A combined experimental and theoretical study of the thermal decomposition mechanism and kinetics of ammonium dinitramide (ADN)

Abstract

In the present study, an overall decomposition mechanism of ammonium dinitramide (ADN) in the gas phase via density functional theory (DFT) calculations was studied. Thermogravimetry-Fourier transform infrared (TG-FTIR) and thermogravimetry-mass spectrometer (TG-MS) techniques were used to verify the calculation results. In the thermal decomposition of gaseous ADN (ADN(g)), ADN(g) first decomposed into dinitraminic acid (HDN) and NH₃, followed by HDN decomposition into other products with small molecules. HDN is found to isomerize into five isomers (HDN-1–5) in the gas phase. For the initial decomposition of HDN, the favorable decomposition pathway of HDN-4 (a structure of HON(O)NNO₂) is more likely to form HNO₃ and N₂O with a huge release of energy (approximately 45 kcal mol⁻¹). Moreover, product HNO₃ and NH₃ can first combine to form NH₄NO₃. Both calculated and experimental results indicate that the product N₂O is first formed in the thermal decomposition of ADN(g). Moreover, the formation mechanism and kinetics of other products (NH₃, H₂O, NO, N₂O, NO₂, HONO, HNO₃, etc.) were also studied and proposed in the thermal decomposition of gaseous ADN. Overall, the systematic mechanistic investigations have provided new and detailed insights on the mechanism and kinetics of the thermal decomposition of gaseous ADN as well as informative factors to further improve the experimental performances, which can surely be beneficial to other energetic material syntheses.