Thermal annealing effects on structure and morphology of micrometer-sized carbon tubes

Micrometer-sized carbon tubes can be conveniently prepared via a new chemic al approach by pyrolyzing the composite fibers consisting of a polypyrrole skin layer and a PET core fiber at 1000 degreesC under a N-2 atmosphere. Th e resultant carbon tubes were found to be amorphous carbon. After further a nnealing at 1000-2400 degreesC, the carbon tube structure was found, on the basis of XRD, Raman, and TEM studies, to change gradually from a disordere d amorphous phase to a highly ordered graphitic phase with preferred orient ation. As the annealing temperature increased from 1000 to 2400 degreesC, t he graphitic crystallites of carbon tubes not only increased their sizes co nsiderably but also tilted their stacking planes gradually toward the tube axis. Both SEM and SAD results implied that the 2400 C annealed sample may have a cylindrical layer-stacking structure similar to those of carbon nano tubes. Accompanying these enhancements of structural ordering and orientati onal preference of the graphitic planes, the conductivity along the tube ax is of the corresponding carbon tubes was also found to increase significant ly.