High efficiency synthesis of ultralong multi-walled carbon nanotubes forest and its electro-mechanical behavior under torsion
Date Issued
2009
Date
2009
Author(s)
Wu, Tsung-Cho
Abstract
This dissertation reports on the effect factors during synthesis of multi-walled carbon nanotubes (MW-CNTs) forest. Utilizing this novel method to synthesize high aspect ratio carbon nanotubes forest, electro-mechanical behaviors when a torque is applied were reported and discussed. A self-assembled apparatus with three individually controlled heating zones constitute a three-zone temperature chemical vapor deposition (TZT-CVD) system. Catalyst film was deposited by electron beam evaporator and temperature difference was fixed in the TZT-CVD furnace. By controlling the catalyst film thickness, carbon source (ethylene) flow rate and synthesis time, ultralong MW-CNTs forest can be obtained. The results reveal that the effect of temperature difference in the TZT-CVD is to sustain the lifetime of the catalyst and hence increase the growth efficiency. By optimizing the growth variables, TZT-CVD produced MW-CNTs forest with a height up to 4.27 mm in 60 min. Compare with other references objectively, the CNT synthesis ratio, an ultimate figure of merit, is 712 times and the carbon source consumption is 4 % compared to that of single-zone temperature CVD. The position and shape was first defined by photolithography on silicon oxide substrate. High aspect ratio CNT turfs can be successfully obtained by a TZT-CVD. A special apparatus was designed to apply a torque to the cylindrical CNT turfs. The apparatus allows simultaneously measuring the electrical resistance and the corresponding torsional angle of the turf. Applied torque will lead to wrinkles on the exterior of CNT turfs. The electrical resistance will rise with the increasing shear strain and will rise suddenly at torsion angle of 80?. It indicates that the structure of CNT turf can sustain large shear strain and go through shear strain, slightly rupture and large break during the torsional process. The critical buckling angle always occurred after the angle at the resistance change rate is over 5 %. From the resistance change rate, the buckling time, critical buckling torque, and critical buckling angle can be forecast. Compared with individual carbon nanotube, the CNT turf possesses relatively low critical shear strength of several MPa only.
Subjects
carbon nanotube forests (or turf)
chemical vapor deposition (CVD)
growth efficiency
torsion
mechanical properties
electrical resistivity
critical shear strength
buckle
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-98-D93522030-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):888649bc28b0f04033f740d4b0fca4f0