Production of Fullerenes from Solar Energy
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(1)Groupe de Dynamique des Phases Condensdes, Universit6 de Montpellier II, F34095 Montpellier, France (2)Institut des Mat6riaux de Nantes, Universit6 de Nantes, F44087 Nantes, France (3)lnstitut de Science et de G6nie des Mat6riaux et Proc~dds, BP5 Odeillo, F66125 Font-Romeu, France (4)lnstitut de Physique Nucl6aire, Universit6 de Paris Sud, F91406 Orsay, France
ABSTRACT The high intensity of solar radiation, obtained with the Odeillo (France) solar furnace facilities, is used to vaporize graphite in inert gas atmosphere. The soot obtained contains C60 , C70 and other heavier fullerenes. We discuss the possibility of increasing the evaporation rate of graphite and the yield of soot with this technique. From our last experiments, we obtain a first 3 estimate of the soluble fullerene yield Y ( greater than 12%) and we have shown that 1 C enriched fullerenes can be easily produced by this process. INTRODUCTION In 1993, various research groups [ 1-3] have shown that it is possible to produce fullerenes in rarefied inert gas atmosphere, by direct vaporization of graphite in focused sunlight. In these first experiments, only a small amount of soot was collected, typically one or two milligrams per hour. This low production is mainly due to the very important radiative and conductive thermal losses of graphite. However this method presents substantial advantages: (i) the starting material can be an insulator such as graphite powder or mixed rod of graphite and other species. (ii) in theory, the evaporation temperature and sublimation rate can be adjusted by a convenient choice of the inert gas pressure and incident light flux if one finds the way to reduce thermal losses. (iii) the U-V radiation from direct sunlight is very small compared with plasma radiation of electrical arc at a temperature of 10,000 K and it seems that photochemical destruction of fullerenes is the main mechanism which prevents high yields of C60 . In this paper we explore the possibility of increasing the evaporation rate of graphite, and the effect of the inert gas. We 3 describe the use of this procedure to produce derivatives of the fullerenes and particularly 1 C enriched fullerenes. EXPERIMENTAL DESIGN We have used a 1.5 kW solar furnace of the Odeillo Institute as described in figure 1.The sunlight is collected by a flat tracking mirror Mp and is vertically reflected towards a parabolic mirror Ms ( diameter 1.5m, 0.65m focal length, aperture half angle a = 600). For a direct solar flux around 850-900 W/m 2 , the focused power on the focal area which has a diameter close to 1.6 cm, can reach 1100W. Its radial distribution is shown on figure 2. The experimental chamber whose position can be adjusted so that the top of the target coincide with the focus, is schematically drawn on figure 3. The stand part R, surrounded by the Pyrex balloon flask S, is a water cooled brass cylinder which supports the target and cellulose filter to collect the soot. 11 Mat. Res. Soc. Symp. Proc. Vol. 359 01995 Materials Research Society
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EW/cm2
0150. f65 cm
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