Figure 3. Scanning electron micrographs of the graphitic carbon nanofibers that represent a class of nanostructured carbon fibers having atomic structures uniquely different from that of carbon nanotubes.
The scanning electron micrographs are illustrated in Figure 4 for the catalytically-grown multi-walled carbon nanotube-reinforced epoxy composite. 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. Carbon nanotubes exist in a variety of forms and have been prepared through the catalytic decomposition of various carbon-containing gases at metal surfaces [51, 52]. Such vermicular carbon deposits have been observed almost since the advent of electron microscopy [53, 54]. Carbon nanotubes are known to have extraordinary tensile strength, including high strain to failure and relatively high tensile modulus [55, 56]. Carbon nanotubes may also be highly resistant to fatigue, radiation damage, and heat [57, 58]. To this end, the addition of carbon nanotubes to composites can increase tensile strength and stiffness. Unfortunately, adding even a small amount of carbon nanotubes to, for instance, a resin matrix to subsequently generate the desired composite can increase the viscosity of the matrix significantly. Moreover, continuous carbon nanotubes are not yet readily available, so as to permit the creation of a substantially continuous carbon nanotube composite, or a substantially continuous composite reinforced with the continuous carbon nanotubes. The availability of either or both composites can allow for a variety of interesting commercial applications. Accordingly, it would be advantageous to provide a substantially continuous composite material reinforced with substantially continuous carbon nanotubes, such that the composite material can be provided with a low density while having high modulus and strength. In addition, it would be advantageous to provide a method for manufacturing such composite materials.