AVS 46th International Symposium
    Topical Conference on Emerging Opportunities and Issues in Nanotubes and Nanoelectronics Friday Sessions
       Session NT+NS+EM+MS-FrM

Paper NT+NS+EM+MS-FrM1
Gas-phase Nanotube Production at High Pressure By Disproportionation of Carbon Monoxide

Friday, October 29, 1999, 8:20 am, Room 6C

Session: Nanotubes: Growth, Characterization and Properties II
Presenter: P. Nikolaev, G. B. Tech Inc. / NASA - JSC
Authors: P. Nikolaev, G. B. Tech Inc. / NASA - JSC
M. Bronikowski, Rice University
K. Bradley, Rice University
D. Colbert, Rice University
K. Smith, Rice University
R.E. Smalley, Rice University
Correspondent: Click to Email
Single-wall carbon nanotubes (SWNTs) were produced in gas phase, in a flow tube reactor in 3 - 15 atm. of CO at 850@super o@ - 1200@super o@C. Nanotube growth was catalyzed by unsupported iron particles created in-situ by decomposition of iron pentacarbonyl vapor which was added to the CO feedstock at a few ppm level. We find that low Fe(CO)@sub 5@ concentration combined with fast heating rate of feedstock gas allows us to produce very small iron particles, while high pressure increases the rate of CO disproportionation, leading to effective nucleation and growth of SWNTs. Unlike pyrolysis of hydrocarbons, CO disproportionation is a "clean" process which proceeds only on the catalyst surface, resulting in essentially no amorphous carbon overcoating. Diameter distribution of the SWNTs is rather narrow and depends on CO pressure. Higher CO pressures (10 atm.) yield smaller nanotubes, with distribution centered at 0.7 nm (which is roughly the size of C@sub 60@ molecule). Nanotube yield relative to the amount of iron catalyst increases as the heating rate and mixing of Fe(CO)@sub 5@ are enhanced, indicating better catalyst utilization. In order to further increase nanotube yield, we have designed a "shower head" injector, in which cold CO/Fe(CO)@sub 5@ feedstock enters furnace through water-cooled injector, surrounded by "shower head" carrying CO pre-heated to 1200@super o@. Nanotube yield is also increased by addition of small amount of methane, while more CH@sub 4@ results in amorphous overcoating on the nanotube surface. In contrast to previously reported SWNT production methods, this scheme constitutes a continuous flow gas phase SWNT production process. It should therefore be readily amenable to scale up for bulk SWNT production.