Browsing by Author "Kaya S."

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Ac Susceptibility Measurements and Mechanical Performance of Bulk MgB2
(2015-07-24) Ozturk O.; Asikuzun E.; Kaya S.; Erdem M.; Safran S.; Kilic A.; Terzioglu C.
The effects of Ar ambient pressure (vacuum and 0, 10, and 20 B) and annealing times (0.5 and 1 h) on microstructural, superconducting, and mechanical properties of bulk superconducting MgB2 are investigated. The samples are produced using the solid-state reaction method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements are performed for determination of the crystal structure and surface morphology of MgB2 samples, respectively. The superconducting properties are studied by AC magnetic susceptibility measurements. Microhardness analyses are made using the Vickers microhardness test for determination of mechanical properties of all samples. Increasing the Ar pressure decreases the lattice parameters and hence the average grain size. Increasing the annealing time results in larger lattice parameters and larger grain formation. The susceptibility measurements revealed a two-step transition which is reminiscent of granular superconductors. The intra-grain transition temperature is determined to be 38.4 K for all samples. The inter-grain transition temperature of 37.2 K is obtained for samples produced under Ar ambient pressure. The samples produced under Ar ambient pressure have better superconducting properties than the ones produced in vacuum. Increasing the annealing time under vacuum further decreases the superconducting properties probably due to Mg loss.
Changes in mechanical and structural properties of Bi-2212 added MgB2 superconductors
(2016-06-01) Koparan E.; Savaskan B.; Ozturk O.; Kaya S.; Aksoy C.; Wang J.; Speller S.; Grovenor C.; Gencer A.; Yanmaz E.
In the present study, we investigate the effects of Bi2Sr2Ca1Cu2O8+κ (Bi-2212) addition on structural and mechanical properties of bulk MgB2 obtained by hot-press method by means of X-ray diffraction, the Scanning Electron Microscopy and Vickers microhardness measurements. The amount of Bi-2212 was varied between 0 and 10 wt% (0, 2, 4, 6, 8 and 10 wt%) of the total MgB2. All samples were prepared by using elemental magnesium (Mg) powder, amorphous nano boron (B) powder and Bi-2212 powder which are produced by hot-press method. As a result of the hot-press process, the compact pellet samples were manufactured. The microhardness results were analyzed by Meyer’s law, Proportional Sample Resistance Model, Elastic–Plastic Deformation Model, Hays Kendall Approach, and Indentation Induced Cracking (IIC) Model. IIC model was identified as the most appropriate model for samples exhibiting the reverse indentation size effect behavior.
Correlation between crystal defects and room temperature ferromagnetism of hydrothermally grown Eu substituted ZnO nanorods
(2022-11-15) Kaya S.; Ozturk O.; Arda L.
The hydrothermal method has been used to grow zinc oxide nanorods on a glass substrate with different Europium (Eu) concentrations. The Eu doping effect on the structural, optical, and magnetic properties of the samples was systematically investigated. The undoped sample exhibited diamagnetic behaviour, while soft room temperature ferromagnetism was observed in all the Eu substituted samples. With regard to the hysteresis loops, the highest coercivity, saturated magnetic moment, and retentive magnetic moment values were observed to be 41.64 Oe, 18.86 × 10−6 emu, and 2.17 × 10−6 emu, respectively, for ZnO:Eu 7%. According to the relationships between the magnetic properties, Eu doping levels, and defects concentrations, it can be concluded that the room temperature ferromagnetism observed in the samples is caused by crystal point defects including oxygen vacancies and zinc interstitials, rather than carrier-mediated exchange interactions, which is also consistent with the bound magnetic polarons theory.
Corrosion behaviour of new oxo-pyrimidine derivatives on mild steel in acidic media: Experimental, surface characterization, theoretical, and Monte Carlo studies
(2022-02-01) Ferigita K.S.M.; AlFalah M.G.K.; Saracoglu M.; Kokbudak Z.; Kaya S.; Alaghani M.O.A.; Kandemirli F.
In this work, the effects of new compounds, namely, 1-amino-5-(4-methylbenzoyl)-4-(4-methylphenyl) pyrimidin-2 (1H)-thione (AMMP), and 1-(5-(4-Methoxybenzoyl)-4-(4-methoxyphenyl) 2-oxopyrimidin-1 (2H)-yl)-3-phenylthiourea (MMOPH) has been successfully investigated as a corrosion inhibitor for mild steel in a 1 M HCl solution. This investigation has been done by electrochemical techniques (potentiodynamic polarization, and electrochemical impedance spectroscopy), surface characterization (scanning electron microscopy with energy dispersive x-ray spectroscopy, and atomic force microscopy), and theoretical calculations (density function theory and Monte Carlo simulation). The electrochemical results showed that both compounds act as mixed-type inhibitors. However, MMOPH is more efficient than AMMP (95.9% compared with 84.1% at 5 × 10−4 M and an immersion time of 1 h). Additionally, the effect of immersion time on inhibitor efficiency was studied. The current density was reduced with the presence of inhibitors from 517.93 to 56.18 and 9.96 μA.cm−2 at 5 × 10−4 M and an immersion time of 1 h for AMMP and MMOPH, respectively. In both substances, the Langmuir isotherm system showed the best fit, with physisorption and chemisorption being the types of adsorption. The results of surface characterization indicated that both compounds can be adsorbed on mild steel surfaces to minimize corrosion. The obtained Monte Carlo simulation results suggest that the inhibitors are adsorbed vertically and the formation of a protective layer on the metal surface. The density function theory calculations for inhibitors found the protonated state is more reactive than the neutral state and agree with experimental results and follow the order MMOPH ˃ AMMP. The results showed that both compounds can be used as new corrosion inhibitors for mild steel in aggressive environments.
Corrosion inhibition of mild steel in acidic media using new oxo-pyrimidine derivatives: Experimental and theoretical insights
(2023-07-15) Ferigita K.S.M.; Saracoglu M.; AlFalah M.G.K.; Yilmazer M.I.; Kokbudak Z.; Kaya S.; Kandemirli F.
Interesting results have been found for new compounds derived from oxo-pyrimidine to protect of mild steel (MS) in 1 M hydrochloric acid. These the compounds are 1-(5-(4-Methoxy-benzoyl)-4-(4‑methoxy-phenyl)-2-oxo-2H-pyrimidin-1-yl]-(4‑methoxy-phenyl)-urea (MMOM) and 1-(5-(4‑methoxy-benzoyl)-4-(4‑methoxy-phenyl)-2-oxo-2H-pyrimidin-1-yl)-3-(4-methlyphenyl)-thiourea (MMOPM). In this study, the impact of immersion time on inhibitor effectiveness was also investigated. Both substances function as mixed-type inhibitors, according to the electrochemical data. At 5 × 10−4 M and a 72-hour immersion duration, MMOM is more effective than MMOPM (98.42% vs. 94.49%). The Langmuir isotherm system provided the best match for both compounds, with chemisorption as the kind of adsorption. According to the findings of surface characterisation, both chemicals may be adsorbed on mild steel surfaces to reduce corrosion. Inhibitor simulations using density functional theory revealed that the protonated state is more reactive than the neutral state and coincides with experimental findings. The outcomes demonstrated that both compounds may be utilised as new mild steel corrosion inhibitors in harsh conditions and long-term immersion. The theoretical study, based on quantum chemical calculations of the compounds, performed by the DFT/BP86 method with a 6–311G(d,p) basis set by using Gaussian 09, Revision A.02 program, were also included to support experimental results. The various quantum chemical parameters such as EHOMO, ELUMO, chemical hardness and chemical softness, electronegativity of the investigated molecules were calculated, and their inhibition efficiency were discussed. The outcomes demonstrated that both compounds may be utilised as new mild steel corrosion inhibitors in harsh conditions and long-term immersion.
Enhanced mechanical properties of yttrium doped ZnO nanoparticles as determined by instrumented indentation technique
(2018-06-15) Kaya S.; Akcan D.; Ozturk O.; Arda L.
Yttrium doped (1, 3 and 5 wt%) zinc oxide nanoparticles were synthesized via sol-gel process. The phase, structural and mechanical properties were investigated using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and micro hardness based on indentation technique. The lattice parameters and grain sizes of the samples were calculated from the XRD data. As the lattice parameters increased, the grain sizes decreased dramatically, resulting in more grain boundaries and strong grain connectivity in the ZnO microstructure. Load-depth curves were obtained by applying indentation loads in the range from 400 to 2000 mN at room temperature. As the Y concentration increased, a significant increase was observed in the hardness values computed from loading-unloading curves using the Oliver and Pharr method. The indentation modulus of the samples reached a saturation value for 3% Y and then decreased as the doping rate increased. Moreover, the crack formation around the indent on the sample surface was examined by electron microscopy and was identified as radial/median type. The fracture toughness of the samples was calculated using the Vickers indentation fracture method. Increased fracture toughness values confirm that ZnO nanoparticles are mechanically strengthened by Y doping.
Experimental and theoretical studies for mild steel corrosion inhibition in 1.0 M HCl by three new quinoxalinone derivatives
(2016-09-01) Tazouti A.; Galai M.; Touir R.; Touhami M.E.; Zarrouk A.; Ramli Y.; Saraçoǧlu M.; Kaya S.; Kandemirli F.; Kaya C.
Three quinoxalinone derivatives, namely (E)-3-styrylquinoxalin-2(1H)-one (SQ), (E)-3-(4-methoxystyryl)quinoxalin-2(1H)-one (MOSQ) and (E)-3-(4-methoxystyryl)-7-methylquinoxalin-2(1H)-one (MOSMQ) were synthesized and characterized. Thus, their inhibition effects on mild steel corrosion in 1.0 M HCl medium were investigated using weight loss method, electrochemical measurements. The effect of temperature on the corrosion behavior of mild steel was studied in the range of 298-328 K. Polarization measurements indicated that, the studied compounds act as a mixed type inhibitors, the inhibition efficiency depends on their concentrations and followed the order MOSQ > MOSMQ > SQ. Electrochemical impedance spectroscopy showed that all compounds act by the formation of a protective film at the metallic surface. The adsorption of three inhibitors on steel surface obeyed Langmuir model, thus the thermodynamic and kinetic parameters were calculated and discussed. In the part based on DFT calculations of this study, some electronic properties of studied molecules were calculated and discussed with the help of B3LYP/6-311G (d,p), B3LYP/6-311 ++G (d,p) and B3LYP/6-311G ++ (2d,2p) methods. The theoretical and experimental results are in good agreement.
Improvement of the nature of indentation size effect of Bi-2212 superconducting matrix by doped Nd inclusion and theoretical modeling of new matrix
(2014-01-01) Ozturk O.; Asikuzun E.; Kaya S.; Yildirim G.; Turkoz M.; Kilic A.
Neodmium (Nd) inclusions at different stoichiometric ratios (x=0.0, 0.001 %, 0.005 %, 0.01 %, 0.05 %, 0.1 %) are doped in the Bi-2212 superconducting samples and the samples obtained are subjected to the sintering process at 840 °C constant temperature for 72 hours. The effect of Nd doping on the structural and mechanical properties of prepared samples is investigated by the standard characterization measurements. XRD and SEM measurements are performed to obtain information about surface morphology, phase ratios, lattice parameters and particle size. Moreover, Vickers microhardness (H V ) measurements are exerted to investigate the mechanical properties of the all samples in detail. It is found that all the properties given above retrogress with the increase of the Nd concentration in the Bi-2212 superconducting core. However, the ISE nature of the materials improves systematically. Additionally, the experimental results of microhardness measurements are analyzed using Meyer's law, PSR, MPSR, EPD models and HK approach. The results show that Hays-Kendall approach is determined as the most successful model. © 2014 Springer Science+Business Media New York.
Nanostructural characterization and defect-mediated room temperature ferromagnetism of Zn1−xFexO (x = 0.00–0.07) nanorods prepared via hydrothermal method
(2021-11-05) Kaya S.; Ozturk O.; Arda L.; Bulut F.
The effect of Iron (Fe) doping on crystal structure, morphology, optical behavior, and magnetism of Zn1−xFexO (x = 0.00, 0.01, 0.03, 0.05, 0.07) nanorods prepared via a hydrothermal method was investigated. According to the X-ray diffraction results, Fe ions were incorporated successfully into the Zn ions sites without any deterioration in the wurtzite crystal structure. According to the photoluminescence spectra, a relative increment was observed in the intensity of the near band edge emissions as the Fe concentration increased. Deep level emissions showed that the yellow-orange and violet emissions, corresponding to the oxygen vacancies and zinc interstitials, respectively, increased with the Fe doping. Magnetic measurement results indicated that the undoped ZnO nanorods are diamagnetic. Room temperature ferromagnetism was observed in the Fe doped ZnO nanorods regardless of the doping rate. Although there was no logical relationship between the saturated magnetic moments and the Fe concentration, an obvious correlation was observed between the concentration of point crystal defects including oxygen vacancies, zinc interstitials, and the ferromagnetic parameters. The defect-mediated interactions and the bound polarons effect are suggested for the possible origins of room temperature ferromagnetism in Fe doped ZnO nanorods. The results of the study also provide detailed data for the production method of the ZnO nanorods with enhanced structural, optical and ferromagnetic properties, which are promising candidates for spintronic device applications in nanoelectronics.
Physical properties and diffusion-coefficient calculation of iron diffused BI-2223 system
(2012-10-01) Ozturk O.; Asikuzun E.; Kaya S.; Coskunyurek M.; Yildirim G.; Yilmazlar M.; Terzioglu C.
This study includes two parts: (I) investigation of the effect of different annealing time (10 h, 30 h, and 60 h) on physical, superconducting, and microstructural properties of Fe-diffused Bi-2223 superconductor ceramics prepared by the conventional solid-state reaction method with the aid of the X-ray diffraction (XRD), scanning electron microscopy (SEM), dc resistivity (φ-T ) and transport critical current density (Jc) measurements, and (II) determination of the diffusion coefficient and the activation energy of iron in the Bi-2223 system. In the former part, the zero-resistivity transition temperature (Tc), phase purity, volume fraction, hole-carrier concentration, lattice parameters, surface morphology, texturing, crystallinity, grain connectivity, grain size, and room temperature resistivity values of the bulk samples are found and compared with each other. The results obtained show that both the zero resistivity transition temperature (Tc) and transport critical current density (Jc) regularly enhance with the increment in the diffusion-annealing time. The maximum Tc of 107 ± 0.2 K and Jc of 50.0 Acm-2 are observed for the sample annealed at 830 °C for 60 h. As for the XRD investigations, according to the refinement of cell parameters done by considering the structural modulation, the enhance-ment in the diffusion-annealing is confirmed by both a decrease of the cell parameter a and an increase of the lattice parameter c of the samples, meaning that the greatest Bi-2223 phase fraction belongs to the sample annealed at 830 °C for 60 h. Moreover, SEM images display that the sample has the best crystallinity, grain connectivity, and largest grain size. Based on the results, the superconducting and microstructural properties improve with the increase in the diffusion-annealing time. In the latter part, Fe diffusion in the Bi-2223 system is examined in a range of 500-830 °C by the variation of the lattice parameters evaluated from the XRD patterns. The temperature dependence of the Fe diffusion coefficient is described by the Arrhenius relation D = 4.27 × 10-5 exp(-1.27 ± 0.10) eV/kBT, and the related activation energy of the iron in the Bi-2223 system is found to be about 1.27 eV. The relatively low value of activation energy obtained illustrates that the migration of the Fe ions primarily proceeds through defects such as pore surfaces and grain boundaries in the polycrystalline structure, leading to the improvement of the microstructural and superconducting properties of the samples, supported by the results of part I. All in all, the aim of the present study is not only to analyze the role of diffusion-annealing time on superconducting and microstructural properties of Fe-diffused Bi-2223 superconductors, but also to find the diffusion coefficient and activation energy of Fe in the Bi-2223 system. © Springer Science+Business Media, LLC 2012.
Quantum chemical and molecular dynamics simulation studies on inhibition performances of some thiazole and thiadiazole derivatives against corrosion of iron
(2016-07-01) Kaya S.; Kaya C.; Guo L.; Kandemirli F.; Tüzün B.; Uǧurlu I.; Madkour L.H.; Saraçoǧlu M.
In the present study, to predict corrosion inhibition performances of 2-amino-4-(4-chlorophenyl)-thiazole (Inh1), 2-amino-4-(4-bromophenyl)-thiazole (Inh2), 4-(2-aminothiazole-4-yl)-phenol (Inh3), 5,5′-(ethane-1, 2-diyldisulfanediyl) bis-(1,3,4-thiadiazole-2-amine) (Inh4), 5,5′-(propane-1,3-diyldisulfanediyl) bis-(1,3,4-thiadiazole-2-amine) (Inh5) against corrosion of Fe metal, density functional theory (DFT) calculations and molecular dynamics simulations approach were performed on these mentioned molecules. Firstly, quantum chemical parameters such as the highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO), the energy gap between ELUMO and EHOMO (ΔE), chemical hardness, softness, electronegativity, proton affinity, global electrophilicity, global nucleophilicity and total energy (sum of electronic and zero-point energies) were calculated and discussed with the help of HF/SDD, HF/6-311G, HF/6-31 ++G, B3LYP/SDD, B3LYP/6-311G and B3LYP/6-31 ++G methods. Then, we calculated binding energies on Fe(110) surface of aforementioned thiazole and thiadiazole derivatives to investigate the strength of the interactions between metal surface and these molecules. The theoretical data obtained are in good agreement with the experimental inhibition efficiency results earlier reported.
Quantum chemical studies on the corrosion inhibition of Fe78B13Si9 glassy alloy in Na2SO4 solution of some thiosemicarbazone derivatives
(2018-08-01) Saraçoğlu M.; Elusta M.I.A.; Kaya S.; Kaya C.; Kandemirli F.
In this study, the density functional theory (DFT) at the gradient-corrected correlation functional of Lee-Yang-Parr (B3LYP) functional with 6-311++G(2d,2p), correlation-consistent, polarized valence, X-zeta (cc-pVTZ) basis sets, BP86 functional with/6-311++G(2d,2p) basis set and ab initio calculations using the Hartree-Fock (HF)/6-311++G(2d,2p) methods in gas and water phase of neutral and protonated forms of molecules were performed on six thiosemicarbazone derivatives, namely 4-methyl acetophenone thiosemicarbazone (Inh 1), 4-methoxy acetophenone thiosemicarbazone (Inh 2), Benzaldehyde thiosemicarbazone (Inh 3), 4-methoxy benzaldehyde thiosemicarbazone (Inh 4), 4-ethyl benzaldehyde thiosemicarbazone (Inh 5) and 4-bromo benzaldehyde thiosemicarbazone (Inh 6). The quantum chemical parameters/descriptors, namely, dipole moment (D), highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO), HOMO-LUMO energy gap (ΔE), absolute electronegativity (X), absolute hardness (η), softness (σ), proton affinity (PA), electrophilicity (ω) and nucleophilicity (ε) were calculated and correlated with the experimental inhibition efficiencies (%IE). It was observed that the theoretical and experimental results were in good agreement.
Roughness and bearing analysis of ZnO nanorods
(2020-07-01) Kaya S.; Ozturk O.; Arda L.
It is essential to analyze the surfaces of thin films precisely to control the production process and the performance of nano-scale devices. Conventional techniques give limited information about the nano-scale surface morphology. Instead, atomic force microscopy (AFM) provides more accurate results about the surface parameters of nanostructures. Hence, in the current study, two-dimensional (2D) and three-dimensional (3D) morphological properties of zinc oxide (ZnO) nanorods (NRs) were investigated using AFM. ZnO NRs were produced via a hydrothermal method at different growth times and temperatures. The surface texture was also examined by scanning electron microscopy (SEM). The results revealed that the morphological parameters such as diameter, length, and shape of the nanorods could be tuned by changing growth time and temperature. Moreover, we analyzed the most crucial roughness and bearing analysis parameters, which affect the functional properties of ZnO in the surface engineering applications. The average roughness increased from 5.86 nm to 17.30 nm as growth time increased from 2 h to 5 h. The average roughness was obtained as 10.92 nm for the temperature of 90 °C and it reached 41.13 nm for 150 °C. In addition, height distribution and bearing area curves associated with the real contact area were reported. 90% of the area was spread at a depth of 48 nm for the growth time of 2 h while this value was obtained 183 nm for 5 h Addition, 90% of the area was spread at a depth of 88 nm and 457 nm for the temperature of 90 °C and 150 °C, respectively. We believe that our study would be a pioneering perspective on bearing analysis of ZnO nanorods.
Significant change in micro mechanical, structural and electrical properties of MgB2 superconducting ceramics depending on argon ambient pressure and annealing duration
(2015-06-01) Ozturk O.; Asikuzun E.; Kaya S.
In this study, the effects of different Ar pressure (vacuum, 0, 10 and 20 bar) and different annealing times (0.5 and 1 h) on microstructural, mechanical and superconducting properties of the bulk superconducting MgB2 are investigated. The samples are produced using the solid state reaction method. X-ray diffraction and scanning electron microscopy measurements are performed for phase formation, crystal structure, lattice parameters, particle size analysis, grain orientations, grain connectivity, and surface morphology of MgB2 samples. The superconducting properties are studied by dc resistivity measurements. In this study we have focused on microhardness measurements to investigate the mechanical properties. Vickers microhardness test is employed for determination of mechanical properties of the samples. The experimental microhardness results are analyzed by Meyer’s law, proportional sample resistance model, elastic–plastic deformation model, Hays Kendall (HK) approach, and indentation induced cracking (IIC) model. HK approach is identified as the most appropriate model for MgB2 superconducting samples exhibiting the indentation size effect behavior; for the other samples that have reverse indentation size effect behavior IIC model is appointed as the most appropriate model.
The Effect of Ar Ambient Pressure and Annealing Duration on the Microstructure, Superconducting Properties and Activation Energies of MgB2 Superconductors
(2017-05-01) Ozturk O.; Asikuzun E.; Kaya S.; Koc N.S.; Erdem M.
MgB2 samples are produced by ex situ reaction method under vacuum, and various (0, 10, 20 Bar) Ar pressure for 0.5 and 1 h. The effect of ambient pressure and annealing duration on the microstructure and electrical properties of bulk samples are investigated. XRD, SEM, and magnetoresistance measurements are made. The a and c lattice parameters and the grain size values are the highest for the samples produced under vacuum and their values decrease with increasing Ar pressure. Moreover, these values increase when the annealing duration increases from 0.5 to 1 h. The increasing pressure reduces the bond lengths between the atoms thus the grain sizes decrease. Smaller grain size promotes the connection between grains which results in an increase of the critical current density (Jc). SEM micrographs reveal that the produced samples have granular structure which is a characteristic feature of MgB2. The decrease of grain sizes and thus enhancement in grain connectivity with increasing pressure is also confirmed by SEM images. Magneto resistivity measurements show that Tc values of the samples produced under vacuum are the highest. Tc values decrease with increasing ambient pressure and applied magnetic field. The activation energies (U0) of the samples are calculated using Arrhenius plots due to thermally activated flux flow theory. Existence and increase of Ar pressure causes increase of activation energies. The samples produced with 0.5-h annealing have higher activation energies than the ones produced with 1-h annealing.
Vertically aligned Nd substituted ZnO nanorods: Morphology, optical characteristics and room temperature ferromagnetism
(2022-03-01) Kaya S.; Ozturk O.; Arda L.
Zn1-xNdxO (x = 0.00, 0.01, 0.03, 0.05, 0.07) nanorods (NRs) are grown vertically, perpendicular to the glass substrate using a hydrothermal method. Nd3+ ions are successfully substituted into the crystal lattice of ZnO. The crystal structure, morphology, optical, and magnetic properties are comprehensively studied by various techniques. Significant changes are observed in the morphological and optical properties of the Nd substituted ZnO NRs. According to the magnetic measurements, the maximum Hc value is observed to be 39.04 Oe at a concentration of 3% Nd and the maximum Ms value is observed to be 20.52 x 10−6 emu at 7% Nd, whereas the maximum Mr value is measured as 1.86 x 10−6 emu at 5% Nd, confirming that the magnitude of magnetic parameters are independent of Nd concentration. An opposing correlation is found between the Hc value and the morphological properties (including crystallite size, average roughness, and aspect ratio) of Nd substituted ZnO NRs.