Particle size adjustment of spherical ammonium dinitramide particles (ADN-Prills) produced by emulsion crystallization

During the last years the high performance, low signature and environmental friendly oxidizer ammonium dinitramide (ADN) gained more and more acceptance for defense and space applications. The application of ADN in solid propellant formulations leads to a requirement of spherical particles of two or three different particles sizes. Therefore a coarse particle size fraction in the range of 200-250 mm and medium particle size fraction in the range of 40-60 mm are demanded. A fine fraction of about 5 mm is desirable, but only producible by milling processes. To achieve these requirements for coarse and medium size (spherical) particles several process parameters of the emulsion crystallization process for ADN, the so-called ADN-Prilling process, were modified. By the variation of process fluids, additives, stirring energy and recrystallization behavior it was possible to generate medium sized ADN-Prills with a mean particle size of 50 mm and coarse ADN-Prills with approx. 200 mm in technical scale. Furthermore targeted seeding during the recrystallization step proved to be a suitable parameter to adjust the particle size of ADN-Prills.