Effect of metal ion impurities on the crystallization and thermal properties of HMX

Metal ions, as common impurities in the crystallization process of explosives, have a significant influence on the crystal quality and performance. The effects of Fe 3+ , Zn 2+ , Ca 2+ and Na + ions on the crystallization and thermal properties of octogen (HMX) were studied. And the defect distribution as well as formation process of the explosive crystals doped with the metal ions were analysed. ICP, XPS and an etching method were utilized to characterize the contents and distributions of residual metal ions in the HMX crystals. The effects of the metal ions on the thermal decomposition and phase transition of HMX were obtained based on DSC-TG and in situ XRD. The mechanism of the influence of the metal ions on the crystallization of HMX was also explored. The results showed that the metal ions would change the nucleation growth mode of HMX to form dispersed crystalline HMX. The residual metal ions were mainly adsorbed on the crystal surface and included in the crystal. The metal ions had a significant influence on the thermal properties of HMX, with Ca 2+ and Fe 3+ inhibiting the thermally induced phase transition of HMX, Na + promoting the phase transition of HMX, and the effect of Zn 2+ on the phase transition of HMX depending on its concentration. The growth mechanism of doped HMX was lamellar stacking, and the metal ions changed the quality of the crystal by hindering the growth step of the HMX crystal. Since the crystal quality is highly related to the thermal performance, the safety of the explosive is affected.