Biomedical Engineering Reference
In-Depth Information
7.1
MWCNTs grown in a CVD process by injecting ferrocene and
toluene in a horizontal tube furnace.
metal supports such as MgO, CaCO 3 ,Al 2 O 3 or Si are used. Higher yields
can be achieved by using a mixture of two catalytic metal particles (Seraphin
and Zhou, 1994, Seraphin et al., 1994). Metallic catalysts can be pre-
deposited as particles or films on a ceramic substrate or injected as colloids
or organometallic vapor along the carbon feedstock. The diameter of the
resulting CNTs roughly matches that of the catalyst particle while lengths
up to millimeters can be obtained with increasing synthesis time (Pan et al.,
1998). CNTs grow by two different methods: (a) tip growth and (b) base or
root growth. A weak interaction between metal and substrate allows the
growth of CNTs by the tip growth mechanism while a strong interaction
favors base growth (Dervishi et al., 2009). Both horizontal and vertical
furnaces are used as reaction chambers; the former is more common in a
laboratory setup and allows control of the CNTs length by controlling
hydrocarbon deposition time, whereas the latter is more often used for
continuous mass production of CNTs (Teo et al., 2003). Figure 7.1 shows an
image of relatively aligned MWCNTs produced by CVD process by
injecting ferrocene and toluene into a horizontal furnace (Subhani et al.,
2011).
The advantages of the CVD-based fabrication route include large-scale
￿ ￿ ￿ ￿ ￿ ￿
Search WWH ::




Custom Search