Reinforced carbon foams prepared by chemical vapor infiltration: A process modeling approach

Carbon foams are attractive potential materials for shock insulation in extremely high temperatures; but the mechanical properties of the as-prepared foams are too low. Chemical Vapor Infiltration (CVI) of carbon or refractory ceramics is an interesting solution to overcome this drawback. The presented work focuses on the deposition of pyrocarbon from pure propane in carbon foam samples with similar to 96% initial porosity, the treatment being stopped when porosity reaches similar to 85%. Depending on the chosen nanotexture of pyrocarbon, some infiltration gradients may appear in the samples. A modeling approach, aimed at determining the importance of gas diffusion and deposition kinetics during deposition, is presented. validated and discussed. The model features (i) determination of internal surface area during infiltration based on X-ray CMT and 3D image analysis, (ii) a simplified chemical model for hydrocarbon pyrolysis and pyrocarbon deposition, (iii) resolution of balance equations at reactor-scale and sample scale. The model results compare favorably with experimental data. A discussion of the interplay between transport and maturation/deposition kinetics is given, as a guideline for the choice of optimal infiltration parameters. (C) 2008 Elsevier B.V. All rights reserved.