4073 K
19 pp.
 
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TitleIron-Doped Carbon Aerogels: Novel Porous Substrates for Direct Growth of Carbon Nanotubes
Author(s)Steiner, S. A.; Baumann, T. F.; Kong, J.; Satcher, J. H.; Dresselhaus, M. S.
Publication DateFebruary 20, 2007
Report NumberUCRL-JRNL-228174
Unique IdentifierACC0421
Other NumbersOSTI ID: 964102
Research OrgLawrence Livermore National Laboratory (LLNL), Livermore, CA
Contract NoW-7405-ENG-48
Sponsoring OrgUSDOE
Subject36 Materials Science; 37 Inorganic, Organic, Physical and Analytical Chemistry; Carbon; Carbonization; Chemical Composition; Formaldehyde; Inert Atmosphere; Ion Exchange; Iron; Iron Carbides; Mixtures; Nanotubes; Polymerization; Potassium; Pyrolysis; Raman Spectroscopy; Substrates; Synthesis; X-Ray Diffraction; X-Ray Photoelectron Spectroscopy
Related Web PagesMildred [Millie] Dresselhaus and her Impacts on Science and Women in Science
AbstractWe present the synthesis and characterization of Fe-doped carbon aerogels (CAs) and demonstrate the ability to grow carbon nanotubes directly on monoliths of these materials to afford novel carbon aerogel-carbon nanotube composites. Preparation of the Fe-doped CAs begins with the sol-gel polymerization of the potassium salt of 2,4-dihydroxybenzoic acid with formaldehyde, affording K{sup +}-doped gels that can then be converted to Fe{sup 2+}- or Fe{sup 3+}-doped gels through an ion exchange process, dried with supercritical CO{sub 2} and subsequently carbonized under an inert atmosphere. Analysis of the Fe-doped CAs by TEM, XRD and XPS revealed that the doped iron species are reduced during carbonization to form metallic iron and iron carbide nanoparticles. The sizes and chemical composition of the reduced Fe species were related to pyrolysis temperature as well as the type of iron salt used in the ion exchange process. Raman spectroscopy and XRD analysis further reveal that, despite the presence of the Fe species, the CA framework is not significantly graphitized during pyrolysis. The Fe-doped CAs were subsequently placed in a thermal CVD reactor and exposed to a mixture of CH{sub 4} (1000 sccm), H{sub 2} (500 sccm), and C{sub 2}H{sub 4} (20 sccm) at temperatures ranging from 600 to 800 C for 10 minutes, resulting in direct growth of carbon nanotubes on the aerogel monoliths. Carbon nanotubes grown by this method appear to be multiwalled ({approx}25 nm in diameter and up to 4 mm long) and grow through a tip-growth mechanism that pushes catalytic iron particles out of the aerogel framework. The highest yield of CNTs were grown on Fe-doped CAs pyrolyzed at 800 C treated at CVD temperatures of 700 C.
4073 K
19 pp.
 
View Document 
  


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