Film boiling chemical vapor infiltration - An experimental study on carbon/carbon composite materials

Several chemical vapor infiltration (CVI) processes have been developed to increase both the carbon yield and the densification rate for a controlled type of pyrocarbon deposit. Recently, the 'film boiling technique' (so-called Kalamazoo) has been successfully developed for making in particular C/C composite materials. To get a better insight on this process, we have built up two small laboratory reactors with an internal resistive heating. In-situ and ex-situ experiments have been carried out with various liquid carbon precursors. The kinetics analysis has shown that the nature of the precursor plays a role but that the fundamental point is the chemical-hydrodynamical coupling. This process is based on a moving reactive hot frontier with a steep densification profile. From our analysis, it results that the precursor feed comes mainly from the molecular diffusion through the porous preform. The balance between chemical and hydrodynamical constraints leads to different types of pyrocarbon microstructures. (C) 2001 Elsevier Science Ltd. All rights reserved.