Fırat Karaboğa

Effect of different-sized h-BN nano-particles on some properties of MgB2 superconductors

The present study reports the effect of hexagonal boron nitride (h-BN) doping on the superconducting properties of bulk MgB2 samples. Structural, electrical and magnetic properties of 3xa0wt% h-BN doped MgB2 samples are studied in terms of three different sized h-BN nanoparticles. The results show that h-BN doping has no significant change on critical transition temperature (±0.5xa0K deviation), but decreases the magnetic Jc with increasing the h-BN particle size. Among the doped samples, a highest Jc (Txa0=xa010xa0K) value of 1.8xa0×xa0104xa0A/cm2 is achieved for the sample doped with the smallest sized h-BN at zero external magnetic field but it is still lower than the 2.5xa0×xa0104xa0A/cm2 obtained for the un-doped sample. In the scope of this study, it is investigated whether or not the nano-sized h-BN particle is a possible candidate to improve the pinning properties of the MgB2 sample and we suggest that particle size is very important parameter in h-BN doping into MgB2.

Design, Fabrication, and Testing of MgB2/Fe Racetrack Coils

We fabricated four superconducting racetrack coils wound by bare <italic>in situ</italic> MgB₂/Fe mono and multifilamentary wires produced in our laboratory by using the wind-and-react method. Transport measurements in self-field were performed in a liquid helium dewar. The magnetic field flux density <italic>B</italic> = 25 mT for <italic>I</italic> = 92 A was measured to verify how the current flowed inside the coil for one of the coils by means of a cryogenic axial Hall sensor placed into the central bore region of the coil. The coil with 36 turns wound by mono MgB₂/Fe wire of <italic>l</italic> = 24 m has a highest current-carrying capacity of more than 150 A at <italic>T</italic> = 4.2 K and self-field among the coils. The coils fabricated by multifilamentary wires have relatively low engineering critical current values of <italic>I</italic>_ce = 67 A for 18 + 1 and <italic>I</italic>_ce = 57 A for 4 + 5 superconducting/copper filament wires at <italic>T</italic> = 4.2 K in self-field. Our results form essential contribution toward determination of the possible use of low-cost MgB₂/Fe wires in low-field superconductor coil applications.

Electrochemical and spectroscopic characteristics of p-acryloyloxybenzoyl chloride and p-acryloyloxybenzoic acid and antimicrobial activity of organic compounds

The purpose of this multidisciplinary work is to characterize title compounds, p-acryloyloxybenzoyl chloride (ABC) and p-acryloyloxybenzoic acid (ABA) by means of experimental and theoretical evidences. As experimental research, Fourier transformation-infrared spectra (in the region 400-4000 cm(-1)) and nuclear magnetic resonance (NMR) chemical shifts (with a frequency of 400 MHz) are examined for spectroscopic properties belonging to the new synthesized compounds. Moreover, the compounds are investigated for antimicrobial activity against various microorganisms (Gram-positive and Gram-negative) by means of the visual inhibition zone technique on the agar media. The experimental results observed indicate that ABA exhibits more powerful inhibitors of microorganisms due to the presence of the hydroxyl group leading to higher reactive system, one of the most striking features of the paper. As for the theoretical studies, the optimized molecular structures, vibrational frequencies, corresponding vibrational spectra interpreted with the aid of normal coordinate analysis based on scaled density functional force field, atomic charges, thermodynamic properties at different temperature, 1H NMR chemical shifts by way of density functional theory (DFT) with the standard (B3LYP) methods at 6-311G++(d,p) basis set combination for the first time. According to findings, the 1H NMR chemical shifts and vibrational frequencies are obtained to be in good agreement with the suitable experimental results. Thus, it would be more precise to say that the calculation level chosen is powerful approach for understanding in the identification of the molecules investigated. At the same time, we determine the electrochemical characteristics belonging to the samples via the simulation of translation energy (HOMO-LUMO), molecular electrostatic potential (MEP) and electrostatic potential (ESP) investigations. It is observed that the strong intra-molecular charge transfer (ICT) appears between the donor and acceptor in the both compounds (especially ABA) due to the existence of the strong electronic donating groups and effective π-π* conjugated segments with high electronic donor ability for the electrophilic attack (intermolecular interactions).