Thermal and evolved gas analyses of decomposition of ammonium dinitramide-based ionic liquid propellant using TG–DSC–HRTOFMS

Thermal and evolved gas analyses were carried out to assess the decomposition of an ionic liquid propellant consisting of ammonium dinitramide (ADN), methylammonium nitrate (MMAN) and urea, using thermogravimetry–differential scanning calorimetry–high-resolution time-of-flight mass spectrometry (TG–DSC–HRTOFMS). This technique simultaneously assesses the thermal and evolved gas behavior and is able to distinguish between products having similar mass-to-charge ratios, based on accurate mass determinations. ADN/MMAN and ADN/MMAN/urea mixtures were found to decompose to form NH₃, H₂O, HCN, CO, N₂, CH₂O, CH₃NH₂, HNCO, CO₂, N₂O and HNO₃, and possible reaction schemes for the decomposition processes were developed. Interactions between ADN and MMAN appear to enhance the generation of N₂, while the presence of urea reduces the net exothermic heat of reaction due to the endothermic pyrolysis reaction of urea to NH₃ and HNCO, followed by the reaction HNCO + H₂O → NH₃ + CO₂.