Physics / Fizik

Permanent URI for this collectionhttps://hdl.handle.net/11147/6

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Scopus Q: search.filters.scopusQuartile.Q2Subject: search.filters.subject.Carbon nanotubes

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  • Article
    Citation - WoS: 28
    Citation - Scopus: 31
    The Effects of Catalyst Pretreatment, Growth Atmosphere and Temperature on Carbon Nanotube Synthesis Using Co-mo/Mgo Catalyst
    (Elsevier Ltd., 2015) İnce Yardımcı, Atike; Yılmaz, Selahattin; Selamet, Yusuf
    The growth of high quality and high yield carbon nanotubes (CNTs) by catalytic chemical vapor deposition (CVD) of CH4 over Co-Mo/MgO catalyst was investigated for different growth temperatures and H2 flow rates. It was observed that CNT yield decreased with the H2 flow rate, however, quality increased with increasing H2 flow rate. CNT yield increased for the temperatures 850-950 °C but dropped significantly above 950 °C. In this study, the highest yield of 1526% was obtained at the growth temperature of 950 °C. The optimum H2 flow rate was 200 sccm; this rate gave both high graphitization and high yield of product. Various CNT growth atmospheres including Ar, H2 and the mixture of both gases were also analyzed and it was observed that the highest quality CNTs were obtained for both pretreatment and growth carried out with H2. This gave a high yield of 292%. On the other hand, CNT growth carried out under Ar atmosphere gave higher CNT yield of 368%, however, the CNTs grown with Ar were more defective and had larger diameters. Prime novelty statement We demonstrate a sorbitol added catalysis synthesis method and importance of the ideal growth conditions to improve high quality single walled carbon nanotube yield up to 1500%.
  • Article
    Citation - WoS: 10
    Citation - Scopus: 10
    Carbon Nanotube Diameter Tuning Using Hydrogen Amount and Temperature on Sio2/Si Substrates
    (Springer Verlag, 2010) Aksak, Meral; Selamet, Yusuf
    Carbon nanotubes (CNTs) were grown on thin iron (Fe) films on SiO 2/Si substrates by chemical vapor deposition (CVD) at four different hydrogen (H2)/methane (CH4) ratios at temperatures ranging from 925 to 1000°C. The effects of temperature and the amount of hydrogen gas on the mean diameter at increasing temperature were examined. We demonstrated that the mean diameter and its distribution depend not only on temperature but also on the H2 amount. We showed that increasing H2 amount strongly affects the structure of CNTs, especially at high growth temperature; the mean diameter at 1000°C reduced from about 383 to 34 nm by increasing H2 amount from 24 to 50 sccm. We observed that at high temperature growth the mean diameter was decreasing very fast initially with increasing H2 amount suggesting the dominance of H2 over the growth temperature. A decrease in the slope of diameter vs. H 2 amount with further increment in H2 amount implied that the temperature was, then, deciding the CNT diameter through catalyst particle coarsening. The statistical analysis presented implies that the H2 amount has to be adjusted according to the growth temperature for given CH 4 amount to keep CNT diameter under control, and the large diameter distributions at high temperature and high H2 amount can be associated with the large variation in the catalyst particle sizes. © 2010 Springer-Verlag.