Cluster evolution during the early stages of heating explosives and its relationship to sensitivity: a comparative study of TATB, β-HMX and PETN by molecular reactive force field simulations

Abstract

Clustering is experimentally and theoretically verified during the complicated processes involved in heating high explosives, and has been thought to influence their detonation properties. However, a detailed description of the clustering that occurs has not been fully elucidated. We used molecular dynamic simulations with an improved reactive force field, ReaxFF_lg, to carry out a comparative study of cluster evolution during the early stages of heating for three representative explosives: 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), β-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and pentaerythritol tetranitrate (PETN). These representatives vary greatly in their oxygen balance (OB), molecular structure, stability and experimental sensitivity. We found that when heated, TATB, HMX and PETN differ in the size, amount, proportion and lifetime of their clusters. We also found that the clustering tendency of explosives decreases as their OB becomes less negative. We propose that the relationship between OB and clustering can be attributed to the role of clustering in detonation. That is, clusters can form more readily in a high explosive with a more negative OB, which retard its energy release, secondary decomposition, further decomposition to final small molecule products and widen its detonation reaction zone. Moreover, we found that the carbon content of the clusters increases during clustering, in accordance with the observed soot, which is mainly composed of carbon as the final product of detonation or deflagration.

On the mechanism of carbon nanostructures formation at reaction of organic compounds at high pressure and temperature

“…Authors of the works 32,33,41,42 assert that the aggregation of carbon occurs already in the reaction zone. V. F. Anisichkin obtained in work 41 that carbon components of molecules of fine-grained mixture HEs completely mix before the oxidation, i.e., inside the reaction zone, and the oxidation occurs later.…”

“…Breusov demonstrated from energy considerations 32 that the formation of carbon clusters is related to the partial breakup of chemical bonds in molecules and to the formation and growth of carbon skeleton. In the work, 33 the clustering of carbon at the heating of molecules of TATB, HMX and PETN was simulated by the molecular dynamics. Carbon nanostructures in the reaction zone were obtained.…”

“…Aggregation of carbon atoms is determined by diffusion and proceeds in picoseconds. 33,40 At thermodynamic parameters characteristic for the detonation, the state of carbon corresponds to the condensed phase, 7,10 in contrast to other substances (N, N 2 , H 2 O, H, O, CO, CO 2 , etc.). Probability of aggregation at a collision of two carbon atoms is close to 100%, whereas reactions of gaseous substances under the detonation conditions require of order of 1000 collisions for one elementary reaction.…”

“…32,33 The data of Table I show the dependence of the maximum conductivity σ max on the mass fraction of carbon r c , and the absence of relation with the critical diameter and the chemoionization.…”

Study of thermal instability of HMX crystalline polymorphs with and without molecular vacancies using reactive force field molecular dynamics

“…The molecular origin of the anisotropic sensitivity was suggested to be the intermolecular steric arrangements across a slip plane induced by shock compression. Wen et al [44] applied ReaxFF-MD to study cluster evolution during the early state of heating of explosives and its relationship to sensitivity. It was observed that clustering tendencies for explosives like β-HMX, TATB and PETN became less pronounced when the oxygen balance was increased.…”