Theoretical calculations on the catalytic growth of multiwall carbon nanotube in chemical vapor deposition

Kamachali, Reza Darvishi

doi:10.1016/j.chemphys.2006.05.015

Cited by 15 publications

(5 citation statements)

References 29 publications

(23 reference statements)

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“…Nevertheless, currently available models do provide some insight into the mechanisms that control CNT growth. The kinetic model of Kamachali predicts a CNT growth activation barrier very close to the observed barrier and explains this barrier as the sum of the activation energies for carbon dissolution in and diffusion through the metal catalyst. The model of Puretzky et al .…”

Section: Discussionmentioning

confidence: 68%

Longer Nanotubes at Lower Temperatures: The Influence of Effective Activation Energies on Carbon Nanotube Growth by Thermal Chemical Vapor Deposition

Bronikowski

2007

J. Phys. Chem. C

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Growth of carbon nanotubes (CNTs) by metal-catalyzed thermal chemical vapor deposition (CVD) upon flat silicon substrates is studied as a function of growth temperature. It is found that the CNT growth rate at a given temperature is constant for a certain amount of growth time, after which growth ceases; the product of the growth rate and the growth time gives the ultimate length of the CNTs. Both the growth rate and the growth time are found to depend on the CVD temperature, and this dependence is such that the ultimate CNT length increases as temperature decreases; that is, longer CNTs can be grown at lower temperatures than at higher temperatures. This surprising and counter-intuitive result reflects the interaction of competing factors affecting the CNT growth: the rate at which carbon is incorporated into growing CNTs versus the rate at which catalytic metal particles become inactive. Both of these rates are found to have an Arrhenius form of temperature dependence, with activation energies of 2.0 and 3.4 eV, respectively, when an Al 2 O 3 diffusion barrier layer is used. These energies are interpreted as "effective" activation barriers arising from activation energy contributions from multiple chemical processes. CNT bundles as long as one millimeter have been grown at a temperature of 600 °C.

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Section: Discussionmentioning

confidence: 68%

Longer Nanotubes at Lower Temperatures: The Influence of Effective Activation Energies on Carbon Nanotube Growth by Thermal Chemical Vapor Deposition

Bronikowski

2007

J. Phys. Chem. C

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“…According to the vapor–liquid–solid (VLS) model, the carbon feedstock is catalytically decomposed by the catalyst particles at elevated temperature, after which it dissolves into the catalyst, before finally forming CNTs when the carbon reaches supersaturation . The distribution of active sites on the catalyst particle surface determines the CNT length, diameter and alignment . Uniform catalyst activity is known to play an important role in the growth of aligned CNT arrays and previous studies suggest that the CNT growth is primarily driven by the carbon concentration gradient in the catalyst particle. , During the stable stage of CNT growth, where carbon dissolution and precipitation rates are in equilibrium, the concentration gradient in the catalyst does not change with growth time, resulting in CNTs that are straight and relatively defect free.…”

Section: Resultsmentioning

confidence: 99%

“…The distribution of active sites on the catalyst particle surface determines the CNT length, diameter and alignment . Uniform catalyst activity is known to play an important role in the growth of aligned CNT arrays and previous studies suggest that the CNT growth is primarily driven by the carbon concentration gradient in the catalyst particle. , During the stable stage of CNT growth, where carbon dissolution and precipitation rates are in equilibrium, the concentration gradient in the catalyst does not change with growth time, resulting in CNTs that are straight and relatively defect free. It has been suggested, that except for islands of catalyst optimal for CNT growth, small particles may lose CNT growth activity as a result of the overfeeding effect, where Ostwald ripening minimizes surface energy and small catalyst particles coalesce into larger particles.…”

Section: Resultsmentioning

confidence: 99%

Pretreatment Control of Carbon Nanotube Array Growth for Gas Separation: Alignment and Growth Studied Using Microscopy and Small-Angle X-ray Scattering

Yang

Yuan

Peterson

et al. 2013

ACS Appl. Mater. Interfaces

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Aligned multiwalled carbon nanotube (CNT) arrays were prepared using chemical vapor deposition of C2H4 on Fe catalyst at 750 °C. CNT array height and alignment depends strongly on the duration of H2 pretreatment, with optimal height and alignment achieved using 10-15 min pretreatment. Small-angle X-ray scattering (SAXS) was used to quantify the alignment, distribution, and size of the CNTs in arrays produced from varying pretreatment times and the results correlated with microscopy measurements. SAXS analysis revealed that the higher section of the CNT arrays exhibited better alignment than the lower section. Combining these insights with transmission electron microscopy measurements of the CNT defects within each array enable a mechanism for the CNT growth to be proposed, where the loss of alignment arises from deformation of the CNTs during their growth. Gas permeation test across densified CNT arrays indicated that the alignment of the CNT array plays an important role in the gas transport, and that the gas diffusion across the well-aligned CNT arrays was enhanced by a factor of ~45, which is much more than that across the poorly aligned CNT arrays, with an enhancement factor of ~8.

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“…(4) corresponds to the following sequence of elementary steps, which consists of equilibrated adsorption of ethylene and of the irreversible surface ethylene decomposition as the ratedetermining step [34]: Activation energy E 2 was found to be equal to around 120 ± 15 kJ mol −1 , standard adsorption enthalpy H • to around −120 ± 20 kJ mol −1 , and standard adsorption entropy S • to around −120 ± 20 J mol −1 K −1 . As a comparison with previous literature, reported activation energies for ethylene decomposition into carbon nanotubes and hydrogen vary between 100 kJ mol −1 and 180 kJ mol −1 , depending on the catalyst nature [28,[34][35][36][37], while reported ethylene adsorption enthalpies with different catalyst vary from −160 kJ mol −1 to −60 kJ mol −1 [28,38,39]. Let us mention that ethylene adsorption enthalpy and entropy, H • and S • , must verify thermodynamic constraints.…”

Section: Kinetic Studymentioning

confidence: 98%

Quantitative study of catalytic activity and catalytic deactivation of Fe–Co/Al2O3 catalysts for multi-walled carbon nanotube synthesis by the CCVD process

Pirard¹,

Heyen²,

Pirard³

2010

Applied Catalysis A: General

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a b s t r a c tThe catalytic deactivation during multi-walled carbon nanotube (MWNT) synthesis by the CCVD process and the influence of hydrogen on it were quantified. Initial specific reaction rate, relative specific productivity and catalytic deactivation were studied. Carbon source was ethylene, and a bimetallic iron-cobalt catalyst supported on alumina was used. The catalytic deactivation was modeled by a decreasing hyperbolic law, reflecting the progressive accumulation of amorphous carbon on active sites. While the initial specific reaction rate was found not to be influenced by hydrogen, catalytic deactivation was found to be modified in the presence of hydrogen, which delayed and slowed down the deactivation by avoiding amorphous carbon deposition, thus leading to a greater relative specific productivity of carbon nanotubes.

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Theoretical calculations on the catalytic growth of multiwall carbon nanotube in chemical vapor deposition

Cited by 15 publications

References 29 publications

Longer Nanotubes at Lower Temperatures: The Influence of Effective Activation Energies on Carbon Nanotube Growth by Thermal Chemical Vapor Deposition

Longer Nanotubes at Lower Temperatures: The Influence of Effective Activation Energies on Carbon Nanotube Growth by Thermal Chemical Vapor Deposition

Pretreatment Control of Carbon Nanotube Array Growth for Gas Separation: Alignment and Growth Studied Using Microscopy and Small-Angle X-ray Scattering

Quantitative study of catalytic activity and catalytic deactivation of Fe–Co/Al2O3 catalysts for multi-walled carbon nanotube synthesis by the CCVD process

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