T.Sakuta, Y.Nishida, K.Miyagoshi, Y.Inamura (Kanazawa University)
and H.Takikawa (Toyohashi University of Technology)
Department of Electrical and Computer Engineering, Kanazawa University
Kodatsuno 2-40-20, Kanazawa 920-0942, Japan
Since the first discovery of macroscopic quantities of C60 form in a low-pressure carbon arc by Kratschmer, several experiments have been carried out for synthesis of C60 and the method has been improved. Yoshie et. al. have, for example, reported a novel method for C60 synthesis by using the hybrid plasma which consists of dc plasma and rf plasma at atmospheric pressure and indicated that fullerene can be formed under such a high temperature thermal plasma condition from injected carbon particles in argon gas.
An attempt is made in this paper to use a radio frequency induction plasma for synthesis of fullerene directly from cold carbon particles. The high temperature field around 10,000 K is adequate for fast evaporation of carbon particle injected into the plasma and the following relatively low temperature field around several thousands K is used for high rate quenching of atomic and molecular particle into fullerene.
The induction plasma system used in the experiments consists of a 1.67 MHz oscillator with a maximum power of 200 kW and a plasma torch with an effective diameter of 80 mm and 160 mm length. Experiments were carried out with Ar, He and CO2 gas mixture at three different pressure conditions of 7, 10 and 20 kPa. Such operation condition for gaseous circumstance (He and CO2) were selected as a suitable one for fullerene synthesis, based on the results obtained in the previous dc carbon arc experiments.
The induction plasma under He/CO2 (with the basis of Ar) gas condition was successfully generated at an rf power level of 30 kW for 7, 10 and 20 kPa pressure. Spectroscopic observation of the plasma was made for atomic emission lines from Ar, C and O, and molecular band spectra from C2. Fig. 1 shows the radial distribution of the atomic emission line from C (476 nm) and the molecular spectrum from C2 (band head of [omitted]; 467 nm) at each pressure conditions. Discussions were made on the individual temperature of atomic excitation and molecular vibration at different pressure conditions. The temperature of O-atomic excitation was found to be 7,000 to 12,000 K at the main discharge zone. An analysis of C60 fullerene was made for the soot collected from the reactor chamber by high speed liquid chromatography(HPLC).
Fig.1 Radial Distribution of Spectrum from CI(476 nm) and C2(467 nm) at Different Plasma Pressure [omitted]