The influences of synthesis temperature and Ni catalyst on the growth of carbon nanotubes by chemical vapor deposition

Multi-walled carbon nanotubes (CNTs), which are with the diameter from 15 to 50 nm and length from several microns to several tens of microns, were synthesized over Ni/Al composite catalyst by CVD of methane at the temperature range of 723 K-923 K. The Ni content in the Ni/Al composite catalyst varied from 5 wt.% to 15 wt.%. As the synthesis temperature increased from 723 K to 923 K and the nickel content increased from 5 wt.% to 15 wt.%, the CNT yield increased by about 17 times. The purity of CNTs decreased and the diameter of CNTs increased with the increase of Ni content in the catalyst. The relative amount of crystalline graphite sheets increased progressively with the growth temperature and a higher degree of crystalline perfection could be achieved at 923 K. These results demonstrated that the growth rate, diameter, and crystallinity of CNTs can be controlled by varying the synthesis temperature and catalyst composition.