Effect of the density of nitric acid on thermal behavior during sulfamate nitration

Ammonium dinitramide (ADN) has attracted significant interest as a potential oxidizer for next-generation rocket propellants, since it is a halogen-free alternative to the widely used oxidizer ammonium perchlorate. Because ADN synthesis requires N-nitration generates a very unstable intermediate to form the N–(NO2)2 group, this study used a reaction calorimeter to assess the heat of decomposition during the nitration of potassium sulfamate with various nitration agents (HNO3/H2SO4 and HNO3) by using the HNO3 density between 1.52 and 1.38 gcm−3. The heat of decomposition of potassium sulfamate in HNO3 was found to decrease with decreasing HNO3 density. In contrast, the heat of decomposition did not decrease with density in HNO3/H2SO4, since a significant temperature rise was generated when combining the lower density HNO3 with H2SO4. The heat of decomposition in high-density HNO3 (1.52 gcm−3) was greater than that in the mixed acid, likely because protonation of the potassium sulfate nitrogen by H2SO4 inhibited the subsequent nitration step.