Chemical vapor infiltration of C/C composites: Fast densification processes and matrix characterizations P. Delhae `s a, * , M. Trinquecoste a , J.-F. Lines b , A. Cosculluela b , J.-M. Goyhe ´ne `che b , M. Couzi c a Centre de Recherche Paul Pascal, CNRS and Bordeaux 1 University, 33600 Pessac, France b Laboratoire des Composites ThermoStructuraux, CNRS, Snecma, CEA, UB1, 33600 Pessac, France c Laboratoire de Physico-Chimie Mole ´culaire, Bordeaux 1 University, 33405 Talence, France Received 20 February 2004; accepted 18 October 2004 Available online 8 December 2004 Abstract Fast densification processes have been developed to improve the fabrication of C/C composite materials. In this work, a com- parison is made between two techniques: the film boiling technique with a liquid reagent and the gas infiltration method. In both methods, the same home-made reactor was used. For the film boiling technique, the preform is either wrapped or not with a porous thermal barrier. Two different substrates have been densified, a carbon felt (RVC-2000 Ò from Le Carbone-Lorraine), and a 3D carbon cloth (Novoltex Ò from Snecma). In situ temperature gradients and their temporal changes during the infiltration process have been recorded together with the delivered power necessary to maintain a constant deposition temperature. From these experiments, we have concluded about the following main points: • the analysis of in situ parameters, powers and temperatures, and the associated profiles of the pyrocarbon deposits, • the matrix quality with their associated microstructures as characterized by helium density, optical microscopy and Raman scat- tering experiments, • the key role of the evolutive preforms as heat and mass exchangers during the process, and the assisted thermal fluxes inside the reactor. This paper presents results which should allow to control automatically the process at an industrial scale. Ó 2004 Published by Elsevier Ltd. Keywords: A. Carbon composites, Pyrolytic carbon; B. Chemical vapor infiltration; C. Optical microscopy, Raman spectroscopy 1. Introduction During the last years, several new densification pro- cesses have been developed to obtain improved carbon– carbon (C–C) composites useful for thermo-structural applications as for example airplane brakes [1]. These novel methods involve strong thermal gradi- ents inside cold wall reactors. Compared to the classical isothermal technique, a mobile densification front is cre- ated in the porous preform because the heat source, delivered by inductive or resistive Joule effect, is located inside the core. The precursor source can either be a vapor phase or a liquid reagent by direct immersion of 0008-6223/$ - see front matter Ó 2004 Published by Elsevier Ltd. doi:10.1016/j.carbon.2004.10.030 * Corresponding author. Tel.: +33 556 845694; fax: +33 556 84 5600. E-mail addresses: delhaes@crpp-bordeaux.cnrs.fr, delhaes@crpp. u-bordeaux.fr (P. Delhae `s). Carbon 43 (2005) 681–691 www.elsevier.com/locate/carbon