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water-assisted pre-deposited catalyst CNTs synthesized via our method are
predominantly DWNTs and FWNTs, whereas the vapor-phase CVD growth largely
results in MWNTs which have much larger diameters (up to 100+ nm). For
composite applications, the percent crystallinity is not as great of a concern when
working with MWNTs, as a defective surface may allow for a greater interaction
with the matrix through surface roughness or perhaps covalent interaction (via any
dangling bonds on the CNT surface). Moreover, the multiple layer structure of
MWNTs already improves their mechanical strength as compared to lesser-walled
CNTs.
2.2.2. Construction of a Vapor-Phase A-CNT Growth Furnace
As with a pre-deposited catalyst CVD system, a stable, high-temperature
growth region is necessary for vapor-phase CVD. For the purposes of this work, a
Lindberg/Blue M 55347 three-zone tube furnace was used to ensure the longest
growth zone. The benefit of a three-zone furnace lies in the ability to extend the
length of the central zone to prevent temperature drops on the ends of the center
zone. By increasing the temperature on the end zones by 5-10 oC as compared to
the central zone, the width of the isothermal central zone is extended, ensuring the
longest-possible region for consistent CNT growth. For the growth runs executed
for this work, the end zones were heated 8 0C higher than the center zone and the
furnace is 35” in-length, allowing for a very large zone for CNT synthesis. This
furnace can accommodate a 3" processing tube, and custom 8’ quartz tubes were