Studies on ammonium dinitramide and 3,4-diaminofurazan cocrystal for tuning the hygroscopicity

Ammonium dinitramide (ADN) is a promising oxidizer with high energy characteristic, which is a relatively new environmentally friendly oxidizer without halogens and carbon elements. However, ADN has high hygroscopicity when exposed to high humidity air, restricting its applications on the solid propellants. In this paper, a novel energetic cocrystal composed of ammonium dinitramide and 3,4-diaminofurazan (DAF) was proposed and successfully synthesized by antisolvent crystallization method, and the properties of the cocrystal were systematically investigated by analytical characterization and theoretical simulation calculations. The formation of the cocrystal was confirmed by powder X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, infrared spectroscopy and Raman spectroscopy, indicating that the synthesized product was a cocrystal. Through theoretical studies, the ADN/DAF cocrystal structure was predicted, and the powder X-ray diffraction, morphology, water sorption capacity of ADN/DAF cocrystal were calculated, which was consistent with experimental phenomena. The results showed that newly prepared cocrystal of ADN/DAF had lower hygroscopicity compared to pure ADN, and the water sorption capacity was reduced from 15.35% to 7.90%. This may be due to the formation of NH⋯O medium-strength hydrogen bonds between the ammonium ion of ADN and the O atom of DAF in the cocrystal, which prevents the binding of water molecules in the air and ammonium ions and reduces the probability of ADN binding to water molecules, leading to the reduction of cocrystal hygroscopicity. The newly prepared energetic cocrystal can provide theoretical and technical guidance for the study of the anti-hygroscopicity of ADN and advance the practical application of ADN.