Surface-Induced Thermal Decomposition of Energetic Cocrystal CL-20/MTNP Based on In Situ Morphology and Crystal Structure Characterizations

Surfacestructures and properties are particularly importantforvarious materials, as they can transport to the bulk properties inspecial cases and affect the applications of materials. Thermal stabilityis one of the key factors that determine the engineering applicationsof energetic cocrystals (ECCs). Here, in situ morphology and crystalstructure characterization techniques were applied to investigatethe thermal decomposition of hexanitrohexoazaisowurtzitane/1-methyl-3,4,5-trinitro-1H-pyrazole(CL-20/MTNP), an important CL-20-based energetic cocrystal, underisothermal conditions. An unexpectedly low thermal stability was observedfor the CL-20/MTNP cocrystal. The decomposition temperature can beas low as 140 & DEG;C with the evolution of surface defects startingfrom 100 & DEG;C. After decomposition, the cocrystal transformed to & gamma;-CL-20 in a porous morphology. Based on the facet indexingresult, the surface model was also constructed for the cocrystal.In combination with the surface structure and channel-like crystalstructure, a surface-induced decomposition mechanism was proposed,which provides a new perspective on the thermal stability of ECCs,and will be valuable for the estimation of thermal/chemical stabilityfor other cocrystal materials. Based on insitu morphology and crystal structure characterizationtechniques, thermal decomposition of energetic cocrystal CL-20/MTNPwas observed at a much lower temperature than previously reported.A novel surface-induced decomposition mechanism was proposed basedon the experimental observation and crystal structure analysis, whichrefreshes the understanding of the thermal stability of energeticcocrystals.