Flame Synthesis of Carbon Nanotubes: Premixed and Diffusion Flame Configurations Illustrating Roles of Gas Composition a
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Flame Synthesis of Carbon Nanotubes: Premixed and Diffusion Flame Configurations Illustrating Roles of Gas Composition and Catalyst Randy
L.
Vander
Wal
Penn
State
University,
John
and
Willie
Leone
Family
Dept.
of
Energy
and
Mineral
Engineering,
&
The
EMS
Energy
Institute,
203
Hosler,
University
Park,
PA
16802,
U.S.A.
ABSTRACT Illustrated in this talk will be the use of premixed and diffusion flames as reaction environments for carbon nanotube synthesis. We have tested both systems using catalysts as aerosols and supported upon substrates. Highlights will be shown demonstrating success and further challenges. For illustration, this abstract illustrates two key parameter spaces, namely gas composition and catalyst size and composition in premixed and diffusion flames, respectively. INTRODUCTION Carbon nanotubes (CNTs) are widely sought for a wide variety of applications including gas storage [1], absorption [2], intercalation media [3-5], catalyst support [6-8], and composite reinforcing material [9-12]. Each of these applications, however, may require redispersal of the collected CNTs and attachment to a support structure. CVD methods are favored for CNT synthesis [13-21], despite subsequent harvesting and purification issues [22-24]. If the CNTs could be synthesized directly upon the support to be used in the end application, a tremendous savings in post-synthesis processing could be realized. A second consideration is that these applications will require large-scale production to generate commercial interest. Current CVD methods are ill-equipped to achieve this goal. Constrained by the confines of an electrically heated furnace, these methods are energy intensive, geometrically confined, and not scalable. We have pursued flame synthesis as an economical method for bulk synthesis of singlewalled nanotubes (SWNTs) and carbon nanofibers using both aerosol catalysts [25-31] and supported catalysts [32,33] Related work has appeared recently [34,35] Flame systems are used in industry for large scale energy production, drying, and material processing [36] With respect to CNT synthesis, a flame can be energy efficient where a portion of the fuel gas is burnt to produce the elevated temperature while the remainder serves as the growth reagent. Moreover, flame systems are geometrically versatile, as illustrated by innumerable boiler and furnace designs [37]. Compared to diffusion flames, premixed flames offer several advantages for CNT synthesis which include the following: 1. A wide selection of fuels. 2. Ability to adjust the stoichiometry of the reaction gases yielding different flame chemical
compositions. 3. Additional freedom to adjust the flame temperature, apart from the stoichiometry. 4. Scalability as premixed flames are not limited by diffusion; the reactive gas profile can be made uniform by the burner system. 5. Ability for continuous, multi-staged processing. EXPERIMENT With these advantages providing motivation, we explored the utility of a premixed flame for CNT synthesis using supported catalysts u
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