Dropwise cooling crystallization of ammonium perchlorate in gas–liquid two-phase suspension systems

Ammonium perchlorate is an important oxidizer in solid rocket propellants, underwater explosives and pyrotechnics. The crystal quality of ammonium perchlorate has an important impact on its application in these fields. In this work, a dropwise cooling crystallization method was proposed to crystallize ammonium perchlorate in gas–liquid two-phase suspension systems. Compared with the typical cooling crystallization method, dropwise cooling crystallization is favorable to control supersaturation and then control the shape and size of ammonium perchlorate crystals. The prepared samples were characterized by scanning electron microscopy, optical microscopy, laser particle distribution measurement, thermogravimetric analysis and powder X-ray diffraction. It is clearly shown that the as-prepared ammonium perchlorate crystals exhibit a high-index faced polyhedron morphology with a uniform shape and a narrow particle size distribution, the size of which can be controlled within the range of 13.64 μm to 50.33 μm. In addition, the gas-phase medium plays a good role in mixing, and it is found that higher gas-phase medium flow rates and higher feed rates of concentrated ammonium perchlorate solution result in a smaller average size of ammonium perchlorate crystals. Moreover, the crystallization method proposed in this study also has a good effect on the crystallization of sodium nitrate and ammonium chloride. This research provides a reference for the crystallization of other crystalline materials in crystal engineering.