碳基烧蚀材料高温氧化反应机理的分子动力学研究

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

本文采用基于紧束缚密度泛函理论的分子动力学,研究高温下碳基烧蚀材料三种模型(无缺陷、原子缺陷以及孔洞缺陷)的氧化反应机制.研究发现高温下的反应产物主要是CO和CO_(2).CO的产生过程主要源于环氧基团中C-C键的裂解,而CO_(2)的形成则较为复杂,主要源于小分子团簇(C_(2) O_(2)、C_(3) O_(1)、C_(4) O_(1))的裂解.C-C键裂解是石墨氧化反应的主要途径,C-O键形成是CO和CO_(2)生成速率的控制因素.此外,体系的温度、缺陷以及孔洞对石墨的氧化反应机制有重要的影响.通过分析氧化反应速率,计算得到三种模型氧化反应的活化能分别为7.56、2.4和1.6 kcal/mol.缺陷越明显活化能越低,则氧化反应速率较高,无缺陷的模型由于活化能最高,其氧化反应速率最低.

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 CO_(2).The production process of CO mainly comes from decomposition of C-C bond in epoxy group.The formation of CO_(2) is relatively complex,mainly from fragmentation of small molecular clusters(C2O_(2),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 CO_(2) 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.