Effect of planetary ball milling process parameters on the nitrogen adsorption properties of multiwall carbon nanotubes

The dependence of multiwall carbon nanotube (MWCNT) length distribution and some nitrogen derived morphological descriptors on various planetary ball milling process parameters was investigated. Ball milling was found to cut nanotubes into smaller pieces, narrow their length distribution and increase their specific surface area and surface fractal dimension. Typical length reduction was from 1300 to 200 nm, specific surface area increase from 160 to 340 m²g⁻¹ and surface fractal dimension increase from 2.47 to 2.70. The pore size distribution of pristine MWCNTs exhibited a mesoporous character dominated by intertube channels. A sharp maximum appeared at d = 3.6 nm diameter when the milling power was increased. This increase was attributed to the opening of intratube voids. Processes involving graphitic platelet detachment, tube wall amorphization or carbonaceous debris accumulation appear to play only minor roles under the studied experimental conditions of planetary milling. Control over the morphology of the milled material is best achieved by varying the diameter and the mass ratio of the grinding balls as well as the classical process parameters like disk rotational speed, milling time and number of balls.