Density Functional Theory Insight into Chemical Vapor Infiltration

Chemical Vapor Infiltration (CVI) has proven remarkably successful in producing strong and lightweight ceramic matrix composite materials. This technology has matured to regular industrial use. However, two fundamental problems remain, and those are the formation of pores and depositing of weaker material than silicon carbide (SiC), namely, Si. Definitive knowledge of the molecular mechanism would catalyze an advance in the chemical precursors used in CVI. In this work, the CVI reaction is modeled using density functional theory (DFT) calculations. The DFT calculations here use the Bayesian Error Estimation Functional with van der Waals correction (BEEF-vdW). The main findings begin with C deposition determining the rate of solid SiC growth due to Si being far more reactive. Therefore, increasing the C content of the precursor is a logical CVI strategy. Methane (CH4) is more reactive than ethane (C2H6) and ethylene (C2H2) and would be effective as an additive to the chemical precursor. Increasing the deposition rate of C has the benefit of decreasing pure Si deposits. Si melts at 1410 °C and CMCs are used in high-temperature settings beyond this melting point, including in aeroengines and nuclear fuel cladding.