Thermal decomposition behavior of CL-20 co-crystals

Abstract

The thermal stability of bimolecular crystals 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazawurtzitane (CL-20) with 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), 1,4-dinitropipyrazine (DNPP), benzotrifuroxan (BTF), and 1-methyl-3,4,5-trinitro-1H-pyrazole (MTNP) has been studied using isothermal and non-isothermal kinetics methods. The studied co-crystals can be divided into two groups: in the case of co-crystallization of two nitramines 2CL-20/HMX and CL-20/DNPP, the molecular structure of the co-crystal does not undergo significant changes up to the decomposition temperature and the stability of the CL-20 does not change. In the case of co-crystallization of CL-20 with compounds of another class 2CL-20/MTNP and 2CL-20/BTF, the intermolecular interaction is weakened. Being more volatile and/or easily melted than CL-20, the second components (BTF and MTNP) of the co-crystals evaporate/melt when heated, leaving the CL-20 in an amorphous form, which leads to a decrease in its stability. Based on the reaction kinetic model, thermal hazard indicators such as adiabatic time to maximum rate (TMRad), and self-accelerating decomposition temperature (SADT) have been predicted to provide necessary safety information concerning the usage and storage of studied co-crystal. The combustion studies of bimolecular crystals showed that the burning CL-20/HMX and CL-20/DNPP co-crystals obey the mechanism with the leading reaction in the condensed phase. The burning rate of CL-20/BTF co-crystal is determined by reactions in the flame.