Department of Mechanical Engineering, Texas Tech University, Lubbock, Texas 79424, USA.
J Chem Phys. 2013 Aug 21;139(7):074701. doi: 10.1063/1.4818167.
Coupling molecular scale reaction kinetics with macroscopic combustion behavior is critical to understanding the influences of intermediate chemistry on energy propagation, yet bridging this multi-scale gap is challenging. This study integrates ab initio quantum chemical calculations and condensed phase density functional theory to elucidate factors contributing to experimentally measured high flame speeds (i.e., >900 m∕s) associated with halogen based energetic composites, such as aluminum (Al) and iodine pentoxide (I2O5). Experiments show a direct correlation between apparent activation energy and flame speed suggesting that flame speed is directly influenced by chemical kinetics. Toward this end, the first principle simulations resolve key exothermic surface and intermediate chemistries contributing toward the kinetics that promote high flame speeds. Linking molecular level exothermicity to macroscopic experimental investigations provides insight into the unique role of the alumina oxide shell passivating aluminum particles. In the case of Al reacting with I2O5, the alumina shell promotes exothermic surface chemistries that reduce activation energy and increase flame speed. This finding is in contrast to Al reaction with metal oxides that show the alumina shell does not participate exothermically in the reaction.
将分子尺度反应动力学与宏观燃烧行为相结合对于理解中间化学对能量传播的影响至关重要，但弥合这一多尺度差距具有挑战性。本研究结合了从头算量子化学计算和凝聚相密度泛函理论，以阐明与卤基含能复合材料（如铝（Al）和五氧化二碘（I2O5））相关的实验测量的高速火焰（即>900 m∕s）的因素。实验表明表观活化能与火焰速度之间存在直接相关性，表明火焰速度直接受到化学动力学的影响。为此，第一性原理模拟解决了促进高速火焰的关键放热表面和中间化学，以促进动力学。将分子水平的放热性与宏观实验研究联系起来，可以深入了解氧化铝壳对钝化铝颗粒的独特作用。在 Al 与 I2O5 反应的情况下，氧化铝壳促进了放热表面化学，从而降低了活化能并提高了火焰速度。这一发现与 Al 与金属氧化物的反应形成对比，后者表明氧化铝壳在反应中不会放热参与。
