Modeling of Chemical Vapor Infiltration Rate Considering a Pore Size Distribution

Abstract

To analyze chemical vapor infiltration (CVI) rates, a simulation model (PC model) was proposed, which is capable of considering difficulties of densification in the internal regions of porous bodies and the pore closure phenomena. In the model, a fictitious tapered pore is constructed based on the pore size distribution of the preform body, and variation of the pore shape during the process is calculated. For simulation study, fictitious tapered pores were constructed using different pore size distribution functions of Gaussian, ␦-function, and flat distribution, and their shapes and characteristics were compared. In the case of the Gaussian flat distribution (large dispersion), the fraction of fine pores was large and these pores became closed near their mouths. Reconversion of temporal fictitious pore shape into the pore distribution function was attempted and the PC model was successfully applied to monitor variations in the pore size distributions during the CVI process.

Chemical Vapor Infiltration Rates of ZrO2 into MoSi2 Porous Bodies and Comparison with Model Calculation

“…The method used to construct the tapered pore is as described in the previous work. 27 (A) Pore Size Distribution and Pore Construction: Tapered pores were constructed based on the pore size distributions of the fine-and coarse-grained preforms (as shown in Fig. 1).…”

“…Some other effects might become significant even at an earlier stage in the process, such as choking in the bottlenecked pores or twodimensional diffusion effects in the winding pores, as discussed in the preceding paper. 27 Precision in determination of the total pore length (L or dx in Eq. (7)) might affect the predictions, as the change of h PC .…”

“…To consider changes in the porosity and the pore structures during CVI in the models, it is necessary to handle the effect of pore closures. In a previous paper, 27 a model (PC model) was presented for analysis of CVI infiltration distances considering the pore closure effect, using a tapered pore geometry constructed from the preform pore size distributions. In this paper, the PC model was applied to an actual CVI system, and comparisons were made between the calculated and the experimental infiltration distances.…”

Modeling of Chemical Vapor Infiltration for Fiber-Reinforced Silicon Carbide Composites Using Meshless Method of Fundamental Solutions

“…An isothermal CVI reaction was modeled in the frame of the 1-D approach in [21]. A tapered pore was considered in [22]. The analytical solutions to the simplified pore models are limited to the infiltration of a singular round pore [6,23].…”