Decreasing the hygroscopicity of ammonium dinitramide (ADN) through cocrystallization

To decrease the hygroscopicity of ADN—a energetic oxidizer, this study developed a new cocrystal composed of ADN and 18C6 (18-crown-6) at a 1:1 ​M ratio through cocrystallization using the solvent evaporation method. The structure of the ADN/18C6 cocrystal, which has been confirmed using single X-ray diffraction (SXRD), indicates that the formation of this cocrystal is attributed to the strong intermolecular hydrogen bond interactions between ammonium ions and crown ether cycles. The ADN/18C6 cocrystal has a melting point of 151.5 ​°C, which is significantly higher than those of its respective components: 93.6 ​°C of ADN and 43.2 ​°C of 18C6. Notably, the ADN/18C6 cocrystal is nearly non-hygroscopic compared with ADN. The cocrystal's hygroscopicity rate is 0.9% when exposed to the air with relative humidity (RH) of 60% and a temperature of 30 ​°C for 12 ​h. By comparison, ADN's hygroscopicity rate is 18% under the same conditions. In addition, the impact sensitivity of the ADN/18C6 cocrystal is 18 ​J, which is substantially lower than that of raw ADN (2.5 ​J). These results show that cocrystallization offers an effective way to reduce the hygroscopicity of ADN.