Yazar "Nezir, S." seçeneğine göre listele
Listeleniyor 1 - 8 / 8
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Eco-Friendly Synthesis and Characterization of Reduced Graphene Oxide(Iop Publishing Ltd, 2017) Ickecan, D.; Zan, R.; Nezir, S.Graphene is a single sheet of sp(2) bonded carbon having a two-dimensional (2D) layer. It has remarkable electronic, mechanical and thermal properties. In this paper, the graphene oxide (GO) was reduced by reducing chemicals such as ascorbic acid and hydrazine and then characterized by transmission electron microscopy (TEM), Raman spectroscopy and Fourier transform infrared spectroscopy. TEM results of the chemically reduced graphene were showed that the structure consists of a mixture of single and few layers of reduced graphene oxide (rGO).Öğe Effects of substrate temperature and post-deposition anneal on properties of evaporated cadmium telluride films(Elsevier Science Sa, 2007) Bacaksız, E.; Basol, B. M.; Altunbaş, M.; Novruzov, V.; Yanmaz, E.; Nezir, S.The effects of substrate temperature and post-deposition heat treatment steps on the morphology, structural, optical and electrical properties of thin film CdTe layers grown by vacuum evaporation were investigated. Scanning electron microscopy and X-ray diffraction (XRD) techniques were employed to study the structural changes. It was observed that the grain sizes and morphologies of as-deposited layers were similar for substrate temperatures of - 173 degrees C and - 73 degrees C. However, CdTe films produced at a substrate temperature of 27 degrees C had substantially larger grain size and clearly facetted morphology. Annealing at 200-400 degrees C in air did not cause any appreciable grain growth in any of the films irrespective of their growth temperature. However, annealing at 400 degrees C reduced faceting in all cases and initiated fusing between grains. XRD studies showed that this behavior after annealing at 400 degrees C coincided with an onset of a degree of randomization in the originally strong (I 11) texture of the as-grown layers. Optical band gap measurements showed sharpening of the band-edge upon annealing at 400 degrees C and a band gap value in the range of 1.46-1.49 eV Resistivity measurements indicated that annealing at 400 degrees C in air forms a highly resistive compensated CdTe film. All results point to 400 degrees C to be a critical annealing temperature at which optical, structural and electrical properties of CdTe layers start to change. (c) 2006 Elsevier B.V. All rights reserved.Öğe Experimental and theoretical approaches on mechanical evaluation of Y123 system by Lu addition(Springer, 2013) Turkoz, M. B.; Nezir, S.; Ozturk, O.; Asikuzun, E.; Yildirim, G.; Terzioglu, C.; Varilci, A.This work is the continuation of a systematic study on the characterization of the Lu-added Y123 bulk superconducting materials prepared by the nitrate compounds and derivatives at 970 degrees C for 20 h. In this part, the effect of Lu inclusions on the physical and mechanical properties of the Y123 superconductors is examined with the aid of microhardness measurements performed at various applied loads in the range of 0.245-2.940 N. The microhardness measurement results allow us to determine the important mechanical characteristics such as Vickers microhardness, elastic (Young's) modulus, yield strength and fracture toughness values being responsible for the potential industrial applications. It is found that all the properties given above are strongly dependent upon the Lu concentration in the Y123 matrix. Especially, Vickers microhardness (H-nu) values of the samples studied in this work are found to suppressed considerably with the enhancement of the Lu addition in the system due to the degradation in the connectivity between superconducting grains. Moreover, the H-nu values of the pure Y123 sample are observed to increase with increasing the applied load whereas those of the Lu-doped superconducting materials are obtained to decrease with the load. In other words, the pure sample exhibits the reverse indentation size effect (RISE) behavior while the others obey the indentation size effect (ISE) feature, confirming the degradation in the mechanical properties with the Lu inclusions in the Y123 matrix. In addition, the microhardness measurement results are estimated using the 5 different models such as Meyer's law, proportional sample resistance model, elastic/plastic deformation model, Hays-Kendall (HK) approach and indentation-induced cracking (IIC) model. According to the results obtained from the simulations, of the mechanical analysis models, the Hays-Kendall (HK) approach is determined as the most successful model for the description of the mechanical properties of the Lu-doped superconducting materials (exhibiting the ISE behavior) where both the both the reversible (elastic) and irreversible (plastic) deformations are produced. On the other hand, the IIC model is found to be superior to other approaches for the pure sample (presenting the RISE feature) where the irreversible deformation becomes more and more dominant compared to the reversible deformation.Öğe Fundamental and high-order harmonic susceptibilities of a BSCCO(2223) bulk superconductor(Elsevier Science Bv, 2003) Aksu, E.; Gencer, A.; Yilmaz, H.; Nezir, S.Measurements of fundamental and high-order harmonic susceptibilities, chi(n), = chi(n)' + ichi(n)" (n = 1, 2, 3, 5 and 7), were made on a cylindrical BSCCO(2223) bulk sample in the range 15-120 K at fields ranging from 8 to 1600 A/m and 1000 Hz frequency. They exhibit dependence on the amplitude of the ac field. The observed dependences were analyzed by using the Bean model. We have obtained an empirical function for the penetration field H-p = H-alpha(1 - t)(beta), with t = T/T-cb. Best fitting to data was obtained with parameters H-alpha approximate to 3.3 x 10(4) A/m and beta = 2.05. In addition, ac losses were calculated at some fixed temperatures to compare theoretical expectations. The experimental values agree well with the theoretical findings. AC losses were calculated under external fields ranging from 0 to 1600 A/m and, at 84.35 K, the experimental results are shown to agree well with the theoretical values. (C) 2003 Elsevier Science B.V. All rights reserved.Öğe Radiological characterization of Cayirhan coal-fired power plant in Turkey(Elsevier Sci Ltd, 2007) Çevik, U.; Damla, N.; Nezir, S.Natural radioactivity of Cayirhan lignite coal treated at Cayirhan (Ankara, Turkey) power plant, its ash and soil samples mixed with ash in the power plant field were investigated. For comparison, soil samples were collected from a distance of 4 kin south of the plant. The analysis shows that the samples include natural radionuclides such as Ra-226, Th-232 and K-40. The mean activity concentrations of Ra-226, Th-232 and K-40 were 57.82, 30.45 and 322.21 Bq . kg(-1), respectively. Obtained values shows that the average radium equivalent activity (Ra-eq), air-absorbed dose rate (D), annual effective dose (AED) and external hazard index (H-ex) for all samples are 123.9 Bq . kg(-1), 58.90 nGy . h(-1), 71.99 mu Sv . y(-1) and 0.34, respectively. The Ra-eq values of samples are lower than the limit of 370 Bq . kg(-1), equivalent to a gamma-dose of 1.5 mSv . y(-1). The measured activity concentrations for these radionuclides were compared with the reported data of other countries. (C) 2007 Elsevier Ltd. All rights reserved.Öğe The Structural and Electrical Study of Lu-Doped YBCO System(Springer, 2013) Soylu, N.; Yahsi, C. C.; Altintas, S. P.; Nezir, S.; Terzioglu, C.We have prepared a series of bulk superconducting samples with the nominal composition of Y1-xLuxBa2 Cu3Oy (where x = 0.0, 0.05, 0.1, 0.2 and 0.3) by the conventional solid-state reaction method. The samples were characterized structurally by means of X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectrometry. The electrical transport properties of the samples were analyzed in the temperature range between 20-140 K under magnetic fields up to 2 T. The superconducting transition temperature, T-c, and activation energy, U-0, were found to decrease with Lu-doping and with increase in applied magnetic field.Öğe Synthesis and characterization of spray pyrolysis Zinc Oxide microrods(Elsevier Science Sa, 2007) Alver, U.; Kilinc, T.; Bacaksiz, E.; Küçükömeroğlu, T.; Nezir, S.; Mutlu, I. H.; Aslan, F.Zinc Oxide (ZnO) microrods were prepared by ultrasonic spray pyrolysis technique on glass substrates. The X-ray diffraction (XRD) patterns and scanning electron microscope images show that obtained rods are composed of wurtzite-type ZnO with diameters of about 1-3 mu m and lengths ranging from 1 to 3 mu m. The XRD patterns also show that hexagonal ZnO rods mainly grow along the [002] direction. The optical measurements reveal that films have a maximum transmittance of about 80% and a direct band gap of 3.6 eV (c) 2006 Elsevier B.V. All rights reserved.Öğe Temperature dependence of ZnO rods produced by ultrasonic spray pyrolysis method(Elsevier Science Sa, 2007) Alver, U.; Kilinc, T.; Bacaksiz, E.; Nezir, S.Zinc oxide (ZnO) microrods were prepared at different substrate temperatures by ultrasonic spray pyrolysis technique on glass substrates. The X-ray diffraction patterns show that obtained rods are composed of wurtzite-type and mainly grow along the [0 0 2] direction. Scanning electron microscope images show that the diameters of ZnO rods and the distances among the rods increase with increasing substrate temperature. In addition, the optical measurements reveal that transmittance and the band gap energies of films increase with increasing substrate temperature. (C) 2007 Elsevier B.V. All rights reserved.
