Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis The Effects of Oxidizers on the Diameters of the Carbon Naotubes Grown by Chemical Vapor Deposition Method(Izmir Institute of Technology, 2012) Bülbül, Gülay; Selamet, YusufThis thesis was focused on growing high quality and small-diameter carbon (C) nanotube (NT) on Fe/Al2O3/SiO2/Si thin film catalyst by ethylene decomposition thermal chemical vapor deposition (CVD) method in the presence of a weak oxidizer (CO2). Moreover, the importance and functional properties of the oxidizer in pretreatment and CNT growth were determined. At first, it was worked in different growth conditions to examine the effects of CO2 in CNT growth. The main parameters were pretreatment time, CO2 gas flow rates during pretreatment and growth, growth temperature. Pretreatment and growth times were kept at 15 min. each and CO2 introduced 5 and 10 min. during pretreatment stage prior to the CNT growth with the flow rates 8:2, 10:2, 10:8 and 10:10 sccm, respectively. Additionally, three different growth temperatures; 750 oC, 760 oC and 770 oC were studied. Secondly, pretreatment time was kept at 15 min. The effects of CO2, which was sent in the system at 8:2, 10:2, 10:8 and 10:10 sccm ratios, on density and height of the catalyst particles were investigated. At last, all catalyst particles and CNTs obtained from the experiments were analyzed by several characterization techniques such as AFM, EDX, SEM, STEM and Raman Spectroscopy, respectively. The optimal values of amount and introduction time of CO2, the ratio of CO2 in growth to that in pretreatment were identified. Moreover, the relation between currently obtained catalyst particles and previously being grown CNTs on them were determined. It was observed that using the appropriate amount of CO2 in pretreatment and growth process positively affected the catalyst sizes and CNT diameter distributions.Master Thesis Optimization of Carbon Nanotube Properties by Controlled Amount Oxidizers(Izmir Institute of Technology, 2011) Söylev, Deniz; Selamet, YusufFinally, all data were subjected through a statistical analysis. From this study we have seen that the majority of the samples had Log-Normal diameter distributions by adjusting oxidizer amount and pretreatment timing. We were able to control CNT diameters within very narrow diameter ranges.This thesis work focuses on growing high quality carbon nanotubes using ethylene as hydrocarbon gas in thermal chemical vapor deposition method in presence of weak oxidizers. We carried out experiments to study the ratio of amount of CO2, O2 and H2O in pretreatment to growth and the timing of the metal-oxide to metal conversion in presence of the oxidizers.Firstly, the effects of CO2 addition were investigated on a variety of growth conditions to study the controlled diameter growth of CNTs. The main growth parameters controlled in this work in the CNT growth were CO2 level, pretreatment time and temperature. Pretreatment times of 15, 10, 5, 2 minutes were studied. CO2 flow rates were send in system during both pretreatment time and growth time at 10:1, 10:2, 5:1, 5:2, 2:1 and 2:2 sccm ratios, respectively. We also studied two different growth temperatures at 740 oC and 760 oC.Secondly, the influence of O2 for effective CNT growth was investigated by utilizing different pretreatment times and O2 levels. Pretreatment times of 15, 10, 5, 2 minutes were studied. O2 gas flow rates during pretreatment time and growth time were studied as 5:1, 5:2, 2:2, 2:1, 2:0.5, respectively. As a result, we obtained small diameters with the pretreatment time of 15 min. in the presence of O2.Thirdly, the effects of H2O vapor for effective CNT growth on Fe/Al2O3/SiO2 were examined. During the experiments, pretreatment time was kept at a constant value of 15 min. and H2O vapor content in Ar was varied. The results of examined analyses show that the best results were obtained at the growth 60 o C (A) / 60 o C (A).