Conventional methods for the synthesis of fullerenes and carbon nanotubes such as laser or electric arc ablation have failed when the process is scaled up. Our ultimate goal is to scale a solar process up from 2 to 250 kW; this paper shows that our method for achieving this scale-up is valid because we were able to predict process performance variables at the 50 kW level from preliminary experimental results from 2 kW experiments. The key parameters that characterize this process are the carbon soot mass flow rate and the desired product yield. The carbon soot production rate is a function of the target temperature and this can be predicted in a straightforward way from a heat transfer model of the larger system. The yield is a more complicated function of specific reactor variables such as patterns of fluid flow, residence times at various temperatures, and the reaction chemistry, but we have found that for fullerenes it depends primarily on the concentration of carbon vapor in the carrier gas, the target temperature and the temperature distribution in the cooling zone. Using these parameters, we scaled our process up to 50 kW and compared the predicted results to the measured performance. A graphite target 6 cm in diameter was vaporized in an argon atmosphere and a reduced pressure of 120–240 hPa with a solar flux density in the range 600-920W/cm2. Vaporization rates as high as 50 g/h were measured with a fullerene production rate equal to about 2 g/h, i.e., the expected results.

This paper deals with the material testing under extreme conditions, mainly around space programs, using the French CNRS (Centre National de la Recherche Scientifique) solar facilities for planetary entry (Earth, Mars), solar corona in situ exploration, and cryogenic propulsion. For these purposes, different facilities were developed around the various solar concentrators: MESOX (Moyen d’Essai Solaire d’OXydation), for the study of the atomic oxygen recombination at the surface of heated materials and the oxidation kinetics of ceramics under plasma atmospheres up to 2300 K. (Some results are given for several materials.); MEDIASE (Moyen d’Essai et de DIagnostic en Ambiance Spatiale Extre^me), for the thermophysical characterization of thermal shield materials up to 2400°K under high vacuum: mass-loss kinetics, mass spectrometry (neutral and ionic species) and thermo-radiative properties (total or spectral directional emissivity). (Results are presented for various carbon/carbon composite materials.); and DISCO (DISpositif de Caracte´risation Optique), for the measurement of changes in the reflectivity of materials at temperatures up to 2500°K and its correlation with the surface behavior (aging, ablation and oxidation). Results concerning a copper alloy used for the combustion chamber of cryogenic motors are given.

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