Synthesis of Fullerenes and Other Nanomaterials in Arc Discharge

Transcription

1 Fullerenes, Nanotubes and Carbon Nanostructures, 16: , 2008 Copyright # Taylor & Francis Group, LLC ISSN X print/ online DOI: / Synthesis of Fullerenes and Other Nanomaterials in Arc Discharge G. N. Churilov L.V. Kirensky Institute of Physic, Krasnoyarsk, Russia Abstract: The technique of some nanosized substances synthesis in arc discharge plasma at atmospheric pressure is considered. The results of synthesis in the arc discharge with different feeding are presented: dc, power current of 50 Hz, ac of 44 khz and their combinations. Also, the investigation results of influence of an acoustic field and a co-phased magnetic field on fullerene synthesis at atmospheric pressure are presented. Keywords: Fullerenes, Fullerene derivatives, Arc discharge, High frequency current, Sound waves INTRODUCTION It is well known that two ways exist for the synthesis of substances the properties, of which are determined by their nanoscaled structures. There are the way from above fragmentation of solid and the way from below atomic or molecular assembling. Accordingly, nanodiamonds form at carbon material explosion, and fullerenes and nanotubes form in arc discharge. In both cases the substances consist of pure carbon, but their properties essentially differ. In this paper, attention will concentrate on the methods of some nanosized materials in the arc discharge plasma. After the appearance of experimental research of sputtering of amorphous carbon with high 13 C content (1), it became obvious that fullerene molecule assembling occurred at the atomic level. The next works devoted to fullerene arc spectroscopy have shown that the Address correspondence to G. N. Churilov, Kirensky Institute of Physics, Siberian Branch, Russian Academy of Science, Akademgorodok, Krasnoyarsk , Russia. churilov@iph.krasn.ru 395

2 396 G.N. Churilov assembling proceeds from carbon atoms and carbon clusters C 2 (2). So, the necessary condition is the sputtering of carbon into atoms. One cannot say that since the discovery of fullerene production method by W. Kraetschmer et al. in 1990 (3) that no new interesting method has been suggested (4). However, the arc discharge method of graphite conversion to fullerene-containing carbon condensate in helium atmosphere at 100 torr pressure remains the most popular until now. For some investigators, fullerenes are the only soluble carbon form that can be used for technological purposes. Also, for some investigators, fullerenes are precursors used for metal-organic compounds synthesis. There would be more interest in fullerenes if they were more readily available and cheaper. Therefore, the search for efficient synthesis remains the actual problem. EXPERIMENTAL We have shown that in the plasma of ac arc discharge of khz frequency, one can obtain fullerenes at atmospheric pressure at her efficiently. Atmospheric pressure synthesis allows excluding vacuum equipment, and this fact decreases the fullerene cost price to some extent (5). The setup allows obtaining carbon condensate containing up to 10% fullerenes. The fullerene composition close to the composition obtained in Kraetschmer s setup with rather more contents of higher fullerenes. The use of the described setup for quantitative fullerene synthesis is not the purpose because the major part (up to 50%) of graphite transforms to turbostratic graphite, not to fullerene-containing soot. This setup is suitable for fullerene derivatives synthesis. The heterofullerenes with boron, silicon and nitrogen were obtained. Among the endohedral fullerenes, the molecules with hydrogen and manganese were obtained. Also in the synthesis products the exohedral complexes with oxygen were registered. Much time passed since the fullerenes discovery, but the industrial method of fullerene production as a mineral product was not realized. In this connection the development of efficient fullerene synthesis technology remains as the actual problem. RESULTS AND DISCUSSION The results of fullerene production method at atmospheric pressure in the same water-cooling chamber with different electrode placement and different frequency current are presented in this paper. In Figure 1 the

3 Fullerene Synthesis in Arc Discharge 397 Figure 1. The water-cooling chamber. water-cooling chamber with changeable electrode placement and arc different feeding (dc, ac 50 Hz, and ac 44 khz) is shown. Only 1% of graphite transforms to fullerenes. The use of dc current as discharge feeding leads to more than 1% of fullerene contents at the 100A current and at the production rate not more than 6 mg per minute (Figure 2). The results of kilohertz frequency range discharge are shown in Figure 3. We can see that the use of high frequency current allows achieving fullerene contents in soot up to 10% at the conversion practically equal to 100%. The cost of a high frequency current generator is much lower than the cost of a vacuum setup; therefore, this method can be considered more applicable for industrial fullerene production. The fullerene contents cannot be considered the only significant parameter characterizing the method of its production. The rate of fullerene-containing soot formation is important. It is necessary to provide the highest erosion at sufficiently high fullerene contents. One should also increase the lifetime of eroded electrodes at keeping high cooling rate in the chamber. At ac and dc current combination supplied to three electrodes, one can produce fullerenes at a rate of 6 gram per hour (Figure 4). Supplement of another electrode pair allowed us to increase the rate up to 10 gram per hour. At a fully automated process of fullerene production, it is predicted that the productivity of one module of the setup will amount to kg per month. Further research of more productive synthesis was conducted with the influence of different fields on the fullerene arc. The transformer with inductors allowed obtaining in arc area co-phased magnetic fields up to

4 398 G.N. Churilov Figure 2. Influence of current on fullerene synthesis at dc: a) soot yield (1), recrystalized graphite yield (2), electrode consumption (3); b) fullerene contents in soot (1), fullerene production rate (2).

5 Fullerene Synthesis in Arc Discharge 399 Figure 3. Influence of current on fullerene synthesis at ac 44 khz: a) soot yield (1), recrystalized graphite yield (2), electrode consumption (3); b) fullerene contents in soot (1), fullerene production rate (2).

6 400 G.N. Churilov Figure 4. Influence of current on fullerene synthesis at combined feeding: a) soot yield (1), recrystalized graphite yield (2), electrode consumption (3); b) fullerene contents in soot (1), fullerene production rate (2) Tesla. The magnetic field parallel to the arc current did not lead to the change in fullerene formation rate, and ratio between different fullerenes in the fullerene-containing soot. The perpendicular magnetic

7 Fullerene Synthesis in Arc Discharge 401 Figure 5. Effect of the sound intensity of: a) fullerene-containing soot percentage (1), recrystallized graphite percentage (2); b) fullerene percentage (1), mass yield of fullerenes (2).

8 402 G.N. Churilov field decreased the carbon condensate production rate by more than two times. It is connected with delocalization of electrode spots and erosion decrease so the energy was spent to electrodes heating and, accordingly, to cooling water. The most interesting results were obtained at acoustic field generation in the chamber. The maximum sound intensity reached in the chamber was 115 db. In Figure 5, there is the dependence of the fullerene yield from soot and recrystallized graphite yield on sound intensity. One can see that with sound power increasing, at first the amount of synthesized soot is increasing and the amount of recrystallized graphite is decreasing; then one can see back trend. Usually, extraction of fullerenes in these experiments was carried out without Soxlet apparatus. In Figure 5, in the region of 120 db the sharp increase of fullerene content is detected. The fullerene content at this point is equal to 8%, but one should remember that it is not a full extraction of fullerenes. Applying the Soxlet apparatus can increase this value up to 13%. CONCLUSION It was shown that the content of fullerenes depends on the conditions of synthesis, and the arc sputtering of graphite is the most effective way of fullerene synthesis. The investigations have shown that magnetic field ((0.36 T) does not influence fullerene synthesis, and the acoustic field (120 db) increases fullerene yield up to 13%. ACKNOWLEDGMENTS The work has been carried out under support of Siberian Division of Russian Academy of Science and Russian Foundation for Basic Research (project ). REFERENCES 1. Ebbesen, T.W., Tabuchi, J., and Tanigaki, K. (1992) The mechanistics of fullerene formation. Chem. Phys. Lett., 191: Afanas ev, D.V., Blinov, I.A., Bogdanov, A.A., Dyuzhev, G.A., Karataev, V.I, and Kruglikov, A.A. (1994) Fullerene creation in arc discharge. J. Tech. Phys., 64(10): Kratschmer, W., Fostiropoulos, K., and Huffman, D.R. (1990) The success in synthesis of macroscopic quantities of C60. Chem. Phys. Lett., 170: 167.

9 Fullerene Synthesis in Arc Discharge Howard, J.B., McKinnon, T., Johnson, M.E., Makarovsky, Ya., and Lafleur, A.L. (1992) Production of C60 and C70 fullerenes in benzene-oxygen flames. J. Phys. Chem., 96: Churilov, G.N. (2000) Plasma synthesis of fullerenes. Instruments and Experimental Techniques, 43(1): 1 10.

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