High efficiency three-temperature segment-CVD synthesis of multi-wall carbon nanotube forests

A high efficiency and well-controlled method to synthesize multi-wall carbon nanotube (MW-CNT) forests is reported. The three-temperature segment chemical vapor deposition (TTS CVD) system contains three individually operated heaters distributed along one quartz tube in CVD that provides controllable temperature gradient in quartz tube. The developed temperature gradient in TTS CVD significantly elongates lifetime of catalyst's actiity and further increase the growth efficiency using ethylene. By optimizing chemical compositions, catalyst film thickness, synthesis time, ethylene flow rate and temperature gradient, TTS CVD produced large scale and well-aligned MWNTs with height up to 2.3 millimeters in 45 minutes. The consumed ethylene was only one-fourth of regular dosages. The ultimate figure of merit is the specific CNT height that was defined as the grown CNT height divided by the product of the ethylene flow rate and the synthesis time. Our experimental results show the specific CNT growth height is 4 times of the published results. Most importantly, this technique sustained life time of catalyst's activity and revealed the possible mechanism for growth of ultra-long CNTs.