The Effect of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Buffer Layer on the Magnetic Properties of Melt-Processed YBCO Superconductor

In this study, two kinds of melt-processed YBCO samples (Y1050-1 and Y1050-2) grown on a buffer layer of Y₂O₃ addition were fabricated. The compacted powders were located on a crucible with Y₂O₃ powder freely poured and a buffer layer of pressed Y₂O₃ to avoid liquid to spread on the furnace plate. The superconducting transition temperature was determined by a standard four-point method at temperatures between 40 and 100 K. The transition temperatures of Y1050-1 and Y1050-2 were found to be 91.6 and 92.9 K at zero magnetic fields, respectively. The magnetization measurements were performed using a vibrating sample magnetometer (VSM) on the same system at 5, 40, and 77 K. The critical current densities for Y1050-1 and Y1050-2 samples were determined to be 6.5×10³ and 5.6×10³ A/cm² at 77 K in zero magnetic fields, respectively. The trapped magnetic field measurements of the samples were performed by using a Hall probe scanning device and a Fe–Nd–B permanent magnet at 77 K. It was found that the trapped magnetic field of the Y1050-1 sample is higher than that of the Y1050-2 sample.     

Improving electrical and mechanical properties of a conductive nano adhesive

In this experimental study, lap shear strength and electrical conductivity of nanohybrid adhesives containing multi-walled carbon nanotubes (MWCNT) and silver (Ag) nanoparticles were investigated. Ag nanoparticles were produced via arc-discharge method in liquid nitrogen. For characterizing the Ag nanoparticles, X-ray diffraction analysis, transmission electron microscopy, and scanning electron microscopy (SEM) were performed. Tensile lap shear properties were determined in accordance with ASTM D 1002-10 standard. Mechanical and the electrical properties of nanohybrid adhesives were compared with neat epoxy adhesive. The best electrical conductivity of nanohybrid adhesive was obtained for the 1% wt MWCNT-2% wt Ag-contained sample. However, the samples which contain 0.5% wt. MWCNT–0.5% wt. Ag nanoparticles reached the highest lap shear strength. The results showed that Ag nanoparticles enhance the conductivity in the presence of MWCNT. It is concluded that the MWCNT act as conductivity bridges among epoxy adhesive and facilitate the electron transfer. As seen in the tensile test results, the ductility of the adhesive was improved by adding the nanoparticles in to the epoxy resin.     

Electrochemical impedance study of polyaniline electrocoated porous carbon foam

Electropolymerization of aniline on mesophase pitch based carbon foam has been studied in order to evaluate the influence of conductive polymer coating on the properties of carbon foam. The surface morphology of the coating was determined by scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of resulting modified carbon foam samples. Polyaniline (PANI) electrocoated-mesophase pitch based carbon foam showed good capacitor behavior in 0.5 M H₂SO₄. Better capacitive behavior is obtained for 100 and 150 mV/s compared to other scan rates, under these faster scan rates thinner films of PANI coatings were combined with more porous structure of carbon foam. Conductivity of the carbon foam was increased from 9.23 to 13.73 S/cm by electrocoating of PANI.     

Effects of biodiesel on a DI diesel engine performance, emission and combustion characteristics

Experimental tests were investigated to evaluate the performance, emission and combustion of a diesel engine using neat rapeseed oil and its blends of 5%, 20% and 70%, and standard diesel fuel separately. The results indicate that the use of biodiesel produces lower smoke opacity (up to 60%), and higher brake specific fuel consumption (BSFC) (up to 11%) compared to diesel fuel. The measured CO emissions of B5 and B100 fuels were found to be 9% and 32% lower than that of the diesel fuel, respectively. The BSFC of biodiesel at the maximum torque and rated power conditions were found to be 8.5% and 8% higher than that of the diesel fuel, respectively. From the combustion analysis, it was found that ignition delay was shorter for neat rapeseed oil and its blends tested compared to that of standard diesel. The combustion characteristics of rapeseed oil and its diesel blends closely followed those of standard diesel.     

Phenolics profiles of olive fruits (Olea europaea L.) and oils from Ayvalık,Domat and Gemlik varieties at different ripening stages

Phenolic compounds in olive fruit and oils obtained from Ayval?k, Domat and Gemlik olive varieties collected at different ripening periods were evaluated by High Performance Liquid Chromatography (HPLC). Gallic acid and p-cumaric acid were identified for Ayval?k and Domat at each period of ripening, respectively. In addition, gallic acid, p-cumaric acid, sinapinic and apigenin acids were detected in Gemlik olive fruit. Hydroxytyrosol, rutin, oleoropein, luteolin, tyrosol, vanilic acid and gallic acid in Ayval?k olive fruit in all ripening periods were determined. The tyrasol contents varied between 0.18 to 1.57 mg/kg. Luteolin contents of olive oils ranged at the levels between 0.12 to 2.28 mg/kg. In contrast, oils had the lowest syringic, p-cumaric, chlorogenic and ferulic acids. Vanillic acid contents of oils ranged between 0.08 to 2.38 mg/kg.     

Magnetic Properties of YBCO Single-Crystal Grown on Y2O3 Layer by a Cold Top-Seeding Method

In this work, single-crystal samples 20 mm in diameter were grown by a cold top-seeding method. In order to study the effect of an Y₂O₃ buffer layer, a compacted precursor was located in a crucible on a buffer layer of freely poured Y₂O₃ powder. The YBCO bulk samples were carefully prepared in the same chemical composition. In order to examine the homogeneity of the samples, rectangular specimens were cut from a sample. The structural orientation of the specimens was measured by a X-ray diffractrometer (XRD). The microstructure was observed with a Scanning Electron Microscope (SEM). The magnetic properties were measured using a Vibrating Sample Magnetometer (VSM) at 77 K with the applied magnetic field parallel to the c-axis. As a result only (00l) peaks were observed in X-ray diffraction data, indicating that all specimens are highly oriented with the c-axis perpendicular to the top surface. Also the cut samples exhibited very fine Y211 inclusion distributed in the bulk sample observed in SEM micrographs. The critical current density J _c (A/cm²) has been estimated by the extended Bean model. The maximum value of the critical current density at 77 K is 5.2×10⁴ A/cm² in a self-field. The trapped magnetic field measurements of the samples were performed by using Hall probe scanning device with static field of 0.5 T at 77 K. The single-domain sample exhibits a trapped field of 1140 G at 77 K.