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Matsumoto N.,Technology Research Association for Single Wall Carbon Nanotubes TASC Central | Oshima A.,Technology Research Association for Single Wall Carbon Nanotubes TASC Central | Yumura M.,Technology Research Association for Single Wall Carbon Nanotubes TASC Central | Yumura M.,Japan National Institute of Advanced Industrial Science and Technology | And 4 more authors.
Nanoscale | Year: 2015

By applying electrical current with heat, we succeeded in improving the graphitization of single walled carbon nanotubes (SWCNTs) without increasing the diameter and wall number. At 800 °C, 150 A cm-2 (1150 W cm-2) for 1 min, we achieved a 3.2-times increase in the Raman G- to D-band ratio, a 3.1-times increase in electrical conductivity (from 25.2 to 78.1 S cm-1), a 3.7-times increase in thermal conductivity (from 3.5 to 12.8 W m-1 K-1), and even a 1.7-times increase in dispersibility (from 1.7 to 2.9 mg L-1). The electrical and thermal conductivities did not only increase simultaneously, but their relative increases were identical across our experimental range that stems from defect healing without any change in diameter and wall number. In contrast, a significant increase in diameter and wall number was observed when current was not applied. These results demonstrate the importance of applying current to improve the graphitization of SWCNTs while maintaining their structure as SWCNTs. This journal is © The Royal Society of Chemistry. Source


Chen G.,Technology Research Association for Single Wall Carbon Nanotubes TASC Central | Chen G.,Japan National Institute of Advanced Industrial Science and Technology | Davis R.C.,Brigham Young University | Kimura H.,Technology Research Association for Single Wall Carbon Nanotubes TASC Central | And 10 more authors.
Nanoscale | Year: 2015

We report an inverse relationship between the carbon nanotube (CNT) growth rate and the catalyst lifetime by investigating the dependence of growth kinetics for ∼330 CNT forests on the carbon feedstock, carbon concentration, and growth temperature. We found that the increased growth temperature led to increased CNT growth rate and shortened catalyst lifetime for all carbon feedstocks, following an inverse relationship of a fairly constant maximum height. For the increased carbon concentration, the carbon feedstocks fell into two groups where ethylene/butane showed an increased/decreased growth rate and a decreased/increased lifetime indicating different rate-limiting growth processes. In addition, this inverse relationship held true for different types of CNTs synthesized by various chemical vapor deposition techniques and continuously spanned a 1000-times range in both the growth rate and catalyst lifetime, indicating the generality and fundamental nature of this behavior originating from the growth mechanism of CNTs itself. These results suggest that it would be fundamentally difficult to achieve a fast growth with a long lifetime. This journal is © The Royal Society of Chemistry. Source

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