Thermal Conversion of Bundled Carbon Nanotubes into Graphitic Ribbons

Abstract

High temperature heat treatment (HTT) of bundled single-walled carbon nanotubes (SWNTs) in vacuum ( approximately 10(-5) Torr) has been found to lead to the formation of two types of graphitic nanoribbons (GNRs), as observed by high-resolution transmission electron microscopy. Purified SWNT bundles were first found to follow two evolutionary steps, as reported previously, that is, tube coalescence (HTT approximately 1400 degrees C) and then massive bond rearrangement (HTT approximately 1600 degrees C), leading to the formation of bundled multiwall nanotubes (MWNTs) with 3-12 shells. At HTT > 1800 degrees C, we find that these MWNTs collapse into multishell GNRs. The first type of GNR we observed is driven by the collapse of diameter-doubled single-wall nanotubes, and their production is terminated at HTT approximately 1600 degrees C when the MWNTs also start to form. We propose that the collapse is driven by van der Waals forces between adjacent tubes in the same bundle. For HTT > 2000 degrees C, the heat-treated material is found to be almost completely in the multishell GNR form.

Sculpting carbon bonds for allotropic transformation through solid-state re-engineering of –sp2 carbon

“…First, the instantaneous local temperature of the SWCNTs because of periodic voltage-pulse cycling could reach up to 1,200 K at V a ¼ 0.8V b (see Method section), and thermally induced changes in À sp 2 carbon structures are usually negligible at such temperatures 28 . Moreover, the transformations are more effective under rapid voltage-switching (smaller values of t on ) rather than higher heat-generating (larger values of t on ) cycles.…”

“…However, these rearrangement studies were carried out only for local changes of junctions in a few individual nanotubes [11][12][13][14][15][16][17][18][19][20][21]25 and by the destruction of carbon layers on electrical breakdown 23,26,27 . Furthermore, the reported reconstruction methods require high to extremely high temperature (750-2,200°C) conditions 20,22,28 , making them power-intensive, and incompatible with various scalable processes. Therefore, developing a fast and scalable method for reproducibly creating particular types of covalently bonded C-C junctions and sp 2 molecular structures in nanocarbon networks that result in repeatable physical properties is still a fundamental challenge.…”

Metallurgical Challenges in Carbon Nanotube-Reinforced Metal Matrix Nanocomposites

“…However, other consolidation techniques such as hydrogen plasma [115], high-pressure/high-temperature annealing heat treatment [116][117][118] and chemical vapor deposition (CVD) [107,108,119] can thermally decompose the structural geometry of nanotubes. As a practical conclusion, the engineers often strive to prevent from the thermal degradation of CNTs in both pure state and composite form, since it can vanish the final properties [120].…”

Graphitization of single-wall nanotube bundles at extreme conditions: Collapse or coalescence route

“…At ambient pressure, SWCNT bundles rearrange upon increasing temperature into multiwalled carbon nanotubes (MWCNT) or more complex graphitic structures called graphitic nanoribbons (GNR). 6,25 Upon imposing high pressure it is possible to convert the bundle into graphite, and possibly diamond crystallites and novel polymerized or jammed structures. 24 The understanding of the possible transformation mechanism is still at a speculative stage, although some insight is provided by the simulations of Refs.…”