Perchlorate-Free Energetic Oxidizers Enabled by Ionic Cocrystallization.

The search for a suitable replacement for the ubiquitous oxidizer ammonium perchlorate (AP) is a top priority to enable more sustainable solid rocket motors. The oxidizing salts ammonium nitrate (AN) and ammonium dinitramide (ADN) are regarded as potential green replacements for AP, but suffer from a plethora of handling and processing issues including poor stability and a needle-like crystal morphology which inhibits dense packing; these prevent their widespread use. In the present work, ionic cocrystallization is leveraged to produce the first cocrystals of these oxidizing salts with an energetic coformer and the first such cocrystals to maintain a positive oxygen balance. The azole-based energetic molecule 5,5'-dinitro-2,2'-3,3″-bi-1,2,4-triazole (DNBT) is successfully cocrystallized with AN to yield the cocrystal 2AN:DNBT. Differential scanning calorimetry data confirms that AN, which in its pure form suffers from a problematic solid-state phase transition, is stabilized in the cocrystal. Application of this cocrystallization strategy to ADN produces 2ADN:DNBT, which has the highest oxygen balance of any organic cocrystal.