Monte Carlo simulations of texture interface formation within pyrocarbon matrix of carbon/carbon composites

Based on the Particle-Filler model (P-F) and Langmuir-Hinshelwood mechanism of pyrocarbon deposition, a multistep heterogeneous reaction kinetic mechanism including adsorption/desorption/dehydrogenation reactions was proposed, by which continuous deposition of pyrocarbon on surface of the carbon fiber in the preparation of carbon/carbon composites and the formation process of texture interface were theoretically modeled. Then a Gibbs ensemble Monte Carlo (MC) method was used to simulate the pyrocarbon texture formation in chemical vapor infiltration (CVI) process. This study shows that P-F bimolecular reaction happening on the surface of deposition will be restricted due to the fact that the adsorption of the light aromatic component in gas phase represented by C6 is more likely to be suppressed, compared to the adsorption of the light linear hydrocarbons represented by C2. With the change of the concentration ratio R of C6 to C2 component, the texture formation process of pyrocarbon exhibits bi-stability distribution leading to the formation of two different metastable phases, i.e. medium-textured (MT) and high-textured (HT) pyrocarbons. And a sharp texture interface appears in the pyrocarbon of the carbon/carbon composites. The further simulation results indicate that the bistable transition of pyrocarbon textures is accompanied by a hysteresis cross domain, which is affected by the composition parameter R of gas phase, initial concentration of light linear hydrocarbons C2 and deposition temperature T. CVI process parameters have to be selected outside the range of hysteresis cross domain to produce pyrocarbon with a pure composition.