Above a critical diameter, single- or few-walled carbon nanotubes spontaneously collapse as flattened carbon nanotubes. Raman spectra of isolated flattened and cylindrical carbon nanotubes have been recorded. The collapse provokes an intense and narrow D band, despite the absence of any lattice disorder. The curvature change near the edge cavities activates a D band, despite framework continuity. Theoretical calculations based on Placzek approximation fully corroborate this experimental finding. Usually used as a tool to quantify defect density in graphenic structures, the D band cannot be used as such in the presence of a graphene fold. This conclusion should serve as a basis to revisit materials comprising structural distortion where poor carbon organization was concluded on a Raman basis. Our finding also emphasizes the different visions of a defect between chemists and physicists, a possible source of confusion for researchers working in nanotechnologies.

No abstract

Kinetic data, for example,a ctivation energy and reaction order,a re crucial for the understanding of chemical reactions and processes.Here,wedescribe anovel method for obtaining kinetic data based on thermogravimetric measurements (TGA) that exploits in each measurement multiple successive isothermal steps (SIS). We applied this method to the notoriously challenging carbon combustion process for vastly different carbons for oxygen molar fractions between 1.4 %a nd 90 %. Our obtained apparent E A values are within the wide range of results in the literature and vary in as ystematic way with the oxygen partial pressure.T he improved accuracy and large amount of obtainable data allowed us to show that the majority of experimentally obtained apparent data for apparent E A are neither in akinetic regime nor in ad iffusion-controlled one but rather in atransition regime.