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.