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Öğe Çok cidarlı karbon nanotüp ve TiO2 tabaka ilavesinin P3Ht: PCBM organik güneş pillerinin performansına etkileri(Selçuk Üniversitesi Fen Bilimleri Enstitüsü, 2011-07-29) Demir, Okan; Avcı, AhmetBu çalışmada, aktif tabakasına kütlece % 0,05 oranında çok cidarlı karbon nanotüp eklenen organik güneş pilleri hava ortamında üretilerek, karbon nanotüpün pil verimi üzerindeki etkisi incelenmiştir. Pil katmanları spin kaplama yöntemiyle kaplanmış ve belirli sıcaklıklarda tavlanmıştır. Ayrıca aktif tabakanın üzeri kimyasal olarak sentezlenen titanyum dioksit (TiO2) katmanıyla kaplanarak fotovoltaik özelliklerdeki değişim incelenmiştir. Üretilen güneş pillerinin karakterizasyonunda Taramalı Elektron Mikroskobu ve Atomik Kuvvet Mikroskobu görüntüleri alınarak morfolojik özellikleri belirlenmiş, güneş pillerinin absorbans ölçümleri alınarak optik özellikleri incelenmiştir. Aktif tabakaya karbon nanotüp ilavesiyle akım yoğunluğu, verim ve dolum faktöründe artış sağlanmıştır. Ayrıca, aktif tabaka üzerine kaplanan TiO2 katmanın pilin dolum faktörünü artırdığı gözlemlenmiştir. Aktif tabakanın havada kaplanması sonucunda tabakanın kısa sürede bozunmaya uğradığı absorbans analizleriyle belirlenmiştir.Öğe Drilling performance of functionally graded composite: Comparison with glass and carbon/epoxy composites(KOREAN SOC MECHANICAL ENGINEERS, 2017) Koklu, Ugur; Demir, Okan; Avci, Ahmet; Etyemez, AyhanFunctionally graded composite (FGC) materials are categorized as advanced materials that display different thermal and mechanical responses compared with well-known composites, such as carbon fiber or glass fiber-reinforced composites. This paper presents the experimental results for the drilling of three materials, namely glass/epoxy, carbon/epoxy, and FGC material. FGC was compared with carbon and glass/epoxy composites in terms of thrust force, delamination factor, diameter of hole, and roundness during drilling. This study illustrated that the drilling performance of FGC is considerably more complicated than that of more common composite materials, such as glass/epoxy and carbon/epoxy. Delamination factor at the exit of hole during drilling of FGC was mainly affected by the material placed at the exit of the hole. The proposed cutting parameters and drill geometries to minimize the occurrence of delamination during drilling of carbon/epoxy and glass/epoxy apparently does not meet the expectation in drilling FGC.Öğe Effects of alumina nanoparticles on dynamic impact responses of carbon fiber reinforced epoxy matrix nanocomposites(ELSEVIER - DIVISION REED ELSEVIER INDIA PVT LTD, 2018) Kaybal, Halil B.; Ulus, Hasan; Demir, Okan; Sahin, Omer S.; Avci, AhmetThe influence of alumina (Al2O3) nanoparticles addition upon low-velocity impact behaviors of carbon fiber (CF) reinforced laminated epoxy nanocomposites have been investigated. For this purpose, different amounts of Al2O3 nanoparticles ranging from 1 to 5 wt% were added to the epoxy resin in order to observe the effect of nanoparticle loadings. CF reinforced epoxy based laminated nanocomposites were produced using Vacuum Assisted Resin Infusion Method (VARIM). The low velocity impact (LVI) tests performed according to the ASTM-D-7136 standard under 2, 2.5 and 3 m/s impact velocities. After LVI testing, the damage formations within composites were examined by using scanning electron microscopy (SEM). The results of this study showed that addition of Al2O3 nanoparticles provided a significant improvement in impact damage resistance. The highest damage resistance and minimum energy absorption were observed for 2 wt% Al2O3 nanoparticles loadings. As a result, we can confidently claim that the addition of the Al2O3 nanoparticles in CF/epoxy composites has considerably affected the dynamic response of the nanocomposites. (C) 2018 Karabuk University. Publishing services by Elsevier B.V.Öğe Enhancing the Efficiency of Air-processed Organic Solar Cells by Pristine MWCNT Incorporation into the Active Layer(Selçuk Üniversitesi, 2014) Demir, Okan; Yar, Adem; Avci, AhmetOrganic solar cells (OSCs) with P3HT:PCBM active layer and 0.05% wt. MWCNT introduced P3HT:PCBM active layer were produced in ambient air atmosphere and the effect of MWCNT addition on the cell performance was investigated. We report open circuit voltage, short-circuit current density, power conversion efficiency, and fill factor of 0.5 V, 1.178 mA/cm2, 0.69, 0.293 respectively. Reference cells without MWCNTs exhibited lower performance. MWCNTs seem to be a low cost and promising candidate for the improvement of OSCs performance.Öğe Evaluating the effectiveness of nanofillers in filament wound carbon/epoxy multiscale composite pipes(ELSEVIER SCI LTD, 2016) Üstün, Tugay; Ulus, Hasan; Karabulut, Salim Egemen; Eskizeybek, Volkan; Şahin, Ömer Sinan; Avcı, Ahmet; Demir, OkanThe performance of filament wound (FW) composite pipes is considered to be fundamentally governed by fiber properties and winding angles; however, matrix dominated properties such as axial and hoop strengths are also responsible in design of FW composite pipes. This paper presents the experimental results of a project aiming to assess the benefits of addition of carbon nanotubes (CNTs) and/or boron nitride nanoplates (BNNPs) as nanofillers within epoxy matrix of FW carbon fiber composite pipes. The nanofillers enhance the burst and hoop strengths up to 17.0% and 31.7%, respectively, over the control samples. Failure analysis revealed that the morphologies of nanofillers play an important role on the matrix toughening and strengthening the fiber matrix interface. Highest mechanical performance of the multiscale composite pipes was obtained with the addition of CNTs and BNNPs within the epoxy matrix concurrently related with the synergetic effect of the two different nanofillers. (C) 2016 Elsevier Ltd. All rights reserved.Öğe Synthesis and characterization of cadmium hydroxide nanowires by arc discharge method in de-ionized water(SPRINGER, 2011) Eskizeybek, Volkan; Demir, Okan; Avci, Ahmet; Chhowalla, ManishIn this study, Cd(OH)(2) nanowires have been synthesized by using arc discharge method in de-ionized water. The morphology and properties of the Cd(OH)(2) nanowires were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy, transmission electron microscopy (TEM), and UV-Vis spectroscopy. TEM observations revealed that Cd(OH)(2) nanowires were abundant morphology in synthesized nanostructures, and the diameter of the Cd(OH)(2) nanowires ranges from 5 to 40 nm with several micrometers of length. In addition, the width of nanowires is not uniform and varies throughout the nanowire. XRD analysis revealed that the Cd(OH)(2) nanowires grow along [001] direction. Furthermore, hexagonal- and irregular-shaped Cd(OH)(2) nanoplates were synthesized during arc discharge. It was obtained that required arc current is 50 A for the effective and large scale production of Cd(OH)(2) nanowires. Furthermore, the optical properties of the nanowires have been characterized by UV-Vis spectra. By the means of the optical studies, the direct band gap of Cd(OH)(2) nanowires was found to be 4.0 eV with strong quantum size effect. It is also shown that a simple and cheap method which does not require relatively expensive vacuum and laser equipment stipulates an economical alternative for the synthesis of Cd(OH)(2) nanowires.
