Development of Mass-Production Technology for Multiwalled Carbon Nanotubes

Since the discovery of multiwalled carbon nanotubes (MWCNTs), although their structures and physical properties have been theoretically predicted, it has been impossible to carry out a validation study because a synthesis method with high and stable yield has not yet been established and separation and purification of these tubes have been extremely difficult. The authors and coworkers began research into their synthesis and purification in 1993 and developed the continuous arc discharge method (rotating cathode method), which has a production amount of 10 g/day with successful separation and purification. In joint research with Mie University using a purified sample, field emission was identified, and thus a great increase in the demand for MWCNTs as industrial materials was anticipated. In order to respond to this increase in the demand for MWCNTs, we began basic research in 1997 for the synthesis of MWCNTs by a heat decomposition method using hydrocarbon as the catalyst. Since 1998, we have participated in the Frontier Carbon Technology Project, conducting joint research with Showa Electric Co. Ltd. to realize mass production based on the results of their basic research. The method we are now developing is a method of growth in fluidized-catalyst. With this method, catalyst flows into the reactor, and by increasing the width of the reactor tube, mass production becomes possible. At the end of 1999, the production of MWCNTs reached 200 g/h in the experimental continuous reactor of internal diameter 200 mm installed at the Showa Electric Co. Ltd. MWCNTs are expected to be core industrial materials for field emission, hydrogen storage, and fuel cells, supporting the industry in the 21 ^st century when the mass production technology will be established and applied for their full-scale production.