FORCED-FLOW CHEMICAL VAPOR INFILTRATION OF POROUS CERAMIC MATERIALS

A mathematical model for forced-flow chemical vapor infiltration (CVI) for densification of porous ceramic composites is presented. The process consists of mass transport of reactants by both convection and diffusion into a porous preform, decomposition of reactants, and subsequent deposition of solid product on pore surfaces. The preform is represented by a Bethe lattice, and percolation theory is used to account for utilized, unutilized, and blocked pore space. The effective medium approach used earlier for modeling conventional CVI is extended here to include forced flow of reactants into the preform. The effect of reactant flow rates, hot face temperature, and pore size distribution on densification is studied and compared with the conventional process. Optimum conditions for uniformity and low residual porosity in the final product are suggested. © 1990, The Electrochemical Society, Inc. All rights reserved.