An approach for obtaining the structural diversity of multi-walled carbon nanotubes on Ni/Al catalyst with low Ni content

A mass of multi-walled carbon nanotubes were fabricated on Ni/Al catalyst with low Ni content (2.5 wt.%) by chemical vapor deposition in the temperature range of 773-923 K and characterized with respect to their structure. The tubular and the bamboo-shaped structure occurred in the 773-873 K and 873-923 K temperature ranges, respectively. In order to figure out the reasons for the observed structural instabilities, the effects of reduction and reaction temperature on the catalyst particle sizes and the carbon nanotube dimensions (lengths and diameters) were investigated in detail using statistical measurements based on transmission electron microscope observations. The reduction and reaction temperatures have strong influences on the catalyst particle sizes and the carbon nanotube diameters. The influence of reaction temperatures on the carbon nanotube length is feeble. Furthermore, mechanisms of the structure formation are discussed as well as open questions are addressed.