Modification of Ammonium Dinitramide (AND) by Co-Crystallization with Crown Ether

Ammonium dinitramide (ADN) is a material for the development of innovative solid propellants with clean-burning characteristics that is chlorine-free with low signature. However, processing and application of ADN is challenging due to adverse material properties as for example its thermal behavior with low melting point and decomposition temperature as well as high sensitivity and hygroscopicity. Modification of such materials and properties can be achieved by co-crystallization. A co-crystal consists of two or more components which form a unique crystalline structure with specific characteristics. This unique crystal structure formed of different materials and hence, combines their individual properties, enables the modification of the material behavior. Embodied in this work is the investigation of the modification of ammonium dinitramide by co-crystallization with crown ether. The work focused on the synthesis of co-crystals by the combination of ADN with the crown ether 18C6,15C5 and 12C4, with the aim of increasing the ADN-fraction in the co-crystal by the reduction of the crown ether size. After synthesis, the ADN/crown ether co-crystal was characterized by spectroscopy as well as X-ray diffraction analysis. A significant improvement of the ADN properties in the co-crystal with the 18C6 could be demonstrated. The co-crystal showed a significant increase of melting and decomposition temperature as well as a reduction of impact and friction sensitivity. Furthermore, the co-crystal exhibited hardly hygroscopic behavior, compared with the significant moisture uptake of pure ADN.