J. Phys. IV France 02 (1991) C2-143-C2-150
THE CHEMICAL VAPOUR IMPREGNATION OF POROUS SOLIDS. MODELLING OF THE CVI-PROCESSE. FITZER, W. FRITZ and G. SCHOCH
Institut für Chemiche Technik der Universität Karlsruhe, Kaiserstrasse 12, D-7500 Karlsruhe 1, Germany
The paper presents a model of the CVD- and CVI- proceses based on the principles for the description of the gas solid reactions on the outer surface of the substrate and the inner surface of the pores. The model parameters mass transfer coefficient and rate constant of the chemical reaction at the surface were determined experimentally. The model for the inpore deposition takes into account that during the CVI- process the geometry of the pores changes and thus no steady state is reached during the process. The precalculation of the CVI- effect using the above model and experimental results are compared for demonstration of the applicability of the mathematical model. Also for porous substrates with a pore size distribution the model describes quantitatively the impregnation effect. The experimental demonstration was performed as SiC- CVI of substrates with micropores between 3 and 15 µm in diameter and as SiC- CVI of SiC- whisker sheets with a diameter distribution ranging from 0.1 µm to 200 µm.
© EDP Sciences 1991