Thermodynamic properties, decomposition kinetics and reaction models of BCHMX and its Formex bonded explosive

As an attractive new energetic material, cis-1,3,4,6- tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX) and its polymer bonded explosive (PBX) with styrene-butadiene rubber (SBR) binder (Formex type) have been investigated with regard to its thermal decomposition kinetics and reaction models by using DSC, TG and SEM techniques. It was found that the decomposition of BCHMX in dynamic nitrogen could be divided into two steps, while there is only one step for its Formex bonded explosive. The activation energy for decomposition of BCHMX/Formex was obtained to be 221.7 ± 4.99 kJ mol ^-1 by modified KAS method, while the mean activation energies for pure BCHMX are calculated as 233.0 ± 2.1 kJ mol ^-1 for first step and 186.0 ± 0.92 kJ mol ^-1 for the second step. It was further proved that the first decomposition step of BCHMX is autocatalytic, during which the crystal of BCHMX could dissolve in the liquid phase of its thermolysis products on the surface. Besides, the JMA and AC models were found to be appropriate to interpret the two-step decomposition of pure BCHMX and JMA model for BCHMX/Formex, the parameterized reaction models for BCHMX could be established as f(α) = α ^0.45(1 - α) ^1.51 and f(α) = 2.33 × (1 - α)[-ln(1 - α)] ^0.57, while for BCHMX/Formex as f(α) = 2 × (1 - α)[-ln(1 - α)] ^1/2.