Carbon nanotubes from polyethylene precursors: Structure and structural changes caused by thermal and chemical treatment revealed by HREM

Autor: J. Hammer, Jeremy Sloan, Dmitri N. Zakharov, John L. Hutchison, E.F. Kukovitskii, N. A. Kiselev, A.S. Kotosonov
Rok vydání: 1998
Předmět:
Zdroj: Carbon. 36:1149-1157
ISSN: 0008-6223
DOI: 10.1016/s0008-6223(98)00092-x
Popis: High resolution electron microscopy (HREM) reveals that carbon nanotubes obtained by heating a polyethylene precursor in the presence of catalytic Ni particles have a structure consisting of stacked conical carbon layers. Two main types of nanotube structures were identified. When the conical angle along the tubes is in the range 16–35 °, “bamboo”-shaped nanotubes are observed, characterized by open carbon edges (OEs) that were assumed to terminate in hydrogen. When the conical angle is in the range 75–85 °, a “fish-bone”-type structure is observed. Following heat treatment in the temperature range 1200–2800 °C, the catalytic Ni particles were removed and the hydrogen content reduced. As a result, the neighboring OEs were linked together, revealed in the HREM by the formation of loops along both the external tube sides and also the insides of the inner channels. Chemically, the pre-heat treated tubes could withstand bromination, but were completely destroyed by treatment with hot concentrated HNO3. Treatment of the pre-heat treated tubes with molten V2O5 revealed no penetration of this material between the OEs along the external wall or into the inner channel. The microstructure of the catalytic Ni particles, present at the tips of the pre-heat treated nanotubes, was also investigated. Outer polycrystalline layers consisting of Ni3C and probably NiO were observed near the periphery of terminal Ni particles not covered with graphitic layers and also near that of open regions of partially covered particles.
Databáze: OpenAIRE
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