A treatment method to give separated multi - walled carbon nanotubes with high purity , high crystallization and a large aspect ratio

CNT agglomerates, prepared by catalytic chemical vapor deposition in a nano-agglomerate fluidized-bed reactor are separated and dispersed. The effects of shearing, ball milling, and ultrasonic and chemical treatments on the dispersing of the carbon nanotubes were studied using SEM, TEM/HRTEM and a Malvern particle size analyser. The resulting microstructures of the agglomerates and the efficiency of the different dispersion methods are discussed. Representative results of annealed CNTs are highlighted. The as-prepared CNT product exists as loose multi-agglomerates, which can be separated by physical methods. Although a concentrated H SO /HNO (v/v53:1) treatment is efficient in severing entangled nanotubes 2 4 3 to enable their dispersion as individuals, damage to the tube-wall layers is serious and unavoidable. A high temperature annealing (2000 8C, 5 h) before the acid treatment (140 8C, 0.5 h) is recommended and can give well separated nanotubes with a high aspect ratio and 99.9% purity. These highly dispersed CNTs contain few impurities and minimal defects in their tube-bodies and will be of use in further research and applications.  2003 Published by Elsevier Ltd.