Plasma Chem Plasma Process (2006) 26:597–608 DOI 10.1007/s11090-006-9036-0 ORIGINAL PAPER
Effects of Precursors and Plasma Parameters on Fullerene Synthesis in RF Thermal Plasma Reactor Ja´nos Sze´pvo¨lgyi Æ Zoran Markovic´ Æ Biljana Todorovic´-Markovic´ Æ Zoran Nikolic´ Æ Ilona Mohai Æ Zsuzsanna Farkas Æ Ma´ria To´th Æ E´va Kova´ts Æ Paul Scheier Æ Stefan Feil
Received: 5 September 2005 / Accepted: 27 July 2006 / Published online: 17 September 2006 Springer Science+Business Media, Inc. 2006
Abstract Synthesis of fullerenes from graphite powders of different grade was studied in a radiofrequency (RF) plasma reactor. Dependence of fullerene yield on the properties and feed rate of precursors and on the helium content of plasma gas was studied in details. The fullerene yield was influenced by the mean size and the thermal conductivity of graphite particles on the one hand, and the helium content of the gas phase on the other. Soot containing fullerene mixture of 5.9% was produced in best conditions found in this work. The main component of the fullerene mixture was C60. In addition, it contained about 30% of C70 (corresponding to a C60/C70 mass
J. Sze´pvo¨lgyi (&) Æ I. Mohai Institute of Materials and Environmental Chemistry, Chemical Research Center, Hungarian Academy of Sciences, H-1525 Budapest, POB 17, Hungary e-mail:
[email protected] Z. Markovic´ Æ B. Todorovic´-Markovic´ ‘‘Vincˇa’’ Institute of Nuclear Sciences, 11001 Belgrade, POB 522, Republic of Serbia Z. Nikolic´ The Faculty of Physics, University of Belgrade, 11001 Belgrade, POB 316, Republic of Serbia Z. Farkas Department of Silicate Chemistry and Materials Engineering, Pannon University, H-8201 Veszpre´m, POB 158, Hungary M. To´th Institute for Geochemistry, Hungarian Academy of Sciences, H-1112 Budapest, Budao¨rsi u´t 45, Hungary E´va Kova´ts Research Institute of Solid State Physics and Optics, Hungarian Academy of Sciences, H-1525 Budapest, POB 49, Hungary P. Scheier Æ S. Feil Institute for Ionphysics, Leopold Franzens University, Techniker Str. 25, A-6020 Innsbruck, Austria
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Plasma Chem Plasma Process (2006) 26:597–608
ratio of 2.64). Higher fullerenes such as C84 were also detected by mass spectroscopy (MS) and high performance liquid chromatography (HPLC). Keywords
Graphite Æ Fullerenes Æ RF thermal plasma Æ Synthesis
1 Introduction The high cost and the insufficient availability of fullerenes raise difficulties against their broader application in different fields [1]. It is a matter of regret because fullerenes may play important role in high-technologies such as optoelectronics and photovoltaics, and advanced products such as batteries and fuel cells [2]. Development of large-scale and low-cost production technologies of fullerenes seems to be a goal of outstanding importance both in scientific and practical terms [3, 4]. Conventional methods of fullerene synthesis are based on the evaporation of graphite electrodes by arc plasmas at relatively low pressure [5–7]. To describe the kinetics of fullerene formation in arc plasma conditions a model was constructed [8] based on Smoluchovski’s equation [9] the basic equation of statistical non-equilibrium physics. Particular model assumes that fullerenes are forming in helium atmosphere at temperatures above 2000 K only. According to the model, formation rate of carbon clusters and thus, yield of fullerenes depend on the following parameters: (i) concentration of evaporated carbon in the arc column, (ii) velocity of carbon–helium leaving the arc column and (iii) maximum plasma temperature and temperature gradient between the arc and reactor wall. The inductively coupled, radiofrequency (RF) thermal plasmas may offer more favorable conditions for fullerene synthesis than arc plasmas. In RF thermal plasma reactors the plasma flames are more voluminous and the gas velocities are lower as compared to arc plasma jets. Thus, the mean residence time of reactive species in the hot region is longer in RF thermal plasmas than in arc ones. Powder-like fullerene precursors can be easily introduced into RF plasmas, contrary to arc plasmas. In addition, the feed rate of powders can be changed independently of the RF plasma parameters. In spite of the apparent advantages, there have been a few attempts on fullerene synthesis from carbon powder in inductively coupled RF or hybrid plasmas [10–13]. The studies were mainly focused on using carbon black precursor of small particle size to improve evaporation efficiency. In a recent study, micron-sized graphite powder was used as precursor of fullerene synthesis [10]. Main results of previous studies are summarized in Table 1. Table 1 Summary of previous results on fullerene synthesis in thermal plasmas Ref. No.
[5] [6] [7] [10] [11] [12] [13]
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Precursor
Graphite electrode Graphite electrode Graphite electrode Graphite Carbon black Carbon black Carbon black
Type of plasma
DC arc DC arc DC arc RF Hybride RF RF
Pressure (kPa)
10 13.3 10 101 101 66 10
Fullerene Yield (%)
Production (g h–1)
