Points of onset of gasification in a multi-walled carbon nanotube having an imperfect structure

The points of onset of gasification were discussed in a multi-walled carbon nanotube which has an imperfect structure. A fixed point observation was conducted, where the same nanotubes were observed with a high-resolution transmission electron microscope before and after gasification by oxygen at 823 or 1023 K. At either temperature, the fixed point observation clearly visualized that carbon nanotubes had been markedly broken by gasification at some points along the cylindrical part, whereas most of the tips remained. This behavior contradicts the earlier beliefs that areas rich in topological defects in a carbon nanotube are more susceptible to gasification. Detailed observation revealed that cracks and amorphous carbons, i.e. structural defects, were originally present at the same points where the marked breakages were observed. These findings indicate that the gasification of a carbon nanotube probably occurs at the structural defects preferentially to the topological defects when it originally has the imperfect structure. Swelling of a nanotube was visible in the observation after the gasification at 823 K, whereas simultaneous gasification of multiple layers at 1023 K. These behaviors can also be ascribed to the preferential attack of oxygen to the structural defects.