Molecular dynamics study on oxidation mechanism of carbon-based ablative materials under high temperature

Abstract:

Molecular dynamics simulations based on the self-consistent charge density-functional tight-binding (SCC-DFTB) method is used to study the oxidation mechanism of three models (defect-free, atomic-defect and pore-defect) of carbon-based ablative materials under high temperature. It is found that the reaction products at high temperature are mainly CO and CO2. The production process of CO mainly comes from decomposition of C-C bond in epoxy group. The formation of CO2 is relatively complex, mainly from fragmentation of small molecular clusters (C2O2, C3O1, C4O1). It is found that C-C bond is the main way of graphite oxidation reaction, and C-O bond is the controlling factor of CO and CO2 generation rate. In addition, the temperature, defects and holes of the system have important effects on the oxidation mechanism of graphite. By analyzing the oxidation reaction rate, the calculated activation energies of the three model oxidation reactions are 7.56, 2.4 and 1.6 kcal/mol, respectively. The model with atomic defects and holes corresponds to a low activation energy and a high oxidation reaction rate, while the case without defects associates with the lowest oxidation reaction rate due to the highest activation energy.