Particle properties and crystal structure of ADN-prills

The particle properties and the crystal structure of spherical ammonium dinitramide particles, so-called ADN-prills, were investigated regarding their suitability for the use in propellant formulations. The particle size, the outer shape and the surface are the most important particle properties. At Fraunhofer-ICT ADN-prills with desired particle size and morphology are formed by the emulsion crystallization process. If necessary the surface may be refined additionally by particle coating technologies. Besides the external appearance, the internal characteristics of particles are of considerable importance. Defects, pores or impurities have unfavourable effects on the particle's properties, e.g. increased sensitivity, whereas the crystal structure of particulate energetic materials may affect the mechanical properties of the particles. In case of ADN-prills, which are generated from molten droplets, e.g. by the emulsion crystallization process, special circumstances are given. The solidification and crystal growth of molten ADN must occur inside the geometrical delimitation of each discrete droplet. Moreover the nucleation inside the ADN droplets is inhibited, which leads to super-cooled melting. It was found that the crystal formations inside the ADN-prills have a layered structure or at least a preferential direction. This phenomenon was investigated by X-ray diffraction, microscopy and measuring of the mechanical strength of the particles.