In Situ TEM Observation of the Gasification and Growth of Carbon Nanotubes Using Iron Catalysts (original) (raw)
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Role of Gas-phase Reactions and Thermal Gradient Control in Carbon Nanotube Synthesis
MRS Proceedings, 2012
ABSTRACTWe investigate the role of precursor thermal rearrangement and surface catalytic reactions in the synthesis of vertically aligned carbon nanotubes (VA-CNTs) by acetylene-based, chemical vapor deposition (CVD) and demonstrate a millimeter-long growth of single-walled CNT (SWNT) without water assistance. A substrate heater was used to create an ascending temperature gradient from gas injection to catalyst substrate. Whereas temperature of catalyst substrates primarily determines their catalytic activity, it is a thermal condition of a gaseous mixture in the CVD chamber that also influence growth yield and structural features of as-grown CNTs. Employing Egloff’s characterization, [1] we discuss the importance of various gas thermal zones in producing high-quality nanotubes with augmented growth efficiency. We continue to report production of millimeter-long, VA-SWNT having a mean diameter of 1.7 ± 0.7 nm, catalyzed by iron on an alumina support. Important finding is that a mill...
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Due to the crucial role of a catalyst in growth of carbon nanotubes (CNTs) by a chemical vapor deposition, it is important to understand the activation and deactivation of a catalyst for controlling production of CNTs. Using molecular benzene as the carbon source and Fe-Co/␥-Al 2 O 3 as catalyst, multi-CNTs were synthesized with a thermal analyzer coupled a mass spectrometer in different atmospheres of N 2 and H 2. Very different thermogravimetry behaviors (TG-DTG) were observed during CNT growth, indicating that CNTs experienced very different activation and deactivation processes. In a N 2 atmosphere, a catalyst particle was activated jumpily, then about half of catalyst surface was covered by the produced CNTs generated on one side of a catalyst, leading to trigger deactivation immediately following activation; in a H 2 atmosphere, a catalyst was activated gradually, and deactivation developed gradually, the total CNT yield in H 2 was higher than in N 2 , suggesting H 2 suppressed the deactivation development of a catalyst by cleaning the amorphous carbon over a catalyst. In combination of the mass spectral measurements, the activation and deactivation mechanism of a catalyst in an inert and reducing reaction atmospheres gas were revealed.
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Carbon, 2000
The properties and formation of nanotubes have been extensively studied, but very few deal with the catalytic production mechanism of nanotubes. Two different techniques, thermogravimetric analysis and UV-Raman, have been applied to analyse the carbon deposition by catalysed decomposition of acetylene over an iron-based catalyst. The nature of the produced carbon materials depends on reaction temperature. Also, TEM allows identification of carbon nanotubes, encapsulated particles, and other nanostructures, while UV-Raman confirms its graphitic and graphite-like nature.
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Journal of Electron Microscopy, 2005
We report in situ environmental transmission electron microscope observations of the nucleation and growth of multi-wall and singlewall carbon nanotubes formed by the catalytic decomposition of acetylene (C 2 H 2 ) on Ni/SiO 2 catalyst. The growth rate, structure and morphology of the carbon nanotubes formed depended upon reaction temperature and pressure. Under 20-100 mTorr of gas pressures at 480 C, serpentine-shaped or zigzag, multi-wall carbon nanotubes grew at an average rate of 35-40 nm sec À1 . At pressures <10 mTorr at the same temperature, straight single-wall carbon nanotubes with nearly uniform diameters ($3.5 nm) formed at average growth rates of 6-9 nm sec À1 .
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Physica B: Condensed Matter, 2009
Multi-wall carbon nanotubes (MWCNTs) were synthesized by catalytic chemical vapor deposition (CVD) on catalytic iron nanoparticles dispersed in a silica matrix, prepared by sol gel method. In this contribution, variation of gelation condition on catalyst structure and its influence on the yield of carbon nanotubes growth was studied. The precursor utilized were tetraethyl-orthosilicate and iron nitrate. The sols were dried at two different temperatures in air (25 or 80 1C) and then treated at 450 1C for 10 h. The xerogels were introduced into the chamber and reduced in a hydrogen/nitrogen (10%v/v) atmosphere at 600 1C. MWCNTs were formed by deposition of carbon atoms from decomposition of acetylene at 700 1C. The system gelled at RT shows a yield of 100% respect to initial catalyst mass whereas the yield of that gelled at 80 1C was lower than 10%. Different crystalline phases are observed for both catalysts in each step of the process. Moreover, TPR analysis shows that iron oxide can be efficiently reduced to metallic iron only in the system gelled at room temperature. Carbon nanotubes display a diameter of about 25-40 nm and several micron lengths. The growth mechanism of MWCNTs is base growth mode for both catalysts.
Nanotechnologies in Russia, 2010
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Growth Phenomena of Carbon Nanotubes Over Co-Mo/MgO Catalyst from the Decomposition of Acetylene
Bangladesh Journal of Scientific and Industrial Research, 1970
Carbon nanotubes (CNTs) were grown over 12Mo:18Co:70MgO catalyst at 500, 700 and 900° C from C2H2 decomposition for 30 minutes using chemical vapor deposition (CVD) method. The highest yield of CNTs was observed at 700O C. The lowest diameter of CNTs appeared at 900° C. Quadruple mass spectroscopy (QMS) study on the species generated from the catalytic decomposition of C2H2 identified that the catalyst consumed C species during the growth stage of CNTs. The consumption period of C varied with temperature and showed a close relationship with the carbon yield. At 500, 700 and 900°C, the consumption periods were 12, 35 and 20 min, respectively, and the corresponding carbon yields were 7, 385 and 89%. From the XRD analysis of catalyst surface, and XRD and Raman analysis of the CNTs, it was realized that Co particles released from Co3O4, CoMoO4 and CoO-MgO were participated in CNTs growth at 500, 700 and 900° C, respectively. The Co particles acted as the transporting medium of carbon to...
Surface and Coatings Technology, 2007
Carbon nanotubes (CNTs) were used as substrate for the growth of secondary carbon nanotubes. Iron was applied as catalyst, and cyclohexane was used as carbon source. The iron nanoparticles were synthesized from iron sulfate by electrodeposition on the primary CNTs by ramping the potential from 0 V to −0.75 V. The influence of subsequent calcination and reduction on the Fe/CNT samples was studied by X-ray photoelectron spectroscopy and transmission electron microscopy. Calcination in air at 400°C was identified as a key step to improve the dispersion of the iron nanoparticles, presumably due to solid-and gas-phase reactions on the Fe-C interface, where iron acts as the gasification catalyst. Secondary CNTs were grown catalyzed by the highly dispersed iron nanoparticles at 700°C in a hot-wall reactor. Nitrogen physisorption isotherms demonstrated the formation of inter-nanotube pores due to the growth of the secondary CNTs into the voids between the primary CNTs. The resulting specific surface area was found to be significantly enhanced by a factor of 6. The obtained hierarchical carbon nanocomposite is very promising as structured catalyst support in fuel cells.