Hydrothermal recrystallization of layered HMX crystals with tunable reactivity and their decomposition mechanisms

In this study, recrystallization of recently reported layered HMX (L-HMX) via hydrothermal methods would produce either HT-LH-7 metastable structure orHT-LH-10 densely packed crystalline architecture. Experimental results demonstrated that although the two-dimensional triaminoguanidine-glutaraldehyde polymer (TAGGP) is no longer intercalated between HMX molecular layers after recrystallization, it can still guide the directional growth of HMX crystals with confinement effects. The decomposition activation energy of received hybrid HMX crystals ranges from 108.8 to 161.2 kJ∙mol⁻¹, depending on the experimental conditions. It means the final crystal structure and reactivity could be well tuned by using the same starting material namely the L-HMX crystals. As the heating rate increases from 2.5 to 10 K∙min⁻¹, The ΔH values of pure HMX varies significantly, from 865.8 to 1816 J∙g⁻¹. Notably, the received hybrid HMX crystals demonstrate more stable ΔH values, owing to their optimized catalytic structures formed via hydrothermal processing. The catalytic effects of free radicals generated by thermolysis of TAGGP makes hybrid HMX crystals follow chain reactions with higher heat releases. Gas-phase product analysis revealed a significant increase in the CO₂/N₂O ratio and a drop in CO/N₂, confirming that TAGGP makes HMX decomposes more completely, and thereby with enhanced energy release. Both hybrid hydrothermal HMX products exhibited a dual-mode decomposition mechanisms: at low conversion rate (α < 0.5), the process followed the A2 model (two-dimensional nucleation and growth), whereas at higher conversion rates (α > 0.5), it has been changed to the L2 model (random chain scission).