Browsing by Subject "Fizikokimya"

Now showing 1 - 6 of 6
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    Free energies and specific heats of the nematics within nonextensive thermostatistics
    (2005) O. KAYACAN; O. AFSAR
    In this study, the free energies and specific heats of the nematic liquid crystals are studied within Tsallis thermostatistics. In equilibrium, free energy of PAA (para-azoxyanisole) vs the order parameter is plotted, as well as its the specific heat vs temperature. The effect of the nonextensivity is illustrated for some values of the entropic index q.
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    Electrocatalytic oxidation of methanol at Pd and Pt ad-layer modified Au(111) electrodes in alkaline solution
    (2011) Fatma Nil Ertaş; Suleyman Kocak; Zekerya DURSUN
    The electrochemical oxidation of methanol was investigated by using various ad-layer modified Au(111) electrodes in alkaline media in comparison to Au(111), polycrystalline Pd, and polycrystalline Pt electrodes. Catalytic activity of gold toward methanol oxidation has tended to increase in more alkaline media, as reflected in the oxidation peak in the concentration range of NaOH (0.1-3.0 M) studied here. The oxidation peak potential of methanol shifted to more negative potentials, indicating a pH-dependent surface reaction. Among the electrodes studied, single-crystal gold electrode surfaces modified with Pd and Pt ad-layers displayed the highest catalytic activity for methanol oxidation. Additional shifts of about 350 mV in the oxidation peak potential of methanol was observed for both ad-layer modified electrodes to more negative potentials compared to that of bare electrodes. The Pd and Pt ad-layer modified Au(111) electrode surfaces did not only supply a superior electrical contact, but also accelerated electron transfer, as shown by the increase in peak current and the positive shift in peak potential. This effect was supported by the doublelayer capacitance measurements of bare Au(111) and Pd ad-layer modified singlecrystal electrodes where the potential of zero charge changed from 15 to 5 mV.
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    NUMERICAL STUDY OF HEAT TRANSFER DUE TO TWINJETS IMPINGEMENT ONTO AN ISOTHERMAL MOVING PLATE
    (2013) Fatih SELİMEFENDİGİL; ANIL BASARAN
    In this study, heat transfer from a moving isothermal hot plate due to double impinging vertical slot jets was investigated for a laminar flow. The rectangular geometry consists of a confining adiabatic wall placed parallel to the moving impingement. The jets are located symmetrically at mid point of upper wall. Water and Al2O3 nanoparticles mixture with different volumetric fraction was used as working medium. In considered jet impingement problem, the effects of the jet exit Reynolds numbers, ranging from 50 to 200, the normalized plate velocity, ranging from 0 to 2, and volumetric fractions of nanofluid, ranging from 0% to 6% were investigated. The commercial software package based on finite volume method FLUENT (version 6.3.26) is used in this study for the computations. It has been observed that increasing normalized plate velocity increases the heat transfer from bottom surface. Similarly, increasing Reynolds number of slot jets leads to enhancement of heat transfer. Besides, increasing volumetric fraction of nanofluid conributes to heat transfer enhancement.
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    NUMERICAL INVESTIGATION OF IMPINGING JETS WITH NANOFLUIDS ON A MOVING PLATE
    (2013) Fatih SELİMEFENDİGİL; ERDEM ERSAYIN
    In this study a numerical investigation of an impinging jet flow, on a heated moving plate, is presented. The purpose of this study is to numerically investigate the effects of various parameters such as nanoparticle volume fraction, pulsating frequency, plate velocity, Reynolds number on the heat transfer characteristics. Navier-Stokes equations and energy equations are solved with a commercial finite volume based code. It is observed that adding nanoparticles increases the peak value of Nusselt number. It is also observed that the value of Nusselt number at the stagnation point is higher at the low velocities of impingement surface. In the unsteady case, heat transfer enhancement is seen at low frequencies.
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    2-klorokinolinin Moleküler ve Spektroskopik Özelliklerinin Kuantum Kimyasal Hesaplama Yöntemleriyle Araştırılması
    (2024) FEHMI BARDAK; Etem Kose
    Mevcut çalışma, kinolin türevlerinin aktif madde olma potansiyeli ve reaktivitesi üzerindeki klor ikame etkisini ortaya çıkarmak için 2-klorokinolin molekülünün temel moleküler özelliklerinin araştırılmasıyla ilgilidir. Buna göre FT-IR, FT-Raman, 1H ve 13C NMR spektrumlarından elde edilen deneysel sonuçlarla ve kuantum kimyasal hesaplamalarla desteklenen 2-klorokinolin için spektroskopik bir araştırmayı içermektedir. Molekülün optimize edilmiş yapısı ve enerji parametreleri, yoğunluk fonksiyonel teorisi B3LYP yöntemi 6-311++G(d,p) temel seti kullanılarak elde edildi. Molekülün titreşim özellikleri, titreşim enerji dağılımı analizi yoluyla ve moleküler modelleme yoluyla elde edilen simüle edilmiş spektrumlara uygun olarak elde edildi. Atomik Orbitalleri İçeren Gauge Yaklaşımı yöntemiyle tahmin edilen 1H ve 13C NMR kimyasal kayma özellikleri deneysel verilerle karşılaştırıldı. Ayrıca bileşiğin moleküler elektrostatik potansiyel yüzey özellikleri, atomik kısmi yükler, elektronik yörüngeler ve olası elektronik geçişler sunuldu. Klor ikamesinin 2-klorokinolin molekülünün temel özellikleri üzerinde önemli etkileri olduğu ve kimyasal reaktivitesini önemli ölçüde arttırdığı gösterilmiştir.
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    The Role of Water on the Oxidation Process of Graphene Oxide Structures
    (2024) Kürşat KANBUR; Işıl Birlik; FATİH SARGIN; N. Funda AK AZEM; N. Funda AK AZEM; Ahmet TÜRK
    Graphene oxide (GO) has recently attracted attention with its unique chemical and physical properties and serves as a raw material for graphene-based materials. GO has been produced for decades by the Hummers Method with the oxidation process of graphite. The properties and structure of GO are significantly affected by the production parameters of Hummers Method. In this study, the effect of the water content on the oxidation level of GO structure was investigated. GO was produced with different amounts of water in the oxidation stage of Hummers Method. The structural characterizations of produced GO were carried out by X-ray Diffraction Technique (XRD), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Energy Dispersive X-ray Spectroscopy (EDS), UV-Visible Spectroscopy (UV-Vis) and Raman Spectroscopy. Additionally, morphological and thermal characterization of the produced GO samples were performed by Scanning Electron Microscopy (SEM) and Thermogravimetric Analysis (TGA)/Differential Thermal Analysis (DTA), respectively. According to XRD, FTIR, XPS, and EDS results, it was determined that the oxidation degree of GO decreased with increasing amount of water. Besides, it was revealed that the post-oxidation step generated more defects in the basal plane of graphene according to the results of the Raman Analysis. Also, it was observed that GO had a smoother surface and was found to have higher thermal stability with increasing amounts of water. The results show that the post-oxidation step reduces the oxidation degree of GO, increases the amount of the defect, provides a less wrinkled structure, and improves the thermal stability of GO.