The preparation and CVD densification of multi-walled carbon nanotube felt synthesized by a catalytic CVD method

Silica-nickel binary aerogels are used as catalysts for the synthesis of multi-walled carbon nanotube (MWCNT) felts. The MWCNT felts are prepared by the catalytic decomposition of methane at 680 degrees C over durations ranging from 30 to 120 min. After purification by a graphitization heat-treatment in argon, the MWCNT felts have a bulk density of about 0.4 g cm(-3). The graphitized MWCNT felts are densified in a CVD furnace under a mixed atmosphere of propene and nitrogen at 1000 degrees C. The morphology and the structure of the MWCNT felt and its CVD-densified product are investigated by SEM, TEM, XRD, and Raman spectroscopy. ne results reveal that the carbon nanotubes in the primary MWCNT felt have a diameter of between 15 and 40 nm, with a high aspect ratio. High-resolution TEM imaging reveals that the walls of the carbon nanotubes show little amorphous carbon covering. After the graphitization treatment, the surface of the carbon nanotubes becomes rough and some "stacked cups" and triangular structures are formed in the core of some of the nanotubes. The graphitization treatment effectively promotes crystal growth and layer orientation of the carbon nanotubes. This high temperature-treated MWCNT felt has a high purity and a low bulk density, as well as low thermal conductivity. Pyrolytic carbon formed by CVD is deposited in between carbon nanotubes and on the walls of the carbon nanotubes, leading to the densification of the MWCNT felt. The CVD-densified MWCNT felt has a higher bulk density and thermal conductivity than that of the corresponding high temperature-treated MWCNT felt. It is suggested that the MWCNT felt could be used as a precursor in the production of carbon nanotube/carbon or carbon nanotube/polymer composites.