Effects of micron-sized/nano-sized aluminum powder on the thermal safety characteristics of ammonium dinitramide under different types of thermal stimulations

Ammonium dinitramide (ADN) is new type of oxidizer in solid propellant formulations. It is known for its high energy, environmentally friendly and halogen-free. The safety of ADN during production, transportation and storage has drawn considerable attention. This study aimed to assess the effects of micron-sized aluminum powder (μ-Al) and nano-sized aluminum powder (n-Al) on the thermal safety characteristics of ADN. The assessment involved various experiments including differential scanning calorimetry (DSC), accelerating rate calorimeter (ARC), slow cook-off test and deflagration point test. DSC results reveal that n-Al decreases the initial decomposition temperature (T₀) of ADN, leading to an 18.8% decrease in its apparent activation energy (E_k) by the Kissinger method. On the other hand, μ-Al has minimal impact on T₀ but can decrease E of ADN by 7.4%. The initial decomposition temperature and apparent activation energy from ARC correspond with those from DSC; in addition, n-Al and μ-Al lead to reductions of T_D24 for 9.5 and 1.9 °C, respectively. In slow cook-off test, n-Al decreases decomposition temperature of ADN by 7.1 °C, and both n-Al and μ-Al can accelerate the process of transformation from decomposition to combustion. Deflagration point test reveals that n-Al decreases the five-second explosion temperature (T_b5) of ADN by 3.1 °C, while μ-Al increases it by 0.7 °C. n-Al and μ-Al reduced the apparent activation energy of thermal explosion (E_b) of ADN by 35.5% and 29.6%, respectively. Overall, both n-Al and μ-Al impact the thermal safety of ADN, with n-Al exhibiting a more pronounced effect than μ-Al. The research results provide important reference for evaluating the thermal safety of ADN/Al mixtures during production, storage, transportation and use.