INDUCTION HEATING CCVD SYNTHESES OF CARBON NANOTUBES

A.R. Biriş1, D. Lupu1, I. Baltog2, M. Baibarac2, S. Lefrant3. G. Filoti2, M. Văleanu2, D. Macovei2, V. Kuncser2, L. Mihuţ2, T. Velula2, D. Predoi2, I. Mişan1

1 National Institute for R&D of Isotopic and Molecular Technologies, 400293 Cluj Napoca, P.O.Box 700, Romania
2 National Institute of Materials Physics, Bucharest, P.O. Box MG-7
3 Institut des Matériaux Jean Rouxel, Laboratoire de Physique Cristalline, 2 rue de la Houssinière, B.P. 32229, 44322 Nantes, France

	Among the methods of carbon nanotube synthesis, the catalytic decomposition (CCVD) of hydrocarbons or other carbon sources is considered the most viable for large-scale production. Recently it was reported [1] that high quality single wall carbon nanotubes (SWNT) can be produced from alcohols as carbon source at low vapor pressures, with the peculiarity that the OH radicals are supposed to act favorably for the etching of amorphous carbon- an undesired by-product often formed during CCVD. We developed a new variant of CCVD, using induction heating [2] which shows additional advantages of time and energy consumption, used later by other authors [3] for the synthesis of SWNTs at the atmospheric pressure, using the same catalyst as in [1], Fe-Co/zeolites. 
	A study has been started to obtain nanotubes on Fe-Co/MgO from alcohools, using induction heating. The MgO as catalyst support, reported for many CCVD syntheses, has the advantage that it allows a high dispersion degree of the catalytic metal(s) and, at the same time, it can be readily removed from the products by dissolution in HCl, which does not alter the structure of the nanotubes. 
	The dispersion degree of Fe on the MgO  studied by Mössbauer Spectroscopy revealed the presence of comparable amounts of α-Fe(Co) and Co(Fe) respectively particles of similar size, below 4 nm.
	The syntheses were performed in a quartz tube in the temperature range 600-900 oC from ethanol,  maintaining continuously a constant ethanol vapor pressure of 5 Torr by pumping to vacuum.
	The products have been characterized by SERS Raman Spectroscopy using three diferent excitation wavelengths (1064, 676.4 and 514.5 nm) for the observation of the G, D, D’ bands and the radial breathing mode (RBM)- characteristic to SWNTs and double wall carbon nanotubes. The results revealed both SWNT and DWNTs in the range of diameters 0.78 – 2 nm, with high ratios of intensity for G/D bands.
	 The high resolution TEM images of the samples synthesized at 900 oC, revealed also high quality nanotubes, without amorphous carbon deposit.

REFERENCES
[1]S. Maruyama, R. Kojima, Y. Miyauchi, S. Chiashi, M. Kohno, Chem. Phys. Lett. 360(2002)229.
[2]D. Lupu, A.R. Biriş, A. Jianu, C. Bunescu, E. Burkel, E. Indrea, G. Mihăilescu, S. Pruneanu, L. Olenic, I. Mişan, Carbon, 42(2004)503.
[3]A. Okamoto, H. Shinohara, Carbon 43(2005)431.