Anisotropic Initial Reaction Mechanism and Sensitivity Characterization of the Layered Crystal Structure Explosive ICM-102 under Shock Loading

The layered crystal structure of the explosive ICM-102 (2,4,6-triamino-5-nitropyrimidine-1,3-dioxide) exhibits an extremely low sensitivity, and furthermore, the layering is observed to induce typical anisotropy. To elucidate the anisotropic initial reaction mechanism, ReaxFF-Ig reactive molecular dynamic simulations were performed to investigate the shock-induced reaction of ICM-102 by the piston impact on the supercell directly along different directions at various velocities. A novel method is proposed, which eliminates the boundary reflection at the supercell edge and studies prolonged simulations of the explosive reaction within a small supercell. When subjected to shock loadings along the x and y axes, which are parallel to the multilayers, the layered structure is at first observed to bend prior to undergoing a dimerization reaction via intermolecular O-O or O-H bond formation between the ICM-102 molecules in the same layer. When subjected to shock loading along the z axis, which is perpendicular to the multilayers, the interlayer space is first compressed leading to a dimerization reaction via N-O or C-N bond formation between the ICM-102 molecules from different layers. The energy for dimerization of the molecules in the same layer is lower, and hence, dimerization is observed to be easier. The reaction of ICM-102 is the most intense when the shock loading along the x axis is of the same strength as the shock loading along the other directions. A critical pressure is observed when the reaction rate of ICM-102 changes from slow to fast regardless of the shock loading direction. The critical pressure correlates well with shock sensitivity. The most sensitive orientation of ICM-102 is x axis > y axis > z axis.