Page 20 - Carbon Nanotube Fibres and Yarns

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CHAPTER 2

Yarn production from carbon

nanotube forests

Menghe Miao
CSIRO Manufacturing, Geelong, VIC, Australia

2.1 Synthesis of vertically aligned CNT arrays
The synthesis of aligned carbon nanotube (CNT) arrays on a substrate of
mesoporous silica containing iron oxide nanoparticles using the chemi-
cal vapor deposition (CVD) method was first reported in the mid-1990s.
Li et al. [1] reported that a mixture of 9% acetylene in nitrogen was intro-
3
duced into the synthesis chamber at a flow rate of 110 cm /min. The CNTs
were formed on the substrate by the deposition of carbon atoms obtained
by the decomposition of acetylene at 700°C. Ren et al. [2] reported the
growth of CNT arrays on nickel-coated glass at temperatures below 666°C
by plasma-enhanced hot filament CVD. Acetylene gas was used as the car-
bon source and ammonia gas was used as a catalyst and dilution gas.
Fan et al. [3] described the production of self-orientated CNT arrays on
porous and plain silicon substrates. Silicon substrates were deposited with
Fe films (5 nm thick) by electron beam evaporation and then annealed in air
at 300°C overnight to oxidize the surface of the silicon and the iron. The
substrate was placed in a cylindrical quartz boat sealed at one end and then
inserted into the center of a quartz tube reactor housed in a tube furnace.
The furnace was heated to 700°C in flowing Argon. Ethylene was then
flown at 1000 sccm for 15–60 min, after which the furnace was cooled to
room temperature. During the initial stage of CVD, ethylene molecules
are catalytically decomposed on the iron oxide nanoparticles. As supersat-
uration occurs, a nanotube grows off each of the densely packed catalyst
particles (average diameter 16 nm) and extends to open space along the di-
rection normal to the substrate. As the nanotubes lengthen, their outermost
walls interact with those of neighboring nanotubes via van der Waals forces
to form a large bundle with sufficient rigidity. This rigidity enables nano-
tubes to keep growing along the original direction. Many research groups
around the world have since investigated methods to fabricate CNT forests

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