3. Results and discussion
The scanning electron micrographs of the multi-walled carbon nanotubes
are illustrated in Figure 1 for the preparation of epoxy matrix
composite materials. Carbon nanotubes differ physically and chemically
from continuous carbon fibers which are commercially available as
reinforcement materials, and from other forms of carbon such as standard
graphite and carbon black. Standard graphite, because of its structure,
can undergo oxidation to almost complete saturation. Moreover, carbon
black is amorphous carbon generally in the form of spheroidal particles
having a graphene structure, carbon layers around a disordered nucleus.
The differences make graphite and carbon black poor predictors of carbon
nanotube chemistry. The morphology of the aggregate is controlled by the
choice of catalyst support. Spherical supports grow multi-walled carbon
nanotubes in all directions leading to the formation of bird nest
aggregates. Combed yarn and open nest aggregates are prepared using
supports having one or more readily cleavable planar surfaces. Single
walled carbon nanotubes typically have smaller diameter than most multi
walled carbon nanotubes. Thus, structures created from single walled
carbon nanotubes will have significantly greater specific surface area
and lower density than structures created from multi-walled carbon
nanotubes. Surface area can be a critical performance parameter for many
applications that use carbon nanotubes structures.