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  • 1
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    Diameter control of single-walled carbon nanotubes using argon–helium mixture gases (2001)
    American Institute of Physics
    Details
    Publication Date: 2001-10-08
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics
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  • 2
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    Spectral measurements in production of single-wall carbon nanotubes by laser ablation (1999)
    Elsevier
    Details
    Publication Date: 1999-03-01
    Print ISSN: 0009-2614
    Electronic ISSN: 1873-4448
    Topics: Chemistry and Pharmacology , Physics
    Published by Elsevier
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  • 3
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    Chemical models for simulating single-walled nanotube production in arc vaporization and laser ablation processes (2004)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Chemical kinetic models for the nucleation and growth of clusters and single-walled carbon nanotube (SWNT) growth are developed for numerical simulations of the production of SWNTs. Two models that involve evaporation and condensation of carbon and metal catalysts, a full model involving all carbon clusters up to C80, and a reduced model are discussed. The full model is based on a fullerene model, but nickel and carbon/nickel cluster reactions are added to form SWNTs from soot and fullerenes. The full model has a large number of species--so large that to incorporate them into a flow field computation for simulating laser ablation and arc processes requires that they be simplified. The model is reduced by defining large clusters that represent many various sized clusters. Comparisons are given between these models for cases that may be applicable to arc and laser ablation production. Solutions to the system of chemical rate equations of these models for a ramped temperature profile show that production of various species, including SWNTs, agree to within about 50% for a fast ramp, and within 10% for a slower temperature decay time.
    Keywords: Life Sciences (General)
    Type: Journal of nanoscience and nanotechnology (ISSN 1533-4880); Volume 4; 4; 368-76
    Format: text
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  • 4
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    Effects of carbonyl bond, metal cluster dissociation, and evaporation rates on predictions of nanotube production in high-pressure carbon monoxide (2003)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The high-pressure carbon monoxide (HiPco) process for producing single-wall carbon nanotubes (SWNTs) uses iron pentacarbonyl as the source of iron for catalyzing the Boudouard reaction. Attempts using nickel tetracarbonyl led to no production of SWNTs. This paper discusses simulations at a constant condition of 1300 K and 30 atm in which the chemical rate equations are solved for different reaction schemes. A lumped cluster model is developed to limit the number of species in the models, yet it includes fairly large clusters. Reaction rate coefficients in these schemes are based on bond energies of iron and nickel species and on estimates of chemical rates for formation of SWNTs. SWNT growth is measured by the conformation of CO2. It is shown that the production of CO2 is significantly greater for FeCO because of its lower bond energy as compared with that of NiCO. It is also shown that the dissociation and evaporation rates of atoms from small metal clusters have a significant effect on CO2 production. A high rate of evaporation leads to a smaller number of metal clusters available to catalyze the Boudouard reaction. This suggests that if CO reacts with metal clusters and removes atoms from them by forming MeCO, this has the effect of enhancing the evaporation rate and reducing SWNT production. The study also investigates some other reactions in the model that have a less dramatic influence.
    Keywords: Life Sciences (General)
    Type: Journal of nanoscience and nanotechnology (ISSN 1533-4880); Volume 3; 1-2; 75-9
    Format: text
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  • 5
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    Intrusive and nonintrusive measurements of flow properties in arc jets (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: While numerous diagnostic techniques are available for determining the flow properties of arc jets, these have to be used complementarily in order to cover all the requisite information. Although intrusive techniques disturb the flow, they yield much information. The determination of total enthalpy remains a major challenge, and accurate heat-flux measurements entail knowledge of atom recombination and chemical energy recombination coefficients. Such state-specific methods as the spectroscopic and laser techniques are useful in understanding the chemistry and nonequilibrium reaction and excitation rates of the flow.
    Keywords: PLASMA PHYSICS
    Type: In: Hypersonic flows for reentry problems. Vol. 1 (A93-42576 17-02); p. 139-169.
    Format: text
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  • 6
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    Wall catalytic recombination and boundary conditions in nonequilibrium hypersonic flows - With applications (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The meaning of catalysis and its relation to aerodynamic heating in nonequilibrium hypersonic flows are discussed. The species equations are described and boundary conditions for them are derived for a multicomponent gas and for a binary gas. Slip effects are included for application of continuum methods to low-density flows. Measurement techniques for determining catalytic wall recombination rates are discussed. Among them are experiments carried out in arc jets as well as flow reactors. Diagnostic methods for determining the atom or molecule concentrations in the flow are included. Results are given for a number of materials of interest to the aerospace community, including glassy coatings such as the RCG coating of the Space Shuttle and for high temperature refractory metals such as coated niobium. Methods of calculating the heat flux to space vehicles in nonequilibrium flows are described. These methods are applied to the Space Shuttle, the planned Aeroassist Flight Experiment, and a hypersonic slender vehicle such as a transatmospheric vehicle.
    Keywords: AERODYNAMICS
    Type: In: Advances in hypersonics. Vol. 2 - Modeling hypersonic flows (A94-10759 01-02); p. 176-250.
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  • 7
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    Survey of measurements of flow properties in arcjets (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 7; 1; p. 9-24.
    Format: text
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  • 8
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    A parametric study of single-wall carbon nanotube growth by laser ablation (2004)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Results of a parametric study of carbon nanotube production by the double-pulse laser oven process are presented. The effect of various operating parameters on the production of single-wall carbon nanotubes (SWCNTs) is estimated by characterizing the nanotube material using analytical techniques, including scanning electron microscopy, transmission electron microscopy, thermo gravimetric analysis and Raman spectroscopy. The study included changing the sequence of the laser pulses, laser energy, pulse separation, type of buffer gas used, operating pressure, flow rate, inner tube diameter, as well as its material, and oven temperature. It was found that the material quality and quantity improve with deviation from normal operation parameters such as laser energy density higher than 1.5 J/cm2, pressure lower than 67 kPa, and flow rates higher than 100 sccm. Use of helium produced mainly small diameter tubes and a lower yield. The diameter of SWCNTs decreases with decreasing oven temperature and lower flow rates.
    Keywords: Life Sciences (General)
    Type: Journal of nanoscience and nanotechnology (ISSN 1533-4880); Volume 4; 7; 762-73
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  • 9
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    Iron catalyst chemistry in modeling a high-pressure carbon monoxide nanotube reactor (2003)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The high-pressure carbon monoxide (HiPco) technique for producing single-wall carbon nanotubes (SWNTs) is analyzed with the use of a chemical reaction model coupled with flow properties calculated along streamlines, calculated by the FLUENT code for pure carbon monoxide. Cold iron pentacarbonyl, diluted in CO at about 30 atmospheres, is injected into a conical mixing zone, where hot CO is also introduced via three jets at 30 degrees with respect to the axis. Hot CO decomposes the Fe(CO)5 to release atomic Fe. Then iron nucleates and forms clusters that catalyze the formation of SWNTs by a disproportionation reaction (Boudouard) of CO on Fe-containing clusters. Alternative nucleation rates are estimated from the theory of hard sphere collision dynamics with an activation energy barrier. The rate coefficient for carbon nanotube growth is estimated from activation energies in the literature. The calculated growth was found be about an order of magnitude greater than measured, regardless of the nucleation rate. A study of cluster formation in an incubation zone prior to injection into the reactor shows that direct dimer formation from Fe atoms is not as important as formation via an exchange reaction of Fe with CO in FeCO.
    Keywords: Life Sciences (General)
    Type: Journal of nanoscience and nanotechnology (ISSN 1533-4880); Volume 3; 1-2; 63-73
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  • 10
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    Survey of measurements of flow properties in arc jets (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This paper reviews techniques for determining flow properties in low density arc jets used for materials and structures testing. Properties measured include flow total enthalpy, pressures, heat fluxes, static temperatures, electron density, species concentrations, and flow velocity. The probe techniques covered are pressure, heat flux, electrostatic, and mass sampling. Nonintrusive techniques include emission spectroscopy, laser-induced fluorescence, laser Thomson scattering, and Raman scattering. It is concluded that several techniques must be used in a single facility to obtain all of the flow field properties necessary to predict heat fluxes in a nonequilibrium expansion.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA PAPER 90-1765
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