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Abstract: Single-walled carbon nanotubes were synthesized in gram quantities with a 50kW solar reactor. Vaporization rate was in the range 6–15g/h and two samples were collected for each run. The structure of the products was studied by SEM, TEM and Raman spectroscopy as a function of the buffer gas (helium or argon), the target length and the collected location. Good quality samples containing 1.2–1.6nm diameter SWNTs were produced with helium at 450hPa, 8Nm3/h and a 15cm target length using 2at.% Ni and 2at.% Co as catalyst. The material quality increased with the target length in helium. On the contrary, poor quality product was obtained whatever the target length in argon. TGA analysis showed that the best product purity was at least 35wt%. [Copyright &y& Elsevier]

Single-walled carbon nanotube samples were synthesized with solar energy. The products are characterized by electron microscopy, Raman spectroscopy and nitrogen isotherms. The maximum value of the hydrogen uptake is 1 wt.% at 253 K and 6 MPa. The results are discussed by taking account of the structure and the BET surface of the samples. The hydrogen capacity is not proportional to the BET surface in these samples and does not seem to be linked to the amount of SWNT. [Copyright &y& Elsevier]

Thermal plasma processes show certain advantages over conventional gas phase synthesis process for the production of carbon nanomaterials. Due to the extreme temperature conditions and the unique flexibility, very different structures can be produced at high selectivity. An overview is given of the three principal families of nanostructures, carbon blacks, fullerenes and nanotubes, produced so far by the original three-phase AC plasma technology presented. Various examples of individual structural types are used to illustrate and explain the multitude of different particle formation processes adjustable in plasma systems. Numerical simulation of arc region, kinetics and fluid dynamics appears as a central tool for the control of the three main process parameters: temperature profile, particle residence time and species concentrations. [ABSTRACT FROM AUTHOR]

Vaporization of carbon particles injected in a plasma flow is an alternative to existing processes for mass production of fullerenes. In order to obtain a large fullerene-soot production the residence time of particle at temperature larger than the vaporization temperature must be large enough. This critical point was checked in the pilot reactor by OES. The helium plasma was generated inside a carbon nozzle by a 3-phase AC plasma source using graphite electrodes. The plasma flow was then cooled in a graphite cylinder. Plasma temperature was measured using H[subβ] line and C[sub2] Swan band in the upper part of the nozzle and at the entrance of the cylinder respectively. The results show that inside this volume, the plasma temperature is larger than or equal to 4500K and is very sensitive to the arc current. [ABSTRACT FROM AUTHOR]

Abstract. We report here some studies of the growth mechanisms of single-wall carbon nanotubes (SWNTs) produced by the solar method as a function of the experimental conditions and the nature of catalysts. A large set of transmission electron microscopy (TEM) pictures seems to confirm the existence of one dominant growth mechanism, close to the model proposed by Saito et al., whatever the used catalyst might be. Nevertheless, the Raman spectra clearly show that the change of catalyst induces differences in diameter, structure, and electronic properties of SWNTs. [ABSTRACT FROM AUTHOR]

Experimental results with a 50 kW solar reactor producing 10-15 g/h single-wall carbon nanotube's rich soot have shown that good quality product was obtained with helium and rather bad product with argon. This result is explained using a computational fluid dynamics model of the reactor accounting for fluid flow, heat transfer, and mass transfer. The bad results in argon were linked to the quenching of carbon vapor in the vaporization zone that resulted in the growth of carbon nanoparticles in spite of carbon-metal clusters (single-wall carbon nanotube precursor). By contrast, the vaporized materials (C, Ni, and Co species) at the target surface were well mixed in helium, and single-wall carbon nanotubes (SWNTs) might grow in the annealing and cooling zone at the backside of the reactor. The same numerical approach may be used to design modifications of the reactor in order to favor the growth of SWNTs. [ABSTRACT FROM AUTHOR]

Abstract: The solar thermochemical decomposition of CH4 is carried out in a solar reactor consisting of a cavity-receiver containing an array of tubular absorbers, through which CH4 flows and thermally decomposes to H2 and carbon particles. A reactor model is formulated by coupling radiation/convection/conduction heat transfer and chemical kinetics for a two-phase solid-gas reacting flow. Experimental validation is accomplished by comparing measured and simulated absorber temperatures and H2 concentrations for a 10 kW prototype reactor tested in a solar furnace. The model is applied to optimize the design and simulate the performance of a 10 MW commercial-scale reactor mounted on a solar tower system configuration. Complete conversion is predicted for a maximum CH4 mass flow rate of 0.70 kg s−1 and a desired outlet temperature of 1870 K, yielding a solar-to-chemical energy conversion efficiency of 42% and a solar-to-thermal energy conversion efficiency of 75%. [ABSTRACT FROM AUTHOR]