Letters to the editor / Carbon 39 (2001) 615 –628 621 graphitic multiwalls were formed as a result of the Science and the Research Institute for Solvothermal Tech- hydrothermal treatment at 6008C. The growth of multiwall nology, Takamatsu, Japan are gratefully acknowledged. nanotubes has been observed in hydrothermal conditions recently [4–6]. Because this is new and interesting evi- dence of carbon reorganization at low temperatures, ob- References tained without optimization of the process or control of any experimental parameters, it seems a very promising [1] Tanaka K, Yamabe T, Fukui K. The science and technology of carbon nanotubes, Elsevier, 1999. method for obtaining nanostructured carbons. [2] Ugarte D. Onion like graphitic particles. Nature HRTEM observations and Raman characterization pro- 1992;359:707–9. vided evidence that carbon atoms rearrange to form curved [3] Dresselhaus MS, Williams KA, Eklund PC. Hydrogen absor- graphitic layers during hydrothermal treatment. The tion in carbon materials. MRS Bull 1999;24(11):45–50. growth of graphitic multiwall structures in hydrothermal [4] Calderon-Moreno JM, Swamy S, Yoshimura M. Carbon conditions takes place by different mechanisms than in the nanocells and nanotubes grown in hydrothermal fluids. Chem gas-phase. Hydrothermal conditions provide a catalytic Phys Lett 2000;329(10):317–22. effect caused by the reactivity of hot water that allows the [5] Gogotsi Y, Libera JA,Yoshimura M. Hydrothermal synthesis graphitic sheets to growth, move, curl and reorganize of multiwall carbon nanotubes. J Mater Res bonds at much lower temperatures than in the vapor phase 2000;15(12):2591–4. [6] Calderon JM. Yoshimura M. Hydrothermal Processing of in inert atmospheres. Such reorganization is induced by the High Quality Multiwall Nanotubes from Amorphous Carbon. physical tendency to reach a more stable structure with J Am Chem Soc 2001;123:741–2. lower energy, by reducing the number of dangling bonds in [7] Libera JA, Gogotsi Y, Carbon 2001, in press. the graphitic sheets. The mechanism by which amorphous [8] Swamy SS, Calderon Moreno JM, Yoshimura M. Stability of carbon rearranges into curled graphitic cells in the hot single wall carbon nanotubes under hydrothermal conditions. hydrothermal fluid is complex and involves the debonding J Mater Res 2000, submitted. of graphitic clusters from the bulk carbon material in [9] Akagaki T, Hokkirigawa K, Okabe T, Saito K. Friction and hydrothermal conditions. Closed graphitic lattices can be wear of wood ceramics under oil and water lubricated sliding favored at increasing temperatures or more chemically contacts. J Porous Materials 1999;6(3):197–204. reactive environments. [10] Cheng HM, Endo H, Okabe T, Saito K, Zheng GB. Graphitization behavior of wood ceramics and bamboo ceramics as determined by X-ray diffraction. J Porous Materials 1999;6(3):233–7. [11] Dresselhaus MS, Dressselhaus G, Pimenta MA, Eklund PC. Acknowledgements Raman scattering in carbon materials. In: Pelletier MJ, editor, Analytical applications of raman spectroscopy, Ox- We thank Prof.Y. Gogotsi, Dept. of Mater. Eng., Drexel ford: Blackwell Science, 1999, pp. 367–434. University, PA, USA for stimulating discussions. Financial [12] Tuinstra F, Koening JL. Raman spectrum of graphite. J support from the Japan Society for the Promotion of Chem Phys 1970;53:1126–30. A chemical vapour deposition process for the production of carbon nanospheres a, b a c d d * Ph. Serp , R. Feurer , Ph. Kalck , Y. Kihn , J.L. Faria , J.L. Figueiredo a ` ´ Laboratoire de Catalyse, Chimie Fine et Polymeres, Ecole Nationale Superieure de Chimie de Toulouse, 118 Route de Narbonne, 31077 Toulouse, France b ´ CIRIMAT CNRS UMR, Ecole Nationale Superieure de Chimie de Toulouse, 118 Route de Narbonne, 31077 Toulouse, France c CEMES-CNRS No. 8011, 2 Rue Jeanne Marvig, 31055 Toulouse, France d ´ ´ ´ Laboratorio de Catalise e Materiais, Departamento de Engenharia Quımica, Faculdade de Engenharia U. Porto, Rua Dr. Roberto Frais, 4200-465 Porto, Portugal Received 1 August 2000; accepted 14 December 2000 Keywords: A. Carbon beads, Carbon microbeads,Vapor grown carbon; B. Chemical vapor deposition; C. Electron energy loss spectroscopy (EELS) *Corresponding author. Tel.: 133-5-6288-5693; fax: 133-5-6288-5600. E-mail address: pserp@ensct.fr (P. Serp). 0008-6223 / 01 / $ – see front matter  2001 Elsevier Science Ltd. All rights reserved. PII: S0008-6223(00)00324-9