Thermal Kinetics of Energetic CL-20/BTF Cocrystal Induced by Strong Intermolecular Coupling

Abstract

Energetic cocrystals are an attractive new family of explosives with a potential for high energy and low sensitivity. The practical application of cocrystal explosives highly requires in-depth understanding of their thermal kinetic behavior, but the relevant research is still rare. In this study, we selected CL-20/BTF (2,4,6,8,10,12-hexanitrohexaazaisowurtzitane/benzotrifuroxan) cocrystal as a typical cocrystal explosive to investigate its thermal kinetics and decomposition mechanism. The thermal behavior of CL-20/BTF shows no phase transition or solid–liquid melting process before decomposition, which is distinct from those of pure CL-20 and BTF crystals. Further, we identified the thermal decomposition of CL-20/BTF as a particular reaction kinetics consisting of two parallel autocatalytic paths, in which the contribution of these two paths to the overall reaction varies with the change of heating rate. Based on the established kinetic model, important thermal safety indicators including TMRad and SADT are simulated. Finally, in situ infrared spectroscopy was performed to detect the molecular evolution of CL-20/BTF cocrystal during thermal decomposition, which is helpful to understand the origin of its thermal kinetics. It is found that the unique decomposition mechanism of strong intermolecular coupling between CL-20 and BTF molecules is responsible for the parallel reaction paths of the thermal kinetics of the CL-20/BTF cocrystal.

Temperature-dependent decomposition of the CL-20/MTNP cocrystal after phase separation

“…The results showed that the first, second, and third processes were all not single reaction pathways, as explained earlier. 27 From the values of DH 1 , DH 2 , and DH 3 , the relative contributions of all individual processes to the overall process were calculated as À1.6 AE 0.4%, 79.3 AE 3%, and 22.3 AE 2%, respectively. Similar contributions were obtained regardless of the heating rate, thus supporting the fact that the different processes occurred independently and that the deconvolution procedure was reasonable.…”

“…According to them, the decomposition mechanism of strong intermolecularly coupled CL-20 and BTF molecules resulted in parallel reaction pathways of the thermal kinetics of CL-20/BTF cocrystals. 27 Since the groups (2) and (3) of CL-20-based cocrystals have melting points, their thermal kinetics behaviors are distinct from those of groups (1) and (4). It was reported that the low-melting-point components of CL-20-based cocrystals having melting points evaporated when heated under isothermal and unsealed conditions, leaving g-CL-20 or amorphous CL-20.…”

Some CL-20 based energetic cocrystals - A review

“…Finally, in situ infrared spectroscopy was performed to detect the molecular evolution of CL-20/BTF cocrystal during thermal decomposition, which is helpful to understand the origin of its thermal kinetics. It is found that the unique decomposition mechanism of strong intermolecular coupling between CL-20 and BTF molecules is responsible for the parallel reaction paths of the thermal kinetics of the CL-20/BTF cocrystal [134].…”

Thermally Stable and Insensitive Energetic Cocrystals Comprising Nitrobarbituric Acid Coformers

“…Azole-based energetic cocrystals have also been reported, such as 5,5′-dinitro-3,3′-bi-1,2,4-triazole (DNBT) with 5-amino-3-nitro-1,2,4-triazole (ANTA) and 3,6-dinitropyrazolo­[4,3- c ]-pyrazole (DNPP) with 3,4-dinitropyrazole (3,4-DNP), which adopts a 2:1 molar ratio with high crystallographic densities varying from 1.858 to 1.889 g cm –3 . Recently, several cocrystals have been reported based on CL-20, BTF, and HMX with different coformers. − In 2022, Bellas and Matzger reported cocrystals based on an energetic oxidizing salt to achieve a melt-castable energetic material . These studies have emphasized that cocrystallization is a valuable technique for enhancing the performance of explosives and pioneered the way for tailored energetic materials and further motivated the exploration of a library of energetic components for cocrystallization and rational design.…”