Hydroxylammonium nitrate (HAN; [NH3OH+] [NO3-]) is currently the most promising oxidizer for use in future green liquid propellants for spacecraft applications. To allow the effective development and use of HAN-based propellants, it is important to understand the associated reaction mechanisms, including auto-catalytic processes. The present work developed a detailed chemical kinetics model for the liquid phase reactions of aqueous HAN, based on quantum chemistry calculations using the G4//ωB97X-D/SMD method. The thermal corrections, formation enthalpies, entropies and heat capacities of chemical species were calculated from the partition functions using statistical machinery based on the G4 level of theory. Rate coefficients were also determined to allow the application of transition state theory and variational transition state theory to reactions identified in our previous studies. Thermal and evolved gas analyzes were also conducted for 92 wt% aqueous HAN solution under specific heating conditions. The new model employed herein simulates the thermal decomposition of such a solution, and successfully predicts the heat of reaction and the gases that result from decomposition under these conditions. This new kinetics model also provides a mechanism for the decomposition of HAN. In this mechanism, the initial reaction HAN → HNO+HONO+H2O triggers the overall decomposition, while the subsequent reactions HAN+HONO → N2O+2 H2O+HNO3 and 2 HNO → N2O+H2O are exothermic and accelerate the decomposition. This mechanism can be summarized by the one-step reaction HAN → 0.75 N2O+1.75 H2O+0.5 HNO3.
hydroxylammonium nitrate, liquid phase reaction, detailed kinetic model