Effect of ball milling in a tumbling ball mill on the properties of multi-wall carbon nanotubes

The effects of ball milling on various properties of ground multi-wall carbon nanotubes were studied. These properties were granulometry, SEM, specific surface area, density, crystalline structure, surface chemical analysis and thermogravimetry. The mean size of agglomerates, initially at 35 mu m, decreases to reach a limit value of 2.5 mu m, corresponding to a competition between agglomeration and fragmentation. A kinetic study, based on a decomposition of size distributions measured for different times, has permitted to propose a grinding mechanism. As grinding proceeds, the specific surface area first increases from 175 to 244 m(2) g(-1) and then decreases, while the real density increases from 1800 to 2150 kg m(-3) to level off at 2070 kg m(-3). Moreover, macroporosity disappears totally, giving access first to mesoporosity and then to microporosity. The nanotubes are probably cut to give access to the internal porosity. An increase of the proportion of oxygen adsorbed on carbon (from 3% to 8.7% after 600 min grinding) implies that it may be possible to functionalise the nanotubes. Thanks to these different morphological changes numerous applications of ground nanotubes can be considered. Moreover, the use of a tumbling ball mill allows a massive production of cut nanotubes. (c) 2007 Elsevier B.V. All rights reserved.