; Terzioğlu, Rıfkı; Yıldırım, Gürcan; Terzioğlu, Cabir
This study aims to investigate the influences of diffusion annealing temperatures on structural, morphological, electrical, and superconducting features of Zr surface-layered Bi-2223 ceramics. The present study also covers an in-depth understanding of correlations between disorders and transition temperatures. The Zr diffusion is carried out via an annealing process between 650 and 840 degrees C. The observed results depict that the Zr ions can easily diffuse into the deeper level of Bi-ceramics and possible Zr/Bi substitution has occurred due to the driving force of high thermal energy. Besides, it is found that the Zr diffusion improves the general crystallinity quantities of Bi-2223 ceramic up to 800 degrees C annealing temperature. In addition, better intergranular couplings with a smoother plate-like structure are extensively observed in surface morphology for the samples annealed at 800 degrees C. Significant refinements of both basic electrical resistivity, hole carrier densities, and critical temperatures with narrow transitions are also obtained for the Zr surface-layered Bi-2223 ceramics after the 800 degrees C annealing process. The obtained improvements in critical fundamental features can be attributed to the optimum pairing mechanism, best crystal structure quality, ideal Cu-O-2 interlayer coupling strengths, and enhanced interaction between adjacent superconductive layers. Besides, the first-order derivative of electrical resistivity versus temperature graphs indicates that the best annealing temperature enables to triggers to stabilize the superconductivity in the homogeneous regions. It can be concluded that the Zr impurity diffusion at 800 degrees C is promising for the improvement in the basic features of Bi-2223 superconducting systems for future applications in superconductor technology.
Effect of Nd/Sr partial replacement on characteristic Bi-2223 phase and related fundamental superconducting parameters
(Springer, 2022) Doğruer, Musa; Yıldırım, Gürcan; Terzioğlu, Cabir
In the present work, the effect of Nd/Sr partial replacement on the crystallographic, morphological, electrical, and superconducting properties of Bi1.8Pb0.35Sr1.9-yNdyCa2.2Cu3Ox materials is studied with the aid of powder X-ray diffraction (XRD), dc electrical resistivity versus temperature (rho-T), scanning electron microscope (SEM), and electron dispersive X-ray (EDX) measurements. The crystal structure of new produced materials is defined in the tetragonal crystal system with the P-4/mmm space group. According to the experimental results observed, the quantity of characteristic Bi-2223 superconducting phase is found to reduce regularly with the enhancement of Nd nanoparticles in the crystal system, confirming that the replacement of Nd impurity at the Sr site causes an increase in the characteristic Bi-2212 superconducting phase. Similarly, the reductions of average crystallite size and c-lattice cell parameter as well as the systematic increment in the a-axis length verify that the partial Nd/Sr substitution deteriorates the Bi-2223 superconducting phase. Moreover, the experimental results display that the offset superconducting transition temperature (T-c(offset)) is observed to decrease dramatically with increasing the concentration level of Nd impurity. In this context, the maximum T-c(offset) parameter is noticed to be about 104.3 K for the pure Bi-2223 superconducting ceramic sample. This may be related to the degradation in the strength quality of transcrystalline regions, intergrain boundary couplings, and especially crystallinity quality. Furthermore, the SEM images demonstrate that the increment of Nd foreign impurities in the bulk Bi-2223 superconducting materials damages the flaky layers of platelet-like shape for the superconducting grains.
Evolution of electrical, superconducting, crystallinity and structural features with aliovalent Nd/Sr replacement in Bi-2223 ceramics
(Elsevier Science Ltd, 2022) Doğruer, Musa; Yıldırım, Gürcan; Terzioğlu, Cabir
This paper blazes the trail for the understanding of fundamental characteristic features for Bi-2223 ceramic with aliovalent Nd/Sr replacement in Bi1.8Pb0.35Sr1.9-yNdyCa2.2Cu3Ox superconducting matrix (0.00 < y < 0.10). Full characterization of superconductors is performed by conventional experimental methods, viz. X-ray diffraction (XRD), dc electrical resistivity based on temperature (rho-T), electron dispersive X-ray (EDX) and scanning electron microscopy (SEM) examinations. Measurement results display that the trivalent Nd+3 ions may partially be substituted by Sr+2 impurities in the Bi-2223 crystal structure. EDX results illustrate that the local elemental composition distributions of Nd atoms increase systematically depending on substitution level. However, it is noted that the replacement mechanism damages seriously fundamental electrical, superconducting, crystallinity and structural features. Dc electrical findings present that the superconducting and electrical properties reduce remarkably with the increment of aliovalent Nd/Sr substitution due to deviation in the mobile holes, in homogeneities of oxidation states in the copper-oxide layers, and formation of new internal and microscopic problems in the crystal system, confirmed by SEM examination. Besides, the characteristic transition temperatures diminish harshly from 116.59 K to 108.74 K for onset and 108.40 K until 78.81 K for offset transition temperature. The dramatic decrements stem from the degradation in bipolaron formations in the superconducting clusters, phonon modes and especially the gap coefficient. Similarly, the presence of Nd impurity damages the amplitude of pairing wave function. In fact, at maximum replacement level the ceramic compound exhibits a slight trace of pseudo-critical transition. The XRD results indicate that both the appearance or disappearance of characteristic diffraction peaks and the reduction of average crystallite size and c lattice cell constant confirm the reduction of high-T-c superconducting phase due to the suppression in the structural quality. The SEM pictures indicate that the appearances of surface morphology and crystallinity quality remarkably deteriorate depending on Nd/Sr replacement level as a consequence of non-uniform grain alignment distributions, structural problems, microvoids, internal defects, porosity, misoriented grain coalescences and micro crystals in the superconducting system. Additionally, the negative effect of Nd/Sr substitution is extensively discussed on the activation energy for the crystallization, thermodynamic stability, reaction kinetics, surface nucleation and growth mechanisms for the first time.
Investigation of frequency-dependent dielectric properties of ZnO nanorods grown on Si wafer: In/ZnO/p-Si heterostructure
(Springer, 2022) Al-Khafaji, Ayssar; Koç, Nevin Soylu; Altıntaş, Sevgi Polat; Doğruer, Musa; Altuğ, Cevher; Gökçen, Muharrem; Varilci, Ahmet
We report the result of an in-depth study of growth, structural properties and frequency-dependent dielectric function of ZnO nanorods (NRs) grown on p-Si as well as the In/ZnO/p-Si heterostructures. The NRs were produced by hydrothermal method on the Si substrate in a Teflon-lined stainless-steel cover at 90 degrees C. Scanning electron microscopy analysis indicates nanorod morphology while LeBail refinement of XRD data showed that the ZnO NRs crystallize in hexagonal wurtzile structure with (002) orientation (space group P6(3)mc). The dielectric properties of the In/ZnO/p-Si heterostructure were calculated with the help of experimental admittance measurements performed in the +/- 5 V voltage range and 1 kHz/1 MHz frequency range under ambient conditions. The real part of the complex relative permittivity (epsilon '), the imaginary part of complex relative permittivity (epsilon '') and loss tangent (tan delta) were obtained. Also, real (M ') and imaginary (M '') parts of the complex electric modulus (M*) were extracted. Frequency dependence in the epsilon ', epsilon '' and tan delta was attributed to the frequency dependence of the space charge polarization. The real part of electrical modulus was found to be nearly independent of frequency and voltage for positive voltages.
The effect of health news perception on the image of healthcare professionals
(Marmara Univ, Fac Communication, 2023) Öcel, Yusuf; Eş, Abdülhamit; Alramazanoğlu, Buket Oğuz
The primary aim of this study is to examine the effect of health news perception on the image of health workers. To achieve this objective, 400 people from the population of Sakarya province were surveyed using a questionnaire. Frequency, factor and regression analyzes were applied to the obtained data. After conducting frequency analysis, it was determined that the internet, physician, TV and social media were the primary sources of health information available. According to the results of the factor analysis, the prominent issues regarding the perception of health news are health news perception dimensions, orientation to consumption, commercial concern and advertisement, abuse of health behavior, belief in health news, and behavior change. According to the factor analysis of health workers' image, the identified dimensions are the positive perception of health worker conduct, the negative perception of health worker conduct, the health worker's communication with the patient, the health worker's thought of financial gain, and the health worker's perceived status. Through the regression analysis, it was concluded that the dimensions of health news perception had an effect on the image of health workers.
Influences of gamma irradiation on structural, morphological and luminescence characteristics of Nb doped TiO2 nanophosphors
(Elsevier, 2023) Büyükuslu, Halim; Kutlu, Nermin; Kaya, Şenol
The irradiation induced effects on structural, morphological and luminescence characteristics of Nb:TiO2 phosphors were systematically investigated. Possible defect centers present in the Nb:TiO2 phosphors were also characterized. Anatase phase of TiO2 with minor parasitic Nb-containing phases was specified in crystallographic structure of phosphors. Crystalline size and internal stress enhance with enhancing the exposed dose. The observed rise in the crystalline size was also confirmed in morphological evolution. Moreover, the Nb:TiO2 phosphor exhibits five different photoluminescence peaks. Intensity variations and blue-green-red shifts on the PL peaks were observed after irradiation exposures. Similarly, various trap sites/centers with depth energies between 1.09 eV and 1.99 eV were found in the thermoluminescence analysis. The irradiation exposures both enhance the oxygen vacancies and cation interstitial defects in the structure. The results have depicted that gamma exposure significantly affects the crystallographic and luminescence features of the Nb:TiO2 nanophosphors.
Role of hemp fiber addition on thermal stability, heat insulation, air permeability and cellular structural features of rigid polyurethane foam
(Sage Publications Ltd, 2023) Soykan, Uğur; Kaya, Şenol
In this current study, rigid polyurethane foams (RPUFs) composites were prepared using different percentage (3, 6, 9 and 12%) of the hemp fibers via one-shut one-step polymerization method. The influences of the hemp fiber addition on the RPUFs were investigated meticulously by means of Fourier-transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), thermal conductivity measurement and scanning electron microscopy (SEM) techniques by evaluating the alternations in the chemical structures of the component, thermal stability, apparent density, insulation performance and cellular topology of the produced samples. The structural analysis revealed that there existed the strong secondary chemical bonds between the functional groups belonging to the components and, depending on that, the improvement in the thermal stability of the foam samples was recorded accompanied by the formation of the better interfacial adhesion. Furthermore, thermal conductivity values of the hemp fiber-loaded RPUFs were observed to increase regularly with the increasing of the content level of the hemp fibers. This was explained by enhancement in the bulk phase conduction level depending of the apparent density rising, reduction in CO2 concentration inside cells as well as the formation of the distorted cellular structures. The obtained air permeability results displayed that the hemp fibers incorporated successfully with RPUF structure, which provides the occurrence of the novel micro barriers and pathways limiting the passage of the air throughout the matrix. The taken scanning electron microscopy images also indicated that the cellular morphology and dimensional stability of the produced foams affected negatively by the hemp fiber addition. At high contents, the wrinkled, non-uniform and irregular cellular structures were observed with ruptured and collapsed walls and struts.
Optimized superconducting MgB2 joint made by IMD technique
(IOP Publishing Ltd, 2023) Avcı, Doğan; Yetiş, Hakan; Gajda, Daniel; Babij, Michal; Tran, Lan Maria; Karaboğa, Fırat; Aksoy, Canan; Zaleski, Andrzej; Belenli, İbrahim
A novel type of superconducting joining technique has been introduced to join unreacted internal Mg diffusion (IMD) single-core MgB2 wires. Our method is based on fabricating a small diameter joint mould obtained by deforming an Nb/Cu composite tube with a longitudinal semi-cylindrical Mg and B core into a thick round wire. The small diameter of the joint provided advantages such as rapid cooling, low resistance, and the unique core design inside the joint ensured a uniform MgB2 phase formation. Scanning electron microscope analysis revealed that the IMD MgB2 wires had excellent contact with the superconducting MgB2 bulk material inside the joint. The joint resistance, calculated from the decay of the trapped magnetic field over time, is a quite low value of 6.44 × 10−16 Ω at 20 K. The transport critical current (Ic) of the joint is 62 A at 20 K under a self-magnetic field, and the n-value of the joint is 66 at 20 K under 1.5 T. The results showed that the Ic of our joint can be determined precisely, regardless of whether the magnetic field is applied from low to high or from high to low value during I–V measurements.
Effects of PCBM loading on high sensitive P3HT based vertical bulk resistive X-ray detector
(Elseiver, 2022) Kalkan, Yalçın; Öztürk, Sadullah; Kösemen, Arif
Recently, semiconductive polymeric materials have attracted attention as an active layer for detecting ionizing radiation because of their excellent properties such as flexibility, easy production, solution processability and low-cost production. This paper presents X-ray detection properties of Poly(3-hexylthiophene) (P3HT):Phenyl C61 butyric acid methyl ester (PCBM) blend structure with different PCBM loading ratios. P3HT:PCBM mixing ratio was changed from 1:0 to 1:2. Top contact of the pure and blend structured device were produced by using a solution based graphite ink. Devices were constructed with vertical bulk resistive architecture within an ohmic electrode structure as ITO/PEDOT:PSS/P3HT:PCBM/Graphite configuration. Graphite electrode was coated on the active layer with the spray coating method. All devices exhibited ohmic current-voltage (I-V) characteristics. The blend structured devices exhibited stable saw-tooth type behaviour in photocurrent responses against the on and off states of X-rays. Saw-tooth type responses could be evaluated as major evidence for a potential usage of organic electronic device technology direct radiation detectors. Although the best sensitivity value to X-ray was obtained with the blend structure with equal ratio, it was observed that the rise and decay times were shortened with the increase in the amount of PCBM in the blend structure from.
Influence of amorphous boron grain size, high ısostatic pressure, annealing temperature, and filling density of unreacted material on structure, critical parameters, n-value, and engineering critical current density in MgB2 wires
(MDPI, 2021) Gajda, Daniel; Zaleski, Andrzej Janusz; Morawski, Andrzej; Malecka, Malgorzata; Akdoğan, Mustafa; Karaboğa, Fırat; Avcı, Doğan; Yetiş, Hakan; Belenli, İbrahim
Our results show that a lower density of unreacted Mg + B material during an Mg solid-state synthesis reaction leads to a significant reduction in the quantity of the superconducting phase and lowers the homogeneity of the superconducting material. It also significantly reduces the irreversible magnetic field (B-irr), critical temperature (T-c), upper magnetic field (B-c2), engineered critical current density (J(ec)), and n-value, despite high isostatic pressure (HIP) treatment and the use of nanoboron in the sample. Our measurements show that samples with large boron grains with an 8% higher density of unreacted Mg + B material allow better critical parameters to be achieved. Studies have shown that the density of unreacted material has little effect on B-irr, T-c, B-c2, J(ec), and the n-value for an Mg liquid-state synthesis reaction. The results show that the critical parameters during an Mg liquid-state synthesis reaction depend mainly on grain size. Nanoboron grains allow for the highest B-irr, T-c, B-c2, J(ec), and n-values. Scanning electron microscopy (SEM) images taken from the longitudinal sections of the wires show that the samples annealed under low isostatic pressure have a highly heterogeneous structure. High isostatic pressure heat treatment greatly improves the homogeneity of MgB2.
The significant influence of packing density of unreacted Mg+2B mixture and heat treatment conditions on some of critical parameters for MgB2/Fe wires
(Elseiver Science SA, 2021) Gajda, Daniel; Zaleski, Andrzej Janusz; Morawski, Andrzej; Czujko‬, ‪Tomasz; Avcı, Doğan; Karaboğa, Fırat; Akdoğan, Mustafa; Yetiş, Hakan; Belenli, İbrahim
Our research show that the higher packing density of the unreacted material (Mg +2B) by 8%, especially for Mg in the solid state, allows to eliminate the large number of large voids (20 mu m), improves the homogeneity and density of the MgB2 superconducting material, allows to obtain a greater number and longer lengths of connections between MgB2 grains, eliminates the formation of the intermetallic phase (iron borides), allows to obtain MgB2 grains of a uniform size and shape, increase irreversible magnetic field (Birr), critical temperature (T-c) and upper magnetic field (B-c2). Research show that spherical grains significantly reduce the number of inter-grain connections in the material with low and high density of unreacted material and allows to obtain the more superconducting phase. Research shows that MgB2 grains with a plate-like and rectangular shape allow to obtain more connections between the grains. Studies show that thermal treatment under high iso-static pressure does not allow to obtain the large amount of superconducting phase for the unreacted material of low density. Moreover, studies show that the high packing density of unreacted material and thermal treatment under high isostatic pressures (0.8 GPa and 1.1 GPa) allow to obtain a large amount of superconducting phase even for Mg in the solid state. Additionally, studies points that heat treatment under medium isostatic pressure (0.3 GPa) significantly reduce B-irr and B-c2. Our results are important for long superconducting wires made by using the powder-in-tube (PIT) technique. Because they indicate that the higher packing density of the unreacted material (Mg +2B) will allow to obtain a the superconducting material with greater homogeneity and density, and improve the critical parameters e.g. coils. (C) 2021 Elsevier B.V. All rights reserved.
Effects of mg-coating and boron type on electromechanical properties of IMD MgB2/Fe wires
(Springer, 2021) Avcı, Doğan; Yetiş, Hakan; Karaboğa, Fırat; Akdoğan, Mustafa; Belenli, İbrahim
In this study, mechanical and electrical characterization measurements were performed on non-bent and gradually bent IMD MgB2/Fe superconducting round wires having 0.81 mm outer diameter. Four straight IMD wires were successively bent to 150 mm, 125 mm, and 100 mm bending diameters and characterized after each bending step. IMD wires were produced using two types of boron powders (PVZ Nano Boron, purity > 98.5%, particle sizes < 250 nm, and PVZ boron, purity of 95-97%, particle sizes < 1 mu m) by filling them into Mg-coated and uncoated iron tubes. The coated Mg was considered as an extra source of Mg that diffuses into the Mg + 2B core without causing any porosity during the reaction. We have investigated the effect of Mg coating on the transport and electromechanical properties of the wires and found that the Mg coating process improves the J(ce) before and after bending. Also, our results have revealed that crack formation in core regions of mono filament bent IMD wires depends on the type of boron, since the use of nano-sized boron significantly increases the hardness of the MgB2 core.

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