Length and the oxidation kinetics of chemical-vapor-deposition-generated multiwalled carbon nanotubes

Oxidation rates are measured and kinetic parameters determined by isothermal analysis for several length ranges of as-grown and processed chemical-vapor-deposition-generated multiwalled carbon nanotubes within a range of 700-900 K. The activation energy barrier is found to be within the range calculated previously by others and follows comparable progression patterns for similar length tubes. The activation energy and frequency factor are not observed to change with the synthesis method, but do increase gradually as oxidation progresses in longer nanotube arrays or peak and decline in shorter arrays. The results also confirm that the oxidation of carbon nanotubes need not originate in the nanotube caps, but may originate in other areas of increased reactivity, such as wall defects. The behavior of the kinetic parameters as oxidation progresses is indicative of the consumption of defective structures followed by the coalescence of etched holes, suggesting lower defect densities in longer carbon nanotubes.