Analytical stability study of the densification front in carbon- or ceramic-matrix composites processing by TG-CVI

Thermal-gradient chemical vapor infiltration (TG-CVI) is a group of alternatives to classical CVI, involving a strong thermal gradient. It allows one to fabricate, e.g. carbon-matrix or ceramic-matrix composite materials starting from a fibrous preform and a gaseous precursor, the cracking of which results in a solid deposit constituting the composite matrix. The main interest of these processes short fabrication time; however, their control is difficult. Past modelling works [Vignoles, G.L., Goyhénèche, J.-M., Sébastian, P., Puiggali, J.-R., Lines, J.-F., Lachaud, J., Delhaès, P., Trinquecoste, M., 2006. The film-boiling densification process for CC composite fabrication: from local scale to overall optimization. Chemical Engineering Science 61, 5336–5353; Nadeau, N., Vignoles, G.L., Brauner, C.-M., 2006. Analytical and numerical study of the densification of carbon/carbon composites by a film-boiling chemical vapor infiltration process. Chemical Engineering Science 61, 7509–7527] have shown that process control and optimization are possible and are based on the notion of densification front. In this paper, a 2D transverse stability study is presented for this front. A condition for stability is worked out; the influence of processing parameters is discussed. It appears that in usual processing cases, the stability criterion is fulfilled, but that it could be violated if some careless process up-scaling is performed.