THE EFFECT OF CHEMICAL COMPONENTS AND DENSITIES ON THE CLUSTERS EVOLUTIONS DURING THE EARLIER THERMAL DECOMPOSITIONS OF TNT, TATB, NM, HMX AND PETN

摘要

The formation mechanism of clusters in detonation reaction zone is of great interest among energetic materials studies. However, a comprehensive study is still lacking today for understanding their clustering behaviors. In this article, we present a systematic study on the clusters formation and dissociation characteristics of five representatives of 1,3,5-trinitrotoluene (TNT), triaminotrinitrobenzene ( TATB ) , Nitromethane (NM) , octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and pentaerythritol tetranitrate (PETN) during the initial thermal decomposition processes using a ReaxFF based molecular dynamics. They were selected in term of their chemical components, sensitivities, decomposition activities and reaction zones. These representatives possess different oxygen balances (OB), which can influence much the cluster formation and dissociation. For an energetic molecule CaHbOcNd, its OB is (c-2a-b/2)/c × 100%. Accordingly, the OB of TNT, TATB, NM, HMX and PETN are -175%, -150%, -75%, -50%and -16.7%, respectively. These representatives all have been investigated using a same method, ReaxFF, which will be adopted in this work too. After relaxation, we performed ReaxFF based NVT-MD molecular dynamic simulations on each cell for 50 ps with three temperatures of 2000, 2500 and 3000 K. After simulating the cluster formation and dissociation of these three representatives, we found that the cluster distributions (size and amount) are variable and much dependent on molecular component (e.g., OB) and reaction temperature. TATB produces the most and biggest clusters because there are less oxygen which can swallow big clusters and tear them into smaller fragments. PETN produces fewest and the smallest clusters due to its highest oxygen content. We also found that there are a positive correlation between the clustering characteristics and the width of reaction zone and the explosive sensitivities. Larger clusters can tone down the speed of the reaction process, making the explosive more insensitive. Our finding is in good agreement with the statement of Manaa et al. Our results presented detail information of carbonaceous clusters formation during the condensed-phase decomposition of TNT, TATB, NM, HMX and PETN crystals under extremely high temperature conditions. This contributes to analyze the evolution of carbon clusters at the early stages of high energy explosives decomposition and provides an atomic level understanding of the influence of chemical components on the clusters evolution. Our study also provides an important insight into the understanding of the correlations between the chemical components and detonation and safety properties.