A. Kılıç

Two-band Ginzburg-Landau theory for the lower critical field Hc1 in MgB2

The temperature dependence of the lower critical field Hc1(T) for the superconducting magnesium diboride, MgB2, is studied in the vicinity of Tc using a two-band Ginzburg–Landau (G–L) theory. The theoretically calculated Hc1(T) near Tc exhibits a negative curvature. The results are shown to be in good agreement with the experimental data. In addition, two-band G–L theory calculations give a temperature dependence of the Ginzburg–Landau parameter κ (T) = λ (T)/ξ (T), which varies little with the temperature in a manner similar to the microscopic single-band BSC theory.

Mechanical, microstructural and magnetic properties of the bulk BSCCO superconductor prepared by two different methods

BSCCO bulk samples have been prepared by solid-state reaction and ammonium nitrate precipitation methods with Bi1.65Pb0.35Sr2Ca2Cu3O10±y stoichiometry. Structural, mechanical and magnetic characterizations of the samples were performed by the X-ray powder diffraction (XRD), the scanning electron microscopy (SEM), Microhardness measurements, AC susceptibility measurements. The XRD patterns showed that the diffraction peaks for our samples belong to the two main phase, namely 2223 and 2212 of the BSCCO. In this study we have focused on microhardness measurements to investigate the mechanical properties. Vickers microhardness, Young’s modulus and yield strength values were calculated separately for all samples. In addition to these, we calculated the load independent hardness values of samples. Experimental results of hardness measurements were analyzed using the Meyer’s law, proportional sample resistance (PSR) model, Elastic–Plastic deformation model (EPD) and indentation induced cracking (IIC) model. The critical transition temperature, phase purity, lattice parameter, surface morphology and crystallinity of the prepared bulk samples were compared with each other.

Effect of re-pelletization on structural, mechanical and superconducting properties of BSCCO superconductors

We have examined the effect of re-pelletization on structural, mechanical and superconducting properties of high temperature superconducting (HTS) bulk samples using Bi1.85Pb0.35Sr2Ca2Cu3Oy stoichiometry. Conventional solid state reaction method is used for preparation of three different bulk samples. XRD measurement of the samples shows that a high percentage of high-Tc phase is determined. Superconducting critical transition temperature of the samples have been obtained from the curves of ρ-T and χ-T. Vickers micro-hardness are also calculated for all samples. Re-pelletization has a positive effect on structural, mechanical and superconducting properties of bulk samples.

Harmonic Response of a Bulk Superconductor MgB2

Magnetic characterisation of an intermetallic bulk superconductor, MgB2, was carried out by use of odd-order harmonic susceptibility χn = χ′n - iχ″n (n is odd) at low fields. The simplified Kim model was found to be suitable to account for the main features of the experimental odd-order harmonic susceptibilities. Full penetration field is fitted to for temperature scaling. The experiments are in good agreement with theory.

Switching and Decoupling Effects in a Single-Phase Transformer Using Extra DC Current

A single-phase current-limiting transformer has been developed based on flux transfer. The transformer consists of two independent iron cores, one primary coil, two separate secondary coils, and superconducting windings/loops. Two iron cores are in a mechanical contact and clamped. Superconducting windings/loops act as coupling/decoupling mechanism between two iron cores. The transformer has been made operational via a switchgear of the applied dc current for a potential use in the current limitation when the transition between the superconducting and normal (quench) states can be triggered. DC and ac currents can be applied simultaneously in fault and no-fault conditions to mimic the realistic cases of use. With decoupling ac energy transfer, we propose that conventional switching off may be replaced with the approach described.

An electron paramagnetic resonance study on irradiated triphenylphosphinselenid single crystal

The single crystals of triphenylphosphinselenid [C18H15PSe] were produced by slow evaporation of concentrated ethyl acetate solutions. These single crystals were exposed to 60Co gamma (γ) rays with a dose speed of 0.980 kGy/h at the room temperature for 72 h. The free radical over the sample was observed using electron paramagnetic resonance (EPR)–X band spectrometer. The EPR spectra were recorded between 120 and 400 K. Furthermore, the sample irradiated was rotated in steps of 10° and analyzed for different orientations of the crystal in the magnetic field. Only one radical structure was determined on the molecule. The hyperfine constants of the sample were found to be anisotropic. The average values of these constants and value of g were calculated as following: g=2.007656, aSe=37.47 G, aP=27.44 G, aHa=17.28 G, and aHb=18.16 G.

Spin-1 Heisenberg ferromagnet using pair approximation method

Thermodynamic properties for Heisenberg ferromagnet with spin-1 on the simple cubic lattice have been calculated using pair approximation method. We introduce the single-ion anisotropy and the next-nearest-neighbor exchange interaction. We found that for negative single-ion anisotropy parameter, the internal energy is positive and heat capacity has two peaks.

The modeling of cobalt ions adsorption on molecular sieves and zeolite AW-300

High concentration heavy metals in the environment can cause serious problem on human health. Cobalt is a heavy metal that has a large application in different fields. In the present work, we aimed to investigate the adsorption of the cobalt ions from aqueous solutions on molecular sieves and zeolite AW-300. Molecular sieves and zeolites were activated at 873 K for two hours before the adsorption experiment. UV-Visible spectrometer was used to measure concentrations of cobalt ions. All adsorption experiments were performed according to statistical designs for response surface methodological approach. A response surface analysis was guided to advance understand the interactions between adsorbent dose and initial concentration of cobalt ions. The removal efficiencies of cobalt ions on sorbents were characterized. The results indicated that molecular sieves and zeolite AW-300 can be used to remove cobalt ions from aqueous solutions.