Modeling and simulation of materials synthesis: Chemical vapor deposition and infiltration of pyrolytic carbon

Chemical vapor deposition and infiltration of pyrolytic carbon for the production of carbon fiber reinforced carbon is studied by modeling approaches and computational tools developed recently. Firstly, the development of a gas-phase reaction mechanism of chemical vapor deposition (CVD) of carbon from unsaturated light hydrocarbons (C2H4, C2H2, and C3H6) is presented. The mechanism consisting of 827 reactions among 227 species is based on existing information on elementary reactions and evaluated by comparison of numerically predicted and experimentally determined product compositions taking into account 44 stable gas-phase compounds formed in a tubular flow reactor. Secondly, a model and a computer code for two-dimensional transient simulations of chemical vapor infiltration (CVI) from methane into carbon fiber reinforced carbon are presented. The chemical model is based on a reduced multi-step reaction scheme for pyrolytic carbon deposition, which is derived from a mechanism based on elementary reactions, and a hydrogen inhibition model of pyrolytic carbon deposition. The coupled governing equations of mass transfer, chemical vapor deposition, surface growth, and gas-phase and surface chemical reactions are numerically solved by a finite element method (FEM). The computer code is applied to reveal densification processes of felts with fiber volume fractions of 7.1% and 14.2%. Numerically predicted bulk density distributions agree well with experimental results.