Kinetics Analysis of the Initial Decomposition Reaction of Ammonium Dinitramide

The condensed phase decomposition reactions of ADN were investigated both experimentally and theoretically. Thermogravimetric-differential thermal analysis coupled with mass spectrometry (TG-DTA-MS) was employed to generate Friedman plots for the thermal decomposition of ADN with the evolution of N2O and N2. The activation energy associated with the evolution of N2O during initial decomposition was found to be 150 kJ/mol. Chemical equilibrium calculations based on the reaction N(NO2)2- + NH4+ ⇌ HN(NO2)2 + NH3 demonstrated that the concentration of HN(NO2)2 gradually increased with temperature, although the HN(NO2)2 to N(NO2)2- ratio was still only approximately 3.1 × 10-6, even at the decomposition temperature of 130°C. Thus, molten ADN was found to contain primarily N(NO2)2 and NH4+ with only minor amounts of liquid HN(NO2)2 and NH3. The reaction ADN → N2O + NH4NO3 was also investigated using ab-initio calculations at the CBS-QB3//ωB97XD/6-311++G(d,p) level. It was determined that four reaction pathways are possible via different transition states. The energy barrier of 161 kJ/mol obtained from these calculations agreed with the experimental value.