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-call ed 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-si tu and ex-situ experiments have been carried out with various liquid carbon precursors. The kinetics analysis has shown that the nature of the precurs or plays a role but that the fundamental point is the chemical-hydrodynamic al coupling. This process is based on a moving reactive hot frontier with a steep densification profile. From our analysis, it results that the precur sor feed comes mainly from the molecular diffusion through the porous prefo rm. The balance between chemical and hydrodynamical constraints leads to di fferent types of pyrocarbon microstructures. (C) 2001 Elsevier Science Ltd. All rights reserved.