Effect of ammonium nitrate doping on the low-temperature thermal stability of ammonium dinitramide

Ammonium dinitramide (ADN), an emerging green oxidizer for rocket propellants, faces application limitations due to its low-temperature thermal decomposition characteristics. This study investigates the impact of a small amount of ammonium nitrate (AN) doped into ADN crystal on the stability of ADN crystal. ADN crystal samples containing AN were prepared by solution evaporation method and solvent-antisolvent method, respectively. The results show that AN and ADN form solid solution crystal by solution evaporation method, while solvent-antisolvent method produces phase-separated AN/ADN mixture. Isothermal thermogravimetric analysis conducted at 318-333 K revealed significant decomposition mass loss (3.2-17.5%) exclusively in solid solution samples, whereas the samples of phase-separated AN/ADN crystals show good thermal stability. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and ion chromatography (IC) were used to investigate the influence of different forms and contents of AN in ADN samples on the low-temperature thermal decomposition properties of ADN. The kinetic models in different decomposition stages were obtained by isothermal kinetic method. Molecular dynamics simulations revealed the decomposition mechanism that the doping of AN induced the elongation of N-N bonds in the surrounding ADN structure, leading to instability of the ADN structure. These findings provide a theoretical basis for improving the stability of ADN in storage and application.