Thermal decomposition and storage safety of mixed isowurtzitane explosives

2-Acetyl-4,6,8,10,12-pentanitro-2,4,6,8,10,12-hexaazaisowurtzitane (MPIW) is a typical incompletely nitrated byproduct (INB) generated during the industrial production of CL-20. It can adversely affect the crystal quality, practical application, and safety performance of CL-20. However, the influence of MPIW on the thermal decomposition behavior and safety of CL-20 remains insufficiently understood. In this work, MPIW was selectively synthesized from 2,6,8,12-tetraacetyl-2,4,6,8,10,12-hexaazaisowurtzitane (TAIW) by controlling the degree of nitration and was characterized by high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS), nuclear magnetic resonance (NMR) spectroscopy, and scanning electron microscopy (SEM). The thermal hazards and decomposition mechanisms of MPIW, as well as its influence on the thermal decomposition behavior of CL-20, were investigated using differential scanning calorimetry (DSC), simultaneous TG–DSC–FTIR–MS, in situ Fourier transform infrared (in situ FTIR) spectroscopy, and finite-temperature string (FTS) simulations. Thermal analysis reveals that MPIW exhibits a markedly lower decomposition peak temperature (222.6–231.9 °C) than CL-20 (243.8–257.3 °C). Increasing the MPIW content from 2 to 15 wt% significantly reduces the exothermic peak temperature of CL-20/MPIW mixtures, with 10%-M/CL-20 exhibiting the most pronounced effect. Analysis of the condensed phase and gaseous pyrolysis products indicates that MPIW does not alter the initial thermal decomposition pathway of CL-20. FTS simulations further suggest that MPIW preferentially melts and decomposes due to its lower Gibbs free energy and higher heat-absorption capacity. The reactive species (NO₂·, NO·, and O·), rapid heat release of MPIW, and interfacial thermal coupling with CL-20 accelerate early N–NO₂ bond cleavage and synergistically promote CL-20 decomposition.