Modeling of Chemical Vapor Infiltration Using Boundary Singularity Method

Abstract

Boundary Singularity Method (BSM) was used to model Chemical Vapor Infiltration (CVI) in a fibrous preform. Straight, long fibers of varying cross-sectional geometry, representing fibers of a preform, were placed within a domain of a pre-determined size. The preparation of dense fiber-reinforced Silicon-Carbon (SiC) composites was considered as a representative of CVI methodology, where methyl-trichlorosilane (MTS) was used as both the silicon and carbon donor for the silicon carbide matrix. Concentrations of MTS were then set at the domain boundaries, and the domain was gradually infiltrated with MTS as time progressed. The concentration of MTS at the surface of the preform fibers was calculated using the adopted BSM. For quasi-equilibrium considered, the reaction rate at solid surface is equal to the diffusion rate towards the surface. The Robin or third type boundary condition, which is a linear combination of the values of a function and the values of its derivative on the boundary of the domain, are developed and implemented to BSM. From the fibers surface concentrations obtained by BSM, deposition rates were calculated, and the geometry was updated to reflect the fiber growth during the time step, therefore, the fiber size growth and pore filling was modeled over time. The BSM analysis was verified by comparisons to a known analytical solution of concentric cylinders with a concentration set at the outer cylinder and a reaction at the inner. BSM solutions were also compared to experimental data as well as computational results obtained by a Level-Set Method (LSM). Obtained dynamics of pore size and location will help to evaluate quality of material manufactured by CVI. Porosity transients were obtained to show the relation between initial and current porosities as time progresses.