Effects of Defects on Thermal Decomposition of HMX via ReaxFF Molecular Dynamics Simulations
Effects of Defects on Thermal Decomposition of HMX via ReaxFF Molecular Dynamics Simulations
复制标题
通过 ReaxFF 分子动力学模拟缺陷对 HMX 热分解的影响
DOI：
10.1021/jp105805w
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发表时间：
2011-01-20
影响因子：
3.3
通讯作者：
Huang, Feng-Lei
中科院分区：
文献类型：
--
作者：
Zhou, Ting-Ting;Huang, Feng-Lei
采用ReaxFF分子动力学模拟方法研究了不同温度下分子空位对凝聚相beta-HMX分解机理和反应动力学的影响。结果表明，在高温和低温下，存在三种主要的初始分解机制，即N-NO2键解离，HONO消除，和协调环分裂。三种机理对HMX初始分解的贡献均受分子空位的影响，且随温度的变化而变化。在高温（2500 K）下，空位能显著促进N-N键断裂和协同环断裂，但阻碍HONO的生成。N-N键解离和HONO消除是两种主要的竞争反应机制，前者在初始分解中占主导地位。凝相HMX在高温下不易发生协同开环。在较低的温度（1500 K），最优先的初始分解途径是N-N键的解离，其次是NO3（O迁移）的形成，虽然所有三个机制是由分子空位促进。在较低的温度下，对协同环的断裂有明显的促进作用。协调环断裂产物出现在有缺陷的体系中，而不出现在完整的晶体中。在较低温度下，HONO消除的机制不太重要。我们还估算了不同空位浓度下的反应速率常数和初始分解活化能。分子空位通过增加反应速率常数和降低活化能垒加速了凝聚相HMX的分解。
Effects of molecular vacancies on the decomposition mechanisms and reaction dynamics of condensed-phase beta-HMX at various temperatures were studied using ReaxFF molecular dynamics simulations. Results show that three primary initial decomposition mechanisms, namely, N-NO2 bond dissociation, HONO elimination, and concerted ring fission, exist at both high and lower temperatures. The contribution of the three mechanisms to the initial decomposition of HMX is influenced by molecular vacancies, and the effects vary with temperature. At high temperature (2500 K), molecular vacancies remarkably promote N-N bond cleavage and concerted ring breaking but hinder HONO formation. N-N bond dissociation and HONO elimination are two primary competing reaction mechanisms, and the former is dominant in the initial decomposition. Concerted ring breaking of condensed-phase HMX is not favored at high temperature. At lower temperature (1500 K), the most preferential initial decomposition pathway is N-N bond dissociation followed by the formation of NO3 (O migration), although all three mechanisms are promoted by molecular vacancies. The promotion effect on concerted ring breaking is considerable at lower temperature. Products resulting from concerted ring breaking appear in the defective system but not in the perfect crystal. The mechanism of HONO elimination is less important at lower temperature. We also estimated the reaction rate constant and activation barriers of initial decomposition with different vacancy concentrations. Molecular vacancies accelerate the decomposition of condensed-phase HMX by increasing the reaction rate constant and reducing activation barriers.